Road Performance And Microstructure Analysis Of Cement-stabilized Weathered Sand

With the main battlefield of traffic construction in China gradually shifting from plain to mountainous area,problems such as padding shortage and insufficient supply of subgrade become more and more serious.How to effectively utilize resources along the project is an urgent problem to be solved in road construction.Most mountainous and hilly areas in China are rich in weathered sand resources.As an intermediate product of weathering process of surface rocks,the physical and mechanical properties of weathered sand are unstable and its durability is worse than that of general packing materials.The scientific evaluation of weathered sand and reasonable improvement measures are put forward to make it have good road performance,which will effectively solve the problems of shortage of high-quality filler and transportation difficulties during road construction in mountainous areas,and reduce the handling and disposal of weathered sand.It is of positive significance to protect the natural environment and reduce project cost.Based on the technical innovation project of Shandong Province,Research and Application of Weathered Sand in Highway Construction in North Middle-low Mountains and Hills,this thesis systematically studied the road performance and micro-characteristics of cement stabilized weathered sand.First,on the basis of grasping basic physical and mechanical properties of weathered sand,a series of laboratory tests were carried out to determine the influence of cement content and curing age on mechanical properties of weathered sand.Secondly,through the dry-shrinkage test,dry-wet cycle test and freeze-thaw cycle test,the influence of external environment changes on the durability of cement stabilized weathered sand is analyzed.Thirdly,the microstructure characteristics of cement stabilized weathered sand under different conditions are analyzed by SEM test.On this basis,the strength growth mechanism of cement stabilized weathered sand and the deterioration mechanism under wet-dry and freeze-thaw cycles are discussed.The main research contents and conclusions are as follows:(1)The natural water content of weathered sand is 3.1%,the content of gravel group is24.5%,and the content of sand group is 75.5%,which belongs to well-graded sand;In the larger weathered sand grains,the main components are quartz and aluminosilicate of sodium;The optimum water content of weathered sand is 8.03%,the maximum dry density is 2.13g/cm~3,the CBR value is 51%,the compressive rebound modulus is 106 MPa,and the unconfined compressive strength is 0.19MPa.When the weathered sand is used as the subbase packing,its compressive strength can not meet the specifications.(2)The compressive strength of cement stabilized weathered sand is linearly related to curing time,when the cement content exceeds 3%,the unconfined compressive strength can meet the requirements of specifications in 7d,but the increasing rate of compressive strength is significantly reduced;Increasing effect of cement content on splitting strength is obvious;When the cement content is 3%,the compressive rebound modulus of stabilized weathered sand for7d is significantly improved,the linear relationship between cement content and compressive rebound modulus is presented when curing age is 28d.Considering economic benefit,environmental benefit and engineering property of cement stabilized weathered sand,the optimum cement content is determined to be 3%.(3)Increasing the cement content can reduce the water loss rate and increase the dry shrinkage of the specimens,the total shrinkage coefficient increases with the increase of cement content;The unconfined compressive strength of cement stabilized weathered sand decreases with the increase of wet-dry and freeze-thaw cycles,first 6 times wet-dry cycles have a great influence on the strength of the specimens,and the loss rate of strength exceeds 36%;After 9freeze-thaw cycles,the strength loss rate of the specimens is as high as 55%.(4)Weathered sand particles are not closely arranged with porous and cracked particles,when cement is added,the hydrated calcium silicate CSH and alunite AFt formed by hydration products adhere to the surface of soil particles and form aggregates,which can effectively fill the pore of soil body,the more orderly orientation of soil particles arrangement results in the transition of the connection between soil particles from point-to-edge connection to edge-to-edge connection and edge-to-surface connection.(5)With the increase of the number of wet-dry cycles,the hydration products gradually disappear,the cracks in the specimen become larger and larger,and the increase of cracks leads to the decomposition of large particles.With the increase of the number of freeze-thaw cycles,the adhesion between the particle surface and hydration products decreases,the particle surface becomes smooth,the distance between the particle and the particle increases,and the dense skeleton structure gradually develops into the framework-pore structure.In general,both wet and dry cycles and freeze-thaw cycles reduce the average diameter of particles,which indicates that the internal failure of the specimen is consistent with the reduction of its macro-mechanical strength.