Antiwashout underwater concrete is an underwater concrete that has improved resistance to segregation as a result of adding an antiwashout admixture. Antiwashout underwater concrete shall have the required strength, durability, compactness, and ability to protect steel materials, and the scatter in quality shall be small. Also, the concrete shall have a workability suitable for the placing operation and shall not cause water pollution.
As in the case of ordinary concrete, antiwashout underwater concrete should have the desired strength and durability, as well as the capacity to protect steel materials from corrosion. However, when a large unit water content is needed to obtain the required fluidity, i.e. greater than 200 kg/m3, the amount of cement as determined from the water-cement ratio sometimes exceeds 400kg/m3. It is therefore necessary to thoroughly examine not only the fluidity and strength needed for the structure, but also the temperature rise due to heat of hydration and whether it is proper to use various admixtures, etc. Furthermore, since the final quality of the concrete depends not only on fluctuations in the quality of the materials and measurement errors, but also on the effects of underwater drop height, underwater flow distance, and water currents in the area of construction, consideration should also be given to these points. That is, the final quality of antiwashout underwater concrete is greatly affected by the construction conditions as well as the materials used and the mix proportion, so it is important that these factors be comprehensively considered if a structure of the required performance is to be obtained.
There are a variety of types of anti-washout admixtures, such as those based on the cellulose system and the acrylic system. Also, the degree of anti washout property and flow property differs depending on the brand of antiwashout admixture, even though the main Ingredient may be the same.
It is thus important to comprehend the performance of the antiwashout admixture to be used using available reference materials, as well as to confirm that the required quality can be obtained by conducting tests in advance using the chosen materials.