Strength Parameters of Stabilized Clay Using Polypropylene Fibers and Nano-MgO: An Experimental Study

Abstract

In this study, the effect of two additives, including recycled polypropylene (PP) fibers and Nano magnesium oxide (MgO), was investigated in the improvement of strength characteristics of clay. Some samples of clay, with or without additives, were prepared and strength characteristics were measured by unconfined compression and direct shear tests. The soil was stabilized by adding 0.2%, 0.5% and 1% of PP fiber and/or 0.2%, 0.4%, 0.8% and 1% of nano-MgO by dry weight of the soil. The results of the unconfined compression tests show that nano-MgO can significantly increase the stiffness of the soil and the undrained cohesion of the clay. Adding 0.2% nano-MgO raises the undrained cohesion about 45%. However, the undrained cohesion slows down to a mild slope after adding more nanomaterial. The direct shear test also demonstrates the significant increase of internal friction angle of the samples with PP fibers and implies proper engagement of the PP fibers within the reinforced soil structure. Besides the increase of the stiffness, adding the fibers increases the ductility of the samples and imparts more failure strain. The study of scanning electron microscope also shows that the nanomaterial has significantly turned clay particles from the layered sheet structures into concentrated ones and created a behavior like granules as far as the internal friction of clay is concerned. Moreover, these conditions and development of a hard mass of nano-soil can provide more interlocking with the fibers due to the pressure from compression and surcharge loading. It therefore increases the strength and mass interlocking and controls the strains in the sample.