Shear Properties of Stabilized Loess Using Novel Reactive Magnesia-Bearing Binders

Abstract

Loess stabilization is an effective approach to solve the deformation and subsidence problems in loess areas. Unconsolidated-undrained direct shear tests were conducted to investigate the improving effect of reactive MgO and MgO fly ash on the shear properties of loess, taking into account four major controlling factors, including MgO amount, curing time, moisture content, and compaction degree. Based on the test results, both the cohesion and internal friction angle of solidified loess achieve a peak at 6% MgO or 14-day curing time. The augment of water content accounts for the enhancement of cohesion before the optimum moisture content is reached, with a drop following afterward, while the friction angle decreases continuously. As the compaction degree grows, the cohesion and friction angle display escalating trends. It is suggested that the following optimum parameters from the viewpoint of shear performance be adopted for construction practices, i.e., 6% MgO content, 14-day curing, optimum water content, and 96% compaction degree. Scanning electron microscopy (SEM), thermogravimetric analysis (TG/DTA), and mercury intrusion porosimetry (MIP) were implemented to explore the microstructure and stabilization mechanisms. The major hydration products of MgO, MgO fly ash, and portland cement–stabilized loess are identified as brucite, magnesium silicate hydrate (M-S-H) plus brucite, and calcium silicate hydrate (C-S-H), respectively. Loess stabilized with reactive MgO-bearing materials has a higher hydration degree and better pore distribution than portland cement–stabilized loess. Reactive MgO and MgO fly ash outperform traditional portland cement (PC) in terms of shear property and microstructure. The MgO fly ash blends elucidate a positive effect on strength gain and decrease in large-size pores.