How to improve the deformation effect crack of cast-in-place concrete (1)
Deformation effect cracks can be divided into five categories: concrete plastic shrinkage cracks, concrete plastic settlement cracks, concrete self-shrinkage cracks, temperature cracks and deformation cracks caused by strong constraints.
1 plastic shrinkage crack of concrete.It is the dry shrinkage crack caused by evaporation of surface water during solidification and hardening of concrete.Such cracks generally occur before the initial vibration of concrete to the final setting.
The main prevention measures are: one is to control water cement (glue) ratio.The water-cement ratio of ordinary concrete should be controlled at 0.Within 6, water-cement ratio of waterproof concrete should be controlled at 0.55 or less.The water-binder ratio of high-strength concrete should not be too small, otherwise the self-shrinkage of concrete is too large, and it is easy to produce cracking.Second, the control of slump.The vertical members of pumped commercial concrete should be controlled at 180 mm ~200 mm, and the horizontal members should be controlled at 160 mm ~180 mm.Third, timely and effective maintenance must be carried out within 12 hours after concrete pouring.The horizontal components should be covered with plastic film and water to prevent the evaporation of water.Column, wall kind vertical component member should take plastic film or straw curtain to wrap and outside filling water the way of photograph union.
2. Plastic settlement crack of concrete.In concrete mixing, coarse and fine aggregate particles, cement slurry, cement particles, water and other components of the specific gravity is different, will occur recombination sub settlement, light component floating phenomenon, namely "settlement" and "bleeding" phenomenon.The internal settlement of fresh wall concrete will cause plastic settlement crack.
Main prevention measures: one is to control concrete slump, strictly prohibit to add water to concrete to increase its slump, has occurred "bleeding" phenomenon of concrete can not be used.Second, adopt "secondary vibration" technology.Third, the column, wall and other vertical members and beam, plate members to separate pouring.
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