Analysis of the causes of concrete sanding

Analysis of the causes of concrete sanding—Construction reasons

1) Formwork reasons

The joints between the formwork used in concrete projects are not tight. After the concrete is poured and vibrated, cement slurry will leak out from the gaps in the formwork. This causes the aggregate on the surface of the concrete to lack cement slurry wrapping and form sand. It was found during on-site construction that part of the sanding was caused by dirt such as mortar remaining on the formwork.

2) Excessive vibration

Concrete vibration is suitable when the concrete surface is flat and basically no bubbles appear, and cement slurry appears on the surface. However, the construction workers violated the construction requirements and inserted the vibrating rod to a position without moving. After sufficient vibration, the vibration equipment was not turned off. This caused partial over-vibration of the concrete.
Furthermore, during the concrete pouring process, the concrete is not fluid enough. In order to achieve a good vibration effect, the construction workers often increase the vibration intensity and time. These wrong vibration methods may cause the concrete to segregate and cause sand.

3) Construction on rainy days

It is difficult to prevent rainwater from entering the formwork when pouring concrete on rainy days. Rainwater enters the concrete being poured. It will make the cement slurry thinner. As a result, the water-cement ratio of the concrete is passively increased. Or the cement on the surface of the concrete has not yet hardened. The surface is washed by rainwater. As a result, the water-cement ratio of the unhardened concrete surface increases or the cement slurry is lost, forming sand.

4) Improper maintenance

The concrete is cured too early after pouring. There is more water in the concrete. As a result, the water-cement ratio of the concrete becomes larger. This causes sand. If the concrete is cured for too long, the concrete will also sand. The reason is: when the cement is hydrated, a large amount of hydration heat cannot be dissipated in time, causing a large amount of water in the concrete to evaporate. The concrete is in a state of water shortage. This slows down the hardening speed of the concrete. The strength and wear resistance of the concrete are significantly reduced. Insufficient maintenance, exposure to the sun or strong winds, and other problems encountered in concrete maintenance will cause the concrete surface to not be fully hydrated. This leads to low strength and sand.

5) Winter construction

Construction is carried out in winter without insulation measures. Concrete is easily frozen during construction. This reduces the surface strength. And after the concrete is frozen, its volume expands.
After thawing, the expanded concrete cannot recover. This increases the porosity of the concrete. Loose particles are formed on the surface. The strength of the surface is greatly reduced. Sand will appear after being disturbed.