Effects of hybrid fibers on the development of high volume fly ash cement composite

High volume fly ash (HVFA) is used as cement substitute in many cementitious materials. In recent years, hybrid fibers such as steel and polypropylene have been added to improve the mechanical characteristics. The usage of three fibers combinations is relatively a new concept in HVFA concrete. In this paper, silane coated basalt fiber has been combined with steel and polypropylene due its availability and low costs. Varied hybrid fiber combinations (both two types and three types) were tested on cement mortar specimens to identify the optimal fiber percentages. Based on the experimental results, equations to predict the compressive and flexural strength were developed. Optimal percentages identified from the experimental data were then used to test concrete specimens. It was found that the compressive strengths of three types hybrid fiber concrete showed appreciable increase by 5.44% and the splitting tensile strength increase was 6.77% in comparison with two type hybrid. Furthermore, the long-term durability issue of the selected basalt fiber was examined using the Scanning Electron Microscopy (SEM) and Computed Tomography (CT) X-ray scan. These two techniques confirmed the reduction in porosity and hence the durability of concrete, suggesting the benefit of the added silane coated basalt fiber. (C) 2019 Elsevier Ltd. All rights reserved.