混凝土早期裂纹发展规律

Expansion of Early Age Cracking of Concrete

通过现场实测,对混凝土早期温度、应变随龄期的变化及分布规律进行了深入研究,并在此基础上对条形混凝土结构早期最可能开裂区域、时段进行了研究.结果表明：混凝土早期拉应变经历了急剧上升、下降及稳定3个阶段,前2个阶段的结束时间分别为混凝土灌注结束后36-48 h,192-240 h;混凝土最大拉应变出现在灌注结束后36-72 h;混凝土早期温度经历了上升、下降及稳定3个阶段,前2个阶段的结束时间分别为灌注结束后9-12 h,264-288 h,温度上升阶段混凝土各部分的温度、温度上升速度与墙高以及温度下降阶段混凝土各部分的温度与时间均有较好的统计关系;条形混凝土结构的中下部区域在混凝土灌注结束后24-48 h内开裂的可能性最大.提出了综合考虑混凝土早期拉应变、最大收缩应变及临近区域应变差的裂纹预测方法,该方法能准确预测混凝土早期开裂区域.

The change and distribution rule of early temperature and strain of concrete were examined. Based on these study, some other researches are made concerning when and where will rise the concrete cracks in strip constructions. It has been shown that the early tension strain of concrete has undergone three stages, i.e. sharp rise, decline and stability. The first stage ends when the concrete is poured for 36 -48 h, and the second is for 192-240 h. The maximum tension strain of concrete starts when the concrete is poured 36-72 h; The early temperature of concrete undergone three phases： i.e. rise, decline and stability. The first phase ends when the concrete is poured for 9-12 h, and the second is for 264-288 hi In the process of temperature rise, some statistical relationship can be found among temperature of concrete, between temperature of concrete rise rate and the height. In the process of temperature descending, the statistical relationship between temperature and time is obvious too. The early age crack occur most likely in the middle lower part of the strip construction when the concrete was poured for 24-48 h. A relatively accurate prediction of possible cracking zone in the early age of concrete was tensile strain of early age, the largest contraction strain and strain difference of the concrete.