Effects of elevated temperature on the tensile properties of NS-modified self-consolidating engineered cementitious composites and property optimization using response surface methodology (RSM)

This paper discusses the influence of elevated temperature on the tensile properties (tensile strength, tensile strain, and energy absorption) and microstructure of nano-silica-modified self-consolidating engineered cementitious composites (NS-modified SC-ECC) mixtures. Response surface methodology (RSM) was utilized to develop a design matrix and predictive models and to perform multi-objective optimization for a matrix of mixtures prepared with polyvinyl alcohol (PVA) fiber at 0.5, 1, 1.5, and 2 volume fractions and NS at 0, 1, 2, 3, and 4 of the weight of cementitious materials at temperatures of 23 °C, 100 °C, 200 °C, 300 °C, and 400 °C. To investigate the influence of elevated temperature on the certain characteristics of NS-modified SC-ECC mixtures, residual compressive strength, tensile properties, and microstructure properties were assessed at elevated temperatures of up to 400 °C for 1 h. Microstructure was examined using scanning electron microscopy before and after the mixtures had been exposed to elevated temperatures; accessible porosity and pore size distribution with cumulative pore volume were measured using mercury intrusion porosity (MIP) to validate the behaviors of the tensile properties and compressive strength of NS-modified SC-ECC mixtures. The results show that the tensile properties of the NS-modified SC-ECC mixtures improve due to pozzolanic reactivity of NS by utilizing the calcium hydroxide (CH) released from cement hydration to produce more calcium-silicate-hydrate (C-S-H) gel, which refines the fiber-matrix and aggregates-matrix interfacial transition zones (ITZ). The pozzolanic reactivity is further facilitated by temperature curing to produce more C-S-H gel, improving the fiber-matrix interactions at elevated temperatures of up to 200 °C. The PVA fiber improves the elevated temperature behavior of the mixtures and prevents explosive spalling behavior even after the incorporation of 2 NS with a PVA fiber volume of up to 2. The responses considered in the RSM were tensile strength, tensile strain, and energy absorption. The established models showed high degrees of correlation between the responses and independent variables. Optimized tensile properties could be achieved at 2 PVA fiber volume, 1.3 NS, and a temperature of 125.7 °C. The measured absolute deviations (error) between the experimental data and the theoretical (predicted) models� results for tensile strength, tensile strain, and energy absorption were 2.83, 4.4, and 1.68, respectively. © 2019 Elsevier Ltd