Concrete Shrinkage Analysis for Bridge Deck Concrete

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CAIT project no.: 180 RU6545

Fiscal Year: 2005/2006

Status: Final

Rutgers-CAIT Author(s): Hani Nassif, Kagan Aktas, Husam Najm

External Author(s): Nakin Suksawang, Florida International University, Edward S. Kondrath



Infrastructure facilities constitute a major part of the national investment. According to the National Bridge Inventory (NBI) (Federal Highway Administration, 2004) [1] there are more than 594,470 bridges and about 150,981 (25.4%) of them are structurally deficient or obsolete. Major decisions are needed to allocate the limited funds available for repair, rehabilitation, and replacement. Over the last decade, the use of High Performance Concrete (HPC) has emerged as an important alternative to deal with deteriorating infrastructure. The concept of HPC in the USA was developed under the Strategic Highway Research Program (SHRP) contract C205. At the end of SHRP program, a major thrust was made for implementation of results. The Federal Highway Administration (FHWA) has initiated programs for the design and construction of HPC bridges and pavements with the aim of reducing both initial construction costs and long-term maintenance costs. A test has been developed by AASHTO (PP 34-99, The Passive or Restrained Ring Test) that compares the relative cracking potentials of concrete mixtures. This cracking tendency was performed on 16 concrete mixes used for bridge decks by NJDOT to identify those that would exhibit high potential for cracking. Although cracking of bridge decks can be attributed to various causes, this study provided a comparative classification of the cracking potential of each mix. A correlation of cracking potential with various parameters is also established. Results show that mixes with high Coarse Aggregate (CA) to Fine Aggregate (FA) ratio (i.e., CA/FA >1.48) and a CA minimum weight of 1800 lb/cu.yd have lower potential for cracking. It is also shown that rate of free shrinkage correlates directly with the rate of restrained shrinkage, and a limit of 450 micro strain for free shrinkage at 56 days is recommended to reduce the cracking potential of concrete mixes.