Effect of Basalt Fiber Content and Length on the Strength and Crack Development of Polyvinyl Alcohol/Basalt Hybrid Fiber-Reinforced Cement Soil

Abstract

Polyvinyl alcohol (PVA) fiber is widely used in geotechnical engineering because of its excellent physical and mechanical properties; however, PVA fibers are prone to aging, while basalt fiber has a natural anti-aging ability, which can be added to cement material to effectively eliminate the effects of aging on PVA fiber. Previous experiments identified that the optimum content of PVA fiber is 0.5% (mass fraction, the same below). Based on this, we continued to add basalt fibers of different lengths (3 mm, 6 mm, 9 mm, 12 mm, 18 mm, 30 mm) and different contents (0%, 0.25%, 0.5%, 0.75%, 1%) to study the effect of both length and content of basalt fibers on the strength of cement soil specimens. It was concluded that adding 0.5 % of 9 mm basalt fiber results in the greatest increase in unconfined compressive strength (UCS). The UCS reached 12.59 MPa, which was 71% higher than specimens without fiber, and a regression analysis was carried out to obtain the relationship among them. The ratio of cement soil in the highest UCS and the relationship among the UCS, the length, and the content of basalt fiber can be used as a reference for practical projects. In addition, digital image correlation (DIC) technology was used to analyze the surface cracks and horizontal strain field when the peak strain was reached at each content and length of the basalt fiber. Finally, the curing mechanism for hybrid fiber cement soil was analyzed by combining the results of the UCS test, DIC test, and SEM test.