Analysis of stress-strain behavior in engineered geopolymer composites reinforced with hybrid PE-PP fibers: A focus on cracking characteristics

Engineering geopolymer composites (EGC) are a promising low-carbon and highly durable composite material. However, the high cost of materials hinders its engineering application. To address this challenge, this study investigates the use of cost-effective PP fibers to partially or completely replace PE fibers, and develops an economical hybrid PE/PP-EGC. Axial tensile experiments were conducted on PE/PP-EGC with different PP fiber replacement ratios (0%, 25%, 50%, 75%, and 100%) to investigate the effect of PP fiber replacement ratios on the tensile behaviour of PE/PP-EGC. Economic feasibility of PE/PP-EGC is also evaluated. The results show that when the replacement ratio is below 75%, PE/PP-EGC still exhibits pseudo-strain hardening and multiple cracking characteristics. As the replacement ratio increases, the crack control ability of EGC decreases, resulting in an increase in the average crack width and a decrease in the crack density. PE/PP-EGC with a replacement ratio of 50% has a highest ultimate tensile strain (9.71%), which is 68% higher than that of PE-EGC, while the tensile strength is only reduced by 15%. Furthermore, PE/PP-EGC with a replacement ratio of 50% exhibits the highest tensile strength, ultimate tensile strain, and tensile strain energy per unit cost. Based on the experimental data and theoretical derivation, this study proposes a semi-empirical bilinear tensile constitutive model of PE/PP-EGC and verifies its reliability. It is recommended to use a 50% replacement ratio of PP fibers for PE/PP-EGC, which offers optimal tensile mechanical performance, along with outstanding comprehensive economical performance. These research findings provide important insights into the design and application of low-cost and high-performance engineering geopolymer composites, and could have significant implications for the development of sustainable and durable infrastructure.