Precast concrete molded body

A method of manufacturing a precast concrete molded body, the method comprising:

• a preparing step of preparing an uncured concrete composition containing microcapsules with a core-shell structure having
• a core made of a water repellent organosilicon material selected from the group consisting of organosilanes, organosilane partial condensation products, and branched siloxane resins, and
• a shell made of a silicon-based network polymer containing silica units;
• and
• a curing and molding step of curing and molding the uncured concrete composition;
• wherein
• the uncured concrete composition contains cement and at least one aggregate, and in the preparing step, the microcapsules are added in a range of 0.01 to 0.35 parts by weight per 100 parts by weight of the cement,
• wherein the organosilane is an organosilane containing at least one silicon-bonded alkyl group having 1 to 30 carbon atoms,
• wherein the branched siloxane resin is a siloxane resin containing a siloxane unit of the formula RSiO3/2 where R represents an alkyl group,
• wherein the precast concrete molded body comprises air in an amount of from 3 to 6 volume %, as measured in a test based on JIS A 1128.

A method for improving strength, and at least one of substance penetration prevention, freeze-thaw resistance, and air content stability, of precast concrete molded bodies, the method comprising:

• an adding step of adding microcapsules to a concrete composition for a precast concrete molded body, the microcapsules having
• a core-shell structure having a core made of a water repellent organosilicon material selected from the group consisting of organosilanes, organosilane partial condensation products, and branched siloxane resins, and
• a shell made of a silicon-based network polymer containing silica units;
• wherein
• the concrete composition contains cement and at least one aggregate, and
• in the adding step, the microcapsules are added in a range of 0.01 to 0.35 parts by weight per 100 parts by weight of the cement,
• wherein the organosilane is an organosilane containing at least one silicon-bonded alkyl group having 1 to 30 carbon atoms,
• wherein the branched siloxane resin is a siloxane resin containing a siloxane unit of the formula RSiO3/2 where R represents an alkyl group,
• wherein the precast concrete molded body comprises air in an amount of from 3 to 6 volume %, as measured in a test based on JIS A 1128.