Abstract: An ultra high strength fiber-reinforced cement composition includes cement, silica fume, coal gasification fly ash, insoluble anhydrous gypsum, and metal fiber having a length between 5 and 30 mm and a diameter of between 0.1 and 1 mm. The coal gasification fly ash is spherical fine particles having a maximum particle size between 5 and 10 ?m. Mass ratio of the silica fume: the coal gasification fly ash is 95 through 50 portions: 5 through 50 portions.

Abstract: Therefore, the problem to be solved by the present invention is to provide highly general purpose ultra high strength fiber-reinforced mortar or concrete that shows a higher fluidity (workability) at the fresh state, a higher bending strength with a less content of metal fiber by enhancing both the absolute value of the compressive strength of mortar -matrix excluding metal fiber and the ratio of the bending strength relative to the compressive strength simultaneously at the hardened state, and acceptability of fine aggregate being used in ordinary ready-mixed concrete. An ultra high strength fiber-reinforced cement composition is characterized in that it contains cement, silica fume, coal gasification fly ash, gypsum and metal fiber and that the mass ratio of silica fume : coal gasification fly ash is 95 through 50 portions: 5 through 50 portions. Ultra high strength fiber-reinforced mortar or concrete contains such a cement composition and fine aggregate.

Abstract: A method of electrochemical treatment of prestressed concrete which comprises supplying a direct current between a steel embedded in the prestressed concrete as a cathode and an anode on the surface or inside of the concrete at a voltage higher than the hydrogen evolution potential, wherein an effective tensile force acting on the PC steel tendon embedded in the concrete is not greater than 80 % of the tensile strength of the PC steel tendon, and a method of electrochemical treatment of prestressed concrete which comprises supplying a direct current between a steel tendon embedded in the prestressed concrete as a cathode and an anode on the surface or inside of the concrete at a voltage higher than the hydrogen evolution potential, wherein the voltage is adjusted to less than the hydrogen evolution potential at least once during electrochemical treatment.

Abstract: According to the invention, a coupling device for a force transmitting member is provided. The coupling device contains a plurality of force transmitting members and a joint for coupling each end of the force transmitting members. A hardened body of a cement composition having a compressive modulus of elasticity of not less than 2.0.times.10.sup.5 kg/cm.sup.2 and a compressive strength of not less than 700 kg/cm.sup.2 is being filled at least in-between the force transmitting members and the joint.