Effect of mineral admixtures on properties of recycled aggregate concrete at high temperature

This study presented experimental results of mechanical properties of RAC containing mineral admixtures at 500 °C. Four different mineral admixtures (fly ash (FA), waste paper sludge ash (PSA), silica fume (SF), metakaolin (MK)) were used in RAC containing 100% coarse RCA through the addition or replacement method. The results indicated that mineral admixtures significantly enhanced the resistance of RAC to the high temperature. The addition method increased the resistance of RAC to the high temperature better than the replacement method. FA improved the residual compressive strength of heated RAC the most followed by MK, PSA, cement, and SF although SF, MK, and PSA concrete showed the higher improvement of compressive strength than others at 20 °C. The addition of 5% and 10% FA in RAC increased 38.45% and 35.23% the residual compressive strength of heated RAC, respectively. The mineral admixtures had an insignificant effect on the UPV values and density of RAC. The addition of mineral admixtures in RAC substantially improved the slope of ascending branch of stress-strain curves of heated RAC. Moreover, the incorporation of mineral admixtures in RAC contributed to an increase in the elastic modulus, toughness, and critical strain of RAC at the elevated temperature. The study also proposed the equations to predict the residual compressive strength and elastic modulus of heated RAC, which can provide references for practical application of RAC.