Sustainable Stabilization of Compacted Clay Using Sodium Alginate for Subgrade Application

Sodium alginate, a low-carbon cementing agent, was used to control the swelling of compacted clay for subgrade applications in this research. A series of geotechnical tests, including Atterberg limits, free swell ratio, standard compaction, and free swelling was conducted on the control (unstabilized) and stabilized soil specimens at different concentrations of sodium alginate (0.25%, 0.5%, 0.75%, 1%, and 1.25%). The specimens were prepared by mixing and spraying methods and cured for 1 and 14 days. The plasticity index (PI) and free swell ratio (FSR) of the stabilized soil were reduced with increasing the sodium alginate concentration due to the reduction in water holding capacity. The lowest PI and FSR (largest soil cluster size) were found at 0.75% sodium alginate concentration and this concentration was designated as the fixation point. Beyond the fixation point, PI and FSR increased with the increasing sodium alginate concentration. This fixation point is simply obtained from the index test and is practically used to determine the optimum sodium alginate concentration providing the lowest swelling. The growth of cementation bonds at the optimum sodium alginate concentration played a significant role in the improvement of swelling potential over curing time. The results of the extensive microstructural tests on the stabilized specimens confirmed that the cementation bonds were due to the presence of palygorskite filling in the pore space; hence the enhancement of inter-particle forces and the reduction in free swelling. The outcome of this research results in the promotion of sodium alginate as an environmental-friendly additive for sustainable subgrade applications and other relevant applications.