Unconfined compressive strength of hybrid fiber cement soil mixed with sand and modified by polyacrylamide

In order to study the influence and mechanism of sand content and negative polyacrylamide (PAM) on the strength of polypropylene fiber, sisal fiber as well as the hybrid fiber reinforced cement soils, sand and PAM were included in polypropylene fiber, sisal fiber as well as the hybrid fiber reinforced cement soil at 4%, 8%, 12%, 16% and 20% by weight of raw soil and 2%, 6%, 10% by weight of cement respectively, ninety-six groups of samples were prepared and subjected to unconfined compression test. The evolution of the surface morphological structure of sisal fiber and polypropylene fiber in cement soil matrix was characterized by using scanning electron microscopy (SEM). The results show that the inclusion of two kinds of fiber has greatly improved the unconfined compressive strength of cement soil, the increased strength ranges from 40.5% to 54.1%. Sands content and PAM content have significant influence on the strength of cement soil, the unconfined compressive strength of fiber reinforced cement soil increases first and then decreases with the increase of sand content and PAM content, the maximum value of unconfined compressive strength is observed at the optimum sand content of 12% and the optimum PAM content of 6%. Besides, the hydration of cement and hard sand particles combined with hydrolysis product of PAM make the surface of fiber become rough, thereby improves the bonding properties of the interface between fiber and cemented soil matrix. The mix of sisal fiber and polypropylene fiber increases the unconfined compressive strength of cemented soil in a certain extent and the confounding effect is found in hybrid fiber cemented soil. The inclusion of PAM and sand has significant effect on hybrid coefficient.