Elevated temperature effects on elastic modulus degradation and microstructural evolution of waste foundry sand concrete

Purpose The present investigation aims to examine the impacts of high temperature on the flexural strength and modulus of elasticity properties of concrete specimens produced by substituting waste foundry sand at 25%, 50%, 75% and 100% of the river sand. The modulus of elasticity and flexural strength of samples with 100% waste foundry sand (CFS-4) content decreases as the temperature increases. At 600°C temperature, the specimens with 100% waste foundry sand (CFS-4) shows lowest values of modulus of elasticity and flexural strength. Scanning electron microscopy images of specimens with 100% waste foundry sand (CFS-4) exhibits uniform distribution of pore structures owing to increased porosity due to increase in temperature. At high temperatures, the stress-strain curve changes its shape from that of unheated concrete, resulting in a flatter stress vs. strain curve. The projected outcomes from the suggested mathematical formulas based on experimental investigation confirm lesser variations when compared to literature models. It is recommended that the suggested mathematical formulas can be employed for predictions of modulus of elasticity at sustained elevated temperature. Design/methodology/approach After casting, concrete samples were allowable to cure for 28 days. The samples were removed from the curing tank after 28 days curing and dried for another 2 days in order to prevent explosive spalling during the heating process. The produced specimen is subjected to 100°C, 200°C, 300°C, 400°C, 500°C and 600°C temperatures for duration of two hours. The MOE, flexural strength test, and SEM analyses were carried out after the specimens had cooled to room temperature (RT). Findings The specimens with higher content of WFS exhibits decline in MOE and flexural strength at high temperatures. A flatter stress vs. strain curve progresses as the rise in temperature and there are changes in shape of the stress-strain curve from that of unheated concrete at high temperatures. From the experimental investigations, it is recommended to use the suggested mathematical formulas to assess the MOE of cylindrical samples after subjected to high temperatures. Originality/value The study is carried out to assess the post-thermal residual mechanical behavior of concrete after completely replacing the natural sand with WFS at the intervals of 25% up to 100%. The post-heat effect on mixes indicates that MOE and flexural strength show lower results than referral mixes. It is found that, higher temperatures have a stronger impact on the MOE of concrete samples with higher WFS contents when compared to compressive strengths.