Comparative Study On Mechanical Properties Of Cement Stabilized Base Course Paved Continuously And Discontinuously

Cement stabilized base is widely used in all kinds of highways in our country because of its high strength and rigidity,good road performance and easy access to materials.According to the structural requirements of the road design,the design value of the thickness of the expressway base in China is generally more than 30 cm,but limited to the lack of large-scale pavers and limited power in the actual project,the whole one-time paving base is prone to construction quality problems.In order to solve this problem,the traditional base construction divides the mixture into two layers and paves them separately,that is,to pave the upper base layer after the lower base layer mixture is paved and rolled and kept in good health for seven days,which is contrary to the design idea of the base layer,and there are many defects in actual use.Therefore,in recent years,there has been a layered continuous paving construction technology.Some studies have shown that the use of this construction technology can shorten the construction period and save costs.At the same time,the level of pollution between layers is greatly reduced,and the connectivity between layers becomes stronger,so as to improve the integrity of the base.Considering the decreasing law of stress transfer along the subgrade depth direction caused by load,when the base course is spread in two layers,the use of the same mixture composition in the upper and lower base courses will cause the waste of the lower mixture strength to a certain extent,and the combination of different base materials will have different effects on the overall mechanical properties of the base course?In this study,two types of test pieces composed of different mixture are designed,each type of test piece simulates the construction technology of two-layer continuous paving and intermittent paving respectively,in which the test pieces of intermittent paving are disposed between layers,and the two types of test pieces are used in different curing period(7d,30d)and three test conditions(normal temperature,low temperature,freeze-thaw),and the same compaction standard is used for unlimited side According to the characteristics of continuous paving,through the unconfined compressive strength and direct shear strength tests,the influence of different compaction degree of lower layer on the mechanical properties of continuous paving base is analyzed.In the research process,the theoretical design system of road cement stabilized base is proposed from the aspects of aggregate mix ratio,paving technology,compaction method,etc.The results show that the unconfined compressive strength and splitting shear strength of the two kinds of materials are better than those of the discontinuous paver,and the order of the mechanical properties of the layered discontinuous paver is:whether there is water slurry pollution between layers>whether there is cement slurry pollution between layers>whether there is cement slurry pollution between layers>whether there is cement slurry pollution between layers;at different temperatures Under the test conditions,the strength data of each group of test pieces show that:low temperature>normal temperature>freeze-thaw,the base of the structure combination of water stabilized macadam and cement stabilized soil is more sensitive to the low temperature and freeze-thaw conditions,and the influence of different interlayer treatment and temperature test conditions on the strength decreases with the increase of curing period.The compressive strength and direct shear strength of the continuous paving base course are related to the compactness of the lower layer:in the process of the compactness of the lower layer increasing from 69%to 96%,when the compactness of the lower layer is low,it can promote the early strength of the base course,the unconfined compressive strength has an increasing trend,while the direct shear strength has a decreasing trend,and the growth rate of the direct shear strength of the base course with two layers of cement stabilized macadam is higher than that with water stabilized macadam and water stabilized macadam In terms of the reduction rate of compressive strength and direct shear strength under the freeze-thaw test conditions,in the range of 75-85%of the compactness of the lower layer,it has a greater impact on the base combined with cement stabilized macadam and cement stabilized soil.The research conclusion has certain theoretical support significance and practical significance for the structure design of water stable base mixture and the expanding application of layered continuous paving construction technology.