Elastic properties of refractory silica concretes

Conclusions The authors have designed an ultrasonic experimental apparatus and developed a procedure for using it to investigate the elastic properties of refractory concretes at 20–1500°C.They have determined the elastic moduli and investigated their pattern of change during heating and cooling of silica concretes based on water glass and aluminophosphate binder. They have established that the dynamic elastic moduli of these concretes vary within a wide range. During heating, the elastic modulus of the concretes sharply decreases within the range 50–500°C, then increases up to 1000°C, decreasing again on further rise in temperature.During cooling, the E_d exhibits the reverse pattern of change, but its values at the corresponding temperature are higher than during heating.The results obtained can be used to perfect the procedure for manufacturing refractory concretes and to determine their optimal conditions of service.Translated from Ogneupory, No. 4, pp. 38–43, April, 1979.     

Ceramic cements and ceramic concretes of quartz-chamotte composition

Conclusions On the basis of quartz sand and scrap chamotte refractories (28.0% Al₂O₃, 67.0% SiO₂) we obtained highly concentrated bonding suspensions (cement slips) of mixed composition enabling us to form castings with a porosity of 12.2–18.3% characterized by bending strengths of up to 4.5 MPa and compressive strengths of up to 32.4 MPa.During the use of quartz-chamotte suspensions as bond and of chamotte scrap (grog) as the filler we obtained ceramic concretes with an original compressive strength of 18.4–25.6 MPa, and a porosity of 14.6–19.2%.We studied the change in the physicomechanical properties of the bonds (cements) and the ceramic concretes during heat treatment in the range 100–1450°C.The chamotte ceramic concretes based on quartz-chamotte bonds of the optimal compositions possess an increased spalling resistance (16 water-heat cycles from 1300°C during testing of specimen cubes with edges of 50 mm).Translated from Ogneupory, No. 5, pp. 5–9, May, 1986     

Influence of structural and phase conversions on the thermomechanical properties of chamotte concrete based on high-alumina cement

Conclusions The dehydration of the calcium hydroaluminates and aluminum hydrates when the concrete is heated causes the binder to lose strength and results in the formation of a porous structure.The structure of the cement block depends on the fineness of the cement. During heating at 1100°C, two processes develop in the binder, viz., solid-phase diffusion sintering accompanied by shrinkage, and coalescence of the pores.The reaction of the cement with the chamotte results in the formation of low-temperature minerals in the form of calcium aluminosilicates, the consequence being that liquid-phase sintering continues accompanied by considerable shrinkage.Above 1200°C and especially above 1300°C a large amount of liquid phase is formed in the concrete and dissolves the crystalline minerals (calcium aluminosilicates, mullite, cristobalite, and corundum).The peak temperature at which the chamotte concrete based on high-alumina cement can be used is 1350°C.Translated from Ogneupory, No. 1, pp. 52–57, January, 1977.     

Properties of hot aluminosilicate concretes with various binders

Conclusions On the basis of results of a study of aluminosilicate concretes in the heated state, the following recommendations can be made for the use of these concretes, depending on the form of the binder and on the concentration of Al₂O₃ in the filler.Semiacid concrete in APB has fairly good strength and deformation properties, a high thermal-shock resistance, and can be used up to temperatures of 1350°C.Chamotte concrete in HAC is clearly not economical to manufacture. For performance, it can be totally replaced by chamotte concrete in AC or APB. The chamotte concrete in APB has better characteristics in the heated state than the concretes in other binders. It can be successfully used under conditions where there are sudden variations in the temperature and mechanical action.Aluminosilicate concretes in WG can reasonably be used in conditions of fairly intense abrasive action up to temperatures of 800°C. In places where the concrete is not subject to the action of molten metal or slag, it would not be reasonable to use concretes in WG containing >60% Al₂O₃.The high-alumina concretes in HAC have greater strength at high temperatures and therefore they must be used in those conditions; analogous concretes in APB can reasonably be used where there are sudden variations in temperature.The properties considered here of the concretes in HAC and APB are improved by increasing the concentration of Al₂O₃ and therefore the form of the filler for the concretes must be chosen in relation to the actual conditions of use.Translated from Ogneupory, No. 7, pp. 52–60, July, 1980.     

Studying the strength of unfired phosphate bonded forsterite refractories

Conclusions Refractory products made with magnesium-phosphate bond have a high strength even 1 h after pressing.After 24-h storage the strength of the products made from dunite and magnesite increases 2–7 times, and of articles based on synthetic briquette 4–12 times. The strength of the products is somewhat increased during further storage for 7 days. During prolonged storage the strength scarcely alters.Heat processing for 2 h at 350°C does not affect the strength, or slightly increases it.Magnesium-phosphate bond increases the strength of forsterite products based on synthetic briquette during heating, especially in the interval 500–700°C, and preserves it even at 900°C; the compressive strength of such products is 7–14 times greater than for similar articles bonded with sulfite lye.The adhesive capacity of magnesium-phosphate bond means that it can be used in the production of unfired forsterite products and concretes based on synthetic briquette.For articles made from raw or fired dunite and magnesite, the phosphate bond does not increase the strength compared with sulfite lye bond.Translated from Ogneupory, No. 6, pp. 50–53, June, 1968.     

Production and service testing of magnesite-chrome concrete

Conclusions In addition to magnesite-chrome concretes with periclase cement base, they can also be manufactured using a periclase-spinel cement. These concretes show less initial strength, but they soften to a lesser degree over the range 400 to 1000–1200°, hence after heating their strength is not lower than concrete with a periclase-cement base.The least softening of magnesite-chrome concretes over the given temperature range is shown by those with the addition of magnesium sulphate solution and soluble glass; as the modulus of the soluble glass is reduced, the compressive strength of the concretes under air-dry conditions and during heating increases. To obtain strong concretes, the soluble glass modulus must come within 1,8–2,2.In pneumatic tamping the strength of magnesite-chrome concretes is much greater than in vibration methods.In the spouts of electric steel-smelting and open-hearth furnaces, magnesite-chrome concrete showed a high degree of resistance, and its use for this purpose should be widely recommended.In the walls of an electric steel smelting furnace, the magnesite-chrome concrete was not inferior in strength to magnesite brick. The concrete containing magnesium sulphate was particularly satisfactory in this respect.The positive results of the test show the advisability of using concretes with a magnesium sulphate bond in the walls of electric furnaces with a view to replacing rammed linings made with a tar and pitch bond.The use of concrete for lining arresters in vacuum steel casting ensures satisfactory steel casting and has no effect on the quality of the metal.     

Effect of high temperatures on high performance steel fibre reinforced concrete

After being subjected to different elevated heating temperatures, ranging between 105 °C and 1200 °C, the compressive strength, flexural strength, elastic modulus and porosity of concrete reinforced with 1% steel fibre (SFRC) and changes of colour to the heated concrete have been investigated.The results show a loss of concrete strength with increased maximum heating temperature and with increased initial saturation percentage before firing. For maximum exposure temperatures below 400 °C, the loss in compressive strength was relatively small. Significant further reductions in compressive strength are observed, as maximum temperature increases, for all concretes heated to temperatures exceeding 400 °C. High performance concretes (HPC) start to suffer a greater compressive strength loss than normal strength concrete (NSC) at maximum exposure temperatures of 600 °C. It is suggested that HPC suffers both chemical decomposition and pore-structure coarsening of the hardened cement paste when C-S-H starts to decompose at this high temperature. Strengths for all mixes reached minimum values at 1000 or 1100 °C. No evidence of spalling was encountered. When steel fibres are incorporated, at 1%, an improvement of fire resistance and crack [F.M. Lea, Cement research: retrospect and prospect. Proc. 4th Int. Symp. On the Chemistry of Cement, pp. 5-8 (Washington, DC, 1960).] resistance as characterized by the residual strengths were observed. Mechanical strength results indicated that SFRC performs better than non-SFRC for maximum exposure temperatures below 1000 °C, even though the residual strength was very low for all mixes at this high temperature. The variations with colour, which occured, are associated with maximum temperatures of exposure.     

Abradability of corrosion-resistant concretes at elevated temperatures

Conclusions The abradability of corrosion-resistant concretes with liquid glass, portland cement and alumina cement with chamotte fillings is considerably less than for chamotte brick up to 600°. When heated to 800° the abradability of these concretes and chamotte brick is more or less the same; it is the same as at the usual temperature.The greater the strength of the concrete and filler, the less the abradability.The abrasion-resistant of corrosion-resistant concretes in the heated state is better than when cooled down from high temperatures.     

Vibrational molding of ceramic concretes. Molding systems and the regularities of the process

Conclusions We developed a vibrational molding process for obtaining ceramic concretes using rigid mixtures and metallic molds. The as-formed semifinished products are characterized by a fairly high mechanical strength. A siliceous (silica-based) ceramic concrete having a porosity of 12–16% and an ultimate compressive strength of 20–25 N/mm² was obtained. The mechanism of structure evolution of the semifinished products was identified; it is determined by the interaction between the phases and fixing (orientation) of the liquid phase of the highly concentrated binder suspensions due to the molecular forces of the filler grains.The decisive effect of the binder on the mechanical properties of the ceramic concretes was established. On decreasing the binder content of the ceramic concretes from 39 to 12%, their specific strength increases by 4 times.Translated from Ogneupory, No. 6, pp. 8–14, June, 1993.     

Properties of silicate ceramic concrete

Conclusions The effect of the pH, the volume concentration of solid phase in the binding suspension, and strengthening on the physicomechanical properties and the volume changes of a silicaceous ceramic concrete with a rigidly set framework of filler has been studied over the temperature interval of 100–1580°C.The silicaceous ceramic concretes of optimum compositions as a function of the factors we studied has an ultimate compressive strength of 20–78 MPa, an open porosity of 15.5–22.6%, and good refractoriness.Translated from Ogneupory, No. 3, pp. 51–54, March, 1981.     

Deformation characteristics of silicon carbide and chamotte refractories

Conclusions It was established that silicon-carbide refractories with bonds of silicon nitride and oxynitride, and also self-bonded silicon carbide articles possess 2–3 times higher elasticity moduli compared with chamotte (firebrick) refractories.The anisotropy of the elasticity modulus determined in the longitudinal and transverse directions of the refractories is markedly higher (anisotropy coefficient n=2.28–2.49) than for chamotte refractories (n=1.22).In high-temperature conditions (1600–1650°C) the compressive strength of SiC refractories is about 28 N/mm², and the tensile strength 2.1 N/mm², i.e., the compressive strength is about 10 times higher than the tensile.At room temperature the strength of SiC refractories is double that of chamotte, while at 1200–1400°C this difference increases to 10 times.Silicon carbide self-bonded articles at high temperatures possess the highest strength properties, which confirms the effectiveness of using them in service under the action of abrasive forces.A new method was developed for determining the deformation and strength characteristics of refractories on the UITS-0.5/2.5 test machine.A method was developed for obtaining tension and compression diagrams from the results of tests for pure and longitudinal-transverse bending.Translated from Ogneupory, No. 7, pp. 8–13, July, 1989.     

Restoring heat-resistant masonry made of concrete

Conclusions In the temperature range 20–1000°C we obtained reliable bonding of new concrete based on water glass with old concrete based on Portland cement, heated to 800°C. With a bonding strength of more than 5 kg/cm² (about 5 kN/m²),there is no need to carry out finishing operations on the repaired sections of the old concrete nor to cut its surface.Coating the surface of the old concrete with water glass markedly reduces the bonding strength and cannot be recommended.Successful repairs of furnaces can be achieved by using plastic concrete (settling of standard cone 3–5 cm). The density of the water glass should not be less than 1.38 g/cm³.Bonding of the concretes has a relatively small value if the old concrete is heated to a temperature of less than 600°C, In this case the increase in the strength of bonding can be obtained by treating the surface of the old concrete with HCl.     

Effect of conditioning temperature on the strength and permeability of normal- and high-strength concrete

In order to evaluate the effect of the conditioning temperature on strength and permeability properties of concrete a series of compressive, indirect tensile and permeability tests were performed on concretes (designed to have 28-day compressive strengths of 40 and 100 N/mm²) conditioned at temperatures of 85 and 105 °C. The results show that, for both the normal- (NSC) and the high-strength concrete (HSC), comparable 28-day test results were obtained from strength tests performed on concrete conditioned at 85 and 105 °C. The permeability results were also somewhat similar for the two conditioning temperatures, although greater differences than previously reported were observed. Conditioning at both 85 and 105 °C was identified as adequate, with the preferred temperature of conditioning being 105 °C.     

Aluminophosphate bonded refractory mortars

Conclusions Chamotte mortars containing aluminophosphate bonds considerably improve the strength of the joint between firebrick refractories after heating to 400–800°C compared with mortars based on Portland cement and water glass. The highest strength for the mortar-firebrick bond is provided with a phosphoric acid density of 1.42–1.43 g/cm³ (60% phosphoric acid), and incorporating 20% bond in the mortar.It is possible to increase the strength of the chamotte mortar containing aluminophosphate bond during air setting and during heating, and also to increase the strength with time, by adding active materials to the mortar.Aluminophosphate-bonded mortar markedly increases the strength of the refractory-metal bonding, which is very important in building linings which are subject to movement during operation for example, in rotary kilns. It is desirable to test mortars containing aluminophosphate bonds in rotary kilns, and also in similar plant in the refractories, ceramic, and cement industries.Translated from Ogneupory No. 1, pp. 37–42, January, 1971.     

Compressive behavior of fiber reinforced high-performance concrete subjected to elevated temperatures

In this paper, the effects of elevated temperatures on the compressive strength stress–strain relationship (stiffness) and energy absorption capacities (toughness) of concretes are presented. High-performance concretes (HPCs) were prepared in three series, with different cementitious material constitutions using plain ordinary Portland cement (PC), with and without metakaolin (MK) and silica fume (SF) separate replacements. Each series comprised a concrete mix, prepared without any fibers, and concrete mixes reinforced with either or both steel fibers and polypropylene (PP) fibers. The results showed that after exposure to 600 and 800 °C, the concrete mixes retained, respectively, 45% and 23% of their compressive strength, on average. The results also show that after the concrete was exposed to the elevated temperatures, the loss of stiffness was much quicker than the loss in compressive strength, but the loss of energy absorption capacity was relatively slower. A 20% replacement of the cement by MK resulted in a higher compressive strength but a lower specific toughness, as compared with the concrete prepared with 10% replacement of cement by SF. The MK concrete also showed quicker losses in the compressive strength, elastic modulus and energy absorption capacity after exposure to the elevated temperatures. Steel fibers approximately doubled the energy absorption capacity of the unheated concrete. They were effective in minimizing the degradation of compressive strength for the concrete after exposure to the elevated temperatures. The steel-fiber-reinforced concretes also showed the highest energy absorption capacity after the high-temperature exposure, although they suffered a quick loss of this capacity. In comparison, using PP fibers reduced the energy absorption capacity of the concrete after exposure to 800 °C, although it had a minor beneficial effect on the energy absorption capacity of the concrete before heating.     

Explosive spalling and residual mechanical properties of fiber-toughened high-performance concrete subjected to high temperatures

In this paper, an experimental investigation was conducted to explore the relationship between explosive spalling occurrence and residual mechanical properties of fiber-toughened high-performance concrete exposed to high temperatures. The residual mechanical properties measured include compressive strength, tensile splitting strength, and fracture energy. A series of concretes were prepared using OPC (ordinary Portland cement) and crushed limestone. Steel fiber, polypropylene fiber, and hybrid fiber (polypropylene fiber and steel fiber) were added to enhance fracture energy of the concretes. After exposure to high temperatures ranged from 200 to 800 °C, the residual mechanical properties of fiber-toughened high-performance concrete were investigated. For fiber concrete, although residual strength was decreased by exposure to high temperatures over 400 °C, residual fracture energy was significantly higher than that before heating. Incorporating hybrid fiber seems to be a promising way to enhance resistance of concrete to explosive spalling.     

A concrete for lining blast furnace shafts

Conclusions A composition of refractory concrete based on mullite-corundum chamotte, silicon carbide, and high-alumina cement has been developed for repair of blast furnace shafts.It has been shown that under normal conditions after hardening the concrete possesses a dense structure and sufficiently high strength. In heating to 1400°C the strength and density of the concrete drop, reaching a minimum at 1100°C which is sufficient for normal service of the blast furnace.Alkali-resistance tests of the concrete were made on a stand under conditions of a reducing medium and it was shown that under the action of alkalis and CO a zonal structure with the greatest change in properties in the working zone is formed.The concrete developed was used for preparation of a large-block cooled panel for the shaft of No. 2 blast furnace of Il'ich Metallurgical Combine. The panel has been in service since 1985.Translated from Ogneupory, No. 6, pp. 47–50, June, 1989.     

Dependence of the properties of chamotte on the firing regime of the briquette

Conclusions The physicomechanical properties and phase composition of chamotte depends on the composition of the gas medium, the firing temperature, and the cooling regime. In the briquettes fired at 1500°C in an oxidizing medium with the cooling temperature lowered from 1500 to 1200°C, the apparent density increases and the porosity decreases. In the briquettes fired in a reducing medium with the cooling temperature lowered from 1500 to 1300°C, there is a reduction in the apparent density and an increase in the porosity but with a further reduction of the cooling temperature to 1200°C, these properties change in the opposite direction.The apparent density of chamotte and its concentration of mullite is increased with a reduction in the cooling rate. The apparent density of the chamotte from the Polozhsk kaolin under analogous cooling conditions increases more rapidly than that from the Novoselitsk kaolin chamotte.The temperature interval in which the cooling rate effectively increases the apparent density of the chamotte fired in an oxidizing medium is 1500–1300°C. In a reducing medium this interval is shifted 100°C toward lower temperatures.The experiments have shown that an increase in the cooling rate of the fired briquettes at temperatures below 1200°C has only a very slight effect on the apparent density and porosity of the Novoselitsk kaolin chamotte. When the chamotte has been obtained from Polozhsk kaolin, a reduction in the cooling rate at temperatures below 1200°C, and particularly in a reducing medium, has a quite perceptible effect on the increase in apparent density and reduction of porosity of the material.Translated from Ogneupory, No. 3, pp. 22–26, March, 1982.     

Aluminosilicate concretes bonded with water glass

Summary A composition was developed for aluminosilicate concrete with a water-glass bond with a density of 1.25–1.30 g/cm³ and with a setting accelerator-Portland cement.By reducing the density of the glass and eliminating the addition of sodium silicofluoride, the RUL is increased by 300° C compared with ordinary concrete used at present. The concrete possesses a high strength over the entire temperature range, a high abrasion resistance and excellent spalling resistance.The technical properties of the fireclay concrete suggest that this material can be used at up to 1300° C, and the aluminous at up to 1450° C in place of piece aluminosilicate goods.To solve the problem of the reliable and mass use of the recommended concretes in heat exchangers and in other parts of rotary cement furnaces it is necessary to carry out extra tests with the concretes on a bigger scale.     

Effect of phosphate binders on the strength of the material based on electrocorundum and pyrophyllite

Conclusions Addition of pyrophyllite to the system of corundum concrete produced using phosphate binders leads to a reduction in the temperature of setting (hardening) up to room temperature, an increase in the strength at moderate temperatures (up to 973°K), a significant resistance to softening in the 973–1273°K range, and an improved thermal shock resistance.The increase in the strength during the heating process can be attributed to the formation of complex polymeric forms of aluminum and silicon phosphates in the material which largely remain amorphous when heated up to 1723°K at a rate of 0.5–1°K/min. Above 1473°K, a small amount of a liquid phase (silicon pyrophosphate) forms in the material whose quantity decrease with increasing pyrophyllite content.Deceased.Translated from Ogneupory, No. 3, pp. 5–8, March, 1987.