Experimental study on the influence of curing methods on the compressive strength of improved sand

The properties of the improved soil are closely related to the properties of the improved materials added, and the curing process is the key process to make the performance of the improved materials play. In this paper, several groups of improvement tests on sandy soil were carried out, and the improved sand was placed under different curing conditions (standard curing, water curing, air drying curing, dry and wet cycle curing) to explore the improvement effects of each material under different curing conditions. Cement (6%, 8%, 12%, 16%), active magnesium oxide (4%, 8%, 12%, 16%), polyvinyl alcohol solution (PVA)(6%, 8%, 12%, 16%) and polypropylene fiber (PPF)(0.25%, 0.5%, 1%, 2%) were used as modified materials. The improvement effect was evaluated by unconfined compressive strength, stress-strain curve and scanning electron microscope observation of internal cementation state. The results show that the improved material has different effects under different curing conditions when the same material is added to the improved soil. The improvement effects of cement, active magnesium oxide, PVA and PPF on sand are all affected by curing conditions. Among them, cement improved sand is suitable for standard curing corresponding to cement. Activated MgO can obtain a higher strength of 2.7 MPa under dry and wet cycle curing. PVA modified sand has almost no strength under standard curing conditions, but can reach 0.9 MPa under dry curing conditions. The unconfined compressive strength of fiber-modified sand decreases with the increase of water content. The SEM results showed that the improved material strengthened by hydration reaction could form dense hydration products and fill the pores between the sand grains under appropriate curing conditions, while the reaction was incomplete or overreacted under other curing conditions, leading to the defects of the sample.