Many State Engineers have observed that a number of high-performance concrete (HPC) bridge decks exhibited cracking and sometimes soon after being poured. Although deck cracking can be attributed to various causes, in many cases, concrete shrinkage is considered the main contributor. Additionally, concrete in bridge decks is considered restrained and there is a need to examine the behavior of HPC mixes under those conditions. The AASHTO test (PP 34-99, The Passive or Restrained Ring Test) is employed to measure the cracking potential and restrained shrinkage behavior of various HPC mixes used in bridge deck projects contracted by the New Jersey Department of Transportation (NJDOT). This paper presents the results of a study which utilized a direct method for measuring the strain development in the concrete ring using Vibrating Wire Strain Gages (VWSG). For each mix, additional tests were performed to determine the corresponding mechanical properties (e.g., elastic modulus, tensile splitting strength, compressive strength, etc.). The effect of pozzolanic material and the potential of cracking for various mixes are also reported. The results of the study are used to correlate strains from restrained shrinkage tests with measured free shrinkage. In general, to minimize HPC cracking potential, this study shows that specified limits on free shrinkage used in bridge decks need to be adjusted to reflect restrained shrinkage conditions. Moreover, coarse to fine aggregate ratio as well as amount and type of coarse aggregate is a major factor affecting shrinkage behavior of HPC.
Samenvatting