Optimization approach of granulated blast furnace slag and metakaolin based geopolymer mortars

This paper aims to find the optimum formulation among 24 geopolymer mortars (GMs) based on granulated blast furnace slag (GBFS), metakaolin (MK) and alkaline solution which is characterized by its molar ratio SiO2/Na2O (MR) and its Activator representing the dry extract. (GBFS + MK)/Activator, GBFS/MK, and MR are the variables used to evaluate the GMs performances. Their effect on the rheology, setting time, porosity, mechanical properties and stability to efflorescence was investigated and the results were compared with those of Portland cement mortar (PCM). The outcomes show that GMs and PCM exhibit a Binghamian behavior where the rheological parameters depend on the MK/GBFS ratio and the MR. The relationship between compressive and flexural strengths is independent of the raw materials while it is not the case for the relationship relating dynamic modulus with the compressive strength. The optimal performances are achieved with: GBFS/MK = 1, GBFS + MK/Activator = 3 and MR between 1.6 and 1.8. The optimum GMs have shown better or comparable properties than those of PCM. (C) 2018 Elsevier Ltd. All rights reserved.