Strength properties of chamotte concretes based on phosphate binders

Conclusions The authors have investigated the strength properties of chamotte concretes based on phosphate binders over a wide range.They have shown the dependence of the compressive strength of the concretes on the type of phosphate binder used, the heat treatment temperature of the concrete, and its test temperature. Maximal compressive strength is exhibited by concretes roasted at 1450°C.They have established a relation between the physicochemical transitions taking place in a phosphate binder during heating and the strength characteristics of the concrete.Simultaneous introduction of phosphate binder and clay to the extent of 10–20% into chamotte concretes increases their strength at 20°C and during heating.Translated from Ogneupory, No. 6, pp. 32–36, June, 1979.     

Use of zeolite-rich rocks and waste materials for the production of structural lightweight concretes

This paper aims at testing the use of mixtures constituted by natural zeolitized products and SiC-bearing industrial wastes (sludge deriving from polishing of porcelain stoneware tiles, hereafter DPM) for the production of lightweight expanded aggregates as constituents of structural and/or thermo-insulating lightweight concretes. Two commercial products have been used as zeolite natural source: Cab70 (Yellow facies of Campanian Ignimbrite) and IZclino (Turkish clinoptilolite-rich epiclastite). Different amounts of a calcareous material (Pozzano limestones — hereafter CP) from the Sorrento peninsula (Naples — Italy) were also added to a Cab70–DPM mixture. All raw materials were characterized by means of mineralogical (XRPD) and chemical (XRF) analyses. All the products and mixtures were tested from a technological point of view by means of fusibility and firing tests in order to evaluate the expanding properties. It was evidenced that the expansion of the mixture was deeply depending on the occurrence of SiC in the industrial waste. The addition of CP (10 wt.%) to the mixtures accounts for an even increased expansion, though this is accompanied by a worsening of the mechanical features of the material.These results along with literature data allowed to select 3 mixtures (70% Cab70–30% DPM, 70% IZclino–30% DPM, 60% Cab70–30% DPM–10% CP) and each of them was used for the preparation of 5 l of lightweight aggregates afterward employed for the manufacture of lightweight concretes. It was remarked that natural zeolitized materials mixed with DPM (30 wt.%) can provide lightweight aggregates with densities ranging between 0.8 and 1.0 g/cm³ suitable for the preparation of structural lightweight concretes. The addition to the mixture of CP (10 wt.%) produces less dense aggregates (0.6–0.7 g/cm³) potentially useful for the manufacture of thermo insulating lightweight concretes.     

Effect of technological factors on the properties of silaceous ceramic concrete

Conclusions Using as an example a silaceous ceramic concrete (dinas filler with an average grain size D _gr ^av =5–10 mm; binder, a quartz sand suspension), the effect of the technological factors on the properties of the ceramic concrete has been studied.Depending on the technological factors, the silaceous ceramic concrete is characterized by an open porosity of 14.4–27.6%, a volume increase of 1.8–18.1%, and an ultimate compressive strength of 15.2–48.8 MPa.Translated from Ogneupory, No. 8, pp. 53–57, August, 1981.     

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     

Properties of vitrified quartzite and refractory concretes based on it

Conclusions Vitrified quartzite (density 2.29 g/cm³) containing 86–96% of a vitreous phase and 14–4% of a crystalline phase (quartz, cristobalite) has been obtained by roasting in a sintering plant by the suction method. The authors have developed compositions of refractory concretes with a vitrified quartzite filler based on sodium hexametaphosphate, aluminophosphate binder, and water glass. The concretes have a nonshrinking structure, high onset temperatures of deformation under a load of 2 kgf/cm², and a high heat resistance.Translated from Ogneupory, No. 6, pp. 26–32, June, 1979.     

Some technological laws and properties for highly porous ceramic concretes

Conclusions Using ceramic concrete made from zirconia as an example we formulated conditions and established the main technological laws for obtaining highly porous ceramic concretes.We analyzed the composition and microstructure of the ceramic concrete from the point of view of the existence in the system of noncompensated shrinkage. It is shown that for ceramic concrete with a high bond shrinkage during drying and heat treatment, with the purpose of reducing the shrinkage stresses in the system, it is necessary to use multifraction (coarse, medium, and fine) fillers.We show the effectiveness of using, as one of the filler components, removable poreforming additive, based on foamed polystyrol.The optimum region of the grain-size distribution of the components was established; this comes within the true specific volumes in the structure of the shaped ceramic concrete and amounts to 20–30% bond, 20–25% fine (0.1–0.4 mm) and 25–40% coarse (5–10 mm) filler made from waste zirconia foamed ceramics, and 20–25% foamed polystrol (0.63–1.6 mm).We studied certain properties of the resulting materials with a porosity of 60–75% and a compressive strength of 5–20 MPa.Compared with other highly porous materials, for example, foamed ceramics, the highly porous ceramic concretes have technological advantages (much lower water capacity of the shaping system, reduced shrinkage in drying and firing) and also improved operating characteristics, for instance, thermal conductivity, thermal-shock resistance and volume constancy.Translated from Ogneupory, No. 2, pp. 20–25, February, 1984.     

Effect of binder content on the performance of alkali-activated slag concretes

This paper assesses the mechanical and durability performance of concretes produced using alkali silicate-activated ground granulated blast furnace slag as sole binder. Alkali-activated concretes are formulated with 300, 400 and 500 kg slag per m³ of fresh concrete, and their performance is compared with reference concretes produced using Portland cement (OPCC). Regardless of the binder content, the alkali-activated slag concretes (AASC) develop higher compressive strength than the comparable reference concretes. A higher binder content leads to increased strength in both AASC and OPCC at 28 days. However, at 90 days, the performance penalty for low binder content is more significant in the OPCC than AASC samples. Permeability, water sorption and carbonation resistance properties are also improved at higher binder contents. By controlling mix design parameters, it is possible to produce AASC with mechanical strength and durability comparable to conventional Portland cement concretes.     

Heat-resistant composites based on a ternary binder suspension

Conclusions Combining the processes of mechanical wet milling of a ternary mixture (quartz sand, scrap of the MKS-83 refractories, and monoclinic zirconium dioxide) and topochemical interaction between its particles and the ions of dissociated sodium silicate facilitates the formation of a gelatinous coating at the surface of the particles and, thereby, imparts adhesiveness (bonding capacity) to the suspensions and ensures thermal volume constancy of the castings.We established the optimum pH value of the suspension for attaining its minimum viscosity and obtaining the maximum levels of the ultimate bend strength of the castings (4–5 N/mm²) and minimum open porosity (18–19%).Based on the obtained suspensions and a corundum filler (the 2–0.5 mm and the minus 0.5-mm fractions), we developed casting bodies and obtained ceramic concretes (firing temperature 1400°C) having an ultimate bending strength of 28 N/mm² and capable of withstanding 54 thermal cycles (1300°C — water).Translated from Ogneupory, No. 1, pp. 4–7, January, 1992.     

Properties and user tests of new types of refractory concretes

Conclusions The results of these experimental studies of concretes in a binder made from natural high-silica glasses under industrial conditions have shown their high efficiency and user stability and that they are significantly more stable than the traditional refractory products. This makes it possible to recommend the new concretes for wide industrial use at operational temperatures of 1200–1600°C.Translated from Ogneupory, No. 7, pp. 47–48, July, 1981.     

Aqueous suspensions of mullite: Their rheology and the properties of cast products from them

Conclusions Concentrated aqueous suspensions of mullite were obtained. These made it possible to produce casts of comparatively high density and strength with low shrinkage on drying.We have studied the effect of stabilization, pH, and concentration of suspensions on their rheological and technical properties.We show the possibility of using mullite suspensions as the bonding (binder) for refractories of a grainy structure (filler: corundum or mullite) and for ceramic concretes.Mullite and mullite-corundum refractories of a grainy structure bonded by mullite suspensions have been made. The properties of these refractories have been studied. The materials have excellent strength and thermal-shock resistance.Translated from Ogneupory, No. 3, pp. 45–50, March, 1980.     

Binders for compacting the products based on nonplastic materials

Conclusions We studied the effect of various components of the binders on the properties of the press-powders and the semifinished products. The binder of the obtained composition can be used for preparing press-powders from nonplastic materials.Translated from Ogneupory, No. 4, pp. 22–24, April, 1986.     

Vibro-cast periclase refractories of a grainy structure and some of their properties

Conclusions We have studied the process of obtaining vibro-cast periclase refractories based on fine- and coarse-grained molding systems using a low-concentration solution of HCl as the binder.Using a combined experimental and calculation method based on the use of a cone, we have carried out studies to optimize the production parameters of the vibro-casting process.The materials obtained in the initial (unfired) state are characterized by fairly high strength (_comp=12–30 MPa) and can be used as refractory concretes.The process of sintering the materials was studied and it is shown that their properties are comparable with the normal periclase refractories of a grainy structure. After firing at 1550–1600°C the refractories show virtually no additional shrinkage and their true porosity is 19–23%, ultimate compressive strength 30–60 MPa, and ultimate bend strength 12–26 MPa.The results were proved industrially. Large details of the smelting unit of induction furnaces were manufactured and successfully tested.Translated from Ogneupory, No. 8, pp. 9–15, August, 1986.     

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.     

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.     

Production and properties of highly porous zircon materials

Conclusions We proposed, using zircon as an example, the principle of forming pores of two types — cellular and capillary — for obtaining highly porous (up to 90%) ceramics. It consists of a combination of the foam method and the introduction of removeable foamed polystyrene. At the stage of forming and drying the system is distinguished by a high volume constancy, uniformity of properties, and the possibility of carrying out rapid drying.On the basis of a zircon suspension as the bond and crushed zircon foamed ceramics as the filler we obtained a highly porous ceramic concrete with a porosity of 50–70% and a compressive strength of 12–24 MPa.A marked influence on the properties of the resulting materials is exerted by the microcracks formed as a result of the removal of the expanded polystyrene (PPS) in the foamed ceramic, and the presence of uncompensated shrinkage in the ceramic concrete. With an increase in the value of the uncompensated shrinkage from 0 to 7%, the thermal-shock resistance of the ceramic concretes is increased 1.3 times and the thermal conductivity is reduced by a factor of 1.25.Translated from Ogneupory, No. 7, pp. 20–25, July, 1984.     

Refractory concretes of a new generation: Relationship between their composition,structure, and properties

Conclusions The structural features of the refractory concrets were characterized. The refractory concretes containing coarse (lumpy) fillers were classified into a separate group. The composition of these refractories is characterized by a significant volume fraction of a coarse (50–150 mm) filler.The dependence of the strength, the elastic properties, and several other characteristics of the refractory concretes on their chemical composition and on the content of the matrix phase and the highly dispersed powders was established.The variation of the strength of the ceramic binders in the as-dried condition as a function of the initial porosity was determined for the HCBS of different groups. At comparable values of porosity, the parameters of strength can differ significantly depending on the composition and different technological factors.Translated from Ogneupory, No. 3, pp. 5–11, March, 1993.     

Critierional evaluation of thermal destruction of corundum concretes

Conclusions The resistance of corundum concretes to thermal destruction was studied using the experimentally plotted deformation diagrams and the standard thermal cycling method. The correlation between the values of thermal shock resistance obtained according to these methods was established for the corundum concretes.It was established that as compared to the concrete produced using a binder based on the Talyum cement, the concretes incorporating a hydraulically hardening (water-setting) binder prepared from the VTs-70 grade high-alumina cement exhibit better resistance to thermal stresses. With increasing strength and density of the concretes, their thermal destruction occurs catastrophically (abruptly) since the elements of a stronger structure (the concretes produced using the Talyum cement-based binder) are incapable of effectively hindering the growth of a potential crack.Modification of the structure of the concrete by introducing Cr₂O₃ additive leads not only to an increased thermal shock resistance in the high-temperature range due to an increased critical crack length, but also to an increased resistance ot crack displacement (opening).Translated from Ogneupory, No. 5, pp. 3–8, May, 1988.     

Properties of heat-treated specimens based on aqueous suspensions of quartz sand

Conclusions The effect of pH of the dispersion medium, the concentration of solid phase in the suspension, and the strengthening of the semifinished products in an aqueous solution of water-glass on the properties of specimens based on aqueous suspensions of quartz sand heat-treated in the 100–1580°C interval have been studied.Depending on the factors we studied, the specimens have an ultimate compressive strength of 9.0–190.0 MPa; bend strength of 2.6–49.7 MPa; open porosity of 11.0–22.9%; and a volume increase of 0.72–19.1%.Translated from Ogneupory, No. 1, pp. 50–54, January, 1981.     

Cast oxide refractories of a grainy structure. Initial compositions and the principles of molding

Conclusions The main principles in the technology of cast ceramic or refractory materials of a grainy structure are considered using some pure oxides or their compounds as an example.The general principles of the change in the rheological properties of the fine-grained suspensions as they are saturated by the grainy filler are considered.A process has been developed for cast-filled systems in inactive molds and it is shown that under specific conditions this method is as good as the method of vibrocasting in active molds.The semifinished product based on the grainy cast systems has adequate mechanical strength and low shrinkage when molded, dried, and sintered.Translated from Ogneupory, No. 6, pp. 6–11, June, 1985.     

New-generation refractory concretes. Thermal processes,structure and high-temperature properties

Regularities of the processes of drying and heat treatment (firing) of new refractory concretes (ceramic concretes, low-cement refractory concretes, etc.) are considered. The conditions for the appearance of the effect of their explosive cracking (destruction) in drying are analyzed. Changes in the porous structure and some characteristics of the concretes (porosity, strength, shrinkage, expansion) are considered as functions of the temperature of their preliminary treatment. Regularities in the formation of the zonal structure and the stress state in use of refractory concretes are described. Data on the thermal conductivity and thermal expansion of refractory concretes of the Al₂O₃-SiO₂ system are presented for a wide temperature range.Translated from Ogneupory, No. 6, pp. 5–12, June, 1995.