Experimental Study On The Durability Of Carbonated Soils

Carbonated curing technology is an innovative CO2 consuming method for ground improvement.In order to research the durability behaviour of carbonated reactive MgO-stabilized soils, a typical sility clay in Nanjing and typical silt in Suqian were used and use reactive MgO as curing agent. Test samples were made by static pressured and carbonized in triaxial carbonation device. Combined with existing research results, laboratory tests, microscopic experiments and theoretical methods, the influence of drying-wetting cycling condition, freeze-thaw cycling condition and sulfate attack condition were studied, and the test results were then compared with those of cemented soils.The main results are as follows:(1) The drying-wetting test shown that the resistance to drying-wetting cycling performance are different among three different carbonated soils. The residual strength of three different carbonated soils(Wuhan soft soil, Nanjing soft soil and Suqian silt) after 6 cycles are 35%,85% and 90% respectively, while the clay contents of three soils were 20%, 10% and 5%, therefore exist a rule that the higher clay content, the worse performance of resistance to drying-wetting cycles. And because the permeability of carbonated soils are higher than cement soils, the resistance to drying-wetting cycling performance of carbonated soils are worse than cement soils. The microstructure analysis reveals that the cumulative volume of pore void of carbonated Suqian silts and Nanjing soft soil are essentially constant, thus the carbonated soils can still show relatively high strength in the unconfined compressive tests. Whereas, the void ratio of carbonated Wuhan soft clay would increase after cyclic drying-wetting test and further reduce the density, which is responsible for the significant strength reduction.(2)The unconfined compressive strength of carbonated soils reduced from about 5 MPa to about 4.5 MPa after several freeze-thaw cycles(6 times), and cemented soil reduced from about 1.6 MPa to about 1.4 MPa after 4 times freeze-thaw cycles, they both have good resistance behaviours to freeze-thaw cycles. Based on microscopic mechanism analysis on mineral composition and pore structure, it shows that hydrated magnesium carbonates generated by carbonation would not change significantly after cyclic freeze-thaw tests. However, the 0.1～1μm pore reduced,1-30μm pore increased, lead to the cumulative increase in porosity, this is why the unconfined compressive strength slightly reduced.(3)The sulfate attack test shown that it remains almost the same strength of carbonated Suqian silts after 28 days sulfate attack, the strength of carbonated Nanjing soft soil slightly decreased after 28 days sulfate attack, and it remains the same with samples in distilled water, while the strength of the cemented soil decreases greatly after sulfate attack with its mass significantly increasing, although cemented silts increased a little at the shorter attacking time (7 days). The microstructure analysis reveals that the hydrated magnesium carbonates generated by carbonation and its pore structure do not change significantly after the sulfate attack, thus ensuring its stable strength. It is presented finally that the carbonated active MgO-stabilised soil has better resistance behaviours to the sulfate attack than the cemented soil.