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小浪底水利枢纽南岸引水口工程洞室衬砌工程混凝土的设计指标为C_(20)P_8F_(100)。施工条件:泵送,洞外拌和,洞内浇筑,洞内恒温17～18℃。为控制裂缝的产生,施工中采取了以下措施。1 控制干缩裂缝混凝土的干缩裂缝主要是由于毛细管压力造成的。毛细管孔隙在干燥过程中逐步失水,产生很大的毛细管张力,混凝土体积产生收缩,由于混凝土周围存在约束,内部又有拉应力,当拉应力超过混凝土材料抗拉强度时,便产生了干缩裂缝。1.1 降低混凝土单位用水量用水量的增加势必使剩余水增加,从确保混凝土耐久性出发,应降低混凝土单位用水量。1.2 水泥的影响不同水泥、混凝土收缩也不同,按收缩值大小排序:矿渣水泥>普通水泥>粉煤灰水泥。1.3 降低混凝土周围约束若混凝土周围约束过大,内部拉应力无法释放,拉应力增大而使混凝土干裂。应减少混凝土的分仓长度,以使混凝土内部拉应力能够充分释放。
The design index of concrete for lining construction of south bank of Xiaolangdi Hydro Project is from C_ (20) P_8F_ (100). Construction conditions: pumping, mixing holes, pouring inside the cave, the cave temperature 17 ~ 18 ℃. In order to control the generation of cracks, the following measures have been taken during construction. 1 Controlled shrinkage cracks Concrete shrinkage cracks are mainly caused by the capillary pressure. The capillary pores lose water gradually during the drying process, resulting in great capillary tension and shrinkage of the concrete volume. Due to the constraint around the concrete, there is tensile stress in the interior. When the tensile stress exceeds the tensile strength of the concrete material, the capillary shrinkage crack. 1.1 to reduce water consumption per unit of concrete Increased water consumption is bound to increase the remaining water, to ensure the durability of concrete, concrete units should be reduced water consumption. 1.2 The impact of cement Different cements, concrete shrinkage is also different, according to the size of the contraction order: slag cement> ordinary cement> fly ash cement. 1.3 to reduce the constraints around the concrete If the constraints around the concrete is too large, the internal tensile stress can not be released, tensile stress increases the concrete cracked. Should reduce the length of the concrete warehouse, so that concrete internal tensile stress can be fully released.