Enhancing the Mechanical and Microstructural Properties of Expansive Soils using Industrial Waste, Nano-material and Polypropylene Fibers: A Comparative Study

Abstract

Lime is a common stabilizer in soil remediation projects. However, in terms of the considerable emissions of greenhouse gases in lime production, the replacement of environmentally friendly stabilizers with lower CO2 emissions has attracted much attention. Accordingly, this study investigated the efficacy of expansive clay remediation employing ground granulated blast furnace slag (GGBS) and nano-metakaolin (NMK) as a substitute for lime. Moreover, polypropylene fibers (PPFs) were added to assess the simultaneous effect of the stabilization/reinforcement (S/R technique). To this end, a set of macro and micro tests including unconfined compressive strength (UCS), free swelling, electrical conductivity (EC), pH, scanning electron microscopy (SEM) analyses, X-ray diffractometer (XRD), and ultrasonic pulse velocity (UPV) were conducted on the samples cured at 20 and 40 °C after 7, 28, and 90 days of curing. The results showed that the ratio of lime to GGBS = 1:4 and replacing NMK with 20% lime as an optimum mixture (with an over 40% decline in lime consumption) increased the strength about 8.1 times that of soil and substantially limited the swelling. An important key factor that accelerated the process of improvement was higher temperature. There was a rising trend for E50 and EU with increasing the additives' quantities. PPFs enhanced strength by around 11.7 times that of soil while reducing the amount of needed lime by 60%. Additionally, specimens' swelling and ductility were improved, EU increased, and E50 slightly decreased. Correlations were obtained between compressive strength with E50 and ultrasonic pulse velocity values (UPV). XRD and SEM results confirmed increasing CSH and CAH amounts and the modification of soil's pore network by forming a denser microstructure.