Refractory concrete is a monolithic castable used in the field of refractory materials and is classified into neutral, acidic, and alkaline types. It is formulated with appropriate binders, refractory aggregates, additives, and water in specific proportions. It can withstand long-term exposure to temperatures above 1,000 °C while maintaining the required physical and mechanical properties under such high-temperature conditions.
Differences between Refractory Concrete and Ordinary Concrete
Ordinary concrete deteriorates when exposed to high temperatures, resulting in mass loss, the formation of numerous pores and cracks, and reductions in strength and elastic modulus. Such deterioration can lead to extensive cracking and even the collapse of ordinary concrete.
Compared with ordinary concrete, refractory concrete uses different constituent raw materials.
Refractory Concrete:
(1) All constituent materials shall possess adequate refractoriness, especially refractory aggregates and fine powders. Generally speaking, all raw materials used to manufacture refractory bricks can meet the requirements for preparing refractory concrete.
(2) To reduce cement consumption and improve the workability and high-temperature performance of refractory concrete, a certain amount of refractory fine powder must be added during batching.
(3) A wider range of admixtures is used in refractory concrete than in ordinary concrete. In addition to retarders and water-reducing agents, small amounts of mineralizers, expanders, and other additives may also be incorporated according to the requirements for modifying the concrete.
Types of Refractory Concrete
ZINFON manufactures refractory concrete, which is classified into three types according to the different binders used: sodium silicate-bonded refractory concrete, cement-bonded refractory concrete, and phosphate-bonded refractory concrete.
Cement-Bonded Refractory Concrete
It contains a high proportion of cement and provides high strength. Its service temperature ranges from 700 to 1,200 °C. It offers good stability and is easy to construct. The recommended construction thickness is 200 mm, and it is suitable for applications where there is no acid or alkali corrosion.
Sodium Silicate-Bonded Refractory Concrete
Its service temperature ranges from 900 to 1,000 °C. It offers good stability, wear resistance, and resistance to acid corrosion. However, it should not be used in sections exposed to water vapor or liquid water.
Phosphate-Bonded Refractory Concrete
It can withstand higher temperatures, with a service temperature range of 1,450 to 1,650 °C. It has excellent wear resistance and impact resistance. It is suitable for high-temperature zones and oil-fired combustion chambers.
Physical and Chemical Indicators of Refractory Concrete
Can be customized according to requirements.
| Item | Refractory Concrete | |||
| Al₂O₃, % | ≥30 | ≥35 | ≥40 | |
| Bulk Density, g/cm³ | ≥2.0 | ≥2.0 | ≥2.0 | |
| Compressive Strength, MPa, ≥ | 110 °C ×24 h | ≥40 | ≥40 | ≥40 |
| 300 °C ×3 h | ≥50 | |||
| Refractoriness | 1350 °C | |||
Advantages of Refractory Concrete
(1) Easy shaping.
Regardless of the complexity of the structural shape or dimensions, refractory concrete can be cast in situ against formwork. It is especially suitable for casting concrete in special sections of thermal equipment.
(2) Excellent integrity.
Refractory concrete can be cast continuously. Furnaces and thermal equipment constructed with refractory concrete feature good integrity, smooth surfaces, and high compactness. Its service life can be increased by at least 30%.
(3) Diverse construction methods.
Taking advantage of its easy-to-shape properties, refractory concrete can be formed by vibration or ramming. Mechanical pressure spraying can also be used depending on project characteristics and requirements. For partial damage to refractory concrete furnace linings, hot or cold gunning repair can be adopted.
(4) Good thermal shock stability.
As an unburned product, refractory concrete can accommodate thermal expansion through voids left by moisture evaporation during heating. Therefore, its thermal shock stability is approximately twice that of refractory bricks made of the same material. Refractory concrete can replace refractory bricks in certain sections subject to severe temperature fluctuations.
Applications of Refractory Concrete
(1) Cement-Bonded Refractory Concrete
High-alumina cement-bonded refractory concrete features high strength at room temperature and good thermal stability at 1,100–1,200 °C.
It is commonly used in working sections such as blast furnace platform foundations and flues.
(2) Sodium Silicate-Bonded Refractory Concrete
It is an acidic material with high thermal stability and wear resistance at temperatures of 900–1,000 °C. It is suitable for projects subject to acid corrosion or for use as a furnace lining.
It is widely used for chimney linings. Chimneys are continuously exposed to acidic flue gas. The sodium silicate bonding system provides excellent resistance to acidic flue-gas corrosion, making it well suited to the service conditions of chimneys.
(3) Phosphate-Bonded Refractory Concrete
It boasts high hot strength, good wear resistance, thermal shock resistance, and alkali corrosion resistance. It is not resistant to strong acidic flue gas. Its service temperature ranges from 1,450 to 1,650 °C.
It is applicable to high-temperature operating zones, such as the high-temperature walls, roofs, and hearths of reheating furnaces and forging furnaces, as well as oil-fired combustion chambers and other high-temperature sections.
Function Mechanism of Raw Materials for Refractory Concrete
(1) Refractory aggregate serves as the skeleton of refractory concrete and plays a critical role in its high-temperature physical and mechanical properties. A wide variety of materials are available; any raw material that can be used to manufacture refractory bricks can also serve as refractory aggregate.
Refractory aggregates are classified into coarse and fine fractions, with specified limits for maximum particle size. In general, the type, particle size, and particle-size distribution of refractory aggregates shall be selected according to the lining thickness of furnaces and thermal equipment, construction methods, service temperature, and requirements for high-temperature physical and mechanical properties.
(2) Refractory fine powder can optimize certain properties of cement binders, reduce cement consumption, improve the workability of refractory concrete mixtures and the compactness of the concrete, and enhance refractoriness. Meanwhile, refractory fine powder can react with certain inorganic binders to bond refractory aggregates together, imparting strength and high-temperature physical and mechanical properties to refractory concrete.
(3) The primary function of binders is to bond refractory aggregates and fine powders together to form refractory concrete with specified properties.
(4) There are many types of admixtures, including setting accelerators, water-reducing agents, mineralizers, and expanders. They are normally added in small amounts. Their main function is to modify and improve the performance of refractory concrete so as to better satisfy construction and service requirements.
Mix Proportion of Refractory Concrete
The mix-proportion design of refractory concrete requires not only satisfactory strength, workability, and durability, but also the specified refractoriness required by the design. The properties of the constituent raw materials are the dominant factors determining the high-temperature performance of refractory concrete. Nevertheless, binder dosage, water-cement ratio (or water-binder ratio), aggregate gradation, admixture content, and additive content also have significant effects on its high-temperature performance. Therefore, the selection of the mix proportion has a significant impact on the overall performance of refractory concrete.
The basic parameters for mix-proportion design mainly include binder dosage, water-cement ratio (water-binder ratio), filler content, aggregate gradation, and sand ratio.
(I) Binder Dosage
Generally, aggregates possess higher refractoriness than binders. When the binder content exceeds a certain threshold, increasing the binder dosage will lower the load-softening point and increase the residual deformation of concrete. Accordingly, to improve the high-temperature performance of refractory concrete, the binder dosage shall be minimized while ensuring adequate workability for construction and sufficient strength at room temperature.
For cement-bonded refractory concrete under different service conditions, the cement dosage can range from 10% to 20%. For cement-bonded refractory concrete with high requirements for load-softening point and refractoriness but low requirements for room-temperature strength, the cement content shall be controlled within 10%–15%.
(II) Water-Cement Ratio / Water-Binder Ratio
Variations in the water-cement ratio have a significant effect on the strength and residual deformation of cement-bonded refractory concrete. Strength decreases sharply as the water-cement ratio increases. Since cement-bonded refractory concrete is frequently exposed to high temperatures, internal moisture tends to evaporate, resulting in increased internal porosity, a looser structure, and reduced strength. For this reason, water consumption and the water-cement ratio shall be reduced as far as practicable while still meeting construction requirements during batching.
For sodium silicate-bonded refractory concrete, the modulus of sodium silicate is normally maintained at 2.6–2.8, with a relative density of 1.36–1.40. The dosage of sodium fluorosilicate hardener is generally 10%–12% of the mass of sodium silicate.
For phosphate-bonded refractory concrete using phosphoric acid as the binder, the phosphoric acid concentration is normally 50%.
(III) Filler Content
Fillers are powdery auxiliary components in refractory concrete formulations that are distinct from aggregates and primary binders. They serve to fill voids and optimize both construction performance and high-temperature service performance.
The proper addition of fillers can significantly improve the high-temperature performance and workability of fresh concrete mixtures while reducing cement consumption.
Common fillers include silica fume, reactive alumina powder, α-alumina micropowder, etc. (Insert product hyperlink)
(IV) Aggregate Gradation
Aggregates account for approximately 80% of the total mass of the refractory concrete mixture. Optimized aggregate gradation has favorable effects on compactness and high-temperature performance. When selecting aggregates, attention shall be paid to the aggregate type and refractoriness to ensure compatibility with the binders, as well as to the appropriate particle size.
Excessively large particle sizes or an excessive proportion of coarse aggregates will result in poor workability of the fresh mixture, difficulty in forming, reduced compactness, and an increased risk of delamination and spalling at high temperatures.
(V) Sand Ratio
Sand ratio = mass percentage of fine aggregate in the total aggregate (fine aggregate + coarse aggregate)
Coarse aggregate: refractory crushed stone/particles, particle size > 5 mm
Fine aggregate (sand): refractory sand, 0.15–5 mm
The sand ratio is recommended to be controlled within 40%–50%.
Low sand ratio: insufficient fine sand and an excessive amount of coarse particles. The mixture becomes loose, difficult to compact, and prone to honeycombing and void formation.
Excessively high sand ratio: excessive fine sand requires more binder, leading to greater shrinkage and deterioration of hot strength.
A reasonable sand ratio optimizes the construction performance of the mixture, reduces porosity, decreases binder consumption, and improves compactness.
Choose ZINFON Refractory Concrete
Customization Available: Please advise your service temperature, working conditions and other requirements. Custom‑tailored products are available upon your request.
Packaging: 25 kg/bag + jumbo bag. Export pallet packaging can be added per customer's requirements.
Transportation: Land transport and sea freight are available.
Samples: Free samples are provided for customer testing.
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