Document - 2.pdf

A23.4-09

Canadian Standards Association

November 2009

16.2 Architectural concrete

All architectural concrete exposed to the weather shall have a

(a) minimum compressive strength of 30 MPa;

(b) minimum air content of 5%; and

16.3 Veneered construction

16.3.1

When two different concrete mixes are veneered in a precast concrete element, the two mixes shall be

compatible as an integral unit. The mixes shall be within 10% of each other with respect to cementing

materials and water/cementing materials ratio.

Note:

Because dissimilar expansion and contraction caused by thermal and moisture changes, and differential shrinkage

and creep, can cause unacceptable cracking, bowing, or warping, any difference in behaviour between the face and the

backup concrete should be minimized. Accordingly, the two mixes should be reasonably compatible with respect to

cementing materials content and water/cementing materials ratio.

16.3.2

When a separate face mix is used for precast concrete, the thickness of the face mix following

consolidation shall be at least 25 mm or 1-1/2 times the maximum size of the aggregate, whichever is

larger. In the case of large aggregates hand-laid in a mould, these dimensions shall apply to the concrete

mix used as the matrix.

17 Durability

Precast concrete shall comply with Clause 4.1.1 of CSA A23.1. Care shall be taken to protect connections

and exposed hardware.

Note:

Durable precast concrete structures are dependent on the protection of reinforcement and hardware, whether

provided by concrete cover or other means.

18 Specifying concrete

Alternative (1) of Table 5 in CSA A23.1 shall be used by the owner for specifying the concrete used in

precast concrete.

In addition to the items specified in Alternative (1) of Table 5 in CSA A23.1, the owner shall specify

(a) the allowable percentage of water absorption for architectural concrete exposed to the weather;

(b) special additives (e.g., colour pigments for architectural concrete);

(d) for special high-quality architectural concrete in severe or polluted environments or when improved

weathering qualities are desirable, the limits for any concrete materials passing a 315 μm sieve.

Note:

For further information, see Clause 4.1.2 of CSA A23.1.

19 Concrete quality

19.1 General

Evaluation of concrete quality for precast concrete shall comply with Clause 4.4 of CSA A23.1 and

Clauses 19.2

19.9

of this Standard.

Licensed for/Autorisé à Jed Friesen Sold by/vendu par CSA on/le June/18/2015.

~Single user license only. Storage, distribution or use on network prohibited. Permis d'utilisateur simple seulement.

Le stockage, la distribution ou l'utilisation sur le réseau est interdit.