Evaluating Thermal Behavior and Use of Maturity Method in Mass Concrete

Large concrete placements with increased amount of cement contents result in higher peak temperatures as well as higher temperature differentials between the concrete surface and the interior. Such high thermal differentials can result in large temperature-induced stresses and increases the risk of early age cracking. To minimize this risk, temperature development within the structure must be known. Throughout the project, fourteen different sub-structures from six different bridge projects and four 6-ft cube blocks, in total of eighteen structural elements in nine different districts were instrumented successfully with sacrificial loggers, and temperature-time histories of these elements were monitored. Laboratory studies involved determination of concrete heat generation, activation energy and compressive strength development at different curing temperatures. In order to predict temperature distribution within large concrete structures, a 3D numerical analysis methodology was developed using finite volume method in which variable heat conductivity and capacity can be handled at early ages. MATLABRTM was then employed to generate a program that solves the governing heat transfer equation. Analysis results were validated with temperature-time histories collected from fourteen different sub-structures at six different bridge projects and four 6-ft cube blocks. Laboratory studies were conducted to determine concrete heat generation, activation energies and compressive strength development at different curing temperatures.;Additionally, equivalent age method was implemented to estimate in-place strength of mass concrete placements. Four inch diameter core samples, with 6-foot (1.8 m) in length, were taken from the 6-ft cubes and the core strengths were compared with the predicted concrete strengths. It was found out that the predicted in-place concrete strength was always higher than the actual core strength on top surface locations and core strength from the bottom section were generally higher than the predicted values.;Overall, the numerical model has proven to produce accurate predictions in 2D and 3D temperature analysis within the concrete elements at early ages. Using the concrete mixture information and the measured concrete hydration properties, this study shows that the temperature predictions can be correlated reasonably well with the field data by means of finite volume model. Moreover, ASTM C1074 Maturity Method was employed successfully to estimate measured core strength for mass concrete structures.