硫酸盐与冻融复合作用下混凝土劣化规律

Damage degradation law of concrete in sulfate solution and freeze-thaw environment

采用快冻法对混凝土分别在1%Na_2SO_4,5%Na_2SO_4,5%MgSO_4(质量分数)溶液以及水中的冻融情况进行试验,从混凝土相对动弹性模量、抗压强度、损伤层厚度及损伤层混凝土抗压强度等方面研究混凝土的损伤劣化规律,并结合扫描电镜方法,分析混凝土在硫酸盐和冻融循环作用下的复合损伤机理。研究结果表明:混凝土相对动弹性模量变化呈现快速下降、缓慢下降和快速下降3个阶段;抗压强度变化表现为缓慢下降和加速损失2个阶段。随着冻融次数增加,混凝土损伤层中超声波速降低,损伤层厚度增大,损伤层混凝土抗压强度明显降低,混凝土损伤劣化程度增大。混凝土在5%Mg SO4溶液中冻融破坏严重,抗冻性能最差;在5%Na_2SO_4溶液中,混凝土在冻融循环前期劣化程度比水冻的小,冻融300次后劣化程度比水冻的大;混凝土在1%Na_2SO_4溶液中的劣化情况比5%Na_2SO_4溶液和水中的大。

The rapid freezing and thawing test of concrete subjected to 1% Na2SO4 solution, 5%Na2SO4 solution, 5%MGSO4 solution and water was carried out. The degradation rule of concrete base on the relative dynamic modulus of elasticity, the compressive strength loss, the damage layer thickness of concrete and the compressive strength in damage layer was investigated. Moreover, the performance of microstructure of concrete was studied by SEM analysis, and the damage mechanism of concrete in the sulfate solution and freeze-thaw environment was analyzed. The results show that the changes in relatively dynamic modulus of elastically can be described by three stages： an accelerated decreased stage, a slowly decreased stage, and then an accelerated decreased stage. The changes in compressive strength exhibit the following two periods： the slowly decreased period and the acceleratingly decreased period. With the increase of freeze-thaw cycles, the ultrasonic velocity in damage layer is reduced, damage layer thickness gradually increases and the compressive strength in damage layer is decreased obviously, showing that the damage degree of concrete increases. The frost resistance of concrete is the worst in 5% MgSO4 solution. The frost resistance of concrete in 5% Na2SO4 solution is better than that in water during the initial freeze-thaw cycles, but the degradation rate of concrete becomes faster after 300 freeze-thaw cycles. And the degradation rate of concrete in 1% Na2SO4 solution is faster than that in 5% Na2SO4 solution and in water.