| This dissertation presents the development of a finite element model for the prediction of the distribution of temperatures within a hydrating massive concrete element. The temperature distribution produced by the finite element thermal analysis of the model is used in the finite element structural analysis to quantify the maximum allowable thermal gradient before cracking will initiate in the concrete.;Temperature differences within the concrete occur when the heat being generated by the concrete is dissipated to the surrounding environment causing the temperature at the surface of the concrete to be lower than the temperature at the interior of the concrete. At the same time the heat generated is a function of the temperature and time history of the concrete. Therefore, individual locations in the concrete will experience different levels of heat. The temperature difference between the concrete at the center of the element and the concrete in the outer region will create stresses. If the induced tensile stresses are larger than the early age tensile strength of the concrete, cracking will occur.;The requirements for the control of heat generation and maximum allowable temperature difference in mass concrete vary on a state by state basis. Currently, there is no agreement on what should be the maximum allowable temperature differential between the center of a mass concrete element and its surface. How the various states arrive at their respective values is not clear. The development of an effective model for analysis of mass concrete behavior will enable the establishment of rational requirements for mass concrete to reduce cracking.;To verify the results obtained in the finite element model, four different mixes of concrete, typical of use in mass concrete applications in Florida, were produced, and each mix used to make two large-scale 3.5ft x 3.5 ft x 3.5 ft (1.07 m x 1.07 m x 1.07 m) concrete blocks. In each mix, one block was insulated on all six sides to simulate a fully adiabatic process, while the other block was insulated on five of the faces with the top face left open and exposed to environmental conditions. Measurements of the temperature and strain at predetermined locations within the blocks were recorded until the equilibrium temperature was achieved.;Using the developed model, a parametric analysis was performed to evaluate the effects of cement heat generation, concrete thermal properties, dimension of concrete structure, insulation of structure, convection of heat, etc. on the temperature distribution and induced stresses in mass concrete structures. Recommendations on methods for evaluating the potential performance of mass concrete structures are presented. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)... |
