Title: Controlling Mass Concrete Effects in Large-Diameter Drilled Shafts Using Full-Length Central Void

Author(s): Gray Mullins, Kevin R. Johnson, and Danny Winters

Publication: Structural Journal

Volume: 115

Issue: 5

Appears on pages(s): 1475-1483

Keywords: differential temperature; drilled shaft; mass concrete; peak temperature; voided shaft

DOI: 10.14359/51702376

Date: 9/1/2018

Abstract:
Mass concrete defines elements where heat formation due to exothermic hydration reactions can induce tension cracking as a result of excessive temperature differentials upon cooling. These conditions are anticipated in dams, large footings, and, in some cases, pier columns and caps where internal cooling systems can be used to moderate the effects. Until 2006, drilled shafts were not recognized by the Florida Department of Transportation as mass concrete due to the relatively small diameters (4 ft [1.2 m] diameter being the most common) and/or the perception that the surrounding environment was not conducive to producing mass concrete conditions. This paper presents the results of a full-scale shaft demonstration project where a 9 ft (2.74 m) diameter shaft was constructed with a 3.8 ft (1.17 m) diameter central void to control temperature and reduce costs. Peak and differential temperatures were shown to stay well within specified limits without the need for internal cooling systems.