Mechanical and impact behavior of lightweight geopolymer concrete produced by pumice and waste rubber

The study examined the impact of incorporating pumice and rubber obtained from waste tires as aggregate in specific ratios on geopolymer concrete (GPC). For this aim, various combinations and replacement percentages of pumice and waste tire rubber (WTR) were tested in GPC. Pumice was replaced with coarse aggregate in varying proportions of 0%, 5%, 10%, and 15% and WTR was added into mixture with same proportions. A total of 144 GPC specimens were cast and tested. Tests were performed to measure the compressive strength (CS), splitting tensile strength (STS), flexural strength (FS) and dynamic drop-weight tests. Evaluations of the setting time and workability were also conducted. When natural coarse aggregate was substituted with pumice in concrete, the strength of the resulting mixtures fell. The second research varied the percentage of WTR in the concrete mixture from 0%, 5%, 10%, and 15% while keeping the pumice percentage stable. The study showed that when the pumice ratio was set as constant, there was a steady loss of strength as the percentage of WTR increased. The experimental results demonstrated that partial replacement of coarse aggregate with pumice (up to 15%) led to a progressive reduction in both CS (up to 18.17%) and STS (up to 37.13%) of GPC. This decline in strength became more pronounced with the concomitant utilization of WTR. The findings demonstrated that as the WTR content elevated from 0 to 15%, there was a consistent decline in FS across all levels of pumice replacement, with reductions ranging approximately between 20 and 26%. Additionally, the study created an empirical formula related to STS and CS and compared with the formulas previously developed by various researchers. Scanning electron microscopy (SEM), Energy dispersive x-ray (EDX), and thermal gravimetric analysis (TGA) are also conducted. According to the data gathered from the impact tests, adding pumice to concrete has a negative impact on its impact behavior; on the other hand, adding 10% WTR has a favorable impact.