Study On The Fracture Behavior Of Lightweight Aggregate Concrete

Lightweight Aggregate Concrete (LWAC) is considered as a three-phase composite material in mesoscopic level. It is composing of matrix (mortar), inclusions (lightweight aggregate) and the bond layer between the mortar and the lightweight aggregate. In this paper, a procedure that adopts the take-and-place method is used to generate random aggregate structures based on the Monte Carlo random sampling principle. The random aggregate structure in which the shape, size and distribution of the aggregate particles resembles real concrete. Then meshing the aggregate domain and the mortar matrix domain separately using finite element analysis software—ANSYS and generating four-node element. After the different material properties are assigned to respective elements according to the locations of elements in individual phases, a two-dimensional numerical model for the compositestructure of LWAC is formed. The numerical experiment can be carried out using nonlinear finite element analysis.Quasi-static simulation of LWAC are performed with LS-DYNA a finite element analysis software. To reduce the computational time, two methods have been used: firstly, increasing the speed of quasi-static loading; secondly, using Mass Scaling method. In order to get accurate results, appropriate failure criterions are adopted in quasi-static simulation about fracture process of LWAC (introducing the maximum tensile stress criterion subjected to uniaxial tension and three point bending test, and adopting Mohr-Coulomb criterion subjected to uniaxial compression).With the finite element method, it can be found that the bond between matrix and lightweight aggregate has few effect on the macroscopic mechanical performance of LWAC, and the numerical test on fracture of LWAC specimen subjected to uniaxial tension further proves that the mechanical properties of the aggregate are important to the fracture of the LWAC. So it is reasonable to consider LWAC as a two-phase composite material in studying fracture process of LWAC.Then numerical simulation is made of the fracture process of LWAC specimens under uniaxial tension, compression and three point bending test, the results show that the fracture characters of LWAC are different from common concrete. Those cracks run through the aggregate instead of being blocked, causing the LWAC breaking abruptly and it shows a stronger brittleness characteristic.Through the model tests of the three-point bending fracture with Scanning Electron Microscope (SEM), the mechanisms and fracture process of LWAC in mesoscale level have been systematically investigated. The experimental results are consistent with numerical simulation outcome. Thus it can be seen that the numerical method above is feasible and effective.