气冻气融作用下混凝土抗冻性及损伤层演化规律研究

摘要

采用气冻气融的方式,分别对C30、C40、C50、C40(商品混凝土,简称商混)4组不同配比试块及1组C40(商混)的足尺(150 mm×300 mm×2 700 mm)钢筋混凝土梁进行冻融耐久性试验.用超声波平测法测定不同冻融循环次数时的混凝土损伤层厚度,研究冻融对混凝土损伤层厚度的影响规律;通过与传统抗冻性评价指标劣化规律的对比分析,提出以冻融损伤层厚度为损伤变量的评价标准,结合实际损伤特点,对所提出损伤变量进行相应修正,并验证其合理性;建立混凝土冻融损伤层厚度的随机预测模型;通过案例分析,验证模型的适用性,讨论冻融环境下混凝土最小保护层厚度的问题.研究结果表明:随着冻融循环次数的增加,混凝土相对动弹性模量、抗压强度逐渐减小;试件质量略有增大;冻融损伤层厚度逐渐增大,即冻融损伤度逐渐增大,且强度越低,损伤度越大;冻融环境下混凝土结构的最小保护层厚度偏于不安全.%This paper studied the damage layer thickness of four groups of specimens of different mix proportion and one group of full-scale (150 mm×300 mm×2 700 mm) reinforced concrete beams by using the methods of air-freezing and air-thawing.The concrete damage layer thickness under different freeze-thaw cycles was detected by using ultrasonic testing method to study the influence of freeze-thaw on the damage layer thickness of concrete.By comparing with the deterioration law of traditional frost resistance evaluation index, the new damage variable based on damage layer thickness of concrete was presented, and was modified according to the characteristics of the actual damage, before the rationality of the variable was verified.The random prediction model of the thickness of freeze-thaw damage layer was established.The applicability of the model was testified by case study and the minimum concrete cover thickness was discussed.The research results showed that, with the increasing of freeze-thaw cycles, the relative dynamic elastic modulus and compressive strength of concrete decreased gradually.The mass of the specimen slightly increased.The damage layer thickness increased gradually under freeze-thaw, causing lower compressive strength of concrete and greater degree of damage.The minimum protective concrete cover thickness of the concrete structure under freeze-thaw environment was considered to be insecure.