The present invention relates to a method and apparatus for producing a slurry, such as a fly ash slurry, mortar, grout and concrete, for use in underwater placement, for example, for the purpose of reclaiming land from sea and lakes.
One of the inventors has proposed as a joint inventor a method for placing a fly ash slurry underwater in Japanese Patent Application No. 57-21836 filed on Feb. 13, 1982. In this prior art method, fly ash and water are mixed by a mixer and then agitated by an agitator to produce a fly ash slurry, which is then fed by means of a pump to a placing pipe of which discharge end is located near the bottom of sea or a lake. The slurry is discharged from the discharge end which is kept within the slurry placed.
However, this method has a drawback in that during underwater placement, a part of the fly ash in the slurry is dispersed in the water as suspended solids because light particles such as cenosphere are involved in the fly ash. The fly ash exhibits high pH in water and hence water near the placed fly ash slurry rather increases in pH and concentration of the suspended solids, resulting in water pollution. The inventors have noted that this is caused by phenomena that during production of the fly ash slurry, particularly during agitation thereof with an agitator, a great number of fine bubbles are formed in the slurry, and that the bubbles are gathered during pumping up to the underwater placement site, where large bubbles are evolved and thereby part of the slurry is scattered in the water, so that a great amount of fly ash in the scattered slurry suspends in the water. This was also noted in underwater placement of a mortar, grout and concrete.