求翻译：（4）在混凝土浇筑后，由于混凝土在水化热自干过程中受到混凝土结构不均衡的预应力制约而形成裂缝。正常情况下，在混凝土浇筑后，水泥的水化热会使混凝土结构内部温度升高，在2～3d 内温度可高达50～80℃。而混凝土的膨胀系数只为50～80℃。这就表明，在无风和没有太阳照射情况下，混凝土表面温度与周围环境温度存在差别， 这时，便出现温度收缩现象，形成裂缝。是什么意思？

(4) after the concrete pouring, because concrete hydration heat in the drying process by the unequal structure of prestressed concrete constraints to form cracks. Under normal circumstances, after the pouring of concrete, cement hydration heat of concrete internal temperature, and temperature can be as high as 50~80℃ in the 2~3D. Concrete expansion coefficient for 50~80℃ only. This shows that, in the absence of wind and sun exposure situations, there is a difference of temperature and ambient temperature on the surface of concrete when the temperature shrinkage, forming cracks.