A concrete for lining blast furnace shafts

Abstract

Blast furnace shafts are lined of dense aluminosilicate refractories primarily of chamotte composition [i]. In some cases high-alumina parts are used for lining the shafts [2]. In recent years silicon carbide parts produced by different methods have been used in the lower portion of the shaft, the bosh, and the bosh parallel.These parts are produced with binders of silicon nitride or silicon oxynitride or are self-bonded, that is, with a silicon carbide binder [3][4][5][6][7].Theparts with a silicon oxynitride binder possess higher heat resistance than parts containing a silicon nitride binder [8].At present the direction of making linings of unformed materials by methods of guniting, ramming, and vibration is promising [9]. The use of these methods makes it possible to completely mechanize the processes in production of the powders and their use.In the USSR there is positive experience in the use of powder materials for lining the upper portion of blast furnaces [i0]. Production experience in the use of gunited concrete for repair of the shaft lining is also known.Concretes are used for repair at low temperatures and also concretes hardening at high temperature, which are used for repair of the shaft lining without shutting down the furnace for major repairs [12].Such concretes contain 76-94% A1203, 0.2-14% Si02, and appropriate hardening additions.The bend strength at low temperatures (100~ is 2.5-9.0 N/mm 2 and at II00-1300~ does not exceed 2-11 N/mm 2 [13]. After 6 months of operation in the upper portion of the stack the bend strength of chamotte concrete with a binder of alumina cement (25%) was 1.4 N/mm 2 [14].In this work mullite-corundum chamotte with 77.5 wt.% A1203 from Zaporozh'e Refractory Plant, black silicon carbide, and high-alumina cement were used for production of the concrete.Potassium carbonate was used as the reagent in determination of alkali-resistance. During selection of the grain size composition it was established that a high bulk density of the compound (2.11-2.16 g/cm 3) is obtained with the use of chamotte of four fractions.The silicon carbide was added in a quantity providing sufficiently high alkali resistance under high temperature conditions and having little influence on the change in mechanical properties of the concrete.The maximum quantity of high-alumina cementdid not exceed 15%. This is the result of the necessity of providing high strength of the concrete in hardening and preservation of sufficient strength at the service temperature [14].In heating of concrete containing high-alumina cement its strength drops up to 1000-1100~ At temperatures of intense sintering the strength increases somewhat.The concrete specimens for conducting the investigations were prepared in the form of a normal brick on a vibrotable with a vibration frequency of 2800 per min and an amplitude of imm.After 7 days of hardening the open porosity of the concrete was about 20%, the apparent density 2.32 g/cm 3, and the compressive strength more than 45 N/mm =. Hardening of the concrete occurs as the r...