ASTM C20 Refractory Porosity & Density

Scope

ASTM C20 applies to burned refractory brick and shapes — dense, fired ceramic products used in high-temperature industrial applications. The standard specifies the specimen preparation requirements, the drying and weighing procedure, the boiling saturation protocol, the suspended weighing technique, and the calculation procedures for all four reported properties.

Refractory product types within the scope of this standard include:

• Fireclay and high-alumina brick — general-purpose refractory brick used across a broad temperature range in furnace linings, kilns, and boilers
• Silica brick — high-silica refractories used in coke ovens, glass tank crowns, and steelmaking applications
• Basic refractories — magnesia, chrome-magnesia, magnesia-chrome, and dolomite brick used in steelmaking furnaces, cement kilns, and non-ferrous smelting
• Specialty oxide refractories — zirconia, mullite, corundum, and spinel-based shapes for high-performance or chemically aggressive service environments
• Carbon and graphite refractories — where the boiling water method is applicable and not contraindicated by material reactivity
• Dense castable and pressed shapes — fired monolithic shapes and pressed components that meet the standard’s physical form requirements.
• Insulating brick — where the open porosity is within the range addressable by boiling water saturation, though highly porous insulating products may require the companion vacuum method of ASTM C830

Applications

• Production quality control — verifying that manufactured refractory brick and shapes meet specified physical property requirements before release for shipment or use
• Material qualification and approval — establishing the physical property baseline for new refractory compositions, manufacturing routes, or supplier qualifications
• Refractory lining design — supplying porosity and density data as inputs to thermal modeling, slag penetration resistance assessments, and lining thickness calculations
• Comparative evaluation — assessing the effect of raw material changes, firing temperature adjustments, or forming process modifications on the physical structure of the fired product
• Failure investigation — characterizing physical properties of refractories removed from service to assess whether abnormal porosity, density change, or absorption behavior contributed to premature wear or failure
• Research and development — supporting the development of new refractory formulations by providing reproducible physical property data across compositional and processing variables

Benefits

• Four properties from one procedure — apparent porosity, water absorption, apparent specific gravity, and bulk density are all derived from the same set of mass measurements, making the test highly efficient relative to the information it yields.
• No specialized equipment is required — the method uses a boiling water bath, a balance with suspension capability, and basic laboratory glassware, making it accessible to production-quality laboratories without capital-intensive instrumentation.
• Reproducible saturation conditions — the boiling technique provides consistent pore filling across different materials and laboratories without the operator-dependent variability associated with simple cold immersion.
• Directly relevant to service performance — apparent porosity is the single most widely specified physical property for dense refractory brick, and the other three values derived from the same test collectively define the physical structure that governs slag penetration resistance, thermal mass, and structural behavior.
• Established industry baseline — ASTM C20 has been in use for decades,s and its results form the basis of the physical property specifications in refractory product standards, purchase specifications, and engineering databases across the refractories industry
• Companion to the vacuum method — for materials where boiling water saturation is insufficient to fill the pore network, ASTM C20 data can be compared against ASTM C830 vacuum saturation results to assess the proportion of porosity not accessible to boiling water