Road Science: Top 5 Trends of 2010
The TIG states that new products, emerging technologies and innovative construction practices should not sacrifice quality, durability and long-term performance; provide a means of accelerating the construction scheduling and sequencing; reduce congestion delays caused by excessive construction work zone time frames; and be economically feasible. “It is our belief that when precast paving elements are properly selected as a pavement or repair treatment, all of these beneficial characteristics are attainable,” the TIG. Its work will have ramifications for road builders and owners as 2010 unfolds.
5. Polymer rebar could supplant steel in concrete pavement
Use of polymer rebar could supplant reinforcing steel in continuously reinforced concrete pavements, if research now underway affirms its use. The 2009 research circular, Evaluating the Use of Fiber-Reinforced Polymer Bars in Continuously Reinforced Concrete Pavement, a product of the FHWA’S Concrete Pavement Technology Program (CPTP), reviewed their status.
Continuously reinforced concrete pavement designs (CRCP) are premium pavement designs that are often used on heavily-trafficked roadways and urban corridors. CRCP designs have no regularly spaced transverse joints, but contain a significant amount of longitudinal steel reinforcement (typically 0.6 to 0.8 percent of the cross-sectional area). The high steel content both influences the development of transverse cracks within an acceptable spacing (about 3 to 6 feet) and serves to hold them tightly together (see The ABCs of Continuously Reinforced Concrete, Road Science, May 2007).
The prevalence of wide cracks in CRCP has frequently been associated with ruptured steel and significant levels of corrosion, and fiber-reinforced polymer (FRP) composite materials are one product being investigated for use in CRCP in place of traditional steel bars. FRP composites consist of a matrix of polymeric material (polyester, vinyl ester, or epoxy) that is reinforced by fibers of other reinforcing materials, typically glass, carbon, or graphite.
Advantages of FRP bars include not only their corrosion resistance, but also their high longitudinal strength, high-fatigue endurance, and lightweight. Disadvantages of FRP bars include high cost, low modulus of elasticity, and low shear strength. There are concerns associated with the potential for large crack spacings and greater crack widths, which may compromise the long-term, aggregate-interlock load transfer needed to ensure long-term performance.
Two field studies have been constructed and are being monitored to help evaluate and improve the performance of FRP-reinforced CRCP designs.v