Abstract
High drying shrinkage is considered as one of the main drawbacks which hinder the mass production of alkali activated slag (AAS). The formation of expansive phases was found to be the dominant factor for drying shrinkage reduction in sodium silicate-activated system. This work aims at studying single and synergistic effects of the prepared nano-magnesia (NM) and -alumina (NA) on compressive strength and drying shrinkage of AAS. A preliminary study revealed that the NM has a positive impact on the early age's compressive strength of AAS; meanwhile NA had an opposite effect. Complementary, the drying shrinkage of AAS-NM significantly decreases with the increase of NM-content. Comparing with reference sample, the hybrid inclusion of 1 wt% NM and 1 wt% NA resulted in a significant drying shrinkage reduction and considerable compressive strength increment. The main reason behind this effect is the synergistic formation of calcium silicate hydrate and calcium aluminosilicate hydrate in parallel with expansive hydrotalcite and stratlingite phases as they have a potential effect on the performance of AAS including the retardation of water evaporation, reduction of pore volume, and drying shrinkage. This makes AAS-NM-NA composite can be beneficially used as a binder in the production of structural concrete with high durability. (C) 2019 Elsevier Ltd. All rights reserved.