Research On Interfacial Properties Of Rubberized Concrete

With the rapid development of transportation industry and rubber sheet industry,waste rubber has caused tremendous pressure on the natural environment.At the same time,as the main building and traffic engineering materials,the brittleness of concrete is one of the important reasons leading to the deterioration of structural performance.Rubberized concrete is a new type of concrete which is mixed with rubber aggregate in ordinary concrete matrix.It can not only make use of waste rubber resources,but also improve the toughness of concrete.One of the main shortcomings of ordinary rubberized concrete is that the interface connection between rubber and cement matrix is poor,which leads to a sharp decline in compressive strength and other properties with the increase of rubber content,which is one of the key problems to be solved in the popularization and application of rubberized concrete.In this paper,by improving the rubber-cement matrix(R-CM)interface,the interface performance of rubberized concrete will be optimized under certain conditions,and the mechanical properties and working properties of rubberized concrete will be improved.The experiments were carried out in four sections.Firstly,the reference concrete(RC)and reference rubberized concrete(RRC)were designed.The different kinds of supplementary cementitious materials(SCM)were selected to replace RRC different portions of cement in RRC with equal quality.The slump,apparent density,compressive strength and IZOD impact strength were measured to determine the best SCM and its content.Secondly,the evaluation index and test method of the bonding property between rubber and cement matrix are put forward.Different kinds of rubbers were selected to bind with binder paste,respectively.The tensile bond strength and shear bond strength of rubber-binder paste(R-B)of all specimens were tested,and the rubber types with better bond performance and economy were selected.Thirdly,rubber type,surface modifier,mixing method,SCM,water-binder(W/B)ratio and mixing time are selected as factors.The bond strength of R-CM was determined by orthogonal test,and the optimum combination conditions of the interface properties of R-CM were determined.Finally,the above properties of improved rubber concrete(IRC)are determined,and the interfacial structure was observed.Then the research and analysis were carried out.The test results show that compared with RRC,the interface connection,compactness and mixtures slump of IRC is obviously improved.Tensile bond strength of R-CM,shear bond strength of R-CM,compressive strength and IZOD impact strength of IRC increased by 75.6%,151%,48%and 17%,respectively.Compared with RC,the impact strength and mixture slump of IRC are improved in varying degrees,and the compressive strength is reduced by only 21.7%.The compressive strength of IRC and its mixture slump meet the highway pavement requirements of strength and construction under light traffic load,respectively.The highest bonding strength of R-CM is "acrylonitrile-butadiene rubber(NBR),W/B of 0.42,mixing time of 150 s,styrene-butadiene latex(SBL)as surface modifier and SCM,premixing of rubber and binder paste".The main factors affecting the bonding performance of R-CM are rubber type,surface modifier,mixing method and W/B.As a surface modifier,SBL plays a strong connecting role between NBR and binder paste.As an auxiliary cementing material,SBL creates conditions for reducing W/B of concrete.When the solid content of SBL or emulsified asphalt(EA)replaces 5%cement,the comprehensive performance of rubberized concrete is the best,and the compressive strength,mixture slump and interface are improved.Due to the effect of emulsifier,SBL has a remarkable effect on improving slump of mixtures.EA is easy to fill the pore of concrete,which increases the apparent density and compressive strength of rubberized concrete.Sodium silicate is not suitable to be added into rubberized concrete as a SCM because it can promote freezing and water absorption from cement mixture.R-B bonding strength from large to small was ranked as fluorine rubber>NBR>Natural Rubber>silicone rubber>polyurethane rubber.When SBL is substituted for 10%cement by same solid content,the average comprehensive bond strength of R-B is the highest.Adhesion between rubber and binder paste are by mechanical occlusion,bonding and molecular entanglement.Emulsifiers and defoamers in latex have influence on interfacial bonding performance.Tensile bond strength and shear bond strength of R-B increase first and then decrease with the increase of SBL content.The peak value of tensile bond strength is higher than that of shear bond strength.The difference is mainly caused by the roughness and friction of the interface between rubber and binder paste.With the improvement of R-CM interface and the increase of bond strength,the compressive strength,impact strength and compactness of rubberized concrete increase correspondingly,and the impact ductility decreases.R-CM interface plays a leading role in the macro-mechanical properties of rubberized concrete.Compressive failure of rubberized concrete occurs preferentially on the CM of R-CM,and its interfacial bond strength is the key factor to resist crack propagation and compressive failure of rubberized concrete.The impact damage of rubberized concrete occurs preferentially in the stone(sand)-cement interface transition zone near the impact site.The R-CM condition is an important factor affecting the impact notch propagation path and impact strength of rubber concrete.The tensile failure mode of RRC is brittle fracture and interfacial failure,while the tensile failure mode of IRC is ductile fracture and mixed failure.