Study On The Effect Of Aggregate Grading On Engineering Properties Of Composite Improved Expansive Soil

The improvement effect of on-site expansive soil improvement fails to achieve the same performance and durability as the results of indoor research,which leads to quality problems.However,there are few studies on the difference of aggregate properties caused by different particle sizes in laboratory expansive soil improvement and field construction improvement.Therefore,a series of experimental studies on the influence of aggregate particle size on expansive soil improvement were carried out in this paper.The main research work and the corresponding findings are presented as follows:(1)The effects of aggregate particle size and curing time on the water stability of composite improved soil with iron tailing sand and calcium carbide slag were studied.The results show that the smaller the particle size and the longer the curing time,the better the water stability of the composite improved soil aggregates.Conversely,the worse the water stability.It is observed that the structure of composite ameliorated soil aggregates is composed of shell,outer reinforcement layer,inner reinforcement layer and center layer through flooding failure test.(2)The variation of unconfined compressive strength of iron tailing sand and calcium carbide slag composite improved soil with different aggregate size grading under wetting and drying cycles was studied.The test results indicated that the higher the content of 20-30 mm particle size aggregates in the improved soil,the lower the strength and durability.(3)The mineral composition of aggregate of iron tailings sand and carbide slag composite improved soil was analyzed by X-ray diffraction method(XRD)and X-ray energy spectrum method(EDS).It was found that the carbide slag can not completely penetrate into the aggregate,but only partially penetrate into the aggregate as time goes by.(4)Scanning electron microscopy method(SEM)was used to analyze the structure of iron tailing sand and calcium carbide slag composite improved soil with different aggregate size distribution under wetting and drying cycles.It was indicated from tests results that,compared with the composite improved soil with 20-30 mm particle size aggregate content of 30%,the composite improved soil with 20-30 mm particle size aggregate content of 0%(laboratory particle size)produces more cementitious compounds,and its structure is significantly more stable.(5)The influence of calcium carbide slag and iron tailing sand on the grain size distribution of the improved soil was analyzed by mixing iron tailing sand,calcium carbide slag and expansive soil with a mechanical agitator.It was found that the addition of iron tailing sand alone has little effect on the grain size distribution of the improved soil.However,in the presence of calcium carbide slag,the addition of iron tailing sand can greatly reduce the content of large and medium-sized aggregates in the soil and promote the mixing efficiency of the mechanical agitator.