Theoretical And Experimental Studies On The Bond-Slip Constitutive Relation Between High Fluidity Reactive Powder Concrete And Reinforcement Bars

Reactive Powder Concrete(RPC),as a new type of concrete material,has been widely used in high-rise buildings and long-span bridge structures with higher mechanical properties and better durability than the ordinary concrete.It has brought great promotion to civil engineering and social and economic development.For the preparation and mix design of RPC,most studies only pursue high mechanical properties,but ignore the ease of construction,fluidity and economy.In addition,the mechanism of bonding and anchorage performance,the distribution of internal bonding stress,the relationship between bonding and slipping,and the length of anchor overlap needed in structural design of this new material are all the directions to be studied urgently,which provide important experimental and theoretical support for the design and application of RPC in civil engineering.In this dissertation,the optimal mix ratio of RPC with high fluidity and the pull-out experiments under different parameters were studied.The specific contents and conclusions are as follows:(1)Based on the orthogonal experiments,the effects of water-binder ratio,sand-binder ratio,steel fiber,fly ash,silica fume and water reducer on the fluidity and compressive strength of RPC were systematically studied.The optimum mixing ratio was obtained by considering the requirements of fluidity,strength and economy.The RPC with flowability of 230 mm and compressive strength of 150 MPa was prepared.The relevant formulas are fitted based on the experimental datas(2)Based on the thick-walled cylinder model,the formula for calculating the annual strength of RPC and steel bars is derived from the analytical method of elasticity,which provides a theoretical support for calculating the bonding strength.(3)A series of pull-out experiments were carried to study bonding performance,where the main parameters including anchorage length,thickness of protective layer,diameter of reinforcing bar,whether or not stirrups,stirrup ratio and steel fiber content.Then,the relationships between the average bonding stress and free-end slip under each parameter are obtained,and the characteristics and causes of these curves are analyzed.Based on the bonding experimengts,the advising anchorage length and ultimate anchorage length are provided for the structural design.(4)Through the groove on the steel and the strain gauge sticking in the groove,the stress was measured along the steel bar in the anchorage section.The relationship curve of the bonding stress with the relative position of the anchorage section was obtained with the strain distribution,and the function between the bonding stress and position along the steel was fitted and obtained under each parameter,which is used to describe the real bonding-slip relationship.A bonding-slip constitutive model of three-fold line segment is proposed.The model takes account of the comprehensive influence of various parameters and agrees well with the experimental results.ABAQUS finite element method is used to verify the accuracy of bonding-slip of RPC,which is in good agreement with the experimental value with good research reference value.