Mechanical Behaviors Of Lime-treated Metakaolin In Compaction And Curing Period

The engineering problems caused by problemtic soils have gradually drawn the attention in road and railway subgrade engineering.For natural soils with high water sensitivity and low strength,lime used as a stabilizer can greatly improve these soil's workability and mechanical properties,thereby effectively reducing engineering disasters caused by problemtic soils.Recently,many scholars have studied the strength of lime-treated soils,and believe that lime can significantly improve the short-term strength of soils.Studies found that the long-term mechanical properties of lime-treated soils are difficult to guarantee due to the long-term exposure in harsh environments under freeze-thaw cycles and drying-wetting cycles.Therefore,it is of great significance to put forward a reasonable method for improving the durability of lime-treated soil.According to the application of metakaolin in high performance concrete,it is proposed to use metakaolin as an additive in lime-treated soil to improve its durability.Taking metakaolin as the research object,this paper explores the mechanical properties of lime-treated metakaolin in compaction period and long-term curing period,and explians the macroscopical mechanical properties through the characteristics of microscopic pore distribution,thus basically studying the reaction mechanism of lime and metakaolin.The main conclusions drawn from the experimental results are as follows:1)The Standard Proctol compaction test was conducted on the metakaolin and lime-treated metakaolin.The results show that the compaction cuvre of untreated metakaolin is bell-shaped while that of metakaolin treated with 5% lime is S shape.In addition,the maximum dry density of lime-treated metakaolin is slightly higher than that of pure metakaolin due to the lubrication effect of hydrated lime.2)MIP test was performed on statically compacted lime-treated samples and untreated samples.The results show that samples both at dry and wet sides of the optimum exhibite uni-modal pore size distribution characteristic,which differs from the pore size distribution of normal clayey soil at dry side with bi-modal distribution.It is indicated that thermal treatment results in uniform structure in metakaolin with single platelet,preventing the formation of aggregates.3)Samples with various water contents and dry densities were compacted statically and then the bender element test and suction measurement test were conducted.The results show that the small shear modulus is mainly dominated by particle contact while suction has insignificant effects on it.The suction of samples has close relationship with water cantent and pore size distribution.When water content and dry density increase at the same time,the suction will decrease at low rate due to the reduced pore size.By contrast,the suction will decrease at relatively higher rate with increasing water content but decreasing dry density.Lime-treated metakaolin and lime-treated kaolin compacted statically at optimum conditions(i.e.maximum dry density and optimum water content)were cured for long term to study the mechanical properties.The results show that the suction of untreated samples keep constant during the curing period while that of lime-treated soils increases rapidly due to pozzolanic reaction with increase by 360% for treated metakaolin and 220% for treated kaolin.4)The suction and water content of samples at different curing time were measured.The results show that the water content of samples at various conditions remains essentially unchanged throughout the whole curing period.Moreover,it is found that water consumption occurs at the beginning of curing period accompanied by lime hydration.For treated metakaolin,the initial water content(40%)decrease to 35% while lime-treated kaolin consumed 2% water.All samples show declined suction in the curing period.5)MIP test was conducted on samples at different cured time.The results show that for untreated samples,curing time has less effect on the pore size distribution;for lime-treated soils,the pore sizes in the new-formed binding compouds are beyond the pore size range of MIP equipment,resulting in a constant accumulative pore rate with decreasing suction.