Bricks: Brick Properties
- Masonry walling unit not exceeding 0.004m³ (double the volume of a standard or traditional clay brick.
- The nominal work size of a traditional clay brick is 230 x 110 x 76 mm
- ‘work size’ is the manufacture size from which dimensional deviations are measured
- AS3700-1988 The Masonry Code
"characteristic unconfined compressive strength" replaced the term "characteristic compressive strength" abbreviated to f’uc
- Characteristic compressive strength is compressive strength of brick + mortar strength. For standard size bricks the characteristic unconfined compressive strength is 60 per cent of that.
- Durability
– three classes:
- Protected (PRO) –used for internal + external walls protected by coping, eaves and/or coating and built above a DPC. Not exposed in saline environment.
- General Purpose (GP) not recommended in saline environments.
- Exposure (EXP) All applications includes saline environments.
- The Australian/New Zealand has no freeze/thaw test method ‘Consumers should rely on manufacturers’ recommendations or local experience.’
- Moisture expansion
(em) is the estimate amount of growth expected over fifteen years after the brick leaves the kiln. This is used to size and space control gaps.
- Most general purpose bricks have a characteristic expansion in the range 0.5 to 1.9 mm/m, but for design purposes the em should be determined by a test, not by following typical values which should only be a guide.
- Control Gaps (also called expansion gaps or joints)
- Essential in long runs of brickwork
- Minimum gaps are based on expansion data available from brick manufacturer.
- Should initially be 20mm wide, clear of mortar dags or bridges, tied at appropriate intervals and sealed with a polystyrene tube or suitable compressive filler.
- Possible control gaps should be placed behind downpipes, at window/door openings or re-entrant corners.
- Initial rate of absorption (IRA) or suction
- No requirement to be met but optimum range for IRA figures would be B/W 0.5 and 1.5
- Water retentivity of mortar should match to brick suction for good bond strength and fast bricklaying
- If the suction of the brick is too high, pre-wetting can reduce it. However this usually leads to efflorescence on finished brickwork.
- Efflorescence
– crystalline deposit on wall units.
Salts in masonry taken into solution by water and then deposited as the moisture dries.
- Movement of the solutions within masonry is controlled to some considerable extent by seasonal weather – efflorescence is usually a cold weather problem.
- Possible sources – masonry materials used, mortar, units and backing as well as outside contaminants such as ground water.
- the standard requires that brickwork efflorescence should nor exceed severe (efflorescence that is accompanied by powder and/or flaking of the surface of the specimen.
Prevention: design to prevent excessive wetting of masonry, selection of materials with a low content of salts of efflorescence.
- Pitting (due to lime particles)
lime turns into quicklime when fired. Water contacting the lime particles will cause them to expand as the lime slakes and particles near the surface of the brick erupt leaving surface pits.
- For face brick work bricks rated as moderate or worse are not recommended
- Nill – no visable pits – any use
- Slight – up to five pits, <5mm diameter – face walls
- Moderate - <10mm diameter – rendered walls
- Severe – pits over 10mm diameter – unseen walling
- Lateral modulus of rupture (LMOR)
measures the extreme fibre tensile stress at the face of a brick in bending.
- Determines horizontal bending capacity of brickwork.
Required for design of brickwork panels subjected to lateral loads (wind, earthquake)