Date of Graduation
Statler College of Engineering and Mineral Resources
Civil and Environmental Engineering
Julio F Davalos
The inclusions of Supplementary Cementitious Materials (SCM) from industrial by products, such as slag, fly ash and silica fume in normal concrete derive several benefits. The use of SCM as partial replacement of portland cement divert these SCM from landfills, reduces CO2 emissions, and produces highly durable concrete leading to development of sustainable and green construction materials. One of the primary aspects of durability is to correctly estimate and predict the shrinkage. Since inclusions of SCM modify the volume, composition, and microstructure of the calcium silicate hydrate (C-S-H) of normal concrete, there are limitations on available prediction equations for shrinkage to concrete containing SCM. Some researchers had used the microstructural properties of the normal cementitious pastes to estimate the shrinkage using multiscale model without considering the complexity of SCM interaction. Other studies that considered the effects of SCM at C-S-H level provided only qualitative estimation of the prediction of shrinkage. Therefore, there is a need to predict the shrinkage of concrete containing fly ash, slag, and silica fume at different percentages using microscale characterizations and subsequent semi-quantitative modeling.;In this study, a new approach to characterize hardened pastes of pure cement as well as those containing cement with SCM was adopted using high resolution scanning electron microscopy (SEM) and energy dispersive x-ray spectra (EDS). The volume stoichiometry of the hydration reactions were used to estimate the quantities of the primary and secondary C-S-H and the calcium hydroxide produced by these reactions. The 3D plots of Si/Ca, Al/Ca and S/Ca atom ratios given by the microanalyses were compared with the estimated C-S-H quantities to successfully determine the Ca/Si ratio of nineteen different cementitious systems at four different ages using a constrained nonlinear least squares optimization formulation by General Algebraic Modeling Software (GAMS). The mixes contained 100% cement with subsequent replacement by 35% slag, 45% slag, 25% fly ash, 35% fly ash, 10% silica fume individually and a few combinations of the SCMs at w/cm ratios of 0.3 and 0.4 for each case. The estimated mass fraction of calcium hydroxide from the above method agreed well with the calcium hydroxide content determined using thermogravimetric analyses (TGA). The effect of the w/cm ratio and the different SCM content on the rate of hydration of the different mixes were evident from the curves obtained using the results from the isothermal calorimeter. The shrinkage of the cement paste was determined in terms of its volume deformation, as a function of its pore volume and elastic modulus. The results were verified using the capillary shrinkage test.;The concept of composite modeling was used to evaluate the shrinkage of the mortar specimens. The properties of the interfacial transition zone between the paste and the fine aggregate were computed using the Hashin-Shkritman bounds for two-phase composite material extended to three phase material. The results of the mortar shrinkage were validated by experimental data. The concept of composite modeling was further extended to predict the shrinkage of concrete in general. Shrinkage experiments were carried out on laboratory-scale concrete samples and the results were used for validation of the equation.;Finally, the results of the experiments and those predictions equations proposed from the composite model were compared favorably with the available shrinkage models: ACI, B3, CEB MC 90-99, and GL 2000.
Kar, Arkamitra, "Prediction of Shrinkage of Concrete Containing Supplementary Cementitious Materials Using Microscale Characterizations and Composite Modeling" (2010). Graduate Theses, Dissertations, and Problem Reports. 4614.