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A23.4-09
©
Canadian Standards Association
November 2009
19.4 Absorption — Frequency and number of tests
As an indication of potential weather staining and durability characteristics, the absorption of all face
mixes subject to weathering shall be established as the average of three tests in accordance with Test
Method A23.2-11C in CSA A23.2. The absorption shall be verified at the beginning of each production
run, every 6 months thereafter, and whenever the materials or production methods are modified.
Notes:
(1)
Acceptable absorption varies in accordance with exposure conditions but normally should not exceed 6% (by mass).
(2)
To obtain an absorption of 6% or less, thorough consolidation and curing are necessary, as well as a low
water/cementing materials ratio and limitations on the percentage of aggregates passing a
315 μm
sieve.
19.5 Accelerated curing tests
19.5.1
During accelerated curing, temperatures within the concrete shall be monitored and recorded in
accordance with
Clause 23.2.2.5
.
Note:
For standard production methods, air temperatures rather than concrete temperatures may be monitored.
19.5.2
When accelerated curing of the concrete elements takes place in accordance with
Clause 23.2.2
, all test
specimens shall be cured with the concrete elements during the accelerated curing, following which the
specimens shall be cured under controlled laboratory conditions in accordance with Test Method
A23.2-3C in CSA A23.2.
Notes:
(1)
Test specimens should be placed in such a way that the curing conditions simulate as closely as possible the condition
of the concrete elements. Specimens should not be subjected to any concentration of heat or any heat exceeding what
is likely to reach the products. During initial castings in new set-ups, the ambient temperature around the test
specimens should be compared to the ambient temperature near the elements.
(2)
The experience of precast producers indicates that the initial curing of
28 d
cylinders with the elements during
accelerated curing will normally result in
28 d
strengths up to 8% below normally cured laboratory cylinders,
depending on how closely the optimum curing temperature cycle is controlled. However, this curing method is
important, as it is the only valid check that the accelerated curing has not been excessive or has otherwise resulted in
significant strength losses of the actual concrete element below the potential
28 d
strength.
(3)
To verify the potential strength of the concrete mix, normal laboratory-cured cylinders should occasionally be made
and tested.
19.6 Intermediate strength levels
For intermediate concrete strength determination, such as strength at handling or transfer of prestress
force, test specimens made in accordance with other Standards may be used if the tests are correlated to
standard cylinder testing.
Note:
Tests for intermediate strength levels may use test samples cast horizontally if the moulds and casting procedures are
in accordance with ASTM C512.
19.7 Low-density concrete
19.7.1
The modulus of elasticity and the shrinkage and creep characteristics of a proposed concrete mix with
low-density aggregate for architectural, prestressed, or precast concrete shall be determined before its use
and reviewed by the owner to ensure that it meets the applicable requirements of this Standard. This
requirement shall apply to concrete where all aggregates are low density and to concrete with only
low-density coarse aggregate.
Note:
The modulus of elasticity, shrinkage, and creep characteristics for low-density aggregate concrete are different from
those for normal-density aggregate concrete. To assess related design and performance requirements (e.g., prestress losses,
deflection, and camber under the proposed production methods and application), it is necessary to know the modulus of
elasticity of low-density aggregate concrete.
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