Cement dispersion agent

#1. Field of the Invention

#The present invention relates to a dispersion agent for cement (hereinafter, cement dispersion agent) capable of providing an excellent dispersibility without causing an alkali-aggregate reaction. The present invention also relates to a cement dispersion agent capable of improving the flowability of a cement mix such as cement paste, mortar, and concrete and of preventing the decrease in the flowability over a period of time when incorporated therein.

#2. Description of the Related Art

#In the following, the present invention is described in more detail by referring to Examples, which by no means limit the scope of the present invention. In the following Examples, "%" and "parts" indicate "% by weight" and "parts by weight", unless otherwise specified.

#A one liter (inner volume) four-necked separable flask was charged with 585 g of dichloroethane, followed by adding 45 g of polystyrene (weight average molecular weight=5500, available from Mitsubishi Petrochemical Co., Ltd. as OS-1000) while stirring. The mixture was dissolved during the stirring. Then, 35 g of sulfuric anhydride was dropwise added, while the reaction temperature was maintained at a temperature of 25.degree. C. to 30.degree. C. After completing the addition of the sulfuric anhydride, the reaction mixture was stirred at the same temperature for 30 minutes, and thereafter, 320 g of water was added to the flask to extract the resultant polystyrene sulfonic acid, followed by filtration. The filtrate was carefully neutralized with 19 g of calcium hydroxide and, after removing the by-product calcium sulfate by filtration, the desired aqueous solution of calcium polystyrene sulfonate was obtained. The weight average molecular weight of the product was 10,000 as determined by GPC measurement. The sulfonation degree was 80% as determined by 'H-NMR measurement.

#The amount of water reduction and degree of the expansion of the concrete were evaluated by using various calcium polystyrene sulfonates having various weight average molecular weights and sulfonation degrees. These calcium polystyrene sulfonates were prepared in the same manner as mentioned above. In addition, the same evaluation tests were carried out in the case of the sodium salt and conventional cement dispersion agents. The results are shown in Table 1.