Influences of silica fume particles and polyethylene terephthalate fibers on the mechanical characteristics of cement-treated sandy soil using ultrasonic pulse velocity

One of the approaches in the geotechnical engineering for coping with poor soils is to modify their mechanical characteristics with the aid of soil improvement strategies such as chemical stabilization using cement. On the other hand, a number of recent investigations considered safeguarding environment by using waste and low-cost materials for engineering purposes. Thus, in the present research, the combined effects of two kinds of these materials, i.e., silica fume particles and randomly distributed discrete waste plastic polyethylene terephthalate (PET) fibers, on the engineering characteristics of cement-treated sand are explored. In this regard, a set of laboratory tests including unconfined compression, ultrasonic pulse velocity (UPV), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests were conducted on various specimens. The cement percentages were 3, 5, and 7%, silica fume percentage was 0.5%, and PET fiber percentages were 0, 0.25, 0.5, 0.75, and 1% by weight of dry sand with the lengths of 5, 10, and 15 mm. The prepared specimens were cured for 42 days. Based on the obtained results, the addition of PET fibers up to their optimum content and length significantly improves the UCS, UPV, and ductility of specimens. Moreover, relationships between UPV-UCS and E-50-E-u (secant modulus-ultrasonic stiffness) of silica fume-cemented sand containing different percentages of PET fibers were proposed. These relationships can be utilized to evaluate the success of reinforcement and stabilization attempts according to the results of non-destructive UPV test. In addition, the findings of microstructural analyses were in full accordance with the results of UPV and unconfined compression tests.