The main reasons for cracking of concrete floors are as follows:

Quality of concrete raw materials

Abnormal coagulation or expansion of cement, such as unstable stability of cement, cement containing quicklime or magnesium oxide, these components will expand in volume after hydration, resulting in cracks.

If the aggregate contains too much mud, irregular network cracks will develop as the concrete dries.

However, the concrete configured with silt with high mud content has large shrinkage and low tensile strength, and is prone to cracks due to plastic shrinkage.

In order to meet the pumping conditions, the pumped concrete has large slump and good fluidity, and is prone to the phenomenon of less local coarse aggregate and more mortar. At this time, when the concrete is dehydrated and shrinks, surface cracks will occur.

construction quality

Excessive vibrating of concrete construction, excessively dry concrete of formwork and cushion after pouring and vibrating, the coarse aggregate settles and squeezes out water and air, and the surface shows bleeding, resulting in vertical volume reduction and sedimentation, resulting in the surface mortar layer, which is more The lower concrete has a large drying shrinkage performance, and condensation cracks are easy to form after the water evaporates.

However, if the formwork and cushion are not sprinkled enough between the pouring concrete and they are too dry, the formwork will absorb a large amount of water, causing plastic shrinkage of the concrete and causing cracks.

Caused by improper construction technology: During the construction process, due to improper construction technology, the negative reinforcement at the support sinks, the protective layer is too large, the fixed support becomes a plastic hinge support, and cracks occur along the beam support on the upper part of the plate.

Shrinkage of concrete (temperature cracks): As we all know, the cause of concrete shrinkage is mainly due to the hydration of cement in the early stage of hardening, forming a new cement crystal.

This crystalline compound is smaller than the raw material, thus causing the shrinkage of the concrete volume, the so-called condensation, which is mainly caused by the evaporation of free water in the concrete in the later stage.

Moreover, if the concrete is exposed to an environment with large temperature changes, it will shrink even more.

For example, under the hot summer temperature during construction, the surface temperature of the stone increases, which causes the volume of the stone to expand. After mixing into concrete, the stone shrinks due to cold, causing hairline cracks on the surface of the concrete.

If the concrete is not watered and maintained in time after pouring and pounding, the concrete loses water and shrinks at a higher temperature, and the hydration heat release is large, and the water is not replenished in time.

Therefore, during the hardening process, the cast-in-place plate is bound by the support, which will inevitably generate temperature stress and cracks. These cracks are also first generated in the weaker parts, that is, at the corners of the plate.

In addition, the large temperature difference between indoor and outdoor will also cause certain cracks.