Mass Concrete Drilled Shafts: Specification Landscape and Recommended Revisions-PPT Presentation

PPT Presentation

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The presentation recommends that drilled shafts be treated as mass concrete, despite limited documented evidence of thermal damage. Damage may go unnoticed, and the long service life and durability demands of large-diameter shafts make prevention important. However, specifications designed for above-ground concrete often fail to account for shafts’ distinct below-ground conditions.<br /><br />For delayed ettringite formation (DEF), the recommended maximum concrete temperature is 160°F without suitable supplementary cementitious materials (SCMs), or up to 185°F when the mix meets ACI guidance for DEF prevention. Temperatures above 185°F should not be permitted.<br /><br />Temperature-differential limits should not apply within permanent steel casing. For uncased shafts, they are generally unnecessary unless ground conditions are aggressive; where needed, limits should account for reinforcement and acceptable cracking. Monitoring should continue until 24 hours after the shaft’s center temperature has peaked and fallen below the applicable limit.<br /><br />Specifications should state clear consequences for exceedances. Temperatures between 160°F and 185°F may be accepted when the mix meets ACI SCM requirements; exceedances of ACI limits should be rejected unless the engineer of record justifies acceptance. Thermal-control plans should be revised to prevent repeated exceedances.<br /><br />Potential long-term strength loss from high curing temperatures is real but uncertain and should be addressed separately from mass-concrete specifications. More targeted approaches include adjusting specified strength requirements or testing specimens cured at representative temperatures.

Keywords

drilled shafts

mass concrete

thermal damage

delayed ettringite formation

DEF prevention

ACI guidance

supplementary cementitious materials

temperature monitoring

temperature differential limits

long-term strength loss