Drilled Shafts as Mass Concrete: Requirements and Methods for Satisfying-Video

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Video Summary

The presentation examines whether large drilled shafts should be treated as mass concrete because cement hydration can cause high peak temperatures, potentially leading to delayed ettringite formation (DEF) or thermal cracking. While agencies increasingly apply mass-concrete specifications to shafts, strict limits can complicate construction, and documented shaft damage is scarce. University of Missouri research developed a procedure to predict temperatures, assess DEF risk and thermal-cracking potential, and identify mitigation when needed. The approach considers concrete mix, shaft geometry, reinforcement, and surrounding soil or rock. ConcreteWorks modeling generally predicted measured shaft temperatures within about 10°F. The research also suggests that allowable temperature differentials can be higher when aggregate properties and the shaft’s reinforcement and geometry are considered, particularly if very narrow cracks are acceptable. Mitigation options include fly ash, reduced cement content, chilled materials, and placement controls. In discussion, participants noted that soil can dissipate shaft heat, questioned DEF temperature thresholds, and raised concerns about future fly-ash availability and changing cement types.

Keywords

drilled shafts

mass concrete

delayed ettringite formation

thermal cracking

ConcreteWorks modeling

cement hydration