ISO 13765-7:2021

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

• ISO 13765-1 (consistency - penetrating cone method)
• ISO 13765-2 (consistency - reciprocating flow table method)
• ISO 13765-3 (joint stability)
• ISO 8656-1 (sampling of raw materials and unshaped products)

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.