Date of Graduation
Statler College of Engineering and Mineral Resources
Civil and Environmental Engineering
Udaya B. Halabe
The manufacturing of portland cement (PC), the main binder of concrete, generates large amount of CO2 (a greenhouse gas), cement kiln dust (solid waste), and consumes significant amount of heat energy. Alkali-activated binder (AAB) is increasingly being considered as an environmentally friendly or green alternative to PC. The AAB is produced by alkali activation of aluminosilicate compounds as precursors with or without calcium ions in them in the temperature range of 60° C to 90° C. Since most of the precursors are waste or by-products, the AAB is regarded as sustainable and green construction material with great potential for its use in civil infrastructures. Previous researches on AAB concretes primarily focused on development of materials using limited number of aluminosilicates or calcium-based compounds, and corresponding qualitative evaluations of their microstructural properties and strengths. However, no systematic studies have been conducted on characterizing a wide range of concretes with AAB comprising various proportions of fly ash and slag cured at relatively lower temperature, followed by correlating their properties from micro to specimen level. This research conducts an extensive study to develop and evaluate 30 different AAB mixtures containing fly ash and/or slag activated by sodium hydroxide and sodium silicate and correlates their properties from micro to specimen level using volume stoichiometry and optimizations. The test results showed that Ms modulus (precursor-activator ratio) of 1.4 provided the best compressive strengths when cured for 24 hours at temperatures of 20°C, 40°C and 60°C. The compressive strength of AAB concrete was in the range of 20.9 to 85.0 MPa (3030 to 12,330 psi). Full replacement of fly ash by slag improved the strength by 126% on an average. Investigations of the AAB microstructure through XRD, FTIR, SEM/EDS, and isothermal calorimetry showed sodium aluminosilicate hydrate gel to be the primary strength contributing phase. Reaction rates increased with the slag content due to formation of additional calcium silicate hydrate (CSH) in the AAB paste matrix. Evaluation of specimen level properties such as compressive strength, splitting tensile strength, flexural strength, dynamic modulus of elasticity, and their correlations confirmed these findings. The results also show that the ultrasonic pulse velocity technique can be effectively used to estimate dynamic modulus of elasticity, compressive strength, and stress level of concrete with AAB for wide range of mixes, curing temperature, and ages. Finally, based on a detailed stoichiometric approach and optimization, the present study proposed a nonlinear regression model to correlate the microstructural characteristics with specimen level properties to predict compressive strength as a function of the ultrasonic pulse velocity and the volume fractions of sodium aluminosilicate gel ( vf,AAB) and calcium silicate hydrate (vf,CSH(S) ). Out of 18 possible model forms, the model with the least mean square error (0.053) was selected as the final prediction model that closely agreed with the experimental data with R2 value of 0.89. The findings of this study can be highly beneficial for promoting the use of AAB in concrete structures.
Kar, Arkamitra, "Characterizations of concretes with alkali-activated binder and correlating their properties from micro- to specimen level" (2013). Graduate Theses, Dissertations, and Problem Reports. 165.