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In recent years, one of the main directions followed in the USSR and other countries for improving the technology and the quality of concrete is to use complex mineral additives. Such additives include the plasticizers facilitating a reduction in the water--cement ratio and a consequent improvement in the strength and the life of concrete, and the setting (hardening) regulators having an effect on the hydration and setting rates of concrete (cement stone) [1][2][3][4].In view of this, the plasticizers are expected to have a similar effect on the refractory alumina (aluminous) cement employed for the production of refractory concretes including the coke-oven concretes.We studied the effect of certain additives on the hydration process of an alumina cement and on the properties of the concrete based on it.In this study we used an alumina cement containin~ 40.42%* Al=Os, 12.1% SiO2, 38.08% CaO, 0.31% Fe~Os, 2.37% FeO, 0.87% TiO=, 0.13% R20, 3.64% SO~, and 2.5% Amca I.Petrographic studiesl showed that the main components of the cement are monocalcium aluminate CaO.Al2Os (51-53%), gehlenite 2CaO'AI~O~'Si02 (22-24%), a cryptocrystalline substance (8-10%), and bicalcium silicate y-2CaO-SiO= (5-7%). There is an insignificant (1-3%) impurity content comprising calcium hexaaluminate CaO.6Al=Os, magnetite Fe~Os.FeO, oldhamite CaS, quartz, a carbonaceous substance, anorthite, calcium ferrites, corundum, and calcite.In order to select the most effective (intense) plasticizer addition, we studied the effect of certain compounds on the spreadability of the alumina cement using the cone test developed at the Scientific-Research Institute AzNII. The studies showed that the addition of sodium polyphosphate ensures the maximum spreadability of the cement (Table i). In view of this, we studied the effect of the addition of 0.5% sodium polyphosphate on the strength and hydration of the cement.The investigations were conducted maintaining a water--cement ratio (w:c) that ensures normal thickness (density) of cement; the w:c of the pure alumina cement amounted to 0.33.An addition of 0.5% (NaPOs) n to the cement at an identical water-cement ratio ensures a strength level close to that of the additiveless (plain) specimens (Fig. i) in that the initial and the rated (standard) (on s 28th day) strength of the cement is slightly higher, and after 90 days it is slightly lower than that of the additiveless specimens. Besides this, addition of 0.5% (NaPOs) n decreases the water-cement ratio from 0.33 up to 0.28, i.e., by 15%. In this case, the strength of the cement increases considerably, but it virtually remains constant from 28 up to 90 days. *Here and elsewhere, weight contents are given; in the case of mineral compositions, volume fractions, %, are given. %Carried out by

With the development of methods of processing steel outside the furnace there has been a change in the function of the ladle -from an intermediate container for transporting the metal it has been changed into a most important unit in which the steel is sequentially subjected to refining, blowing with inert gas, and vacuum treatment. Thus, the conditions of service for the refractory lining have been made much rigorous, since the dwell time of the metal in the ladle has increased from 20-30 min to 2-3 h, which has led to a reinforcement of the corrosive action of the steel and slag on the lining. Furthermore, there has been an increase in the abrasive action of the liquid steel on account of the more intense mixing during blowing and vacuum treatment [1][2][3].The use of chamotte linings in such conditions is undesirable, not only because of the sharp fall in the resistance of the ladle, but also as a result of its unfavorable influence on the purity of the metal [i, 2].For lining ladles used in processing steel outside the furnace more resistant high-alumina refractories are bing used [1][2][3][4], including those with additions of chromite [5].In Soviet and foreign practise there is experience with the use of unfired refractories of various compositions for lining ordinary steelcasting ladles [6][7][8][9].The unfired refractories compared with fired products possess a higher resistance to scaling under the action of liquid steel and slag, and low porosity, as a result of which they are less prone to penetration by metal and slag [8, 9].The present article presents the results of investigations into the development of a technology for unfired, mullite-corundum, and fired, mullite-siliceous refractories with additions of chromium ore, and also the results of comparative tests on experimental batches of the newly develope products and industrial mullite-corundum articles in the linings of steel ladles used in treating steel outside the furnace.The following material were used in the investigations: high-alumina chamotte containing 68% AI203 by weight, electrocorundum, Latnensk clay, and chrome ore. The chemical compositions of the starting materials are shown in Table i. Orthophosphoric acid was added to the bodies for the unfired products.The laboratory investigations established the optimum content of orthophosphoric acid in the bodies, e,~uring the production of high-quality green bricks and products, and these results also established the heat process schedule for the unfired and fired refractories.On the basis of the studies at the Semiluksk refractories factory we prepared trial batches of unfired mullite-corundum articles in amounts of about 220 tonnes and fired mullitesiliceous articles with additions of chrome ore in amounts of 50 tonnes.The articles were pressed on SM-I085 toggle presses with a moisture content in the body of 4-4.5%; the apparent density of the green brick for the unfired mullite-corundum articles was on average 2.73, and for fired brick containing chrome ore 2.90 g/cm 3.

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