CHAPTER 3—REPAIR MATERIALS
3.1—Introduction
This chapter contains descriptions of the various categories
of materials that are available for repair or rehabilitation
of concrete structures. Typical properties, advantages,
disadvantages or limitations, typical applications, and
applicable standards and references are discussed for each
repair material. Also, general guidance on selection of
repair materials is provided.
3.2—Cementitious materials
To match the properties of the concrete being repaired as
closely as possible, PCC and mortar or other cementitious
compositions using similar proportions of ingredients are the
best choices for repair materials. The new cementitious
repair material should be compatible with the existing
concrete substrate.
3.2.1 Conventional concrete—Conventional concrete
composed of portland cement, aggregates, and water is often
used as a repair material. Admixtures are used to entrain air,
accelerate or retard hydration, improve workability, reduce
mixing water requirements, increase strength, or alter other
properties of the concrete. Pozzolanic materials, such as fly
ash or silica fume, may be used in conjunction with portland
cement for economy, or to provide specific properties such
as reduced early heat of hydration, improved later-age
strength development, reduced permeability, or increased
resistance to alkali-aggregate reaction and sulfate attack.
Concrete proportions should provide workability, density,
strength, and durability necessary for the particular application
(ACI 211.1). To minimize shrinkage cracking, the repair
concrete should have a w/cm as low as possible and a coarse
aggregate content as high as possible. According to ACI
201.2R, frost-resistant normalweight concrete should have a
w/c not to exceed 0.45 for thin sections, such as 40 to 75 mm
(1.5 to 3 in.), and 0.50 for all other structures. Mixing, transporting,
and placing of conventional concrete should follow the guidance given in ACI 304R, ACI 304.1R, ACI 304.2R,
ACI 304.5R, and ACI 304.6R.
a) Advantages—Conventional concrete is readily available,
well understood, economical, has similar properties to the
parent concrete, and is relatively easy to produce, place,
finish, and cure. Generally, concrete mixtures can be proportioned
to match the properties of the underlying concrete;
therefore, conventional concrete is applicable to a wide
range of repairs.
Conventional concrete can be easily placed under water
using a number of well-recognized techniques and precautions
to ensure the integrity of the concrete after placement
(ACI 304R and 546.2R). Concrete is typically placed under
water using a tremie or a pump.
b) Limitations—Conventional concrete should not be used
in repairs where the aggressive environment that caused the
original concrete to deteriorate has not been eliminated,
unless a reduced service life is acceptable. For example, if
the original deterioration was caused by acid attack,
aggressive water attack, or even abrasion-erosion, repair
with conventional concrete may not be successful unless the
cause of deterioration is removed.
When used as a bonded overlay, the shrinkage properties
of the repair material are critical because the new material is
being placed on a material that has exhibited essentially all
of the shrinkage that it will experience. Full consideration of
the shrinkage properties and the curing procedure should be
addressed in the specification for the repair.
Concrete that is mixed, transported, and placed under hot
weather conditions of high temperature, low humidity, or
wind requires measures to be taken to eliminate or minimize
undesirable effects (ACI 305R). There are special requirements
for producing and placing satisfactory concrete during
cold weather (ACI 306R).
c) Applications—Conventional concrete is often used in
repairs involving relatively thick sections and large volumes of
repair material. Typically, conventional concrete is appropriate
for partial- and full-depth repairs and resurfacing overlays
where the minimum thickness is greater than 50 mm (2 in.)
or the overlay extends beyond the reinforcement, or when the
repair area is large. Conventional concrete is most commonly
used for repairs of slabs, walls, columns, piers, and hydraulic
structures (McDonald 1987), as well as for full-depth repairs
or overlays on bridge or parking structure decks.
Conventional concrete is particularly suitable for repairs
in marine environments because the typically high humidity
in such environments minimizes the potential for shrinkage
(Troxell, Raphael, and Davis 1958).
d) Standards—ASTM C 94 covers ready-mixed concrete
manufactured and delivered to a purchaser in a freshly mixed
and unhardened state. Properties such as shrinkage and bond
are not included in this specification, and they should be
specified separately if they merit special consideration in a
given repair.