Abstract
Black cotton soil (BCS) forms a major soil group in Kenya and is characterized by high shrink/swell potential when exposed to water. A comprehensive series of laboratory tests were performed on BCS treated with lime (0–9%), volcanic ash (VA, 0–25%), and their combinations in order to study the physical–mechanical properties and mineralogical changes of the stabilized BCS. Moreover, a test road which replaced the BCS with the lime–VA-stabilized BCS was constructed to investigate the moisture change and soil movement in the BCS foundation. The results revealed that BCS stabilized with combinations of lime and VA shows larger California bearing ratio (CBR) and unconfined compressive strength (UCS) values when compared with a single stabilizer. BCS stabilized with 3% lime + 15% VA meets the performance requirements of roadbed materials in accordance with JTG D30-2015. The increase of pH and electrical conductivity (EC) in the stabilized soil promotes chemical reactions between the stabilizers and BCS to form new cementing agents, which are confirmed by X-ray diffraction (XRD) and transmission electron microscope (TEM) findings. The replacement of BCS with 3% lime + 15% VA-stabilized BCS shows an obvious effect on controlling the moisture change and soil movement in the foundation BCS. This research provides a low-cost strategy for making use of the vast resources of BCS in Kenya obtained from foundation excavation.
Highlights
With the fast development of infrastructure construction in Kenya, many highways, municipal roads, and railway lines have been constructed in recent years, such as the Nairobi–Mombasa railway line and Southern Bypass in Nairobi
black cotton soil (BCS) stabilized with combinations of lime and volcanic ash (VA) shows larger California bearing ratio (CBR) and unconfined compressive strength (UCS) values when compared with a single stabilizer
The increase of pH and electrical conductivity (EC) in the stabilized soil promotes chemical reactions between the stabilizers and BCS to form new cementing agents, which are confirmed by X-ray diffraction (XRD) and transmission electron microscope (TEM) findings
Summary
With the fast development of infrastructure construction in Kenya, many highways, municipal roads, and railway lines have been constructed in recent years, such as the Nairobi–Mombasa railway line and Southern Bypass in Nairobi. The increase of the discarded BCS results in serious environmental disaster To overcome these problems, a facile but low-cost strategy has to be found to make use of such clay in highway construction. Studied soil stabilization using the Atterberg limits, swell percent, and swell pressure tests, and found that lime significantly improved the physical–mechanical properties of expansive soil. VA-stabilized soil presents a decrease in the plasticity index and expansive potential and an increase in the strength and durability [29]. The use of VA will decrease the cement or lime dosage in the soil stabilization and results in a low-cost subgrade material. The influence of VA, lime, and their combinations on the physical–mechanical properties of BCS was researched using compaction, Atterberg limits, California bearing ratio (CBR), and unconfined compressive strength (UCS) tests.
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