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A23.4-09
©
Canadian Standards Association
November 2009
(2)
When repairs of grey concrete have to be colour-matched, white cement normally has to be included in the repair
batch, especially when curing of elements has been accelerated.
33.2.5
The repair mix shall be proportioned to provide at least the strength and durability of the original mix.
When appearance is important, proportions may be adjusted to obtain the best match, but the strength
and durability shall not be less than that of the original mix.
Notes:
(1)
It is possible that the repair mix will need an altered cement content (see
Clause 33.2.4
) or that some of the larger
aggregate pieces will have to be eliminated or hand-placed in the patch.
(2)
When colour-matching is desired for elements exposed to the weather, care should be taken to obtain similar
absorption characteristics so that patches do not become too obvious in alternating dry and wet weather. For this
reason, bonding agents should normally not be included in the repair mix.
33.2.6
Preparation of the repair area and the actual repair shall consist of the following steps:
(a) All loose material shall be removed and chipped back to sound concrete.
(b) Cut-outs shall be at least 6 mm deep. For exposed aggregate finishes, cut-outs shall be a minimum of
6 mm plus the maximum size of the exposed aggregate. Feather edges shall not be permitted.
Note:
A slight undercut should be used.
(c) The repair area shall be cleaned by brushing or with compressed air.
(d) The repair area and surrounding concrete shall be saturated with water to prevent absorption of
water from the patching mix and to facilitate bonding.
(e) When surface water has evaporated, but before complete drying, the repair mix shall be placed by
vibration or hand tamping for consolidation and for proper contact with the old concrete surface.
Note:
For larger repair areas, placement of the repair batch should be preceded by brushing a bond coat (cement and
fine sand) onto the repair surface.
(f) Proper curing shall be provided and care shall be taken to retain moisture and avoid excessively high
or low ambient temperatures (see
Clause 23
).
Note:
The curing procedure should be part of the development of the trial mix, particularly where colour-matching is
important (see
Clause 33.2.4
.)
(g) The area shall be finished as required, depending on the particular finish treatment.
33.3 Structural repairs
33.3.1 General
Repairs of a structural nature shall not be undertaken until the manufacturer’s engineer has
(a) investigated the structural implications of the defect or damage;
(b) established the cause of the defect or damage; and
(c) received approval of the proposed repair procedures from the owner.
33.3.2 Conditions
A defect or damage shall be deemed to be of a potentially structural nature when one or more of the
following conditions occur:
(a) main reinforcement or tendons are exposed;
(b) connection hardware anchorage is exposed;
(c) cracking occurs in bearing areas;
(d) cracking extends from one face of the element through to the opposite face; and
(e) cracks are wider than 0.3 mm or more than 300 mm long.
33.3.3 Repair procedures
The procedures for repairs shall include the requirements of
Clause 33.2.6
or additional methods, such as
drypacking, pressure grouting, or injection of epoxy under pressure or by vacuum. The procedures shall
also state whether any load test is required following repairs.
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