Influence of different admixtures on the mechanical and durability properties of one-part alkali-activated mortars

One-part AAM is low carbon binder having low energy requirements coupled with excellent working properties and strength characteristics. This study examined the influence of silica fume, magnesia, cement clinker, and metakaolin on the shot term and long term hardened properties and durability performance of one-part alkali-activated (AAM) mortars. The durability of AAM mortars was investigated by exposing the samples to sodium sulfate and sulfuric acid solution for 270 days. Fly ash and ground granulated blast furnace slag were used as main precursors in control mortar and were replaced by silica fume, magnesia, cement clinker, and metakaolin admixtures to evaluate their influence. Admixtures were used at replacement level of 1.5%, 3% and 4.5%. Results revealed a significant improvement in long term compressive strength and water absorption performance of one-part AAM with the increase in admixture content. In addition, the AAM mortar incorporation various admixtures. Mortar specimens did not show any visual signs of discoloration, change in mass, or length during the immersion in sulfate solution. The residual strength of AAM mortars exposed to sulfate solution was in the range of 83–99%. However, mortars samples exposed to sulfuric acid solution underwent cracking and deterioration with the visible leaching out of binder paste accompanied with significant strength loss. AAM mortars containing 4.5% metakaolin showed the highest residual strength against sulfate and acid attack. SEM analysis shows that alkali activated mortars containing admixtures showed no microcracks and micropores and supported the results of mechanical testing.