Best Practices and Specifications for Massive Concrete Drilled Shafts

PI# 0016327American Concrete Institute (ACI) Guide to Mass Concrete defines massive (mass) concrete as \u201cany volume of concrete with dimensions large enough to require that measures be taken to cope with the generation of heat from hydration of the cement and attendant volume change to minimize cracking.\u201d Specifically, in the case of drilled shafts, Georgia Department of Transportation defines mass concrete to be any shaft with a greater than six-foot diameter. Once a drilled shaft has been classified as mass concrete, additional general GDOT specifications for mass concrete apply. These specifications detail temperature, material selection, thermal control, placing, and curing. Because the current specification lacks details specific to drilled shafts, a multitude of methods can be used, which can reduce the economic efficiency of the structure. Additionally, because the specifications are vague, the contractor and designer often avoid the specification by installing multiple smaller shafts in place of one single larger shaft. This practice of adding multiple smaller shafts often adds additional cost and the possibility for less effective designs. This project developed best practices and specifications for mass concrete drilled shafts to reduce the hesitance for use in practice and promote better overall construction practice. The objectives of the research are to: (1) understand the major deterrents from utilizing mass concrete for drilled shafts in practice, (2) determine and specify the appropriate thermal conditions, monitoring, and other requirements for drilled shafts specific to Georgia, (3) utilize ongoing GDOT research for temperature control to determine best practices for application on drilled shafts, and (4) make recommendations to GDOT for specifications to advance best practices