Research On Compression Resilient Modulus And Meso-skeleton Characteristics Of Cement Stabilized Crushed Rock Material

The range of cement dosage has been increased in the new edition of “Technical Guideline for Construction of Highway Roadbase”,which leads to an increase of base modulus.Noticeably,the increase not only caused confusion for pavement designers in how to determine material modulus value of a base,may but also aggravate the contradiction between the base modulus and cracks.Furthermore,material modulus of a semi-rigid base is still a significant index of construction quality control,but the parameter of semi-rigid base construction quality control(Unconfined Compressive Strength)does not match the structure design parameters(Compression Resilient Modulus and Flexural tensile Strength),which makes design conformity testing not achieved.Therefore,it is relatively important to carry out research on the compression resilient modulus of cement stabilized crushed rock materials(CCRM)based on the new technical guideline.On the other hand,vertical vibration compaction method(VVCM)has been paid much attention to when the mechanical properties of CCRM are evaluated,but the determination of indoor vibration parameters like vibration time are too empirical,which results in the fact that it is still impossible to accurately establish the matching relationship between the indoor compaction work and the field compaction work.Meso-skeleton characteristics of CCRM can not only reflect the meso-structure characteristics of CCRM,but also indirectly capture the macroscopic mechanical properties of CCRM.Obviously,it is reasonable to use CCRM meso-skeleton indices to analyses the matching performance between laboratory-produced CCRM using different compaction methods and the field CCRM.First of all,the compression resilient modulus evaluation tests of laboratory-produced CCRM compacted by different compaction methods and different compaction works were carried out based on the cement and the crushed rock of Guangdong Province.Furthermore,the elastic-plastic properties of CCRM at different load stages and the impact of different loading stages on the accuracy of resilient modulus measurement were analyzed,and the comprssion resilient modulus values matching the new technical guideline were obtained.Next,the regression relationships between the compression resilient modulus and the compressive strength,flexural tensile strength and dry shrinkage coefficient of CCRM were established.The results show that it is more reasonable to divide the preload pressure into 5-6 equal parts as compression resilient modulus of CCRM is measured.CCRM mainly experiences false elastic deformation stage,elastic deformation stage and elastic-plastic deformation stage.The compression resilient modulus of CCRM matching the new technical guideline ranges between 1387 MPa and 1986 MPa.Moreover,the research on the meso-structure evaluation method of CCRM was carried out.The extraction process of coarse aggregate in CT digital images of CCRM was elaborated,and the relationship between manual revision and computer automatic processing for digital images was summarized.Different skeleton tightness influenced regions of coarse aggregates were defined and compared through the self-developed MATLAB program.Next,the skeleton comprehensive embedding index in cross sections and the skeleton stability index in longitudinal sections were defined to capture tightness and stability of CCRM skeleton respectively.Subsequently,the skeleton comprehensive embedding index of different cross sections in CCRM specimens compacted by VVCM and gyratory compaction method were compared,and the variation laws of the meso-skeleton indices of CCRM as different compaction methods and their different compaction works were explored.The correlations between meso-skeleton indices and compressive strength for a 7-day period,resilient modulus for a 90-day period of CCRM were established.Finally,the test fields were constructed in the Qingyun Expressway project.Compactness,compressive strength and meso-skeleton indices of the field CCRMs compacted by different rolling schemes were detected,and the correlations between Compactness,compressive strength and meso-skeleton indices of the field CCRMs,and specific rolling process were analyzed.Next,the compression resilient modulus of the base was predicted based on the established regression relationships between compressive strength and compression resilient modulus of CCRMs compacted by different methods.Subsequently,the compressive strength and meso-skeleton indices of the field CCRMs compacted by a standardized rolling scheme were compared to that of laboratory-produced CCRMs compacted by different compaction methods.The results show that the compaction of a rubber wheel mainly improves the degree of skeleton tightness of CCRM,while the vibration compaction of a 22 t steel wheel mainly enhances skeleton stability of CCRM.The representative strength and meso-skeletion indices of the field CCRM compacted by a standardized rolling scheme have an agreement with that of the CCRM compacted by VVCM for 90 s,and thus the CCRM compacted by VVCM for 90 s matches the field CCRM with common gradation compacted by the representative rolling scheme when constructing semi-rigid bases in Guangdong Province,China.