Properties of concrete incorporating recycled coarse aggregates and recycled plastic fine aggregates

Great efforts are made to utilize waste in the construction industry for many different reasons, including the limited non-renewable sources of concrete constituents and getting rid of the burdens of deploying waste and its environmental impact. This study aims to assess the suitability of using recycled coarse aggregate (RCA) and plastic waste (PW) as fine aggregates to produce a hybrid recycled aggregate concrete (HRAC). Natural coarse aggregates (NCA) were replaced with 40% and 60% by volume of the RCA. High-density polyethylene (HDPE) in the form of granules was used with replacement ratios of 0%, 10%, 20%, 30%, and 40% of sand volume. Silica fume (SF) has also been used to partially replace the cement with 0% and 10% replacement ratios. These three factors resulted in twenty mixes on which slump, compressive strength, ultrasonic pulse velocity (UPV), rebound hammer number, dry density, and microstructural analysis using scanning electron microscopy (SEM) was conducted. The results indicate that good quality concrete with 28 days of compressive strength above the ACI-318 limit of structural concrete (17.5 MPa) is easily achievable. As expected, the compressive strength, UPV, and density decrease with the increase of PW and RCA, and the negative impact of PW content is higher than that of RCA. The inclusion of PW significantly improves workability, especially at higher replacement percentages. For 40% PW content, the maximum reduction in compressive strength is about 29% and 28% for cases of 0% and 10% SF, respectively. The reduction in density was found to be 9% and 7% for 40% PW in the case of 0% and 10% SF content, respectively. The reduction in UPV values was found to be insignificant after the replacement of aggregates with PW and RCA.