混凝土坝低温入仓致裂问题探讨

Discussion on cracks caused by low-temperature placing of concrete dam

在大体积混凝土结构温度控制中常采取低温入仓措施来降低混凝土的最高温度，而低温入仓却会给下部已浇混凝土带来一些不利影响，低温入仓对下部已浇混凝土而言是一个冷击过程，会在其表面产生冷击拉应力，该拉应力过大时会导致下部混凝土的开裂，成为后期大坝冷却时出现宏观长大裂缝的诱因。同时部分低温入仓应力会残留于混凝土内，与后期温降应力迭加，也可能引起混凝土开裂。本文对低温入仓引起的冷击温度应力进行分析，并研究了其残余应力对后期应力的影响，从而提出了合理的措施以避免低温入仓引起裂缝。

Low-temperature placing is a main measure in the temperature controlling of mass concrete structures, but this measure will bring some adverse effects if not be used properly. If the pour temperature is too low, it will cause a temperature drop for the old concrete bellow as a cold-blowing process, and this process can cause tensile stress at the surface of lower part. If the tensile stress exceeds the strength of concrete, it will generate cracks at the old concrete of lower part, and these cracks can propagate to some big and long cracks at the latter cooling period. At the same time, partial tensile stress caused by low-temperature placing will remain in concrete, and overlap with the latter thermal stress, which may cause cracking of concrete. This paper calculated the cold-blowing thermal stress caused by low-temperature placing, and analyzed the influence of residual stress on latter stress, and then put forward the reasonable measures to avoid cracks caused by low-temperature placing.