Predicting early-age thermal behavior of mass concrete for bridge foudnation

Abstract

<p>Large volume concrete continues to present increasing concern in the construction of bridges. Due to the increased heat generation during massive concrete foundation construction, the concern for cracking, resulting from thermal contraction, is increased. To reduce the thermal cracking potential and ensure the safety and durability of the foundation structure, several practices are utilized, such as using low heat generating cement, proper insulation, cooling pipes and so forth.</p> <p>The objectives of this research are to explore the current available early age mass concrete thermal analysis software packages and provide recommendations for mass concrete construction practices. Currently, there are several computer software packages capable of evaluating the early age development of concrete. 4C Temp&Stress, which is discussed in detail in this study, is a user friendly and flexible software package capable of analyzing mass concrete structures.</p> <p>The sensitivity study results of using 4C Temp&Stress indicate that a reduced least dimension, extended for removal time, and reduced fresh placement temperature could reduce the maximum temperature and decrease cracking potential. Current insulation and formwork materials and practices are confirmed to be to a practical approach in mass concrete construction. The recommended layout and dimensions of post cooling systems will be discussed to provide the most efficiency cooling system. Besides these, other methods and strategies are investigated in case study for controlling the thermal cracking of massive concrete placements.</p> <p>The findings of this study also indicate relationship between maximum temperature difference and maximum tensile stress/strength ratio at different time interval, and between the concrete maximum temperature and maximum temperature difference with the fresh placement temperature of the concrete and the depth of concrete for a specific mix design in mass concrete projects. The models allow contractors, or the Iowa Department of Transportation (Iowa DOT) to roughly estimate the thermal behavior and cracking potential.</p>