Performance of concrete with fly ash and recycled HDPE plastic aggregates after fire exposure

• Main Authors: Koa, Nicole Clarice T., Lao, Angel Lisette S., Lao, Rachele Nicole A., Tan, Jiro Charles Mikail U.
• Format: text
• Language: English
• Published: Animo Repository 2018
• Subjects: Fly ash; Concrete
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/7734
• Institution: De La Salle University

Due to the amount of energy required and emissions produced in the production of its components, concrete can have negative impacts to the environment and society. With the hope of advancing sustainable concrete production, the study sought to explore waste materials, namely HDPE and fly ash, as concrete constituents. The alternative concrete specimens were made by partially replacing sand with HDPE pellets at 5%, 10%, 15% by volume of fine aggregates, and cement with fly ash at 30% and 60-% by weight of binder. To assess the feasibility of the alternative concrete, the study investigated the compressive strength (FC'), post-fire relative residual strength (RRS) and fire resistance rating (FRR). The study focused on the mechanical and fire performance, because given the inevitability of fire, the proposed alternative material should not only be strong enough for structural use but also safe enough to withstand fire. The results of the tests were then used to form response surface model equations to find the optimum amount of HDPE and fly ash substitution. The compressive strength tests were done on 100-mm by 200-mm cylindrical specimens at varying curing periods (7, 24, 28, and 120 days), while the fire performance test were done on 50 mm-cubes cured for 28 days. The cubes were fired on one side until the temperature on the unexposed surface reached 139°C above the initial temperature. This duration is taken as the FRR. The fired cubes were then subjected to compressive strength tests to obtain the RRS. The results show that HDPE slightly increased or did not have a significant effect on the 28th-day compressive strength, whereas fly ash generally decreased the strength. Due to the delayed pozzolonic action, the fly ash mixes still showed an increase in strength after curing beyond 28 days. As with the fire performance, replacement of up to 5% HDPE increased the RRS. Fly ash generally decreased the RRS except for 10% HDPE samples which increased with 30% fly ash. The more the HDPE content, the less fly ash was more beneficial for the RRS. In the other hand, the FRR was at the highest at 60% fly ash. It was found that fly ash improved the FRR of samples with 5% and 10% HDPE. Using response surface method, the optimum percent substitution to maximize the compressive strength and fire performance was found to be 11.46% fly ash and 12.71% HDPE. This proportion is predicted to yield a 28th-day compressive strength of 30.80 MPa, RRS of 73.45% and FRR of 9.96 min.