Page 125 - Design of Reinforced Masonry Structures

MATERIALS OF MASONRY CONSTRUCTION 3.19

5. ASTM A775/A775M-01: Specification for Epoxy-Coated Reinforcing Steel Bars
[3.30]. These steel bars are covered with a thin coat of epoxy of the order of 7 to 12 mil
(1 mil = 1/1000) thick in order to provide protection from corrosion. The specification
covers requirements for the epoxy-coating material, surface preparation of bars prior to
application of the coating, the method of application of the coating material, limits on
coating thickness, and acceptance tests to ensure that coating was properly applied.
6. ASTM A996/A996M-06: Standard Specification for Rail-Steel and Axle-Steel
Deformed Bars for Concrete Reinforcement [3.31]. This specification covers reinforc-
ing bars manufactured from discarded railroad rails or discarded train car axles; the bars
are generally less ductile than billet steel.
Coated reinforcing bars are recognized by both concrete and masonry professionals as
viable corrosion-protection systems. Both epoxy-coated and zinc-coated (galvanized) bars
can be used for reinforced concrete and masonry construction when protection from corro-
sion is desired. Corrosion of steel reinforcement can occur when a structure is subjected to
severe environmental conditions, such as marine environment or to deicing salts.
Performance of epoxy-coated bars has been controversial in the past. Many studies have
shown that these bars can effectively reduce reinforcement corrosion and extend the service
life of structures. Care should be taken during transportation, handling, storage, and place-
ment of epoxy-coated bars to prevent damage (cracking, nicks, and cuts) to coating. Any
damage to the coating must be repaired prior to placement of bars in the masonry. It is noted
that epoxy coating of the bars leads to reduced resistance to slippage; consequently a longer
development would be required for such bars. MSJC-08 Section 2.1.9.3 [3.2] requires that
development length of epoxy-coated bars be 1½ times that required for uncoated bars.
Zinc-coated (galvanized) bars, like epoxy-coated bars, are covered with a thin layer of
zinc as a means to provide protection from corrosion. Although zinc would protect the steel
bar, zinc would corrode in concrete and eventually lead to corrosion of steel bars [3.32].
Unlike epoxy-coated bars, galvanized bars provide the same slip resistance as uncoated
bars; consequently, modification of development length is not required for these bars.
An alternative to zinc-coated and epoxy-coated reinforcement used for corrosion pro-
tection is the fiber-reinforced polymer (FRP) reinforcement that has been successfully used
for concrete structures. Typically available up to No. 8 size, FRP reinforcement is light,
has high specific strength (ratio of tensile strength to weight), high specific modulus (ratio
of modulus of elasticity in tension to weight), and is corrosion resistant [3.33]. The light
weight of FRP reinforcing bars results in savings in transportation, handling, and erection
costs. Also, because these bars are corrosion resistant, they can be used with smaller cover
than required for steel reinforcing bars. The potential of this type of reinforcement for
masonry structures has not been explored by research and field demonstration projects.
Consequently, presently its use is not permitted by design codes for masonry structures.

3.6.2 Joint Reinforcement
Joint reinforcement is typically used in locations where available space would not permit
placement of deformed bars with proper cover and clearance. Three types of joint reinforce-
ment are generally used: (1) truss or ladder type joint reinforcement, (2) deformed reinforc-
ing wire, and (3) welded wire fabric.
Truss- or ladder-type joint reinforcement conforms to ASTM A951-02: Standard
Specification for Masonry Joint Reinforcement [3.34]. Typically, two types of joint
reinforcement are permitted: the truss type (Fig. 3.6a) and the ladder type (Fig 3.6b).
Specifications require maximum spacing of cross wires in ladder-type joint reinforcement
and points of connections in the truss-type reinforcement to be 16 in. Both types of