Engineering properties of natural pozzolan/slag based alkali-activated concrete

The current study aims to assess engineering properties of alkali-activated concretes made with hybrid aluminosilicate precursors having different proportions of natural pozzolan as a low calcium precursor and blast furnace slag as a high calcium precursor which activated with different concentrations and combinations of sodium hydroxide and sodium silicate. The studied parameters included aluminosilicate precursor combination (natural pozzolan/slag proportions of 70/30, 50/50 and 30/70), sodium hydroxide concentration (1, 1.75 and 2.5 M), and activator combination (sodium silicate/sodium hydroxide proportions of 20/80, 25/75 and 30/70). The resulting concrete mixtures were tested for slump, setting time, unit weight, compressive strength, tensile strength, elastic modulus, drying shrinkage, absorption, and chloride penetration. The performance of developed alkali-activated concretes was also compared with that of a reference portland cement concrete. The findings of this study revealed that alkali-activated concretes can be designed to perform similar or superior to portland cement concrete. In view of overall performance, an equal proportion of natural pozzolan and slag (50/50) and a 30/70 combination of sodium silicate and sodium hydroxide proved to be the optimum precursor and activator combinations, respectively. The optimum sodium hydroxide concentration was dependent on the precursor and activator combinations as well as the expected fresh, strength, dimensional stability and transport properties. (C) 2019 Elsevier Ltd. All rights reserved.