CRCP with Elastic Joints – Concrete Overlay Project – Greene County, Iowa
PDF courtesy of the American Concrete Pavement Association’s (ACPA’s) technical resources archives.
The Welded Wire Fabric Industry and its association, the Wire Reinforcement Institute, are pleased to cooperate in the Greene County, Iowa Overlay Project. We particularly wish to congratulate Mr. C. Arthur Elliott, County Engineer, Greene County, for his foresight and initiative in developing this much needed project.
Welded Wire Fabric will be actually used in two different installations–for Continuous Reinforced Concrete Overlay with Elastic Joints and for a conventionally reinforced section which will act as a control section along with a plain pavement section.
Highway engineers are familiar with Continuous Reinforced Concrete Pavement (CRCP). There are no transverse joints (except at structures) in CRCP. The steel reinforcement is heavy-usually 0. 5 to 0. 7 percent of the cross-sectional area and is designed to hold cracks closely together. Ramdom transverse cracking is expected in CRCP with cracks forming at 2 to 6 or 8-ft intervals. As mentioned previously, the reinforcing steel is designed to hold these cracks closely together.
CRCP with elastic joints is a new concept designed to control and minimize transverse cracking, Several installations have been constructed and are in service in Europe. There have also been several types of similar joints in the United States.
The elastic joints will be spaced on 8′ 0″ centers. The elastic joint has two distinct features. In order to form the joint from the underside, a piece of 20 gage metal will be placed upright on 8′ 0″ centers. It will serve to support the welded wire fabric and to create a crack at this weakened point. It is called the crack initiator. The second feature consists of coating the longitudinal wire with asphalt in the section immediately above the crack initiator. The transverse wires of the welded wire fabric are on 16-in. centers and all longitudinal wires in the 16-in. spacing immediately above the crack initiator are coated to prevent bonding. A secondary effect will be to offer some corrosion protection. The bond is broken for a 16-in. long section in order to reduce stress on the
steel and thus reduce the amount of steel required. The steel percentage for this project will be 0. 45 percent. It is expected that cracks will form over the crack initiator. There will be some additional intermediate cracks formed between the elastic joints. However, the number should be greatly reduced when compared to conventional CRCP. Polyethylene sheeting will be placed between the existing pavement and the concrete overlay to prevent bond between them. Two test sections 3 and 4-in. thick will be evaluated.