Compressive behaviour of high performance lightweight concrete after high temperature

Through the post-fire mechanical tests on all-lightweight concrete, semi-lightweight concrete, steel fiber all-lightweight concrete and steel fiber semi-lightweight concrete after the exposure to five temperature levels, i.e., 25, 200, 400, 600, 800℃, the influence of high temperature on the mechanical properties of high performance lightweight concrete (HPLWC) with different steel fiber volume content was studied. The test results show that: with the increase of exposure temperature, both peak stress and elastic modulus have a certain decrease, and the loss of elastic modulus and cubic compressive strength is faster than that of the axial compressive strength, the axial peak strain and lateral deformation have a certain increase, the stress-strain curves are gradually flattened, the linearly ascending portions of the stress-strain curve are shortened and the area surrounded by the curve and the X axis is also reduced significantly. Compared with normal-weight concrete, both the all-lightweight concrete and semi-lightweight concrete have excellent capacity in resistance to high temperature, but their potential of explosion spalling is higher after exposure to temperatures higher than 800℃. Adding steel fibers did not eliminate the phenomena of explosion spalling, but it reduces the surface crack width after exposure to temperature. The inclusion of steel fibers also improves the mechanical property of HPLWC, improves the elastic modulus of lightweight concrete to an extent before and after the exposure of high temperature. Through regression analysis, the segmented constitutive equation of HPLWC under uniaxial compression was proposed to fit the test results, and the fitting curve was in good agreement with the test results. © 2019, Editorial Office of Journal of Building Structures. All right reserved.