| Popis: |
The durability of mass concrete structures may be compromised due to stresses and cracking induced by temperature rise due to cement hydration and concrete’s insulating capacity. Delayed ettringite formation and thermal cracking may occur when maximum temperatures and maximum temperature differences are greater than the allowable limits. Through a real-world case study in Douglasville, Georgia, this work investigates how modeling, construction decisions, and thermal limits influence the construction decisions of a mass concrete footing and abutment wall. Thermal control measures deemed necessary to satisfy thermal limit criteria for the abutment wall construction included precooling the concrete using liquid nitrogen and post-cooling the abutment wall using internal cooling pipes. Both measures, however, increased the cost and complexity of construction. The footing also required pre-cooling of the concrete even though it was not classified as mass concrete. In this work, the temperature development of the footing and the wall is modeled through a progressive approach based on laboratory-scale isothermal calorimetry. Based on the modeling, alternative design and construction options to satisfy thermal limits imposed by several Department of Transportation (DOT) guidelines, but at lower cost and complexity, are considered. A performance-based temperature difference limit (PBTDL) that considers a certain project’s mechanical performance and material properties is introduced as an alternative to the current difference limit prescribed by DOTs, which in certain cases can be inflexible, overly conservative, and overly simplified. The analysis also investigates the geometric hard limit specified by certain DOTs to classify mass concrete. The investigation shows that the cost and complexity of mass concrete construction can be significantly reduced with progressive modeling, performance-based decision-making, and a holistic outlook on the mass concrete problem. |
