Mix design optimization and early strength prediction of unary and binary geopolymer from multiple waste streams

Highlights: • Multiple waste streams were evaluated as geopolymer source materials by isothermal calorimetry. • The geopolymer mixtures derived from various wastes were optimized. • The early strength of unary and binary geopolymers was correlated to the cumulative heat. Geopolymer has received increasing amounts of attention recently due to its potential utilization of industrial and urban wastes. However, the variability of source materials and the complexity of mixture design hinder geopolymer applications derived from various waste streams. There is a need for a practical and quick scanning tool for material evaluation and mixture design optimization. Six types of industrial and urban wastes, two types of reagents, and two curing temperatures were employed in this study to systematically evaluate the feasibility of using isothermal calorimetry to optimize the geopolymer mixture design and predict the three-day strength. Test results show that isothermal calorimetry has the potential to quantify the compositional differences between source materials, identify the different kinetics of geopolymers, and determine the mechanical properties of final products. For the source materials with similar microstructure and fineness, fairly strong correlations between heat and strength could be found with R² = 0.91 for the NaOH solution and R² = 0.90 for the composite solution.