Optimization of the strength properties of expansive soil stabilized with agricultural wastes

• Main Author: Valbuena, Kigia R.
• Format: text
• Language: English
• Published: Animo Repository 2019
• Subjects: Swelling soils; Rice hulls; Binders (Materials); Civil Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/6406; https://animorepository.dlsu.edu.ph/cgi/viewcontent.cgi?article=13460&context=etd_masteral
• Institution: De La Salle University

Expansive soils are problematic soils that exhibit the shrink-swell behavior. Previous research has shown that rice husk ash (RHA) effectively reduces the swelling potential of expansive soils but it does not increase the strength of the soil. The soil used in this study was identified as expansive due to its index properties meeting most of the criteria set by the National Structural Code of the Philippines for expansive soils. An improved admixture composed of RHA and a binder is used to treat the expansive soil. Different types of binders are used; three of which are agricultural wastes namely coconut shell ash (CSA), rice straw ash (RSA), and sugarcane bagasse ash (SCBA). Ordinary Portland cement (OPC) is used as a comparison for the other binders. The physical and chemical composition of the materials were studied using Scanning Electron Microscope and Energy Dispersive X-ray Spectroscopy. The untreated and treated soil mixtures were evaluated through their geotechnical properties such as specific gravity, Atterberg limits, moisture-density relationship, unconfined compressive strength (UCS), and expansion index (EI). The EI of the mixtures ranged from 0 to 2 only. This confirms the effectivity of RHA as a stabilizer and suggests that the binder does not increase the potential expansion of the soil. The effectivity of the admixture is evaluated through ASTM D4609. Test results show that only the RSA and cement mixtures showed an improvement in the Atterberg limits. None of the binders improved the compaction characteristics of the soil. Most of the soil mixtures met the required provisions set by ASTM D4609 for t he indication of improvement in the strength. The treated specimens exhi bited an increase in the strength by as much as 745.38 kPa, 859.90 kPa, 799.46 kPa, 2428.31 kPa for the mixtures with CSA, RSA, SCBA, and cement, respectively. It has been found that as the CSA, RSA, and SCBA content increases, the UCS generally decreases. The UCS generally increases as the curing period increases. A response surface methodology was performed for the UCS of the soil mixtures with the binder types CSA, RSA, and SCBA. The binder content and curing period are the numerical factors and the response is the UCS. Contour plots and response surface plots show that the optimum strength for the mixtures with CSA, RSA, and SCBA is at the highest curing period (35 days) and lowest binder content (5% content). The binder type that has the highest maximum value for the predicted response is the RSA, therefore, the optimum mixture is the soil with 5% RSA.