An Experimental Study On Thermophysical Properties Of Unsaturated Cement-Treated Expansive Soils

Expansive clay is widely distributed in Hefei area.In order to ensure the safety of projects found on the expansive clay,people often use cement to improve the properties of expansive clay,but so far the research on the thermophysical properties of cement-treated expansive soil is not deep enough.Therefore,with the continuous developments of urban underground engineering construction,the engineers have paid more attention on the thermal physics characteristics of expansive clay and cement-treated expansive soil.The influence of cement admixture,cement curing age,compaction work and environmental temperature on the thermal physical parameters of cement-treated expansive soil was here addressed by a series of tests.Moreover,corresponding microscopic features are quantitatively analyzed by the scanning electron microscopy test and the image processing technology,and the relationship between thermophysical properties and microscopic features was also preliminaries discussed.And some interesting conclusions are drawn as follows:(1)It was found that the thermal conductivity and specific heat capacity of unsaturated cement modified expansive soil behaved a downward trend with the increase in cement content,while the temperature coefficient showed a rising law.At the room temperature of 15°C,amounts of the thermal conductivity and specific heat capacity obtained from specimens of 30mm high and 9%cement,and prepared by a light compaction method reduced by 15.20%and 45.50%compared with specimens prepared with the expansive soils,while amounts of the temperature coefficient increased by 56.25%.Values of the thermal conductivity and specific heat capacity obtained from the cement-treated expansive soil specimen of 9%cement and prepared by a heavy compaction method decreased by 8.76%and 41.54%,respectively,but the temperature coefficient increased by 56.30%.(2)For cement-treated specimens with 9%cement,the thermal conductivity and specific heat capacity decreased with the increase of the curing time,and the temperature coefficient showed a linear increase law.For 30mm thickness specimens prepared with cement-treated expansive soils and cured for 28 days,their amounts of the thermal conductivity and the specific heat capacity obtained at a room temperature of 15°C reduced by 7.01%and 19.62%compared with those of specimens cured for 0 day,but the temperature coefficient increased by 15.38%.Values of the thermal conductivity and specific heat capacity of heavy-duty compacted specimens decreased by 5.60%and11.02%respectively,while the temperature coefficient increased by 6.29%.(3)The thermal conductivity measured at a room temperature for the unsaturated cement–treated expansive soil specimens prepared by the heavy compaction method was higher than that of specimen prepared by the light compacted method,while the thermal conductivity measured at a negative temperature was lower than that obtained at a room temperature.It was also found that the thermal conductivity values under negative temperature conditions were greater than those measured under room temperature conditions.This indicates that the ambient temperature has an effect on thermophysical parameters for the cement-treated expansive soil.(4)The EDS tests showed that chemical elements in the unsaturated cement-treated expansive soil are mainly oxygen,silicon,aluminum,iron and a small amount of calcium,potassium and magnesium,and the content of calcium and magnesium increases with the increase of cement content.It was seen from SEM electron microscopy tests that the particles in the light compacted specimens are agglomerates while in the heavy-duty compacted specimens the particles were flat or flocculated.Particles contact modes were mainly in forms of face to face and face to side.The pores were mainly pores with pore area of less than 1?m~2,pore diameter of less than 1?m and pore circumference within 1to 5?m.These results suggest that changes in thermophysical properties of the cement-treated expansive soil may be due to the changes in the composition and microstructure feature and micro-pores distribution.