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Wang, Jinsong. "Membrane curing and performance of concrete." Thesis, University of Dundee, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257442.
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Pheeraphan, Thanakorn. "Accerlated curing of concrete with microwave energy." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10733.
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Heritage, Ian. "Direct electric curing of mortar and concrete." Thesis, Edinburgh Napier University, 2001. http://researchrepository.napier.ac.uk/Output/6571.
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Direct electric curing is the method by which the hydration reactions within concrete are thermally accelerated by passing an alternating electric current through the sample. This use of electricity as a means of supplying heat to young concrete and mortar has become recognised as a more effective and energy efficient form of accelerating the curing process than traditional steam curing. The present investigation involves studying the affects of thermally accelerated curing of cementitious materials in comparison to normally non-heated curing. Prior to mixing, tests are performed on the constituents of the cementitious mixes. Results of these tests are used in the creation of mix designs for mortar and concrete samples. A range of concrete mixes are designed with and without additives and admixtures are used to make cubes, slabs and beams. From the testing results, the factors affecting the short and long term properties of electrically cured cementitious materials are investigated and heating regimes are presented to achieve specific properties of both strength and durability at specific ages. A substantial section of reinforced concrete is required to gain representative results in electrically curing reinforced concrete slabs. Compressive strength is difficult to measure due to the electrical distortion affects of inserts and the damage caused by coring so that at present, basic maturity concepts are used as a compressive strength guide which limits the validity of results obtained. This research looks at refining these concepts to include early age heating effects induced by direct electric curing. The microstructural development of concrete when subjected to accelerated curing is also considered. The affect of delay periods and maximum temperature is studied using a scanning electron microscope and the results presented.
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Rostami, Vahid. "Development of early carbonation curing to replace steam curing for precast dry-mix concrete." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114470.
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Early carbonation curing technology was developed to replace steam curing for precast dry-mix concrete production. To facilitate carbon dioxide diffusion in concrete within 24-h after casting, presetting is necessary. It was accomplished by a short steam curing or by a controlled air curing. Carbonation was carried out after presetting at a gas pressure of 0.15 MPa and in a period of two hours. The performance of carbonated concretes was characterized by their carbon uptake, strength gain, pH values, calcium hydroxide content, permeability, sorptivity, freeze-thaw damage resistance and sulphate and acid resistance. It was found that the early carbonation curing could produce concrete with comparable strength by steam curing and lead to reduced calcium hydroxide on surface while maintaining pH higher than the corrosion threshold at the core. Carbonated concretes also exhibited improved resistance to sulphate attack, water absorption, and ion penetration. The early carbonation curing also demonstrated CO2 sequestration potential as an added value to the process. The microstructure of the cement paste subject to early carbonation was studied to understand the mechanism of early carbonation of concrete. Calcium carbonates produced by the process were integrated in calcium-silicate-hydrate while maintaining its initial silicate structure. The wetting procedure applied in subsequent hydration was essential to produce more hydration products in the carbonated zone and increase strength and durability. Both ordinary Portland cement (OPC) and Portland limestone cement (PLC) were investigated for their carbonation behaviour. PLC was found to be more CO2 reactive.La technologie de cure par carbonatation précoce a été développée pour remplacer la cure par étuvage pour la production du béton mélange-à-sec préfabriqué. Afin de faciliter la diffusion du dioxyde de carbone dans le béton dans les 24 heures après le moulage, le préréglage est nécessaire. Ceci a été accompli par une cure par étuvage de courte durée ou par une cure par air contrôlé. Après le préréglage, la carbonatation a été effectuée à une pression de gaz de 0,15 MPa et dans une période de deux heures. La performance des bétons carbonatés a été caractérisée par leur absorption de carbone, le gain de résistance, les valeurs de pH, la teneur en hydroxyde de calcium, la perméabilité, la sorptivité, la résistance au gel-dégel ainsi qu'aux sulfates et à l'acide. Il a été constaté que la cure par carbonatation précoce pourrait produire du béton avec une résistance comparable à la cure par étuvage. Aussi, il a été noté que la carbonatation précoce pourrait résulter à une réduction de l'hydroxyde de calcium sur la surface tout en permettant le pH au coeur d'être supérieure à la valeur seuil de la corrosion. Des bétons carbonatés ont également présenté une résistance améliorée aux attaques des sulfates, à l'absorption de l'eau et à la pénétration des ions. En plus, la cure par carbonatation précoce a démontré le potentiel de séquestration du CO2 comme une valeur ajoutée au processus.La microstructure de la pâte de ciment soumise à la carbonatation précoce a été étudiée afin comprendre le mécanisme de carbonatation du béton. L'hydrate silicate de calcium (HSC) dans le ciment carbonaté était fortement intégré avec les carbonates de calcium tout en conservant sa structure silicatée initiale. La procédure de mouillage appliquée à l'hydratation ultérieure a été essentielle afin de produire plus de produits d'hydratation dans la zone carbonatée et d'augmenter la résistance et la durabilité. Le ciment Portland ordinaire (CPO) et le ciment Portland au calcaire (CPC) ont été étudiés pour comprendre leur comportement lors de la carbonatation. Le CPC est en mesure d'absorber plus de dioxyde de carbone et de produire une résistance plus élevée à un âge précoce.
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Idowu, Olusola Ige. "Effect of improper curing on concrete properties that may affect concrete durability." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/19158/.
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The use of concrete increasing annually due its favourable properties and readily availability. Demand for concrete will continue to increase and it will remain the world’s most important construction materials for many years to come. However, the use of Portland cement concrete has an environmental burned, and so in a drive to reduce the carbon footprint of construction, there is widespread attention directed towards the utilisation of wastes and industrial by-products to minimise Portland cement (PC) consumption. The cement industry increasingly uses additions, such as fly ash. The literature has established the use of fly ash as partial replacement of Portland cement to increase strength at later age and exhibit considerable enhancement in durability. However, such binders hydrate more slowly, so proper curing conditions become more important. Ideally, the durability of concrete should not be a concern. Some degree of weathering should be expected, but improper concreting procedures can cause the deterioration to be earlier than expected. Furthermore, since durability issues cannot be seen immediately, some assessment of the impact of improper concrete curing is needed. The study has involved casting of concretes prepared with either CEM I or a CEM I blend with 30% replacement with fly ash to investigate the impact of improper curing. Performance was evaluated in terms of compressive strength, drying shrinkage, transport properties and resistance to carbonation. Paste samples were characterised by TGA, XRD and SEM to follow hydration and microstructural development. Also since the degree of saturation is known to affect the compressive strength of concrete, and curing under ambient conditions will lead to changes in the degree of concrete saturation, the work checked the impact of the degree of saturation on compressive strength; to enable an accurate understanding of the impact of improper curing. Improper curing leads to reduced compressive strength development and increased drying shrinkage. Sorptivity and permeability values were increased. This is due to reduced levels of cement hydration, as water evaporates from the concrete surface. The effect of improper curing on resistance to carbonation revealed that samples improperly cured carbonated more than those ideally cured. This study has shown that the impact on sorptivity and permeability is far greater than the impact on compressive strength, with implications for the long-term durability of concrete. Composite cements, containing 30% fly ash, showed comparable strengths to CEM I concretes and improved transport properties when ideally cured. Additions of fly ash reduced the drying shrinkage. Improper curing however led to reduced performance. Strength was compromised by improper curing to a greater degree than for equivalent CEM I mixes. However, it was sorptivity and permeability which were most severely affected. This was due to the reduced degree of cement hydration leading preventing the pozzolanic reaction between the fly ash and portlandite. Also, higher carbonation depth was seen on fly ash samples that were not cured. Low strength concrete, which already has an inherently higher porosity, is more greatly affected by improper curing than high strength concrete. This is presumed to be due to the ease with which water can evaporate from the surface of the more porous matrix. Also, concrete workability has been found to be a factor which can help to reduce the embodied carbon of concrete, with stiffer mixes having lower carbon footprints. However, this study has shown that stiff concrete mixes may be less durable and more susceptible to improper curing. This may be explained by the lower overall water contents within the stiff mixes, and therefore the greater impact of surface water evaporation. The effect of changes in the degree of saturation showed the deleterious effects of improper curing, with the saturated, ambient cured samples all exhibiting lower strengths than the equivalent ideally cured samples. The large capillary pores developed due to improper curing was seen with lower calcium hydroxide contents. The reduced hydration products obtained support the result that lower degree of hydration was produced due to improper curing since the hydration of cement cannot continues in the dry environment. This study confirms the need for good site practice, and shows that embodied carbon should not be the only factor when considering the environmental performance of concrete. Rather, durability and whole life performance should also be considered.
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Agbasi, Chukwuemeka Chijioke. "New approaches for assessing the curing of concrete." Thesis, University of London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249326.
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Catley, David Gerald. "Thermal curing of concrete with conductive polymer technology." Thesis, Sheffield Hallam University, 2009. http://shura.shu.ac.uk/19431/.
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Concrete is used on the majority of all construction projects. It is manufactured using the core constituents of a cement binder, typically Portland Cement, proportions of coarse and fine aggregates and water. The strength development of concrete is achieved by the addition of water that reacts with the binder in the form of a hydration reaction. This hydration reaction or strength development is dependant on two primary curing factors, time and temperature. Increasing the rate of strength development of concrete by elevating the curing temperature at early ages has advantages of maximising concrete production and reducing manufacturing time. Increasing the temperature of early age concrete up to 70 deg C is used in precast plants where it is critical for a minimum strength to be achieved within a certain time period to allow the removal of the concrete sections from moulds and forms. Various practices are adopted by precast concrete manufacturers to achieve the early strengths required to maximise production, both thermal and non-thermal. These include heating the various mix constituents of the concrete, using unnecessarily high cement contents within the mix, using large quantities of chemical admixtures or by increasing the ambient temperature of plants within which the elements are manufactured. In precast concrete plants the use of steam to elevate the curing temperature of the concrete is the most commonly adopted technique. However, it is inefficient and rarely provides controlled temperatures to the concrete as recommended in approved codes of practices and standards. This research programme has investigated the use of an alternative heating technology for concrete curing, optimising a unique Conductive Polymer Technology (CPT). The application and optimisation of the CPT material to provide heat curing to concrete within the laboratory, in-situ and within precast concrete plants has been investigated. The electrical properties of the CPT were investigated to determine their relationship with the size of the concrete elements. This was done for various CPT materials with different Characteristic Resistances. Having gained an in depth understanding of the electrical properties of the CPT, various heating Jackets were designed and manufactured to thermally cure concrete elements at early ages. The Jackets were designed with various outer protective materials. The effect of CPT curing on the strength and shrinkage, both at early ages and long-term, was determined. The thermal performance of the heating jackets was determined for each application including the uniformity of the heating provided into the concrete element. The interaction of the heat generated by hydration and CPT heating for larger elements was also investigated. The results showed that the CPT materials varied depending upon their manufacture and required target resistance. The thermal blankets had the capability to uniformly heat concrete elements at various ambient temperatures, to temperatures required by standards and approved codes of practice for accelerated curing of concrete. This uniform heating resulted in greater compressive strength of laboratory scale concrete elements with reduced shrinkage. The research identified the important parameters for CPT jacket design andmaterials selection e.g. the importance of the contact between CPT heating elements and the concrete element and the selection of appropriate insulation materials. The test programme also investigated the durability of CPT under different exposure conditions. The results from testing the CPT material under conditions such as freeze thaw, heating & cooling and wetting & drying showed that wetting and drying had the most significant affect on the CPTs resistance, altering by 10%. Other tests of durability included punching holes of various sizes into the CPT samples to determine their effect on the CPT's resistance. This was found to be directly linked to the area of CPT material removed. The manufacture, performance and operation of the CPT materials has also been investigated to provide an understanding of its mode of heating and its effect on concrete curing. The concept of maturity has been used to determine relationships between strength development and thermal curing and energy requirement for thermal curing when using CPT.
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Prada, Julian Ignacio. "Development of high performance concrete for prestressed bridges." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/19487.
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Morshed, Md Abu. "Early carbonation curing of fresh concrete and its applications in precast concrete production." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117115.
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Carbonation curing of fresh concrete at early age and the feasibility to integrate the technology into precast concrete production were investigated. It was found that equilibrium of relative humidity between ambient environment and interior concretes was not possible to achieve in early carbonation of fresh concrete even with preconditioning. Instead, the degree of carbonation was dominated more by the water content in the concrete than by its internal humidity. A fan-drying precondition seemed to be necessary and practically feasible to justify the water content in industry scale application. The process was applied to the production of precast lightweight concrete panels and normal weight hollow core concrete slabs. The lightweight aggregates were utilized as internal water reservoirs to balance the moisture equilibrium during preconditioning, carbonation reaction and subsequent hydration. Water movement from the internal reservoirs was postulated by resistivity measurements; and was further verified in terms of CO2 uptake, strength development, plastic shrinkage compensation and alkalinity regain. A near-surface diffusion carbonation curing was developed to partially replace the heat curing in hollow-core concrete slab production. The hollow core slab so produced had shown much better strength than the hydration reference or by the heat curing alone, with reduced porosity and less vulnerability to delayed ettringite formation. Besides the technical benefits, CO2 sequestration potential is an added value to the process. An average 15% CO2 uptake could lead to sequestration of approximately 10,000 tonnes of CO2 per year by precast hollow-core concrete plants in Canada alone.La carbonatation du béton frais effectuée à son plus jeune âge, ainsi que la possibilité de potentiellement intégrer cette technologie dans la production du béton préfabriqué a été analysé dans cette étude. Il a été constaté que l'équilibre de l'humidité relative entre l'intérieur du béton et le milieu ambiant dans lequel il se trouve n'était pas possible à établir au début du processus préalable de la cure du béton frais par carbonatation. De plus, la quantité d'eau présente affecte le degré de carbonatation bien plus que l'humidité relative interne. Le séchage préalable du béton par ventilateurs d'es trouvé nécessaire et pratique afin de justifier la présence d'eau à l'échelle industrielle. Le processus a été utilisé pour la production des panneaux de béton préfabriqué de poids léger, ainsi que pour les dalles de béton alvéolées de poids ordinaire. L'utilisation des granulats légers en tant que réservoirs d'eau internes a servi à balancer l'humidité d'équilibre durant le déroulement de tout le processus, voir du début de l'étape préalable, durant la période de carbonatation jusqu'à l'hydratation postérieure. La circulation d'eau des réservoirs internes est due aux mesures de résistivité; ceci a été validé en termes de l'étendu de carbonatation, du développement de la résistance mécanique, par la compensation du rétrécissement plastique, et par le regain de l'alcalinité. De plus, la carbonatation dynamique près de la surface du béton a été conçue afin de partiellement remplacer le procédé d'étuvage compris dans la production de dalles de bétons alvéolées. Ce type de dalles a démontré un bien meilleur niveau de résistance mécanique que celui atteint par les dalles ordinairement hydratées ou par les dalles étuvées. En plus d'avoir une meilleure résistance, ces dalles possèdent moins de porosité et sont moins vulnérables au développement tardif d'ettringite. Outre les avantages techniques, la possibilité de séquestration du CO2 est un gain ajouté au procédé. En moyenne, un contenu de 15% de CO2 dans la production Canadienne des dalles de bétons alvéolées pourrait séquestrer 10,000 tonnes de CO2 chaque année.
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Ye, Gang. "Carbon dioxide uptake by concrete through early-age curing." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19587.
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Due to the anthropogenic activities, the increasing carbon dioxide concentration in the atmosphere is disturbing the natural equilibrium of the greenhouse gas, and causes the global temperature rise. In 1990, the CO2 emission from fossil fuel fired power plants contributed 30% of global emissions. In the same year, the cement industry contributed about 5% of the total. According to Kyoto Protocol, a tremendous effort is required to reduce the carbon dioxide emission. One potential technology in CO2 mitigation responses is the use of concrete products as carbon sink through the early age fast curing. The cement compounds C3S and C2S are instantaneously carbonized into calcium carbonate and silica gel, once cement is mixed with water and exposed to the carbon dioxide gas. If it works, concrete production lines can be set next to the power plants or cement kilns to produce the concrete products using the captured CO2 as curing agent. This thesis reports a feasibility study based on a preliminary work. The purpose of the research was to find a proper combination of a large number parameters to use cement, slag or waste cement to sequester CO2 emitted from industrial point sources, and at the same time to make high performance concrete products. In order to understand the carbonation curing, this study was directed towards the mix designs, carbonation conditions and the mechanical properties of carbonated products. More than 40 batches of carbonated concrete specimens were prepared with the following variables in their preparation: chemical additive, CO2 concentration, carbonation time, carbonation pressure, thickness of specimen, and CO2 supply method. The performance of the carbonated specimens was assessed through the mass gain, the compressive strength, the bending strength, the pressure drop, the temperature rise in the curing chamber, the carbonation depth and the microstructure characteristics. Two-hour carbonated concrete products can have a strength equivalent to 2-month air curing, and take up 8% carbon dioxide by weight without special treatment.
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Schmidt, Markus Norbert. "Early age concrete curing based on capillary pressure measurement." Thesis, University of the West of Scotland, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.645202.
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Molloy, Brian T. "Steel fibre and rebar corrosion in concrete under marine curing." Thesis, University of Aberdeen, 1990. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU032222.
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Concern for durability of reinforced concrete structures has, in recent years, coincided with an increasing interest in the use of steel fibre reinforcement. In this investigation the corrosion behaviour of conventional and steel fibre reinforcement in concrete under long term marine curing have been studied. The corrosion behaviour of reinforcement has been assessed visually, and by using electrochemical techniques. Three types of steel fibre were investigated namely low carbon steel, stainless steel melt extract, and galvanised steel. Previous studies have shown that steel fibres exhibit good corrosion resistance in concrete exposed to marine curing. It has been suggested that this is due to the discrete nature of the individual steel fibres which prevents the development of electrochemical cells with large cathode/anode area ratios. In order to determine, therefore, whether a 'size-effect' phenomenon influences steel fibre corrosion rates, concrete specimens were cast with different lengths and diameters of steel wire and subsequently exposed to marine curing. Parallel concrete specimens containing samples of conventional reinforcing bar were also manufactured. Cement replacement materials such as pulverised fuel ash, ground granulated blast furnace slag and microsilica are widely used in order to enhance specific properties of fresh or hardened concrete. In this investigation durability characteristics of concrete containing cement replacement materials were studied. These characteristics, including alkalinity of pore fluid and diffusion rates of chloride ions are of importance in relation to the passivation or corrosion of steel reinforcement.
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Kashef, Haghighi Sormeh. "Carbon dioxide transport and uptake in concrete during accelerated carbonation curing." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107639.
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Carbon dioxide (CO2) is the dominant greenhouse gas resulting from many anthropogenic activities, mainly combustion of fossil fuels. One of the strategies to mitigate CO2 emissions is considered to be carbon dioxide capture and storage (CCS). The current storage methods focus on enhanced oil recovery, underground geological storage, disposal in deep oceans, and ex situ mineral carbonation of abundant metal oxide minerals such as olivine, serpentinite and wollastonite.During mineral carbonation, a gas stream rich in CO2 is reacted with mineral metal oxides to form thermodynamically stable carbonates. These carbonated minerals, however, store CO2 but do not produce any materials that are of value. Accelerated carbonation curing of concrete can be used as a mineral sequestration method with the advantage of producing a value-added concrete product. During accelerated carbonation curing of concrete, CO2 is reacted with cement and stored as a solid calcium carbonate in concrete construction products. Among the concrete products, non-reinforced precast concrete, such as blocks and bricks, can be used for carbonation curing. In previous studies, pressurized chambers have been used for accelerated CO2 curing of concrete, where a high pressure of CO2 is required for sufficient gas diffusion in concrete and homogeneous carbonation. In this research, a flow-through carbonation reactor was used for concrete curing and the rate and extent of CO2 uptake by concrete was studied. One of the advantages of the carbonation reactor applied in this study is that significantly less energy for gas mixture compression is required compared to a CO2 pressure chamber.The overall objective of this thesis was to develop and assess the performance of an accelerated carbonation curing reactor for concrete using an advective flow of flue gas. The rate and extent of CO2 uptake by concrete in a 1-D flow-through carbonation reactor were studied and compared with the published results on CO2 uptake in pressurized chambers using diffusive flow of CO2. The factors limiting the CO2 uptake were studied through experimental observation as well as mathematical modeling of CO2 transport and reaction in concrete during accelerated carbonation curing. Carbonation efficiencies of 16-20% attained in the flow-through reactor were comparable to those obtained for static CO2 pressure chambers. The extent of CO2 uptake was limited by formation of solid calcium carbonate in micro-scale pores. Intermittent carbonation experiments showed that the carbonation efficiency was limited in part by slow dissolution and/or diffusion of dissolved reactive components in the concrete matrix. The electron microprobe imaging technique used in this study also confirmed formation of solid calcium carbonate which filled up the narrow pores (<4 µm). The uptake efficiency reached 67% when cement was carbonated in an aqueous suspension in a completely mixed flow-through reactor where the effect of pore blockage was eliminated and a higher percentage of reacting surface area was exposed to dissolved CO2. However, formation of a calcium carbonate layer still inhibited diffusion of dissolved calcium and CO2 through this layer. In the presence of the calcium carbonate layer and other carbonation products like silica (SiO2 gel), and at partial pressure of CO2 used for carbonation, the aqueous solution reached a chemical equilibrium and carbonation ceased before the maximum theoretical uptake could be achieved. The effect of physico-chemical processes on CO2 uptake during carbonation curing was also studied using a mathematical model. Equations describing the CO2 transport by advection and dispersion in concrete pore space, dissolution in pore water and reaction with reactive cement species were solved numerically. The initial concentration of cement species were calculated based on a hydration model which was developed to simulate the 4 hours of hydration time before carbonation starts.Le dioxyde de carbone (CO2) est le gaz d'effet de serre dominant, résultat des plusieurs activités anthropogènes, dont le plus important est la combustion des combustibles fossiles. Une des stratégies qui a pour but d'atténuer des émissions de CO2 est le captage et le stockage du dioxyde de carbone (CCS en anglais). Les méthodes courantes de stockages incluent la récupération assistée du pétrole, le stockage géologique souterrain, la disposition sous les océans profonds, et la carbonatation minérale ex situ des gisements abondants des oxydes métalliques, comme l'olivine, la serpentinite et la wollastonite. Pendant la carbonatation minérale, un jet de gaz riche en CO2 est mis à réagir avec les oxydes des métaux minéraux pour former des carbonates thermodynamiquement stables. L'élimination des minerais carbonatés, cependant, stocke le CO2 mais ne produit pas des matériaux de valeurs ajoutées. La carbonatation accélérée pour murir du béton peut être employée comme une méthode de la séquestration minérale avec l'avantage de produire un produit de béton à valeur ajoutée. Pendant la carbonatation accélérée pour murir du béton, le CO2 est mis à réagir avec le ciment et stocké comme carbonate de calcium solide dans les produits de béton utilisés en construction. Les produits en béton non-armés et préfabriqués tel que les blocs et les briques sont ceux qui peuvent être faits avec la méthode carbonatation pour murir le béton. Lors des études précédentes, des chambres sous pression ont été employées pour accélérer le durcissement du CO2 au béton, où une haute pression de CO2 est exigée pour une diffusion suffisante de gaz et une carbonatation homogène. Dans cette recherche, un écoulement à travers le réacteur de carbonatation a été utilisé pour le durcissement du béton; le taux et l'ampleur de la prise de CO2 par le béton ont été également étudiés. Un des avantages du réacteur de carbonatation appliqué dans cette étude est que l'énergie exigée est nettement inférieure, comparé à une chambre sous pression de CO2. L'objectif global de cette thèse est de développer et d'évaluer la performance de l'exécution d'une carbonation accélérée traitant le réacteur pour le béton en utilisant un flux advectif des émissions gazeuses. Le taux et l'ampleur de la prise de CO2 par le béton dans un écoulement unidimensionnel (1-D) à travers le réacteur de carbonation ont été étudiés et comparés aux résultats publiés sur la prise de CO2 dans les chambres pressurisées en utilisant l'écoulement diffusif du CO2. Les facteurs limitant la prise de CO2 ont été étudiés à travers l'observation expérimentale ainsi que la modélisation mathématique du transport et de la réaction du CO2 dans le béton durant le traitement accéléré de la carbonation. Les efficacités de carbonatation de 16-20% atteintes dans l'écoulement à travers le réacteur sont comparables à celles obtenues pour les chambres de pression statiques de CO2. L'ampleur de la prise de CO2 a été limitée par la formation du carbonate de calcium solide dans des micro et macro-pores. Les expériences intermittentes de carbonatation ont prouvé que l'efficacité de carbonatation a été limitée en partie par la dissolution et/ou la diffusion lente des composants réactifs dissous dans la matrice de béton. La technique d'imagerie du micro-probe d'électron utilisé dans cette étude a également confirmé la formation du carbonate de calcium pendant la carbonatation, qui a rempli les micropores. L'efficacité de prise a atteint 67% quand le ciment a été carbonaté sous la forme de boue dans un réacteur qui contienne un mélange de suspension aqueux (à travers du quel écoule le CO2), où l'effet du colmatage des pores a été éliminé et un pourcentage plus élevé de la superficie de surface de réaction a été exposé au CO2 dissous. Cependant, la formation d'une couche de carbonate de calcium empêchait encore la diffusion du calcium dissous et du CO2 à travers cette couche.
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Igarashi, Hasegawa Lucia. "Carbonation curing and performance of pervious concrete using Portland limestone cement." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104896.
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Pervious concrete is an innovative material with several environmental advantages. Studies on the properties and performance of ordinary Portland cement (OPC) pervious concrete have been done worldwide. Portland limestone cement (PLC) has recently been introduced into the Canadian market as a greener option than OPC. This thesis explores the possibility of using PLC in pervious concrete to achieve technical and environmental benefits.Since the major application of pervious concrete is pavements, it is important to find a way to accelerate the concrete curing process, as one of the most important factors in determining the cost and impact of road work is the construction time. Pervious concrete is the ideal material to cure by carbonation in a feasible way. It is usually designed without reinforcement, so the reduction of the concrete pH value resulting from the process has no impact. Additionally, the open massive pore structure provides a larger surface to optimize CO₂ penetration during the curing process. This study focuses on the effect of carbonation on early age strength and freezing and thawing durability of PLC pervious concrete. It was found that, under the same conditions, PLC pervious concrete shows lower compressive strengths and higher absorption than the OPC counterpart. The optimization of the mixture proportion by including admixtures would permit the use of PLC to generate a pervious concrete with strengths equivalent to OPC pervious concrete. Carbonation curing of PLC pervious concrete increased early age compressive strength, and maintained a comparable final strength. In addition, carbonation curing increased resistance to absorption, but decreased the resistance to freezing and thawing cycles in saline solution. Therefore, carbonation curing of pervious concrete is not recommended for cold climates.Le béton drainant est un matériau innovant avec plusieurs avantages environnementaux. Des études portant sur les propriétés et la performance du béton drainant au ciment Portland ordinaire (CPO) ont été réalisées internationalement. Le ciment Portland au calcaire (CPC) a fait son arrivée sur le marché canadien récemment et s'avère une option plus écologique que le CPO. Cette thèse explore la possibilité d'utiliser CPC en béton drainant pour obtenir avantages techniques et environnementaux. Une des applications majeures du béton drainant est le pavage. Pour cette raison, c'est important de trouver une façon d'accélérer le processus de durcissement du béton, puisque le temps de construction est l'un des facteurs les plus importants déterminant le coût et l'impact des travaux routiers. Le béton drainant est le matériau idéal à mûrir au carbone de manière faisable. Il est fabriqué sans armature et donc, la réduction du pH du béton résultant du processus de carbonatation n'a aucun impact. De plus, la structure ouverte massive des pores offre une surface plus grande permettant d'optimiser la pénétration de CO₂ au cours du processus de mûrissement. Cette étude a pour but de déterminer l'effet de la carbonatation sur la résistance à jeune âge et la durabilité au gel/dégel du béton drainant fabriqué avec le CPC. Les résultats indiquent que, pour les mêmes conditions, il y a une réduction de la résistance à la compression et une meilleure absorption avec le béton drainant au CPC comparé avec ceux au CPO. L'optimisation du dosage par l'inclusion d'ajouts cimentaires et chimiques, permettrait l'utilisation du CPC pour générer un béton drainant avec des résistances équivalentes au béton drainant au CPO. Le mûrissement au carbone du béton drainant au CPC a augmenté la résistance à la compression à jeune âge, et a maintenu une résistance finale comparable. De plus, le mûrissement au carbone a augmenté la résistance à l'absorption, mais a réduit la résistance aux cycles de gel/dégel en solution saline. Par conséquent, le mûrissement au carbone du béton drainant n'est pas recommandé pour les climats froids.
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Krook, Andre. "An investigation of concrete curing practice in the Cape Town area." Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/8459.
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Includes bibliographical references.[Watermark not visible] This project describes the results from the use of durability index tests as a tool for the investigation of the concrete curing practice in the Cape Town area. The object of the tests was to determine the effect environmental conditions have on the physical properties of the outer skin of concrete. The laboratory work involved the exposure of three concrete strengths to various relative humidities. The site work involved testing the cured outer surface of concrete at 28 days on six construction sites. The oxygen permeability and water sorptivity tests were used to investigate the outer surface of concrete. The laboratory work showed that curing at a relative humidity of 90 had a beneficial effect on the durability index values, while curing at 60 relative humidity was less effective. The permeability and sorptivity of the site results remained constant as the actual strength increased. Furthermore, permeability and sorptivity increased as the average evaporation rate increased.
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Yaede, Joseph Michael. "Internal Curing of Concrete Bridge Decks in Utah: Mountain View Corridor Project." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3995.
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The objectives of this research were to 1) monitor in-situ moisture and diffusivity for both conventional concrete and concrete containing pre-wetted lightweight fine aggregate (LWFA), 2) compare deck performance in terms of early-age cracking, compressive strength, and chloride ingress, and 3) compare concrete properties in terms of compressive strength, chloride permeability, elastic modulus, and water content in the laboratory using cylinders cast in the field at the time of deck construction. The research involved field and laboratory evaluations of four newly constructed bridge decks located in northern Utah, two constructed using conventional concrete and two constructed using pre-wetted LWFA to promote internal curing. Data from sensors embedded in the concrete decks indicate that the moisture content of the internally cured concrete was consistently 1.5 to 4 percentage points higher than the moisture content of the conventional concrete for the first 6 months following deck construction. By 1 year, however, the internally cured concrete showed little difference in moisture content compared to the conventional concrete. While the internally cured concrete decks had a higher average moisture content, the electrical conductivity values were not consistently higher than those measured on the conventional concrete decks during the first approximately 8 to 10 months. However, after 8 to 10 months, both internally cured concrete decks exhibited higher electrical conductivity values than those measured on the conventional concrete decks. Laboratory compressive strength data indicate that, for the first 6 months following deck construction, the two concrete mixtures exhibited very similar strength gain characteristics. However, at 1 year, the conventional concrete was stronger by an average of 12.9 percent, or nearly 900 psi, than the internally cured concrete. In rapid chloride permeability testing, the internally cured concrete consistently passed between 13.1 and 17.5 percent less current than that passed by the conventional concrete. Laboratory free-free resonant testing at 1 year showed that the modulus of the internally cured concrete was 3.9 percent lower, on average, than that of the conventional concrete. For the tested specimens, the moisture content of the internally cured concrete was 0.5 percentage points higher, on average, than that of the conventional concrete. In the field, Schmidt rebound hammer testing showed that the internally cured concrete was neither consistently stronger nor weaker than the conventional concrete. On average, the internally cured concrete exhibited higher chloride concentrations than the conventional concrete. On average, the conventional concrete bridge decks had 4.6, 21.5, and 2.8 times more cracking than the internally cured concrete decks at 5 months, 8 months, and 1 year, respectively. At 1 year, very distinctive reflection cracks from the joints between the underlying pre-cast half-deck panels were observed on all of the decks.
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Lin, Xiaolu 1975. "Effect of early age carbonation on strength and pH of concrete." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100230.
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Carbonation curing of concrete products has shown potentials for CO2 capture and storage with environmental, technical and economical benefits in global greenhouse gas mitigation exercise. The primary objective of this study is to investigate the effect of early age carbonation on mechanical performance and pH of concrete in an attempt to understand the process and promote large scale applications.It was found that significant early strength was developed in cement and concrete through early age carbonation curing. The early strength could be maintained and improved due to subsequent hydration. Twenty-eight-day strength of carbonated cement and concrete was comparable to that of hydrated reference if subsequently cured in the air in a sealed bag, but was lower if subsequently cured in water. Treatment with either internal curing using lightweight aggregates or chemical admixture can effectively enhance late strength development in carbonated concrete.
For three typical cement-based products including cement paste compacts, concrete compacts and precast concrete, two-hour carbonation reduced pH value from 12.8 to 11.8 as the lowest and subsequent 28-day hydration could slightly increase pH by 2% as maximum. At any time pH of early age carbonated concrete was always higher than 11.5, a threshold value under which the corrosion of reinforcing steel is likely to occur in concrete. The high pH in early-age carbonated concrete was likely attributed to the fact that early age carbonation was an accelerated hydration process, which was totally different from weathering carbonation in which pH of concrete could be neutralized due to the decomposition of calcium hydroxide and calcium silicate hydrates gel. Therefore, early age carbonation technology is applicable not only to concrete products such as masonry units and paving stones, but possibly to precast concrete with steel reinforcement as well.
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Quezada, Ivan. "Investigating Rapid Concrete Repair Materials and Admixtures." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7398.
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This dissertation presents a literature review of the state-of-practice for the use of IC in concrete mixtures and how structural engineers and construction engineers can adapt IC to their present and future work. Current high early strength concrete mixtures have natural cracking and shrinkage problems due to the high content of cementitious material or their chemical components. Using IC allows for early strength, enhanced durability, reduced shrinkage and a better curing by providing water that can be absorbed by the cement past after the final set. Rapid hydration and high early strength Portland cement and calcium sulfoaluminate (CSA) concretes are commonly used as pavement repair media. The fresh properties (slump, setting time), mechanical properties (elastic modulus, compressive and tensile strength), and volume stability (autogenous shrinkage, drying shrinkage, restrained ring shrinkage, and creep) of rapid repair media were evaluated with and without internal curing with saturated lightweight aggregate. Significant improvements in volume stability were also noted. Results indicate that internal curing can successfully improve volume stability and mitigate restrained shrinkage cracking in rapid repair media without compromising fresh properties or ultimate mechanical strength. Maturity was observed for CSA mixtures and exhibited a correlation with compressive strength development which could be beneficial for rapid repair media on the field.
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Alamri, Abdulla Mohammed. "Influence of curing on the properties of concretes and mortars in hot climates." Thesis, University of Leeds, 1988. http://etheses.whiterose.ac.uk/603/.
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This investigation deals with the influence of initial curing periods and different curing environments, similar to those found in Middle Eastern countries, on the pore size distribution, permeability, water absorption and compressive strength of cement mortars and concretes made with and without pulverized fuel ash (pfa) and ground granulated blast-furnace slag (ggbs). Three 00 environments were chosen as follows: 1) 20C+70%RH, 2) 35C+70%RH, and 3) 45C+30%RH. To simulate in-place casting, the initial mix temperatures were controlled to be as close as possible to that of the environment in which the mixes were to be kept and moisture loss was allowed to occur from only the top-as-cast face of the specimen. Durability of the mortar specimens was assessed using pore size distribution, oxygen permeability, air permeability and water absorption. In addition to strength, the following tests were carried out on the concrete specimens to assess durability: initial surface absorption (ISAT), water absorption,relative air permeability and porosity. An the tests carried out on all specimens were undertaken at an age of 28 days. 7be test results showed that the durability properties of all specimens were significantly improved as curing periods increased. While curing durations had some significant effect on the strength of OPC/ggbs samples, the effects on OPC and OPC/pfa were in general only minimal. Furthermore, as to the effects on the pore size distribution and permeability, a critical curing duration (beyond which no further significant changes in these properties were observed) was seen to exist which depended on both curing environment and cement type. Enviromnents hotter than 20C+70%RH adversely affected the durability properties of uncured samples of all mixes. Furthermore, the durability properties of plain OPC samples were adversely affected by the two hot environments when compared to 20C+70%RH for all curing durations. On the other hand, while OPC/pfa and OPC/ggbs samples cured for one day or more at 35C+70%RH showed similar or worse durability results compared with those cured at 20C+ 70%RH, better results were obtained at 45C+30%RH than in either of the other two environments. As to the effects on strength, for any given curing period, environments hotter than 20C +70%RH adversely affected the OPC and OPC/ggbs samples but not those containing pfa. AT 20C+70%RH,the pfa specimens showed generally similar or worse durability results and weaker samples than plain OPC for all curing periods. This trend was reversed in the two hot environments. On the other hand, while OPC/ggbs samples showed similar or worse durability results at 20C+70%RH and 35OC+70%RH compared to plain OPC, at 450C+30%RH the slag specimens showed better durability results for curing periods of one day or more. Tbe 28-day strength of OPC and OPC/ggbs concretes were similar to each other in all envimnments for all curing periods except for those which were uncured. The uncured OPC specimens were stronger than the slag specimens in all envimnments.
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Niven, Robert A. J. "Physiochemical investigation of CO₂ accelerated concrete curing as a greenhouse gas mitigation technology." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99193.
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There is an emerging demand for natural and engineered CO2 sinks to combat the effects of global warming. Carbon capture and storage (CCS) processes are expected to play a predominant role within a broad portfolio of technical innovations to mitigate greenhouse gas (GHG) emissions. A range of CCS methods will be required to provide GHG control technologies for the broad scope of industrial sectors. Within this class of technologies carbon dioxide accelerated concrete curing has the global potential to permanently and safely sequester up to 550 Mt CO2/yr while producing non-reinforced concrete products with improved physical properties and in less time than traditionally cured products. Previous research has exhibited shallow CO 2 penetration depth and modest CO2 uptake in grout and concrete samples despite using severe process conditions such as high pressures, temperatures and long experimental durations. Chemical and microstructural changes during carbonation were investigated to clarify the previously unexplained limitations in CO2 uptake and provide solutions to enhance CO2 storage. Loss of exposed particle surface area was identified as the most significant factor limiting complete carbonation of cement grout samples. The findings were applied to design a bench scale, flow-through carbonation curing reactor that sequestered CO2 at an average of 8.3 wt % of the cured cement with complete depth of penetration. The sequestration results were achieved with ambient temperature (20°C), 40% relative humidity, atmospheric pressure (1 atm), as-captured flue gas CO2 partial pressure (0.20) and low flow (1 Lpm) in less than 60 minutes.
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Rønning, Terje F. "Freeze-Thaw Resistance of Concrete : Effect of: Curing Conditions, Moisture Exchange and Materials." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, 2001. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-91.
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Research on freeze-thaw resistance of concrete in general and on curing and moisture conditions in particular is motivated from an economic and product sustainability point of view. Specifically, it is argued for the importance of considering the effect of curing and test exposure conditions on the moisture uptake and performance during freeze-thaw. Due to the demonstrated importance of moisture conditions on performance, they should be related to those of field service conditions when choosing a test procedure in a particular case. This is vital for adequate testing of new
and more sustainable concrete materials.
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Titherington, Melissa Prevey. "The influence of steam curing on the chloride resistance of high performance concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/MQ40929.pdf.
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Martin, Michael. "The influence of curing techniques and chemical admixtures on the properties of concrete." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/14556.
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Includes bibliographical references.The deterioration of concrete in South Africa is becoming of major concern to the construction industry. The maintenance of reinforced concrete structures is an extremely expensive exercise and is a continuing necessity. Concrete curing is a practice that is understood to be a necessity within industry, but is often overlooked as a result of time and/or economic constraints. The objective of the study is to ascertain whether or not the implementation of better quality and alternative curing techniques will improve the durability properties of the concrete. Curing is defined as the maintenance of appropriate moisture and temperature conditions to permit the continuation of the hydration or pozzolanic reaction. The objective of curing is to ensure the progress of hydration reactions causing the filling and discontinuity of capillary voids by hydrated compounds in newly placed concrete. Modern curing methods are generally classified as wet or sealing. Wet methods include fogging, sprinkling, ponding, immersion and wet coverings. Sealing methods include plastic coverings and membrane forming curing compounds. Crystallising permeability reducing admixtures may be included in the concrete mix design in order to decrease the penetrability of concrete by decreasing the interconnectivity of the pore structure. Curing methods need to be employed in order to assure specified durability limits are acquired, as durability constraints are implemented in industry. Various methods of curing were tested in order to establish the effect of the techniques on the durability properties of concrete. Samples were placed in water and in winter (Western Cape, South Africa) and simulated summer environments. Various curing techniques were then employed within each of the exposure environments. The curing methods were damp hessian, cling wrap, two curing compounds and two crystallising permeability reducers (PRA's). Samples were also left untreated in each environment as reference samples. Compressive strength, oxygen permeability, water sorptivity, chloride conductivity, bulk diffusion and accelerated carbonation tests were conducted. The results obtained in the study concur with those presented in literature. Prolonged periods of moist curing are significantly beneficial to the compressive strength and durability properties of concrete , however, full water immersion is not a feasible alternative for large or insitu-cast concrete elements. Results of the study show that d amp hessian was the best method to ensure superior durability properties. The sealing of samples with curing compounds in a cool and wet environment (winter) is not recommended, whereas it is marginally beneficial, as was clingwrap, in a hot and dry environment (summer). The crystallising PRA's provided mixed results and were favourable where excess moisture was available and fairly ineffective in dry conditions. The durability properties of concrete are markedly affected by the curing technique implemented .
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Armstrong, Cale. "Effects of different curing methods and aggregate salt treatment on concrete freeze-thaw durability and how these methods can be used to accelerate KDOT aggregate qualification procedures." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/32569.
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Master of ScienceCivil Engineering
Kyle Riding
The Kansas Department of Transportation (KDOT) currently practices a six-month procedure for determining freeze-thaw durability of coarse aggregate intended for use in concrete pavement. In addition to the excessive amount of time required to conduct this procedure, the testing conditions fail to replicate the accelerated rate of concrete deterioration commonly caused by deicer salt exposure in freeze-thaw environments. An experimental study was conducted in an attempt to reduce the duration of this aggregate qualification procedure. Limestone course aggregates from different quarries were used to batch concrete specimens. These specimens were subjected to curing regimes of different durations before being exposed to repeated cycles of freezing and thawing. The effects of the curing methods on freeze-thaw durability were then investigated. Another segment of this study entailed the immersion of coarse aggregate in salt brine solution prior to concrete batching. Salt-treated and non-salt-treated specimens were subjected to two different methods of freeze-thaw cycling to determine if the presence of salt could differentiate between aggregates with high and low performance. This study found that shorter curing methods, along with adjusted performance requirements, could be used to develop a shorter aggregate qualification procedure. It also found that shorter periods of time in more severe freeze-thaw conditions produced comparable concrete durability results to those of the current test method. Salt treatment of aggregates could indicate a difference in performance of aggregates when exposed to salts in freeze-thaw conditions. It could also be useful in determining frost resistance of hardened cement paste.
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Aslan, Ozlem. "Predicting Long Term Strength Of Roller Compacted Concrete Containing Natural Pozzolan By Steam Curing." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607727/index.pdf.
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Roller Compacted Concrete (RCC) is new technology gaining popularity in the recent years due to its low cost, rapid construction, and using opportunity of by-products. RCC is widely used in the world. However, the use of RCC has been restricted to construction of few cofferdams, and limited to local use in dam construction up to date.
In this thesis, two types of cement, two types of natural pozzolan, aggregates with varying gradations, and a type of water reducing chemical admixture were used. Prior to carrying out the tests, the chemical and physical properties of materials were determined. Additionally, steam curing was applied to the test specimens in order to get long term compressive strength at early ages. Differences between steam cured specimens and normal cured specimens have been discussed in the discussion part.
In the study, the results indicate that usage of water reducing chemical admixture improves compressive strength of RCC. Moreover, it is revealed that usage of fine material is essential to obtain desired results since the amount of cementitious materials is considerably low in RCC. Steam curing is known as its property of providing long term compressive strength at early ages. It was observed that application of steam curing in CEM I type cement used RCC mixtures generated expected results. However, in CEM IV type cement used RCC mixtures compressive strength results did not behave in the same manner.
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Uribe, Ramirez Ana M. "Concrete carbonation as a sink for carbon dioxide: results for simulated field curing conditions." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1282574502.
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Maleki-Toyserkani, Majid. "Effect of poor curing conditions and remedies on the durability of steel in concrete." Thesis, Aston University, 1987. http://publications.aston.ac.uk/14277/.
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An investigation was undertaken to study the effect of poor curing simulating hot climatic conditions and remedies on the durability of steel in concrete. Three different curing environments were used i.e. (1) Saturated Ca(OH)2 solution at 20oC, (2) Saturated Ca(OH)2 solution at 50oC and (3) Air at 50oC at 30% relative humidity. The third curing condition corresponding to the temperature and relative humidity typical of Middle Eastern Countries. The nature of the hardened cement paste matrix, cured under the above conditions was studied by means of Mercury Intrusion Porosimetry for measuring pore size distribution. The results were represented as total pore volume and initial pore entry diameter. The Scanning Electron Microscope was used to look at morphological changes during hydration, which were compared to the Mercury Intrusion Porosimetry results. X-ray defraction and Differential Thermal Analysis techniques were also employed for looking at any phase transformations. Polymer impregnation was used to reduce the porosity of the hardened cement pastes, especially in the case of the poorly cured samples. Carbonation rates of unimpregnated and impregnated cements were determined. Chloride diffusion studies were also undertaken to establish the effect of polymer impregnation and blending of the cements. Finally the corrosion behaviour of embedded steel bars was determined by the technique of Linear Polarisation. The steel was embedded in both untreated and polymer impregnated hardened cement pastes placed in either a solution containing NaCl or an environmental cabinet which provided carbonation at 40oC and 50% relative humidity.
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Wang, Sanwu 1971. "Carbonation of cement-based products with pure carbon dioxide and flue gas." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100734.
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CO2 absorption behaviour of four commonly used cement based building products: cement paste, concrete block, expanded polystyrene bead (EPB) and cement-bonded cellulose fiberboard are studied. Cement products are manufactured following industry formulation and process, and carbonation curing takes place in a chamber under a pressure of 0.5 MPa, at ambient temperature, for durations of mostly 2 to 8 hours with both pure carbon dioxide gas and flue gas. The flue gas of 13.8% CO2 content is collected from a typical cement kiln without separation. Influencing factors on carbon uptake, long-term strength as well as microstructure development are studied.It is found that the CO2 uptake ability of those cement-based products follows the same order when exposed to either pure gas or flue gas: fiberboard has the highest uptake capacity, followed by cement paste, bead board and concrete. For fiberboard, the best CO2 uptake in flue gas is 8.1%, it reaches 23.6% if pure gas used. Introduction of cellulose fiber in the fiberboard significantly increases voids volume and cement paste surface area through dispersing the paste onto fiber surface, effectively increasing carbonation reaction sites and thus CO2 uptake.
For pure gas carbonation with high reaction rate, it takes longer time for carbonated products to further develop strength from subsequent hydration, due to the high water loss during carbonation, the densified cement matrix structures and even fast decalcified cement minerals. Fast carbonation with pure gas is detrimental to cement paste in its long-term strength. For flue gas carbonation, both immediate strengths and long-term strength of the products are comparable with those by pure gas carbonation, although with less CO 2 uptake ability.
Five CO2 uptake determination methods are evaluated. Weight gain method is suitable for both pure gas and flue gas carbonation systems. Mass curve method is more suited for pure gas carbonation. For flue gas carbonation, CO2 concentration method agreed well with the weight gain method. Pressure drop method is relatively less accurate because of water vapor generation during carbonation.
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Dudziak, Lukasz. "Mitigating autogenous shrinkage of Ultra-High Performance Concrete by means of internal curing using superabsorbent polymers." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-224382.
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Application of smart curing concept called internal curing (IC) is the most promising strategy for mitigating autogenous shrinkage and related early-age cracking in cement-based materials with low water-to-cement ratio. There are still many theoretical and practical questions that need to be answered before IC could become a standard method. Many of these questions concern the most appealing of water-regulating additives for IC called Superabsorbent Polymers (SAP). The clear linkage between SAP material properties, the moment of water release and the effect on autogenous shrinkage is still missing, which blocks formulating recommendations for use of particular potential IC agents in concrete construction. In this treatise various aspects that are decisive for effectiveness of IC in mitigating autogenous shrinkage were examined. The choice of materials was purposefully limited to two compositions of Ultra-High Performance Concrete (UHPC), one fine-grained and one coarse-grained mixture, and one particular, in-depth characterized SAP. The objectives of examination which shaped the final experimental programme were: assessment of IC agent absorption capacity, specification of periods of water migration from fresh concrete mixture into SAP and from SAP back into hardening concrete, determination of effect of SAP addition on cement hydration, evaluation of IC influence on and determination of start of effective autogenous shrinkage and, finally, assessment of autogenous shrinkage with selfsame IC agent but for different matrices. Ideally, description of the mechanisms behind the action of IC at different stages of concrete life and reasoning of differences observed for the UHPCs under investigation had to be provided. First, the main components of the system – UHPC and SAP material – were characterized as to their suitability for IC application. Special attention was paid to the material properties which affect water transport. Usage of different testing methods was necessary here and included: testing with ESEM, FT-IR, tea-bag test, sol fraction content examination and X-ray computed tomography (for SAP) as well as air content measurement and various methods for characterization of the porosity and other features of the microstructure. The observed delay in the start of pozzolanic reactions in case of fine-grained UHPC was rather surprising, but, under consideration of porosity, shed new light on permeability of young UHPC. The work at hand revealed numerous methods that can be used for studying the absorption capacity of polymers, but hardly representative for the behaviour of those polymers within concrete matrix. Because of its general availability and the relatively robust testing procedure, it was decided to focus on possibilities and limitations of using tea-bag test for evaluation of absorption capacity of SAP. New interpretation of tea-bag test results was deduced which enabled assessment of maximum absorption capacity of SAP from measurement of consistency of concrete before and after modification with IC. Influence of IC on hydration process was revealed by using two non-destructive methods, in particular ultrasonic measurement and concrete temperature record. It could be shown that the ionic polymer exhibits complex effects including retardation and acceleration of individual chemical processes. Additionally, X-ray computed tomography (CT) and instrumented ring tests were performed in order to understand scientific significance of the characteristic event appearing during shrinkage measurements, taken as time-zero (= starting point for evaluation of autogenous shrinkage data). Linkage of time-zero with certain phenomenon, e.g., changes of the SAP particles volume or specific value of yield stress, but not with final set, was suggested for the future investigations. By using two setups based on corrugated tube protocol it was possible to register and compare autogenous shrinkage of both UHPCs without and with modification by IC. The effectiveness of IC was shown to be dependent on the matrix in which IC was implemented. This was related to the observed changes in pore percolation that resulted from different absorption behaviour of SAP in the two UHPCs under investigation. Furthermore, the effect of fibres on effectiveness of IC was discussed. Description and discussion of mechanisms behind IC was supported by measurement of capillary pressure, total shrinkage tests with simultaneous mass loss measurement, free autogenous shrinkage tests and the CT measurement. Valuable source of information was furthermore the in-depth literature review. The most appealing finding of the work and the biggest paradox revealed was high efficiency of IC in mitigating autogenous shrinkage and simultaneously appearance of stage where very clear reverse in mode of polymer volume change was observed. This suggests partial reabsorption of water initially released. This puts interpretation of operative shrinkage mechanisms and ones standing behind IC effect in a new perspectiveDie innere Nachbehandlung (Internal Curing – IC) ist die derzeit aussichtsreichste Strategie, um das in zementgebundenen Baustoffen mit niedrigen Wasser/Zement-Werten ausgeprägt auftretende autogene Schwinden wirksam zu verringern und die damit einhergehende Rissbildung in jungem Beton zu vermeiden. Vor einer breiten baupraktischen Anwendung des IC sind noch viele offene Fragen zu beantworten. Die meisten dieser Fragen betreffen die derzeit interessanteste Klasse von wasserregulierenden Stoffen für das IC – die superabsorbierenden Polymere (SAP). Von entscheidender Bedeutung ist hier der noch weitgehend unerforschte Zusammenhang zwischen den Materialeigenschaften der SAP, dem Zeitpunkt der Wasserabgabe und der Auswirkung auf das autogene Schwinden. In der vorliegenden Arbeit werden verschiedene Einflussfaktoren auf die Wirksamkeit von SAP zur Verringerung des autogenen Schwindens untersucht. Für die Experimente wurde ein feinkörniger und ein grobkörniger ultra-hochfester Beton (UHPC) sowie ein schon detailliert charakterisiertes SAP genutzt. Das experimentelle Programm wurde auf folgende Untersuchungsziele ausgerichtet: Absorptionsvermögen der SAP, Zeitfenster der Wassermigration aus dem Frischbeton in das SAP sowie vom SAP in den erhärtenden Beton, autogenes Schwindmaß sowie effektiver Beginn des autogenen Schwindens. Ziel der Arbeiten ist die Beschreibung der Mechanismen, die IC zugrundliegen – und dies zu verschiedenen Betonaltern und unter Berücksichtigung der an den untersuchten UHPC beobachteten Unterschiede. Bei der Charakterisierung der Hauptkomponenten des betrachteten Systems – UHPC und SAP – wurde auf die Materialeigenschaften fokussiert, die den Wassertransport beeinflussen. Dazu wurden u. a. folgende Untersuchungsmethoden angewendet: ESEM, FT-IR, Teebeuteltest, Sol-Fraction Test, Röntgentomographie (für SAP) sowie verschiedene Verfahren zur Charakterisierung der Poren im Beton. Im feinkörnigen UHPC wurde überraschenderweise ein verzögerter Beginn der puzzolanischen Reaktion festgestellt, der bei Berücksichtigung der vorliegenden Porosität zu einer Neubewertung der Permeabilität von UHPC in jungem Alter führte. In der vorliegenden Arbeit werden verschiedene Methoden zur Beschreibung des Wasserabsorptionsvermögens von SAP benannt, deren Aussagekraft bei Anwendung dieser Polymere im Beton aber sehr eingeschränkt ist. Aufgrund seiner einfachen Verfügbarkeit und Robustheit wurde daher der Teebeutetest zur Bestimmung der Wasserabsorption des SAP genutzt. Die Wasserabsorption der SAP im Beton wurde durch Gegenüberstellung von Konsistenzmessungen am Beton vor und nach Zugabe von SAP und Ergebnissen der Teebeuteltest abgeschätzt. Der Einfluss des IC auf die Hydratation wurde zerstörungsfrei mit Ultraschall- und Betontemperaturmessungen erfasst. Auf dieser Grundlage konnten Hypothesen zu den komplexen Wechselwirkungen zwischen ionischem Polymer und der Beschleunigung oder Verzögerung einzelner chemischer Prozesse formuliert werden. Mit Hilfe von instrumentierten Ringversuchen und X-ray Computertomographie wurden die Auswirkungen des IC mit SAP auf das autogene Schwinden, den Aufbau von Zwangsspannungen bei behindertem Schwinden und Time-Zero diskutiert. Dabei konnte ein Zusammenhang zwischen Time-Zero und verschiedenen Phänomenen, wie z. B. Volumenänderung des SAP oder der Fließgrenze des erhärtenden Betons, nicht aber zum Ende des Erstarrens aufgezeigt werden. Das autogene Schwinden beider untersuchter UHPC (jeweils mit und ohne IC) wurde mit Hilfe von Corrugated Tube-Versuchen gemessen. Es konnte gezeigt werden, dass wie Wirksamkeit des IC von der Betonzusammensetzung sowie der in den UHPC infolge Wechselwirkungen mit den SAP verschieden ausgebildeten Porenstruktur der Matrix abhängt. Weiterhin konnte ein Einfluss von Faserzugaben auf die Wirksamkeit des IC gezeigt werden. Die Beschreibung und Diskussion der Mechanismen des IC wurde durch Messungen des Kapillardrucks, des Gesamtschwindens, des freien autogenen Schwindens, des Masseverlustes und Computertomographie unterstützt. Eine wichtige Erkenntnisquelle war zudem die umfangreich gesichtete und diskutierte Literatur. Das interessanteste und zugleich paradoxe Ergebnis der Untersuchungen ist die Tatsache, dass die bei Einsatz von SAP beobachtete Verringerung des autogenen Schwindens eindeutig mit einer zeitgleichen Umkehr der Volumenänderung der SAP einhergeht: die bis dahin dominierende Wasserabgabe geht in eine erneute Wasseraufnahme über. Dies stellt die Interpretation der Triebkräfte des Schwindens und die dem IC zugrundliegenden Mechanismen in einen neuen Zusammenhang
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Dolphyn, Bradley P. "Laminar cracking in post-tensioned concrete nuclear containment buildings." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55017.
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As a critical public safety-related structure, the long-term integrity of post-tensioned concrete containment buildings (PCCs) is necessary for continued operation of the reactors they house. In 2009, during preparations for a steam generator replacement, extensive subsurface laminar cracking was identified in a portion of the Crystal River 3 (CR3) PCC in Florida, and the plant was permanently shut down in 2013. This study investigates potential contributing factors to the identified cracking with particular focus on the effects of high early-age temperatures on the cracking risk of the concrete, on the development of the concrete properties, and on the late-age structural behavior of the concrete. Two planar, full-scale mock-ups of a portion of the CR3 PCC were constructed and instrumented with temperature and strain gauges to monitor the thermal and mechanical behavior during representative concrete curing and post-tensioning loading. Standard- and match-cured concrete specimens were tested for determination of the time- and temperature-dependent development of thermal and mechanical concrete properties, and hydration parameters were determined for the mock-up cement paste for modeling the heat generation in the concrete. These properties and parameters were utilized in 3D finite element analysis of the mock-ups in COMSOL Multiphysics and compared with experimental results. Non-destructive evaluation via shear wave tomography was conducted on the mock-ups to identify flaws and determine the effectiveness of the methods for identifying delaminations between post-tensioning ducts approximately 10 inches beneath the concrete surface. Though early-age thermal stresses were determined not to have caused cracking in the mock-ups, the high early-age concrete temperatures resulted in decreased late-age mechanical properties that were shown to contribute to greater concrete cracking risk when the mock-up was post-tensioned. Tensile stresses exceeding the tensile strength of the concrete were identified along the post-tensioning ducts when biaxial post-tensioning loads were applied in finite element analysis, but the stresses decreased rapidly with increased distance from the ducts. Through parametric modeling, increasing the tensile strength of the concrete was identified as an effective means of reducing the cracking risk in PCCs. Additionally, relationships between the mechanical properties for the standard- and match-cured specimens were identified that could enable prediction of in-place or match-cured concrete properties based only on the results of tests on fog-cured specimens.
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BESERRA, Simone Ataíde. "Influência do tipo e do tempo de duração de cura nas propriedades mecânicas de concretos de alto desempenho (CAD) produzidos em períodos quente (t>25°C) e de baixa umidade relativa do ar (h<50%)." Universidade Federal de Goiás, 2005. http://repositorio.bc.ufg.br/tede/handle/tde/686.
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Previous issue date: 2005-06-07In the case of conventional concrete, small constructive defects, variations of mix proportion or even inadequate curings can not compromise significantly the material. No longer HPC demands a severity in the control since its dosage until the execution, therefore any imperfection can bring serious damages to the material or the structure. Amongst the relative aspects most important to the total quality of any concrete it is the curing, that becomes basic when is about HPC. The curing of the high performance concrete constitutes in a controversial subject in the technician area as well as the type and duration of it, therefore the necessity of a deeper refined study on this subject. This research verifies the influence of the type and time of duration of curing in the mechanical properties of the HPC (compressive strength, flexion tensile strength and module of deformation), produced in Goiânia in hot period (t>25ºC) and of low relative humidity of air (h<50%) situation this considered critical for NBR 14931/2003 and predominant in the months of May the September in this region. In the experimental study were produced HPC of target compressive strength 60, 80 and 100MPa, from the Furnas Mix Proportion Method, using cement CP II-F-32, silica fume, polycarboxylate based superplasticizer, natural sand and crushed stones nº 0 of the granulite. 14 cures of different type and times of duration had been applied: curing with permanence of 1, 3, 7, 14, and 28 days inside of the humid chamber; curing with aspersion of water during 1, 3, 7, 14 and 28 days; chemical curing based on paraffin and chemical curing based on chloride rubber; cure for aspersion of water during 7 days and later sealing of the part with membrane of curing based on chloride rubber and air curing. For concretes of target compressive strength to the 28 days of 60 MPa and 80 MPa, the best type of curing was "saw humid" (curing in humid chamber and curing with aspersion of water) and the best time of duration humid was 7 days. For the one of 100 MPa the best type of curing also was "saw humid", however the duration time was 14 days. According to the chemical curing, some times the results had been even though less than to the one of reference (air curing). Among the two types of used chemical curing, difference in the results of compressive strength was not verified, despite the chemical membrane based on paraffin has an inferior cost to the chloride rubber base.
No caso de concreto convencional, pequenos defeitos construtivos, variações de dosagem ou mesmo curas inadequadas podem não comprometer significativamente o material. Já no CAD exige-se um rigor no controle desde sua dosagem até a execução, pois qualquer falha pode trazer sérios prejuízos ao material ou a estrutura. Dentre os aspectos mais importantes relativos à qualidade total de qualquer concreto está a cura, o que se torna fundamental quando se trata de CAD. A cura do concreto de alto desempenho constitui assunto polêmico no meio técnico assim como o tipo e duração desta, por isso a necessidade de um estudo mais apurado sobre este tema. Esta pesquisa verifica a influência do tipo e tempo de duração de cura nas propriedades mecânicas do CAD (resistência à compressão, resistência à tração na flexão e módulo de deformação), produzidos em Goiânia em período quente (t>25ºC) e de baixa umidade relativa do ar (h<50%), situação esta considerada crítica pela norma NBR 14931 (ABNT, 2003) e predominante nos meses de maio a setembro na região. No estudo experimental foram produzidos CAD de resistência à compressão estimada 60, 80 e 100MPa, a partir do Método de Dosagem de Furnas, utilizando cimento CP II-F-32, sílica ativa, superplastificante à base de éter carboxilato, areia natural e brita 0 de granulito. Foram aplicados 14 curas de diferentes tipos e tempos de duração: cura com permanência de 1, 3, 7, 14, e 28 dias dentro da câmara úmida; cura através de aspersão de água durante 1, 3, 7, 14 e 28 dias; cura química com membrana à base de parafina e à base de borracha clorada; cura através de aspersão de água durante 7 dias e depois selagem da peça com membrana de cura à base de borracha clorada e cura ao ar. Para os concretos de resistência estimada aos 28 dias de 60 MPa e de 80 MPa, o melhor tipo de cura foi via úmida (cura em câmara úmida e cura através de aspersão de água) e o melhor tempo de duração foi 7 dias. Para o de 100 MPa o melhor tipo de cura também foi via úmida , porém o tempo de duração foi 14 dias. Quanto à cura química, algumas vezes os resultados foram até mesmo inferiores ao de referência (cura ao ar). Dentre os dois tipos de curas químicas utilizados não verificouse diferença nos resultados de resistência à compressão, salientando-se que a membrana química à base de parafina tem custo inferior à base de borracha clorada.
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Al-Kindy, Adil. "Macro and microclimate effects on cover zone properties of field cured concrete." Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/12446.
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Three sets of concrete blocks were cast to investigate the effects of natural exposure conditions, at the macro and microclimate scale, and field curing on the performance and durability of OPC and OPCjGGBS concretes. These are termed the Loughborough winter series, the Loughborough summer series and the Muscat summer series. Three concrete mixes were investigated in the two Loughborough series (30 and 50 MPa OPC concrete mixes and a 30 MPa OPCjGGBS concrete mix) and two in the Muscat weather series (the two 30 MPa concretes). A group of specimens were cast with each mix consisting of 600 x 500 x 150mm concrete blocks plus control cubes and prisms. The samples were cured in-situ and exposed to a range of curing methods and microclimates. Surface zone properties (up to 50mm depth) were evaluated by air permeability, sorptivity, carbonation, thermogravimetry (TG) and mercury intrusion porosimetry (MIP) tests, conducted after 3 and 12 months of site exposure. The results revealed distinct variations due to macroclimate, microclimate, curing, concrete type and age. The air permeability, sorptivity and carbonation of the concrete exposed under moderate and rainy conditions of a Loughborough summer season were lower than identical concrete cast and cured during a very cold and dry Loughborough winter season. Further, the sorptivity of concrete subjected to the hot and dry climatic conditions of Muscat was significantly higher than companion samples subjected to the temperate Loughborough climate. Significant variations in properties were observed within the two sides of the same concrete element, each subjected to a different microclimate. The air permeability, sorptivity, carbonation and porosity were reduced with increased hessian curing duration. However, premature drying of wet hessian during curing had an adverse effect on concrete quality as this produced concrete of higher permeability and carbonation than non-cured concrete. The application of controlled permeability formwork was effective in improving the concrete's sub-surface properties. The curing affected zone (CAZ) extended to approximately 20mm below the surface of the concrete that was exposed to the Loughborough winter and summer climate, and 40-50mm for the concrete exposed to the Muscat climate, with notable variation in properties due to climate and curing. The TG and MlP results provided insights into the mechanisms associated with the variations in the three concrete's properties due to natural field exposure.
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Conroy-Jones, Gene A. "The effects of curing, and aggregate type upon the tensile strength measurement of medium to high strength concrete." Thesis, Cardiff University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301797.
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Gillmer, Marc. "Investigating repair mortars containing superabsorbent polymers as a method of internal curing to improve concrete patch repair performance." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/14553.
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Includes bibliographical references.Concrete structures are designed with a specific service life in mind and deteriorate over time due to their exposure to environmental conditions. In order to increase the service life of concrete structures, they can sometimes be rehabilitated and repaired using concrete overlays. However, problems may develop between the new and old concrete due to differential shrinkage between the concrete substrate and overlay. These differential shrinkages typically result in the build - up of tensile stresses within the overlay. If the concrete does not possess sufficient tensile strength, the overlay will crack and or delaminate, which is usually considered failure. To prevent cracking, the quantity of shrinkage that occurs in the overlay needs to be minimised. Literature suggests that the addition of superabsorbent polymers (SAP's) to the concrete overlay can reduce the total shrinkage that occurs. A large amount of research exists pertaining to the use on SAP's in high performance concrete (HPC), while very little research has been done regarding their influence of overlays. This research investigated how the addition of SAP's to overlays containing silica fume (SF) would improve bonded concrete overlay performance. Testing was conducted on overlay samples with a water:binder (W/b) ratio of 0.45 and 0.55 with SAP contents of containing 0%, 0.2%, 0.4% and 0.6% of the total binder content. Samples were subjected to a large number of tests including compressive, tensile and shear bond strength, durability, tensile relaxation, elastic modulus, carbonation, bulk diffusion and free and restrained shrinkage. The results of this research indicate d that the SAP's had a greater influence on samples with a higher w/b ratio. The results also suggested that an increase in SAP content resulted in improved tensile strength, tensile relaxation and durability while also reducing the rate of drying shrinkage at early ages . This indicated that SAP's can be used in mix design to improve bonded concrete overlay performance.
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Al-Ghamdi, Hamed A. "Effect of curing and mix design parameters on durability of Portland cement and Portland cement-silica fume mortars in a hot-marine environment." Thesis, University of Aberdeen, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301075.
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This study was conducted to evaluate the effect of curing and mix design parameters, such as cement content and water to cementitious materials ratio, on the strength and durability characteristics of plain and silica fume cements exposed to a hot-marine environment. Specifically, the effect of curing and mix design parameters on chloride diffusion, shrinkage and carbonation of cement mortar specimens exposed to a hot-marine environment was evaluated. The results indicated that high water to cement ratio significantly influenced the durability performance of concrete through: (1) accelerating chloride diffusion and carbonation, (2) increasing the shrinkage and weight loss, and (3) reducing the compressive strength. Similarly, increasing the cement content increased the shrinkage for a given w/c ratio. However, the chloride diffusion and carbonation were minimized and strength was enhanced due to increasing cement content. The mix design parameters, namely, water-cement ratio and cement content significantly influenced the performance of both Type I and Type V cements, while the influence of these parameters on the performance of silica fume cements was insignificant. Although Type I cement mortars performed better than Type V cement mortars, the performance of silica fume cement was the best in terms of reduced chloride diffusion, carbonation and shrinkage, and enhanced strength. The beneficial effects of silica fume cements, were however, only evident in specimens subjected to good curing. Therefore, to extend the useful service-life of reinforced concrete structures exposed to hot-marine environments, the following mix design is recommended: (i) cement content should not be less than 350kg/m3; (ii) Type I cement with 10% silica fume; (iii) water to cementitious materials ratio of not more than 0.45; (iv) good curing.
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Lopez, Mauricio. "Creep and Shrinkage of High Performance Lightweight Concrete: A Multi-Scale Investigation." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11222005-122831/.
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Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006.Kurtis, Kimberly E., Committee Co-Chair ; Kahn, Lawrence F., Committee Co-Chair ; Lai, James S., Committee Member ; Gokhale, Arun M., Committee Member ; Castrodale, Reid W., Committee Member. Vita.
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Ye, Dan. "Early-age concrete temperature and moisture relative to curing effectiveness and projected effects on selected aspects of slab behavior." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1472.
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Evans, Christopher Michael. "The influence of fly ash and early-age curing temperature on the durability and strength of high-performance concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28830.pdf.
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Acquaye, Lucy. "Effect of high curing temperatures on the strength, durability and potential of delayed ettringite formation in mass concrete structures." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013837.
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Antolini, Mariah Ben. "RETRAÇÃO TOTAL E PENETRAÇÃO DE CLORETOS EM CONCRETOS COMPOSTOS COM CINZA DE LODO DE ETA E OUTRAS ADIÇÕES MINERAIS." Universidade Federal de Santa Maria, 2015. http://repositorio.ufsm.br/handle/1/7912.
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The use of mineral additions and substitutions in concrete production is highly beneficial to society. When used as substitutes for cement, they provide an alternative destination to polluting waste while contributing to reducing the power consumption and air pollution associated with cement production. This study investigated the influence of different concentrations of additions and curing periods of concrete mixes with water treatment plant sludge ash (CLETA), rice husk ash (CCA) and blast furnace slag (EAF) on total shrinkage and chloride penetration in concrete prepared with high early strength Portland cement. Ten mixes with water/binder ratios of 0.35, 0.50 and 0.65, with wet cure periods of 3 and 7 days were tested. CLETA substitutions for Portland cement ranged from 0% to 30%. Three-component mixes with 20% CLETA and 5% EAF, 20% CLETA and 10% EAF and a four-component mix with 15% CLETA, 5% EAF and 5% CCA were also tested. Shrinkage was measured using a length comparator at 0, 7, 14, 21, 28, 35, 56, 91, 182 and 365 days after removing the sample from the controlled humidity chamber. After 91 days of drying, samples were tested for chloride penetration to check chloride penetration depths in shrinking test samples. Results indicate that even though shrinkage values at 3 days are slightly higher, no significant variation was found for different curing periods. The lowest shrinkage value was found in the reference sample for all tested periods and in the two curing periods. Next, in an increasing shrinkage values, came the following samples: 5%CLETA (5 L), 10% CLETA (10 L), 15% CLETA (15 L), which displayed, for most mixes, a similar behavior to that of 10% CLETA (10 L), followed by mixes 20% CLETA (20 L), 25 %CLETA (20 L) and 30% CLETA (30 L). Chloride penetration resistance increased when the curing time was increased from 3 to 7 days. Three- and four-component mixes showed improved performance when compared to binary samples with CLETA and Portland cement.O uso de adições minerais e de substituições destas no processo de produção do concreto traz grande benefício à sociedade, por dar um destino a resíduos poluentes e, principalmente, por reduzir o consumo de energia e a poluição do ar gerados pela produção do cimento, ao substituir grande parte desse produto na indústria da construção civil. Neste estudo, investigou-se a influência do teor e do período de cura na utilização de misturas contendo diferentes teores de cinza de lodo de ETA (CLETA), cinza de casca de arroz (CCA) e escória de alto forno (EAF), frente à retração total e à penetração de cloretos de concretos com cimento Portland de alta resistência inicial. Para isso, foram testadas dez misturas aglomerantes, nas relações água/aglomerante 0,35, 0,50 e 0,65, com períodos de cura úmida de 3 e 7 dias. As substituições do cimento Portland por CLETA variaram de 0% a 30%, havendo ainda misturas ternárias, 20% CLETA e 5% EAF, 20% CLETA e 10% EAF, e quaternária, 15% CLETA, 5% EAF e 5% CCA. As leituras de retração foram realizadas com o uso do comparador de expansibilidade nas idades de ensaio, 0, 7, 14, 21, 28, 35, 56, 91, 182 e 365 dias após a retirada da câmara úmida. Após o período de 91 dias de secagem, foi realizado o ensaio de penetração de cloretos por imersão, a fim de analisar a profundidade de penetração de cloretos em corpos de prova em estado de retração. Dos resultados obtidos, constatou-se que, de maneira geral, embora tenham sido observados valores de retração pouco maiores para a cura de 3 dias, não foi constatada variação pronunciada entre os prazos de cura. De todas as misturas investigadas, a que apresentou menor valor de retração foi a de referência, em todas as idades de ensaio e nos dois períodos de cura. Seguido desta, em ordem crescente de retração, vem 5%CLETA (5 L), 10% CLETA (10 L), 15% CLETA (15 L), que tiveram na maioria das misturas um comportamento similar ao de 10% CLETA (10 L), seguido das misturas 20% CLETA (20 L), 25 %CLETA (20 L) e 30% CLETA (30 L). No que diz respeito à penetração de íons cloreto, houve um aumento na resistência quando o tempo de cura passou de 3 para 7 dias. Constatou-se que as misturas ternárias e quaternárias apresentam melhores desempenhos quando comparadas às misturas binárias, compostas por CLETA e cimento Portland.
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Sadi, Jarjes, and Safaa Aqel. "Skillnader i betongens härdningsprocess : Lämplighet enligt den europeiska och svenska standarden." Thesis, Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-40356.
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Betongindustrin ska enligt standard, varje vecka gjuta minst en kub per betongfamilj för att avstämma att hållfastheten som tillverkas inte understiger hållfastheten som kunden efterfrågat. Hållfastheten får inte vara lägre än den efterfrågade, men ingen standard påpekar hur mycket den kan överstiga. Dock kan en högre hållfasthet påverka konstruktionen negativt. En liten blandningsmassa tas ut från blandaren innan den skickas iväg till arbetsplatsen för att härdas i 28 dygn innan den trycks. Massan hälls i en kub och härdas i olika steg som ska utföras enligt standard. Det finns två olika härdningsprocesser, en enligt den svensk standarden och en enligt den europiska standarden. Det europeiska alternativet säger att betongkuben efter dag ett av härdning ska placeras i vattenbad med temperaturen 20±2 ºC fram till tryckningen. Den svenska standarden däremot säger att kuben efter första dagen av torkning ska härdas i vattenbad i 4 dygn och därefter placeras i ett härdningsutrymme med en relativ luftfuktighet mellan 40–80% med en temperatur på 20±2 ºC. Den luftlagrade ger en högre hållfasthet och ska därför räknas om med en omräkningsfaktor för att efterlikna den europiska standarden. Enligt de olika betongindustrierna kan dessa två härdningsprocesser ge samma hållfasthet vissa gånger, men andra gånger inte. Detta arbetet har därför gått ut på att jämföra de två processerna för att kunna komma fram till varför det kan variera och vad dessa faktorer beror på. För att kunna komma fram till ett resultat har arbetet valt att fördjupa sig i hållfastheten för betong genom litteraturstudier och även gjuta kuber som senare skulle tryckas för att se över hur hållfastheten varierar för de olika kuberna. Det studien har kommit fram till är att kuber inte alltid kommer ge samma hållfasthet fastän de utgår från samma blandning och härdning. Detta på grund av att betong består av olika beståndsdelar såsom ballast med olika storlekar som är svårt att fördela lika mycket i varje kub. Utrustningen och genomförandet under kubgjutning kan även vara en faktor som kan påverka hållfastheten där en kub kan ha vibrerats eller blandats lite mer än de andra. En annan faktor som kan ha gjort skillnad mellan härdningsprocesserna är omräkningsfaktorn för kuber som har härdat i luftutrymmet. Den relativa fuktigheten i lokalen låg nära 40% för kuberna och omräkningsfaktor enligt standard ska vara den samma för den relativa luftfuktigheten mellan 40–80%, detta antas vara något som bör varas tydligare med då det i betonghandboken stod att omräkningsfaktor kan ändras beroende på hur många procent den ligger på. Detta är en av anledningar till att den europiska standarden anses vara den mer effektiva processen. En annan anledning är även att kuber i vatten hela tiden får tillräckligt med luft runt om, till skillnad från härdningsutrymmet där fuktigheten varierar konstant.According to the standard, the concrete industry must, every week, cast at least one cube per concrete family to reconcile that the strength produced is not less than the strength demanded by the customer. To calculate the compressive strength of the concrete, two different curing processes can be used, both processes occur over 28 days and then can test the compressive strength. The processes are the Swedish standard and the European standard where the difference is the curing process and that’s the Swedish standard provides a higher strength and needs to be applied according to the European currency by means of a conversion factor. This work has therefore been to compare the two processes in order to be able to determine why it can vary and what these factors depend on. This study has come up with that the cubes will not always give the same strength even though they are based on the same formula and curing. This is because concrete consists of different components such as aggregates with different sizes that are difficult to allocate as much in each cube. This is one of the reasons why the European standard is considered to be the more effective process.
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Peres, Luciano Donizeti Pantano. "Avaliação de propriedades mecânicas de peças pré-moldadas submetidas à cura térmica pelo método da maturidade : estudo de caso /." Ilha Solteira : [s.n.], 2006. http://hdl.handle.net/11449/94559.
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Resumo: O Método da Maturidade é um ensaio não-destrutivo utilizado para avaliação das propriedades do concreto que estejam relacionadas ao desenvolvimento do grau de hidratação do material, a partir do seu histórico de temperaturas. O presente trabalho apresenta a aplicação dos conceitos do Método da Maturidade para analisar o desenvolvimento da resistência à compressão de elementos pré-moldados de concreto submetidos à cura térmica, a partir do monitoramento dos dados de tempo e temperatura junto à empresa Protendit, em São José do Rio Preto - SP, assim como a realização de ciclos térmicos no Laboratório CESP de Engenharia Civil (LCEC), em Ilha Solteira - SP, para elaboração da curva de calibração para utilização do método. A determinação da energia aparente de ativação, parâmetro necessário à aplicação do Método da Maturidade relacionado à velocidade da reação, foi realizada segundo o procedimento ASTM C 1074-98, permitindo verificar a influência das temperaturas de cura sobre os valores de energia de ativação determinados experimentalmente. Em conseqüência dos ciclos térmicos realizados na empresa, foi possível avaliar a distribuição de temperaturas nos elementos estruturais, com evidências do aparecimento de gradientes térmicos durante a realização da cura térmica, assim como a validação da aplicação do Método da Maturidade para estimar valores de resistência à compressão ao final do ciclo térmico.Abstract: The Maturity Method is a non-destructive test used for evaluation of the concrete properties related with the development of concrete hydration degree, calculated from the time and temperature histories. This work presents the application of the Maturity Method concepts to analyze the development of the compression strength for precast concrete elements submitted to steam curing, starting from data of time and temperature acquired in a precast concrete factory, in São José do Rio Preto city - Brazil, as well as the execution of thermal cycles in the CESP Civil Engineering Laboratory (LCEC), in Ilha Solteira city - Brazil, for elaboration of the calibration curves used by Maturity Method. The determination of the apparent activation energy, necessary parameter for use of Maturity Method related to the reaction speed, it was executed according to the ASTM C 1074-98 procedure, allowing to verify the influence of curing temperatures on activation energy values. In consequence of the thermal cycles executed in precast concrete factory, it was possible to evaluate the temperature distribution in the structural elements, with evidences of thermal gradients appearance during steam curing, as well as the validation of Maturity Method application to esteem compression strength values at the end of thermal cycle.
Orientador: Mônica Pinto Barbosa
Coorientador: Roberto Caldas de Andrade Pinto
Banca: Cassio Roberto Macedo Maia
Banca: Marcelo de Araújo Ferreira
Mestre
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Santos, Liane Ferreira dos. "A influência do patamar de cura térmica sobre a resistência dos concretos auto-adensáveis elaborados com diferentes tipos de cimento : avaliação pelo método da maturidade /." Ilha Solteira : [s.n.], 2010. http://hdl.handle.net/11449/94478.
Full textAbstract:
Orientador: Mônica Pinto BarbosaBanca: Cassio Roberto Macedo Maia
Banca: Oswaldo Cascudo Matos
Resumo: O concreto auto-adensável (CAA) é um material que representa um dos maiores avanços na tecnologia do concreto das últimas décadas. O desenvolvimento do CAA propiciou eficiência e melhora nas condições de trabalho em canteiro de obras e na indústria de pré-moldados. Do ponto de vista reológico, o CAA é uma mistura fluida que proporciona diferenças de comportamento quando comparado ao concreto convencional. Neste contexto, a proposta desta pesquisa foi estudar, num primeiro plano, as características reológicas nas fases de pasta, argamassa e concreto do CAA no estado fresco e seu comportamento no estado endurecido. Para isso, optouse por empregar a metodologia de Repette e Melo (2005), que considera a resistência à compressão como ponto de partida para a composição do traço do CAA e que estuda os aspectos reológicos envolvidos nas diferentes fases de sua dosagem. Os materiais empregados para estudo de dosagem foram o fíler basáltico como adição, areia média, brita 19 mm, aditivo superplastificante e dois tipos de cimento. Foram elaborados dois concretos, com cimentos distintos, ambos com mesma classe de resistência igual a 40 MPa. Num segundo plano, foi realizado um estudo da avaliação da resistência à compressão desses concretos quando submetidos à cura térmica a vapor, variando-se as temperaturas de cura (entre 65oC e 80oC), assim como o patamar isotérmico de cura em 4 h,6 h e 8 h para cada temperatura. A avaliação das propriedades mecânicas dos concretos foi realizada empregando o Método da Maturidade. No emprego da maturidade foram utilizados as funções de Nurse e Saul e a proposta por Freiesleben-Hansen e Pedersen (FHP). As análises comparativas foram realizadas em função do tipo de cimento empregado, temperatura de cura e tempo de patamar isotérmico
Abstract: The self-compacting concrete (SCC) is a material that represents one of the greatest advances in concrete technology in recent decades. The development of SCC has resulted in improved efficiency and working conditions at the construction site and the precast industry. Rheological point of view, the SCC is a fluid mix that provides behavior differences when compared to conventional concrete. In this context, the proposal of this research was to study, in the foreground, the rheological phases of paste, mortar and concrete of SCC in the fresh state and its behavior in the hardened state. For this, we chose to employ the methodology Repette e Melo (2005), which considers the compressive strength as a starting point for the composition of the trace of SCC and studying the rheological aspects involved in the different stages of their dosage. The materials used to study the dosage was basalt fillers such as addition, medium sand, gravel 19 mm, superplasticizer additive and two types of cement. We prepared two concretes with different cements, both with the same strength class of 40 MPa. In the background, a study assessing the compressive strength of concrete when subjected to steam curing, varying the curing temperatures (between 65oC and 80oC) as well as the level of isothermal cure at 4 h, 6 h and 8 h for each temperature. The evaluation of mechanical properties of concrete was carried out using the Maturity Method. Employment of maturity was used to Nurse e Saul function, as well as function proposed by Freiesleben-Hansen and Pedersen (FHP). Comparative analysis were performed according to the type of cement used, curing temperature and isothermal plateau
Mestre
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Peres, Luciano Donizeti Pantano [UNESP]. "Avaliação de propriedades mecânicas de peças pré-moldadas submetidas à cura térmica pelo método da maturidade: estudo de caso." Universidade Estadual Paulista (UNESP), 2006. http://hdl.handle.net/11449/94559.
Full textAbstract:
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O Método da Maturidade é um ensaio não-destrutivo utilizado para avaliação das propriedades do concreto que estejam relacionadas ao desenvolvimento do grau de hidratação do material, a partir do seu histórico de temperaturas. O presente trabalho apresenta a aplicação dos conceitos do Método da Maturidade para analisar o desenvolvimento da resistência à compressão de elementos pré-moldados de concreto submetidos à cura térmica, a partir do monitoramento dos dados de tempo e temperatura junto à empresa Protendit, em São José do Rio Preto - SP, assim como a realização de ciclos térmicos no Laboratório CESP de Engenharia Civil (LCEC), em Ilha Solteira - SP, para elaboração da curva de calibração para utilização do método. A determinação da energia aparente de ativação, parâmetro necessário à aplicação do Método da Maturidade relacionado à velocidade da reação, foi realizada segundo o procedimento ASTM C 1074-98, permitindo verificar a influência das temperaturas de cura sobre os valores de energia de ativação determinados experimentalmente. Em conseqüência dos ciclos térmicos realizados na empresa, foi possível avaliar a distribuição de temperaturas nos elementos estruturais, com evidências do aparecimento de gradientes térmicos durante a realização da cura térmica, assim como a validação da aplicação do Método da Maturidade para estimar valores de resistência à compressão ao final do ciclo térmico.
The Maturity Method is a non-destructive test used for evaluation of the concrete properties related with the development of concrete hydration degree, calculated from the time and temperature histories. This work presents the application of the Maturity Method concepts to analyze the development of the compression strength for precast concrete elements submitted to steam curing, starting from data of time and temperature acquired in a precast concrete factory, in São José do Rio Preto city - Brazil, as well as the execution of thermal cycles in the CESP Civil Engineering Laboratory (LCEC), in Ilha Solteira city - Brazil, for elaboration of the calibration curves used by Maturity Method. The determination of the apparent activation energy, necessary parameter for use of Maturity Method related to the reaction speed, it was executed according to the ASTM C 1074-98 procedure, allowing to verify the influence of curing temperatures on activation energy values. In consequence of the thermal cycles executed in precast concrete factory, it was possible to evaluate the temperature distribution in the structural elements, with evidences of thermal gradients appearance during steam curing, as well as the validation of Maturity Method application to esteem compression strength values at the end of thermal cycle.
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Melo, Aluísio Bráz de. "Influência da cura térmica (vapor) sob pressão atmosférica no desenvolvimento da microestrutura dos concretos de cimento Portland." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-13062012-151141/.
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Os investimentos iniciais em moldes na indústria de pré-moldados de concreto de cimento Portland, em geral, são altos, havendo a necessidade de utilizá-los o mais intensivamente possível entre uma e outra moldagem. A conseqüência é que a desforma pode ocorrer em instantes inadequados, comprometendo a durabilidade do produto. Isto contraria o conceito fundamental da pré-moldagem que está relacionado ao rigoroso controle de qualidade do produto. A cura térmica é uma alternativa, pois é utilizada para acelerar a resistência mecânica inicial do concreto. Esse beneficio imediato é acompanhado por uma redução na resistência final comparativamente à cura normal em câmara úmida. Esta redução é atribuída ao desenvolvimento de uma microestrutura modificada. Para investigar esse fenômeno, com base nos conhecimentos em ciência e engenharia dos materiais, desenvolve-se um estudo experimental, aplicado a pré-moldados com pequena espessura. O objetivo principal é analisar tais modificações e os compostos hidratados, formados ao longo do tempo após a cura térmica, considerando os materiais empregados e estabelecendo relações com a perda de resistência final. Leva-se em conta a influência das adições e da duração dos ciclos térmicos. A análise da microestrutura está baseada nos seguintes ensaios: porosimetria por intrusão de mercúrio, microscopia eletrônica de varredura, termogravimetria e difração de raio-X. Confirma-se com base nos resultados que a cura térmica favorece a maior formação de portlandita e também acelera a reação pozolânica. Para a composição entre cimento Portland, a escória de alto forno (30%) e a sílica ativa (10%), submetidas a ciclos térmicos longos (12 horas Tmax=61°C), observa-se a maior perda na resistência mecânica a longo prazo. Neste caso, há fortes indícios de que há formação de fases com menor desempenho mecânico. Através de micrografias, para essa amostra, sugere-se a formação da etringita secundária com maior prejuízo na interface pasta-agregado. As conclusões sugerem que para minimizar as interferências no processo de cura e garantir resistências mínimas nas desmoldagens rápidas, com poucas perdas a longo prazo, é interessante associar ciclos térmicos curtos, cimento de alta resistência inicial, sílica ativa e superplastificante.The initial investments of molds in the industry which makes pre-cast of Portland cement concrete is usually very high, thus creating a necessity to maximize the utilization of each moldings. The consequence is that the forms can be removed at inadequate time, which compromise the durability of the product. This contradicts the fundamental concepts of the pre-castings, which is related to a severe quality control. Steam curing is an alternative treatment and is used to accelerate the initial mechanical resistance of the concrete. This immediate benefit is accompanied by the decrease on final resistance compared to normal curing in humid chamber. This reduction is attributed to the development of a modified microstructure. To investigate this phenomenon, based on knowleledge of materials science and engineering, an experimental study is developed which is applied in pre-cast wich small thichness. The main objective of this work is to analyze the microstructure modifications and the hydrated compounds formed, after a period of steam curing, taking in account the used materiaIs, also to establish a relations with the loss of final strength. The influence of additions and duration of steam cycles are considered. The analyses of microstructures are based on the following tests: mercury intrusion porosimetry, scanning electron microscope, thermogravimetry and X-ray diffraction. Based on the results it can be confirmed that steam curing favors a large formation of ponlandite and also accelerates pozzolanic reaction. For the composition of Portland cement, slag fumace blast (30%) and active silica (10%), submitted for long period of thermal cycles (12 hours, Tmax=61°C), a great loss strength was observed. In this case it is possible the formation of phases with poor mechanical performance. Through micrographs, for this sample, it is observed the formation of secondary ettringite with a large damage in the interface aggregate-paste. The conclusions suggest that to minimize the interference in the process of curing and to guarantee a minimum strength during the rapid separation of the concrete from the molds, with a minor loss in a long term, it is interesting to associate short steam cycles, high initial resistance cement, adive silica and superplasticizer.
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杜方祥. "self-curing concrete." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/80839335881898391912.
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陳俊佑. "High Performance Self-Curing Concrete." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/75474157490461423706.
Full textAbstract:
碩士國立交通大學
土木工程系所
95
Good cure, have is the key to concrete performance, such as durability, strength, water-tightness, volume stability, etc. High hydrateion of Portland cement will reduce voids pores and crack of inner concrete and make the strength higher. The mineral admixtures for SCC(Pozzolanic materials) hydrate in later stage. If there is not enough water, then pozzolanic reaction will not be activated, and the characteristics will not be improved. This study investigates the effectiveness of the self-curing material. There are four self-curing materials, namely A, B, C, and D. There is no need to cure the concrete after pouring. The material A, B, C and D can absorb water from the air and then release to concrete. The material A, B, C are in liquid state, and material D is powder. The water loss, volume change, and mechanical properties were studied.
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Liang, Geng-Hao, and 梁耿豪. "Self-Curing High Performance Concrete." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/58394585505130293993.
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碩士國立交通大學
土木工程系所
96
A good curing to avoid the evaporation of water to achieve sufficient hydration is very helpful for the durability, strength, volume stability.Self-compacting concrete uses more powders and pozzolans than ordinary concrete, a good curing is even more important.This study is to develop a self-curing concrete not only to reduce the water loss but also can absorb the moisture from the air for curing. Three types of self-curing agents A, B, C were developed and tested. The concrete specimens mixed with self-curing agents were left in air after they were casted. Water loss, compressive strength, and volume stability were studied for the self-cured concrete and very satisfactory results were found. For all the cases, the compressive strengths of self-cured concrete show a higher value than the strengths of ordinary concrete. If the relative humidity is higher than 80%, the compressive strengths of self-cured concrete demonstrate a even higher value than the specimens under standard curing.
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Chung, Hsien-Chih, and 鍾憲治. "Self-Compacting Self-Curing Concrete." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/13998579907877352657.
Full textAbstract:
碩士國立交通大學
土木工程系所
94
Self-compacting concrete had been studied since 1991 by many countries, such as Japan and Europe. Taiwan started the development and application since year 2000 and is gaining the momentum rapidly. Due to the high powder content, the curing is very important for the development of the mechanical properties of the concrete, such as durability, strength, water-tightness, volume stability, etc. This study investigates the effectiveness of the self-curing material. There are four self-curing materials, namely A, B, C, and D. There is no need to cure the concrete after pouring. The material A, B, and C can absorb water from the air and release to concrete.The material D is a highly water absorbing material.These four materials were added into concrete during mixing.The water loss, volume change, and mechanical properties were studied.
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Ballim, Yunus. "Curing and the durabilty of concrete." Thesis, 2016. http://hdl.handle.net/10539/20449.
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A thesis submitted to the Faculty of Engineering,
University of the Witwatersrand, Johannesburg, in
fulfilment of the requirements for the degree of Doctor
of Philosophy.
Johannesburg, 1994.This thesis presents the details and results of an investigation into the effects of early age curing on the durability of concrete The two main objectives of the investigation were: to develop simple test methods, applied at relatively early ages, for measuring the effects of early-age moist curing on the advance of hydration in the cover zone of concrete; to quantify the effect of early age curing on the durability performance of concretes of various strength grades and made with different binder types. [Abbreviated Abstract. Open document to view full version]