Shrinkage Mechanism of Laterite Modified by Lime and Metakaolin

In this study, effects of metakaolin and lime on the microstructural characteristics, unconfined compressive strength (UCS), shrinkage, suction, and shear resistance of laterite were investigated. Soil samples treated with 5 wt% of lime (LaL) or 4 wt% metakaolin and 5 wt% of lime (LaLM) were prepared. Samples with an optimal water content of 32% were compacted and cured for 180 days, followed by saturation and dehydration until the desirable water content of the samples was attained. Then, the UCS, shrinkage, and suction and shear resistance of the samples at a normal stress of 200 kPa were determined. In addition, scanning electron microscopy imaging as well as mercury intrusion porosimetry tests were performed to examine the microstructural changes. Results indicate that the shrinkage of treated soil samples is significantly improved in comparison with that of the untreated soil samples. Lime effectively improves the UCS and shearing resistance of laterite. Moreover, metakaolin is composed of amorphous silicon and aluminium oxides and shared edge-face structures on the microscopic scale; hence, it can considerably capture calcium ions from a lime solution, generating cementitious hydrates in the interaggregates of laterite. Results also revealed that the combination of 5 wt% of lime and 4 wt% of metakaolin can improve the UCS and shearing resistance, but the linear shrinkage is particularly restrained, significantly decreasing by 4 times compared with that of the lime-treated soil sample and by 8 times compared with that of the untreated soil sample. The study results demonstrate that metakaolin and lime can be effectively used to improve laterite in lieu of the conventional lime treatment for mitigating geotechnical engineering disasters.

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