Effect of polymeric capsules on one-dimensional compression and creep of carbonate sand

Carbonate sand, widely distributed in coastal regions, presents challenge due to its high stress-dependent and time-dependent (creep) compressibility. While soil stabilization techniques have traditionally focused on enhancing the strength of carbonate sand, the evaluation on the compressibility performance of cemented carbonate sand remains a critical aspect for most envisaged practical applications. In light of recent developments in self-healing approaches for soil stabilization, this study investigated the potential of calcium alginate/Tung oil capsules to mitigate compressibility in carbonate sand. The encapsulated Tung oil serves as a healing agent, gradually releasing within the sand matrix when subjected to void ratio changes during compaction, hardening and bonding sand grains after a 30-day drying. Long-term stepwise one-dimensional compression tests were conducted on both clean sand and sand-capsule composite with different initial relative density and particle size. The overall and stress-dependent compressibility was reduced for fine sand-capsule composite, while capsules had adverse effect on the compressibility of medium and coarse sand-capsule composite. Capsules could not reduce the creep but increase the elastic response of all sand-capsule composites. The Tung oil bonding could reduce the compressibility by preventing particle breakage of sand during loading. The stabilization mechanism of capsules in carbonate sand with different particle size was further investigated through thermal analysis, CT scan and microscopic analysis, revealing that the compressibility mitigation by capsules depended on the amount of Tung oil release from capsule, which was controlled by the pore structure of sand-capsule composite.