In recent years, there is an increasing demand for highly durable concrete whose strength is highly increased, for example, by reducing a water content used in the concrete, and this tendency will further increase in the future. For reducing the water content, a polycarboxylic acid-based water reducing agent excellent in water reducing properties and flow retention is used. As the water content is reduced, however, fresh concrete viscosity (also referred to hereinafter as concrete viscosity) is increased which causes the problem of deterioration in workability and operativeness in delivery by pressurization with a pump, in placing, or in compacting into a form. This problem of increased viscosity cannot sufficiently be solved by the polycarboxylic acid-based water reducing agent, and there is a need for additives having higher effects on reduction of concrete viscosity.
On one hand, techniques wherein a phosphate-based additive is used as an additive for hydraulic compositions are disclosed. For example, JP-B 2508113 discloses a technique of using an additive composition containing a specific polycarboxylic acid-based cement dispersant, a specific nonionic compound, and a polyoxyalkylene alkyl ether phosphate as one compound selected from compounds used as air entraining agents. JP-A 1-219050 discloses a composition containing a phosphate of specific structure as a cement dispersant and a specific nonionic surfactant.
JP-A 2002-121058 discloses an admixture containing a polyoxyalkylene alkyl ether phosphate and a polymer obtained by polymerizing a monomer having a specific polyoxyalkylene group.