19 June 2001
Shrinkage of the repair is the most common reason for delamination of the repair
from the substrate.
Curing is important to allow strength development and minimize drying
shrinkage. For Portland cement mixes, water curing by ponding with water, fog
misting, or covering with wet burlap are the best methods. If continuous moisture
curing is not possible, then use two applications of a liquid curing compound. The
repaired concrete should be kept wet or moist for a minimum of 7 days. When
water evaporates from the concrete, drying shrinkage occurs. Shrinkage of a
repair patch can cause the patch to crack or partially debond.
Curing for epoxy concrete is to provide the correct temperature for the
epoxy resin to develop full strength. Epoxy resins that use 100 percent solids and
no solvents do not shrink. Epoxy resins do, however, have a much greater
coefficient of expansion than concrete. This often leads to failure in large patches
and in environments that experience large temperature differentials between day
and night. Epoxy can be mixed with sand (1 part epoxy : 7 parts sand) to
minimize the difference in the thermal expansion characteristics.
Guidelines. General guidelines for concrete used in waterfront
Use 35 MPa (5000 psi) concrete.
Use only Type I or II.
Use a minimum of 360 kg (8.3 bags) to a maximum of 445 kg (10.4
bags) of cement per cubic meter in the concrete mix.
Use a maximum water-cement ratio of 0.40 by weight (17 L per
bag of cement).
For most small volume repairs, use aggregate no larger than 2 cm
Make sure the concrete cover over reinforcing steel is at least 8 cm
(3 1/5 inches).
Use epoxy-coated reinforcing steel, or epoxy coat exposed steel,
in situations where steel is particularly susceptible to corrosion per
ASTM A 934.
Pay particular to the use of admixtures: DO NOT use an admixture
For concrete subject to freeze-thaw cycles, use air-entraining agent
to obtain 5 to 7 percent air content.