DURABILITY AND MECHANICAL PERFORMANCE OF GROUND GRANULATED BLAST FURNACE SLAG BASED GEOPOLYMER MORTARS INCORPORATING VARIOUS EARTH MATERIALS

Abstract

The present experimental research aimed to examine the influence of various earth precursors partially replaced with ground granulated blast furnace slag (GGBFS) at different replacement levels of 0 – 25% with 5% increment on engineering properties of geopolymer mortar (GPM). The experimental program contains mechanical and durability testing as well as microstructural analyses. The fresh properties were measured via slump flow and fresh density. The hardened properties were investigated in terms of compressive and flexural strengths, dry density, ultrasonic pulse velocity (UPV), water absorption and sorptivity tests at various ages of 28, 56 and 90 days. Moreover, free shrinkage behaviour was evaluated over 90 days of drying. In order to observe resistance to physical deterioration, the abrasion test was applied. SEM, XRD and FTIR analyses at 90 days age were applied to monitor microstructural properties. Additionally, the influence of aggressive regime (sulfuric acid and magnesium sulfate) on the compressive and flexural strengths, UPV, weight loss and SEM analysis were performed for one and two months of exposure. For this purpose, the precursors obtained from aluminosilicate sources, including metakaolin (MK), pumice powder (P), waste ceramic powder (C), and bentonite (B), were used for the synthesis of geopolymer mortars. In addition, all results of the mixtures were compared to the control mixture produced of 100% GGBFS as precursor. All mixes had constant solid binder and alkaline activator with quantities of 550 and 275 kg/m3 , respectively. The proportion of Na2SiO3 /NaOH was 2.5, and the molarity of NaOH was 12 M. Totally, 21 various mixtures of 4 different series were designed. Depending on the outcomes of the experimental program, it was found that all utilized earth materials positively influenced all properties at various replacement ratios. The optimal results were obtained at a replacement level of 10% for all precursors at all curing ages, except for bentonite, which was attained at a replacement level of 5%. The pumice powder had the best influence rather than other precursors on all test results at a 25% replacement level. The resistance to chemical attack was enhanced by the addition of any precursors in GPM mixes up to optimum ratio compared to the control mix. Hence, they proved to have a positive influence on the improvement of performance. The statistical evaluation by using the twoway variance analysis (ANOVA) technique revealed that all variables had a remarkable effect on such properties of the geopolymer mortars.