Physical-Chemical Investigation And Modification Mechanism On Cement Treatment Of Highly Expansive Clay

Expansive soil is a special type of clay, with the engineering properties of swelling, disintegration, softens when absorbing water and shrinkage, desiccation, hardening when losing water. The engineering property will damage to the subgrade, foundation, slopes and light steel structure house constructed in the expansive soil areas. This kind of harm tends to have long-term, unexpected and recurring characteristics, and often cause huge economic losses. According to the characteristics of expansive soil and improvement thought, we often use cement modifying expansive soil to reduce or eliminate the swell-shrink characteristic of the expansive soilSelecting highly expansive soil of south-to-north water transfer project in Hebei Handan region. We have carried on the experimental research on cement treatment of highly expansive soil. Prepare air dried highly expansive soil through0.5mm sieve and mix a certain quality of cement in the air dried highly expansive soiL The quality of cement is equals to12%quality of dried highly expansive soil. Make samples with a ring (inside diameter of61.8mm and height of20mm) under the optimal water content of35.7%and maximum dry density of1.28g/cm3. These samples cured in a certain temperature and humidity condition for a long time. Then take out these samples and dry them. At the end, we crusted down them and passed at0.5mm sieve. Based on the standard of soil test procedures/SL237-1999, a large number of laboratory experiment was carried out on highly expansive soil and cement modified soil at different curing time, generally for curing after zero hour,1hour,4hours,1day,7days,28days,90days and180days. Test contents and test results mainly include the following aspects:(1) Through the grain size analysis test, atterberg limits test, free swell test and one-dimensional swell test, we came to the conclusion that the clay mineral composition of highly expansive soil was principally hydrophilic mineral. When we took the plasticity index and free swell as the basis of expansion potential, the expansion potential of cement modified soil at different curing time was obtained and from these data we found that the expansion potential reduced from highly expansive soil to unexpansive soil, which proved the validity of cement modification on highly expansive soil. Through the unconfined compressive strength test and triaxial compression test, we obtained the strength index of highly expansive soil and cement modified soil at different curing time, including unconfined compressive strength, friction angle and cohesion. Test results showed that the strength of cement modified soil will increase with the increase of curing time, and the increase of strength was mainly in early time (within7days of curing time).(2) Through X ray diffraction experiment, scanning electron microscopy test and ion content determination test, we got the phase-mineral composition, micro structure morphology, cation concentration of K+, Ca2+, Na+, Mg2+and cation exchange capacity between highly expansive soil and cement modified soil at different curing time. Based on these changes, we reasonably explained the modified mechanism in the process of cement modified highly expansive soil, and pointed out cation exchange capacity was not an effective index for the swelling potential on cement treatment of highly expansive sofl.Through the above tests, we proved that the cement can effectively reduce expansion potential, increase soil strength and sustain water stability, as well, we explained the modification mechanism in the process of cement treatment on highly expansive soil. These provide scientific and valuable basis for the designing and constructing about cement modified expensive sofl.