Analysis Of Filling Capacity And Interfacial Failure Characteristics Of Rock-filled Concrete

With the rapid development of economy and infrastructure,as a new technology for mass concrete construction in recent years,rock-filled concrete(RFC)is developed on the basis of selfcompacting concrete(SCC)technology and has many advantages such as faster construction speed,low cost,high comprehensive performance,less CO2 emission,etc.RFC technology has been widely applied in concrete engineering such as water conservancy,hydropower,dam,railway and port.However,the filling performance of self-compacting concrete used in the actual RFC construction greatly affects the mechanical properties and durability of RFC.Therefore,two core problems in RFC construction are the compactness of SCC filling the gap of rockfill under the action of dead weight without vibration,and the large-size interface bonding state between rockfill and SCC after RFC forming.By conducting a series of experiments and simulations,this thesis aims to explore the fundamental mechanism of these two issues and analyze the influence of related parameters,which may provide theoretical and experimental basis for designing,choosing suitable parameters and quality evaluation of RFC construction projects.The main contents and conclusions are as follows:(1)Through the improvement of the expression of ellipsoid in Matlab2016a,an efficient and fast random polyhedron particle generation method was proposed to simulate the real shape of the coarse aggregate,which was close to the actual state.Then,the clump generated by Bubble Pack algorithm was used to fill the polyhedron shell to simulate the coarse aggregate element.SCC discrete element model was established according to real gradation,the rheological characteristics of the yield stress τ0(normal bonding strength σc)and plastic viscosity η(the critical damping ratios βn/βs)were verified as Bingham model parameter.Finally,L-box simulation tests with different rheological properties were carried out and compared with laboratory test results.(2)Based on excess paste theory,a 3D numerical model based on the discrete element method(DEM)was proposed through secondary development of contact model.The SCC was assembled from the granular elements that are enveloped by the virtual mortar with a certain thickness.Slump test was used to calibrate the microscopic parameters of SCC,the pouring process of the calibrated SCC in a rockfill was simplified as L-type flow.Then a standard L-box had been modified with different size glass marbles inside which could replace the actual rockfill.The filling capacities and casting speed of SCCs with different properties in different types of rockfill were analyzed.The results showed that the filling effect increased with the decrease in the yield stress of the SCC and the increase in the void ratio of the rockfill.Average compactness of the SCC increased with the increase in the void ratio of the rockfill and the compactness of each part of a SCC decreased with an increase in the filling distance.(3)18 sets laboratory tests of uniaxial compression,cubic splitting tensile and four-point bending of SCC were carried out,and the relevant mechanical strength indexes and macroscopic interface failure characteristics were obtained.Meanwhile,a discrete element model of the same size mechanical test was established by using the flat joint contact model(FJM)to achieve the mechanism of crack formation and propagation in the failure process of SCC.Finally,the influence of interface transition zone(contact between mortar particles and aggregate particles)and initial defects(non-bonded contact Type S in FJM model)on the strength and failure characteristics of SCC was analyzed,which laid a foundation for the subsequent RFC research.(4)Two large RFC samples of 450 mm × 450 mm × 1200 mm were prepared.They were cut into RFC samples of different sizes.The axial uniaxial compression,cubic splitting tensile and four-point bending tests were conducted,and the strength and interface failure characteristics of RFC were acquired by comparing with SCC.At the same time,a three-dimensional discrete element model of RFC containing a breakable rockfill(cluster)was established using Brick technology,and the mechanism of crack formation and propagation in the failure process of RFC was achieved.Finally,the influence of rockfill content,SCC strength and the strength of the interface between rockfill and SCC on the strength and interface failure characteristics of RFC were researched.