饱和度对混凝土三轴抗压强度的影响试验研究

Experimental Study on Influence of Saturation on Tri-Axial Compressive Strength of Concrete

混凝土结构服役环境非常复杂,其孔隙中自由水饱和度和受力状态因服役环境不同而有较大的区别.为研究不同含水饱和度混凝土在三向受力状态下的力学性质,本文通过干燥、真空饱水、自然蒸发3个步骤制作了0、50%和100%3种饱和度、2种强度等级的混凝土试件.试验采用了长径比2∶1的圆柱体和边长50 mm的立方体两种形状的试件.对总共60余个混凝土试件进行了无侧限单轴压缩试验和不同围压下的三轴压缩试验.试验结果表明:随着饱和度的增加,混凝土材料的单轴抗压强度逐渐降低,且普通强度混凝土的下降幅度比高强度混凝土高;在围压条件下,不同含水饱和度的混凝土试件轴向抗压强度均有所提高,普通强度混凝土的三轴强度比高强混凝土提高的幅度更大,且饱和度高的试件对侧向压力更为敏感,这主要是由于多向应力条件下产生的孔隙水压力作用;根据所得到的试验结果,基于Mohr-Coulomb强度准则建立了考虑饱和度影响的混凝土强度模型,用于指导混凝土结构在不同湿度服役环境下的设计,提高设计的可靠性.

The service environment of concrete structures is complex,and the free water saturation in pores and the stress state of concrete vary greatly due to different service environments.To study the mechanical properties of con-crete with different water saturations under tri-axial loads,two grades of concrete specimens with 0,50%and 100%saturations were fabricated by oven drying,vacuum suction and natural evaporation processes.Two forms of speci-mens were used,i.e.,cylindrical specimens with a slenderness ratio of 2∶1 and cubic specimens with a side length of 50 mm.Uniaxial compressive tests without lateral confinements and tri-axial compressive tests under different confin-ing pressures were carried out on more than 60 concrete specimens.Test results show that the uniaxial compressive strength of concrete gradually decreased with the growing saturation,and the decline degree of ordinary strength concrete(OSC)was higher than that of high strength concrete(HSC).Under confining pressures,the axial compressive strength of concrete specimens with different saturations all increased,the improvement in the triaxial strength of OSC was higher than that of HSC,and the specimens with high saturations were more sensitive to the lateral pressure,which was contributed to the effect of pore water pressure under the condition of multi-axial stress state.According to the obtained test data,a strength model of concrete which is based on the Mohr-Coulomb criterion and takes into account the influence of water saturation is established to guide the design of concrete structures under service environ-ments with different humidities,thereby improving the reliability of structural design.