Preparation and Testing of Drilled Shafts with Self-Consolidating Concrete

About the report:

In this study, self-consolidating concrete (SCC) was evaluated in drilled shafts and the integrity of drilled shafts was determined using cross-hole sonic logging (CSL), a low-strain nondestructive integrity testing technique.  SCC has very high flowability.  It was placed in the drilled shafts of the bridge on Route 28 over Broad Run in Bristow in Prince William County, Virginia.  There were two bridges at the site; the one carrying the northbound traffic had drilled shafts using conventional concrete with high consistency (i.e., flowability).  Half of the shafts of the bridge carrying the southbound traffic were cast with SCC. 

During placement, properties of the fresh concrete were tested, and specimens were prepared to determine the hardened properties.  The integrity of the shafts within the reinforcing cage was determined using CSL, with sonic echo/impulse response also used to evaluate several test shafts.  The use of acousto-ultrasonic (AU) measurements to determine the cover depth outside the reinforcing cage was also evaluated during laboratory testing.  In addition to the Route 28 shafts, three test shafts with conventional and SCC concretes were cast in an area headquarters.  These shafts had intentional voids created through the use of sandbags and Styrofoam to investigate further the ability of the nondestructive test equipment.

The results indicated that SCC is highly desirable for drilled shafts; it flows easily, filling the hole, and the removal of the temporary casing is facilitated by this highly workable material.  CSL is a satisfactory nondestructive method to determine the integrity of shafts.  Sonic echo/impulse response also showed promise as a method that complements CSL for determining the integrity of a shaft.

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