(2) the vibration is not correct
(1) Vibration is not dense, uneven, honeycomb, pockmarked, hollow, is the origin of steel corrosion or other load crack.
(2) vibration time is too short, vibration is not dense, the formation of concrete strength is insufficient or uneven; Time is too long, resulting in stratification, coarse aggregate into the bottom, fine aggregate to stay in the upper layer, uneven strength, than the lower concrete has a larger dry shrinkage, after water evaporation, easy to form plastic shrinkage crack.
(3) unauthorized change of water-cement ratio in the construction process
Pumping concrete construction, for the convenience of construction, without adding water to improve the fluidity of concrete, or because of other reasons to increase the ratio of water cement, resulting in concrete hardening shrinkage increases, the structure appears mesh or irregular crack of different lengths.
