Material characterization and thermal performance of polyethylene fiber-reinforced lightweight engineered geopolymer composites subjected to sulfate attacks

The purpose of this research is to use different amounts of fly ash (FA) and ground granulated blast furnace slag (GGBS) to replace ordinary Portland cement (OPC) in polyethylene (PE) fiber-reinforced lightweight engineered geopolymers (LEGP). The mechanical characteristics and durability of these composites are examined, and the results were compared with lightweight engineered cementitious composites (LECC). Expanded glass aggregates were used to produce lightweight LEGP and LECC composites. The composites were exposed to a 5 % $N{a}_{2}S{O}_4$ solution for up to 180 days. The performance of LEGP and LECC specimens under normal and sulfate environments was assessed using a variety of tests and analyses, including evaluations of relative slump, density, compressive stress-strain behavior, flexural strength, load-deflection response, split tensile strength, ultrasonic pulse velocity, initial surface absorption, mass change, and mercury intrusion porosimetry (MIP). Microstructural and mineralogical analysis of the composite matrix was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) were employed to evaluate the thermal stability of the composites. The results showed that in both normal and sulfate conditions, LEGP specimens with 100 % GGBS showed higher residual compressive, flexural, and split tensile strengths while having minimum initial surface absorption and mass loss as compared with LECC specimens. MIP analysis showed that LEGP mixes with 100 % FA exhibited a more notable increase in pore volume under sulfate exposure leading to reduced performance. LECC specimens subjected to 5 % $N{a}_{2}S{O}_4$ solution showed peaks of quartz, mullite, portlandite, and ettringite at higher intensities with calcite and nepheline minerals at lower intensities, while LEGP samples subjected to 5 % $N{a}_{2}S{O}_4$ solution were characterized by the formation of quartz, mullite, portlandite, calcite, zeolite, gypsum, and ettringite peaks. FTIR and DTG results showed that $C-S-H$ and $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ were transformed into gypsum and mullite after a sulfate attack for 180 days.