ALBERT

Description: The realization of reducing concrete self-weight is mainly to replace ordinary aggregates with lightweight aggregates; such replacement usually comes with some intrinsic disadvantages in concrete, such as high brittleness and lower mechanical properties. However, these shortages can be effectively remedied by external confinement such as fiber reinforced polymer (FRP) jacketing. To accurately predict the stress-strain behavior of lightweight concrete with lateral confinement, it is necessary to properly understand the coupling effects that are caused by diverse aggregates types and confinement level. In this study, FRP-confined lightweight concrete cylinder with varying aggregate types were tested under axial compression. Strain gauges and linear variable displacement transducers were used for monitoring the lateral and axial deformation of specimens during the tests. By sensing the strain and deformation data for the specimens under the tri-axial loads, the results showed that the lateral to axial strain relation is highly related to the aggregate types and confinement level. In addition, when compared with FRP-confined normal weight aggregate concrete, the efficiency of FRP confinement for lightweight concrete is gradually reduced with the increase of external pressure. Replace ordinary fine aggregate by its lightweight counterparts can be significantly improved the deformation capacity of FRP-confined lightweight concrete, meanwhile does not lead to the reduction of compressive strength. Plus, this paper modified a well-established stress-strain model for an FRP-confined lightweight concrete column, involving the effect of aggregate types. More accurate expressions pertaining to the deformation capacity and the stress-strain relation were proposed with reasonable accuracy.

Description: Natural rock masses have many internal joints, fractures and faults, which greatly influence their mechanical properties during geological processes. In this paper, considering different joint angles and rock-bridge angles, uniaxial compression numerical tests on double-fractured red sandstone based on particle flow code (PFC) were carried out. The influence laws of the mechanics, acoustic emission (AE) and damage evolution characteristics of double-fractured sandstone under different crack geometry conditions were analysed. The results indicated that the peak stress and elastic modulus increase with increasing fracture angle. The peak stress and elastic modulus of rock samples first increase and then decrease with the increase in the rock-bridge angle, exhibiting a nonlinear distribution; when the angle β (rock-bridge angle) is less than or equal to 45°, the peak strain differs only slightly and decreases gradually with the increase in the rock-bridge angle. There are three stages in the AE evolution of fractured red sandstone: The initial emission of AE, the increase in AE and the decline in AE. The influences of different fracture angles and rock-bridge angles on the AE characteristic rule of rock samples vary. The damage evolution process of sandstone specimens with different joints can be divided into four stages: Initial damage, stable increase, accelerated development and stable damage. The fracture angle mainly affects the damage stage. The smaller the angle of the crack is, the greater the strain value in this stage. The rock-bridge angle mainly influences the damage variable evolution during the stable increase, accelerated damage development and stable damage stages.