| This project studies the prediction and prevention of cracking in high performance concrete due to temperature and shrinkage during construction. Models are developed to predict concrete physical properties, as well as thermal properties. Computer models are then developed to predict temperature development and distribution in concrete under field conditions. This information is then used as input to determine the time-dependent stresses caused by temperature fluctuations and concrete shrinkage.; During construction, the primary cause of temperature fluctuation is heat generated by cementitious material hydration. A hydration model for high performance concrete is developed that considers the rate of hydration and the influence of concrete composition on heat of hydration. Concrete thermal properties, which influence the magnitude, distribution, and rate of temperature change, are also described. The hydration model is then incorporated into a three-dimensional, transient, finite element thermal analysis using an existing computer program FETAB3D as a basis to predict the temperature history and distribution in a concrete structure. The computer program FETAB3D, which takes into account variable thermal conditions including thermal radiation and boundary energy transfer, is modified further to account for multi-lift construction procedures, and to accept custom ambient temperature and solar radiation input files. To reflect these modifications, the computer program is renamed FETAB3DH.; Physical properties of high performance concrete, such as tensile and compressive strength, elastic modulus, creep, and shrinkage are discussed and modeled as a function of concrete maturity. Using these material properties, concrete stresses due to temperature change and shrinkage are calculated using the commercially available structural analysis computer program, ABAQUS. The effects of creep are considered by using the general step-by-step method.; The thermal and stress analysis techniques presented in this study are used to study the construction of the Confederation Bridge, in Eastern Canada, and the Tsable River Bridge, on Vancouver Island, both constructed using high performance concrete. Temperature field measurements on both bridges confirm the validity of the hydration and temperature models incorporated in the computer program FETAB3DH. The stress analyses are used to determine the significance of tensile stresses induced by thermal and shrinkage effects. The significance of tensile stresses is quantified as a probability of causing cracking. The calculated stresses and probability of cracking compare favorably with the onset, location, and orientation of observed cracking.; Using the results of this study, guidelines for the prevention and prediction of cracking in high performance concrete structures are proposed. These guidelines can be used by contractors and designers to assist with construction planning and conceptual design. The computer models and analysis procedures outlined in this study can be used to quantify temperature and shrinkage loading and resulting stresses for detailed design purposes. |
