Abstract: Provided is a method of producing a roadbed material from which less hexavalent chromium leaches out through use of a crushed product of a cementitious hardened body containing hexavalent chromium as a raw material. The method includes a carbonation treatment step of subjecting the crushed product of the cementitious hardened body to carbonation treatment with a carbon dioxide-containing gas having a temperature of 50° C. to 140° C. and a water content of 1.5% or more to obtain the roadbed material from which less hexavalent chromium leaches out than before the treatment. Preferably, the method includes, before the carbonation treatment step, a crushing step of crushing the cementitious hardened body to obtain a crushed product consisting of grains having a grain size of 100 mm or less at a ratio of 50 mass % or more and a grain size of 2.36 mm or less at a ratio of 1 mass % or more.

Abstract: A silicon carbide powder which, when used as a raw material in a sublimation recrystallization method, enables improvement in productivity of a silicon carbide single crystal by exhibiting a high sublimation rate and allowing a small amount of silicon carbide to remain without being sublimated, and enables an increase in size of the silicon carbide single crystal (for example, a single crystal wafer). The silicon carbide powder has a Blaine specific surface area of from 250 cm2/g to 1,000 cm2/g and a ratio of a silicon carbide powder having a particle size of more than 0.70 mm and 3.00 mm or less of 50 vol % or more with respect to a total amount of the silicon carbide powder. When a silicon carbide powder accommodated in a crucible is heated to be sublimated, a silicon carbide single crystal is formed on a seed crystal provided on an undersurface of a lid.

Abstract: A particle formed of silica and carbon having a low impurity content and an excellent reactivity is provided. Also provided is a method of producing a silica and carbon-containing material including: (B) a carbon mixing step of mixing an aqueous alkali silicate solution having a silicon concentration within the liquid portion of at least 10 wt % with carbon so as to obtain a carbon-containing aqueous alkali silicate solution; and (C) a silica recovery step of mixing the carbon-containing aqueous alkali silicate solution with a mineral acid so as to cause carbon and silicon within the liquid portion to precipitate as particles formed of silica and carbon and thus obtaining a particle-containing liquid substance, then solid-liquid separating the liquid substance so as to obtain a solid portion of a silica and carbon-containing material which is an assembly of particles formed of silica and carbon and a liquid portion containing impurities.

Abstract: A high-purity silicon carbide powder and its production method enable mass production of the high-purity silicon carbide powder at low cost in a safe manner. The content of impurities in the silicon carbide powder is 500 ppm or less. The silicon carbide powder can be obtained by heating a raw material for silicon carbide production in an Acheson furnace using a heat generator. The raw material for silicon carbide production is prepared by mixing a siliceous raw material and a carbonaceous raw material. The raw material for silicon carbide production contains the siliceous raw material and the carbonaceous raw material at a mixture mole ratio (C/SiO2) of 2.5 to 4.0 and has a content of impurities of 120 ppm or less.

Abstract: A silicon carbide powder which, when used as a raw material in a sublimation recrystallization method, enables improvement in productivity of a silicon carbide single crystal by exhibiting a high sublimation rate and allowing a small amount of silicon carbide to remain without being sublimated, and enables an increase in size of the silicon carbide single crystal (for example, a single crystal wafer). The silicon carbide powder has a Blaine specific surface area of from 250 cm2/g to 1,000 cm2/g and a ratio of a silicon carbide powder having a particle size of more than 0.70 mm and 3.00 mm or less of 50 vol % or more with respect to a total amount of the silicon carbide powder. When a silicon carbide powder accommodated in a crucible is heated to be sublimated, a silicon carbide single crystal is formed on a seed crystal provided on an undersurface of a lid.

Abstract: A high-purity silicon carbide powder and its production method enable mass production of the high-purity silicon carbide powder at low cost in a safe manner. The content of impurities in the silicon carbide powder is 500 ppm or less. The silicon carbide powder can be obtained by heating a raw material for silicon carbide production in an Acheson furnace using a heat generator. The raw material for silicon carbide production is prepared by mixing a siliceous raw material and a carbonaceous raw material. The raw material for silicon carbide production contains the siliceous raw material and the carbonaceous raw material at a mixture mole ratio (C/SiO2) of 2.5 to 4.0 and has a content of impurities of 120 ppm or less.

Abstract: A particle formed of silica and carbon having a low impurity content and an excellent reactivity is provided. Also provided is a method of producing a silica and carbon-containing material including: (B) a carbon mixing step of mixing an aqueous alkali silicate solution having a silicon concentration within the liquid portion of at least 10 wt % with carbon so as to obtain a carbon-containing aqueous alkali silicate solution; and (C) a silica recovery step of mixing the carbon-containing aqueous alkali silicate solution with a mineral acid so as to cause carbon and silicon within the liquid portion to precipitate as particles formed of silica and carbon and thus obtaining a particle-containing liquid substance, then solid-liquid separating the liquid substance so as to obtain a solid portion of a silica and carbon-containing material which is an assembly of particles formed of silica and carbon and a liquid portion containing impurities.

Abstract: A hydraulic composition including: a ground burned product A having a hydraulic modulus (H.M.) of 1.8 to 2.3, a silica modulus (S.M.) of 1.3 to 2.3 and an iron modulus (I.M.) of 1.3 to 2.8; and a gypsum. The hydraulic composition is capable of reducing heat of hydration and producing a mortar or a concrete excellent in flowability and strength development.

Abstract: A soil improvement material comprising a ground burned product A and gypsum, the burned product A having a hydraulic modulus (H.M.) of 1.8 to 2.3, a silica modulus (S.M.) of 1.3 to 2.3, and an iron modulus (I.M.) of 1.3 to 2.8. The soil improvement material is useful for improving the ground, especially through solidifying soft soil, such as water-rich soil or organic-rich soil.

Abstract: A hydraulic composition including: a ground burned product A having a hydraulic modulus (H.M.) of 1.8 to 2.3, a silica modulus (S.M.) of 1.3 to 2.3 and an iron modulus (I.M.) of 1.3 to 2.8; and a gypsum. The hydraulic composition is capable of reducing heat of hydration and producing a mortar or a concrete excellent in flowability and strength development.