| 摘要 |
A cement additive that without the need to limit the type of water reducing agent, improves false setting characteristics attributed to rapid dissolution rate of natural anhydrous gypsum and realizes stable securing of high-strength developing capability; a cement composition containing the additive; and a process for producing a mortar or concrete product with the use of the additive. There is provided a cement additive containing, as main components, natural anhydrous gypsum and at least one member selected from among fired clay mineral, clay mineral, slaked lime and quicklime, characterized in that the cement additive exhibits such a dissolution rate that when sampled in a 1 g equivalent amount of the natural anhydrous gypsum thereof and brought into contact with 100 g of a 0.05% aqueous solution of Na2HPO4 of 20‹C for 1 hr, the SO4 ion concentration of the aqueous solution is in the range of 0.027 to 0.30 mass%/hr. Further, there is provided a cement composition characterized by being composed of cement loaded with the above cement additive. Still further, there is provided a process for producing a mortar or concrete product, characterized in that a mortar or concrete material loaded with the above cement additive is subjected to atmospheric steam curing. ® KIPO & WIPO 2008
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