Post-heating air curing and compressive strength recovery of concrete incorporating electric arc furnace slag and ceramic waste: An experimental and predictive study

The reduction of concrete compressive strength after fire exposure is one of the critical challenges in structural engineering. Evaluating the impact of air curing on the recovery of the mechanical characteristics of heat-damaged concrete has a crucial impact on the design and strengthening strategies. The use of industrial waste materials such as electric arc furnace slag (EAFS) and ceramic waste (CW) also contributes to sustainability and reduces the environmental effects affiliated with cement production. In this study, the impact of post-heating air curing on the recovery of the compressive strength of concrete containing CW and EAFS was investigated. For this purpose, nine concrete mixtures were prepared with different volumetric replacement levels of CW (0, 10, and 20%) and EAFS (0, 50, and 100%), used as replacements for natural coarse and fine aggregates, respectively. The concrete specimens were exposed to ambient temperature as well as to 300 °C and 600 °C. After being removed from the furnace, they were re-cured in ambient air for 365 days under an average relative humidity of 80%. The samples were exposed to ambient temperature, 300, and 600 °C, and after heating, specimens were re-cured for 365 days in air under an average relative humidity of 80%. Subsequently, the specimens were tested in compression, and the results were compared with those of unheated specimens. The findings showed that post-heating air curing can lead to a significant recovery of the compressive strength of concrete; the extent of this recovery depends on the mixture composition, heating temperature, and the curing regime and duration. In the mixture incorporating 20% ceramic waste and 50% electric arc furnace slag exposed to 300 °C, the recovered compressive strength reached about 99% of the original pre-heating compressive strength, indicating an almost complete restoration of compressive strength. The results of the other mixtures also demonstrated that concretes containing CW and EAFS exhibit a superior ability to regain compressive strength after heating compared with conventional concrete. Moreover, under non-heated conditions, after 365 days of air curing, specimens containing 10% CW and 50% EAFS, as well as those with 20% CW and 50% EAFS, showed a considerable improvement in compressive strength, whereas the reference mix (without CW and EAFS) exhibited no improvement. This confirms the beneficial role of combined CW and EAFS in enhancing the long-term mechanical performance of the investigated concrete mixtures under the tested experimental conditions. Moreover, a prediction model for the compressive strength of concretes containing CW and EAFS after re-curing was developed employing an artificial neural network (ANN) algorithm, and subsequently, a high-accuracy nonlinear regression equation was proposed to make the predictions practically accessible. In addition, response surface methodology (RSM) was employed to provide an optimal set of input parameters to enhance the compressive strength of concrete after curing. • Strength recovery in EAFS/CW concrete after post-heating curing was investigated. • 365‑day post‑heating air curing restored strength, varying by mix and temperature. • Mix with 20% CW and 50% EAFS at 300 °C regained 99% of its pre-heating strength. • CW–EAFS concrete showed better post-heating strength recovery than normal concrete. • 10–20% CW and 50% EAFS mixes showed strength enhancement after 365‑day re‑curing.