Response Surface Methodology for Compressive Strength of Nano-Modified Concrete at High Temperatures

This study utilizes response surface methodology (RSM) to examine the effectiveness of several nanomaterials on the residual compressive strength (CS) of concrete exposed to high temperature. Three nanoparticles were used as partial cement replacement by weight at replacement ratios up to 5%: nano-granodiorite (NG), nano-magnetite (NM), and nano-lead oxide (NL). The specimens were exposed to temperatures of 400 °C, 600 °C, and 800 °C, and the residual compressive strength was determined. The experimental results exhibited that all nanoparticles in concrete specimens reduced the loss of strength at high temperature. The control specimen lost 48.39% of its compressive strength at 800 °C. A dose of 4% NG and NM resulted in an increase in residual strength of 37.87% and 22.06%, respectively, while 3% NL specimens resulted in 11.4% improvement. A regression model for predicting concrete CS was developed using RSM. The model was successful in capturing the high correlation between the input variables (temperature, type of nanomaterial, and nanoparticle dose) and the output of CS. A good agreement between model predictions and the experimental data was obtained. The results of CS optimization showed that 5% NG at 126 °C resulted in the highest compressive strength of 61.80 MPa, confirming its superiority over NM and NL for the formulation of concrete under thermal conditions. The results reveal that the utilized nanoparticles, especially NG, have great potential to be used as cementitious materials to improve the high-temperature resilience of concrete.