Properties of Self-Compacting Concrete Incorporating Rice Husk Ash and Waste Foundry Sand

Abstract

The widely available rice husk (RH) is burned to produce rice husk ash (RHA), an agricultural by-product that may be used in place of cement which will limit environmental hazards. Worldwide, the casting industry produces more than 60 million metric tonnes of Waste Foundry Sand (WFS) each year, causing environmental issues. Disposal of WFS generated from the casting industry poses serious environmental problems. On the other hand, continuous extraction of natural resources is depleting the environment at a rapid pace increasing the cost of production due to an insufficiency of natural resources. These issues may be resolved with the use of waste materials in concrete. The present study has been carried out to explore the use of RHA and WFS as partial replacement of cement and fine aggregates in SCC. In this research study, RHA up to 30% by weight is used as a partial replacement for cement as one of the ingredients in self-compacting concrete (SCC). The fresh properties of SCC were investigated by experimental programmes. Compressive strength, splitting tensile strength, sorptivity, water absorption and porosity, rapid chloride permeability test (RCPT), and sulphate resistance were all assessed up to a 365-day curing period. It was determined that the strength properties improved with replacement of cement with RHA. RHA up to 15% replacement level yielded the maximum value. While the durability properties increased noticeably at all replacement levels of RHA. The results of the compressive strength tests were confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM) microstructure analysis. Waste Foundry Sand (WFS) has been studied for use in SCC to test its strength and durability. Self-Compacting Concrete prepared with various proportions (0-30%) of WFS as a partial replacement of fine aggregates. In this study, its fresh, strength, durability, and microstructural properties were investigated at 28, 90 and 365 days of curing. Fine aggregates were substituted with 5, 10, 15, 20, 25, and 30% of WFS by volume after control mix design of SCC. Testing was performed for the following characteristics: fresh properties, compressive strength, splitting tensile strength, water absorption, sorptivity, rapid chloride permeability, sulphate resistance, SEM, and XRD. According to EFNARC, all SCC mixes confirmed fresh state properties such as slump flow, T500, V-funnel box, and U-box test. There was a vii marginal reduction in compressive strength with the inclusion of WFS up to 10% as compared to the control mix at 28, 90, and 365 days of curing. Incorporating WFS up to 30% increase the volume of permeable pore space from 13.43 to 16.67%, water absorption increased by 2.11 to 3.07 mm, chloride permeability decreased by 2119 to 3553 Coulombs, and compressive strength of samples cured with sulphate decreased nearly 5% when compared to samples cured with water at 28 days of curing. The concrete samples improved in terms of pore structure, permeation, sulphate attack, and chloride permeability after 90 and 365 days of curing. With the usage of 5 to 30% WFS at 28 days, the strength of SCC was reduced from 6.38 to 18.76%. The experimental results are validated by the microstructural results of XRD and SEM. It was observed that by utilizing WFS up to 10%, cost-effective SCC with performance comparable to control mix could be obtained. In this research study, the effects of RHA as a partial substitute for cement and WFS as a partial replacement for fine aggregates in the SCC mix have also been examined. After 7, 28, 90, and 365 days of curing, percentage variation in compressive strength for the mixes R0WFS0, R5WFS5, R10WFS10, R15WFS15, R20WFS20, R25WFS25, and R30WFS30 was observed. Increased compressive strength was obtained with inclusion of RHA and WFS up to 10% in comparison to control mix at 28, 90, and 365 days of curing. It was possible to prepare SCC of the strength above 49 MPa with utilization of RHA and WFS up to 30% as a replacement of cement and fine aggregates. Sorptivity value decreased up to 10% partial replacement levels at all ages and thereafter values increased for 15% to 30% of replacement levels. At ages 28, 90, and 365 days, the water absorption of the control mix was 4.64%, 4.23%, and 1.40%, respectively, whereas it was 5.07%, 4.47%, and 1.59% for mix R30WFS30. Additionally, research has been done to determine the relationships between the compressive and tensile strengths of all blends which have been cured for 7, 28, 90, and 365 days. SEM images of the SCC mixes with RHA and WFS were obtained to investigate the microstructure aspects in the transition zone and paste around the aggregates. It was found that the permeability of RHA and WFS blended SCC mixes decreased at all ages, up to 15% replacement levels. SCC specimens that had been cured in a sulphate solution showed compressive strengths that were comparable to control mixes up to 10% replacement levels of RHA and WFS blends at all ages.