Dissertations / Theses on the topic 'Cementitious materials'

The study of self-sensing cementitious materials is a constantly expanding topic of study in the materials and civil engineering fields and refers to the creation and utilization of cement-based materials (including cement paste, cement mortar, and concrete) that are capable of sensing (i.e. measuring) stress and strain states without the use of embedded or attached sensors. With the inclusion of electrically conductive fillers, cementitious materials can become truly self-sensing. Previous researchers have provided only qualitative studies of self-sensing material stress-electrical response. The overall goal of this research was to modify and apply previously developed predictive models on cylinder compression test data in order to provide a means to quantify stress-strain behavior from electrical response. The Vipulanandan and Mohammed (2015) stress-resistivity model was selected and modified to predict the stress state, up to yield, of cement cylinders enhanced with nanoscale iron(III) oxide (nanoFe2O3) particles based on three mix design parameters: nanoFe2O3 content, water-cement ratio, and curing time. With the addition of a nonlinear model, parameter values were obtained and compiled for each combination of nanoFe2O3 content and water-cement ratio for the 28-day cured cylinders. This research provides a procedure and lays the framework for future expansion of the predictive model.

A general conclusion from the work is that both systems require considerable development before being ready for industrial application. However, of the two systems investigated, it is the latter which shows the greatest potential to not only greatly enhance the durability of cementitious composites, but also to improve their strength and ductility.

Laser scabbling of concrete is the process by which the surface layer of concrete may be removed through the use of a high power (low power density) laser beam. The aim of this study was to investigate the mechanism(s) responsible for laser scabbling. This was achieved in three stages. The first stage was a test series used to establish an experimental procedure for assessing the effects of various parameters that may be critical for the effectiveness of the process, such as material composition and initial moisture content. The second stage was a test series investigating the effect of concrete composition on laser scabbling. The first two test series identified that the driving force of laser scabbling in concretes originates from the mortar, therefore, the third test series concentrated on the factors that influence laser scabbling of mortars. Throughout the study, infra red recordings have been used to quantify laser scabbling behaviour, along with the volume removal due to laser scabbling and characterisation techniques such as XRF, DTA and TGA. The results suggest that scabbling is mainly driven by pore pressures, but strongly affected by other factors. The removal of free water from mortars prohibits scabbling, but resaturation allows mortar to scabble. A reduced permeability, either due to a reduction in the water/binder ratio or the use of 25% PFA replacement, enhances laser scabbling. Results show that the biggest effect of ageing is due to specimens drying. Mortars and cement pastes were seen to scabble at a constant rate, whereas concretes experienced a peak rate, after which volume removal reduced dramatically. Basalt aggregate concrete was less susceptible to laser scabbling than limestone aggregate concrete due to vitrification. A higher fine aggregate content increases volume removal and fragment sizes during laser scabbling.

This thesis presents a new bonded particle model that accurately predicts the wideranging behaviour of cementitious materials. There is an increasing use of the Discrete Element Method (DEM) to study the behaviour of cementitious materials such as concrete and rock; the chief advantage of the DEM over continuum-based techniques is that it does not predetermine where cracking and fragmentation initiate and propagate, since the system is naturally discontinuous. The DEM’s ability to produce realistic representations of cementitious materials depends largely on the implementation of an inter-particle bonded-contact model. A new bonded-contact model is proposed, based on the Timoshenko beam theory which considers axial, shear and bending behaviour of inter-particle bonds. The developed model was implemented in the commercial EDEM code, in which a thorough verification procedure was conducted. A full parametric study then considered the uni-axial loading of a concrete cylinder; the influence of the input parameters on the bulk response was used to produce a calibrated model that has been shown to be capable of producing realistic predictions of a wide range of behaviour seen in cementitious materials. The model provides useful insights into the microscopic phenomena that result in the bulk loading responses observed for cementitious materials such as concrete. The new model was used to simulate the loading of a number of deformable structural elements including beams, frames, plates and rings; the numerical results produced by the model provided a close match to theoretical solutions.

A micromechanical constitutive model for concrete is proposed in which microcrack initiation, in the interfacial transition zone between aggregate particles and cement matrix, is governed by an exterior-point Eshelby solution. The model assumes a two-phase elastic composite, derived from an Eshelby solution and the Mori-Tanaka homogenization method, to which circular microcracks are added. A multi-component rough crack contact model is employed to simulate normal and shear behaviour of rough microcrack surfaces. It is shown, based on numerical predictions of uniaxial, biaxial and triaxial behaviour that the model captures key characteristics of concrete behaviour. An important aspect of the approach taken in this work is the adherence to a mechanistic modelling philosophy. In this regard the model is distinctly more rigorously mechanistic than its more phenomenological predecessors. Following this philosophy, a new more comprehensive crack-plane model is described which could be applied to crack-planes in the above model. In this model the crack surface is idealised as a series of conical teeth and corresponding recesses of variable height and slope. Based on this geometrical characterization, an effective contact function is derived to relate the contact stresses on the sides of the teeth to the net crack-plane stresses. Plastic embedment and frictional sliding are simulated using a local plasticity model in which the plastic surfaces are expressed in terms of the contact surface function. Numerical simulations of several direct shear tests indicate a good performance of the model. The incorporation of this crack-plane model in the overall constitutive model is the next step in the development of the latter. Computational aspects such as contact related numerical instability and accuracy of spherical integration rules employed in the constitutive model are also discussed. A smoothed contact state function is proposed to remove spurious contact chatter behaviour at a constitutive level. Finally, an initial assessment of the performance of the micromechanical model when implemented in a finite element program is presented. This evaluation clearly demonstrates the capability of the proposed model to simulate the behaviour of plain and reinforced concrete structural elements as well as demonstrating the potential of the micromechanical approach to achieve a robust and comprehensive model for concrete.

The complexity of cementitious matrices and their application in the immobilisation of radioactive waste has led to detailed examination of their ability to condition permeating water to high pH by both experimental and thermodynamic studies. This thesis considers the stability and solubility of pure hydrate phases: Ca(OH)₂; CaO-SiO₂-H₂O gel, Ca:Si = 0.85, 1.1, 1.4, 1.8; 3CaO.Al₂O₃.6H_zO; 3CaO.Al₂O₃.CaSO₄.12H₂O and 3CaO.Al₂O₃.3CaSO₄.32H₂O, and the phase formation and stability within CaO-SiO₂-CaCO₃-H₂O and CaO-Al₂O₃-SiO₂-H₂O compositions aged in saline solutions, up to 1.5M NaCl and 0.05M MgSo₄, at 25°, 55° and 85°C. The two main high pH conditioning phases of cementitious systems are Ca(OH)₂ and C-S-H gel. Sodium chloride enhances the solubility of Ca(OH)₂ and causes a slight reduction in the Ca:Si ratio of C-S-H gels by the progressive leaching of calcium. Silicate polymerisation within C-S-H phases is inhibited by sodium chloride though it is uncertain how this alters the crystallisation kinetics. The pH buffering capacity is maintained when aged in sodium chloride concentrations 0.5, 1.0 and 1.5M at 25°, 55° and 85°C. The stability of calcium sulfoaluminate aged in sodium chloride is greater than of 3CaO.Al₂O₃.6H₂O, which is unstable with respect to 3CaO.Al₂O₃.CaCl₂.10H₂O in NaCl < 0.5M. These phases undergo a progressive phase change to the 3CaO.Al₂O₃.0.5CaSO₄.0.5CaCl₂.10-12H₂O and 3CaO.Al₂O₃.CaCl₂.10H₂O at increasing aqueous Cl:SO₄ ratios. The formation of a limited solid solution region within 3CaO.Al₂O₃.xCaSO₄.l-xCaCl₂.yH₂O: 0.00 ≤ SO₄:Cl ≤ 0.06, was characterised. In magnesium sulfate, 5 - 50m.mol/l, calcium within hydrate phases is progressively replaced by magnesium with formation of Mg(OH)₂, MgO-SiO₂-H₂O gel, 4MgO.Al₂O₃.xH₂O and gypsum. The pH conditioned by the resultant solid assembly decreases to less than that desirable for containment of radioactive waste, to < 9. Consideration of the phase formation and persistence within the CaO-SiO₂-CaCO₃-H₂O and CaO-Al₂O₃-SiO₂-H₂O systems was examined in solutions containing both sodium chloride and magnesium sulfate. The chemical interactions observed were dominated by the replacement of calcium by magnesium within the solid phases with the formation and persistence of mixtures of Mg(OH)₂, MgO-SiO₂-H₂O gel and gypsum. At low Mg:Ca-CO₃ ratios the persistent stability of gehlenite hydrate at 25°C was observed in appropriate samples. The chemistry of the aqueous phase is dependent on the Mg:Ca-CaCO₃ ratio as well as the Ca:Si ratio. At high Mg:Ca-CaCO₃ ratios the high pH conditioning properties are destroyed and buffering occurs at a value below pH 9.

A self-healing cementitious material could provide a step change in the design of concrete structures. There is a need to understand better the healing processes, to predict accurately experimental behaviour and to determine the impact on mechanical properties. Micromechanical modelling, with a two-phase Eshelby inclusion solution, is chosen as a suitable framework within which to explore self-healing. The impact of micro-cracking and other time-dependent phenomena are considered alongside self-healing experiments and the numerical mechanical strength response. A new approach describes simulating inelastic behaviour in the matrix component of a two-phase composite material. Quasi-isotropic distributed micro-cracking, accompanying volumetric matrix changes, is combined with anisotropic microcracking arising from directional loading. Non-dilute inclusions are homogenised and an exterior point Eshelby solution is used to obtain stress concentrations adjacent to inclusions. The accuracy of these solutions is assessed using a series of three dimensional finite element analyses and a set of stress/strain paths illustrate the model’s characteristics. The problem of autogenous shrinkage in a cementitious composite is applied using a volumetric solidification and hydration model, which quantifies the effects of micro-cracking. Experiments on early age concrete and mortar beams showed that autogenous healing is primarily due to continued hydration. A novel self-healing model focuses on mechanical strength recovery of micro-cracked material and considers healing whilst under strain as well as allowing for re-cracking the healed material. The constitutive model is combined with a layered beam model to allow successful comparisons with experimental results.

The work described in this thesis is an attempt to provide improved understanding of the effects of several factors affecting diffusion in hydrated cement pastes and to aid the prediction of ionic diffusion processes in cement-based materials. Effect of pore structure on diffusion was examined by means of comparative diffusion studies of quaternary ammonium ions with different ionic radii. Diffusivities of these ions in hydrated pastes of ordinary portland cement with or without addition of fly ash were determined by a quasi-steady state technique. The restriction of the pore geometry on diffusion was evaluated from the change of diffusivity in response to the change of ionic radius. The pastes were prepared at three water-cement ratios, 0.35, 0.50 and 0.65. Attempts were made to study the effect of surface charge or the electrochemical double layer at the pore/solution interface on ionic diffusion. An approach was to evaluate the zeta potentials of hydrated cement pastes through streaming potential measurements. Another approach was the comparative studies of the diffusion kinetics of chloride and dissolved oxygen in hydrated pastes of ordinary portland cement with addition of 0 and 20% fly ash. An electrochemical technique for the determination of oxygen diffusivity was also developed. Non-steady state diffusion of sodium potassium, chloride and hydroxyl ions in hydrated ordinary portland cement paste of water-cement ratio 0.5 was studied with the aid of computer-modelling. The kinetics of both diffusion and ionic binding were considered for the characterization of the concentration profiles by Fick's first and second laws. The effect of the electrostatic interactions between ions on the overall diffusion rates was also considered. A general model concerning the prediction of ionic diffusion processes in cement-based materials has been proposed.

The primary aim of this research was to investigate the fundamental acoustic properties of several cementitious materials, the influence of mix design parameters/constituents, and finally the effect of the physical and mechanical properties of cementitious material concrete/mortar on the acoustic properties of the material. The main objectives were: To understand the mechanism of sound production in musical instruments and the effects of the material(s) employed on the sound generated; To build upon previous research regarding selection of the tested physical/mechanical properties and acoustic properties of cementitious materials; To draw conclusions regarding the effect of different constituents, mix designs and material properties upon the acoustic properties of the material; To build a model of the relationship between the acoustic properties of a cementitious material and its mix design via its physical/mechanical properties. In order to meet the aim, this research was conducted by employing the semi-experimental (half analytical) method: two experimental programmes were performed (I and II); a mathematical optimization technique (least square method) was then implemented in order to construct an optimized mathematical model to match with the experimental data. In Experimental Programme I, six constituents/factors were investigated regarding the effect on the physical/mechanical and acoustic properties: cementitious material additives (fly ash, silica fume, and GGBS), superplasticizer, and basic mix design parameters (w/c ratio, and sand grading). 11 properties (eight physical/mechanical properties: compressive strength, density, hardness, flexural strength, flexural modulus, elastic modulus, dynamic modulus and slump test; and three acoustic properties: resonant frequency, speed of sound and quality factor (internal damping)) were tested for each constituents/factors related mortar type. For each type of mortar, there were three cubes, three prisms and three cylinders produced. In Experimental Programme I, 20 mix designs were investigated, 180 specimens produced, and 660 test results recorded. After analysing the results of Experimental Programme I, fly ash (FA), w/b ratio and b/s ratio were selected as the cementitious material/factors which had the greatest influence on the acoustic properties of the material; these were subsequently investigated in detail in Experimental Programme II. In Experimental Programme II, various combinations of FA replacement level, w/b ratios and b/s ratios (three factors) resulted in 1122 test results. The relationship between these three factors on the selected 11 properties was then determined. Through using regression analysis and optimization technique (least square method), the relationship between the physical/mechanical properties and acoustic properties was then determined. Through both experimental programmes, 54 mix designs were investigated in total, with 486 specimens produced and tested, and 1782 test results recorded. Finally, based upon well-known existing relationships (including, model of compressive strength and elastic modulus, and the model of elastic modulus and dynamic modulus), and new regressioned models of FA-mortar (the relationship of compressive strength and constituents, which is unique for different mixes), the optimized object function of acoustic properties (speed of sound and damping ratio) and mix design (proportions of constituents) were constructed via the physical/mechanical properties.

Major tunnelling projects in London have generated enormous amounts of excavated clay, and there will be even larger production of excavated London clay in the next few years. This research focuses on investigating the technical feasibility of processing excavated London clay into a supplementary cementitious material (SCM) suitable for the use in concrete. Excavated London clay was calcined at a range of temperatures between 600 and 1000 °C for 2 hours. The as-received and calcined London clay samples were characterized using techniques including XRF, XRD, FTIR, TGA/DTG, ICP, SEM, nitrogen adsorption, laser diffraction, isothermal conduction calorimetry and pycnometry. London clay is a complex mix of various types of clay and non-clay minerals, such as kaolinite (30.2 wt.%), illite (11.9 wt.%), montmorillonite (41.3 wt.%), chlorite, pyrite, goethite, feldspar and quartz (16.6 wt.%). Calcining excavated London clay resulted in oxidation, dehydration, dehydroxylation, amorphization and recrystallization, causing significant compositional and structural changes to clay and non-clay minerals. The degree of change depended on the calcining temperature. At 600 °C, kaolinite was entirely dehydroxylated, and the removal of octahedral hydroxyls led to a collapse of the 1:1 layered structure. As a result, metakaolin was formed. In contrast, the dehydroxylation of illite and montmorillonite started below 600 °C but finished at around 800 °C. Additionally, the two clay minerals did not suffer significant loss in crystallinity from complete dehydroxylation. The collapse of the 2:1 layered structure of illite and montmorillonite took place only when the calcining temperature was 900 °C and above. It was also observed that the recrystallization of spinel occurred above 950 °C. The assessment of pozzolanic reactivity for calcined London clays was performed using the strength activity index (SAI) test, Frattini test, portlandite consumption test and the Chapelle test. The results showed that excavated London clay can be transformed into a SCM by calcining, and the optimum calcining temperature is 900 °C. The decrease at 950 °C can be attributed to the occurrence of spinel recrystallization. London clay calcined at 900 °C was used to produce concrete at replacement levels up to 30 wt.% and three water-to-binder ratios (0.3, 0.4, 0.5). A CEM-I replacement of up to 30 wt.% showed no detrimental effect on workability or the compressive strength of concrete. In addition, the concrete with 30 wt.% of CEM-I substituted by calcined London clay and a w/b ratio of 0.3 had greater strength than control concrete after 28 days curing. At a replacement of 20 wt.% and a w/b ratio of 0.4, the concrete containing calcined London clay had similar 90-day compressive strength to those incorporating pulverised fuel ash, ground granulated blastfurnace slag and silica fume. Carbon emission estimation showed that a 30 wt.% substitution of CEM-I by calcined London clay in concrete produces 27% less CO2 emission compared to 100 wt.% CEM-I. This study has demonstrated that it is technically feasible to use calcined London clay as a supplementary cementitious material for use in concrete.

Global cement production is continuously increasing from 1990 till 2050 and growing particularly rapidly in developing countries, where it represents a crucial element for infrastructure development and industrialisation. Every tonne of ordinary Portland cement (OPC) produced releases, on average, about 800 kg of CO2 into the atmosphere, or, in total, the overall production of cement represents roughly 7% of all man-made carbon emissions. The present paper aims to deepen the re-use of agricultural solid waste materials as partial replacement of OPC, which can positively contribute to the sustainability of the concrete industry because of their availability and environmental friendliness. In particular, rice-husk ash (RHA) and oat-husk ash (OHA), burned under the right conditions, can have a high reactive silica content, representing very potential pozzolans. The mechanical and physical characteristics of both materials are investigated to evaluate the influence on concrete properties. Subsequently, using the environmental product declarations (EPDs) of the material used, a comparative environmental impact analysis between RHA concrete and ordinary concrete having the same resistance class, is presented. It is concluded that the use of RHA as supplementary cementitious material can serve a viable and sustainable partial replacement to OPC for the reduction of CO2 emissions and global warming potential.
Den globala cementproduktionen ökar från 1990 till 2050 och växer särskilt snabbt i utvecklingsländer, där den utgör en viktig del för infrastrukturutveckling och industrialisering. Varje ton vanligt portlandcement (OPC) släpper i genomsnitt ut cirka 800 kg koldioxid i atmosfären, och, totalt, representerar den totala cementproduktionen ungefär 7% av alla koldioxidutsläpp från mänsklig verksamhet. Det här examensarbetet syftar till att fördjupa kunskapen om och därmed i förlängningen återanvändningen av fasta avfallsmaterial från jordbruket som delvis ersättning av OPC, vilket kan bidra till hållbarheten i betongindustrin på grund av deras tillgänglighet och miljövänlighet. I synnerhet kan risskalaska (RHA) och havreskalaska (OHA), som bränns under rätt process, ha en hög reaktiv kiseldioxidhalt, vilket representerar mycket potentiella puzzolaner. De mekaniska och fysiska egenskaperna hos båda materialen har undersökts för att utvärdera deras inverkan på betongegenskaper. Därefter presenteras en jämförande miljökonsekvensanalys mellan RHA-betong och OPC-betong med samma motståndsklass med användning av miljövarudeklaration (EPD) för det använda materialet. Man drar slutsatsen att användningen av RHA som alternativt bindemedel (SCM) till OPC kan hjälpa till att minska koldioxidutsläppen och den globala uppvärmningspotentialen.

Two metakaolins were evaluated for use as supplementary cementitious materials in cement-based systems. The metakaolins varied in their surface area (11.1 v. 25.4 m2/g), but were quite similar in mineralogical composition. Performance of metakaolin mixtures was compared to control mixtures and to mixtures incorporating silica fume as partial replacement for cement at water-to-cementitious materials ratios of 0.40, 0.50, and 0.60. In this study, the early age properties of fresh concrete and the mechanical and durability properties of hardened concrete were examined. Early age evaluations aimed to determine the reactivity of metakaolin (heat of hydration) and its effect on mixture workability (slump, setting time, unit weight). In addition, three types of shrinkage were monitored in metakaolin-cement systems: chemical, autogenous, and free. Compressive, tensile, and flexural strength and elastic modulus were measured at various concrete ages. The influence of metakaolin addition on durability was assessed through accelerated testing for sulfate resistance, expansion due to alkali-silica reaction, and through rapid chloride permeability measurements. To further quantify the underlying mechanisms of metakaolin's action, the microstructure of pastes was examined. Calcium hydroxide (CH) content was determined using thermogravimetric analysis and verified using differential thermal analysis. Surface area and pore size distribution were evaluated via nitrogen adsorption. These analyses yielded information about the pozzolanic reactivity of metakaolin, associated CH consumption and pore structure refinement, and resulting improvements in mechanical performance and durability of metakaolin-concretes.

Presented in this thesis are the test results of combined processing and mechanical property characterisation studies using a developed cementitious mix reinforced by various fibre types and forms (with short and continuous lengths). The research is aimed to identify new Fibre Reinforced Cementitious (FRC) composites that have post-cracking ductility, much higher flexural strength and higher toughness than the control (matrix) material without reinforcement, and higher than traditional FRC composites. Laboratory work uses two methods to process the green forms, one by novel compression moulding and the other by hand lay-up that were both adapted from the fibre reinforced polymer industry. Results show a reduction in the hand lay-up water/binder ratio of 24 to 41% can be achieved by applying compression moulding with a pressure of 9MPa. One key processing challenge with short recycled milled carbon fibres is to make the mix uniform, even when the volume fraction is low at 2%. Microstructural investigations confirm that the carbon fibres, having mean length of 0.085 mm, always gave a very poor dispersion, and this is due to static electricity causing the fibres to form into balls (5 to 30 mm diameter). Overall, the study with short fibre reinforcements found that, by adding 2% by volume of the polyvinyl alcohol (PVA) fibres, the stress-strain curve exhibits strain-hardening behaviour accompanied by multiple cracking. Furthermore, the flexural properties show the material to possess ductility, toughness and mean strength that, at 13 MPa, is two times higher than the control material. It is observed that the hydrophilic nature of PVA and the fibres surface roughness play a significant role in an increased bonding strength with this short fibre. When introducing continuous fibre reinforcement in the form of fabrics it is shown that the volume fraction of fibres should be no more than 5%. Unsuccessful green form specimens were a consequence of having a higher volume fraction by introducing more fabric layers. Test results show that materials reinforced with carbon fabrics give an FRC material with much improved mechanical properties, in terms of post-cracking strength, strain at peak stress and toughness (energy absorption) at peak stress. Higher overall bond strength might be attributed to an apparent increase in interfacial contact area between fibres and cement matrix and improved mechanical anchoring from the fabric’s construction. Microstructural investigations confirm that good matrix penetrability between the filaments of the tow or bundle is essential in order to maximise the reinforcing efficiency of the fabric. Investigated are two novel methods for modifying the continuous unidirectional carbon fibre reinforcements to improve the overall bond strength, by enhancing matrix penetration through and across the reinforcement plane. In one method the fabric is cut into strips to leave spaces (holes) between parallel reinforcement units for the matrix material to bridge across, while in the second method the fabric receives a surface treatment by immersion in Ethanol alcohol. Test results show that, with compression moulding and the strip form of reinforcement at 5% volume fraction the FRC composite has a flexural strength of 75 MPa. This flexural strength is ten times higher than the measured strength of the control material. The experimental research reported in this thesis shows that to achieve ‘unusual’ composite action and a relative high stress at loss of proportionality requires a continuous fibre reinforcement that can be treated or non-treated. Given the considerable increase in mechanical properties achieved using such fibre reinforcement at 5% the most promising FRC materials require to be further evaluated to find suitable candidates for load bearing products.

The rheological behaviour of cementitious pastes has been studied by various means. Six different cements have been studied in main parts of the work and all of them have been characterized according to the Rietveld method in order to determine the exact content of minerals. Easily soluble alkalis were measured by plasma-emission- spectroscopy of the fluid filtered from paste. Three types of plasticizers namely naphthalene sulfonate formaldehyde condensate (SNF), lignosulphonate and polyacrylate grafted with polyether (PA) have been used throughout the work. The influence of the plasticizer type on the rheological properties of the cementitious pastes, their adsorption characteristics and their effects on heat of hydration of the pastes has been studied. Limestone has been used as a nonreactive model material for cement in some parts of the work.

All rheological measurements were performed with a parallel plate rheometer. Rather than describing the shear stress-shear rate flow curve with the usual Bingham model resulting in plastic viscosity and yield stress, the area under the curve (Pa/s) was used as a measure of “flow resistance”.

The effect of silica fume and limestone on the rheology of cementitious pastes

The rheological behaviour of cementitious pastes, with the cement being increasingly replaced by densified and untreated silica fume (SF) or limestone was studied. Three plasticizers were investigated namely two types of polyacrylate (PA1 and PA2) and SNF. PA2 proved to be the most efficient plasticizer of the three while PA1 and SNF provided comparable results.

The flow resistance was found to increase with increasing silica fume replacement when SNF and polyacryalte (PA1) were added as plasticizers which was explained by ionization of the silica fume surface and possible bridging with polyvalent cations like calcium. The flow resistance decreased, however, with increasing silica fume replacement when the second and more efficient type of polyacrylate (PA2) was utilized which was believed to occur since the cement pastes were better dispersed by PA2 than SNF and PA1. The silica fume particles could thus pack between the cement grains and displace water. An alternative explanation for reduced flow resistance with increasing silica fume replacement could be a ball-bearing effect of silica spheres.

There was found a trend of increasing gel strength with increasing silica fume replacement of cement even though the pastes seemed to be dispersed by PA2. Cement pastes with densified SF developed lower gel strengths than pastes with untreated SF. This phenomenon was attributed to more grain shaped agglomerates with lower outer surface in densified SF compared to dendritic agglomerated in untreated SF. Decreasing gel strength was found for pastes with increasing limestone filler replacement. Thus silica fume may be advantageous as stabilizing agent for self-compacting concrete preventing segregation upon standing due to a more rapid gel formation.

Effect of cement characteristics on flow resistance

Rheological experiments were performed on pastes prepared from 4 cements originating from the same clinker, but ground to different finenesses (Blaine). The results showed that the flow resistance increased exponentially with increasing Blaine number. No correlations between single cement characteristics such as Blaine, content of C₃A, cubic C₃A (cC₃A) and C₃S with the flow resistance were however found when cements from different clinkers were used. This finding indicates that cement should not be treated as a univariable material. However, the combined cement characteristic (Blaine•{d•cC₃A+[1-d]•C₃S}) was found to correlate with flow resistance, where the factor d represents relative reactivity of C₃A and C₃S. The flow resistance was found to be either a linear or exponential function of the combined cement characteristic depending on plasticizer type and dosage. Correlations were found for a mix of pure cement and cement with fly ash, limestone filler (4%), as well as pastes with constant silica fume dosage when the minerals were determined by XRD.

Influence of cement and plasticizer type on the heat of hydration

The initial heat of hydration peak was measured for the 6 main cements with 0.32% SNF, lignosulphonate and PA2 by cement weight. Correlations were attempted between the maximum heat of hydration rates of the initial peaks with various cement characteristics. The maximum heat of hydration rate seemed to correlate with the product of the cement fineness and C₃A content regardless of plasticizer type. The fly ash cement had to be left out of the correlation plots due to its low initial heat of hydration.

The second, third and fourth hydration peaks were measured on the cement pastes with 0-0.8% SNF, lignosulphonate and PA2 by weight of cement. Lignosulphonate was found to be the strongest retarder while SNF had the least effect on the setting time of the three plasticizers. No correlations could be found between the setting times and cement characteristics such as cement fineness, aluminate and alkali contents for un-plasticized pastes probably because the setting times might have been too close to each other to be able to obtain accurate values. Correlations between setting time and cement characteristics were however found for pastes with plasticizers. The setting times did not correlate with the cement fineness (Blaine) as a single parameter. The product of cement Blaine and C₃A content, however, resulted in a correlation. Furthermore the setting time correlated with the cubic modification of C₃A. It may seem that the setting times depend more on the cubic modification of C₃A than the sum of orthorhombic and cubic aluminate. This finding indicates that the cubic aluminate modification is more reactive than the orthorhombic. The setting time decreased with increasing content of easily soluble K-ions in the cements probably due to the formation of syngenite, K₂SO₄·CaSO₄·H₂O, which removes some sulphate from solution that would otherwise retard C₃A hydration. A similar correlation was not found between the setting time and the sodium equivalent.

Cement interactions with plasticizers

Three plasticizers were studied namely SNF, lignosulphonate and polyacrylate (PA2). PA2 was the most efficient plasticizer of the three tested even thought it was found to adsorb to a lesser extent on cement than SNF and lignosulphonate. SNF and lignosulphonate brought about comparable results.

PA2 was observed to induce flow gain within the 2 hours of rheological measurements which might be caused by the polymer expanding in the water phase and thus improve the dispersion of the paste. Furthermore the grafted side chains of the polymer are considered to be long enough to provide steric dispersion even thought the backbone might be embedded in the hydration products. Cement pastes with SNF and lignosulphonate exhibited flow loss as a function of time which indicates that the plasticizer molecules were consumed by the hydration products.

The concentrations of superplasticizer in the pore water were not found to change markedly in the time range 20-95 min after water addition, indicating that most of the plasticizer molecules were consumed (i.e. adsorbed or intercalated in surface hydration products) within the first 20 minutes after water addition.

The adsorption characteristics were found to depend on the plasticizer type. The adsorption curves of SNF and lignosulphonate reached a plateau at saturation characterizing high-affinity adsorption or increased continuously as a sign of low affinity adsorption. The adsorbed amounts of polyacrylate decreased, however, after saturation had been reached which might indicate that surplus molecules in the water phase compress the ionic double layer or that adsorbed molecules expand and hinder molecules in the water phase to attach at the surface (i.e. osmosis).

The plasticizer saturation dosages were found to depend on cement surface area (Blaine), amount of cubic C₃A and easily soluble sulphates. The saturation dosage of lignosulphonate seemed to have a dependency on the amount of soluble alkali that was somewhat stronger than observed for pastes with SNF. This difference might be caused by lignosulphonate forming complexes with solvated ions in a higher degree than SNF. Moreover alkali sulphates are furthermore often added to commercial SNF based products as the one used in this work. The best correlation, overall, was found for the product of cubic C₃A and Blaine which is logical since high surface and cubic aluminate contents accounts for high cement reactivity and since the plasticizers are known to coordinate with calcium sites. Correlations were also found between saturation dosage with the product of Na_eqv and Blaine as well as the product of Na_eqv and cubic C₃A. The investigations seemed to indicate that the plasticizer saturation concentration increase with increasing alkali content. These findings, however, are rather unclear. According to literature an increased concentration of alkali sulphate in solution results in both an increased hydration rate (which would lead to a higher plasticizer intercalation) and a reduced plasticizer adsorption (due to SO₄^2- - superplasticizer competition). The easily soluble sulphates might, of course, entail the opposing effects of Blaine and C₃A in a way that smoothen the correlation plots of the plasticizer saturation dosage with the cement characteristics.

Effect of temperature on rheology and plasticizer adsorption

Flow resistance and adsorbed amounts of SNF, lignosulphonate and PA2 were measured at temperatures ranging from 11 to 40^oC. Limestone was used as a nonreactive model material for cement. The adsorbed amounts of SNF and lignosulphonate on limestone were found to decrease after reaching a maximum which occurred at approximately 25^oC. Decreased amounts of adsorbed plasticizer with increasing temperature might be explained by increased kinetic energy to the molecules or by an entropy effect. The adsorption of PA2 on limestone seemed to be independent of paste temperature in the range of 16-34^oC which might be caused by low reduction of entropy at adsorption due to its short backbone and long, grafted side chains. The flow resistance of the limestone pastes generally increased with increasing temperature which may be caused by reduced amounts of adsorbed plasticizer and/or dehydration of the paste during the rheological measurements.

Two types of cements were used to study adsorption and flow resistance with increasing temperature namely CEM I 42.5 RR and CEM I 52.5 R-LA. Amounts of plasticizer adsorbed and intercalated (consumed) by cement reached a plateau or even decreased with increasing temperature in the case of SNF and lignosulphonate. This finding might be caused by two opposing effects namely: increased number of adsorption sites due to increased hydration rate with increasing temperature and reduced adsorption due to increased kinetic energy and/or reduced entropy of the plasticizer. Amounts of PA2 consumed by cement increased linearly with increasing temperature as might be explained by the experiments with limestone where the adsorbed amounts of PA2 seemed to be independent of temperature. Increased consumption of plasticizer by the cements with rising temperature is thus probably governed by the increased number of adsorption cites due to increased hydration rate. The flow resistance of CEM I 52.5 R-LA cement increased exponentially with increasing temperature as a function of temperature most likely because of the increased hydration rate. The pastes of CEM I 42.5 RR cement were generally highly viscous and probably agglomerated. The flow resistance reached a plateau value with increasing temperature in this case.

During the past few decades, concrete technology has been developing rapidly followed with huge popularity of high-performance concrete (HPC). However, the mix design for HPC still remains a major challenge due to the wide adoption of mineral and chemical admixtures, the effects of which are rather complicated and not yet fully understood. To resolve this issue, this thesis presents a comprehensive experimental study focused on the physical effects of some supplementary cementitious materials (SCM) on the fresh and hardened properties of mortar. Based on the experimental results, some fundamental parameters governing the performance of mortar were investigated. It has been postulated by some researches that increasing the packing density of the particle system would improve the rheology and strength of concrete. Through adding SCM finer than cement to increase the packing density, the voids between solid particles will be reduced so that more excess water can be released to provide better lubrication. Through adding two kinds of SCMs with different fineness, the packing density will be further enhanced by the successive filling action. In this study, a wet packing method, which is newly developed at the University of Hong Kong, was used to directly measure the packing densities of mortars with binary and ternary blended cementitious materials. The filling effect and successive filling action were both quantified through the packing density results. The study revealed that the addition of fine SCM will, not only increase the packing density, but also increase the solid surface area, which will have negative effect on the rheology of mortar. To combine the effects of water content, packing density and solid surface area together, we proposed a new parameter called water film thickness (WFT), defined as the average thickness of water films coating the solid particles and evaluated as the excess water to solid surface area ratio. The results demonstrated that the WFT plays a key role in controlling the rheology and strength of mortar. Hence, it is the WFT, rather than the packing density, that should be maximized at given water content in the mix design of HPC. The addition of fine SCM will increase both the excess water content and solid surface area. The effects on the both sides can be quantified by the WFT no matter how complex the cementitious system is. Therefore, the WFT could be used as an effective indicator to adjust the SCM content. Joint addition of fine SCM at different level finer than cement to make a ternary cementitious system can effectively increase the packing density without excessively increasing the solid surface area. As a result, the ternary cementitious system has higher effectiveness than the binary cementitious system in improving the performance of mortar.
published_or_final_version
Civil Engineering
Master
Master of Philosophy

Advances in multiscale material modeling of structural concrete have created an upsurge of interest in the accurate evaluation of mechanical properties and volume fractions of its nano constituents. The task is accomplished by analyzing the response of a material to indentation, obtained as an outcome of a nanoindentation experiment, using a procedure called the Oliver and Pharr (OP) method. Despite its widespread use, the accuracy of this method is often questioned when it is applied to the data from heterogeneous materials or from the materials that show pile-up and sink-in during indentation, which necessitates the development of an alternative method. In this study, a model is developed within the framework defined by contact mechanics to compute the nanomechanical properties of a material from its indentation response. Unlike the OP method, indentation energies are employed in the form of dimensionless constants to evaluate model parameters. Analysis of the load-displacement data pertaining to a wide range of materials revealed that the energy constants may be used to determine the indenter tip bluntness, hardness and initial unloading stiffness of the material. The proposed model has two main advantages: (1) it does not require the computation of the contact area, a source of error in the existing method; and (2) it incorporates the effect of peak indentation load, dwelling period and indenter tip bluntness on the measured mechanical properties explicitly. Indentation tests are also carried out on samples from cement paste to validate the energy based model developed herein by determining the elastic modulus and hardness of different phases of the paste. As a consequence, it has been found that the model computes the mechanical properties in close agreement with that obtained by the OP method; a discrepancy, though insignificant, is observed more in the case of C-S-H than in the anhydrous phase. Nevertheless, the proposed method is computationally efficient, and thus it is highly suitable when the grid indentation technique is required to be performed. In addition, several empirical relations are developed that are found to be crucial in understanding the nanomechanical behavior of cementitious materials.

The research described in this thesis deals with the use ofcement-based carbon fibre reinforced composites forstrengthening of existing structural concrete.

There is a large world-wide need for simple and reliablemethods to repair and strengthen aging infrastructure andbuildings. The use of cementitious fi- bre composites offersseveral advantages over the existing methods. No other work onstrengthening of structural concrete with cementitiouscomposites reinforced with continuous high strength fibres wasidentified when the present work started in 1998. At presenttime, 2003, it still is a new technique and very littleresearch has been internationally reported. This work includesa literature survey describing the state of the art of thestrengthening of structural concrete with cement based fibrereinforced composites.

Due to the novelty of this technique no specially adaptedmaterials are available and ready for use in cementitiouscomposites. In order to make many small scale tests to optimizethe composite, a new test beam has been developed. Severalparameter studies have been done in this work to determine howdifferent parameters, for example fineness of grading of thecement, additives, and fibre configuration affect thecomposite.

Large scale tests of ordinary concrete beams strengthenedwith a cementitious fibre composite are reported. The compositeused was made of a polymer modified mortar and a unidirectionalsheet of continuous carbon fibres, applied by hand. Bothflexural strengthening and shear strengthening were tested. Arelatively new method for measuring strains with digitalcameras was used on the shear strengthenings with a goodresult. It is concluded that the large scale tests have proventhat this method works and has great potential for futureuse.

Design methods for strengthenings were studied andevaluated. It is concluded that design methods formulated forstrengthening of structural concrete with carbon fibrereinforced polymers can be adapted also to cementitiouscomposites by introducing an efficiency factor.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2020
Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 177-203).
Alkali-activated, geopolymeric, and other novel binders offer an opportunity to curb the carbon footprint associated with ordinary Portland cement (OPC). CO₂ emissions inherent to source-material processing (i.e., firing of limestone at 1450 °C) and annual OPC production volumes of 4.1 billion metric tons cause an estimated 5-11% of global annual greenhouse gas (GHG) emissions. Material substitution with lower-footprint resources is therefore necessary for GHG impact mitigation. Glassy silica-, alumina-, lime-, and/or alkali-rich industrial byproducts (IBs) exhibit the properties necessary to achieve emissions reductions while preserving final product attributes expected of cementitious binders. Research and industry have both focused primarily on metakaolin and IBs such as blast furnace slag and coal fly ash as supplementary and alternative cementitious precursors.
Given projected limitations in such IB supply, it is imperative that we efficiently expand the materials search to other useful precursor candidates. This thesis focuses on chemical characterization and kinetic reactivity analysis of lesser-studied glassy materials through a combined experimental-computational approach, resulting in (1) physicochemical drivers for material aqueous reactivity and (2) a framework for evaluating new materials. First, I describe laboratory experiments involving reaction of a siliceous mixed-feedstock Indian biomass ash in aqueous sodium hydroxide solutions with selectively present lime and alumina sources. These experiments respectively yield tobermoritic calcium silicate hydrate products (Ca/Si ~~ 0.6-1) and semi-crystalline zeolite / geopolymer products (Si/Al ~~ 1); shown compositional ratios are known to be relevant to final material properties.
Through this work, I demonstrate a novel approach to calculating reaction product composition using spectroscopic solution analysis of dissolution / precipitation experiments. Subsequently, I describe computational efforts to mine literature-reported data for potential precursor materials. This results in a database of material compositional and physical property data represented by a SiO₂-Al₂O₃- CaO ternary diagram. Finally, I employ supervised and semi-supervised computational models, which confirm log-linear relationships between glass dissolution rates (i.e., log₁₀(rate)) and pH, inverse temperature (1/K), and glass connectivity (i.e. non-bridging oxygens per tetrahedron). While less interpretable, black-box models are observed to be more robust to the presence of additional features. Throughout the research program, reactivity is understood via material dissolution in aqueous solutions.
by Hugo Jake Uvegi.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

EU Sustainable Development Strategy planned to achieve improvement of life-quality by promoting sustainable production and consumption of raw materials. On November 2018, EU Commission presented a long-term strategy, aiming among others a climate-neutral economy by 2050. Cement production is contributing to 6-10% of the anthropogenic CO2 emissions. Thus, several strategies for total or partial replacement of Portland cement in concrete production have been developed. The use of supplementary cementitious materials (SCM) and alkali-activated materials (AAM) is considered the most efficient countermeasure to diminish CO2 emissions. The broadening of knowledge with particular attention to the sustainable goals is the primary requirement to be fulfilled when novel materials are investigated. This study aims to develop a novel clay-based binder that can be used as a sustainable alternative to produce SCM as well as AAM. Clay is a commonly occurring material, with large deposits worldwide. However, natural clay has a low reactivity and various compositions, depending, e.g. on the weathering conditions. The present research aims exactly at enhancing the reactivity of natural clays occurring in Sweden subjecting them to mechanical activation in a planetary ball mill. Ball milling (BM) is considered a clean technology able to enhance the reactivity of crystalline materials without resorting to high processing temperatures or additional chemicals. BM was able to induce amorphization in clay minerals and to transform the layered platy morphology to spherical shape particles. The efficiency of the process was strictly related to the used process parameters. Higher ball to processed powder (B/P) ratio, longer time of grinding and higher grinding speeds increased the degree of the obtained amorphization. However, an undesired extensive caking and agglomeration occurred in certain setups. The potential of activated clay as a SCM was investigated in specific case studies. The measured compressive strength results showed a direct correlation between the enhanced amorphization degree of the mechanically activated clay and the increased strength values. The pozzolanic activity was induced and enhanced after the mechanical activation of the clay. The reactivity was assessed by the strength activity index (SAI). Furthermore, preliminary tests have shown that the alkali activation of the processed clays produced solidified matrixes with considerable strength.

Le ciment est le matériau le plus utilisé de nos jours pour plusieurs raisons: de bonnes propriétés mécaniques à la compression, un faible coût et une facilité d'utilisation. Cependant, le ciment est fragile lorsqu'il est soumis à des charges élevées et il est susceptible de se dégrader par des agents externes. Pour cette raison, différents additifs sont utilisés pour modifier le processus de prise et ainsi les propriétés finales du ciment. Parmi ces additifs, il y a un type appelé « accélérateurs de prise » qui permet la prise de la matrice de ciment plus rapidement. Il existe un type d'additifs « accélérateurs » qui constituent des points de germination pour la formation de gel C-S-H autour d'eux. L'objet de ce travail a été de développer une nouvelle voie de synthèse, basée sur la technologie eau supercritique, de deux nanoadditifs d'hydrates de silicate de calcium : la xonotlite et la tobermorite.Dans un premier temps, la synthèse a été effectuée dans des conditions souscritiques. Ensuite, il a été développé un réacteur continu supercritique adapté à la synthèse de ces nanoadditifs. Les synthèses ont été réalisées à 400 ° C et 23,5 MPa. La xonotlite et la tobermorite ont toutes deux été obtenues en réduisant drastiquement les temps de réaction d'heures/semaines (dans des conditions souscritiques) à quelques secondes seulement, dans des conditions supercritiques.Le dernier point étudié a été l'effet d'ensemencement par ces deux additifs de la pâte de ciment. Dans tous les cas, il a été observé, une accélération de la réaction et également une amélioration de la résistance du ciment.En conclusion, ce travail présente une nouvelle méthode ultra-rapide pour synthétiser des hydrates de silicate de calcium très cristallins, et prouve également l'effet « accélérateur » de ces particules lorsqu'elles sont utilisées comme germes dans des pâtes de ciment. Cette recherche propose une nouvelle méthodologie pour la synthèse des additifs pour ciments
Cement is the most used material nowadays due to several reasons: its good mechanical properties to compression, its low cost, and its easy use. However, cement is fragile when submitted to high charges and it is susceptible to degradation by external agents. For this reason different additions are used modify the setting process or the final properties of the cement paste. Among them there are one type called “setting accelerators” that develop the cementitious matrix faster. There is one type of accelerating additions that act as seeds; these are nucleating points for the formation of C-S-H gel around them. The aim of this work is to develop a new synthesis route, based on supercritical water technology, of two calcium silicate hydrates nanoadditions. These products are xonotlite and tobermorite.The first approach to the synthesis was done under subcritical conditions. After that it was developed the supercritical continuous reactor in order to adapt it to the necessities of the synthesis of the nanoadditions. The syntheses were carried out at 400ºC and 22.5 MPa. Both xonotlite and tobermorite were obtained reducing drastically the reaction times from hours/weeks (under subcritical conditions) to just some seconds under supercritical conditions.The last point studied was the seeding effect of both particles into cement paste. In every case it was observed, an acceleration of the reaction and also an improvement of the strength trough mechanical test.As a conclusion this work presents a new ultrafast method to synthesize highly crystalline calcium silicate hydrates, and also proves the accelerating effect of these particles when they are used as seeds in cement pastes. This research proposes a new methodology for the synthesis of additions to cement

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2003.
Includes bibliographical references (leaves 141-145).
Characterization of defect is one of the important objectives of nondestructive evaluation (NDE) for condition assessment of structures. Among many other NDE techniques, ultrasonic methods play a prominent role in the both quantitative and qualitative assessment of discontinuities in reinforced cementitious materials. Due to the heterogeneous nature of concrete, ultrasonic waves are highly scattered and attenuated, leading to the difficulty of concrete inspection using conventional ultrasonic techniques, including those that work well on relatively homogeneous materials such as metals. This thesis presents an advanced method for sizing and imaging of defects in reinforced cementitious materials. A two-dimensional, three-phase composite model of concrete is proposed to study the propagation and interaction behaviors of ultrasonic waves in concrete structures, and to gain a knowledge about wave diffraction with multiple cylindrical obstacles. The response of the modeled concrete structure to an incident ultrasonic pulse input signal (pulsed ultrasonic P-wave) is analytically investigated and simulated. A characteristic profile of the defect sizing as a function of focal depth is formulated via the synthetic focusing technique. A defect sizing parameter, called characteristic width, is obtained empirically to represent the defect sizing information for the concrete. Conventional 2-D ultrasonic B-scan imaging, for example, by migration, may introduce artifacts. In this thesis, the fundamental theory for synthetic aperture beam-forming through synthetic steering and focusing of array transducers is investigated. It is possible to achieve high spatial and temporal resolution ultrasonic image free of artifacts. A time-frequency signal processing and image reconstruction algorithm are also studied. The proposed defect sizing and imaging methodology is tested with numerically simulated ultrasonic waveform signals based on the mechanical properties of a custom-made concrete specimen. Experimental works confirm the feasibility of defect sizing and imaging of the method. With the knowledge about the concrete structures being tested this method may provide a useful tool for ultrasonic NDE application to reinforced cementitious materials.
by Ji-yong Wang.
Ph.D.

Cement based composites i.e. paste, mortar and concrete are the most utilized materials in the construction industry all over the world. Cement composites are quasi-brittle in nature and possess extremely low tensile strength as compared to their compressive strength. Due to their low tensile strength capacity, cracks develop in cementitious composites due to the drying shrinkage, plastic settlements and/or stress concentrations (due to external restrains and/or applied stresses) etc. These cracks developed at the nanoscale may grow rapidly due to the applied stresses and join together to form micro and macro cracks. The growth of cracks from nanoscale to micro and macro scale is very rapid and may lead to sudden failure of the cement composites. Therefore, it is necessary to develop such types of cement composites possessing higher resistance to crack growth, enhanced flexural strength and ductility. The development of new technologies and materials has revolutionized every field of science by opening new horizons in production and manufacturing. In construction materials, especially in cement and concrete composites, the use of nano/micro particles and fibers in the mix design of these composites has opened new ways from improved mechanical properties to enhanced functionalities. Generally, the production or manufacturing processes of the nano/micro sized particles and fibers are energy intensive and expensive. Therefore, it is very important to explore new methods and procedures to develop less energy intensive, low cost and eco-friendly inert nano/micro sized particles for utilization in the cement composites to obtain better performance in terms of strength and ductility. The main theme of the present research work was to develop a family of new type of cementitious composites possessing superior performance characteristics in terms of strength, ductility, fracture energy and crack growth pattern by incorporating micro sized inert carbonized particles in the mix design of cementitious composites. To achieve these objectives the micro sized inert carbonized particles were prepared from organic waste materials, namely: Bamboo, coconut shell and hemp hurds. For comparison purposes and performance optimization needs, another inorganic waste material named as carbon soot was also investigated in the present research. The experimental investigations for the present study was carried out in two phases; In the first phase of research work, a methodology was developed for the synthesis of the micro sized inert carbonized particles from the above mentioned organic raw materials. In the second phase of research, various mix proportions of the cementitious composites were prepared incorporating the synthesized micro sized inert carbonized particles. For micro sized inert carbonized particles obtained from bamboo and coconut shell three wt.% additions i.e. 0.05, 0.08, 0.20 were investigated and for particles synthesized from hemp hurds 0.08, 0.20, 1.00 and 3.00 wt.% additions were explored. The cement composites were characterized by third-point bending tests and their fracture parameters were evaluated. The mechanical characterization of specimens suggested that 0.08 wt.% addition of micro sized inert carbonized bamboo particles enhances the flexural strength and toughness of cement composites up to 66% and 103% respectively. The toughness indices I5, I10 and total toughness of the cement composites were also enhanced. The carbonized particles synthesized from coconut shell resulted in improved toughness and ductility without any increase in the modulus of rupture of the cement composite specimens. Maximum enhancements in I5 and I10 were observed for 0.08% addition of both carbonized and carbonized-annealed particles. For the carbonized hemp hurds cement composites the results indicate that the micro sized inert carbonized particles additions enhanced the flexural strength, compressive strength and the fracture energy of the cement composites. The microstructure of the cement composites was also studied with the help of field emission scanning electron microscope (FESEM) by observing small chunks of cement composite paste samples. The FESEM observations indicated that the micro sized inert carbonized particles utilized in the mix design of these mixes were well dispersed in the cement matrix. It was also observed that the fracture paths followed by the cracks were tortures and irregular due the presence of micro particles in the matrix. The cracks during their growth often contoured around the inert particle inclusions and resulted in enhanced energy absorption capacity of the cement composites. The study was further enhanced to the cement mortar composites and their performances were studied. The results indicated that the energy absorption behavior of the composites was enhanced for all the cement composites containing micro carbonized particles. Finally, it is concluded that the ductility and toughness properties of the cement composites can be enhanced by incorporating the micro sized inert carbonized particles in the cement matrix. The fracture energy, ductility and toughness properties enhancement of the cement composites greatly depends upon the source and synthesis procedure followed for the production of micro sized inert carbonized particles.

Cementitious materials are commonly and extensively used worldwide by construction industry for various types of infrastructures. Despite of their exceptional strength in compression they still possess limited tensile strength and tensile strain capacity. Different types of fibers have been investigated since last fifty decades to reinforce the cementitious matrix against tensile failures and to impart ductility. The size of the reinforcing fillers has diminished from macro to micro and now even to the nano scale with the recent advancements in nanotechnology. Due to exceptional intrinsic properties and large aspect ratio, carbon nanotubes have been successfully investigated as a reinforcing filler to modify the mechanical strength, fracture toughness, electrical and electromagnetic wave absorbing properties of cementitious composites. However the problems associated with its effective dispersion and bonding with the host material limit its widespread applications on large scale. To overcome the aforementioned issues concerning the dispersion and bonding of nano reinforcing materials with the host matrix, graphene nano sheets were explored for the first time as a reinforcing agent for high performance cementitious matrices. Graphene sheets are free form entanglement problems and therefore need comparatively lesser energy for proper dispersion. Due to very high specific surface area and large aspect ratio in comparison with carbon nanotubes they are much capable to develop strong interfacial bond with the host medium. In the commercialization of these nano carbon particles filled cementitious composites, another major concern would be the related expenses. Therefore in parallel, research work was also done to explore the cost effective alternatives for the production of carbon nano particles to be used for modification or improvement in the properties of cement matrices. In recent wok by Prof. Ferro’s research team it has been explored that carbon nano particles produced from coconut shells can be effectively used to improve the mechanical strength and fracture toughness of cementitious composites with limited dispersion issues (G. Ferro et al. 2014, 2015). To continue with the productive research pertaining the cost effective production of carbon nano particles for high performance cementitious composites, bio-waste in the form of bagasse fibers, hazelnut shell and peanut shell was investigated. These particular types of agricultural wastes were selected keeping in view their economic availability as well as the excellent conversion efficiency via pyrolysis. The present work encompasses complete characterization of the investigated materials, detailed study on their dispersion ability in water and the cement matrix, entire mechanical characterization of reinforced cementitious composites at varying proportions as well as their electromagnetic wave absorption properties in 2-10 GHz frequency range. It was determined that graphene nano-platelets can be uniformly dispersed in water as well as in the cementitious matrix without any addition of separate dispersant or surfactant or stabilizing agent. It was found that even at a very low content of addition remarkable improvements in the mechanical strength and fracture toughness were attained. The optimum content of addition for the grade 4 graphene nano-platelets was found as 0.08 wt% providing with a significant increase of 89% and 29% in compressive and flexure strength along with 115% improved fracture toughness. Similarly the carbonized particles produced for bio-waste were found quite effective in modifying the mechanical performance of cementitious composites. Maximum enhancement by 139% and 88% in flexural and compressive strength were achieved on 0.2 wt % addition of nano/micro carbonized particles produced from peanut shell with an increase of 69% in the fracture toughness as well. Microstructural investigations evidenced the proper homogeneous dispersion of GNPs and NMCPs throughout cementitious matrix along with their efficient filling action to refine the pore-structure of the cementitious composite. The phenomena of crack bridging, crack deflections, crack contouring and crack branching were observed via scanning electron microscopy revealing the mechanism behind the remarkable improvements of mechanical properties achieved in the present research. A novel cost effective material in the form of cement composites containing carbonized agricultural residue (comprising CPS and CHS) was proposed for shielding against electromagnetic waves. The investigated material was found much efficient for electromagnetic interference shielding applications, providing the advantage of better dispersion, simple manufacture at a much lower cost (cost saving ˃ 85%) compared to the corresponding carbon nanotubes based cement composite material.

La détérioration prématurée des réparations en béton est le résultat de divers processus physico-chimiques et électrochimiques. La fissuration du béton de réparation est une des causes de dégradation les plus importantes et peut entraîner et accélérer le processus de corrosion des barres d’armature et ainsi diminuer significativement la durée de vie, non seulement de la réparation, mais de l’ouvrage dans son ensemble. Ce travail de recherche avait pour objectif de contribuer à identifier et développer une méthode d’essai objective et établir une corrélation avec des techniques d’essai indirectes. L’essai proposé utilise une dalle de béton de référence comportant en surface une cavité à combler avec le matériau à tester. Cet essai permet de simuler une réparation superficielle réelle, avec un degré de restriction représentatif et la possibilité de réaliser le vieillissement dans des conditions d’exposition diverses. Afin d’être en mesure d’apprécier le caractère représentatif de l’essai de performance et des techniques d’essai indirectes, des réparations expérimentales de grandeur nature ont aussi été réalisées sur des structures exposées en conditions extérieures.
The premature deterioration of concrete repairs in service is a result of a variety of physico-chemical and electrochemical processes. Among the most serious causes of repair failures is cracking of the repair. Cracking may result in the reduction of an effective cross-sectional area of the repaired structure and increase the effective permeability of the concrete cover, thus promoting corrosion of the reinforcement and further deterioration. The main objective of this project was to contribute to the development and assessment of a reliable test method for evaluating the sensitivity to cracking of repair materials. A performance test was developed and used to establish correlations with existing indirect test methods (ring test, beam deflexion test, drying shrinkage test, etc.). The performance test method uses of a reference slab containing a cavity on the top surface to be filled with the repair material to be tested. The reference test slab, which offers a degree of restraint comparable to what is found in reality, allows simulating the behavior of the material in real concrete repair conditions. In order to better evaluate the test methods, experimental repairs have also been made on existing structures exposed to service conditions.

Master of Science
Department of Civil Engineering
Kyle Riding
Concrete is the most widely used construction material. Concrete strength and durability develop from a series of exothermic reactions involving water called hydration. Long-term durability and performance of concrete is very much dependent on the early hydration behavior of cementitious materials. This study examined the effects of curing temperature and access to moisture on the early age reaction rate of cementitious materials, and methods for quantifying these effects. Apparent activation energy (Ea) relates the effects of temperature on the cement hydration reaction. There are various methods and calculation techniques for estimating Ea that result in greatly varying values. Cement paste and mortar are often used to calculate Ea and used later for concrete. Ea values were calculated using cement mortar and paste by isothermal calorimetry and showed excellent correlation. This validates the use of Ea based on cement paste in modeling concrete behavior. Ea values were also calculated by chemical shrinkage and it showed potential for use in calculating Ea. Cementitious materials need free water to be available for hydration to continue. Curing with either waxy curing compounds or ponded water are common practices. The thickness of distilled water, lime-saturated water, and cement pore water used as a curing method affects the rate of hydration. Water-cementitious material ratio (w/cm) and sample depth affect the performance of water curing, with low w/cm being the most significant. Partial replacement of sand by fine lightweight aggregate also improves the hydration of cementitious material much more than conventional water ponding. Curing compounds showed improvements in cement hydration compared to uncured samples.

This thesis presents details of a numerical programme of study on the themo-hygrochemical (THC) processes occurring during the self-healing of cementitious materials. A comprehensive THC model, which is mechanistic in nature, is proposed and implemented in the framework of the finite element method. The aim of this model is to develop a useful computational tool that is capable of realistically predicting damage recovery in terms of the crack filling observed under specific environmental conditions. The early age and long term behaviour of the cementitious materials is simulated by solving a boundary value problem which couples moisture-temperature-ion transport mechanisms by means of mass and enthalpy balance equations. The model assumes that all the transport processes occur at the capillary pore level and that the selfhealing is driven by ongoing hydration. In this context, attention is focused on developing an innovative microstructural model that can predict the quantitative evolution of the capillary porosity. The microstructural model is based on an existing colloidal classification of the water forms present in the clinker hydrates, on hydration kinetics principles and on the stoichiometry of the Portland cement. The effect of the aggregate absorption on the capillary porosity is also examined. Firstly, the adopted theoretical considerations regarding the transport of moisture and temperature in cement-based materials are validated by comparing the numerical findings of the TH component with the reported results of three different sets of drying experiments. Then the THC model is applied to the simulation of a crack recovery experiment undertaken at Cardiff University. In both cases the proposed model was found to capture the essential characteristics of the thermo-hygro-chemical behaviour of cementitious materials.

La détérioration prématurée des réparations en béton est le résultat de divers processus physico-chimiques et électrochimiques. La fissuration du béton de réparation est une des causes de dégradation les plus importantes et peut entraîner et accélérer le processus de corrosion des barres d’armature et ainsi diminuer significativement la durée de vie, non seulement de la réparation, mais de l’ouvrage dans son ensemble. Ce travail de recherche avait pour objectif de contribuer à identifier et développer une méthode d’essai objective et établir une corrélation avec des techniques d’essai indirectes. L’essai proposé utilise une dalle de béton de référence comportant en surface une cavité à combler avec le matériau à tester. Cet essai permet de simuler une réparation superficielle réelle, avec un degré de restriction représentatif et la possibilité de réaliser le vieillissement dans des conditions d’exposition diverses. Afin d’être en mesure d’apprécier le caractère représentatif de l’essai de performance et des techniques d’essai indirectes, des réparations expérimentales de grandeur nature ont aussi été réalisées sur des structures exposées en conditions extérieures.
The premature deterioration of concrete repairs in service is a result of a variety of physico-chemical and electrochemical processes. Among the most serious causes of repair failures is cracking of the repair. Cracking may result in the reduction of an effective cross-sectional area of the repaired structure and increase the effective permeability of the concrete cover, thus promoting corrosion of the reinforcement and further deterioration. The main objective of this project was to contribute to the development and assessment of a reliable test method for evaluating the sensitivity to cracking of repair materials. A performance test was developed and used to establish correlations with existing indirect test methods (ring test, beam deflexion test, drying shrinkage test, etc.). The performance test method uses of a reference slab containing a cavity on the top surface to be filled with the repair material to be tested. The reference test slab, which offers a degree of restraint comparable to what is found in reality, allows simulating the behavior of the material in real concrete repair conditions. In order to better evaluate the test methods, experimental repairs have also been made on existing structures exposed to service conditions.

Actuellement, les méthodes d’essais normalisées, couramment utilisées pour étudier la carbonatation du béton, s’appuient sur l’évaluation de la chute du pH (<9) de la solution interstitielle d'un échantillon de béton exposé à des concentrations ambiantes ou très élevées de CO2 (2% à 50% en volume). Ces méthodes sont souvent critiquées car soit, elles nécessitent beaucoup de temps (plus d’une année pour la carbonatation naturelle), soit elles sont coûteuses et d’une faible fiabilité (la carbonatation accélérée, notamment quand la concentration de CO2 est supérieure à 3% CO2). Deux mécanismes principaux pilotent la carbonatation: le transport diffusif du dioxyde de carbone gazeux, qui est régi par le coefficient de diffusion effectif de cette espèce dans le milieu poreux, et la consommation de CO2 par la quantité de produits carbonatables présente dans la matrice cimentaire. Ces deux propriétés du matériau sont requises pour les modèles prédictifs de la profondeur de carbonatation des matériaux cimentaires. L’objectif de ce travail est donc de développer deux méthodes d’essai simples et fiables pour déterminer ces deux propriétés.D’abord, nous avons développé et validé une méthode d’essai permettant de déterminer le coefficient de diffusion effectif d’oxygène (De,O2) de neufs pâtes de ciment durcies et 44 bétons pré-conditionnés à différentes humidités relatives. L'influence de la durée d'hydratation, du rapport eau sur liant, de la carbonatation accélérée (1% CO2) et du type de liant sur la diffusivité de l'oxygène est étudiée sur des bétons et pâtes de ciment durcies. L’influence de l’épaisseur de l’échantillon de béton testé sur le De,O2 est évaluée à l'état sec et après conditionnement des bétons à une humidité relative de 93%. La corrélation entre la perméabilité à l'oxygène et le coefficient de diffusion effective d’oxygène est étudiée sur 44 mélanges de béton.Une deuxième méthode d’essai est développée pour étudier le taux instantané de fixation de CO2 et la quantité de produits carbonatables de pâtes de ciment hydratées, de phases pures d’hydrates et anhydres synthétisées. Les échantillons ont été carbonatés dans des systèmes ouverts sous humidités relatives contrôlées et concentration ambiante de CO2, puis le système bascule en configuration fermée pour mesurer la quantité de CO2 fixée par le matériau testé pendant une courte période. Cette méthode d’essai permet de déterminer l’évolution en fonction de temps du taux instantané de réaction de carbonatation et de la capacité de fixation de CO2 sous différents environnements. Un bon accord entre les résultats de la nouvelle méthode d’essai et l'analyse thermogravimétrique a été observé, ce qui met en évidence la fiabilité et la précision de la méthode de test développée.Les résultats obtenus des essais de diffusion et les quantités de produits carbonatables sont intégrés dans des modèles de prédiction de la profondeur de carbonatation. Ces profondeurs de carbonatation ont été comparées aux profondeurs de carbonatation déterminées directement sur les mêmes matériaux par pulvérisation de phénolphtaléine, en carbonatation naturelle et accélérée
The current standardized methods used to investigate the carbonation performance of concrete are based on the direct determination of the pH variation on the surface of a concrete specimen exposed to ambient or higher CO2 concentration. These methods are either time-consuming (natural carbonation) or of a questionable accuracy (accelerated carbonation). The carbonation physicochemical process involves two major mechanisms: gaseous CO2 diffusion into the cementitious material’s porous network and its dissolution and reaction with CaO of the hardened cement paste. Most carbonation depth prediction models require the CO2-effective diffusion coefficient and the amount of carbonatable products as input parameters. Hence the aim of this work is to develop two simple and reliable test methods to determine these two properties in a reliable and cost-effective manner.First we developed and validated a test method to determine the oxygen-effective diffusion coefficient (De,O2) of nine different hardened cement pastes preconditioned at different relative humidity levels, and 44 concrete mixtures. The influence of the hydration duration, water-per-binder ratio, accelerated carbonation, and binder type on the oxygen diffusivity was investigated. The dependence of the De,O2 on the tested concrete specimen thickness was investigated at the dry state and after conditioning at 93%RH. The De,O2 was determined before and after full carbonation of six concrete mixtures previously conditioned at different RH. A correlation between oxygen permeability and diffusivity is investigated on 44 concrete mixtures.A second test method is developed to determine the instantaneous CO2 binding rate and the amount of carbonatable products of powdered hydrated cement pastes and synthetic anhydrous and hydrates. The samples were carbonated in open systems at ambient CO2 concentration and controlled relative humidity, and then the system switches into a closed configuration while the measurement of the CO2-uptake is performed over a short period of time. The test method allows for the measurement of the carbonation reaction rate and capacity; and their evolution as function of time under different RH. The developed method shows advantages for being nondestructive, allowing the samples to carbonate at controlled CO2 concentration and humidity, and providing measurements with low cost equipment. A good agreement between the test method results and thermogravimetric analysis was observed, which highlights the reliability and accuracy of the developed test method.The results obtained from the gaseous diffusion coefficient and carbonatable products test methods were used as inputs for carbonation depth prediction models. A correlation was investigated between the measured carbonation depth on different concrete and hydrated cement pastes mixtures by means of phenolphthalein solution under both natural and accelerated exposure. The results were compared with the calculated carbonation depth using our experimental results
Die zurzeit verwendeten Methoden zur Untersuchung des Karbonatisierungs-widerstandes von Beton basieren auf der direkten Bestimmung des pH-Wertes der oberflächennahen Betonrandzone, die zuvor einer bestimmten Prüflagerung ausgesetzt war (relative Luftfeuchte, spezifische CO2-Konzentrationen). Diese Methoden sind jedoch entweder sehr zeitaufwändig (natürliche Karbonatisierung) oder von fraglicher Praxisnähe (beschleunigte Karbonatisierung). Der physikalisch-chemische Karbonatisierungsprozess beinhaltet zwei Hauptmechanismen: die Diffusion von gasförmigem CO2 in das poröse Netzwerk des Betons und dessen Auflösung und Reaktion mit CaO der ausgehärteten Zementsteins. Die meisten Modelle zur Vorhersage der Karbonatisierungstiefe erfordern den effektiven CO2-Diffusionskoeffizienten und die Menge an karbonatisierbarer Masse als Eingabeparameter. Ziel dieser Arbeit ist es, zwei einfache und zuverlässige Testmethoden zu entwickeln, um diese beiden Eigenschaften zuverlässig und kostengünstig zu bestimmen.Nach Entwicklung und Validierung einer geeigneten Testmethode zur Messung von Sauerstoffdiffusionskoeffizienten (De,O2), wurden diese an neun verschiedenen Zementproben gemessen, die bei unterschiedlichen relativen Luftfeuchten vorkonditioniert wurden. Anschließend wurden 44 verschiedene Betonmischungen geprüft. Bei diesen wurde die Hydratationsdauer und der Wasserbindemittelwert variiert. Die Abhängigkeit des Sauerstoffdiffusionskoeffizienten De,O2 von der getesteten Betonprobendicke wurde im trockenen Zustand und nach Konditionierung bei 93% relativer Luftfeuchtigkeit untersucht. Der Sauerstoffkoeffizient De,O2 wurde vor und nach der vollständigen Carbonisierung von sechs Betonmischungen bestimmt, die zuvor bei unterschiedlicher relativer Luftfeuchtigkeit vorkonditioniert worden waren. Eine zweite Testmethode wurde entwickelt, um die momentane CO2-Bindekapazität und die Menge an karbonatisierbarer Masse aus pulverförmigen Zementhydratpasten und synthetischen wasserfreien Produkten und Hydraten zu bestimmen. Die Proben wurden zunächst in offenen Systemen bei einer CO2-Konzentration in der Umgebung und einer kontrollierten relativen Luftfeuchtigkeit gegeben, um danach dann in eine geschlossene Konfiguration umzuwechseln. So konnte man die CO2-Aufnahme über einen kurzen Zeitraum nachverfolgen. Die Testmethode ermöglicht die Messung der Karbonatisierungsreaktionsrate und –kapazität in Abhängigkeit der Zeit unter verschiedenen relativen Luftfeuchten der Umgebungsluft. Es wurde eine gute Übereinstimmung zwischen den Ergebnissen der Testmethode und der thermogravimetrischen Analyse festgestellt, was die Zuverlässigkeit und Genauigkeit der entwickelten Untersuchungsmethodik unterstreicht.Die Ergebnisse beider Tests wurden als Input für Vorhersagemodelle für den zeitabhängigen Karbonatisierungsfortschritt von Beton verwendet. Es wurde eine Korrelation zwischen der gemessenen Karbonatisierungstiefe an verschiedenen Beton- und Zementhydratmischungen mittels Phenolphthaleinlösung untersucht, wobei u. a. Karbonatisierungstiefen bestimmt nach natürlicher Lagerung mit berechneten/vorhergesagten Karbonatisierungstiefen, die mithilfe der vorgestellten Modellierung und Inputdaten aus Test miteinander verglichen wurden

Several benefits are gained from using cold mix asphalt (CMA) instead of hot mix asphalt (HMA). The benefits include conservation of materials and reducing energy consumption, preservation of the environment and reduction in cost. One of the common types of CMA is cold bitumen emulsion mixture (CBEM) which is the mixture produced by mixing mineral aggregate with bitumen emulsion. Despite the efforts applied in the last few decades in order to improve and develop CBEM utilization, certain deficiencies remain that make it inferior to HMA, resulting in restricting or minimizing of its use. However, the development of CBEM for road construction, rehabilitation and maintenance is steadily gaining interest in both pavement engineering industrial and research sectors. The present study was primarily aimed at evaluating the effect of using different cementitious materials on the performance of CBEM. The idea of the research is to provide a sustainable filler from supplementary cementitious materials (SCMs) to be used as fillers to provide enhanced properties of CBEMs. By achieving this aim it is expected that the utilization of CBEM would increase, allowing them to be used as structural pavement materials with some confidence. Research was first undertaken to optimize the mix design of CBEM using a statistical approach known as response surface methodology (RSM), as an alternative approach to achieve acceptable engineering properties. The optimization of CBEM was investigated, to determine optimum proportions to gain suitable levels of both mechanical and volumetric properties. This optimization focussed on the mix design parameters, namely bitumen emulsion content (BEC), pre-wetting water content (PWC) and curing temperature (CT). This work also aimed to investigate the effect of the interaction between these parameters on the mechanical and volumetric properties of CBEMs. The results indicate that the interaction of BEC, PWC and CT influences the mechanical properties of CBEM. However, PWC tends to influence the volumetric properties more significantly than BEC. The individual effects of BEC and PWC are important, rather than simply the TFC which is used in conventional mix design of CBEM. Furthermore, the experimental results for the optimum mix design corresponded well with model predictions. It was concluded that optimization using RSM is an effective approach for mix design of CBEMs. The study also investigated in-depth the performance characteristics of CBEMs using different filler treatments. The study was extended to understand the performance enhancement through mineralogical and microstructural investigations. The research was designed to use cement, binary and ternary blended fillers (BBF and TBF). Fly ash (FA) and ground granulated blast-furnace slag (GGBS) were used as BBF while silica fume (SF) was added to the BBF to obtain TBF. A significant improvement was achieved in mechanical and durability properties of CBEMs due to incorporation of both cement and blended fillers. Also, the results indicated that TBF was more suitable than BBF for the production of CBEMs. The microstructural assessment indicated that the effect of BBF on the internal microstructure of CBEMs was slightly negative and more noticeable in CBEMs containing FA. Mineralogical and microstructural assessments also suggested that the presence of bitumen emulsion might not affect the hydration of the silicates in treated CBEMs. The formation of additional CSH was observed due to the replacement of conventional limestone filler by cement, BBF and TBF. However, it seems that this can cause a delay in the formation of other hydration products (Ettringite) resulting from the hydration of aluminates in cement. Furthermore, it is proposed that the addition of SF to BBF mixtures can eliminate the delay in formation of hydration products caused by the bitumen emulsion. The present work was also aimed at better understanding the curing mechanism of CBEMs and to bridge the gap between laboratory curing and field evolution of these mixtures. This was achieved by evaluating the effect of the curing process on CBEM performance and developing a prediction model to assess in-situ CBEM performance using maturity relationships. Different contributory factors affecting the curing process were investigated such as curing temperature and relative humidity (RH) in addition to the impact of curing time and the presence of cement/active fillers. The results indicated that high curing temperature is responsible for additional stiffness gain by increasing the binder stiffness due to ageing and by increasing the moisture loss by evaporation during the curing process. However, at high curing temperature the moisture loss by evaporation may hinder the hydration of cement/active fillers. Moreover, the results also indicated that the high RH level influences the stiffness modulus of CBEMs negatively. The laboratory results were then used to develop a tool to assess in-situ curing of CBEMs using the maturity approach, which is widely used to estimate in-situ concrete properties. A strong correlation was found between maturity and the stiffness values obtained from the laboratory tests, which resulted in development of maturity-stiffness relationship. The application of this relationship to assess the in-situ stiffness of CBEMs is presented using three hypothetical pavement sections in the United Kingdom, Italy and Qatar; to simulate different curing regimes. A pavement analysis and design study was conducted to evaluate the incorporation of treated CBEMs into a pavement structure. CBEMs are suggested to be used in two scenarios: the first is as a surface course and the second is as a base course. The scope of the study is limited here to design based on the fatigue criterion only. Although, the structural design was based on practical hypothetical layer thicknesses, the results provided useful insight into the structural capabilities of CBEMs.

As the most important materials in civil engineering, bituminous and cementitious materials have been used widely in pavements and constructions for many years. Accurate determination of adhesion is important to the bonding properties of bituminous and cementitious materials. In this work, we presented a novel approach to measure the adhesion between binders and aggregate mineral particles at microscopic scale. Particle probe scanning force microscopes (SFM) were used to study the adhesion between mineral microspheres representing the primary aggregate constituents (Al2O3, SiO2 and CaCO3) and various control (PG 64-22 and PG 58-22) and modified binders. Results showed that these modified SFM probes could effectively measure the adhesion between binders and aggregate minerals. Consistent adhesion measurements were obtained between different asphalt binders and aggregate mineral particles. Statistical analyses were performed to evaluate effects of different factors on the aggregate-modified binder adhesion, including aggregate constituents, binder types, modifier types and cantilever properties. Due to the stronger polarity of alumina particles, stronger interactions occur within alumina-binder pairs than within silica- and calcium carbonate-binder pairs. Meanwhile, morphologies of different modified binders clearly demonstrated microstructural variations in these binders. The adhesion between steel and different cement hydrated products was measured using particle probe SFM. Adhesive forces are collected between steel microspheres and new (four-week old) and old (six-month old) cement in air and saturated lime water. Mixed Gaussian models were applied to predict phase distributions in the cement paste, i.e., low density C-S-H, high density C-S-H, CH, other hydrated products and the unreacted components. For new cement in saturated lime water, adhesive forces between steel and low density C-S-H, high density C-S-H and other hydrated products are intermediate among all groups selected. The adhesive forces between steel and calcium hydroxide are smallest, whereas the adhesive forces between steel and the unreacted phases are largest. For the six-month old cement, the interweaving of calcium carbonate crystals and C-S-H during the carbonation produces greater adhesive forces to steel, consistent with the adhesive forces between steel and the control calcium carbonate specimen. CH turned into calcium carbonate by reacting with carbon dioxide in air. An increase in adhesive forces was found between steel and calcium carbonate in the old cement than those between steel and CH in the new cement. Particle probe SFM is able to measure the adhesion in bimaterials. For bituminous materials, this methodology provides opportunities to evaluate the effects of different processing methods and to generate quantitative information for the development of multi- scale asphalt mixture cracking models. For cementitious materials, these studies opened new avenues to study the interactions between steel and cement at microscale under a variety of environmental conditions and can be formulated as crack initiation and propagation criteria incorporated in multiscale models for reinforced concrete structures.

Ultrasonic velocity and attenuation measurements have been used to characterise a range of phosphate bonded, alumina filled, magnesia ceramics and other ceramic materials... Measurements were made over a range of frequency from 50kHz - 1 OM Hz, using a variety of commercial probes and equipment, and a variety of techniques. An ultrasonic double-probe method was used to monitor the setting process of the cementitious ceramics using commercial 2.25MHz and 2MHz transducers, for compressional and shear wave modes, respectively, in samples with alumina content in the range of 0 - 60 wt 0/0. The elastic properties of the material were determined from ultrasonic velocity measurements and were found to be dependent upon the filler volume fraction. The measured elastic moduli were found to Increase as porosity decreased, and this effect might possibly be used to estimate porosity. The composition dependence of the elastic moduli is compared with the Hashin and Shtrikman theoretical bounds for the elastic moduli of two-phase materials. All data lie between these bounds, suggesting that the alumina particles were well dispersed and well bonded to the matrix. However, the fact that the data are slightly above the lower bound suggested that the particles are not spherical, and this, together with other evidence obtained from an analysis of reaction rates, indicates the predominence of plate-like gram structures.

Cementitious materials such as mortar or concrete are brittle and have an inherent weakness in resisting tensile stresses. The addition of discontinuous fibers to such matrices leads to a dramatic improvement in their toughness and remedies their deficiencies. It is generally agreed that the fibers contribute primarily to the post-cracking response of the composite by bridging the cracks and providing resistance to crack opening. On the other hand, the multifield theory is a mathematical tool able to describe materials which contain a complex substructure. This substructure is endowed with its own properties and it interacts with the macrostructure and influences drastically its behavior. Under this mathematical framework, materials such as cement composites can be seen as a continuum with a microstructure. Therefore, the whole continuum damage mechanics theory, incorporating a new microstructure, is still applicable. A formulation, initially based on the theory of continua with microstructure Capriz, has been developed to model the mechanical behavior of the high perfor-mance fiber cement composites with arbitrarily oriented fibers. This formulation approaches a continuum with microstructure, in which the microstructure takes into account the fiber-matrix interface bond/slip processes, which have been recognized for several authors as the principal mechanism increasing the ductility of the quasi-brittle cement response. In fact, the interfaces between the fiber and the matrix become a limiting factor in improving mechanical properties such as the tensile strength. Particularly, in short fiber composites is desired to have a strong interface to transfer effectively load from the matrix to the fiber. However, a strong interface will make difficult to relieve fiber stress concentration in front of the approaching crack. According to Naaman, in order to develop a better mechanical bond between the fiber and the matrix, the fiber should be modified along its length by roughening its surface or by inducing mechanical defor-mations. Thus, the premise of the model is to take into account this process considering a micro field that represents the slipping fiber-cement displacement. The conjugate generalized stress to the gradient of this micro-field verifies a balance equation and has a physical meaning. This contribution includes the computational modeling aspects of the high fiber rein-forced cement composites (HFRCC) model. To simulate the composite material, a finite element discretization is used to solve the set of equations given by the multifield approach for this particular case. A two field discretization: the standard macroscopic and the micro-scopic displacements, is proposed through a mixed finite element methodology. Furthermore, a splitting procedure for uncoupling both fields is proposed, which provides a more convenient numerical treatment of the discrete equation system. The initiation of failure in HPFRCC at the constitutive level identified as the onset of strain localization depends on the mechanical properties of the all compounds and not only on the matrix ones. As localization criteria is considered the bifurcation analysis in combination with the localized strain injection technique presented by Oliver et al. It consists of injecting a specific localization mode during the localization stage, via mixed finite element formulations, to the path of elements that are going to capture the cracks, and, in this way, the spurious mesh orientation dependence is removed. Model validation was performed using a selected set of experiments that proves the via-bility of this approach. The numerical examples of the proposed formulation illustrated two relevant aspects, namely: 1) the role of the bonding mechanism in the strain hardening be-havior after cracking in the HPFRCC and 2) the role that plays the finite element formulation in capturing the displacement localization in the localization stage.

A reactive transport model is proposed to simulate the reactivity of cement based material in contact with CO2-saturated brine and supercritical CO2 (scCO2) under CO2 geological storage conditions. This code is developed to solve simultaneously transport and chemistry by a global coupled approach, considering the effect of temperature and pressure. The variability of scCO2 properties with pressure and temperature, such as solubility in water, density and viscosity are taken into account. It is assumed that all chemical processes are in thermodynamical equilibrium. Dissolution and precipitation reactions for portlandite (CH) and calcite (CC) are described by mass action laws and threshold of ion activity products in order to account for complete dissolved minerals. A chemical kinetics for the dissolution and precipitation of CH and CC is introduced to facilitate numerical convergence. One properly chosen variable is able to capture the precipitation and dissolution of the relevant phase. A generalization of the mass action law is developed and applied to calcium silicate hydrates (C-S-H) to take into account the continuous variation (decrease) of the Ca/Si ratio during the dissolution reaction of C-S-H. The changes in porosity and microstructure induced by the precipitation and dissolution reactions are also taken into account. Couplings between transport equations and chemical reactions are treated thanks to five mass balance equations written for each atom (Ca, Si, C, K, Cl) as well as one equation for charge balance and one for the total mass. Ion transport is described by using the Nernst-Plank equation as well as advection, while gas and liquid mass flows are governed by advection. Effect of the microstructure and saturation change during carbonation to transport properties is also considered. The model is implemented within a finite-volume code, Bil. Principles of this method and modeling approach are discussed and illustrated with the help of a simple example. This model, with all the efforts above, is able to simulate the carbonation processes for cement based materials, at both saturated and unsaturated conditions, in a wide CO2 concentration, temperature and pressure range. Several sets of experiments, including sandstone-like conditions, limestone-like conditions, supercritical CO2 boundary and unsaturated conditions reported in the literature are simulated. Good predictions are provided by the code when compared with experimental observations. Some experimental observed phenomena are also explained by the model in terms of calcite precipitation front, CH dissolution front, porosity profile, etc

The use of cement based materials could be widespread in the long term management of radioactive materials in the United Kingdom. In the Geological Disposal Concepts proposed by the Radioactive Waste Management Directorate of the Nuclear Decommissioning Authority (NDA), several cement based materials are used in the long-term management of intermediate-level wastes. Much of the waste will be immobilised within stainless steel containers using cement grouts based on ordinary Portland cement (OPC) blended with blast furnace slag (BFS) or pulverised fuel ash (PFA). The resulting waste packages will be placed underground in a Geological Disposal Facility (or Repository) after a period of storage at the waste producers’ sites. The repository will then be filled with cement based backfill. The encapsulation grouts and the backfill materials will perform as both a physical barrier and chemical barrier for confining the radioactive wastes. During storage and disposal, some wastes may generate carbon dioxide from the degradation of organic materials and this will react with the cement based materials. Therefore, carbonation of the cementitious encapsulation grouts and backfill materials is of interest because of the resulting changes to their physical and chemical properties and also because of its ability to remove carbon-14 labelled carbon dioxide from the gas phase. It is also important to understand the reaction kinetics under a range of conditions, due to the long-term nature of storage and disposal. In this work, the carbonation progress of one backfill material and of two encapsulation grouts used in the UK has been studied in batch reactors. These materials are known as Nirex Reference Vault Backfill (NRVB), 3:1 PFA/OPC and 3:1 BFS/OPC. Based on the single dimensional carbonation experiments, fundamental parameters affecting the rate of carbonation were investigated and the carbon dioxide uptake capacity of each material was determined. For these three materials, an increase in relative humidity (75% to 100%) decreases the carbonation rate. A higher reaction pressure can facilitate the carbonation, but its effect was less obvious than the effect of relative humidity. The progression of the carbonation fronts have also been observed by various techniques and the shape of carbonation front was proved to be influenced by the relative humidity. Special attention was given to the modelling of the kinetics and mechanism of the carbonation reaction of these materials. This work provides fundamental understanding of the carbonation reaction of NRVB, 3:1 PFA/OPC and 3:1 BFS/OPC of relevance to the future optimization of a geological disposal facility in the UK and to assessments of the performance of such a facility.