Although refractory concrete and ordinary concrete have similar names and appearances, and both are mainly formed by pouring or ramming during construction, they have fundamental differences in material systems, physical and chemical properties, service environments, functional positioning, and engineering application logics. They belong to two different technical categories, namely refractory materials and civil building materials, and cannot be used interchangeably or substituted for each other.
I. Material Composition and Bonding Mechanism
Refractory concrete is a typical amorphous refractory material, with its core lying in "high-temperature stability" and "structural retention capacity". Its aggregates are usually high-melting-point mineral raw materials such as high-alumina bauxite clinker, fused alumina, mullite, sillimanite, or silicon carbide that have undergone high-temperature calcination. The particle size distribution is strictly designed to balance density and thermal shock resistance; the powder materials include fine powders and active micro-powders of corresponding materials (such as alumina micro-powder, silica micro-powder), used to fill voids and enhance sintering activity. The binder is the key to its room-temperature strength and high-temperature performance, with common types including: high alumina cement (water-hardening binder, suitable for medium and low-temperature conditions), sodium/potassium silicate (hardened by acid, with certain resistance to alkali erosion), phosphate (such as aluminum dihydrogen phosphate, forming a three-dimensional network structure, transforming into a ceramic phase at high temperatures, endowing excellent hot-state strength and anti-spalling properties), and the rapidly developing sol-gel binders in recent years (such as aluminum sol, silica sol). Different bonding systems correspond to different construction window periods, curing regimes, and final service temperature ranges.
In contrast, ordinary concrete belongs to a typical water-hardening cementitious material system, with general Portland cement (P·O 42.5 or 52.5 grade mainly) as the cementitious component, and aggregates using natural river sand, crushed stone, or manufactured sand and gravel, strictly following gradation specifications; the mixing water participates in the hydration reaction of cement clinker minerals (C₃S, C₂S, etc.), generating a network structure with calcium silicate hydrate (C-S-H gel) as the main body, supplemented by calcium hydroxide, ettringite, and other products, forming the basis of load-bearing capacity at room temperature. Its performance development is highly dependent on the degree of hydration and environmental temperature and humidity conditions, lacking the ability to restructure at high temperatures.
II. Service Temperature and Refractory Performance
The design objective of refractory monolithic concrete is to withstand high-temperature thermal loads for a long time. According to the national standard GB/T 29921-2013 "Refractory Castables" and industry practice, the long-term service temperature of conventional aluminate cement-bonded refractory concrete is 900–1250°C, with a short-term peak temperature of up to 1350°C. In contrast, the phosphate-bonded system, due to dehydration and polycondensation during heating and the formation of high-melting-point ceramic phases such as AlPO₄, can maintain a long-term service temperature of 1450–1650°C, with a refractoriness generally above 1700°C, and some chromium alumina or zirconia alumina systems even exceed 1800°C. Besides high-temperature resistance, its key properties also include good thermal shock stability (resistance to cracking and spalling under repeated rapid heating and cooling), high-temperature volume stability (residual linear change rate controlled within ±0.5%), and resistance to wear and erosion under high-temperature gas flow.
Ordinary concrete is completely unsuitable for high-temperature environments. When the temperature rises to about 300°C, calcium hydroxide in the hydration products begins to dehydrate; above 400°C, the C-S-H gel structure deteriorates significantly, and the strength drops sharply; after 500°C, the cement stone basically loses its bonding ability, showing obvious powdering and spalling. If exposed to open flames or sudden high temperatures, it may also experience explosive spalling due to a sudden increase in steam pressure caused by the vaporization of internal free water. Therefore, its design service temperature limit is strictly limited to below 400°C from room temperature, and it is only suitable for structural load-bearing and enclosure functions under normal climatic conditions.
III. Chemical Properties and Atmosphere Adaptability
Refractory concrete has a clear classification system based on the acidity or alkalinity of its main components and their reaction tendencies with furnace gases at high temperatures. It is divided into three major categories: acidic (such as silica, semi-silica), neutral (such as high alumina, corundum, silicon carbide), and alkaline (such as magnesia, magnesia-alumina spinel, dolomite). This classification directly serves the complex and changeable operating atmospheres within industrial furnaces. For instance, in the combustion chamber of a coke oven, where resistance to reducing gases (CO, H₂) is required, neutral or alkaline systems are preferred; in the regenerative chamber of a glass melting furnace, where exposure to highly oxidative high-temperature flue gas and alkali vapor occurs, zirconia or fused mullite-based materials with alkali resistance are prioritized; and in the reverberatory furnaces for non-ferrous metal smelting, where contact with sulfur-containing corrosive flue gas is involved, special phosphate-bonded high alumina castables with resistance to SO₂ erosion are necessary.
Ordinary concrete is strongly alkaline (with a pH value above 12.5), and its hydration products readily undergo neutralization reactions with acidic media (such as industrial acid mists, acid rain, and acidic soil solutions), leading to the dissolution of calcium salts, an increase in porosity, and a decline in strength. It also lacks effective resistance to corrosive ions such as chloride and sulfate ions. Moreover, it is not stable in special atmospheres like reducing, carburizing, or nitriding conditions. Therefore, its application environment is extremely limited, and it is only recommended for dry, neutral, or weakly alkaline general atmospheric conditions. It must not be exposed to strongly corrosive media or sealed high-temperature reducing atmospheres.
IV. Application Fields and Functional Positioning
The core value of refractory concrete lies in constructing a "thermal barrier" for high-temperature industrial equipment. Its functions are complex and specialized: it must not only support the lining structure but also achieve multiple tasks such as heat insulation and preservation, resistance to slag penetration, protection against gas flow erosion, and buffering of thermal stress impacts. Typical application scenarios include the iron tapping channel of blast furnaces, the working layer of molten iron ladles, the spherical top and checker brick bedding of hot blast stoves in the steel industry; the flash smelting furnace reaction tower, the cover and slag line of rotary anode furnaces in the non-ferrous metallurgy field; the front and rear kiln mouths and decomposition furnace cones of cement rotary kilns in the building materials industry; and the lining of the radiant section of ethylene cracking furnaces and the inner lining of regenerators in catalytic cracking units in the petrochemical industry. In these areas, refractory concrete often works in conjunction with shaped refractory bricks, fiber modules, and anchor bolts to form a complete thermal system.
Ordinary concrete, on the other hand, focuses on mechanical reliability and environmental adaptability throughout the entire life cycle of civil engineering projects. It emphasizes properties such as compressive strength, impermeability, resistance to freeze-thaw cycles, grip strength of reinforcing bars, and long-term creep control under normal temperature and conditions. Its applications cover a wide range of fields including building structures (beams, slabs, columns, shear walls, foundation slabs), transportation infrastructure (highway base and surface layers, railway sleepers, bridge piers and abutments), water conservancy facilities (dam spillways, channel linings), and municipal engineering (tunnel structures, inspection wells, road base layers). The design basis for ordinary concrete is the "Code for Design of Concrete Structures" (GB 50010) and the "Code for Proportioning of Ordinary Concrete" (JGJ 55), emphasizing standardization, mass production, and economy rather than high-temperature functionality.
V. Construction Techniques and Curing Systems
Although both types of concrete involve common processes such as forced mixing in a mixer, pumping or manual pouring, and vibration compaction, the technical control points are quite different. Fire-resistant concrete is highly sensitive to the amount of water added: too much water will increase porosity, reduce high-temperature strength, and increase the risk of cracking during the baking stage; too little water will result in insufficient fluidity and difficulty in achieving dense compaction. In actual construction, the workability is often regulated by adding high-efficiency water reducers and retarders, and the fluidity value of the slurry (such as determined by the slump test) and the initial and final setting times are strictly monitored. After forming, it must go through two critical stages: first, a natural drying period (usually no less than 24–48 hours) to allow free water to slowly escape and prevent surface shrinkage cracking; then, a systematic baking regime is implemented - with staged heating rates (such as ≤15°C/h), constant temperature platforms (such as holding at 300°C, 600°C, and 900°C for several hours), and a final target temperature. The total period is generally no less than 7 days to ensure complete conversion of the binder, thorough removal of moisture, and the formation of a complete ceramic bonding network. Fire-resistant concrete that has not undergone standardized baking is prone to structural spalling or even collapse after operation.
The construction of ordinary concrete, on the other hand, is oriented towards efficiency and controllability: parameters such as water-cement ratio, slump, and mold temperature have clear limits; vibration is aimed at eliminating honeycomb and pitted surfaces and ensuring density; standard curing is carried out under conditions of covered moisture retention, constant temperature (20±2°C), and saturated humidity (≥95%), and can reach over 95% of the designed strength grade after 28 days. For large-volume structures, temperature control measures are also taken to prevent excessive temperature differences between the inside and outside from causing cracks. The entire process does not require any high-temperature heat treatment steps, has a short commissioning period, and low management costs.
although refractory concrete and ordinary concrete both fall under the category of "concrete", their natures are fundamentally different: the former is a functional special material that takes high-temperature service as a prerequisite, is based on the inherent refractoriness of the material, and is designed with multi-factor coupling conditions as the boundary; the latter is a basic structural material that centers on mechanical properties at normal temperature, is guaranteed by long-term durability, and follows a standardized construction path. Both have their own systems in terms of raw material sources, preparation principles, performance characterization methods, quality acceptance standards, and technical service chains. In engineering practice, it is necessary to conduct specialized selection and scheme design in collaboration between refractory material engineers and structural engineers based on comprehensive factors such as equipment operating temperature, atmosphere properties, heat load characteristics, mechanical wear strength, and maintenance requirements. Empiricism, application by analogy, or simplification and substitution are strictly prohibited. Only by precisely matching material characteristics with operational requirements can the safe, efficient, and long-term operation of high-temperature industrial equipment be ensured.
