Impact of Ca+ content and curing condition on durability performance of metakaolin-based geopolymer mortars

Abstract

To overcome massive pollution and energy consumption resulting from cement production in addition to concrete’s durability problems, geopolymer concretes (GPC) and mortars (GPM) are recently gaining increasing interest. GPCs are manufactured based on different ingredients such as Fly Ash, GGBS, and other Alumina-Silicate rich materials and polymerized by using alkali activator. However, based on the major polymeric constituent material and curing condition, the properties of GPC are determined. In Egypt, metakaolin (MK) is available in several locations, which after calcination exhibits satisfactory pozzolanic activity. MK is a good replacement of cements in concrete and GPC as it consumes less fuel and produces much lower pollutants. In this research, the durability of MK mixes, that can be utilized in normal construction locations are investigated. Metakaolin based geopolymer mortars (MK-GPM) with up to 60% OPC are made to investigate the effect of OPC inclusion on durability related characteristics. The influence of curing conditions at ambient temperature (23 ± 2 °C) as well as at 60 °C heat curing is also investigated. Water transport properties are evaluated. Durability related characteristics in terms of change in weight and compressive strength with time after exposure for 10 weeks to chemical solution (10% MgSO4, H2SO4 (pH=3) and 10% NaCl). Furthermore, microstructure properties are investigated through X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) with energy dispersive X-ray spectroscopy (EDS) to identify the phase and chemical composition. The results reveal that, heat curing of MK-GPM reduces its sorptivity by 9 ± 2% and water absorption by 13 ± 3%. On the other hand, the inclusion of OPC in MK-GPM (by more than 5%) increases water absorption and sorptivity and consequently reduces durability. Although, MK-GPM shows better durability when exposed to aggressive environmental attacks, incorporating cement up to 20% demonstrates better durability performance than OPC mortar. The study of the microstructure of tested mixes explains and confirms the experimental results.