Abstract. The article deals with issues of the thermal cracking resistance in massive concrete and reinforced concrete structures during the building period. The paper gives the calculation results of thermal stressed state in massive foundation slabs with different time organization of the thermal protection. It was found that the thermal crack resistance is fully guaranteed when the insulation is installed immediately after concrete has been placed or it has been placed with short delay. The delay can be allowed if the relative tensile strain of the concrete does not exceed the tensility limit. The acceptable delay ranges from 8 to 30% of time it takes to reach the maximum temperature in the concrete block. The surface insulation installation at the time of the temperature peak inevitably leads to the formation and development of cracks.

No abstract

No abstract

No abstract

In the Converter Shop of Azov Steel Combine periclase-lime refractories previously heat treated using a special cycle are used for fining the working layer of the walls of steel teeming ladles. In this shop the method of ladle treatment of steel includes desulfurization of the metal in ladles by treatment with liquid slag synthetic or solid slag-forming mixtures and in some cases with both simultaneously.The liquid synthetic has a composition of (%)* 4045 CaO, 35-40 A1203, <5 SiO2, 4-6 TiO2, and < 1 iron oxides. The temperature of the liquid synthetic slag during pouring into the ladle is 1680-1720~ (superheated, that is, 160-200~ over the liquidus temperature).Lime and fluorespar in a 4:1 ratio are used as the solid slag-forming mixture. Freshly fired lime containing not less than 92% CaO + MgO and fluorspar containing not more than 10% SiO 2 are used. The grain size composition of the solid slag-forming mixture is 40-50% 15-30 mm fraction, 30-35% 5-15 mm fraction, and _<30% finer than 5 ram.The liquid synthetic slag is poured into the steel teeming ladle immediately before tapping of the metal from the converter into it. The weight of metal in the ladle is 340-360 tons. The specific consumption of liquid synthetic slag is 10-20 kg/ton of steel treated (3.44.0 tons/heat). The time of the liquid synthetic slag in the ladle before tapping of metal from the converter is 10-20 min and the metal is in the ladle for 1.5-2.5 h from the start of tapping of it from the converter to the end of teeming of it. Recently for the purpose of economy in scarce and expensive liquid synthetic slag and electric power for production of it a portion or all of the liquid synthetic slag has been replaced by solid slag-forming mixtures.The results of investigations and operating experience showed that in degree of desulfurization the use of 1 kg of solid slag-forming mixture per ton of steel on the average is equivalent to the use of 4 kg of liquid synthetic slag per ton of steel with a basic lining of the ladle. The solid slag-forming mixture is placed in the steel teeming ladle at the time of tapping of the steel from the converter directly under the stream of metal, which significantly accelerates melting of the solid slagforming mixture and desulfurization.The method of ladle treatment of steel includes holding back of the melting slag in turning down of the converter by covering the tap hole with a plug.The steel is deoxidized in the ladle. A portion of the aluminum is added at the start of tapping of the metal from the converter. Upon reaching 1/3-1/2 of the height of filling of the ladle the solid slag-forming mixture is added with subsequent addition of ferroalloys and the remainder of the aluminum. In treatment of steel only with the solid slag-forming mixture the slag formed from the mixture contains 50-60% CaO, 7-13% SiO 2, 20-28% A1203, 1.0-2.0% FeO, 0-1.0% MnO, 0.01-0.08% P205, and 0.2-0.9% S at the end of ladle treatment.The metal is deoxidized in the ladle in tapping based on calculation of obtaining a silicon content at ...