What are the causes of cracks in construction?
1. Low masonry strength: the quality of materials was not carefully controlled during construction, the strength of brick masonry materials was lower than the design requirements, or the compressive strength met the requirements, but due to the long length of masonry, the masonry itself broke from the middle after the completion of masonry construction.
2. Mixed masonry with different strengths: In the construction process, different masonry materials are used as supporting blocks, resulting in various masonry combinations, and the wall cracks due to the strength, thermal expansion and contraction and water absorption of different masonry materials.
3. Excessive vibration during construction, too dry formwork and cushion lead to floor cracks: after concrete pouring and vibrating, coarse aggregate sinks to squeeze out water and air, and the surface water seepage forms vertical volume shrinkage and sinking, resulting in surface mortar layer, which has greater drying shrinkage performance than the lower concrete, and it is easy to form condensation cracks after water evaporation. However, if the formwork and cushion are not watered enough and are too dry between concreting, the formwork will absorb a lot of water, resulting in plastic shrinkage of concrete and cracks.
4. Cracks caused by premature construction and overload: In order to seize the construction period and catch up with the progress, the newly poured cast-in-place slab or concrete is still in the initial setting and final setting stage, and materials, bricks, mortar, templates, etc. are trampled at will. They are all piled up in a centralized way. Premature loading will lead to irregular stress cracks. Once these cracks are formed, it is difficult to close them and form permanent cracks.
5. Improper maintenance of concrete leads to floor cracks: Improper maintenance is also the main cause of cracks. Premature curing will affect the cementation ability of concrete. When the curing is too late, the free water on the concrete surface evaporates too quickly, and the cement lacks the necessary hydration water, which leads to the sharp shrinkage of the volume. At this time, the early strength of concrete is low, so it can't resist this stress and crack. In addition, excessive smoothing and calendering will make the fine aggregate of concrete float to the surface too much, forming a cement slurry layer with high water content. The calcium hydroxide in the cement slurry reacts with carbon dioxide in the air to generate calcium carbonate, which will shrink the surface volume and cause the surface of concrete slab to crack.
6. Slab cracks caused by steel bar sinking: the correct position of the upper negative bar on the floor surface was not noticed, and the construction workers were barbaric and trampled on the steel bar at will, resulting in the sinking of the negative bar, too large protective layer, and the failure to repair it in time before and during pouring, which reduced the effective height of the floor section, made the negative bar fail to play its due role, and the bearing capacity of the floor failed to meet the design requirements, resulting in floor cracks.