Research On Shear Characteristics Of Interfaces Between Different Geosynthetics And Recycled Concrete Aggregate

In recent years,with the rise of construction projects and the deepening of urbanization,construction and demolition(C&D)waste increases year by year,As the main component of C&D waste,waste concrete is recycled and effectively used as one of the current research hotspots.In order to make the waste concrete better used in roadbed engineering,its interface shear strength is one of the key technologies.At present,the direct shear test is the most widely used technique to study the behavior of the interface between soil and reinforced materials.In this paper,through sheartrac III indoor large-scale direct shear apparatus manufactured by geocomp company in the United States,A series of experimental studies on the interface monotonic direct shear and cyclic shear characteristics of interface between different geosynthetics and recycled concrete aggregate under different conditions are carried out,Mainly completed the following tasks:(1)In order to investigate the interface shear characteristics between different geosynthetics and Recycled Concrete Aggregate(RCA),focused on the analysis of five kinds of geosynthetics including the biaxial polypropylene geogrid(PG),geonet(GT),warp knitted polyester geogrid(WK),glass fiber geogrid(FG)and woven geotextile(WG)Influence on the interface shear characteristics of Recycled Concrete Aggregate(RCA).The results show that the shear strength of the interface increases and decreases with the addition of five different reinforced materials;the reinforced geosynthetics-recycled concrete can effectively suppress the shear dilation of RCA,and the change law of internal friction angle is consistent with the change law of material interface enhancement coefficient.Finally,the aperture size of the bidirectional polypropylene geogrid has a significant effect on the mechanical properties of the RCA reinforced interface: the interfacial shear strength first increases and then decreases with the increase of the ratio of mesh size to material median particle size(grain-hole ratio).It is concluded that there is an optimal range of grain-hole ratio between geogrids and RCA.(2)In order to study the cyclic shear and post direct shear characteristics of the interfaces between five different geosynthetics and Recycled Concrete Aggregate(RCA),a series of Monotonic Direct Shear(MDS),Cyclic Direct Shear(CDS)and Post Cyclic Direct Shear(PCDS)tests were carried out under different normal stresses and cyclic shear displacement amplitudes.a comprehensive comparative analysis of the results of the post-cyclic direct shear test and the monotonic direct shear test is carried out.Under the action of cyclic direct shear the test results show that the five types of stiffened interface interface become obvious shear hardening,the shear stiffness and damping ratio of the five types of stiffened interfaces showed a development trend of gradually increasing and gradually decreasing with the increase of the number of cycles.The amount of shrinkage the PG-RCA interface under the 5,10,15 mm cyclic shear amplitude conditions of this test increases significantly with the shear amplitude,the shrinkage increased respectively by 18.6% and 22.2%.In the post-cyclic direct shear test,the five stress-displacement curves of reinforced interfaces show obvious post-peak softening,and the apparent adhesion and the internal friction angle of the interface increase significantly with the cyclic shear.The results of the peak and residual cohesion and internal friction angle in the post-cycle direct shear test are greater than the corresponding results in the monotonic direct shear test.(3)Based on the large-scale monotonic direct shear test of different geosynthetics and recycled concrete aggregates(RCA),The test results show that: The peak values and residual shear stresses of the five different reinforced interfaces have a corresponding relationship with the corresponding dilatancy curve,the peak shear strength of the interface appears when the dilatancy rate begins to decrease,and the residual shear strength occurs at the dilatancy rate When it becomes stable.During the shearing process,the interface strength is softened due to the shearing of the recycled concrete aggregate(RCA)asperities and the wear and fracture of the reinforced materials.Based on the direct shear test of recycled concrete aggregate-geogrids,Based on the direct shear test of recycled concrete aggregate-geogrids,a combined model containing three relational expressions was established to describe the shear change law of different geosynthetics and recycled concrete aggregate(RCA)reinforced interface: The envelope curve of the peak and residual shear strength of the RCA stiffened interface;the hyperbolic function model before the peak of the RCA stiffened interface;the dilatancy model expressed by polynomial.The prediction results of the combined model proposed this time are highly consistent with the direct shear test results of the RCA stiffened interface,indicating that the model is better applicable and accurate.