Refractory Concretes Research Articles

High Temperature and Wear Resistant Materials with Improved Operating Properties

Results are provided for studies of self-sintering refractory mix preparation. New technology is proposed for their manufacture. The basis of the mixes obtained is barite-containing components (barite or witherite concentrates). Good chemical resistance, refractoriness, mechanical strength, hardness and wear resistance determine the scope of their application, i.e., manufacture of refractory products, linings, pastes, and concrete.

Cement-Free Refractory Concretes. Part 2. High-Alumina and Corundum Ceramic Concretes1

On the basis of refractory bauxite and very fine quartz glass (VFQG) by means of stagewise combined wet grinding HCBS are prepared having a low moisture content and good binder properties that are achieved due to an optimum content within them of very fine particles (nano-particles and colloidal component). These HCBS are used as a matrix system in the manufacture of many forms of ceramic concrete in the systems Al2O3–SiO2, Al2O3–SiO2–SiC, and Al2O3–SiO2–SiC–C. All of them are distinguished by improved thermomechanical and operating properties. Based on electrocorundum and VFQG similar HCBS and corundum ceramics are prepared (95% Al2O3) with their use. Corundum ceramic concretes are prepared based on a vibration-cast mixture with a moisture content of 3.8% having porosity up to 11% and good strength at elevated temperature.

Refractory and Mechanical Properties of Dealuminated Kaoline-Based Geopolymer Concrete

This study has been performed to evaluate the performance of the industrial by-product dealuminated kaolin (DK) as geopolymer paste in production a refractory concrete. The paper study the thermal and mechanical properties of concrete mixtures containing crushed refractory brick as combined aggregate and geopolymer paste produced from the blend of 10%, 20% and 30% of DK, ordinary Portland cement (OPC), solution of sodium hydroxide and sodium silicate as alkaline activator. These concrete mixtures were tested for workability, shrinkage at 400,800 and 1200 °C, thermal shock resistance at temperature of 950 °C, Cold crushing strength, tensile strength, and elastic modulus. The results of these mixtures compared with the results of concrete mixtures containing 100% OPC and 100% aluminous cement (AC) .The results show that the thermal and mechanical properties of geopolymer concrete produced by dealuminated kaolin (DK) are enhanced. Also, it is found that mixture contains 20% of DK appears to be the optimal geopolymer concrete mixture.

Cementless refractory concrete. Part 2. High alumina and corundum ceramics

The HCBS of a composite composition based on refractory bauxite and highly dispersed quartz glass (HDQG) were obtained by one-stage joint wet grinding. The HCBS are characterized by low humidity and high astringent properties, which are achieved due to the optimal content of highly dispersed particles (nanoparticles and colloidal component) in them. These HCBS are used as a matrix system in the manufacture of many types of ceramic concrete in the systems Al 2 O 3 ‒SiO 2 , Al 2 O 3 ‒SiO 2 ‒SiC, Al 2 O 3 ‒SiO 2 ‒SiC‒C. All of them are distinguished by improved thermomechanical and operational characteristics. Similar HCBS and corundum ceramics (95 % Al2O3) with their use were obtained on the basis of electrocorundum and HDQG. Corundum ceramic concrete, characterized by porosity up to 11 % and high strength at elevated temperatures, are obtained on the basis of vibrocast masses with a moisture content of 3,8 %. Ill. 10. Ref. 46.

Modeling refractory concrete lining of fluid catalytic cracking units of oil refineries

This work presents a numerical modeling procedure to simulate the refractory concrete lining in fluid catalytic cracking units of oil refineries. The model includes the simulation of the anchors that reinforce the contact between the refractory concrete and the steel casing. For this purpose, the constitutive relations of an interface finite element are set to values that represent the homogenized behavior of the anchored interface. The parameters of this constitutive relation can be obtained by experimental tests. The model includes also multi-surface plasticity, in order to represent the behavior of the refractory concrete lining. Since the complexity of real case applications leads to high computational costs, the models presented here were implemented in a high-performance parallelized finite element platform. A case study representing a riser similar to the ones used by the refinery industry demonstrates the potential of the model.

High temperature materials: properties, demands and applications

High-temperature materials are used in a wide range of industries and applications such as gas turbine engines for aircrafts, power and nuclear power plants, different types of furnaces, including blast furnaces, some fuel cells, industrial gas turbines, different types of reactors, engines, electronic and lighting devices, and many others. Demands for high-temperature materials are becoming more and more challenging every year. To perform efficiently, effectively and at the same time to be economically viable, the materials used at high temperatures must have certain characteristics that are particularly expected for applying under such extreme conditions, for example, the strength and thermal resistance. In the present review, some important requirements that should be satisfied by high temperature materials will be discussed. Furthermore, the focus is put on refractory concretes, ceramics, intermetallic alloys, and composites as four different categories of these materials, which are also considered in respect to possibilities to overcome some of the current challenges.

Cement-Free Refractory Concretes. Part 1. General Information. Hcbs and Ceramic Concretes

The general nature of the dependence of engineering and service characteristics of refractory concretes with an average cement content, and also low-cement (LCRC), ultra-low cement (ULCRC) and cement-free (CFRC), on the content of CaO (or HAC) in them is analyzed. Significant advantages of cement-free concretes are the reduced moisture content of the concrete mixture, which determines their increased density, a continuous increase in strength (absence of a softening temperature range typical for LCRC and ULCRC), and improved thermomechanical and operational characteristics. With use of CFRC, the insurmountable complexity of the LCRC and ULCRC connected with their initial heating in the dehydration temperature range of the HAC (up to 450°C) is resolved. The main provisions and stages of creating HCBS or artificial ceramic binders as a matrix system of ceramic concrete, i.e., LCRC with improved characteristics, are described. Classification of HCBS groups proposed by the author based on the chemical nature of their solid phase is considered.

Nanomodification of Refractories with Finely-Dispersed Additives with the Use of a Vortex Electromagnetic Homogenizer

The article presents the laboratory and industrial research and the analysis of the impact of modification of refractory concretes and products with finely-dispersed nanomaterials. The dependence of the structural and physical-mechanical characteristics of mullite-corundum refractories of different types (for ladle furnace lances and for supporting blocks of rolling mill carriages) on nanomodification by electromagnetic homogenization is shown. The possibility of using a vortex electromagnetic homogenizer to significantly improve the performance of refractories is shown. In addition, the efficiency of using nanodispersed silicon dioxide is established and its optimal concentration is determined.

Thermo-mechanical behavior of stainless steel fiber reinforced refractory concrete: Experimental and numerical analysis

Stainless steel fibers are widely used as reinforcement in the refractories due to advantages such as high thermal compatibility, cost-effective on account of long life and effective resistance to corrosion at high temperatures. The purpose of this research is to investigate the thermomechanical behavior of alumina based refractory concrete reinforced with different shapes of stainless steel fibers. Straight, wavy and knurled shaped stainless-steel fibers were selected for the study. These refractory composites are extensively procured for the industrial applications. A research program of experimental test and numerical simulations was carried out. Three-point bending, fiber pull-out, direct tensile and compression tests were performed at temperatures ranging from 25 to 1200 °C to obtain the mechanical residual values. The experimental test results allowed the development of the material’s constitutive model that was implemented in the finite element program ABAQUS. The constitutive model was validated through thermomechanical simulations of the round panel test. The flexural results showed the behavior of the reinforcement with knurled fibers was superior for all temperatures due to its higher bond with the matrix. The experimental tests and the numerical simulations showed that the reinforcement benefits the pre-peak and post-peak behavior of the refractory concretes. The influence of the fibers on the shape of the softening curve allows the prediction of the fracture behavior of the composites.

The Effect of Andreasen ́s Packing Distribution Modulus on the Physical and Mechanical Properties of a Low Cement Refractory Castable

Among modern refractory concretes (MRC), those with low cement content (LCC) where CAC = 4-6wt%, are widely commercialized, considering that their properties approximate those of burned bricks of the same class. In this work, the effect of the modulus q of Andreasen ́s particle size distribution, on the physical (porosity, bulk density) and mechanical (flexural strength and dynamic elastic modulus) properties, of either pre-fired or simply dried specimens of a ≥85% Al2O3 LCC ́s, was investigated. The different LCC ́s samples were formulated according to the Andreasen ́s model, using several distribution modulus (q = 0.22, 0.26, 0.30, 0.33 and 0.42). Measurements of the Dynamic Elastic Modulus (DEM) as a function of temperature (25 to 1500°C), using the Impulse Excitation Technique (IET), were taken as a key indicator of the microstructure dynamic behavior. For the sake of just a punctual comparative term, the physical and mechanical properties of a conventional type refractory concrete (CRC) with a higher CAC percentage (15%) formulated with q = 0.26 was also evaluated. The results indicated that distribution modulus values of; q =0.22, 0,26, 0.30 and 0.33 lead to higher DEM values. While q=0.42 lead to the smallest value in the LCC series. Also, higher DEM values ​​were obtained for LCC ́s (CAC = 5%) than for conventional concrete with CAC = 15% under the same value of q for pre-fired samples. In addition, by observing the occurrence of damping effects in specific temperature ranges, the loss of crystallization water from the calcium aluminate hydrates, as well as the development of pyroplastic behavior could be inferred. The gathered information is relevant to predict the behavior of LCC ́s and CRC ́s when put into service for the first time.

Cementless refractory concretes. Part 1. General information. HCBS and ceramic concrete

The general nature of the dependence of the technological and service characteristics of refractory concretes with an average cement content, as well as low-cement (LCRC), ultra-low cement (ULCRC) and cementless (CLRC), on the content of CaO (or НАC) in them is analyzed. Significant advantages of cementless concretes are the reduced moisture content of the concrete mixture, which determines their increased density, a continuous increase in their strength (the absence of a softening temperature range typical for LCRC and ULCRC), and improved thermomechanical and operational characteristics. With the use of BSCH, the insurmountable complexity of the SCB and SSCB associated with their initial heating in the temperature range of the dehydration of the HАC (up to 450 °C) is solved. The main provisions and stages of creating HCBS or artificial ceramic binders as a matrix system of ceramic concrete --- CLRC with improved characteristics are described. The classification of HCBS groups proposed by the author based on the chemical nature of their solid phase is considered. Ill. 6. Ref. 51. Tab. 1.

Special Binding for Refractory Concretes

Abstract The paper shows data related to coexistence of various binding systems, which could be present during the hardening of special concretes. It is taken into account the Ultra Low Aluminous Cement Concretes additivated with different materials (phosphates and mineral ultra dispersed powders - Condensed Silica Fume, Hydrated Alumina etc). In correlation to the pH-value, these substances can favour the forming of new binding systems besides the hydraulic binder (which is not important in this case). The new system is the coagulation binding form. The coagulation binding system has a very important role in the advanced compactness and in the increasing mechanical strengths of concrete structures.

Mesoscale experimental investigation of thermomechanical behaviour of the carbon textile reinforced refractory concrete under simultaneous mechanical loading and elevated temperature

In comparison with carbon fiber reinforced polymer material, the carbon textile reinforced concrete (TRC) is usually coted to have a better fire behaviour. The aim of this paper is to analyse the elevated temperature behaviour of TRC. This paper presents the experimental results conducted on carbon TRC at mesoscale in the range of temperature from 25 °C to 700 °C. The carbon TRC consists of refractory matrix and carbon textile which has been treated with amorphous silica products for a good bond with the cement matrix. As a result, carbon TRC showed the strain-hardening behaviour with different phases and brittle behaviour depending on the temperature. The evolution of carbon TRC properties with elevated temperature (the ultimate stress, the crack stress, the initial stiffness) was experimentally identified. The mechanical property evolution of carbon textile and refractory concrete (the ultimate strength, the Young’s modulus) depending on temperature was also presented. The thermal tests on carbon TRC cylinder specimens were also performed to identify the diffusivity coefficient of this composite. All results obtained were analyzed in order to find the contribution of carbon textile and refractory matrix to fire resistance of carbon TRC. Its ultimate strength has been improved about 2 times compared with non-reinforced matrix at elevated temperature ranging from 25 °C to 400 °C. The efficiency coefficient of carbon textile could be calculated in this study.

Correlation of damage after first cycle with overall fatigue resistance of refractory castable concrete

Abstract Cyclic thermal loads experienced in service by castable refractory concrete often cause fatigue failure. Displacement controlled cyclic fatigue measurements were performed on samples of corundum-andalusite refractory concrete at room temperature and at 1000 °C. The aim was to correlate the damage introduced in the first cycle (primary damage) and the overall fatigue performance. Damage was quantified by acoustic emission, dynamic Young’s modulus and irreversible strains. Regarding the amplitude, three zones of fatigue resistance demonstrating specific degradation patterns were seen. The magnitude and microstructural type of primary damage correlates with the zones and can explain the patterns. Samples with higher primary damage demonstrate lower number of cycles to failure. Primary damage based limits seem to be able to determine the boundary loads for the zones of fatigue resistance.

Effect of pozzolans on mechanical behavior of recycled refractory brick concrete in fire

Reusing building materials and concrete of old buildings can be a promising strategy for sustained development. In buildings, the performance of materials under elevated temperatures is of particular interest for determining fire resistance. In this study, the effect of pozzolan and aggregate type on properties of concrete exposed to fire was investigated. In doing so, nanosilica with cement-replacement levels of 0,2, and 4% as well as silica fume and ultrafine fly ash with cement-replacement levels of 0, 7.5, and 15% were used to study effect of pozzolan type, and recycled refractory brick (RRB) fine aggregate replacing natural fine aggregate by 0 and 100% was utilized to explore effect of aggregate type. A total of 126 cubic concrete specimens were manufactured and then investigated in terms of compressive strength, ultrasonic pulse velocity, and weight loss at 23 degree celcius and immediately after exposure to 400 and 800 degree celcius. Results show that replacing 100% of natural fine aggregate with recycled refectory brick fine aggregate in the concretes exposed to heat was desirable, in that it led to a mean compressive strength increase of above 25% at 800 degree celcius. In general, among the pozzolans used here, silica fume demonstrated the best performance in terms of retaining the compressive strength of heated concretes. The higher replacement level of silica fume and ultrafine fly ash pozzolans in the mixes containing RRB fine aggregate led to a greater weight loss rate, while the higher replacement level of nanosilica reduced the weight loss rate.

Effect of Pyrocatechin on the Properties of Cement-Free Refractory Concrete Mixtures Based on Silica-Containing Colloidal Binders

It is shown that the pyrocatechin (1, 2-dihydrohybezene) in an amount of 0.005 – 0.010 wt.% solid components has a pronounced plasticizing effect on mixtures of polyfraction corundum filler and colloidal SiO2-solution binder, stabilized with ammonia ions, intended for preparing cement-free refractory concrete. Self-consolidating refractory compositions are prepared with minimum water content.

Refractory concrete based on alumina cement out of low-grade raw materials

The development results are given for the refractory concretes based on the modifed alumina cement with the using of the chemical industry wastes. The quantitative ratio for the near-gravity materials, the technological factors' influence on the concrete strength, the dependence of its strength properties on the flling aggregate's kind and its curing conditions were defned in the article. It was shown that the physical and mechanical properties of the developed concretes are as good as those of the commercial concretes. According to all technical characteristics this kind of production can be introduced for using as the high temperature vessels' lining material.Ill.6. Ref. 11. Tab. 4.

The pyrocatechin's effect on the cement-free colloidal silica bonding refractory concrete mix properties

It was shown that the pyrocatechin (1, 2-dihydrohybezene) in the amount of 0,005‒0,010 weigh percent of the solid components has the pronounced plasticization effect on the mixtures of the polifraction corundum aggregate with the bonding colloidal SiO2-solution stabilized by the ammonium ions, the mixtures being intended for the cement-free refractory concrete's manufacturing. The article is concerned with the refractory self-consolidating compositions preparation under the condition of minimum water. Ref. 13. Tab. 3.

The modeling of the moisture movement inside the refractory concrete when drying by means of percolation structures

The refractory concrete dehydration process was investigated by applying of the statistical percolation model of the concrete structure. The various moisture evacuation mechanisms were regarded at various steps of this process, the diffusion in the solid phase and the movement through the open pores including. The temperatures were defned at which the moisture removing mechanisms were working in the concretes. It was shown how the model could be applied to the calculation of the moisture removing out of the real lining or out of the concrete product. The concrete percolation model was used to analyze the mass loss plots for the dense concretes and to evaluate the coefcients for the water diffusion inside the concretes in various conditions.Ill.5. Ref. 31. Tab. 3.

The investigation of the modified refractory concrete in terms of the clay filler's kind

The properties of the conventional refractory concrete modified by means of the microsilica and the antiflocculant additions including the different kinds of the fire clay filler were investigated in the article. It was established that the refractory concrete with the filler Bos145 (about 44 % of Al2O3) had the smaller open porosity, and both high density and the ultimate compressive strength comparing to these characteristics which the concretes with the fillers Bos125 and Bos135 had (about 26 and 37 % of Al2O3respectively). Also it was found out that independently of the fire clay filler's kind another SiO2-based addition promoted the increase of the concrete's alkaline resistance by the factor of 5 and more. It was shown that this SiO2-based addition is effective at the temperatures up to 1100 °C, as at 1200 °C the chamotter concrete's porosity grew up and the resistance of the material against the alkaline melt decreased considerably.