Invention Title: A Ductile Strip Used for Eliminating Shrinkage and Temperature Cracks in Concrete Pavements and Bridge Decks

Inventors: V.C. Li and J. Zhang
US Patent No. 6,694,690
Issued on February 24, 2004

Suggested Key Words: concrete pavements, bridge decks, shrinkage cracks, ductile strips, crack localization

Non-Proprietary Description: Reinforced concrete slabs have been widely used in modern transportation engineering, such as highway and airport pavements and bridge decks. Cracking in slabs reduces the load capacity, and has been linked to fatigue failure. In addition, cracks allow water and other chemical agents, such as deicing salt, to go through the cover layer to come into contact with the reinforcements, leading to reinforcement corrosion and rupture. Concrete shrinkage and temperature changes are the principle reasons for the initial crack formation and propagation afterward in slabs. Therefore, in order to prolong the service life of concrete pavements and bridge decks, shrinkage and temperature induced cracks have to be reduced or eliminated.

In the present invention, a kind of ductile structural element specifically designed for crack control in concrete pavements and bridge decks is presented. By inserting (pre-cast or cast on-site) these ductile strips in concrete pavements and bridge decks, cracking in concrete due to shrinkage and temperature changes can be avoided.

In the present invention, cracks, especially shrinkage and temperature cracks, are localized into designated strips, where ductile material with tensile strain-hardening and high strain capacity (typically several percent) is used. As a result, while microstructure damage exists in the ductile strip, the concrete remains intact. Due to the special material properties of the ductile material, the strain energy produced by shrinkage (under restrain condition) of hardened cement and temperature changes can be released by the high strain ability of ductile material so that cracking in plain concrete can be avoided. By replacing standard joints in concrete pavements, common deterioration (e.g. D-cracking) problems associated with joints can be also eliminated. A possible ductile material for the ductile strip is a fiber reinforced engineered cementitious composite (ECC).