Calcium ferroaluminate compound, cement admixture and its manufacturing methods, and cement composition

Abstract

It is the object of the invention to provide a cement admixture, and a cement composition that can impart good enough rustproofness to reinforcing bars in hardened cement concrete, and can have resistance to penetration of chloride ions entering from the outside, prevent the hardened cement concrete from getting porous due to reduced leaching of Ca ions and have a self-recovery capability. The invention provides a cement admixture characterized by containing a calcium ferroaluminate compound comprising a CaO—AlO—FeOsystem, and having a FeOcontent of 0.5 to 15% by mass and a CaO.2AlOstructure with a CaO/AlOmolar ratio ranging from 0.15 to 0.7. It is preferable that the fineness is 2,000 to 7,000 cm2/g as represented in terms of the Blaine's specific surface area value; the potentially hydraulic substance and/or pozzolan substance (pozzolan substance or the like) is also used; the pozzolan substance or the like contains one or two or more selected from the group consisting of finely pulverized, quenched, granulated blast-furnace slag, fly ash, silica fume, metakaolin, incinerated pulp sludge ash, incinerated sewage sludge ash, and waste glass powder; and the blending proportion of the calcium ferroaluminate compound to the pozzolan substance or the like ranges from 10/1 to 1/10 by mass. The invention also provides a cement composition containing cement and the cement admixture.