Effect of elevated temperature on polypropylene fiber reinforced alkali-activated high calcium fly ash paste

Abstract This paper examined the mechanism of polypropylene fiber (PP) reinforced alkali-activated high calcium fly ash paste (AHFP) exposed to high temperature. The PP was added into the AHFP mixture at the dosages of 0, 0.5, 1.0 and 1.5 % wt of fly ash. The 10 M (molar) NaOH, Na2SiO3/NaOH ratio of 2.0, and liquid/binder ratio of 0.60 were used. Compressive and flexural strengths, and microstructure of AHFP after exposed to 200, 400, 600 and 800 °C were studied. The results showed that the use of PP at 0.5 % wt of fly ash resulted in the best improvement in compressive strength of paste. For flexural strength, a slightly higher PP content at 1.0 % wt of fly ash was the optimum. For exposure to high temperature, the residual flexural strength was nearly one third at 400 °C and reduced to 8-12 % for temperatures beyond this. With the increasing exposed temperature, the air void and large capillary pore increased, but the medium capillary pore and gel pore reduced. The results indicated that the mechanisms of weight and strength losses of AHFP were due to thermo-hygral damage around 220-320 C, followed by thermo-mechanical damage at 430-660 C and thermo-chemical damage at 700 C onwards.