Correctly specify masonry units, retaining walls and more with Electronic Blueprint
Masonry units (bricks and blocks) are some of the most common
building materials, yet are often incorrectly specified and ordered. The revised
Australian Standard covering these units, AS/NZS 4455-2007, is close to publication
in three parts:
Part 1: Masonry units (bricks and blocks) to be laid in mortar to construct walls,
piers and the like.
Part 2: Retaining wall units, intended to be dry-stacked without the aid of mortar.
Part 3: Pavers and flags, for segmental pavements.
Specifiers and builders should bear in mind that the standard does not specify
particular values for the relevant properties (strengths, tolerances, exposure
grades, contractions, expansion and the like). The designer must determine this
information and ensure it is included in the specification.
A typical specification (subject to modification and confirmation by the designer)
for bricks and blocks, complying with AS/NZS 4455 Part 1, is set out below.
Masonry Units
Unless specified elsewhere in the documents, masonry units shall be fired clay,
concrete or calcium silicate units complying with AS/NZS 4455.1 and the following
requirements;
- Masonry units shall comply with Dimensional Category DW1 (determined using AS/NZS 4456.3
Method A), except that split or irregular faces may be DW0. Concrete units usually comply
with Dimensional Category DW4 (determined using AS/NZS 4456.3 Method B), which is more
stringent than for DW1.
- Masonry units shall meet General Purpose Salt Attack Resistance Grade, except for
applications requiring Exposure Grade in accordance with AS 3700 Table 5.1 or Table 12.2.
Applications requiring Exposure Grade are:
- saline wetting or drying,
- aggressive soils,
- severe marine environments,
- saline or contaminated water including tidal or splash zones, or
- within 1 km of a industry producing chemical pollutants.
- Masonry units shall have a Characteristic Compressive Strength not less than a value
specified by the Engineer. In the absence of such specification, masonry units shall have
Characteristic Compressive Strengths not less than the following values.
- Masonry units intended for face applications and exposed to the weather shall have:
- Permeability not more than 2 mm/minute.
- Efflorescence Potential of Nil or Slight.
- Colour and texture within an agreed range.
- Masonry units intended for exposure to lateral loads in excess of 0.5 kPa shall have
a Characteristic Lateral Modulus of Rupture not less than 0.8 MPa.
- Concrete masonry units shall have a Mean Coefficient of Residual Drying Contraction
not more than 0.6 mm/m.
- Clay masonry units shall have a Mean Coefficient of Expansion not more than 1.0 mm/m.
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