Amending foamed lightweight soil with tailings sand for embankment applications: Physical properties, durability, and microstructure

Abstract

Making lightweight soil with bubbles from raw soil and cement, i.e., foamed lightweight soil (FLS), is an environmentally sustainable way to utilize tailings sand (TS) as a replacement of cement in embankment applications, enlightened by its excess strength. However, a comprehensive evaluation of its engineering performance is needed. Thus, this study develops a foamed lightweight soil amended with tailings sand (TS-FLS) and explores its physical and mechanical properties, durability, and microscopic properties. The results reveal that the fluidity, volumetric water absorption, and compressive strength of TS-FLS mixtures are within 164–182 mm, 13.3–16.0 %, and 0.76–1.74 MPa, which could satisfy the requirement of the embankment applications. After dry-wet cycles, freeze–thaw cycles, sulfate erosion, and long-term outdoor exposure, most compressive strength is applicable in the application of embankment (>0.3 MPa). Note that the strength and durability show a decreasing trend with the TS content, and the critical content is less than 50 %. Besides, the increasing TS content shifts the failure mode from brittle to ductile (33 % and 40 %), which is favorable for engineering applications, while overused content (50 %) decreases the ductile response. The microstructure observation indicates that the TS increases the pore diameter size and worsens its uniformity, making the walls more vulnerable to compression rupture by stress concentration, thereby increasing water absorption. Moreover, a large number of crystals (i.e., secondary gypsum and ettringite) are generated under sulfate solution, making mechanical properties either improved by void-filling or damaged by microstructure-destroying. Therefore, TS-FLS is promising for embankment applications when an appropriate TS content is chosen.