Impact of Alkali Concentration and Metakaolin Content on Accelerated Ageing of Egyptian Slag

摘要

The present work aims to study the coupled effect of alkali concentration and metakaolin (MK) on the resistivity of ground granulated blast-furnace slag (GGBFS) to strength regression during ageing. GGBFS was activated by 6 and 10 wt., % containing mixture of sodium hydroxide (SH) and liquid sodium silicate (LSS) at a ratio of 1:1, respectively (namely GGBFS6 and GGBFS10). On the other hand, GGBFS10 was replaced by 10, 20, 30, 40 and 50 wt., % of MK, respectively. All hardened specimens were cured in 100% relative humidity (RH) at 37 ± 2°C for 28 days (zero time) then, aged at 95°C for 56 days. Experimental results showed that, the pH value of alkali activated samples (AAS) decreased as the amount of MK increased. Also, the pH of AAS derived from GGBFS10 was higher than that of GGBFS6. The strength regression resistivity (SRR) during accelerated ageing enhanced with the decrease of alkali concentration. The compressive strength for different investigated mixes was evaluated. Also, some selected hydration products were analyzed using infrared spectroscopy (FTIR), thermo-gravimetric analysis (TG/DTG) and X- ray diffraction (XRD) techniques to determine the mineralogical phase transition. The results of mechanical properties are in a good agreement with those of FTIR, TG/DTG and XRD techniques and confirm that the SRR during ageing increases with MK content.