Discrete fiber reinforcement efficiency in the mechanical properties and wet-dry performance of fat clay treated with industrial sewage sludge ash

Abstract

This paper presents a laboratory evaluation of the strength and durability behavior of treated clay with industrial sewage sludge ash (ISSA) and Polyvinyl alcohol (PVA) fiber. Unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests were conducted on treated clay with different percentages of ISSA and short PVA fiber content after different curing period to evaluate strength properties. In this study, UPV tests were used as a non-destructive method to determine the optimum curing period. The UCS test results indicated that the ISSA inclusion caused an increase in UCS values and a decrease in the axial strain at failure, while fiber inclusion within the ISSA treated soil increases UCS and failure strain, hence decreases brittle index. A good correlation of UPV values (P-wave velocity or VP) and UCS test results is seen by an exponential function. The microstructure of untreated and ISSA treated soil as well as the interaction between PVA fiber surface and ISSA treated soil matrix were investigated by scanning electron microscopy (SEM) tests and image processing analysis. SEM images show that soil porosity increases with the addition of ISSA and, the created scratches and formation of cement bonding on fiber surface increase the interlocking force. This study also assessed the durability of ISSA treated and fiber-reinforced soil against wetting–drying (W–D) cycles. UCS and UPV tests were performed after wetting–drying cycles for this study. Results showed that in ISSA treated soil with fiber inclusion, strength increased with an increase in W-D cycles from zero to three cycles and decreased afterward.