Strength Performance and Stabilization Mechanism of Fine Sandy Soils Stabilized with Cement and Metakaolin

Enhancing strength performance while reducing cement consumption for soil stabilization is the key to improving the economic benefits of engineering construction projects like retaining structures of underground engineering, subgrade bases, and foundation reinforcement. This study employed metakaolin as the additive to realize these two aims. A series of compression and microstructural observation tests on cement- and metakaolin-stabilized fine sandy soils (CMSFSS) were conducted with different cement–metakaolin ratios, water–binder ratios, dosages of the binder (the mixture of cement and metakaolin), and curing ages. The influences of these factors on the mechanical performance of the CMSFSS were studied. The empirical relationships between compressive strength and these influence factors were discussed. Then, the strengthening mechanism of the CMSFSS at different curing ages was investigated. The results showed that the optimal cement–metakaolin ratio for fine sandy soil stabilization was 5:1, which did not change with the total consumption of cement and metakaolin. The compressive strength of the CMSFSS decreased linearly with the water–binder ratio but increased linearly with the curing age. Four empirical prediction formulas about these strength-influencing factors were summarized. The evolution of microstructural characteristics discovered by scanning electron microscope and mercury intrusion tests showed that the hydrated gels in CMSFSS were being formed during the early curing age and resulted in decreasing pore sizes with an initial rapid rate and then a slower rate over the curing age. The gradual disappearance of calcium hydroxide (by-products of cement hydration) over the curing age proved the promoting effect of metakaolin on the strength improvement of cement-stabilized fine sandy soils. This study can provide a reference for applying cement and metakaolin in soil stabilization practices.