早龄期持续拉力对混凝土性能的影响

为研究早龄期持续拉力对混凝土后期力学性能的影响,设计了7个系列共77个混凝土试件,探讨早龄期持荷轴拉比、持荷时间、混凝土强度等3个因素对混凝土后期轴心抗压性能的影响规律。为此,制作了对6个混凝土试件同时施加持续拉力的试验装置,龄期1.5d时开始施加轴向拉力,持荷一定时间后卸载,龄期28d时进行轴心抗压试验。持荷轴拉比和持荷时间对混凝土后期轴心抗压性能有一定的影响:持荷时间为7d时,轴拉比为0.15和0.3试件后期轴心抗压性能基本没有劣化,而轴拉比为0.5时试件产生了不可自愈的损伤,初始弹性模量、轴压峰值应力下降、峰值应变增大;轴拉比为0.3的试件持荷时间增加到14d,混凝土后期性能产生了劣化。混凝土强度等级越低,早龄期持续拉力对其弹性模量的影响较大,但峰值应力和峰值应变的影响相对较小。在试验结果的基础上,采用最小二乘法回归得到了持荷时间和持荷轴拉比对混凝土初始弹性模量、峰值应力与峰值应变的早龄期持荷影响系数。最后,在普通混凝土的应力应变关系的基础上考虑早龄期持荷影响因数,得到了受早龄期持荷影响的混凝土应力应变关系。

Experimental study of early continuous tension influence on concrete properties

In order to study the influence of early continuous tension on the mechanical properties of concrete in the later period including concrete''s axial compressive properties and cleavage strength, the tensile test of 7 series of concrete specimens which bear early continuous load is carried out, with three factors of the axial tension ratio, loaded time and concrete strength in consideration. Meanwhile, test device is designed that applied continuous tensile load on 6 prism specimens at the same time when the early age is 1.5 days. The tensile load is applied for some time then unloaded and at 28 days age the test of prism specimens'' axial compressive strength is carried out. The results show that the ratio of axial tension and continuous time of load have some effects on concrete''s axial compressive properties in later days. When loaded time of is 7 days, there is no obvious influence on concrete''s axial compressive properties no matter what the ratio of axial tension is 0.15 or 0.3. However, when the ratio of axial tension is 0.5, prism specimens'' damage is irreversible, with its initial elastic modulus, peak compressive strength decreasing and peak strain increasing. When loaded time is 14 days, the properties of the prism specimens whose axial tension ratio is 0.3 deteriorate. The lower the strength grade of concrete, the larger the early age continuous tension influence on elastic modulus, but the influences on peak stress and peak strain is relatively small. The least square method is used to get the influence coefficient, which bases on loaded time and loading conditions'' effect on concrete''s initial elastic modulus, peak stress and peak strain. Based on the stress-strain formula of ordinary concrete, the stress-strain formula of concrete that bear continuous loading at early ages are proposed.