Effects of freeze-thaw cycles on the characteristics of the expansive soils treated by nanosilica and Electric Arc Furnace (EAF) slag

Abstract

The problematic expansive soils are spread in many countries and require significant improvement. The impacts of nanosilica and the Electric Arc Furnace (EAF) slag on the improvement of the swelling potential, volume changes, and Unconfined Compressive Strength (UCS) of the expansive clay samples were experimentally investigated in this study. In addition, the durability of the stabilizers against adverse effects of consecutive freeze-thaw cycles was also assessed using macro and micro tests. The results showed that the expansibility of the soil samples improved by 20% of the EAF slag and 0.5% of nanosilica decreased by 77.5% after one day of curing. To evaluate the durability of the samples, the number of freeze-thaw cycles was repeatedly increased until the dynamic equilibrium was reached. Then, the volume and water content changes and also the strength reduction rate of the treated and untreated samples were measured at the end of each cycle. The results revealed that the dynamic equilibrium for both untreated and treated samples was recorded during the 2nd to 4th cycles. The highest strength reduction rate occurred after the 1st and 2nd cycle and it was respectively 29% and 36% for the untreated and only 14% and 18% for the treated samples by the optimal amount of the EAF slag and nanosilica after 7 days of curing. However, the strength reduction rate decreased to 5.4% and 6.4% after 28 days of curing, thus curing time brought the significant improvement and promising results for the treated samples against the freeze-thaw cycles. In addition, the maximum volumetric strain was measured as 6% for the untreated expansive clay, occurring after the 4th freezing cycle. However, this value decreased significantly to 2.75%, occurring after the 3rd freezing period, for the sample improved by nanosilica and the EAF slag simultaneously. Thus, the results confirmed the strong potential use of the mixture of the EAF slag and nanosilica in reducing the negative effects of freeze-thaw cycles on the soil characteristics. Finally, to identify the underlying improvement mechanisms, the microstructural analyses were also carried out on different soil samples by using the X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) tests.