1 September 1999
Table 4-1. Continued
Concrete deposited under water (tremie concrete).
25 Mpa (3000 psi)
Columns in multistory buildings carrying heavy loads.
30 Mpa (4000 psi)
Reinforced concrete in contact with sea-water, alkaline soils
30 Mpa (4000 psi)
or waters, or other destructive agents.
Prestressed concrete construction.
35 Mpa (5000 psi )
4-5. DESIGN CHOICES. The selection of the structural concrete framing system, strength of
concrete and reinforcement, conventional versus lightweight concrete, conventional versus
prestressed design, and cast-in-place versus precast construction will be based on economic
and functional considerations. Designers should take into account the specific type and size
of structure, architectural features or special performance requirements, seismic exposure,
construction cost factors for the building site, and the availability of materials and labor. For
further discussion of considerations in selecting appropriate composition and properties for
concrete, see ACI Committee 201 Report, "Guide to Durable Concrete."
4-6. SERVICEABILITY. Buildings must remain serviceable throughout their service life. This
means for concrete buildings and concrete structural elements, the concrete must be durable,
free from objectionable cracking, and with adequate protection of the reinforcing steel to
prevent corrosion. In additions, structural deflections that can damage interior partition walls,
ceilings and various architectural features must be kept within acceptable limits.
a. Durability. Durability of Portland cement concrete is defined as its ability to resist
weathering action, chemical attack, abrasion, or any other process of deterioration. Durable
concrete will retain its original form, quality, and serviceability when exposed to its
environment. Causes of concrete deterioration, such as freezing and thawing, aggressive
chemical exposure, abrasion, corrosion of steel and other materials embedded in concrete,
and chemical reactions of aggregates are described in the ACI Committee 201 Report, "Guide
to Durable Concrete". This report also covers various preventive measures to assure durability
problems do not occur. The most significant causes of concrete deterioration are freezing and
thawing, and corrosion of reinforcing steel.
(1) Freeze-thaw Protection. Concrete made with good aggregates, low water-cement
ratio, and air entrainment will have good resistance to cyclic freezing. Air entrained concrete
which contains an appropriate distribution of air voids provides good freeze-thaw protection,
because when the concrete freezes there is room for any water which has saturated the
concrete to expand without causing damage to the concrete. Table 4-2 provided
recommended air contents to prevent freeze-thaw damage.