Effect of elevated temperatures on the compressive strength of nano-silica and nano-clay modified concretes using response surface methodology

In this paper, the effect of elevated temperatures of nano-modified concrete mixtures on compressive strength is investigated. Response surface methodology (RSM) was utilized to construct prediction models and perform multi-objective optimization by maximizing the compressive strength of modified concrete with nano-silica (NS) and/or nano-clay (NC) as partial cement substitutions in concrete at various dosages of (1-4 %) and (1-9 %), respectively, and a hybrid inclusion of both NS and NC as cement partial substitutions in concrete subjected to temperatures ranging between 25 degrees C and 800 degrees C for 1 and 2 h. Experimental data from 208 cubic specimens with dimensions of 100 x 100 x 100 mm, which were obtained from the literature were used as the database for the developed predictive models to assess the influence of curing ages and various temperatures on the compressive strength of modified nano-concrete. The proposed models were evaluated and validated for their significance and adequacy, and the contribution of each parameter was examined utilizing ANOVA and other statistical criteria. The best correlations were found between compressive strength and substituting NS and/or NC for cement. The optimum cement replacement levels with nanoparticles and temperature for maxi-mizing the compressive strength of concrete were defined using numerical optimization. The results from the developed models were in good agreement with the experimental data.