Identifying the microstructure and mechanical properties of expansive soil stabilized using fly ash and waste foundry sand

Abstract

Expansive soil causes road construction damage in the form of cracks or deformations due to changes in moisture content. One method to address this issue is soil stabilization using additive materials. Special additives can sometimes be expensive; hence it is necessary to use additive materials based on industrial waste as a waste management solution to solve the problem of expansive soil as a road construction subgrade. This study aims to analyze the effects of adding two types of industrial waste, namely fly ash (FA) and waste foundry sand (WFS), regarding the microstructure, physical, and mechanical properties of expansive soil. The method of stabilizing expansive soil involves mixing the soil with 9 % FA and various levels of WFS (0 %, 7.5 %, 10 %, 15 %) based on the dry weight of the soil. Microstructure testing includes quantitative X-ray diffraction and scanning electron microscopy. Physical property testing includes specific gravity, Atterberg limits and sieve analysis. Mechanical testing, i.e. compaction, California Bearing Ratio, swelling, and Triaxial tests were conducted. Soil stabilized with 9 % FA and 15 % WFS shows a significant increase in the internal friction angle and cohesion, reducing swelling by 67.18 % compared to the original soil swelling. The addition of 9 % fly ash and 15 % WFS to expansive soil reduces the content of montmorillonite. Natural expansive soils have a very poor soaked CBR of 0.94 %, while stabilized soils with 9 % FA and 15 % WFS have a soaked CBR of 6.46 %. This means that the soaked CBR of the stabilized soil meets the minimum CBR required for road subgrade construction. A mixture of 9 % FA and 15 % WFS in expansive soil can be recommended as a material for stabilizing expansive soil due to its ability to improve microstructure and mechanical properties