Performance of autoclaved alkali-activated metakaolin pastes blended with micro-size particles derivative from dehydroxylation of kaolinite

Abstract

In the present paper, alkali-activated metakaolin (AAMK) pastes modified with micro-size particles derivative from dehydroxylation of kaolinite (m-MK) at ratios fluctuated from 2% to 10% with an increment of 2%, by weight, were prepared. The workability and compressive strength, up to 450 days, were measured. After curing for 28 days, various pastes were autoclaved at a temperature of 170 °C and a pressure of 800 kPa for various times up to 10 h. A fixed concentration of liquid sodium silicate dosage of 30%, by weight, measured from the total weight of the powders was used to activate each mixture. The formed and the decomposition phases were monitored by X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and its (DTG), respectively, whilst the microstructures were studied by scanning electron microscopy (SEM). The results revealed a positive effect of autoclaving conditions, up to 10 h, on the compressive strength and microstructures of different pastes. In comparison with the plain AAMK pastes, the incorporation of m-MK particles had a positive effect on the compressive strength before and after autoclaving. On the other hand, the incorporation of m-MK particles decreased the workability.