Development of Specifications for ALDOT Mass Concrete Construction

Abstract

In mass concrete construction, concrete temperature requirements must be established to prevent delayed ettringite formation (DEF) and thermal cracking. This involves limiting the maximum allowable concrete temperature and maximum allowable concrete temperature difference. It is also necessary for a mass concrete specification to define an appropriate size designation for mass concrete members. These size and temperature specifications are investigated for their potential inclusion in a future ALDOT mass concrete specification. Six ALDOT mass concrete members were instrumented with temperature sensors and examined for signs of DEF and thermal cracking. These six members were also modeled in ConcreteWorks to assess the accuracy of this software’s temperature predictions. Based on all of the recorded temperature data, predicted temperature data, and site observations, guidelines were developed for a future ALDOT mass concrete specification. Because concrete materials, specifically SCMs and low-CTE coarse aggregates, play a major role in the occurrence of thermal cracking, tiered specifications for mass concrete size designation and temperature difference limit were developed. Depending on the condition, it is recommended to use a least dimension of 4 to 6 ft for an element to be designated as mass concrete. If the concrete CTE or aggregate type is known, then an age-dependent temperature difference limit is recommended for the first 7 days after placement. The lowest tier (worst case) specifies a mass concrete least dimension designation as 4 feet and a temperature difference limit of 35 °F. Although the concept of raising the maximum concrete temperature limit of 158 °F was investigated, it is recommended that a limit of 158 °F be used for ALDOT mass concrete elements.