高性能轻骨料混凝土高温后受压本构关系研究

通过对无纤维全轻混凝土、无纤维次轻混凝土、钢纤维全轻混凝土、钢纤维次轻混凝土进行25、200、400、600、800℃五个温度水平的高温后力学性能试验，研究高温作用对未掺钢纤维和掺入不同体积掺量钢纤维增强轻骨料混凝土力学性能的影响。研究结果表明：随受火温度升高，高性能轻骨料混凝土的强度、弹性模量逐渐下降，立方体抗压强度和弹性模量下降幅度大于轴心抗压强度，纵向峰值应变和横向变形逐渐增大，应力-应变曲线渐趋扁平，上升段线性段比例变小，曲线与横轴包围面积逐渐减小;高性能全轻和次轻混凝土均表现出比普通混凝土更好的抗火性能，但是在高温800℃后，高性能轻骨料混凝土也发生了爆裂，掺入钢纤维后并没能消除爆裂现象，但是减小了高温后试块的表面裂缝宽度；钢纤维改善了高温前后轻骨料混凝土的力学性能，使高温前后轻骨料混凝土的弹性模量和峰值应变均有一定程度的提高。通过回归分析，建立高性能轻骨料混凝土的单轴受压分段应力-应变本构方程，其与试验结果吻合较好。

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.