Rizkalla, Dawood, and Shahawy 123 Reinforcement for Concrete Structures One-dimensional CFRP and glass FRP (GFRP) bars are commercially fabricated and used as reinforcements for concrete structures. Due to their excellent corrosion resistance, FRP reinforcing bars have been extensively used as reinforcement for a number of concrete structures including bridges, underground precast chambers, highway pavements, maglev rails and structures housing magnetic resonance imaging (MRI) equipments.

FRP reinforcing bars were used exclusively in the construction of a portion of the concrete deck and barrier wall of a highway bridge (Rizkalla et al., 1998). The five-span bridge, which was constructed in 1997, consisted of eight 33-m-long, simply supported AASHTO-type prestressed concrete girders. A 16 m x 8 m portion of the deck was exclusively reinforced with 10 mm diameter CFRP bars. The CFRP bars were placed in two layers with bars oriented in both the longitudinal and transverse directions to create a two-dimensional reinforcement grid. Casting of the deck is shown in Figure 1a. A 14.2-m-long portion of the concrete barrier wall was also reinforced using two layers of 15-mm GFRP rods since these type of elements are subjected to severe environmental conditions including wet and dry cycling as well as splash of salt from the roadway.

To facilitate rapid construction, FRP materials are also fabricated as two-dimensional grids, in a similar fashion of conventional steel welded wire fabric, which were used as reinforcement for a concrete bridge deck as shown in Figure 1b (Benmokrane et al., 2000). Portions of the concrete barrier and sidewalk were also reinforced using different CFRP and GFRP reinforcements. Various types of gauges were used to monitor the behavior of the bridge including structurally integrated optical sensors to monitor the behavior under field conditions.

Shear stirrups represent another application of FRP in bridges since these particular reinforcements are the most susceptible to deterioration due to corrosion. Typically a minimum concrete cover is provided for shear reinforcements. Moisture ingress into cracked cover concrete can cause corrosion of the stirrups and spalling of the cover concrete. Two of the precast AASHTO girders used for construction of the Taylor Bridge were also reinforced using two different types of CFRP stirrups. The stirrups were extended out of the top surface of the

(a) (b)

FIGURE 1 FRP-reinforced concrete bridge decks: (a) Taylor Bridge and (b) Joffre Bridge.

124 Transportation Research Circular E-C105: 50 Years of Interstate Structures: Past, Present, and Future girders to act as shear connectors and provide composite action between the prestressed girders and the concrete deck slab. The fully assembled reinforcing cage for one of the girders is shown in Figure 2.

Buried structures are continuously exposed to moist soils and aggressive corrosion-causing minerals which accelerate the deterioration of the conventional steel reinforcing bars and can lead to cracking of the concrete structure. Thousands of steel-reinforced chambers require replacement on an annual basis due to corrosion of the conventional reinforcing steel. Due to the limited access to these structures, replacement can be costly and time consuming. Typical chambers constructed using GFRP reinforcements and installed underground are shown in Figure 3 (Benmokrane, 1999). The chambers were constructed to demonstrate the feasibility of using composite materials to reduce the need for replacement of underground structures.

FIGURE 2 CFRP stirrups for prestressed girders.

FIGURE 3 GFRP reinforced underground precast concrete chambers.