The production of high-performance concrete having all-rounded high performance has been promoted for the last few decades. Meanwhile, environmental concerns have quested for minimizing cement consumption to reduce carbon footprint. However, contradictory requirements are often imposed on the mix parameters in order to satisfy all the required performance attributes and environmental limitations. The addition of inert fillers such as limestone fines (LF) is a promising way to overcome these difficulties. In this thesis, the packing density and overall performance of mortar and concrete containing different amounts of LF are investigated. The test results revealed that blending of fine aggregate with LF or with both LF and cement could significantly increase the packing density because the LF and cement particles are much smaller than the aggregate particles and are thus able to fill into the voids between the aggregate particles. However, LF with similar fineness as cement has no filling effect for increasing the packing density when added to cement to a mortar mix in which the powder content is already enough to fill the voids between aggregate particles. Its filling effect is contributed mainly by filling into the paste to increase the paste volume. In fact, the addition of LF to mortar would slightly decrease the packing density, significantly decrease the water film thickness (WFT) and significantly increase the paste film thickness (PFT). The actual effects of LF volume on the packing density, WFT and PFT are dependent on the cement paste volume. In-depth analysis of the test results showed that the apparently complicated effects of the LF volume are caused by the corresponding changes in the WFT and PFT of the mortar. The overall effects of LF are dependent on the net outcome of the decrease in WFT and the increase in PFT due to the addition of LF. The addition of LF would increase the flow spread when the WFT is relatively large as the decrease in WFT has smaller effect than the increase in PFT, increase the cohesiveness when the LF volume is relatively small as the decrease in WFT has greater effect and increase the early strength provided the WFT would not become too small. However, the addition of LF would always decrease the flow rate because the decrease in WFT always has greater effect than the increase in PFT. Finally, the possible use of LF as cement paste replacement to reduce cement paste volume is studied. From the correlation of the ultimate shrinkage strain to the cement paste volume and W/C ratio, and to the concrete strength and cement paste volume, it may be concluded that cement paste replacement by the addition of LF would reduce the shrinkage of concrete by both decreasing the cement paste volume and increasing the concrete strength. Moreover, since the reduction in cement paste volume would allow less cement to be used, this would also lead to the production of concrete more ecological. More research on this possible usage of various inert fillers with different fineness is recommended. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

The stress-strain relationship of concrete in flexure is one of the essential parameters in assessing the flexural strength and ductility of reinforced concrete (RC) structures. An overview of previous research studies revealed that the presence of strain gradient would affect the maximum concrete stress and respective strain developed in flexure. Previously, researchers have conducted experimental studies to investigate and quantify the strain gradient effect on maximum concrete stress and respective strain by developing two strain-gradient-dependent factors k3 and ko for modifying the flexural concrete stress-strain curve. In this study, the author established a new analytical concrete constitutive model to describe the stress-strain behavior of both normal-and high-strength concrete in flexure with the effect of strain gradient considered. Based on this, comprehensive parametric studies have been conducted to investigate the combined effects of strain gradient and concrete strength on flexural strength and ductility design of RC beams and columns with concrete strength up to 100 MP a by employing the strain-gradient-dependent concrete stress-strain curve using non-linear moment-curvature analysis. From the results of the parametric studies, it is evident that both the flexural strength and ductility of RC beams and columns are improved under strain gradient effect. A design value of ultimate concrete strain of 0.0032and anew equivalent rectangular concrete stress block incorporating the combined effects of strain gradient and concrete strength have been proposed and validated by comparing the proposed theoretical strength with the strength of 198 RC beams and 275 RC columns measured experimentally by other researchers. It is apparent from the comparison that the proposed equations can predict more accurately the flexural strength of RC beams and columns than the current RC design codes. Lastly, for practical engineering design purpose, design formulas and charts have been produced for flexural strength and ductility design of RC beams and columns incorporating the combined effects of strain gradient and concrete strength. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

This research project concentrated on determining whether or not a correlation existed between laboratory aggregate tests and observed aggregate field performance. For this purpose, aggregate samples were collected from the majority of the U.S. states as well as several Canadian provinces and subjected to a variety of strength, soundness, and intrinsic particle property tests. Additionally, performance data on the aggregates was obtained by contacting multiple DOT's where aggregates were in use in several categories - hot-mix asphalt, portland cement concrete, base course, and open-graded friction course. Numerical and qualitative analyses were performed to evaluate the success of separating good performers from fair and poor performers using the micro-Deval test alone as well as the micro-Deval test combined with another test. Furthermore, attempts were made to determine if a correlation exists between any two tests.

Not available / text

Self-consolidating concrete (SCC) is an advanced type of concrete that can flow under its own mass without vibration, pass through intricate geometrical configurations, and resist segregation. SCC constituent materials and mixture proportions must be properly selected to achieve these flow properties. The effects of any changes in materials or mixture proportions on hardened concrete performance must be considered in evaluating SCC. A research project was conducted to investigate the role of aggregates in SCC. The objectives of this research were to evaluate the effects of aggregate characteristics and mixture proportions on the workability and hardened properties of SCC, to identify favorable aggregate characteristics for SCC, and to develop guidelines for proportioning SCC with any set of aggregates. The research indicated that although SCC can be proportioned with a wide range of aggregates, the selection of favorable aggregates can significantly enhance the economy and performance of SCC. The effects of aggregate grading; maximum size; shape, angularity, and texture; apparent clay content; and packing density were evaluated. The main effect of aggregates larger than approximately 75 [mu]m was found to be on the minimum required paste volume for achieving SCC workability. It was found that dust-of fracture microfines, defined as mineral material finer than approximately 75 [mu]m produced during the crushing of aggregates, could be an economical choice to comprise part of the paste volume. Based on the results of this research, a mixture proportioning procedure for SCC was developed. The procedure is based on a consistent, rheology-based framework and was designed and written to be accessible and comprehensible for routine use. In the procedure, SCC is represented as a suspension of aggregates in paste. Aggregates are selected on the basis of grading, maximum size, and shape and angularity. The paste volume is set based on the aggregate characteristics in order to achieve workability requirements. The paste composition is established to achieve workability and hardened property requirements. / text

The hydration of cement in concrete is exothermic, which means it gives off heat. In large elements, the heat caused by hydration can dissipate at the surface, but is trapped in the interior, resulting in potentially large thermal gradients. The thermal expansion of concrete is greater at higher temperatures, so if the temperature differential between the surface and the interior becomes too great, the interior will expand more than the exterior. When the thermal stress from this mis-matched expansion exceeds the tensile strength of the material, the concrete will crack. This phenomenon is referred to as thermal cracking. Accurate characterization of the progress of hydration of a concrete mixture is necessary to predict temperature gradients, maximum concrete temperature, thermal stresses, and relevant mechanical properties of concrete that will influence the thermal cracking risk of concrete. Calorimetry is the most direct test method to quantify the heat evolution from a concrete mixture. There is currently no model, based solely on calorimetry, which completely describes the effects of mixture proportions, cement and SCM chemistry, and chemical admixture dosages on the temperature sensitivity and adiabatic temperature rise of concrete. The objective of this study is to develop a comprehensive model to describe these effects. First, the temperature sensitivity of the hydration reaction (described with activation energy, E[subscript a]) is needed to accurately predict the behavior of concrete under a variety of temperature conditions. A multivariate regression model is from isothermal calorimetry testing to describe the effects of water-cementitious materials ratio, cement chemistry, supplementary cementing materials, and chemical admixtures on the E[subscript a] of portland cement pastes. Next, a multivariate regression model is developed from semiadiabatic calorimetry testing that predicts the temperature development of concrete mixtures based on mixture proportions, cement and SCM chemistry, and chemical admixture dosages. The results of the models are validated using data from literature. The final model provides a useful tool to assess the temperature development of concrete mixtures, and thereby reduce the thermal cracking risk of the concrete structure.

Controlling the placement and hydration temperature of concrete is important to concrete durability. Thermal gradients and delayed ettringite formation (DEF) result in cracking when concrete in the plastic state becomes too hot. Cooler placement temperatures slow hydration reaction, increase working time, reduce the maximum temperature in the concrete member, and reduce thermal gradients. Furthermore, cooler concrete achieves better long-term strength and microstructural development. Concrete producers have been using multiple methods of reducing the placement temperature of concrete, such as cooling mixtures with ice or chilled water, shading aggregate piles, placing concrete at night, and using evaporative cooling of aggregate piles. More recently, concrete producers have turned to liquid nitrogen for cooling fresh concrete. The objective of this research was to determine the effects of liquid nitrogen on concrete hydration, microstructural development, and performance. The following concrete mixture properties and methods were investigated: cement type, the effects of selected supplementary cementing materials and chemical admixtures, placement temperature, and the time at which liquid nitrogen dosing occurs (delayed dosing). Concrete performance was tested in terms of slump, setting time, yield, compressive and splitting tensile strength, elastic modulus, rapid chloride permeability, and hardened and fresh air void analysis. Hydration and microstructural development were monitored by isothermal calorimetry, semi-adiabatic calorimetry, x-ray diffractometry, inductively coupled plasma, and environmental scanning electron microscopy. Additional testing was performed on concrete mixing drums to determine the effects of liquid nitrogen on the durability of steel mixing drums. The results indicate that performance, hydration, and microstructural development of fresh concrete are relatively unaffected when cooled with liquid nitrogen to room temperatures. Significant findings show that the slump of liquid nitrogen cooled concrete is similar to hot concrete mixtures and not room temperature mixtures. Additionally, setting time results show that liquid nitrogen dosing of hot concrete can be delayed for up to 1 hour and setting times will still be similar to room temperature mixtures. Based on findings from this research study, liquid nitrogen is recommended as a primary cooling option to reduce the placement temperature of fresh concrete.

The present work is concerned with the development of finite element techniques for nonlinear transient dynamic analysis of reinforced concrete plates and shells. Computational models have been developed and coded, which are applied to various engineering problems under static and dynamic loading conditions. The first part of the thesis deals with some aspects of linear-elastic, geometric and material nonlinear finite element formulations of general thin and thick shell analysis under static or quasistatic loading. A generalized displacement method is proposed to overcome the 'shear locking' problem for the degenerated thick shell element when used in the context of thin shell structures. The basic concept and mathematical formulation of the generalized displacement method are detailed and its application is illustrated by numerical examples. The method is also extended to the geometrically nonlinear analysis of thin shells based on both Updated and Total Lagrangian formulation. An elasto-viscoplastic analysis of anisotropic plates and shells is developed by means of the finite element displacement method. A discrete layered approach is adopted to represent different material properties and gradual plastification through the thickness. Viscoplastic yielding is based on the Huber-Mixes criterion extended by Hill for anisotropic material and special consideration is given to the evaluation of the viscoplastic strain increment for anisotropic situations. The second part of this thesis is concerned with nonlinear dynamic transient analysis of reinforced concrete shell structures. Direct integration methods are reviewed and discussed. In particular, the general single step explicit, implicit and implicit-explicit algorithms with predictor - corrector forms are presented and corresponding stability conditions are deduced by invoking the energy method. The modelling of reinforced concrete behaviour in shell structures under fast loading conditions is considered. Both a strain rate sensitive elasto-viscoplastic model and a strain rate sensitive elasto-plastic model are presented for describing concrete nonlinearities due to multiaxial compressive or tensile yielding under dynamic loads. The models are used in conjuction with a tensile crack monitoring algorithm to trace concrete crack opening and closing. Various reinforced concrete plates and shells are analyzed and reported in detail, with the results obtained being compared with those from other sources.

Not available / text

Not available / text