Effect of alkali content and activator modulus on mechanical properties of alkali activated mortars

Alkali activation is a promising method of reducing cement production considerably without further significant investments. Utilization of these materials are of extreme importance when environmental aspects such as CO2 emissions and energy consumptions are considered. In this article, effect of activator modulus and alkali content on fresh behavior and mechanical properties were investigated. 12 M NaOH solution and sodium silicate solution with a modulus of 3 were used. Water-to-binder ratio was selected as 0.5 for all specimens where binder content was calculated as the total of slag content plus activator solids. Slag content was 500 kg/m3 for all mixtures. Mechanical tests were conducted on 40 x 40 x 160 mm prismatic specimens. Results indicate that mechanical properties of alkali activated mixtures are highly dependent on both parameters hence proper optimization of these two parameters becomes compulsory. In this study, it is concluded that alkali content (Na2O/slag) should be selected 9% and whereas activator modulus should be leveled near a value of 1.5. Flexural properties were also highly affected from optimization of these parameters and similar findings are deduced. Early strength evaluations are highly dependent on activator modulus. Workability of the mixture were also diagnosed and it should be noted that flowability of mixture were adversely affected with the increasing activator solids content.