The main cause of cracks in chimney maintenance

Main reasons for cracks in chimney maintenance:

(1) chimney maintenance ratio: water ash is relatively large, sand rate is larger, thinner, gravel is smaller, ashes is relatively small, together with concrete strength requirements, cement content is also large, is the reason for the generation of cracks. 

(2) chimney maintenance water cement ratio is too large, excess water dry off, the occurrence of large physical shrinkage, in the early concrete crack resistance capacity is insufficient under the condition of surface cracking; 

(3) concrete in the fine powder and fine aggregate content is too large and the ratio of needle flake is too high, resulting in shrinkage cracks similar to the above properties;

(4) chimney maintenance is not good or timely, surface water loss rate is too fast, resulting in shrinkage crack; 

(5) when concrete slump is too large, aggregate will sink in a large amount, and plain pulp will rise up too much, leading to large shrinkage surface cracks.

Other factors:

(1) steel protection layer is too thin, steel spacing is small, chimney maintenance along the steel crack;

(2) there is no reinforcing steel bar at the stress concentration places like the entrance and corner;

(3) lack of stirrup bars, oblique bars, temperature bars, chimney maintenance cracking;

(4) premature removal of the template, improper force will be concrete pry crack;

(5) premature stacking of concrete surface materials.

Measures to prevent chimney maintenance cracking

1. Strengthen the internal quality of concrete itself

Good inspection of raw materials, especially the stability of cement must meet the requirements;Admixture such as fly ash, control within 10%, admixture must be strictly controlled dosage;Control water cement ratio, sand ratio should not be too large, mix ratio should be calculated first, try again, keep improving, minimize slump, and meet the site construction requirements.At the same time, extension of time delay slump method with construction;Concrete slump must be detected regularly before chimney maintenance and use. Chimney whose slump is too large shall not be used for maintenance.

2. Reinforcement:

Steel plate construction to be in place, steel protection layer strict control;The reserved opening must be reinforced strictly in accordance with the design requirements, and the radial reinforcement should be added at the Angle of the floor slab with large span.The steel bars distributed on the plate shall be bound in place according to the design requirements.

3. Other measures

Chimney maintenance vibration to be compact, but especially not excessive vibration.Platform plate must be vibrator vibrator, chimney maintenance surface to find usually must be at the beginning of the collection of water, before the final coagulation, with croucher plate compaction. 

Arch the formwork in strict accordance with the design requirements, arch degree is about 3‰ span, and the formwork must be removed after the chimney maintenance intensity reaches.And do a good job of dismantling the mold control work, the upper cast concrete, the lower layer of the mold is not removed, and the next layer of pillars to leave part, 4m span beam pillars spacing is not more than 3m. 

Protection of finished products after chimney maintenance and construction;Chimney maintenance should be timely maintained by specially-assigned persons and maintenance records should be made.Chimney maintenance surfaces must be kept moist during maintenance.