12 Causes For Cracks In RCC Slab
1– Plastic shrinkage: When water dries up rapidly from the surface, plastic shrinkage occurs. As a result, the top surface of the slab dries more quickly than the bottom one that leads to its pulling apart. Weather conditions like wind and low humidity accelerate this process. The shrinkage can be avoided by keeping the surface moist.
2– Settlement: Owing to certain factors like poorly compacted soil, sand in the soil and water erosion, the ground under the slab displaces leading to settlement cracks. Poorly compacted soil can be remedied by digging it out and replacing it with crushed stone. In the event of water drains across the sidewalk, backfill first with a few inches of gravel.
3– Drying shrinkage: When a slab that is restrained is drying, it causes shrinkage.
4– Chemical factors: When the aggregates and cement present in the concrete are not harmonious with each other, it causes some chemical reactions that lead to cracks.
5– Corrosion: Sometimes, the steel wire mesh inside the concrete catches rust on getting moist and coming in contact with air. This happens due to any of the above-mentioned reasons when a crack on the slab surface develops and air and water seeps in.
6– Overloads: Concrete is designed to withstand only a limited amount of load. If it exceeds that limit, cracks are bound to develop.
7- Lack of knowledge about the spacing between main to main as well as distribution to distribution bars.
8- Inadequate curing at the time of settlement of concrete leads to cracks due to heat.
9- Improper control on material proportions especially the silt content, water-cement ratio.
10- Excessive vibrations during casting resulting in opening up of the binding wires ( stirrups opening )
11- Insufficient precautions during striking off. ( maybe early opening of the slab before it attains the strength )
12- Excessive deformation of the cantilever slab at the ends (or in case of simply supported slabs in the mid-span )due to settlement of any of the staging props.
