Tesi sul tema "Cementious materials"

L'impression 3D connaît un essor remarquable dans l'industrie de la construction, ouvrant la voie à la digitalisation attendue du secteur. Alors que de nouvelles techniques sont étudiées pour associer optimisation technique et limitation des émissions de CO2, cette étude se concentre sur l'impression 3D par lit de poudre. Encore relativement niche, cette technique pourrait permettre d'imprimer avec une forte teneur en fibres naturelles, franchissant ainsi une étape supplémentaire vers la neutralité carbone. Le processus est simple, impliquant trois étapes répétées : déposer une couche de poudre réactive - compacter - injecter de l'eau sur la surface.Par conséquent, contrôler la pénétration de l'eau dans la poudre est la clé pour améliorer la qualité d'impression. Pour confiner l'eau dans la zone désirée et permettre une hydratation optimale du liant, nous avons modifié les propriétés physiques de la poudre (compacité, perméabilité) ou celles du fluide injecté (tension superficielle, viscosité, limite d'écoulement) pour étudier leur impact sur la cinétique de propagation de l'eau en surface et dans la poudre. Nous avons donc étudié la cinétique de propagation verticale d'eau dans des échantillons de poudres cimentaires compactées. Pour mieux s'approcher des phénomènes advenant dans l'imprimante, l'imbibition verticale dans les deux sens de pénétration est suivie par analyse d'image et par IRM, bénéficiant ainsi d'informations complémentaires sur la quantité et la répartition de l'eau dans les échantillons.Après avoir développé un dispositif ambivalent, nous avons étudié des poudres pures (ciment, calcite, métakaolin, sable) et d'autres contenant des agrégats poreux (pâte de ciment recyclée ou chanvre micronisé) pour mieux comprendre leur impact sur la pénétration de l'eau dans une poudre imprimable biosourcée. En effet, cette technique apporte de nouvelles pistes de compréhension sur la saturation et, combinée à la RMN, les transferts d'eau entre la matrice et les agrégats poreux. Les agrégats poreux naturels comme le chanvre sont en effet bien connus pour interférer sur la répartition de l'eau car ils absorbent et gonflent au contact de l'eau. Les résultats indiquent que la cinétique ne ralentit pas toujours avec le temps et nous amènent à discuter de la validité de la loi de Washburn, pourtant communément utilisé pour décrire les phénomènes de propagation d'eau dans des milieux poreux.Enfin, le développement complet d'une imprimante 3D sur lit de poudre a permis d'imprimer des cubes qui permettront d'étudier l'influence du choix des paramètres d'impression (type d'injection et compacité) sur la forme des pièces. Nous pourrons ensuite envisager de considérer les matériaux biosourcés comme un outil possible pour améliorer la précision d'impression
3D printing is experiencing a significant rise in the construction industry, paving the way for the expected digitalization of the sector. As new techniques are explored to combine technical optimization and CO2 emission reduction, this study focuses on powder-bed 3D printing. Despite still being relatively niche, this method could facilitate printing with a high natural fiber content, thus taking a further step towards carbon neutrality. The process is simple, involving three iterative steps : depositing a layer of reactive powder, compacting it, and then injecting water onto the surface.Hence, controlling water penetration into the powder is crucial to improve print quality. The objective is to confine the available water to the desired area, ensuring optimal binder hydration and preventing leaching from previous layers. Several factors may limit penetration depth, including the physical properties of the powder (compactness, permeability) and those of the injected fluid (surface tension, viscosity, yield stress) to study their impact on the kinetics of water propagation on the surface and within the powder. Consequently, we examined the vertical water propagation kinetics in compacted cementitious powder samples. To better simulate the phenomena occurring within the printer, vertical imbibition in both penetration directions was monitored through image analysis and MRI, providing additional insights into the quantity and distribution of water in the samples.Following the development of a versatile setup, we investigated pure powders (such as cement, calcite, metakaolin, sand) and those containing porous aggregates (recycled cement paste or micronized hemp shives) to better understand their impact on water penetration in a bio-sourced printable powder. Indeed, this technique sheds new light with a saturation sensibility and, when combined with MRI, water transfers between the matrix and porous aggregates. Natural porous aggregates like hemp are well-known to affect water distribution as they absorb and swell on contact with water. The results indicate that kinetics do not always slow down over time which opens discussions on the validity of Washburn's Law, commonly used to describe water propagation phenomena in porous media.Finally, the complete development of a powder-bed 3D printer has enabled the printing of cubes, which will facilitate the study of the influence of printing parameter choices (injection type and compactness) on part geometry. We will then be able to consider biobased materials as a possible tool for improving printing precision

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.

This thesis provides a detailed study on optimisation of cementitous treated soft clay soils in the South East Queensland region. A comparative study has been performed comparing the behaviour of cement and lime treated compressible clays from both Bangkok and South East Queensland. The purpose of the comparative study was to evaluate change in strength properties of treated soft clay soil as well as providing parameters for case studies using different analysis methods. This thesis compares the behaviour of soft clay treated with cementitous materials in South East Queensland and Bangkok. Overall it was concluded that the addition of cement and lime has favourable effects on the strength characteristics of South East Queensland soft clays.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text

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.

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.

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.

Doctor of Philosophy
Department of Civil Engineering
Kyle A. Riding
Finely ground glass has the potential for pozzolanic reactivity and can serve as a supplementary cementitious material (SCM). Glass reaction kinetics depends on both temperature and glass composition. Uniform composition, amorphous nature, and high silica content of glass make ground glass an ideal material for studying the effects of glass type and particle size on reactivity at different temperature. This study focuses on how three narrow size ranges of clear and green glass cullet, 63–75 [mu]m, 25–38 [mu]m, and smaller than 25 [mu]m, as well as combination of glass types and particle sizes affects the microstructure and performance properties of cementitious systems containing glass cullet as a SCM. Isothermal calorimetry, chemical shrinkage, thermogravimetric analysis (TGA), quantitative analysis of X-ray diffraction (XRD), and analysis of scanning electron microscope (SEM) images in backscattered (BS) mode were used to quantify the cement reaction kinetics and microstructure. Additionally, compressive strength and water sorptivity experiments were performed on mortar samples to correlate reactivity of cementitious materials containing glass to the performance of cementitious mixtures. A recently-developed modeling platform called “[mu]ic the model” was used to simulated pozzolanic reactivity of single type and fraction size and combined types and particle sizes of finely ground glass. Results showed that ground glass exhibits pozzolanic properties, especially when particles of clear and green glass below 25 [mu]m and their combination were used at elevated temperatures, reflecting that glass cullet is a temperature-sensitive SCM. Moreover, glass composition was seen to have a large impact on reactivity. In this study, green glass showed higher reactivity than clear glass. Results also revealed that the simultaneous effect of sizes and types of glass cullet (surface area) on the degree of hydration of glass particles can be accounted for through a linear addition, reflecting that the surface area would significantly affect glass cullet reactivity and that the effects of SCM material interaction on reaction kinetics were minimal. However, mechanical properties of cementitious systems containing combined glass types and sizes behaved differently, as they followed the weaker portion of the two particles. This behavior was attributed to the pores sizes, distruibution, and connectiity. Simulations of combined glass types and sizes showed that more work on microstructural models is needed to properly model the reactivity of mixed glass particle systems.

It is perhaps paradoxical that many material properties arise from the absence of material rather than the presence of it. For example, the strength, stiffness, and toughness of a concrete are related to its pore structure. Furthermore, the volume, size distribution, and interconnectivity of porosity is important for understanding permeability, diffusivity, and capillary action occurring in concrete, which are necessary for predicting service lives in aggressive environments. This research advances the state-of-the-art of multiscale characterization of cement-based materials, and uses this characterization information to model the material behavior under competing durability concerns. In the first part of this research, a novel method is proposed to characterize the entrained air void system. In the second and third parts of this research, microstructural characterization is used in tandem with mechanical models to investigate the behavior of cementitious materials when exposed to rapid rates of loading and to cyclic freezing and thawing. First, a novel analytical technique is presented which reconstructs the 3D entrained air void distribution in hardened concrete using 2D image analysis. This method proposes a new spacing factor, which is believed to be more sensitive to microstructural changes than the current spacing factor commonly utilized in practiced, and specified in ASTM C457, as a measure of concrete's ability to resist to damage under cyclic freeze/thaw loading. This has the potential to improve economy by improving the quality of petrographic assessment and reducing the need for more expensive and time-consuming freeze/thaw tests, while also promoting the durability of concrete. Second, quantitative measurements of the sizes, shapes, and spatial arrangements of flaws which are through to drive failure at strain rates above 100/s were obtained in order to model mortar subjected to high strain-rate loading (i.e., extremes in load rate). A micromechanics model was used to study the ways in which flaw geometry and flaw interaction govern damage. A key finding suggests that dynamic strength may be multimodal, with larger flaws shifting the dynamic strength upwards into the highest strength failure mode. Third, a robust theoretical approach, based upon poroelasticity, is presented to further validate the utility of the novel spacing factor proposed this research. The model is truly multiscale, using in its formulation pore size data ranging from the nanoscale to the micro-scale, entrained air data from the micro-scale to the millimeter scale, and infers a representative volume element on the centimeter scale. The results provide an underlying physical basis for the performance of the novel spacing factor. Furthermore, the framework could be used as a forensic tool, or as a tool to optimize the entrained air void system against freeze/thaw damage.

A engenharia de materiais proporcionou os avanços mais notórios sobre o desempenho mecânico dos materiais cimentícios nas últimas décadas, ora por meio das técnicas de conformação, ora pelo projeto da microestrutura. Com isso, demonstrou-se ser falsa a idéia de que baixas resistências mecânicas seriam inerentes aos materiais cimentícios, mas, ao mesmo tempo, o restrito advento desses novos materiais aos setores de maior demanda os relegou à condição de alternativos apenas. O fato de cada tonelada de cimento Portland gerar outra tonelada de gases do efeito estufa indica que o quadro anterior precisa ser revisto. É por isso que uma das principais contribuições desse trabalho foi desenvolver a conformação por técnicas altamente produtivas e capazes de propiciar excelente desempenho mecânico, além da durabilidade, aos materiais cimentícios. A concepção e a construção de uma linha de prensagem por rolos foi o primeiro passo para que as placas cimentícias com resistência à compressão superior à 200MPa e reprodutibilidade compatível à das cerâmicas técnicas fossem obtidas de modo eficaz. Por sua vez, a extrusão, uma técnica capaz de produzir perfis com geometrias complexas e em grande quantidade, também foi bem adaptada aos materiais cimentícios, com excelente reprodutibilidade e resistência à flexão superior à 20MPa. Em ambas, prensagem e extrusão, o domínio da técnica nos permitiu obter componentes cimentícios cujas resistências mecânicas não sofrem influências de quaisquer que sejam os ambientes ao quais são expostos. A isso atribuímos o mais amplo conceito de durabilidade para um material cuja utilização depende da resistência mecânica ao longo de sua vida útil. Ainda, um método inovador para a durabilidade desses materiais foi desenvolvido neste trabalho: trata-se de sua impregnação por TEOS, um precursor de sílica molecular que reage com o hidróxido de cálcio para selar os poros pelos quais penetrou. Em números, significa a possibilidade de reduzir a porosidade dos corpos à base de cimento Portland para valores inferiores a 1% em volume, ao que se associa à concomitante redução de uma ordem de grandeza no coeficiente de difusão do íon cloro. Em resumo, os resultados que serão apresentados estão em ressonância com os mais rigorosos critérios de sustentabilidade num setor que urge por melhores perspectivas para o definitivo ingresso na era da industrialização: a construção civil. Porém, a maior virtude deste trabalho é não apenas aprimorar as etapas da engenharia dos materiais cimentícios, mas também aplicar a ciência para o entendimento da origem de sua resistência mecânica. De acordo com nossas comprovações experimentais, a resistência mecânica desses materiais é governada pelas moléculas de água confinadas em películas nanométricas entre as fases que se hidratam do cimento Portland. Essas moléculas de água se comportam como uma fase vítrea e, por sua vez, promovem adesão às superfícies que a confinam. Essa é também uma contribuição deste trabalho para tornar viável a nanotecnologia desses materiais por intermédio de um tema até então inexplorado: a adesão por água confinada. Acreditamos também que o grau de inovação sobre esse tema poderá extrapolar o material em si, visto que a vida como conhecemos é uma conseqüência direta das intrigantes propriedades da água e suas ligações hidrogênio.
The materials engineering afforded the most paramount known advances on the mechanical performance of cementitious materials in the last decades, through either casting techniques or microstructure design. Therewith, it was demonstrated to be false the idea that low mechanical strengths should be inherent to cement-based materials, but, at the same time, the limited ingress of these new materials to fields of great demands relegated them to the condition of merely alternative. The fact that each ton of Portland cement does create another ton of gases related to global warming indicates that the former situation needs to be reviewed. That is why one of the main contributions of this work was to improve casting techniques to render massive production and excellent mechanical performance, in addition to durability, for the cementitious materials. The concept and the construction of a roll compaction equipment were the first step to the cost-effective production of cementitious plates with compressive strength in excess of 200MPa, in addition to a reproducibility inasmuch as that of a technical ceramic. In the same way, the extrusion, a technique able to largely produce components of complex geometries, was also well adapted to cement-based materials which, again, showed excellent reproducibility and bending strength of more than 20MPa. In both, pressing and extrusion techniques, the control of processing steps was enough to get cement-based products whose mechanical strength barely changes, even after exposure to deleterious environments. Hereby, we attribute the widest concept of durability to a material which depends on the mechanical strength throughout its service life. Anyway, we also developed an innovative method to improve the durability of these materials along this work: TEOS impregnation. TEOS is a molecular precursor of silica which reacts with calcium hydroxide to seal the cementitious pores wherefrom it penetrated. Quantitatively, the porosity of Portland cement-based products dropped down to values around 1% in volume, what is related to concomitant reduction of chlorine ion diffusion coefficient of an order of magnitude. In summary, the results that will be demonstrated in the following chapters are in resonance with the most rigorous rules for sustainability, precisely in a field where such an initiative is welcome to help encouraging its industrialization: the building construction. However, it seems that the biggest virtue of this work is not only the improvements for cementitious materials engineering, but also to apply the science for the understanding of the origin of their mechanical strength. According to our experimental evidences, the mechanical strength of these materials is ruled by water molecules which are confined in nanometric layers between the hydrating phases of Portland cement. These water nanolayers behave themselves as glassy phase and, in their turn, promote adhesion to the surfaces which confine them. To the best of our knowledge, this work is one of the most promising contributions to become possible the nanotechnology of these materials, through a subject up to that time unexplored: the adhesion by confined water. Hence, it is likely that the innovation about this subject could exceed the material itself, once life as we know owes its peculiarities to the intrigant properties of water and to their hydrogen bonding.

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.

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.

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.

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

Geopolymers have received increasing attention as a promising sustainable alternative to ordinary Portland cement (OPC). However, the relationship among the synthesis, geopolymerization process, microstructures, molecular strucutres and mechanical properties of geopolymers remains poorly understood. To fill this knowledge gap, this dissertation focuses on the correlation of chemical composition-reaction kinetics-microstructure-mechanical properties of geopolymers. This study also sheds light on the durability, environmental impact and engineering applications of geopolymers from practical perspectives. The first part of this dissertation presents a comprehensive study on red mud-class F fly ash based geopolymers (RFFG). Firstly, RFFG with a high 28-day mechanical strength were successfully synthesized under the ambient condition of 23°C and 40 to 50% relative humidity. A nominal Na/Al molar ratio of 0.6 ~ 0.8 with a Si/Al ratio of 2 was found to be a good starting chemical composition for RFFG synthesis. Secondly, the reaction kinetics and its relation to the mechanical properties of RFFG were investigated by monitoring the development of geopolymer gels, reaction rate, porosity and mechanical properties of RFFG samples cured at room temperature, 50°C and 80°C for up to 120 days. The asymmetric stretching FTIR band of Si-O-T (T is Si or Al) centered around 960-1000 cm-1, which is the characteristic band of geopolymer gels, was observed to shift to a lower wavenumber at the early stage of the synthesis and shift to a higher wavenumber later on during the synthesis. The shift of Si-O-T band indicates that the geopolymerization took place in three stages: dissolution to Al-rich gels at Stage I, Al-rich gels to Si-rich gels at Stage II and Si-rich gels to tectosilicate networks at Stage III. The mechanical strength of RFFG barely increased, increased slowly by a limited amount and developed significantly at these three stages, respectively. An elevated curing temperature enhanced the early strength of RFFG, whereas an excessively high curing temperature resulted in a higher pore volume that offset the early-developed strength. Lastly, the remaining mechanical properties of the RFFG samples after soaking in a pH = 3.0 sulfuric acid solution for up to 120 days and the concentration of heavy metals leached from RFFG samples after the soaking were measured. The RFFG samples’ resistance against sulfuric acid was found to be comparable to that of OPC, and leaching concentrations of heavy metals were much lower than the respective EPA limits for soil contaminations. The degradation in mechanical properties of the RFFG samples during soaking in the acid was attributed primarily to the depolymerization and dealumination of geopolymer gels. The second part of this dissertation is devoted to the investigation of nano-scale mechanical properties and molecular structures of geopolymer gels with grid-nanoindentation and molecular modeling. Four phases (e.g., porous phase, partially developed geopolymer gels, geopolymer gels and unreacted metakaolin or crystals) and their nano-mechanical properties were identified in metakaolin based geopolymers (MKG) with grid-nanoindentation technique. It was found that the proportion of geopolymer gels largely determines the mechanical strength of the resulting geopolymers while other factors (e.g., pores and cracks) also play some roles in macro-scale mechanical strength of geopolymers. The final setting time of the geopolymers increased with the increase in Si/Al ratio and the decrease in Na/Al ratio, while the proportion of geopolymer gels and macro-mechanical strength of geopolymers increased with the increase in both Si/Al and Na/Al molar ratios, within the range of 1.2~1.7 and 0.6~1.0, respectively. In the molecular modeling, a combined density function theory (DFT)-molecular dynamic (MD) modeling simulation was developed to “synthesize� geopolymers. DFT simulation was used to optimize reactive aluminate and silicate monomers, which were subsequently used in reactive MD simulations to model the polymerization process and computationally synthesize geopolymer gels. The influence of Si/Al ratio and simulation temperatures on geopolymerization and resulting molecules of geopolymer gels was also examined. The computationally polymerized molecular structures of geopolymer gels were obtained. The distribution of Si4(mAl) and radial distribution fuctions of Si-O, Al-O, O-O and Na-Al for the models were compared and qualitatively agreed well with the experimental results from nuclear magnetic resonance (NMR) and neutron/X-ray pair distribution function in previous literature. Three polymerization stages: oligomerization, ring formation and condensation, were identified based on the nature of polymerization process, which were found to be affected by the temperature and Si/Al ratio. A higher temperature enhanced the reaction rate while a lower Si/Al ratio resulted in more compact geopolymer networks. The final part of this dissertation presents an experimental feasibility study of using geopolymer in shallow soil stabilization, in which a lean clay was stabilized with MKG at different concentrations. The study confirmed that MKG can be used as a soil stabilizer for clayey soils and the unconfined compressive strength, Young’s modulus and failure strain are comparable to or even better than OPC when the MKG’s concentration is higher than 11%. The binding effect of geopolymer gels on the soil particles was confirmed as the main mechanism for the improvement in mechanical properties of the stabilized soils with the scanning electron microscopy imaging, energy dispersive X-ray spectroscopy analyses and X-ray diffractometry characterization.

This thesis describes a portion of the ongoing development of a novel self-healing cementitious material system named LatConX originally proposed by a group of researchers at Cardiff University. The research reported was undertaken with the aim of furthering understanding of the system’s long-term behaviour, ultimately with a view to providing predictions for the performance of the system over a structure’s working life. This aim is accomplished through a combination of experimental and numerical research. An experimental series is presented which investigates the stress relaxation behaviour of polyethylene terephthalate in order to establish how the stress induced by heat-activated restrained shrinkage varies with time. Results of these experiments displayed very little stress reduction from the peak stress, with less than a 5 % loss observed over a 124 day period. The development of a new one dimensional transient thermomechanical model for viscoelastic behaviour of pre-drawn polyethylene terephthalate is then described. This model is shown to be able to reproduce the observed experimental behaviour with good accuracy. The polymer model is coupled with a number of other constitutive models for the behaviour of steel and concrete, thus forming a model for the material system as a whole. This coupling is undertaken within the framework of an idealised simply supported beam with a strong discontinuity for the simulation of a central crack hinge. The model is validated against experimental data and design code predictions. Design considerations for the LatConX system are discussed and modified design equations derived. Parametric studies are presented investigating the structural performance and material costs of beams incorporating the LatConX system compared with that of standard reinforced concrete beams. Encouraging results are reported suggesting that the LatConX system has the potential to simultaneously improve long-term durability and structural performance of reinforced concrete structures and reduce the initial material costs by replacing a percentage of the reinforcing steel with shape memory polymer.

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.