Investigation on mechanical properties of steel fiber reinforced reactive powder concrete containing nano-SiO2: An experimental and analytical study

Very limited attention has been directed to the application of nano-SiO2 (NS) in steel fiber reinforced reactive powder concrete (SFRRPC), and most of the past studies have examined the effects of up to three factors on the mechanical properties of reactive powder concretes. But, this study evaluated the effects of seven factors on the properties by the adoption of the Taguchi method. To fulfil such a requirement, 171 cubic and prismatic samples were prepared and tested following compression strength, splitting tensile strength, and flexural strength tests. Then, Taguchi's experimental design methodology was used to design the experiments and obtain the optimal mechanical strengths of SFRRPC. The laboratory results were examined by Taguchi and analysis of variance (ANOVA) methods. The optimal levels of mix proportions were obtained for maximization of mechanical strengths of SFRRPC. Based on the verification results, the optimum compressive, splitting tensile, and flexural strengths of SFRRPC were obtained by 155.3 MPa, 8.3 MPa, and 53.9 MPa, respectively. The results suggested that cementitious materials, including cement and micro-silica, were the most influential factors on the mechanical properties of SFRRPC. Furthermore, SEM test results showed that NS particles could enhance the microstructure of SFRRPC by means of filling the pores and producing more C-S-H gels, which led to improving the mechanical properties of SFRRPC. According to XRD analysis, the introduction of NS resulted in a high degree of hydration process of cementitious materials in which the CH content was reduced.