Strength Characteristics And Mechanism Of Lime-metakaolin Modified Soil Under Acid Attack

Soil site is an important cultural heritage,but because it is exposed to the natural environment for a long time,it is easy to appear cracks,collapse and other diseases,so the restoration and protection of soil site is urgent.The key to the restoration and protection of soil sites lies in the proper application of materials.This paper added simulated acid rain solution to the dry-wet cycle based on acid rain environment,explored the strength evolution law,mass loss and microscopic mechanism of Lime-Metakaolin（L-MK）modified soil under the acid-dry-wet cycle coupling,and analyzed the color applicability of samples.The comparison between the modified soil and Natural hydraulic lime（NHL）is also analyzed.Secondly,a 12-month immersion test with simulated acid rain solution was carried out,and alkaline solution and neutral distilled water environment were set as the control group.The main research contents and achievements are as follows:（1）Under the action of SO₄^2-and H⁺,the hydration products in L-MK and NHL modified soil dissolved to form Ca SO₄·2H₂O and other expansive substances.The mechanical properties of L-MK modified soil increased first and then decreased with 10 cycles as the boundary point.The NHL modified soil showed a monotonously decreasing trend with serious attenuation.The strength decreased by 89.84%at the maximum after 20 acid-wet and dry cycles,and the compressive and tensile strength decreased to 0.52MPa and 0.23MPa at the minimum,which was only about 1/6-1/10 of that of L-MK modified soil under the same conditions.（2）With the increase of acid-wet and dry-wet cycles,the color of L-MK modified soil yellow and red decreased,while the brightness value increased gradually.With the increase of metakaolin content,the red saturation increased significantly and gradually approached the color parameter of undisturbed soil.After 20 cycles,L-MK modified soil reached the minimum valueΔE（color difference with undisturbed soil）at 8%metakaolin content.NHL modified soil showed a large color shift,which was 6.88 after 20 cycles,reaching the stage of easy recognition by human eyes.（3）Under the condition of long-term acid erosion,the compressive and tensile strength of L-MK modified soil increased in the early stage,and then decreased under the combined action of ion exchange and the formation of expansive substances,and the increasing range of strength increased with the increase of the content of metacolin.The NHL modified soil decreased monotonously,and its strength after erosion in December was only about 1/7 of that of L-MK modified soil under the same conditions,and its strength decayed seriously.（4）The strength of L-MK modified soil increased first and then decreased in alkaline environment due to the presence of a large amount of hydroxyl to promote the polymerization reaction.However,long-term exposure to alkaline environment caused damage to the micro-cementative structure of soil,and a certain amount of silico-oxygen tetrahedron dissolved and the bonding bond of soil particles broke.NHL modified soil showed poor alkali erosion resistance,and its strength decreased by 148%after one age.In water environment,due to the high humidity environment,hydration reaction continued,the content of gelling products increased significantly,and the strength of L-MK increased.（5）Parameter n was introduced into the exponential attenuation model,and combined with linear regression method,the intensity attenuation models of L-MK and NHL modified soil under different erosion and degradation environments were established respectively.The results obtained showed good correlation and high overall goodness of fit.（6）Based on the macro performance and microstructure of L-MK modified soil in acid-dry-wet coupling and long-term erosion environment,it is considered that L-MK has certain color consistency and durability,and can be used as a soil site restoration material in the field of soil site protection.