Abstract: Disclosed is a rust preventive composition for steel reinforcements for concrete, which comprises 100 parts by weight of Portland cement, 0.3 to 3 parts of a hydroxycarboxylic acid, 0.3 to 3 parts of a saccharide, 2 to 10 parts as a solid content of a polymer latex, 0 to 5 parts of an optional additive and 30 to 45 parts of water, all parts being by weight. In this composition, an excellent synergistic effect is attained by the combined use of the hydroxycarboxylic acid and saccharide. That is, hydration is almost completely suppressed in this composition under ordinary rust preventing treatment conditions, but hydration is effectively promoted under high-temperature high-pressure hydrothermal curing conditions. Gluconic acid and sorbitol are especially preferred as the hydroxycarboxylic acid and saccharide, respectively.

Abstract: Porous material comprising a plurality of intersecting cut carbon fibers each having a diameter of 3 to 20 microns, the fibers being covered with a thin metal film and being substantially completely and randomly dispersed, accumulated and bound with a binder at portions of the intersections of the fibers, to form a porous structure through which a plurality of pores extend continuously from one surface of the material to the other.