Overview
ISO 13765-7:2021 - Refractory mortars: Determination of permanent change in dimensions on heating specifies a laboratory method to measure the permanent dimensional change (shrinkage or expansion) of refractory mortars when subjected to drying and/or firing. The procedure quantifies dimensional stability after heating by measuring distances between marks on mortar-bonded refractory bricks before and after heat treatment and expressing changes as percentage values.
Key topics and technical requirements
- Scope: Method for determining permanent change in dimensions on heating (drying and/or firing) of refractory mortars.
- Test specimens: Each specimen is formed by two compatible refractory bricks (recommended size: 114 ± 1 mm × 65 ± 1 mm × 32 ± 1 mm). Initial mark spacing on diagonals: 90–100 mm.
- Joint preparation: Mortar joint thickness 2–4 mm using a 2 mm thick rectangular frame; nylon filter cloth and fine refractory powder (≤ 0.1 mm) are used during assembly.
- Apparatus and conditions:
- Mixer and balance (≤ 10 kg, 1 g resolution).
- Drying oven capable of 110 °C ± 5 °C and electrical temperature control.
- Furnace with maximum temperature ≥ 1 600 °C, temperature uniformity ±10 °C.
- Length measuring device with 0.05 mm accuracy.
- Heating regime:
- Air-dry then oven-dry at 65 °C (4 h) followed by 110 °C (24 h).
- Firing heating rate normally 5 °C/min (silica mortar 3 °C/min); soak 3 h ± 0.5 h (silica 5 h ± 0.5 h) at agreed temperature; oxidizing atmosphere; cooling in furnace to room temperature.
- Calculations & reporting:
- Permanent change on drying, firing and overall heating expressed as percentage change: (l_after − l_before) / l_before × 100.
- Test requires three specimens; report individual values and mean to nearest 0.1%. Use “+” for expansion and “–” for shrinkage.
- Precision: Interlaboratory tests and precision data are provided (Annex A). Repeatability and reproducibility clauses apply.
Applications and users
- Quality control and acceptance testing of refractory mortars used in furnaces, kilns, boilers and high-temperature linings.
- Product development and R&D for mortar formulations to assess dimensional stability during drying/firing.
- Test laboratories, refractory manufacturers, specification engineers, procurement teams and construction/installation contractors who require documented performance data on mortar shrinkage/expansion.
Related standards
Keywords: ISO 13765-7:2021, refractory mortars, permanent change in dimensions, dimensional stability, drying and firing test, shrinkage, expansion, refractory testing, furnace testing, oven drying.