Performance of polypropylene fiber-reinforced cellular lightweight fly ash geopolymer mortar under wet and dry cycles

This research investigated the effect of wet and dry cycles on the performance of polypropylene fiber-reinforced cellular lightweight fly ash geopolymer (PPF-CLFAG). The fly ash (FA) was used as the primary material. The polypropylene fiber (PPF) contents of 0, 1, and 2% by fly ash weight and the air foaming agent (AF) contents of 0, 1, and 2% by total weight were used. The research analyzed the durability and microstructural properties of the PPF-CLFAG samples under number of wetting-drying cycles (N). The compressive strength, flexural strength, dry density, weight change, physical appearance, and FESEM-EDX of the PPF-CLFAG samples were conducted under various solution types, including H2O, Na2SO4, MgSO4, and HCl. The results showed that AF, PPF, and N affected the durability and microstructural properties of the PPF-CLFAG samples. Compressive strength, flexural strength, dry density, and weight change in Na2SO4-exposed PPF-CLFAG samples increased with N, in contrast to samples exposed to H2O, MgSO4, and HCl solutions, which demonstrated the reduction of compressive strength, flexural strength, dry density, and weight change. Notably, samples with 0%AF and immersed in Na2SO4 solution exhibited maximum compressive strength and flexural strength, particularly at PPF concentrations of 1% and 2%, reaching 38.30 MPa and 8 MPa, respectively. Moreover, the highest dry density of the sample with 0%PPF and 0%AF was at 1887 kg/m3, while the lowest dry density of 914 kg/m3 was observed in samples with 2%PPF and 2%AF. Additionally, samples soaked in MgSO4 exhibited surface discoloration and slight corrosion, while those in HCl displayed a yellow color due to the formation of a yellow FeCl3 solution. Examination through FESEM images revealed voids within the samples caused by AF and induced a transition zone between the PPF and paste, leading to increased porosity. The elements Si, Al, Na, and Ca in all samples subjected to the w-d cycle in various solution types indicated the coexistence of C-S-H and C-A-S-H gels with N-A-S-H gel.