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 H 2 O, Na 2 SO 4 , MgSO 4 , 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 Na 2 SO 4 -exposed PPFCLFAG samples increased with N, in contrast to samples exposed to H 2 O, MgSO 4 , 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 Na 2 SO 4 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/m 3 , while the lowest dry density of 914 kg/m 3 was observed in samples with 2%PPF and 2%AF. Additionally, samples soaked in MgSO 4 exhibited surface discoloration and slight corrosion, while those in HCl displayed a yellow color due to the formation of a yellow FeCl 3 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.