Effect of Waste Basalt Fines and Recycled Concrete Components on Mechanical, Water Absorption, and Microstructure Characteristics of Concrete

In this paper, the recycled fine aggregates and powders produced from crushing old basaltic concrete and natural basalt were used to produce new concrete. The sand was partially replaced by two types of recycled wastes at five percentages: 0%, 20%, 40%, 60%, and 80%. The cement was partially replaced by recycled powders and silica fume (SF) at four percentages: 0, 5%, 10%, and 20%. The concrete strengths and water absorption were obtained at several curing ages. The obtained results emphasized the positive effects of increasing the curing time on enhancing the concrete properties, regardless of the types or the waste sources. Moreover, the recycled powders retarded the hydration reaction. In addition, the recycled fine aggregates and powders could achieve about 99.5% and 99.3% of the ordinary concrete strength and enhance the tensile strength. Furthermore, the mix containing 40% of recycled fine concrete aggregate diffused the highest contents of both calcium and silicate, which led to enhancing the interfacial transition zone (ITZ) and concrete properties, compared to the other tested mixes. Finally, the water absorption of all tested concrete mixes decreased with an increase in the curing age, while the mixes integrating 10% and 20% of SF experienced the lowest values of water absorption.

Automated summary

This paper explores the use of recycled fine aggregates and powders from old basaltic concrete and natural basalt to produce new concrete. The study replaces part of the sand and cement with different percentages of recycled wastes. The results show that increasing the curing time has a positive effect on enhancing concrete properties, regardless of the waste source. The recycled powders also slow down the hydration reaction. Additionally, the recycled aggregates and powders achieve comparable strength to ordinary concrete and improve tensile strength. Notably, the mix with 40% recycled fine concrete aggregate demonstrates the highest calcium and silicate content, leading to enhanced interfacial transition zone and concrete properties. Moreover, water absorption decreases with curing age, with the mixes containing 10% and 20% silica fume experiencing the lowest values.