Effect of hybrid fibers and high temperatures on the properties of geopolymer composites based on slag, metakaolin, and natural zeolite

This study examined the impact of incorporating hybrid fibers of polypropylene (PPF) and basalt fibers (BF) into geopolymer composites (GCs) at rates from 10 to 20 kg/m3, in addition to the effect of high temperatures of 250 degrees C, 450 degrees C, and 650 degrees C for two hours. The ternary mixture of granulated blast furnace slag (GBFS)70 %, metakoline (MK) 15 %, and natural zeolite (NZ)15 % was alkali activated by alkaline solutions of sodium silicate (Na2SiO3) and solid sodium hydroxide (NaOH). Water sorptivity tests were performed to evaluate the properties of GCs, hardened density, compressive strength, flexural strength, apparent porosity, and water absorption, in addition to the effect of high temperatures on compressive strength, mass loss, and microstructure. The mechanical and transport properties slightly improved when adding 10 and 20 kg/m3 of BF. On the other hand, the addition of PPF contributed to a decline in GC properties. Including BF mitigated the effect of high temperatures on both compressive strength and mass loss of GCs. The GC mixture containing 10 kg/m3 of BF achieved the highest compressive strength of 67 MPa and flexural strength of 7.52 MPa. The mixtures of GCs containing 10 BF kg/m3 also exhibited enhanced resistance to the effects of elevated temperatures.