Utilization of waste foundry sand and fly ash in the production of steel fibre reinforced concrete

As the main raw materials for concrete preparation, natural sand and cement are in increasing demand. Meanwhile, the large accumulation of waste foundry sand (WFS) and fly ash (FA) seriously pollutes the environment. The research on the application of waste materials in concrete preparation has become a hotspot for scholars. This study attempts to respectively use WFS and FA to substitute natural sand and cement in the preparation of steel fibre reinforced concrete (SFRC). 3-factor, 3-level orthogonal experiment was designed, and the study variables include the WFS substitution rate (20%, 40%, and 60%), FA substitution rate (10%, 20%, and 30%), and SF content (1%, 2%, and 3%). The workability, dry density and mechanical properties of concrete were tested and discussed. Range analysis and variance analysis were used to analyse the effect of various factors on the different properties of concrete. Efficacy coefficient method was used to specifically determine the optimum substitution rate of waste materials for raw materials. Additionally, microanalysis was carried out to investigate the influencing mechanism of waste materials on the properties of concrete. It was observed that the workability of concrete deteriorated with the addition of waste materials, while the change of mechanical properties closely correlated with the content of waste materials. The workability and compressive strength were most significantly affected by the WFS content, while the density, tensile strength, flexural strength and elastic modulus were most significantly affected by the SF content. The mechanical properties of concrete were optimum at 34%, 20% and 2.3% of WFS, FA and SF content respectively. In this case, the compressive strength, split tensile strength, flexural strength and elastic modulus increase by 28.8%, 33.5%, 33.8% and 17.7% respectively compared to the control concrete. Microanalysis proved that moderate amount of WFS and FA could increase the beneficial pores, decrease the harmful pores, and reduce the porosity of concrete, but excessive WFS (60%) and FA (30%) would inhibit the hydration process and enlarge the porosity of concrete. This study demonstrates the feasibility of the application of WFS and FA in SFRC preparation, contributing to overcoming the pollution of waste material accumulation and alleviating the shortage of natural resources.