Concrete admixtures have been widely used for cement compositions such as cement paste, mortar and concrete as a water-reducing agent and the like. They are now essential in constructing civil engineering and building structures and the like from cement compositions. Such concrete admixtures increase the fluidity of cement compositions to thereby reduce the water requirement of the cement compositions, and therefore are effective in improving the strength, durability and the like, of hardened (cured) products. Among such water reducing agents, polycarboxylic acid concrete admixtures comprising a polycarboxylic acid polymer exhibit superior water-reducing performance to naphthalene and other conventional water reducing agents, thus have already led to good results in many cases as air-entraining and high-range water-reducing admixture.
With respect to conventional concrete admixtures, the following documents have been disclosed.
Japanese Kokai Publication Hei-10-081549 discloses a concrete admixture comprising a copolymer having the alkylene oxide chain length of 25 to 300 moles. Japanese Kokai Publication 2000-233956 discloses a cement dispersant containing, as a main component, a copolymer obtained by copolymerizing 5 to 35 mole % of alkyl (meth)acrylate and having the alkylene oxide chain length of 5 to 40 moles and the weight average molecular weight of 20000 to 80000.
Japanese Kokai Publication Hei-05-213653, Hei-06-191918, Hei-06-206750, Hei-08-109057, Hei-08-290955, Hei-09-227205 and Hei-11-171619 disclose cement dispersants comprising water-soluble vinyl copolymers having copolymerization ratios of alkyl (meth)acrylate in a range of 0 to 20 mole %. Among these, in particular, Japanese Kokai Publication Hei-09-227205 discloses a copolymer of phenoxymethacrylate having the polyethylene glycol chain length of 15 and 25 mole % of methyl acrylate.
Japanese Kokai Publication 2000-290056 discloses hydraulic compositions obtained by combinedly using a material segregation reducing agent having no dispersing ability (dispersibility) which comprises a (meth)acrylic acid polymer containing a hydrocarbon group with not less than 4 carbon atoms and a polyoxyalkylene chain, and a high-range water-reducing admixture. Japanese Kokai Publication 2002-053358 discloses a ternary polymer comprising polyalkylene glycol monoacrylate/alkyl (meth)acrylate (the number of carbon atoms of an alkyl group: 5 to 30)/(meth)acrylic acid. Furthermore, European Patent Publication No. 1103570 discloses a copolymer for cement admixtures comprising a constitutional unit derived from an unsaturated polyalkylene glycol ether monomer and a constitutional unit derived from an unsaturated monocarboxylic acid monomer as essential constitutional units. International Publication WO 02/096823 discloses a cement admixture comprising two polymers, namely a polymer (A1) comprising a constituent unit derived from an unsaturated (poly)alkylene glycol ether monomer and a constituent unit derived from an unsaturated monocarboxylic acid monomer, and an oxyalkylene group- or polyoxyalkylene group- and carboxyl group-containing polymer (B1).
However, there was a room for contrivance in order to improve of these concrete admixtures so as to simultaneously satisfy the properties such as decreasing the concrete viscosity, improvement of slump-retaining ability and suppression of bleeding water required for the cement compositions. By satisfying all these properties, the workability of cement compositions becomes excellent; the working efficiency in construction sites for civil engineering, building construction and the like can be improved; and the abilities to improve the strength and the durability of hardened products, which are required for concrete admixtures, can sufficiently be exhibited. Accordingly, concrete admixtures satisfying these properties have been highly desired.