| Although underwater concreting has been in use | | | | washing action of water, and rarely separates |
| for a long time, development of the technique has | | | | even when dropped under water |
| mainly proceeded in the areas of concrete placing | | | | * Its yield value is small and viscosity high, so the |
| method and improvements to the construction | | | | concrete components never segregate and it |
| machinery. The prepacked concrete method, | | | | displays high fluidity. |
| tremie method, concrete pump method, and | | | | * As a result of the high fluidity, filling property |
| others are now the representative underwater | | | | and self-leveling ability are improved. |
| concreting methods. With all these concreting | | | | * Almost no bleeding occurs. |
| methods, the essential aim of technological | | | | These qualities are taken full advantage of in |
| development has been to improve how the | | | | work which would be difficult to handle using |
| concrete is placed and to minimize contact | | | | conventional underwater concrete. This includes |
| between the water and mortar so as to prevent | | | | work where high reliability is required, work in |
| the concrete from segregating under water. | | | | flowing water, work where water turbidity is |
| On the other hand, anti-washout underwater | | | | restricted due to environmental considerations, |
| concrete is quite different in concept from the | | | | and work where construction stretches over a |
| methods mentioned above; the development in | | | | considerable area and good flatness is necessary. |
| this case was improved performance of the fresh | | | | On the other hand, however, handling is more |
| concrete. That is, the viscosity of the concrete | | | | difficult than with ordinary concrete, and in order |
| was increased and its resistance to segregation | | | | to produce concrete of the required quality and a |
| under the washing action of water was enhanced | | | | structure of the required performance, careful |
| by mixing an anti-washout admixture with the | | | | consideration of mix proportion, mixing, transport, |
| concrete. The effect of this is not only to greatly | | | | and placing, etc. is necessary when anti-washout |
| improve the reliability of Concrete placed | | | | underwater concrete is used. |
| underwater, but it also has remarkable effects on | | | | In particular, when producing the underwater |
| environmental preservation in the construction | | | | anti-wash concrete it is necessary to mix it for |
| area. In addition, the earlier tremie and concrete | | | | longer than ordinary concrete in a mixer large |
| pump placing methods can be adopted for | | | | enough to uniformly disperse the anti-washout |
| construction. | | | | admixture. Also, when using concrete pumps for |
| The specific advantages of anti-washout | | | | placement, it is necessary to design a pumping |
| underwater concrete include the following: | | | | plan with care as regards pumping equipment, |
| * Compared with ordinary concrete, anti-washout | | | | pumping distance, etc., because the pumping |
| underwater concrete is highly resistant to the | | | | resistance is increased by the higher viscosity. |