Evaluation of shrinkage cracking potential of concrete used in bridge decks in Florida

A research study was done to evaluate the different concrete mixtures that have various different admixtures added for reducing the shrinkage in the concrete, and to make recommendations for concrete mix designs for improved resistance to shrinkage cracking in service. Also, an effective and convenient laboratory set-up and procedure for evaluating concrete mixtures for their resistance to shrinkage cracking in service was developed as a result of this study.; The results of the testing program indicated that the use of a shrinkage-reducing admixture was effective in reducing the free shrinkage strains and shrinkage-induced stresses of all the concrete mixtures tested, while the compressive strength, splitting tensile strength and elastic modulus of the concrete were not significantly affected. The addition of fly ash as a mineral admixture was found to be effective in reducing the free shrinkage strain and shrinkage-induced stresses of all concrete mixtures. This research study presents a very promising testing and analysis method for evaluating the potential shrinkage-induced stresses in concrete and its potential for shrinkage cracking in service. The developed Constrained Long Specimen (CLS) test method was used to evaluate the effects of a shrinkage-reducing admixture on the potential shrinkage-induced stresses of 15 different concrete mixes and their potential for shrinkage cracking in service. From the test data and the analysis results obtained from the 15 concrete mixes tested in this set of experiments, the developed Constrained Long Specimen method demonstrated that it provided reasonable assessment of expected shrinkage-induced stresses in the concrete. Due to the creep of concrete at early age, the shrinkage-induced stress in the concrete is much lower than that estimated by multiplying the shrinkage strain by the elastic modulus of the concrete. Using the CLS test method enables the creep component to be properly considered, and a realistic determination to be made of the expected induced shrinkage stresses in concrete in service. The results of the CLS tests on the 15 concrete mixes showed the possible benefits of using a shrinkage-reducing admixture in reducing the potential shrinkage cracking of concrete in service.