Expansion characteristics of microbial mineralized consolidated expansive soils under freeze-thaw action

The use of the green reinforcement technology of microbial-induced calcium carbonate precipitation to improve the expansion and contraction characteristics of expansive soils is an emerging direction in the field of geotechnical engineering, but the effects of its mineralized reinforcement under the freeze-thaw action are not clear. The Bacillus pasteurus is used to carry out the expansion characteristic tests on microbial reinforcement of expansive soils. The influences of microbial mineralization reinforcement under different of cementing agent concentrations on the expansion rate of free expansion rate, no-load expansion rate and load expansion rate of expansive soils are analyzed. The change laws of the reinforced expansive soils of the no-load expansion rate and load expansion rate under the freeze-thaw cycles are studied. The results show that the use of microorganism-induced calcium carbonate precipitation reinforcement of expansive soils can effectively improve the expansion characteristics, and the improvement effects are more and more significant with the growth of the concentration of the cementing agent. The reinforcement effects of microbial mineralization are the best when the concentration of the cementing agent is 1.25 mol/L, and the corresponding free expansion rate, no-load expansion rate and load expansion rate of the specimen are reduced by about 17.9%, 6.6%, and 0.7%, respectively. Compared with those of the concentration of 1.25 mol/L, the mineralized reinforcement effects of the specimen with the concentration of 2.0 mol/L are significantly reduced, and the no-load expansion rate and load expansion rate increase by about 1.6% and 0.24%, respectively. The repeated freeze thaw action weakens the expansion characteristics of microbial- reinforced expansive soils. After three freeze thaw cycles, the no-load expansion rate and load expansion rated of the specimen with a cementing concentration of 1.25 mol/L reach the lowest values which are 3.4% and 0.87%, respectively.