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1
Boursier, Thomas. "Synthèse et caractérisation de copolymères à base d’acide méthacrylique et de nouveaux macromonomères hydrophiles : rôle de leur solvatation sur la fluidité et la viscosité des compositions cimentaires." Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10006.
Повний текст джерелаАнотація:
Le but de cette thèse est d'évaluer le rôle de la solvatation des PCP (copolymère greffé utilisé en tant qu'additif du béton) sur la fluidité et la viscosité des bétons. Pour répondre à cette problématique, des copolymères greffés différant par la nature chimique des chaînes latérales sont synthétisés. L'état de solvatation des PCP est évalué à l'aide du paramètre de Flory-Huggins χ. Ce dernier est calculé à partir du 2nd coefficient du viriel A2, déterminé par diffusion de la lumière. Des valeurs du paramètre χ de 0,37 ; 0,43 ; 0,47 et 0,48 ont été obtenues pour des PCP comportant des chaînes latérales à base d'éthylène glycol (EG), de 2-méthyloxazoline (MOx), de N-vinylpyrrolidone (NVP) et de N-acryloylmorpholine (NAM), respectivement. Le pouvoir couvrant des PCP et leur épaisseur de couche peuvent être calculés par l'intermédiaire d'une formule proposée par Flatt. L'introduction des PCP à différents dosages (donc différents taux de recouvrement) à des suspensions de calcite a permis de montrer qu'à même taux de recouvrement de surface, tous les PCP induisaient la même fluidité, alors que l'épaisseur de couche de PCP diffère de plus de 50% dans les cas les plus extrêmes. Le taux de recouvrement de surface joue un rôle tout aussi important en ce qui concerne la viscosité des suspensions. Appliquer ces conclusions sur un mortier s'avère délicat car les PCP pourraient entrainer des retards d'hydratation différents en fonction de la nature des chaînes latéralesThe objective of this PhD work is the evaluation of the role of the solvation of PCP (grafted copolymer used in concrete as additive) on the concrete fluidity and viscosity. Grafted copolymers with different side-chains were synthesized. The solvation state of the PCP was estimated by mean of the χ Flory-Huggins parameter. The latter was calculated from the 2nd virial coefficient A2, itself determined by light scattering measurements. χ -parameter values of 0,37 ; 0,43 ; 0,47 and 0,48 are obtained for PCP respectively possessing ethylene glycol (EG), 2-methyloxazoline, N-vinylpyrrolidone and N-acryloylmorpholine-based side-chains. The surface coverage of the PCPs and their layer thickness can be calculated with Flatt’s formula. The introduction of the PCPs at different contents (therefore different surface coverage ratio) to calcite suspensions showed that at same surface coverage ratio, all PCPs induce the same fluidity, although the adsorbed PCP layer thickness differed up to 50% in the certain cases. The surface coverage played also a keyrole in the suspensions viscosity. The transposition of these results to a mortar seemed however risky since PCPs might lead to hydration delays depending on the chemical nature of the side-chains
2
Namango, Saul Sitati. "Development of cost effective earthen building material for housing wall construction: investigations into the properties of compressed earth blocks stabilized with sisal vegetable fibres, cassava powder and cement compositions." [S.l.] : [s.n.], 2006. http://se6.kobv.de:8000/btu/volltexte/2006/6.
Повний текст джерела
3
Шумейко, Віта Миколаївна. "Цементвмісні композиції з модифікуючими добавками для неформованих мас". Thesis, Національний технічний університет "Харківський політехнічний інститут", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/39051.
Повний текст джерелаАнотація:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.17.11 – технологія тугоплавких неметалічних матеріалів. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2018 р.
Дисертаційна робота присвячена вирішенню науково-практичної задачі по розробці рецептурно-технологічних параметрів отримання неформованих мас цементвмісних композицій з використанням фізико-хімічних особливостей модифікуючих добавок, які сприяють формуванню щільної і міцної структури цементного каменю і забезпечують покращення експлуатаційних властивостей. За удосконаленою методикою синтезовано полікарбоксилатні добавки, знижуючи їх собівартість по відношенню до відомих суперпластифікаторів і встановлено перспективність їх використання в цементвмісних композиціях для отримання матеріалів з підвищеними фізико-механічними властивостями. Досліджено кремнеземвмісні відходи, які утворюються при виробництві фосфоровмісних добрив, та показано еколого-економічну доцільність і можливість часткової заміни різних видів цементів. Термодинамічними розрахунками спрогнозовано можливість утворення нітридів заліза при отриманні портландцементного клінкеру, які можуть бути джерелами шкідливих для життєдіяльності людей виділень аміаку з будівельних матеріалів і конструкцій, виготовлених із застосуванням портландцементу. Розроблено та оптимізовано комплексну добавку на основі сумішей електролітів, яка передбачає зниження відповідних ризиків та отримання матеріалів з підвищеними експлуатаційними властивостями і екологічністю. В результаті проведених випробувань встановлено, що цементвмісні композиції з розробленими і всебічно дослідженими модифікуючими добавками є перспективними для застосування їх в різних галузях промисловості, які були апробовані з позитивним результатом, а результати досліджень впроваджені у практику навчального процесу.Thesis for the degree of candidate of technical sciences in specialty 05.17.11 – Technology of refractory nonmetallic materials. – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2018. The thesis is devoted to the solution of the scientific hands-on problem related to the development of formulation technology parameters required to obtain unmolded masses of cement-containing compositions using physical and chemical peculiarities of modifying additives that contribute to the formation of a dense and firm structure of the cement stone and improve service properties. Using the sophisticated technique we synthesized polycarboxylated additives that have a reduced cost price in comparison with the known superplasticizers and defined the prospects of their use for cement-containing compositions to create the materials with improved physical-&-mechanical properties. The silica-containing waste that is formed during the production of phosphorcontaining fertilizers has been studied and the ecologic and economic appropriateness and a possibility of a partial replacement of the different types of cement have been shown. Thermodynamic computations were done to predict a possibility of the formation of iron nitrides when producing the Portland cement clinker that can be a source of ammonia harmful for the vital activities of people that is released by the construction materials and structures manufactured using Portland cement and the solution was suggested as for the development of special measures taken to reduce the ammonia emission through the introduction of additives. A complex electrolyte mixturebased additive was developed and optimized that anticipates a reduction of appropriate risks and production of the materials with improved service properties and environmental compatibility. The tests carried out showed that the cement-containing compositions with developed and comprehensively studied modifying additives are rather promising for the use by different industry branches. The tested additives gave a positive outcome and the research data were accepted for the teaching process practice.
4
Шумейко, Віта Миколаївна. "Цементвмісні композиції з модифікуючими добавками для неформованих мас". Thesis, Національний технічний університет "Харківський політехнічний інститут", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/39050.
Повний текст джерелаАнотація:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.17.11 – технологія тугоплавких неметалічних матеріалів. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2018 р.
Дисертаційна робота присвячена вирішенню науково-практичної задачі по розробці рецептурно-технологічних параметрів отримання неформованих мас цементвмісних композицій з використанням фізико-хімічних особливостей модифікуючих добавок, які сприяють формуванню щільної і міцної структури цементного каменю і забезпечують покращення експлуатаційних властивостей. За удосконаленою методикою синтезовано полікарбоксилатні добавки, знижуючи їх собівартість по відношенню до відомих суперпластифікаторів і встановлено перспективність їх використання в цементвмісних композиціях для отримання матеріалів з підвищеними фізико-механічними властивостями. Досліджено кремнеземвмісні відходи, які утворюються при виробництві фосфоровмісних добрив, та показано еколого-економічну доцільність і можливість часткової заміни різних видів цементів. Термодинамічними розрахунками спрогнозовано можливість утворення нітридів заліза при отриманні портландцементного клінкеру, які можуть бути джерелами шкідливих для життєдіяльності людей виділень аміаку з будівельних матеріалів і конструкцій, виготовлених із застосуванням портландцементу. Розроблено та оптимізовано комплексну добавку на основі сумішей електролітів, яка передбачає зниження відповідних ризиків та отримання матеріалів з підвищеними експлуатаційними властивостями і екологічністю. В результаті проведених випробувань встановлено, що цементвмісні композиції з розробленими і всебічно дослідженими модифікуючими добавками є перспективними для застосування їх в різних галузях промисловості, які були апробовані з позитивним результатом, а результати досліджень впроваджені у практику навчального процесу.Thesis for the degree of candidate of technical sciences in specialty 05.17.11 – Technology of refractory nonmetallic materials. – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2018. The thesis is devoted to the solution of the scientific hands-on problem related to the development of formulation technology parameters required to obtain unmolded masses of cement-containing compositions using physical and chemical peculiarities of modifying additives that contribute to the formation of a dense and firm structure of the cement stone and improve service properties. Using the sophisticated technique we synthesized polycarboxylated additives that have a reduced cost price in comparison with the known superplasticizers and defined the prospects of their use for cement-containing compositions to create the materials with improved physical-&-mechanical properties. The silica-containing waste that is formed during the production of phosphorcontaining fertilizers has been studied and the ecologic and economic appropriateness and a possibility of a partial replacement of the different types of cement have been shown. Thermodynamic computations were done to predict a possibility of the formation of iron nitrides when producing the Portland cement clinker that can be a source of ammonia harmful for the vital activities of people that is released by the construction materials and structures manufactured using Portland cement and the solution was suggested as for the development of special measures taken to reduce the ammonia emission through the introduction of additives. A complex electrolyte mixturebased additive was developed and optimized that anticipates a reduction of appropriate risks and production of the materials with improved service properties and environmental compatibility. The tests carried out showed that the cement-containing compositions with developed and comprehensively studied modifying additives are rather promising for the use by different industry branches. The tested additives gave a positive outcome and the research data were accepted for the teaching process practice.
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Richardson, I. G. "The microstructure and composition of hardened cement pastes." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302868.
Повний текст джерела
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Peřina, Tomáš. "Vliv kolísání složení cementů na vznik bleedingu a zpracovatelnosti malt v čase." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2019. http://www.nusl.cz/ntk/nusl-392330.
Повний текст джерелаАнотація:
This diploma thesis is divided into two parts, the theoretical and practical part. The theoretical part is to study of factors influencing the workability and bleeding of concrete. There is mentioned the production of cement and standard requirement. The task of the practical part is to assess the cements produced by the cement works Hranice and Prachovice. These cements test in terms of water separation. In combination with these cements use superplasticizing admixtures from Mapei and Stachema and determine the impact of water separation on cement pastes. Determine rheology on the cement pastes. Define influence of variations in cement composition affect the stability of cement mixtures.
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McCulloch, Caroline E. "The immobilization of Cs in cement based matrices." Thesis, University of Aberdeen, 1985. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU363262.
Повний текст джерелаАнотація:
Ordinary Portland Cement (OPC) is a material of complex chemical and phase composition. Therefore its sorption characteristics were determined by examining the properties of its individual phases, as well as bulk OPC. The principal constituents of OPC along with its hydration products were tested for their potential to sorb Cs using radiocaesium tracer studies. Results showed that OPC had no significant sorption potential for Cs. It was therefore suggested that the cement composition required to be tailored by including materials which were likely to sorb Cs and moreover, improve the physical properties of the cement matrix. Two categories of materials were chosen for study:- (i) those which are normally permitted in civil engineering practice, including amorphous silica, pulverised fuel ashes (PFA) , natural pozzolari and blast furnace slag (BFS); (ii) those which were known or suspected to be good Cs sorbers but whose stability in cement were as yet unknown. These included hydrous titanium dioxide, calcined kaolin, acid zirconium phosphate, tobermorite and xonotlite. Amorphous silica, several PFA's, natural pozzolan and BFS were all examined for their sorption potential. All the materials showed, to a greater or lesser degree, a potential for immobilising Cs. The amorphous silica showed the greatest uptake of Cs and was chosen for further study. The sorption of Cs by amorphous silica was determined over a- wide range of Cs concentrations. daData were treated by the Freundlich isotherm and indicated that different sorptive mechanisms may be operating at different concentration aranges. The effect of water: solid ratio and initial pH were examined. Results showed that pH had 2 opposite effects on the silica:- (a) the high pH (-12.5) increases its sorption efficiency for Cs, compared to neutral conditions, presumably due to an enhanced negative charge on the silica surface; (b) the presence of Ca(0H)2, which was used to adjust the pH arid would be present in hydrated OPC, decreases the available silica content due to pozzolanic reactions consuming silica to form Calcium Silicate Hydrate gels (C-S-H). Hence if a silica containing material was added to cement and was the only sorbing material present, it might have to be proportioned carefully to maintain a permanent excess of silica. Leach tests were carried out on mixes of cement with amorphous silica, PFA and BFS. All gave significant improvements in leach characteristics compared to OPC alone. The effects-of curing, conditions were studied. Results showed that increasing the curing time from 28 days to 84- days or 168 days or increasing the curing temperature from 20 G to 4-0 C or both improved the leach resistance. Mercury intrusion porosimetry gave little indication that this was totally due to physical encapsulation and studies of the pore fluids on the samples showed beyond doubt that a strong chemical mechanism was involved. It was hypothesised that C-S-H with a high silica content was responsible for the chemical retention of Cs. In OPC the C-S-H has a C/S ratio of -1.7 but when amorphous silica or PFA is added this ratio is reduced and can be as low as 0.8. BFS hydrates independently from OPC but it also produces a C-S-H with a low C/S value. This hypothesis was confirmed by studies on synthetic C-S-H with a range of C/S ratios and by analysing OPC/PFA and OPC/silica pastes in the analytical electron microscope. Sorption experiments were also carried out on the second category of materials. All showed good sorption potential for Cs in neutral solutions. Sorption remained significant in the presence of Na and K as competitive species. However, the effect of Ca (OH)2, differed. Tobermorite and Xonotlite appeared to show the most significant sorption of Cs in the presence of Ca(OH,)2 while the others either reacted with Ca(OH)z or discharged Cs - presumably by exchange for Ca. Tobermorite and Xonotlite were further studied. Desorption experiments and the effect of varying the Cs concentration as well as pH effects were investigated. Both materials gave straight line plots on a Freundlich isotherm indicating that one sorptive mechanism operated over a wide concentration range. Sorption increased with pH but unfortunately desorption studies showed that the Cs was easily removed. Leach studies were carried out on composites with OPC containing 5-10% tobermorite. Such additions decreased the leach rate of Cs compared to OPC.
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James, S. D. "The relationship between the compressive strength of cement mortar and the chemical composition and fineness of cement." Master's thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/8451.
Повний текст джерелаАнотація:
Includes bibliography.The purpose of this research was to determine a method whereby predictions of compressive strength could be made with regard to the chemical composition and fineness of Portland cement. Tests were performed on cement paste and mortar to determine which mixture would yield the most accurate, reproducible results. Paste was found to have a high degree of variation due to its mechanism of failure. Mortar, on the other hand, yielded reproducible and accurate results. In an attempt to prevent the high variations in the compressive strength of the paste, the paste was evacuated in a special evacuation chamber. The evacuation removed a large volume of air but did not alleviate the variations in the paste strength.
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Maldonado, Fernando. "Microstructure, composition and crystallography of Aalbrog Lion Brand Danish White cement." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1997. http://handle.dtic.mil/100.2/ADA341133.
Повний текст джерелаАнотація:
Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, September 1997."September 1997." Thesis advisor(s): Alan G. Fox. Includes bibliographical references (p. 69-71). Also available online.
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Anderson, Cecilia P. "Effects of carbonation on the mineral composition of cement kiln dust /." Available online. Click here, 2006. http://sunshine.lib.mtu.edu/ETD/THESIS/andersonc/thesis.pdf.
Повний текст джерела
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Dehwah, Hamoud Ahmad Farhan. "Influence of cement composition on concrete durability in chloride-sulfate environments." Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/27457.
Повний текст джерелаАнотація:
The poor durability performance of reinforced concrete structures is a major problem facing the construction industry throughout the world. It IS estimated that more than $200 billion will be required to repair and rehabilitate deteriorated concrete structures in the USA. Similarly, it is estimated that more than £2 billion will be needed to repair deteriorated concrete structures in the UK Also, considerable resources have to be diverted towards the repair of deteriorated concrete structures in the countries along the Arabian Gulf. Concrete deterioration, worldwide, is mainly attributed to reinforcement corrosion that is caused by chloride ions. However, the effect of other ions, particularly sulfates, on reinforcement corrosion has not been adequately studied. Reinforced concrete structures in marine environments and those built in ‘sabkha' soils are exposed to both chloride and sulfate salts The combined presence of these two ions may accelerate reinforcement corrosion. Cement chemistry may also Significantly influences the mechanisms of reinforcement corrosion. The quantity of C3A and the alkali content of cement effects its chloride-binding capacity. While considerable research has been conducted on the effect of C3A content of cement on its chloride-binding and reinforcement corrosion, meagre data exist on the effect of cement alkalinity on chloride-binding, while no study has been conducted to evaluate the effect of cement alkalinity on reinforcement corrosion.
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Abubaker, Farhat. "Controls on thaumasite in buried concrete : effect of clay composition and cement type." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/6809/.
Повний текст джерелаАнотація:
Problems due to the thaumasite form of sulfate attack (TSA), which has a significant influence on the strength and durability of buried concrete, have been extensively reported in the UK and worldwide. Thaumasite forms as a result of the presence of high levels of sulfate in pore waters in the ground surrounding concrete, particularly where sulfate is formed by the oxidation of pyrite and the ground temperature is less than about 12°C. In spite of this association with pyrite-bearing ground, an extensive literature search revealed that most previous research, including studies on which current concrete design recommendations are based, was carried out by exposing test specimens to sulfate-rich solutions rather than to natural ground materials. In fact, the present study appears to be the first extensive investigation of TSA in which various concretes have been tested in simulated field conditions. The changes in chemistry of different clays and clay pore solutions were also investigated. The work includes the long-term exposure (nine years) of Portland cement (PC), Portland limestone cement (PLC), sulfate-resisting Portland cement (SRPC) and Portland cement blended with 25% pulverized - fuel ash to slightly weathered Lower Lias Clay of sulfate design class DS-2 at 5°C. Parts of the exposed concrete were coated with bitumen to test the performance of this method of protection. The study also includes an investigation into the influence of clay composition (weathered and slightly weathered Lower Lias Clay and Coal Measures mudstone) on the severity of TSA in various concretes made with CEM I, CEM I blended with 10% limestone filler (LF), CEMI - 50% PFA and CEMI - 70% GGBS; this was complemented by parallel studies which assessed the performance of specimens of the same concretes, placed in sulfate solutions equivalent to DS-2 and DS-4 and simulated pore waters at the same temperatures. The performance of the different concretes in these tests was assessed by means of visual observation, supported by X-ray diffraction (XRD), infra-red scanning (IR) and scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) to identify the deterioration products. The change in the chemistry of clay was assessed by the determination of water- and acid-soluble sulfate, total sulfur, rate of pyrite oxidation and change in carbonate content. Where applicable, the compositions of the different clays and clay pore solutions were also investigated. It was found that deterioration due to the thaumasite form of sulfate attack occurred in all four concretes exposed for nine years to slightly weathered Lower Lias Clay. PLC concrete was the worst affected, with complete loss of binding of up to 47 mm thickness of concrete, but PC- 25% PFA replacement and SRPC concretes were also badly deteriorated. The degree of attack decreased with increasing burial depth, probably as a result of reduced access to air. The bitumen coating proved to be effective at preventing deterioration in all concretes. Exposure to clay of design sulfate class DS-2 was found to cause similar or greater deterioration than that in case of exposure to DS-4 sulfate solution, so the aggressivity of clay may be under-estimated if only the total potential sulfate (TPS) value currently used for aggressivity classification is considered. X-ray diffraction analysis revealed that gypsum and thaumasite were the main products in the concrete exposed to solutions, whilst thaumasite and carbonate were formed in the samples exposed to clay, suggesting that the more complex chemistry of clay results in a different chemical interaction. Replacement of CEM I with 50% PFA and 70 % GGBS revealed a very good performance, as no deterioration was observed after two years in any of the exposure conditions, including DS-4 solution and pyritic clays. However, thaumasite solid solution was detected in both concretes exposed to pyritic clay at 5 , which suggests that even these binders may be susceptible to thaumasite formation and TSA with time. Changes to the clays confirmed that pyrite oxidation resulted in elevated sulfate levels, and the generation of sulfuric acid, which reacted with calcite and clay minerals in the clays. It is concluded from this that the carbonate content of the clay affects its aggressivity, although current standards do not take this into account.
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Phillips, Jason B. "Pervious concrete paste composition a thesis presented to the faculty of the Graduate School, Tennessee Technological University /." Click to access online, 2009. http://proquest.umi.com/pqdweb?index=17&sid=1&srchmode=1&vinst=PROD&fmt=6&startpage=-1&clientid=28564&vname=PQD&RQT=309&did=1759989161&scaling=FULL&ts=1250626528&vtype=PQD&rqt=309&TS=1250626549&clientId=28564.
Повний текст джерела
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Rubert, Sílvia. "Contribuição ao estudo de cimentos supersulfatados: formulação e mecanismos de hidratação." Universidade Tecnológica Federal do Paraná, 2015. http://repositorio.utfpr.edu.br/jspui/handle/1/1242.
Повний текст джерелаАнотація:
Nos últimos anos, uma atenção considerável tem sido dada para o desenvolvimento de cimentos especiais, capazes de reduzir as emissões de CO2 e de energia, bem como o consumo de calcário. Cimentos supersulfatados são compostos principalmente de escória de alto forno (80-90%), sulfato de cálcio (10-20%) e um ativador alcalino, tal como o cimento Portland (cerca de 5%) ou hidróxidos de metais alcalinos. Os cimentos supersulfatados (CSS) foram usados nos anos entre 1950- 1960 na Europa, especialmente para aplicações em concretos, mas o seu menor ganho de resistência em idades iniciais limitava a sua aplicação comercial. Mais tarde, mudança no processo de fabricação do ferro gerou implicou na geração de escórias que deixaram de apresentar o conteúdo mínimo de Al2O3 exigido para CSS, levando a sua utilização alternativa em misturas com cimento Portland (Cimento de alto forno). Recentemente, a norma para o cimento supersulfatado na Europa foi substituída pela norma EN 15743 (2010), no entanto, o mecanismo de hidratação bem como a sua composição ótima não são bem compreendidos. Nesta pesquisa, o efeito do tipo e teor de ativador alcalino (hidróxidos) e das proporções de escória e anidrita foi estudado. Os hidróxidos de cálcio e potássio foram estudados em teores de 0,2, 0,5 e 0,8% em formulações de CSS contendo entre 80 - 90% de escória de alto-forno e 10-20% de sulfato de cálcio (anidrita). Através de análise de resistência à compressão verificou-se que os teores de ativadores alcalinos apresentaram maior influência em comparação às proporções de anidrita e escória. Argamassas moldadas com KOH como ativador alcalino, com 0,2 e 0,5% apresentaram os maiores valores para resistência à compressão enquanto que as argamassas elaboradas com Ca(OH)2 apresentaram maior valor 0,8%. Todos os cimentos elaborados com utilização de 0,5% de KOH como ativador alcalino, e as proporções com 85% de escória e 15% de anidrita encontram-se dentro das exigências da EN 2010. Entretanto, nenhum dos cimentos elaborados com 0,8% de KOH atingiram o limite, apenas aqueles elaborados com 0,8% de Ca(OH)2. As medidas calorimétricas confirmaram que a utilização de KOH fornece maiores fluxos de calor e maior calor acumulado quando comparado com Ca(OH)2. Para ambos os ativadores, maiores teores aumentaram o fluxo de calor e o calor acumulado. As análises microestruturais (DRX, TG/DTG, MEV) comprovam que os principais produtos de hidratação dos cimentos supersulfatados são as fases de etringita, gipsita e C-S-H, e também que o teor de ativador alcalino influência na disposição de anidrita (sulfato de cálcio) na matriz sólida de cimento. A anidrita ue deveria ser consumida para formação de etringita, quando muito solúvel, propicia a maior formação da fase hidratada gipsita.In recent years, considerable attention has been given to the development of special cements that can reduce CO2 emissions and energy and the consumption of limestone. Supersulfated cement are mainly composed of blast furnace slag (80- 90%), calcium sulfate (10-20%) and an alkaline activator such as Portland cement (around 5%) or alkali metal hydroxides. The supersulfated cements (SSC) were used in the years between 1950 to 1960 in Europe, especially for applications in concrete, but its lower gain strength at initial age limited their commercial application. Later changes in iron manufacturing processes generated slag which Al2O3 no longer met the requirement of minimum content required for SSC, leading to its alternative use mixtures of Portland cement (blast furnace cement). Recently, the standard for Europe supersulfated cement was replaced by EN 15743 (2010), however, the hydration mechanism and its optimum proportion are not well understood. In this study, the effects of the type and content of the alkali activator (hydroxides) and the content of slag and anhydrite were studied. The calcium and potassium hydroxide were studied in 0.2, 0.5 and 0.8% with SSC formulations containing 80 - 90% blast furnace slag and 10-20% sulfate calcium (anhydrite). Compressive strength tests showed that the content of alkaline activators influenced more than slag/anhydrite content. Mortars made with KOH with of 0.2 and 0.5% presented the highest compressive strength values; however, mortars made prepared with Ca(OH)2 presented the highest values with 0.8%. All cements prepared with 0.5% KOH as alkaline activator containing 85% of slag and 15% of anhydrite reached the EN 15743 requirements. The calorimetric measurements confirmed that the KOH provided higher heat flow rate and increased the total heat in relation to Ca(OH)2. The microstructural analysis (XRD, TG/DTG, SEM) confirmed ettringite, gypsum and C-S-H as main phases. The anhydrite should be consumed for the formation of ettringite, however when very soluble, provided a higher formation of gypsum phase.
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Vikström, Amanda. "Separate Calcination in Cement Clinker Production : A laboratory scale study on how an electrified separate calcination step affects the phase composition of cement clinker." Thesis, Umeå universitet, Institutionen för tillämpad fysik och elektronik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-184038.
Повний текст джерелаАнотація:
Cement production is responsible for around 7% of the global anthropogenic carbon dioxide emissions. More than half of these emissions are due to the unavoidable release of carbon dioxide upon thermal decomposition of the main raw material limestone. Many different options for carbon capture are currently being investigated to lower emissions, and one potential route to facilitate carbon capture could be the implementation of an electrified separate calcination step. However, potential effects on the phase composition of cement clinker need to be investigated, which is the aim of the present study. Phases of special interest are alite, belite, aluminate, ferrite, calcite, and lime. The phase composition during clinker formation was examined through HT-XRD lab-scale experiments, allowing the phase transformations to be observed in situ. Two different methods of separate calcination were investigated, one method in which the raw meal was calcined separately, and one method where the limestone was calcined separately. The former yielded an alite amount similar to that of the reference experiments, whereas the latter method yielded a lower amount. It could, unfortunately, not be excluded that the difference was due to poor experimental conditions, and additional experiments are needed to investigate the matter further. The study does, however, indicate that a calcined raw meal might be used to produce a clinker of similar phase composition concerning major phases belite, aluminate, ferrite, alite, and free lime. A raw meal containing calcined limestone might, however, need longer residence time at clinkering temperature too obtain similar phase composition. In addition, a raw meal containing calcined limestone was observed to be carbonated to a greater extent upon reheating than a calcined raw meal. Further experiments are needed to fully understand the effects on clinker composition of an electrified separate calcination step, and several improvements to the experimental method are given in the study.
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Chelberg, Matthew. "The Effect of Fly Ash Chemical Composition on Compressive Strength of Fly Ash Portland Cement Concrete." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555611247091087.
Повний текст джерела
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Dalod, Estelle. "Influence de la composition chimique de mortiers sur leur biodétérioration par les algues." Thesis, Saint-Etienne, EMSE, 2015. http://www.theses.fr/2015EMSE0777/document.
Повний текст джерелаАнотація:
L’encrassement des façades d’immeuble est causé par un phénomène d’altération biologique essentiellement esthétique. Leur vieillissement naturel favorise la colonisation de micro-organismes. La cinétique de biodétérioration dépend de plusieurs paramètres, tels que la situation géographique, les conditions environnementales et les caractéristiques physico-chimiques du matériau. L’objectif de la présente étude est d’établir un lien entre la composition chimique de mortiers à base de ciments et leur cinétique de colonisation par des microorganismes. Deux bancs d’essais sont utilisés : un banc d’essai in situ et un banc d’essai de biodétérioration accélérée de laboratoire. Deux ciments Portland (OPC) et deux ciments alumineux (CAC) de minéralogies différentes ont été sélectionnés. L’effet de la porosité, de la rugosité et de la carbonatation a également été étudié. Le microorganisme sélectionné pour les essais de laboratoire est l’algue Klebsormidium flaccidum qui se développe de manière prépondérante sur les façades en France. Les résultats obtenus en laboratoire et in situ montrent que la biocolonisation des mortiers à base de CAC est plus lente que celle des mortiers à base d’OPC. Lorsque la porosité augmente, la vitesse de biocolonisation augmente et l’effet de la composition chimique est en grande partie masqué. La biocolonisation des mortiers carbonatés se réalise plus rapidement que celle des mortiers non carbonatés surtout dans le cas des mortiers à base d’OPC. Enfin, les mortiers de surface rugueuse sont colonisés plus rapidement quelle que soit la formulation testée. Cet effet est plus marqué pour les mortiers exposés in situ que pour ceux testés en laboratoireThe fouling of building-facade is caused by a main aesthetic phenomenon of biological weathering. The natural weathering favors the micro-organisms development. The biofouling kinetics depends on several parameters such as geographical situation, environmental conditions and physicochemical parameters of substrates. The main objective of this study is to highlight the influence of the mortar chemistry in relationship with its physical properties on the algal growth. The biofouling kinetics was followed on samples exposed outdoor and on samples tested in a laboratory bench which consists in spraying an algal culture on mortar specimens. In order to characterize the influence of the mortar chemistry on biofouling, two Portland cements (OPC) and two calcium aluminate cements (CAC) were tested. The influence of roughness, porosity and carbonation was also studied. The green algae Klebsormidium flaccidum were chosen for the accelerated laboratory tests because of its representativeness. The results obtain in laboratory and in situ show that CAC based mortars slow down the colonization kinetics compared to OPC based mortars. When porosity increases the biofouling kinetics increases and the effect of the mortars chemical composition is largely hidden. The carbonated mortars biofouling is achieved more quickly than uncarbonated ones especially for OPC based mortars. Finally, the rough surfaces are colonized faster whatever formulation tested. This parameter is mostly highlighted for in situ tests
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Ivanov, Raphael Coelli. "Influência do dicromato de potássio no comportamento do cimento aluminoso visando ao processo de S/E de resíduos com cromo." Universidade Tecnológica Federal do Paraná, 2013. http://repositorio.utfpr.edu.br/jspui/handle/1/650.
Повний текст джерелаАнотація:
A quantidade de resíduos gerados em diversos segmentos industriais vem aumentando com o passar dos anos. Temas como a disposição final de resíduos e os riscos de poluição de sistemas biológicos onde esses são depositados, denotam-se como grandes problemáticas envolvidas nos avanços destes segmentos. Dentre as técnicas mais utilizadas de disposição final de resíduos, o processo de Solidificação/Estabilização (S/E) em matriz de cimento é apresentado como uma tecnologia de destaque para imobilização de materiais residuais contendo metais pesados. Neste estudo, os cimentos Aluminosos Fondu e Secar (51) e cimento Portland (ARI) foram empregados como materiais aglutinantes objetivando a imobilização do dicromato de potássio, o qual apresenta como principal constituinte o Cr no estado hexavalente. As variações ocorridas durante a hidratação dos cimentos frente à adição de dicromato de potássio foram investigadas utilizando técnicas de monitoramento da temperatura de hidratação e determinação das principais fases consumidas e formadas. Para isto difratometria de raios X, microscopia eletrônica de varredura e análises térmicas (diferenciais e termogravimétricas) foram utilizadas. Os resultados obtidos para esta etapa mostram que as adições de dicromato de potássio acarretaram em reduções no consumo das fases anidras, bem como, na formação das principais fases hidratadas para os três cimentos estudados, sendo a adição de 2,5% de cromo (VI) a responsável pelas maiores quedas. Para investigação da eficiência da retenção do cromo (total e hexavalente) e a avaliação da integridade estrutural dos produtos formados, técnicas de lixiviação e resistência mecânica foram empregadas. Como resultados, foram verificadas que as matrizes de cimento Aluminoso registraram os maiores valores de eficiência na retenção do cromo atingindo níveis superiores a 99%. Entretanto, o parâmetro resistência à compressão apresentou quedas de até 60% em relação às argamassas de referência com 0% de cromo. Já para o cimento Portland, a adição do sal de cromo não influenciou de maneira significativa nas resistências à compressão, entretanto a análise de retenção do metal indica a menor eficiência deste tipo de cimento, uma vez que as concentrações acima de 0,5% de cromo foram lixiviadas a níveis superiores ao estabelecidas pela norma.The increasing amount of waste generated in several industries has been increasing over the years. Topics such as waste disposal and pollution risks of biological systems where these are deposited denote as main issues involved in advancing these sectors. Among the most widely used techniques of waste disposal process, Solidification / Stabilization (S / E) in the cement matrix are a prominent technology for immobilization of waste materials containing heavy metals. In this study, the aluminous cement (Fondu and Secar 51) and Portland cement (ARI) were used as binder materials aimed at immobilizing the potassium dichromate, which has as its main constituent Cr in the hexavalent state. The variations during hydration of cements before the addition of potassium dichromate were investigated using techniques of hydration heat monitoring and determination of the main phases formed and consumed. For this purpose, X-ray diffraction, scanning electron microscopy and thermal gravimetric analysis and differential thermal analysis were used. The results show that for this step adding of potassium dichromate resulted in reductions in the consumption of anhydrous phases, as well as the formation of the main hydrated phases for the three cements studied, being the addition of 2.5% of chromium (VI) responsible for the biggest decay. To investigate the efficiency of retention of chromium (hexavalent and total) and the evaluation of the structural integrity of the products formed, leaching techniques and mechanical strength were used. As results, the aluminous cement matrices showed the highest values of efficiency in retaining chrome, achieving more than 99%. However, the compressive strength parameter showed declines of up to 60% compared to the references folders with 0% chromium. As for the Portland, adding the chromium salt did not have a significantly influence in the compressive strength, however, the metal retention analysis indicates the ineffectiveness of this type of cement, since the concentrations above 0.5% chromium were leached to levels above the established norm.
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Shanahan, Natalya G. "Influence of C3S Content of Cement on Concrete Sulfate Durability." Scholar Commons, 2003. https://scholarcommons.usf.edu/etd/1474.
Повний текст джерелаАнотація:
The influence of tricalcium silicate content of cement on concrete durability has long been a topic of discussion in the literature. The objective of this investigation was to determine whether increasing tricalcium silicate content of cement has a negative effect on concrete sulfate durability. Several mill certificates were reviewed to select cements with similar tricalcium aluminate content and variable tricalcium silicate contents. Cements selected for this study were randomly labeled as cements C, D, D2, E, and P.
The following properties were assessed for the as-received cements: Blaine fineness, particle size distribution, chemical oxide content, and mineralogical content. Three different methods were employed to determine the mineralogical composition of the as-received cements: Bogue calculation, internal standard method, and Rietveld refinement analysis. Despite the attempt to select cements with similar composition, it was determined that the as-received cements had compositional differences other than their C3S content. These cements had a variable tricalcium aluminate and alkali content, as well as differences in the amount and form of calcium sulfates. In order to eliminate these variances, doped cements were prepared by increasing the C3S content of the as received cements to 69 % by Bogue calculation.
Durability of as-received cements and doped cements was assessed through several measurements including length change, compressive strength, and phase transformation in sodium sulfate solution. For as-received cements, compressive strength of mortar cubes stored in saturated lime solution was evaluated as well. Semiquantitative x-ray diffraction analysis and scanning electron microscopy observations were performed on mortar bars to evaluate the relative amounts and morphology of the hydrated phases.
It was concluded at the end of this study that cements with high tricalcium silicate content generally have poor durability in sodium sulfate environment. All the cements experienced higher expansion with increased C3S content. High C3S content combinedwith high C3A content was particularly detrimental to mortar resistance to sodium sulfate attack.
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Dorfman, Jake. "CEMENT COMPOSITION EFFECTS ON ENAMEL DEMINERALIZATION ADJACENT TO ORTHODONTIC BRACKETS: AN IN VITRO STUDY USING THE CANARY SYSTEM." Master's thesis, Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/458512.
Повний текст джерелаАнотація:
Oral BiologyM.S.
Incipient caries lesions or white spot lesions are one of the most common clinical problems resulting from orthodontic treatment with fixed appliances. Literature has shown that infrared photothermal radiometry and modulated luminescence (PTR-LUM), used by The Canary System for caries detection, is capable of monitoring artificially created carious lesions and their evolution during demineralization. Recently, a water-based calcium aluminate glass ionomer luting cement, Ceramir, has shown bioactive surface apatite formation that may influence local remineralization. This in vitro study’s objective was to evaluate effects of bioactive cement on enamel demineralization around orthodontic brackets compared to composite resin cement. A sample of 32 caries-free extracted human teeth was collected under an IRB-exempt protocol. Orthodontic brackets were cemented to each tooth with either Transbond XT or Ceramir. A 3x3 mm window adjacent to the bracket was created with acid-resistant varnish f
Temple University--Theses
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MOTNY, RIYADH M. "COMPOSITIONAL ANALYSIS OF CERIUM AND CESIUM IN RAPID SETTING CEMENT AS AN IMMOBILIZATION AGENT FOR NUCLEAR WASTE." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5749.
Повний текст джерелаАнотація:
A feasibility of rapid setting cement (RSC) as an agent of immobilization for certain elements such as fission products or radioactive materials was explored. Cerium (Ce) and cesium (Cs) have been selected as a surrogate for U and/or Pu and fission products, respectively, in this study in three phases. In Phase I, RSC was evaluated for physical properties (e.g., porosity, density, pH values, etc.) using two groups methods—the cement powder at different concentrations of Ce (2 – 10 wt%) with deionized water (DIW) and artificial seawater (ASW). The results showed that the final setting time and compressive strength of RSC in DIW and ASW solutions decreased as Ce content increased. The X-ray diffraction patterns revealed two newly identified phases, namely CeAl11O18 and Ce4.667 (SiO4)3O. The morphology of matrix samples showed that the existence of Ce distributed on the pore wall or clustered with Si, Al, Mg, K, P, Fe, and O. In Phase II, laser-induced breakdown spectroscopy (LIBS) technique together with univariate and multivariate analyses of the principal component analysis (PCA) and partial least squares (PLS) were applied to detect the surrogate elements (Ce (0.5 – 8 wt%) and Cs (0.5 – 4 wt%)) for nuclear materials captured in ceramic materials. The best calibration curves for Ce and Cs in samples were created using the peak areas of the Ce 571.8 nm line and Cs 697.1 nm line, respectively. PCA method was applied to explain 85.5 % for Ce-cement samples in DIW and 91.4 % for those in ASW. Samples with Cs indicated similar PCA trends. The PLS calibration curves for Ce and Cs samples in DIW and those in ASW were made using seven and eight latent variables (LV). In Phase III, the leaching behaviors of Ce and Cs mixture with DIW and ASW under both dynamic and static leach conditions were investigated according to the ANSI/ANS 16.1-2003 standard method. Elemental compositions were analyzed using an inductively coupled plasma-mass spectrometry (ICP-MS) for the leaching periods of 2, 7, and 24 hours and 2, 3, 4, 5, 14, 28, 43, and 90 days. Three mathematical models—first-order reaction model (FRM), diffusion model (DM), and first-order reaction/diffusion model (FRDM)—were fitted to assess the leaching parameters of immobilized radionuclides in the RSC matrix. Results showed that leaching of 140Ce and 133Cs from RSC matrices with (DIW and ASW) under both dynamic and static leach conditions was less than 20%. It was found that the leaching phenomena of 140Ce and 133Cs was dominantly controlled by FRM with a weak effect of DM, which was best fitted by FRDM. Here, the average leachability index (L) for 140Ce and 133Cs, are greater than the recommended minimum of 6 that allowed their acceptance for disposal. These studies indicated a good feasibility of using RSC with DIW and ASW for immobilizing non-radioactive Ce and Cs and RSC had a potential for applying to actual radioactive materials.
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Staněk, Theodor. "Vztah parametrů přípravy belitického cementu a jeho hydraulických vlastností." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2009. http://www.nusl.cz/ntk/nusl-233286.
Повний текст джерелаАнотація:
The dissertation thesis is devoted to the study of belite clinkers and to the possibilities of the increase in their hydraulic activity. The mechanism and the kinetics of belite clinker formation were studied together with the relation of the velocity of these processes and the hydraulic activity of clinker. The influence of various parameters (degree of lime saturation, duration and temperature of burning) of the belite clinker preparation on the belite clinker development in time, on belite polymorphism, on the chemical composition of belite crystals and on the belite cement hydraulic activity was studied, too. The research methods used for the investigation involved electron microscopy, optical microscopy, X-ray diffraction analysis, high-temperature microphotometry and calorimetry. The resulting clinkers were hydraulically activated by addition of calcium sulfate. The experiments have proven that the higher rate of belite formation does not lead to the increase of its hydraulic activity, as opposed to that of alite. On the other hand, the chemical activation by sulfate anions enables to prepare clinker with relatively higher degree of lime saturation with minor admixture of alite and anhydrite, which is hydraulically activated. The work was concluded by experimental burning of belite clinker doped with sulfate anions in a model rotary kiln and by the preparation of cements blended with common industrial alite clinker. The results indicate the possibility of separate industrial production of special belite clinker alongside with common alite clinker and the production of economically and environmentally beneficial blended Portland cements with suitable technological parameters, or targeted production of special cements with properties corresponding to their required utilization.
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Whittaker, Mark James. "The impact of slag composition on the microstructure of composite slag cements exposed to sulfate attack." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/9307/.
Повний текст джерелаАнотація:
The work presented here focuses on the impact of slag composition on the resistance of slag composite cements exposed to sulfates. Such composite systems can be an effective way to provide better sulfate resistance of the binder. However, the differing composition and hydration kinetics between slag and cement results in a change in the phases present and their quantities, the effect of which is often overlooked when assessing their sulfate resistance. Rather, the composition of the slag is typically considered. Compared to cement, slags are richer in Si, Al and Mg, but poorer in Ca. Blended with cement, they hydrate much more slowly to produce comparable hydrates including a C-S-H phase deficient in calcium plus a hydrotalcite-like phase. Furthermore, aluminium from slag can promote the formation of other aluminate hydrates. The changes in microstructure and ultimately performance is then dependent on the composition of the slag. The aim of the work was to determine how slag composition affected the performance of slag cements in sulfate rich environments by means of the developed microstructure. A first hydration study was carried out to follow how slag composition affected microstructural developments by comparing a neat (control) cement with several slag blends curing in idealised lab conditions. Subsequently, the same samples were exposed to a 3g.L-1 Na2SO4 solution. By comparing hydration in controlled conditions and in aggressive media in parallel, analysing only the degraded zone in the latter case, the role of slag composition on phase assemblage and composition and, ultimately, on sulfate resistance was highlighted All the slag blended systems showed great resistance to sulfate attack during the testing period. This can be attributed to several changes in the microstructure in slag blended systems including (i) a lowering of the calcium content of the C-S-H phase which led to (ii) an increase in the amount of alumina bound to a possibly water rich silicate hydrate, (iii) a greater amount of a hydrotalcite phase varying in alumina content and (iv) a diluted calcium hydroxide content. Furthermore, monosulfate had formed in the slag blended systems during attack whereas ettringite had only formed in a neat system. This implies an availability of alumina from the slag keeping the $/Al of the pore solution low favouring monosulfate formation. Lastly, the role of calcium and ettringite stability was tentatively probed at.
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Curosu, Iurie. "Influence of fiber type and matrix composition on the tensile behavior of strain-hardening cement-based composites (SHCC) under impact loading." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-233204.
Повний текст джерелаАнотація:
Strain-hardening cement-based composites (SHCC) are a special class of fiber-reinforced concrete which develop multiple, fine cracks when subjected to increasing tensile loading, reaching strain capacities of up to several percent. The tensile behavior of SHCC is a result of a purposeful material design accounting for the mechanical and physical properties of the cementitious matrix, of the reinforcing fibers and of their interaction. The exceptionally high energy dissipation through inelastic deformations before reaching tensile strength makes SHCC suitable for manufacturing or strengthening of structural elements which may be subjected to impact loading. However, the tensile behavior of SHCC is highly strain rate dependent, both in terms of tensile strength and strain capacity. The different strain rate sensitivities of the constitutive phases of SHCC (matrix, fiber and interfacial bond) lead to disproportionate dynamic alteration of their mechanical properties under increasing strain rates and, consequently, to an impairment of the micromechanical balance necessary for strain-hardening and multiple cracking. Thus, high energy dissipation under impact loading can only be ensured through a targeted material design. This work presents a series of mechanical experiments at different strain rates and different scales of investigation with the goal of developing a qualitative and quantitative basis for formulating material design recommendations for impact resistant SHCC. Three different types of SHCC were investigated, consisting of two types of polymer fibers (polyvinyl-alcohol and high-density polyethylene) and cementitious matrices (normal-strength and high-strength). Uniaxial tension experiments were performed on SHCC specimens and on non-reinforced matrix specimens with different testing setups at strain rates ranging from 10-4 to 150 s-1. Besides the measured mechanical properties, special attention was paid to the crack patterns and the condition of fracture surfaces. Additionally, micro-scale investigations were performed to quantify the strain rate dependent changes in the mechanical behavior of individual component phases, i.e., matrix, fibers and fiber-matrix bond. The results obtained from the micromechanical investigations were used in an analytical model for crack bridging. The model links the micromechanical parameters and their strain rate sensitivities to the single-crack opening behavior under increasing displacement rates, making it useful for material design purposes. If given an extensive experimental basis for the fracture mechanical properties of the non-reinforced cementitious matrices, the model can be extended for predicting the strain capacity (multiple cracking) of SHCC under different strain ratesDie hochduktilen Betone (Engl.: Strain-Hardening Cement-based Composites – SHCC) bilden eine besondere Klasse von Faserbetonen, die eine multiple Rissbildung unter zunehmenden Zugspannungen aufweisen, was zu einer sehr hohen Bruchdehnung führt. Das dehnungsverfestigende, hochduktile Zugverhalten der SHCC wird durch eine gezielte Materialentwicklung erreicht, die die mechanischen und physikalischen Eigenschaften der zementgebundenen Matrizen, der Kurzfasern und deren Zusammenwirkung berücksichtigt. Das außergewöhnliche Energieabsorptionsvermögen der SHCC durch plastische Verformungen vor dem Erreichen der Zugfestigkeit qualifiziert diese Verbundwerkstoffe für die Herstellung oder Verstärkung von Bauteilen, die Impaktbeanspruchungen ausgesetzt sein könnten. Jedoch weisen SHCC sowohl bezüglich deren Zugfestigkeit als auch deren Dehnungskapazität ein ausgeprägtes dehnratenabhängiges Verhalten auf. Unter zunehmenden Dehnraten führen die unterschiedlichen Dehnratensensitivitäten der gestaltenden Phasen von SHCC (Matrix, Faser und deren Verbund) zur Beeinträchtigung des mikromechanischen Gleichgewichts, welches für die Dehnungsverfestigung und multiple Rissbildung erforderlich ist. Eine hohe Energiedissipation unter Impaktbeanspruchungen kann deshalb nur durch eine gezielte Materialentwicklung der SHCC hinsichtlich deren Verhaltens unter hohen Dehnraten gewährleistet werden. Die vorliegende Arbeit umfasst eine Reihe von experimentellen Untersuchungen mit verschiedenen Dehnraten und an unterschiedlichen Betrachtungsebenen, mit dem Ziel eine qualitative und quantitative Basis für Empfehlungen zur Materialentwicklung von Impakt-resistenten SHCC zu schaffen. Drei verschiedene SHCC-Zusammensetzungen wurden untersucht. Die Referenz-Zusammensetzung aus einer normalfesten zementgebundenen Matrix und Polyvinyl-Alkohol-Kurzfasern wurde mit zwei unterschiedlichen SHCC verglichen (hochfest und normalfest), die mit Kurzfasern aus hochdichtem Polyethylen bewehrt wurden. Einaxiale Zugversuche wurden an SHCC-Proben und unbewehrten Matrix-Proben mit verschiedenen Prüfvorrichtungen bei Dehnraten von 10-4 bis 150 s-1 durchgeführt. Zusätzlich zu den gemessenen mechanischen Eigenschaften wurden die Rissbildung und die Bruchflächen detailliert untersucht. Darüber hinaus wurden mikromechanische Untersuchungen durchgeführt, um die Dehnratensensitivität der einzelnen Phasen, d.h. Matrix, Faser und deren Verbund zu beschreiben. Die aus den mikromechanischen Untersuchungen erzielten Ergebnisse wurden als Eingangswerte in einem analytischen Einzelriss-Modell verwendet. Das entwickelte Modell verbindet die mikromechanischen Parameter und deren Dehnratenabhängigkeit mit dem Rissöffnungsverhalten von SHCC bei zunehmenden Verschiebungsraten. Das macht es vorteilhaft für Materialentwicklungszwecke. Das Modell kann für die Vorhersage der Dehnungskapazität von SHCC bei diversen Dehnraten weiterentwickelt werden, wenn eine umfassende experimentelle Basis für die bruchmechanischen Eigenschaften der Matrizen vorliegt
25
Halešová, Adéla. "Studium tvorby a kinetiky hydratace belitického slínku." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-265435.
Повний текст джерелаАнотація:
DIPLOMA THESIS IS DEVOTED TO THE STUDY OF PREPARATION OF PURE BELITE CLINKER FOR THE POTENTIAL INCREASE OF KINETICS OF THE HYDRATION PROCESS BY CHEMICAL ACTIVATION. THE THESIS OF THIS WORK IS BASED ON RESEARCH FINDINGS CONCERNING BELITE CLINKER AND RESEARCH AT THE INSTITUTE OF THD. THE THESIS AIMS TO DESIGN COMPOSITION OF THE RAW MEAL BURNING BELITE, FOLLOWING MODIFICATION BY SULPHATE AND POTASSIUM CARBONATE IN ORDER TO POTENTIALLY INCREASE THE REACTIVITY OF THE BURNT BELITE CLINKER AND THE LABORATORY FIRING OF PREPARED SAMPLES. THE LAST STEP WAS TO ASSESS THE MINERALOGICAL COMPOSITION OF BURNED SAMPLES XRD ANALYSIS AND FOLLOWING COMPARISON CELL PARAMETER OF BELITE WITH AND WITHOUT ADDED MODIFYING ADDITIVES.
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Havlík, Leoš. "Příprava a vlastnosti belitického slínku." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2019. http://www.nusl.cz/ntk/nusl-392334.
Повний текст джерелаАнотація:
DIPLOMA THESIS IS FOCUSED ON THE PREPARATION AND PROPERTIE OF BELITE CLINKER. IT IS BASED ON THE STUDY OF SCIENTIFIC ARTICLES DEALING WITH THE ABOVE MENTIONED TOPIC AS WELL AS THE ANALYSIS OF THE BRNO THD INSTITUTE´S RESEARCH RESULTS. AS PART OF MY EXPERIMENTAL WORK, A PROPOSAL OF THE COMPOSITION OF RAW MEAL TO EXTRACT BELITE CLINKER IN THE PRESENCE OF POTASSIUMS CARBONATE AND SULPHATE WAS MADE TO MODIFY RAW MEAL. THE PURPOSE OF MODIFYING RAW MEAL IS A POTENTIAL INCREASE IN BELITE CLINKER REACTIVITY. FURTHER THE EXTRACTION OF BYPASS DUST FROM A LOCAL CEMENT PLANT WAS CONDUCTED. THE EVALUATION OF THIS RESEARCH WAS MADE BY THE X-RAY DIFFRACTION (XRD) ANALYSIS METHOD.
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AQUINO, AFONSO R. de. "Caracterizacao e estudo termoanalitico de clinquer produzido em industrias brasileiras." reponame:Repositório Institucional do IPEN, 1996. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10800.
Повний текст джерелаАнотація:
Made available in DSpace on 2014-10-09T12:44:08Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:07:00Z (GMT). No. of bitstreams: 1 02948.pdf: 2171704 bytes, checksum: 896d566852d96a5900bc907e2d478a43 (MD5)
Tese (Doutoramento)
IPEN/T
Instituto de Química - Universidade de São Paulo - IQ/USP
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Kashani, Mitra A. M. P. "Effect of cation substitutions in an ionomer glass composition on the setting reaction and properties of the resulting glass ionomer cements." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4548/.
Повний текст джерелаАнотація:
This study investigated the effect of Ba\(^2\)\(^+\) and Sr\(^2\)\(^+\) substitutions for Ca\(^2\)\(^+\) in an ionomer glass composition 4.5SiO\(_2\)-3Al\(_2\)O\(_3\)-1.5P\(_2\)O\(_5\)-3CaO-2CaF\(_2\) on the setting reaction and properties of the resulting glass ionomer cements (GICs). Experimental GICs (Ca-GIC, Ca-Sr-GIC and Ca-Ba-GIC) were characterized via various techniques: Diametral tensile strength, compressive strength, flexural strength, Vickers hardness and nano-indentation measurements were conducted at different time points during setting. Real time Fourier transform infrared (FTIR) spectroscopy was used to study the effect of the glass composition on cement setting reactions. A resistance to penetration method evaluated the cement setting time. Additionally, the wear resistance of the experimental GIC was measured by a ball-on-flat wear test. Furthermore, fluoride (F\(^-\)) release and the antimicrobial behaviour of cements were investigated. The compressive, diametral and flexural strength of the cements in which Ca\(^2\)\(^+\) was substituted by Sr\(^2\)\(^+\) and Ba\(^2\)\(^+\) were both statistically significantly higher than the unsubstituted control at 1 hour after setting (P < 0.001). FTIR results confirmed that enhanced metal salt crosslinking occurred in the ion substituted materials, especially from 1 to 60 minutes. Therefore, it can be concluded that replacing Ca\(^2\)\(^+\) with larger cations (Sr\(^2\)\(^+\) and Ba\(^2\)\(^+\)) affects the setting reaction and resulting mechanical properties in the short term. All three experimental GICs inhibited growth of Streptococcus mutans over a period of 48 hours. The F\(^-\)release analysis showed that there was less F\(^-\) release in artificial saliva (AS) than in deionized water over 40 days.
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Dufournet, Françoise. "Adaptation des ciments magnesiens au stockage souterrain des dechets nucleaires." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0088.
Повний текст джерелаАнотація:
Une etude de la composition mineralogique des ciments fait apparaitre un enrichissement en mgo et un appauvrissement en mgcl::(2) et en eau. La maniabilite, avant prise, est regie par la teneur en mgcl::(2). Les ciments riches en mgo varient beaucoup avec leur composition. Deux ciments de composition tres differente sont soumis a lessivage intensif en soxhlet double. Cela provoque l'augmentation de la permeabilite et la migration des acces de pores vers des acces plus gros pour l'un des ciments et l'inverse pour l'autre qui est un ciment hypermagnesien
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Tixier, Raphaël. "Etude mineralogique et mecanique de la phase liante de graves routieres." Toulouse 3, 1987. http://www.theses.fr/1987TOU30133.
Повний текст джерелаАнотація:
Comparaison des caracteristiques mineralogiques et des proprietes mecaniques de melanges equiponderaux de fillers calcaires, dolomitiques ou quartzeux avec 5 liants : ciment portland, ciment alumineux, ciment au laitier, cendres volantes chaux eteinte et fumees de silice condensees chaux residuaire. Evocation d'un nouveau liant routier, par melange de cendres volantes, fumees de silice condensees et chaux (l'additivite des proprietes se realisant pour des proportions particulieres)
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Okeyinka, Oriyomi M. "The applicability of recycled waste paper as lightweight building materials." Thesis, University of Wolverhampton, 2016. http://hdl.handle.net/2436/620495.
Повний текст джерелаАнотація:
In this era of increasing standard of living and rapid growth of civil engineering construction, environmental issues pertaining to natural resources depletion, global warming, energy crisis, waste pollution and greenhouse gas emission have been major issues of concern throughout the world and most especially in the construction industry. This research was conducted to investigate the applicability of recycled wastepaper as lightweight building materials with focus on contributing to sustainability in the creation of the built environment. The major aim was to develop an eco-friendly lightweight non-loadbearing block from recycled wastepaper without the use of cement as binder. This study specifically addressed the drawback of low strength development that usually occur with increasing wastepaper content in the existing cement-based-wastepaper blocks. It also indirectly addresses; the environmental impacts associated with the construction industry (including; high consumption of natural resources, greenhouse gas emission, high energy consumption and so on), the environmental pollution resulting from unsustainable waste generation, and the generic drawback of high water absorption that plagues wastepaper-based blocks. To achieve this, research methods including; laboratory experimentation and simulation modelling were employed. The research outcome is an eco-friendly block unit designated as Cement-less Wastepaper-based Lightweight Block (CWLB) which contains 75% waste content and exhibiting properties that satisfy the requirements for application as non-loadbearing lightweight blocks in building construction. CWLB displayed compressive strength that far outweighs those recorded for the existing cement-based wastepaper blocks available in the literature. The properties recorded for the optimal CWLB includes; 2.71 MPa average compressive strength, 901.5 kg/m3 average density, 0.19 W/m.k thermal conductivity, 989.9 m/s ultrasonic pulse velocity, 0.0026 g/m2.S0.5 average coefficient of capillary water absorption and 883.38 MPa estimated elastic modulus. The approximate compressive strength of 2.38 MPa and 1.58 MPa were respectively predicted and recorded for the solid and hollow finite element model samples of CWLB. The impressive satisfactory properties of CWLB for the intended application and its eco-friendliness in terms of natural resources conservation and improved compressive strength suggests that CWLB shall indeed serve as a more sustainable alternative to the reigning/existing cement-based-wastepaper blocks and to the conventional masonry blocks of the same category. Amongst other things, future work will address the validation of the approximate compressive strength predicted for the solid and hollow CWLB insitu samples in order to take further the subject matter.
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Curoşu, Iurie [Verfasser], Viktor [Akademischer Betreuer] Mechtcherine, Ulrich [Gutachter] Häußler-Combe, and Ravi [Gutachter] Ranade. "Influence of fiber type and matrix composition on the tensile behavior of strain-hardening cement-based composites (SHCC) under impact loading / Iurie Curosu ; Gutachter: Ulrich Häußler-Combe, Ravi Ranade ; Betreuer: Viktor Mechtcherine." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://d-nb.info/1156169380/34.
Повний текст джерела
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Autier, Caroline. "Etude de l’adjuvantation de pâtes cimentaires par différents polycarboxylates : la mésostructure : un lien entre interactions organo-minérales et propriétés macroscopiques." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20061/document.
Повний текст джерелаАнотація:
Les superplastifiants sont des adjuvants développés pour conférer aux matériaux cimentaires une plus grande fluidité pour un même rapport eau/ciment (E/C) en favorisant la dispersion des particules. De nombreuses études ont été réalisées pour approfondir la compréhension de leur mode d'action. La plupart du temps, elles relient directement la quantité adsorbée au comportement rhéologique des matériaux dans lesquels ils sont incorporés. Cependant, à une échelle intermédiaire, l'organisation mésostructurale de la pâte cimentaire contrôle non seulement sa fluidité, mais également son homogénéité et sa stabilité physicochimique.Ces travaux de thèse portent sur une dernière génération de superplastifiant : les polycarboxylates (PCE). Une approche expérimentale multi-échelles a été développée en intégrant les caractéristiques mésostructurales de la pâte de façon à faire le lien entre les interactions organo-minérales, notamment l'adsorption des PCE, et les propriétés macroscopiques (comportements en sédimentation et rhéologique). L'identification et la caractérisation granulaire de la pâte a été abordée à l'échelle de la particule, par une approche morpho-granulométrique. Des indices de dispersion ont été définis de façon à quantifier l'influence des PCE sur l'organisation mésostructurale des particules (particules unitaires ou agglomérées). Dans un second temps, l'évolution de cette organisation a été étudiée par l'analyse des colonnes de sédimentation. Un indice de séparation de phase a été défini, mettant en évidence l'existence de plages de stabilité en fonction du dosage et de la structure moléculaire du PCE incorporé.La mise en relation de ces observations avec l'étude des interactions organo-minérales a permis d'approfondir la compréhension du mode d'action et de l'influence des PCE. Cette démarche analytique représente un outil potentiel au développement de superplastifiants novateursSuperplasticizers are admixtures developed to give the cementitious materials greater fluidity for the same water to cement ratio (w/c), promoting the particles dispersion. Many studies were conducted to deepen the understanding of their mode of action. Usually, they connect directly the amount adsorbed with the rheological behavior of the materials in which they are incorporated. However, at an intermediate scale, mesostructurale organization of the cement paste controls not only its fluidity, but also its homogeneity and physicochemical stability.This work focuses on a new generation of superplasticizers: polycarboxylates (PCE). A multi-scale experimental approach has been developed by integrating mesostructural characteristics of cement paste to make the link between the organo-mineral interactions, particularly PCE adsorption, and the macroscopic properties (sedimentation and rheological behavior). Identification and granular characterization of cement paste was discussed, at the level of the particle, by a morpho-granulometric approach. Dispersion indices were defined to quantify the influence of PCE on mesostructural organization of particles (unit particles or agglomerates). In a second step, the evolution of this organization has been studied by analysis of sedimentation columns. A phase separation index has been defined, highlighting the existence of stability ranges as a function of the dosage and molecular structure of the PCE incorporated.Linking these observations with study of organo-mineral interactions has allowed to deepen the understanding of the mode of action and influence of PCE. This analytical approach is a potential tool to the development of innovative superplasticizers
34
Rassineux, François. "Altération des mortiers : étude expérimentale et analogues anciens." Poitiers, 1987. http://www.theses.fr/1987POIT2314.
Повний текст джерелаАнотація:
Etude de l'evolution de matrices cimentes soumise a une lixiviation par des solutions diluees. La stabilite des deux mortiers de compositions mineralogiques differentes depend du ph et de la pression en co::(2). Le mecanisme de dissolution est le processus dominant durant la lixiviation. L'identification du phases sur les liants modernes et ceuxs de l'epoque gallo romaine permet de connaitre la durabilite a long terme. Une simulation thermodynamique du processus ete realisee
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Bernard, Ellina. "Magnesium silicate hydrate (M-S-H) characterization : temperature, calcium, aluminium and alkali." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCK025/document.
Повний текст джерелаАнотація:
Les différentes options envisagées par la France et la Suisse pour le stockage de déchets radioactifs en couches géologiques profondes argileuses prévoient l’utilisation d’importants volumes de matériaux cimentaires. Les liants dits bas-pH ont été développés afin de limiter la perturbation de la roche encaissante par le panache alcalin. Les études expérimentales menées sur les interfaces béton bas-pH-argile mettent systématiquement en évidence la formation de phases silico-magnésiennes, potentiellement de silicate de magnésium hydraté (M-S-H), mal modélisées à cause de données thermodynamiques limitées. Cette étude a pour objectif de caractériser ces phases en température, en présence d’aluminium, calcium et d’alcalins pour alimenter les bases de données thermodynamiques et améliorer les calculs sur les évolutions physico-chimiques des bétons bas pH et éventuellement des bétons de Portland. Des suspensions de M-S-H ont été synthétisées à partir d'oxyde de magnésium et de fumée de silice à différentes températures, à différents temps de réaction et différents rapports Mg/Si. Un panel de techniques d’analyses de chimie du solide et des mesures en suspensions couplées à des analyses des phases liquides a été utilisé pour caractériser les phases synthétisées. Initialement, et quel que soit le Mg/Si total choisi pour la synthèse, un M-S-H avec un rapport Mg/Si ~1 précipite en présence de brucite et de silice amorphe. Lorsque l’équilibre du système est atteint, 2 à 3 ans à 20 °C ou 1 an à 50 et 70 °C, le Mg/Si varie de ~0,8 à ~1,4. La température a peu d'influence sur le M-S-H formé même si le M-S-H se forme plus rapidement et qu’il est légèrement moins stable thermodynamiquement lorsque la température augmente. A l'équilibre, sa structure mal définie est comparable à des nano-cristallites de phyllosilicates hydratés avec une surface spécifique supérieure à 200 m2/g. Un modèle de solution solide pour le M-S-H a été calculé et ajouté à la base de données.Dans un second temps, les travaux ont été focalisés sur la formation de M-S-H à partir de silicate de calcium hydraté (C-S-H) avec un faible Ca/Si (= 0,8) et de magnésium. Le C-S-H n’est pas stable à des pH avoisinant un pH = 10, ce qui favorise la précipitation de M-S-H. Des recherches détaillées montrent que du calcium peut être faiblement incorporé dans le M-S-H (Ca/Si ≤ 0,10), et des solutions solides contenant du calcium ont été ajoutés à la base de données. Pour des pH supérieurs à 10-10,5, les C-S-H et M-S-H coexistent. L’observation par MEB-EDS d’une interface en cellule de diffusion entre C-S-H (Ca/Si=0,8 représentant un liant bas pH) et M-S-H (Mg/Si=0,8), couplée à la modélisation de celle-ci en transport réactif, sur la base des nouvelles données thermodynamiques dérivées des expériences précédentes, montrent la détérioration rapide du C-S-H et la précipitation de M-S-H dans le disque C-S-H, ainsi qu’une absorption homogène du calcium dans le disque de M-S-H.L’augmentation du pH en solution favorise la sorption de cations. Des M-S-H présentant une sorption de sodium jusqu'à Na/Si ~ 0,20 en absence de brucite ont été observés à des pH avoisinants 12,5. La sorption sur le M-S-H est favorisée dans l'ordre Na+ < Mg2+ < Ca2+. Enfin, l'aluminium s’incorpore dans le M-S-H pour former du M-A-S-H. Un rapport Al/Si jusqu’à 0,2 est observé dans des suspensions synthétisées en présence d’aluminate de sodium ou de métakaolin. Les données de RMN de l’aluminium ont montré que celui-ci est présent dans les sites tétraédriques et octaédriques du M-A-S-H. La phase formée a une structure similaire à celle du M-S-H avec un degré de polymérisation des silicates et une charge effective de surface comparablesThe various options to store radioactive wastes in deep geological strata considered in France or Switzerland include the use of large volumes of cementitious materials for infrastructure in contact with argillaceous rocks. So-called low-pH binders were developed to minimize disruption to the surrounding rock by the alkaline plume. Studies conducted on the interaction zone between concrete and clay systematically highlighted the formation of magnesium silicate phases including magnesium silicate hydrate (M-S-H) at the interfaces, which can presently be modeled only partially due to incomplete thermodynamic data. The purpose of this study was to characterize these phases in temperature, aluminum, calcium, and alkali conditions in order to provide the thermodynamic data and improve the calculations on physicochemical evolutions of low-pH concretes and possibly Portland concretes.M-S-H phases were synthesized from magnesium oxide and silica fume in batch experiments at different temperatures, for various times and varying Mg/Si. A large number of different techniques such as chemical solid characterizations coupled with suspension investigations and liquid analyses were used to characterize the phases synthesized. Initially a M-S-H phase with Mg/Si equal to 1 was precipitated in addition to amorphous silica and brucite whatever the total Mg/Si used for the synthesis. After long equilibration times, 2 to 3 years at 20°C or 1 year at 50 and 70°C, the Mg/Si in M-S-H ranged from ~0.8 to ~1.4. The temperature had little influence on the M-S-H formed even if the M-S-H formation occurred faster and M-S-H was thermodynamically slightly less stable when the temperature was increased. At or near to equilibrium, M-S-H phases were characterized with ill-defined structure comparable to nano-crystallite, hydrated phyllosilicates with a surface area greater than 200 m2/g. A M-S-H solid-solution model was calculated and implemented in the thermodynamic database.It was observed that M-S-H also form from calcium silicate hydrate (C-S-H) with a Ca/Si = 0.8 in the presence of additional magnesium. In batch experiments, a low pH of the suspensions (pH ≤ 10) destabilized C-S-H or prevented its formation and favored the precipitation of M-S-H. Detailed investigations showed that small amounts of calcium could be incorporated in M-S-H (Ca/Si ≤0.10), such that also calcium containing end-members were added to the M-S-H solid-solution. At pH ≥ 10-10.5, two separate silicate phases coexist: C-S-H and M-S-H. The interface between a simplified “low-pH” binder mimicked by C-S-H with Ca/Si = 0.8 and a magnesium-rich environment mimicked by M-S-H with Mg/Si = 0.8 confirmed these phenomena. SEM-EDS observations and reactive transport modelling using the thermodynamic data derived in the batch experiments showed the fast deterioration of the C-S-H and the precipitation of M-S-H in the C-S-H disk at the interface and a homogeneous uptake of calcium in the M-S-H disk.The increase of pH favors the sorption. M-S-H with a sodium uptake up to Na/Si ~ 0.20 and without brucite formation were observed at high pH (12.5). The sorption on M-S-H was favored in the order Na+ < Mg2+ < Ca2+. Finally, aluminum was incorporated into M-S-H to form magnesium alumino-silicate hydrate (M-A-S-H). An Al/Si ratio up to 0.2 was observed in presence of sodium aluminate or metakaolin. 27Al MAS NMR data showed that aluminum was present in both tetrahedral and octahedral sites of M-(A-)S-H. The M-(A-)S-H formed had a similar structure as M-S-H with a comparable polymerization degree of the tetrahedral silicates and a similar surface charge
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Homrich, Jefferson Teixeira Olea. "Avaliação do comportamento do cimento supersulfatado em concreto autoadensável." Universidade Tecnológica Federal do Paraná, 2018. http://repositorio.utfpr.edu.br/jspui/handle/1/3230.
Повний текст джерелаАнотація:
O concreto autoadensável (CAA) tem a capacidade de fluir por obstáculos, preenchendo as fôrmas e resistindo à segregação, entretanto esse concreto apresenta proporção pasta-agregado alta, o que ocasiona um maior desprendimento de calor durante a hidratação do cimento bem como maior suscetibilidade a retração. Os cimentos oriundos da utilização de subprodutos industriais vêm ganhando atenção, devido à preocupação ambiental, sendo um deles o cimento supersulfatado (CSS). O CSS tem como constituintes a escória granulada de alto forno (80-90%), fonte de sulfato de cálcio (10-20%) e um ativador alcalino (até 5%), podendo, este último, ser o próprio clínquer Portland. Além do baixo gasto energético e da redução de emissão de CO2 o CSS, pode-se destacar pelo consumo de resíduos industriais que seriam descartados ao meio ambiente. Como principais características, este aglomerante apresenta baixo calor de hidratação e maior formação de etringitta nas primeiras idades, o que poderia viabilizar seu uso como um compensador de retração, características desejáveis no concreto autoadensável (CAA). Este trabalho busca estudar a adequação do CSS na produção de CAA e, para isso, dosou-se concretos autoadensáveis, utilizando o CSS e o cimento Portland pozolânico (CP IV) como referência, por ser um cimento de baixo calor de hidratação. Realizaram-se ensaios de autoadensibilidade, calor de hidratação, retração plástica e por secagem, módulo de elasticidade aos 28 dias, resistência à compressão aos 7,28 e 56 dias, absorção de água aos 28 dias e MEV aos 7 e 28 dias de hidratação. Os CAA’s produzidos com CSS apresentaram resultados superiores do que os produzidos com o CP IV que atenderam aos limites estabelecidos da NBR 15823 (2010) e, além disso, apresentaram menor taxa de liberação de calor e calor total liberado. O CSS obteve maiores valores de retração plástica, porém para retração por secagem o mesmo apresentou uma compensação de retração aos 28 dias de hidratação, apresentando valores inferiores ao CP IV. O CAA dosado com CP IV apresentou melhor desempenho na resistência mecânica, módulo de elasticidade e absorção de água, porém, apesar da menor resistência, o CSS apresentou valores que podem ser aplicados para diversas situações da construção civil, pois chegou a valores próximos a 40 MPa aos 28 dias.SCC has the ability to flow through obstacles, filling the molds and resisting to segregation. However, this type of concrete has high cement paste-aggregate ratio, which causes higher heat release during cement hydration as well as higher susceptibility to retraction. Cements native from factory sub products are gaining attention due to environmental issues, being one of these the super sulfated cement (SSC). SSC has in its constitution granulated blast furnace slag (80%-90%), calcium sulfate (10-20%) and an alkaline activator (up to 5%), possibly Portland clinker. Besides low energy expense and a reduction in CO2 emission, SSC might stand out by its usage of factory waste which would be discarded to the environment. As its main characteristics, this type of binder presents low hydration heat release and higher formation of ettringite in the earlier ages, which could make it feasible to be used as a retraction compensator, characteristics desired in self-compacting concrete (SCC). This thesis studies the adequacy of SSC in SCC production, and for that reason SCC mixes were dosed using SSC and pozzolanic Portland cement type CP IV for benchmarks, as it is a low hydration heat release type of cement. Self-compacting tests were performed, as well as hydration heat tests, drying and plastic shrinkage, elasticity modulus at 28 days, axial compression resistance at the ages of 7, 28 and 56 days, water absorption at 28 days and SEM at 7 and 28 days of hydration. SCC’s produced with SSC presented superior results compared to CP IV cements that attended to the established limits is NBR 15823 (2010). SSC exhibited higher values for plastic shrinkage, but for drying shrinkage it presented retraction compensation at 28 days of hydration, showing inferior values compared to CP IV. SCC mixed with CP IV exhibited better performance on mechanical resistance, elasticity modulus and water absorption, but, despite its inferior resistance, SSC presented values that could be applied to a variety of situations in civil construction because its values reached around 40 MPa at 28 days.
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Ther, Olivier. "Élaboration de carbures cémentés à gradient de propriétés par procédé d’imbibition réactive : Application aux inserts WC-Co et aux taillants en diamant polycristallin pour le forage pétrolier en conditions sévères." Thesis, Paris, ENMP, 2014. http://www.theses.fr/2014ENMP0067.
Повний текст джерелаАнотація:
Dans l'industrie du forage pétrolier, les conditions de travail de plus en plus sévères requièrent sans cesse de nouveaux outils plus résistants à l'usure abrasive et à l'impact. Afin de répondre à ce défi, les travaux présentés ici, ont pour but l'élaboration de matériaux en carbure cémenté à gradient de composition par le procédé d'imbibition réactive. Ce procédé peut être décomposé en deux procédés de gradation, à savoir : l'imbibition et le revêtement réactif. L'imbibition a pour rôle d'enrichir graduellement, en phase liante, le coeur d'une pièce en carbure cémenté dense et repose sur le principe de migration de phase liquide dans un corps solide-liquide. Le revêtement réactif est un procédé qui s'applique également sur un carbure cémenté dense sur lequel est déposé un revêtement de nitrure de bore. Après avoir atteint le liquidus de la phase liante du carbure cémenté, une précipitation de borures ternaires prend place à la surface du matériau et s'étend graduellement sur des distances millimétriques. Dans le cas de pièces industrielles (inserts tricône et supports de taillants PDC (Polycrystalline Diamond Compact)), le traitement d'imbibition réactive permet de générer des gradients de dureté pouvant atteindre 450 HV sur 25 mm. L'élaboration de tels gradients a nécessité une meilleure compréhension des cinétiques ainsi que des phénomènes mis en jeu durant l'imbibition et le revêtement réactif. Dans le cas des taillants PDC, l'influence des paramètres du procédé HPHT de synthèse de la plaquette diamantée, sur le gradient de composition présent dans le support WC-Co après imbibition réactive, a été étudiée. Ces travaux se sont également intéressés à l'effet de ces gradients de composition sur les propriétés des plaquettes diamantées ainsi obtenues. A la suite d'essais mécaniques, les inserts WC-Co et taillants PDC gradués montrent une augmentation significative de leur résistance à l'abrasion (de 30 à 100%) et de leur tenue à l'impact (de 20 à 40%)In oil drilling industry, harsher working conditions require ever new and more abrasive wear and impact resistant tools. To meet this challenge, the work presented here, is to develop graded cemented carbide materials by reactive imbibition process. This method can be divided into two gradation processes, namely, reactive coating and imbibition. Imbibition gradually enriches the core of dense cemented carbide with binder phase and is based on the principle of liquid phase migration in a solid-liquid body. Reactive coating also takes place in dense cemented carbide on which a boron nitride coating is deposited. After reaction with the WC-Co liquid binder, some ternary boride precipitations take place from surface to several millimeters deep. For industrial parts (inserts for roller cone bits and PDC (Polycrystalline Diamond Compact) cutters substrates), hardness gradients obtained can reach 450 HV on 25 mm. Such gradients development is passed through a better understanding of kinetics and phenomena occurring during imbibition and reactive coating. In case of PDC cutters, influence of HPHT process parameters, allowing diamond table synthesis, on the WC-Co substrate gradient, generated by reactive imbibition, was studied. This work was also interested in gradient effect on the obtained diamond tables properties. After mechanical tests, graded WC-Co inserts and graded PDC cutters show a significant increase of both wear resistance (from 30 to 100%) and impact resistance (from 20 to 40%)
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Шиліна, О. П., В. П. Перегончук, Е. П. Шилина, В. П. Перегончук, E. P. Shilina та V. P. Peregonchuk. "Порошкова композиція для газотермічного зміцнення деталей машин". Thesis, ВНТУ, 2013. http://ir.lib.vntu.edu.ua/handle/123456789/7704.
Повний текст джерелаАнотація:
В роботі показано, що внаслідок екзотермічних реакцій, що протікають в процесі напилювання, досягається оптимальна об’ємна структура, у якої тверді зони, що складаються з більш крихкого матеріалу, ізольовані одна від однієї, а між ними розташована матриця з в’язкого матеріалу – виконується так званий принцип Шарпі-Бочвара.В работе показано, что в результате экзотермических реакций, протекающих в процессе напыления, достигается оптимальная объемная структура, в которой твердые зоны, состоящие из более хрупкого материала, изолированные друг от друга, а между ними расположена матрица из вязкого материала - выполняется так называемый принцип Шарпи-Бочвара.
Іt is shown that due to exothermic reactions during spraying, achieved optimal three-dimensional structure, which has a solid zone consisting of a brittle material, isolated from one another, and between them is a viscous matrix material - performed so called Sharp-Bochvar.
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Chabi, Edem. "Étude de la formulation et des propriétés mécaniques et thermiques du béton de balles de riz." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0232/document.
Повний текст джерелаАнотація:
Chacun s’accorde à reconnaître aujourd’hui que les activités humaines impactent significativement le climat de la planète. Le secteur de la construction est l’un des principaux responsables de cette situation car c’est le premier consommateur d’énergie et le deuxième émetteur de CO2 dans le monde. Il importe par conséquent de réaliser des bâtiments éco-respectueux, qui consomment peu d’énergie et émettent moins de gaz à effet de serre sur l’ensemble de leur cycle de vie. La présente étude s’intègre alors dans une problématique générale de développement de matériaux de construction innovants à impact environnemental réduit. Nous nous proposons ainsi d’utiliser la balle de riz comme granulat végétal dans une matrice cimentaire. L’objectif du travail est de proposer une méthode de formulation des bétons à bases de granulats végétaux et d’étudier le comportement mécanique et thermique du béton de balle de riz. Les essais de prise réalisés sur de la pâte de ciment pure formulée avec de l’eau issue de l’infusion de la balle de riz ont montré que ces granulats n’ont pas d’effet inhibiteur sur la prise du ciment. Pour confirmer cette hypothèse, une analyse chimique de la balle de riz a été réalisée et les résultats ont montré le taux d’extractibles des balles de riz est quasi nul contrairement à d’autres granulats végétaux tels que le chanvre et le bois. La méthode de formulation proposée consiste à déterminer la compacité du squelette végétal pour un mode de mise en œuvre déterminé, puis à formuler la pâte liante qui va occuper le volume poreux intergranulaire résiduel. La pâte est constituée du liant, de l’eau efficace, des additions et adjuvants éventuels, et de l’air piégé et/ou entrainé. Pour un volume d’air donné (et d’additions), les quantités de ciment et d’eau efficace sont alors ajustées pour atteindre les performances visées, sur la base de la loi de Féret. Cependant, pour ce type de béton, l’important volume d’air entrainé dépend (lui aussi) de la quantité de ciment et d’eau présents dans le mélange, de l’intensité du malaxage et du mode de coulage. Un modèle décrivant le volume d’air résiduel a été alors calibré à partir d’essais réalisés avec les constituants du béton que l’on souhaite fabriquer. Enfin le problème de la formulation est solutionné en recourant à un module d’optimisation numérique. Dans le but de valider le modèle, la méthode de formulation a été appliquée à cinq échantillons dont les résistances visées sont 0,5 ; 1 ; 2 ; 4 et 8 MPa. Les performances obtenues sont assez proches de celles visées. Par ailleurs il a été constaté que le mode de conservation des éprouvettes influe beaucoup sur les résistances mécaniques du matériau. En effet, une cure en condition dessiccation peut faire chuter les résistances mécaniques jusqu’à 60%. Les meilleures résistances obtenues ont été observées sur les éprouvettes conservées à 95 % de HR. Les mesures de la conductivité thermique ont montré que le béton de balle de riz constitue une très bonne alternative à des systèmes plus conventionnels en termes d’isolation thermique. La valeur moyenne de la conductivité thermique du béton de balle de riz varie en fonction du dosage en liant entre 0,070 W/(m.K) et 0,171 W/(m.K). L’évolution de la conductivité thermique en fonction de la masse volumique et du dosage en ciment est linéaireEveryone agrees today that human activities significantly affect the climate of the planet. The construction sector is one of the main contributors to this situation as it is the largest energy consumer and the second largest CO2 emitter in the world. It is therefore important to build eco-friendly buildings, which consume little energy and emit less greenhouse gases throughout their life cycle. The present study is then integrated into a general problem of development of innovative building materials with reduced environmental impact. We propose to use the rice husk as a vegetable aggregate in a cementitious matrix. The objective of the work is to propose a method for the mix design of concretes based on plant aggregates and to study the mechanical and thermal behavior of rice husk concrete. Setting tests on pure cement paste formulated with water resulting from the infusion of the rice husk showed that these aggregates had no inhibiting effect on the setting of the cement. To confirm this hypothesis, a chemical analysis of the rice husk was carried out and the results showed that the extractable ratio of rice husks is almost zero, unlike other plant aggregates such as hemp and wood. The proposed formulation method consists in determining the packing density of the plant skeleton for a given method of implementation and then in proportioning the binder paste which will occupy the residual intergranular pore volume. The paste is consisted of the binder, the effective water, the possible additions and admixture, and trapped air and/or entrained air. For a given volume of air (and additions), the quantities of cement and effective water are then adjusted to achieve the targeted performances, based on the law of Féret. However, for this type of concrete, the large volume of entrained air also depends on the quantity of cement and water present in the mixture, the intensity of the mixing and the casting mode. A model describing the volume of residual air was then calibrated from tests carried out with the components of the concrete that it is desired to manufacture. Finally, the problem of formulation is solved by using a numerical optimization module. In order to validate the model, the method for the mix design was applied to five samples with a target resistance of 0.5; 1; 2; 4 and 8 MPa. The performances obtained are quite similar to those targeted. In addition, it has been observed that the preservation mode of the specimens has a significant influence on the mechanical strength of the material. Indeed, a cure in desiccation condition can reduce the mechanical resistances up to 60%. The best resistances obtained were observed on the specimens preserved at 95 % RH. Measurements of thermal conductivity have shown that rice husk concrete is a very good alternative to more conventional systems in terms of thermal insulation. The average value of the thermal conductivity of the rice husk concrete varies depending on the binder dosage between 0.070 W/(m.K) and 0.171 W/(m.K). The evolution of the thermal conductivity as a function of the density and the cement dosage is linear
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Namango, Saul Sitati [Verfasser]. "Development of cost effective earthen building material for housing wall construction: investigations into the properties of compressed earth blocks stabilized with sisal vegetable fibres, cassava powder and cement compositions / by Saul Sitati Namango." 2006. http://d-nb.info/982828748/34.
Повний текст джерела
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Khanna, Om Shervan. "Characterization and Utilization of Cement Kiln Dusts (CKDs) as Partial Replacements of Portland Cement." Thesis, 2009. http://hdl.handle.net/1807/19198.
Повний текст джерелаАнотація:
The characteristics of cement kiln dusts (CKDs) and their effects as partial replacement of Portland Cement (PC) were studied in this research program. The materials used in this study were two different types of PC (normal and moderate sulfate resistant) and seven CKDs. The CKDs used in this study were selected to provide a representation of those available in North America from the three major types of cement manufacturing processes: wet, long-dry, and preheater/precalciner. Two fillers (limestone powder and quartz powder) were also used to compare their effects to that of CKDs at an equivalent replacement of PC. It was found that CKDs can contain significant amounts of amorphous material (>30%) and clinker compounds (>20%) and
small amounts of slag and/or flyash (<5%) and calcium langbeinite (<5%). The study found that CKDs from preheater/precalciner kilns have different effects on workability and heat evolution than CKDs from wet and long-dry kilns due to the presence of very reactive and high free lime contents (>20%). The blends with the two CKDs from preheater/precalciner plants had higher paste water demand, lower mortar flows, and higher heat generation during initial hydrolysis in comparison to all other CKD-PC blends and control cements. The hardened properties of CKD as a partial substitute of PC appear to be governed by the sulfate content of the CKD-PC blend (the form of the CKD sulfate is not significant). According to analysis of the ASTM expansion in limewater test results, the CKD-PC blend sulfate content should be less than ~0.40% above the optimum sulfate content of the PC. It was also found that the sulfate contribution of CKD behaves similar to gypsum. Therefore, CKD-PC blends could be
optimized for sulfate content by using CKD as a partial substitute of gypsum during the
grinding process to control the early hydration of C3A. The wet and long-dry kiln CKDs contain significant amounts of calcium carbonate (>20%) which could also be used as
partial replacement of limestone filler in PC.
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Chen, Jian-an, and 陳建安. "Waste printed circuit board non-metallic composition resources in the cement concrete." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/67317490345910153783.
Повний текст джерелаАнотація:
碩士國立中央大學
土木工程研究所
100
In this study, (WPCB, which is short for) the non-metallic fractions of waste printed circuit board, is used as resource in related practices. The direction of the practices is focused on partial replacement of natural fine aggregates in the cellular mortar and the lightweight aggregate concrete products. WPCB in the use of cellular mortar, if the replacement ratio of natural fine aggregates is over 50%, the property of new mixture will be effected. However, the effect on the property of robustness eases whilst the replacement ratio increases. The decreasing trend gradually moderates until after the ratio reaches 50%. WPCB in the use of lightweight aggregate concrete, under the condition of water-cement ratio=0.6, the replacement ratio within 10% has no obvious effect on property of new mixture; however, if the replacement ratio rises over 10%, in order to improve the working performance, adding the superplasticizer is needed. As soon as the adding of superplasticizer reaches 0.75% of the weight of the concrete, the working performance of the lightweight aggregate concrete is close to the control group. To the composition of which the WPCB replacement ratio reaches above 30%, even the adding of superplasticizer does not help with improving the working performance. Because adding WPCB affects the property of new mixture of cellular mortar and lightweight aggregate concrete, it is recommended that the replacement ratio of WPCB do not rise above 50% for cellular mortar, and 25% for lightweight aggregate concrete.
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Faulkner, Sean. "The Distribution, Composition, and Formation of Sahara Desert Microbialites From the Base of the Meski Plateau, outside Erfoud, Morocco." 2010. https://scholarworks.umass.edu/theses/527.
Повний текст джерелаАнотація:
Seven distinctly different museum-quality concretionary morphotypes of elongate, spheroidal, banded, botryoidal, columnar, rosette, and speleothem in regolith at two small sites at the base of the Meski Plateau near Erfoud, Morocco are described. Although most are isolated hand samples, the largest concretions are meter-sized blocks. Not one sample resembles any surrounding outcrop or bedrock. The barite rosettes formed first via periodic mixing of Ba2+/SO42- saturated solutions. They provided nuclei for cyclical precipitation-based concentric concretion development. The speleothem formed via precipitation from a carbonate-saturated solution in a large void within porous sandstone. The sand concretions formed when calcite precipitated around grains in unconsolidated quartz sands with cyclic fluctuation of Ca2+/CO32- saturated ground water. Petrographic analyses, stable isotope data, sample morphology, coupled with light and scanning electron microscopy indicate that microbial processes induced the periodic cement precipitation that produced the unique concretions.
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Leung, Albert. "Mineral composition of hypothermally induced ankylosis in rat molars." 2010. http://hdl.handle.net/2440/60949.
Повний текст джерелаАнотація:
This study used Backscattered electron imaging (BSE) and X-ray Microanalysis to qualitatively and quantitatively investigate morphology and elemental composition of ankylotic adaptation in the periodontium following hypothermic insult to their maxillary first molars. This method has been shown in previous studies to induce aseptic root resorption along with ankylotic changes within the periodontal ligament (PDL). A secondary objective was to assess the pulpal changes that occurred concurrent with the changes in the periodontium. Twenty-eight eight week old Sprague Dawley rats were divided into four groups of seven animals corresponding to one of four observation periods i.e.: t₁= 7 days, t₂= 14 days, t₃= 21 days, t₄ = 28 days. At t=0 days, six animals in each group received a thermal insult as a continuous 20 minute application of dry ice (CO₂ at -81⁰C) to the crowns of their upper right maxillary molar. The untreated left molars were used as controls. The remaining rat within each group did not receive the dry ice. All rats were given two sequential bone labels, calcein 5mg/kg and alizarin red 30mg/kg, administered intraperitoneally 8 days apart. The timing of the labels was such that all rats were euthanased 2 days after the last label. Following sacrifice, the maxillae were dissected out, fixed in ethanol and embedded in methylmethacrylate. Ten microns thick, undecalcified maxillary first molar coronal sections through the furcation were obtained. For every 3 out of 10 sections: the first was left unstained and undecalcified; the second stained with Von Kossa/haematoxylin & eosin; and the third decalcified and stained with haematoxylin & eosin. Unstained sections were viewed under fluorescence, while transmitted light microscopy was used for the other sections. Following initial analysis, the unstained, undecalcified sections were de-coverslipped and carbon coated. These sections were investigated with scanning electron microscopy and Energy Dispersive X-ray Spectrometry (EDS). Quantitative spot analysis and element mapping was performed on alveolar bone, ankylotic areas, cementum and dentine. A linear mixed effects model was employed to investigate any interaction between the four tissues of interest. A focal pattern of ankylosis was observed at days 14 and 21 in three rats. No ankylosis was observed in the control teeth. SEM revealed a focal type of ankylosis with central nodules of mineralized tissue forming within the PDL. Bridging between bone and dentine occurred with fine trabeculae which extended from the central mineralized nodule. Bridging was progressive and was more extensive at day 21 compared to day 14. At day 28, no ankylosis was observed. EDS analysis revealed that the ankylotic tissue was composed of major constituents Calcium and Phosphorous along with trace elements of Mg and Na. This was comparable to the surrounding alveolar bone, cementum and dentine. There was no statistically significant difference in the Ca/P ratios, Mg when ankylotic material was compared to bone. There was a trend towards elevated Na levels in ankylosis but this was not statistically significant relative to bone. Mg in dentine was lower than for all the other tissues and Na was higher in dentine when compared to bone and cementum. In the pulp, hypothermic injury demonstrated alteration of the odontoblast layer, reduction in cellularity, vascular alterations and tertiary dentin formation. At the 28 day observation period, the cellular and vascular changes had returned to levels comparable to the control teeth, indicating successful pulpal healing and regeneration. Marked tertiary dentine deposition was also observed at days 14, 21 and 28. Pulp chambers were visibly smaller due to tertiary dentine formation, however no pulp necrosis was observed. Thus the aseptic root resorption model, using a continuous 20 minute application of dry ice, suggested the occurrence of reversible pulpal tissue alterations compatible with an inflammatory repair process. The observation of ankylosis initiating as centralised nodules within the PDL suggest that the origins may be a consequence of osteogenic potential from PDL stem cells. The null hypothesis that a single, prolonged thermal insult on a rat molar does not have an effect on mineralized tissue formation and that ankylotic tissue is similar to bone was rejected. ABSTRACT There is a presumption that the ankylotic region formed after periodontal ligament (PDL) injury represents an unremarkable bony repair process. Essentially, the injury triggers an osteogenic repair response and the ankylotic tissue merely represents alveolar bone. There is uncertainty whether the oestogenic event is predominantly osteoblast driven, cementoblast directed, or a consequence of osteogenic potential from PDL stem cells. In this study, twenty-eight Sprague Dawley rats were divided into four groups of six animals, corresponding to one of four observation periods, and received a thermal insult as a continuous 20 minute application of dry ice to the crowns of their upper right maxillary molar. The appearance of ankylotic tissues was examined using backscattered electron images using a scanning electron microscope (SEM) equipped with an Energy Dispersive X-ray Analyser (EDS). The Ca, P, and trace elements contents were determined by EDS from four different hard tissue regions: ankylosis; bone; dentine and cementum, and the Ca/P ratios were calculated. Ankylosis was observed at days 14 and 21 in 3 rats and was not seen at day 28. No ankylosis was observed in the control teeth. BSE imaging revealed a focal type of ankylosis with central nodules of mineralized tissue forming within the PDL. The morphological features of ankylotic tissue differed to that of alveolar bone and dentine. Bridging between bone and dentine occurred with fine trabeculae which extended from the central mineralized nodule. EDS analysis showed that the ankylotic tissue was composed of major constituents Ca and P along with trace elements of Mg and Na. This was comparable to the surrounding alveolar bone, cementum and dentine. There was no statistically significant difference in the Ca/P ratios, Mg, and Na between ankylotic material and bone. Statistically significant differences was evident in Mg content between ankylotic material compared to dentine and cementum. Na content was higher in dentine than in ankylotic material. The results of this study indicate that, histochemically, ankylotic material is similar to bone. However, the appearance of ankylotic material as centralised foci with a morphology different from bone suggest that ankylosis may originate from an osteoblastic phenotype originating within PDL.http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1522156
Thesis (D.Clin.Dent.) -- University of Adelaide, School of Denstistry, 2010
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Kozlovcev, Petr. "Vliv mineralogického složení suroviny na vznik fází při výpalu hydraulického vápna a přírodního cementu." Doctoral thesis, 2018. http://www.nusl.cz/ntk/nusl-383076.
Повний текст джерелаАнотація:
Natural hydraulic lime and natural cement have been used in the building industry for centuries. These inorganic hydraulic binders are called "traditional" or "alternative" because they can, in some cases, substitute modern Portland cement. The recent increased interest in these binders is due not only to their use in restoration practices, but also because their production and use is less energetically demanding than in modern cements. Historically, many types of hydraulic binders were produced in the regions of Bohemia and Moravia. However, much information has been lost about their manufacturing process, which raw materials were used, and we are uncertain of the exact character and properties of the burned material. To date, studies have only addressed the impact of the chemical composition of raw material on the parameters of the burned material - all this is well known for Portland cement, much less for other types of hydraulic binders. The aim of this dissertation was to study the various types of raw materials (limestone containing non- carbon admixtures) and to understand the characteristics of their respective hydraulic lime and natural cement. This was done by analyzing the impact of conditions (highest achieved burning temperature and time of burning) and the mineral and chemical...
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Curosu, Iurie. "Influence of fiber type and matrix composition on the tensile behavior of strain-hardening cement-based composites (SHCC) under impact loading." Doctoral thesis, 2017. https://tud.qucosa.de/id/qucosa%3A30801.
Повний текст джерелаАнотація:
Strain-hardening cement-based composites (SHCC) are a special class of fiber-reinforced concrete which develop multiple, fine cracks when subjected to increasing tensile loading, reaching strain capacities of up to several percent. The tensile behavior of SHCC is a result of a purposeful material design accounting for the mechanical and physical properties of the cementitious matrix, of the reinforcing fibers and of their interaction.
The exceptionally high energy dissipation through inelastic deformations before reaching tensile strength makes SHCC suitable for manufacturing or strengthening of structural elements which may be subjected to impact loading. However, the tensile behavior of SHCC is highly strain rate dependent, both in terms of tensile strength and strain capacity. The different strain rate sensitivities of the constitutive phases of SHCC (matrix, fiber and interfacial bond) lead to disproportionate dynamic alteration of their mechanical properties under increasing strain rates and, consequently, to an impairment of the micromechanical balance necessary for strain-hardening and multiple cracking. Thus, high energy dissipation under impact loading can only be ensured through a targeted material design.
This work presents a series of mechanical experiments at different strain rates and different scales of investigation with the goal of developing a qualitative and quantitative basis for formulating material design recommendations for impact resistant SHCC. Three different types of SHCC were investigated, consisting of two types of polymer fibers (polyvinyl-alcohol and high-density polyethylene) and cementitious matrices (normal-strength and high-strength).
Uniaxial tension experiments were performed on SHCC specimens and on non-reinforced matrix specimens with different testing setups at strain rates ranging from 10-4 to 150 s-1. Besides the measured mechanical properties, special attention was paid to the crack patterns and the condition of fracture surfaces. Additionally, micro-scale investigations were performed to quantify the strain rate dependent changes in the mechanical behavior of individual component phases, i.e., matrix, fibers and fiber-matrix bond.
The results obtained from the micromechanical investigations were used in an analytical model for crack bridging. The model links the micromechanical parameters and their strain rate sensitivities to the single-crack opening behavior under increasing displacement rates, making it useful for material design purposes. If given an extensive experimental basis for the fracture mechanical properties of the non-reinforced cementitious matrices, the model can be extended for predicting the strain capacity (multiple cracking) of SHCC under different strain rates.Die hochduktilen Betone (Engl.: Strain-Hardening Cement-based Composites – SHCC) bilden eine besondere Klasse von Faserbetonen, die eine multiple Rissbildung unter zunehmenden Zugspannungen aufweisen, was zu einer sehr hohen Bruchdehnung führt. Das dehnungsverfestigende, hochduktile Zugverhalten der SHCC wird durch eine gezielte Materialentwicklung erreicht, die die mechanischen und physikalischen Eigenschaften der zementgebundenen Matrizen, der Kurzfasern und deren Zusammenwirkung berücksichtigt. Das außergewöhnliche Energieabsorptionsvermögen der SHCC durch plastische Verformungen vor dem Erreichen der Zugfestigkeit qualifiziert diese Verbundwerkstoffe für die Herstellung oder Verstärkung von Bauteilen, die Impaktbeanspruchungen ausgesetzt sein könnten. Jedoch weisen SHCC sowohl bezüglich deren Zugfestigkeit als auch deren Dehnungskapazität ein ausgeprägtes dehnratenabhängiges Verhalten auf. Unter zunehmenden Dehnraten führen die unterschiedlichen Dehnratensensitivitäten der gestaltenden Phasen von SHCC (Matrix, Faser und deren Verbund) zur Beeinträchtigung des mikromechanischen Gleichgewichts, welches für die Dehnungsverfestigung und multiple Rissbildung erforderlich ist. Eine hohe Energiedissipation unter Impaktbeanspruchungen kann deshalb nur durch eine gezielte Materialentwicklung der SHCC hinsichtlich deren Verhaltens unter hohen Dehnraten gewährleistet werden. Die vorliegende Arbeit umfasst eine Reihe von experimentellen Untersuchungen mit verschiedenen Dehnraten und an unterschiedlichen Betrachtungsebenen, mit dem Ziel eine qualitative und quantitative Basis für Empfehlungen zur Materialentwicklung von Impakt-resistenten SHCC zu schaffen. Drei verschiedene SHCC-Zusammensetzungen wurden untersucht. Die Referenz-Zusammensetzung aus einer normalfesten zementgebundenen Matrix und Polyvinyl-Alkohol-Kurzfasern wurde mit zwei unterschiedlichen SHCC verglichen (hochfest und normalfest), die mit Kurzfasern aus hochdichtem Polyethylen bewehrt wurden. Einaxiale Zugversuche wurden an SHCC-Proben und unbewehrten Matrix-Proben mit verschiedenen Prüfvorrichtungen bei Dehnraten von 10-4 bis 150 s-1 durchgeführt. Zusätzlich zu den gemessenen mechanischen Eigenschaften wurden die Rissbildung und die Bruchflächen detailliert untersucht. Darüber hinaus wurden mikromechanische Untersuchungen durchgeführt, um die Dehnratensensitivität der einzelnen Phasen, d.h. Matrix, Faser und deren Verbund zu beschreiben. Die aus den mikromechanischen Untersuchungen erzielten Ergebnisse wurden als Eingangswerte in einem analytischen Einzelriss-Modell verwendet. Das entwickelte Modell verbindet die mikromechanischen Parameter und deren Dehnratenabhängigkeit mit dem Rissöffnungsverhalten von SHCC bei zunehmenden Verschiebungsraten. Das macht es vorteilhaft für Materialentwicklungszwecke. Das Modell kann für die Vorhersage der Dehnungskapazität von SHCC bei diversen Dehnraten weiterentwickelt werden, wenn eine umfassende experimentelle Basis für die bruchmechanischen Eigenschaften der Matrizen vorliegt.