Impact of fly ash on slag-based engineered geopolymer composites: Multiple-scale investigations

This study investigates the impact of varying fly ash dosages on slag-based engineered geopolymer composites (EGC). The single-fibre pull-out, single-crack tensile, and dog-bone specimen tensile tests were carried out for the multiple-scale investigations. Results indicate that increasing the fly ash dosage from 20 % to 40 % enhanced the tensile strength, compressive strength, flexural strength, and tensile strain capacities by 150 %, 32 %, 34 %, and 319 %, respectively. The maximum bridging stress increased from 1.5 MPa to 3.72 MPa as the fly ash content raised from 20 % to 40 %, resulting in a 12.6 % tensile strain capacity in EGC. However, the mechanical performance of EGC started to deteriorate when using 50 % of fly ash. This study revealed that different geopolymer products exhibited varying interfacial properties with polyethylene fibre. According to the SEM-EDS and XRD results, low-calcium phase in geopolymer matrix provide a larger real contact area compared to high-calcium phases. Additionally, chemical bonding existed as the EGC transformed from being slag-based to fly ash-based. The impact of fly ash on slag-based EGC is significant, as it changes the interfacial properties of fibre and matrix by changing the chemical and physical properties of matrix.