Concrete – Underwater Anti-Wash Concrete

Shotcrete has been widely used for tunneling works and slope protection, it is also used for architectural purposes. There are two types of shotcrete application, the wet and dry process. Shotcrete is a concrete transported by means of air under pressure with high velocity. It is applied and compacted in the same time against a surface.

Shotcrete components

As mentioned earlier, shotcrete differ from normal concrete by the way to apply it. Here below some points that should be observed and respected when producing shotcrete mixes.

On the other hand, anti-washout underwater concrete is quite different in concept from the methods mentioned above; the development in this case was improved performance of the fresh concrete. That is, the viscosity of the concrete was increased and its resistance to segregation under the washing action of water was enhanced by mixing an anti-washout admixture with the concrete. The effect of this is not only to greatly improve the reliability of Concrete placed underwater, but it also has remarkable effects on environmental preservation in the construction area. In addition, the earlier tremie and concrete pump placing methods can be adopted for construction.

The sun is the most powerful force which cracks slabs. In the daytime, the sun warms throughout the day causing the slab to expand. At night, the night comes and the slab contracts. This movement happens twice daily. It is the sun/night cycle.

Additionally, it is not so much the physical movement of any cycle but it is the frequency of the cycle that causes these cracks. For example, there are probably 40 to 70 freeze/thaw cycles per year. However, the sun/night cycle happens twice a day or 728 times per year. It is this great frequency of the sun/night cycle that causes concrete to crack. Even though the freeze/thaw cycle may move the concrete more physically, it is the frequency of the sun/night cycle that causes all of the problems.

Sand / Aggregate ratio

This ratio must satisfy a few conditions. The S/A ratio must allow easy shotcrete pumping or rotor filling. As a rule it is clear that mixes containing fines in excess would cause dust, increase the water demand. A contrary, mixes containing aggregates in excess would increase rebound. It has been observed that good pumping properties are achieved when the particles smaller than 1.18 mm represent around 40% of the sand / aggregate combination.

In particular, when producing the underwater anti-wash concrete it is necessary to mix it for longer than ordinary concrete in a mixer large enough to uniformly disperse the anti-washout admixture. Also, when using concrete pumps for placement, it is necessary to design a pumping plan with care as regards pumping equipment, pumping distance, etc., because the pumping resistance is increased by the higher viscosity

Resource Author Francisco Rodriguez H.
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