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Abutment 1 (left) used SCC for its three caissons,
while Abutment 2 (right) used a traditional caisson mix.
Self-Consolidating Concrete for Caissons in the Stalnaker Run Bridge
Joseph G. Sweet and Roger H. L. Chen, West Virginia UniversitySelf-consolidating concrete (SCC) was used in the construction of three caissons for a rural bridge replacement of the Stalnaker Run Bridge in West Virginia. The project was part of an Innovative Bridge Research and Deployment (IBRD) initiative with support from the Federal Highway Administration (FHWA) and the West Virginia Department of Transportation (WVDOT). The Stalnaker Run Bridge is located on Old Route 219 in Elkins, WV. SCC was used to cast elements of both the substructure and the superstructure of the single-span bridge, with traditional vibrated concrete being used to cast identical elements in the same bridge for purposes of comparison. This bridge was the first construction project for WVDOT that included the use of SCC.
The caissons for the Stalnaker Run Bridge were designed to consist of 3.5-ft (1.1-m) diameter, 6-ft (1.8-m) deep drilled shafts overlying integral 3-ft (0.9-m) diameter, 12-ft (3.7-m) deep rock sockets. Each abutment is supported by three caissons. The caissons all contained twenty No. 11 longitudinal reinforcing bars that were placed in two-bar bundles, giving a clear spacing of approximately 3.5 in. (90 mm).
Special Provisions for SCC Caissons
At the time of the development of the special provisions for this project, some states had recently adopted guidelines for use of SCC in cast-in-place applications,(1,2,3) even some specifically for drilled shafts using SCC.(4) Furthermore, Brown et al. had reported cast and exhumed drilled shafts using SCC in South Carolina.(5) These precedents, as well as previous laboratory experiences at West Virginia University (WVU) with SCC mix design and testing using WV aggregates,(6) were all used to help develop the desirable characteristics for the drilled shaft SCC. Some of the most important fresh and hardened properties specified for the SCC caissons included:
SCC Mix Design
The mix design development for the cast-in-place SCC used in this project involved collaboration between the potential concrete suppliers, admixture representatives, and WVU researchers. The development of the mix included a laboratory casting of a trial caisson section that simulated wet casting conditions as discussed in more detail elsewhere.(7) The mix proportions for the final, approved SCC mix included 750 lb/yd3 (445 kg/m3) of total cementitious materials with 15% Class F fly ash, a water-cementitious materials ratio (w/cm) of 0.38, and a fine aggregate to total aggregate ratio of 0.50. The fresh properties for the mix, as provided by the concrete and admixture suppliers, included a 23-in. (584-mm) spread, a J-ring value of zero, and an air content of 5.5%. It is noted that although blending of more than one type of aggregate was permitted by the project specifications, the final mix design used only No. 67 aggregates for the sake of simplicity, but including an aggregate blend could help optimize the performance.
The SCC mix was used to construct the three caissons for Abutment 1 of the bridge. The caissons for the other abutment were made using a traditional vibrated WVDOT Class B Modified mix concrete, which included 634 lb/yd3 (376 kg/m3) of total cementitious materials with 11% Class F fly ash, a w/cm of 0.39, and fine aggregate to total aggregate ratio of 0.41. As anticipated, all six caissons were placed into water-filled holes using tremie placement techniques. The fresh properties were measured for all concrete as delivered by each truck to the site. Both sets of caissons were cast successfully, and they eventually became integral parts of their respective bridge abutments.
No noticeable defects were detected within the cages of any of the six caissons by cross-hole sonic logging (CSL) when tested 5 or more days after casting. With its higher fluidity and better passing ability, SCC has the potential to eliminate or reduce the presence of large voids that may form on the outside of the reinforcement cage. However, no verification of this was done in the field.
The compressive strengths (ASTM C39), splitting tensile strengths (ASTM C496), modulus of elasticity values (ASTM C469), and rapid chloride permeability test (RCPT) results (ASTM C1202) for the trial caisson and both types of concrete for the bridge caisson castings are summarized in the table below:
*The trial caisson was cast in the laboratory prior to construction.
All concrete strengths exceeded the 28-day, specified compressive strength of 4500 psi (31 MPa).
In addition to the use of SCC for the three drilled shafts, a second SCC mix was used in the construction of two of the five precast, prestressed concrete box beams that were used to construct the superstructure. The other three box beams were constructed using a traditional vibrated concrete mix. Both the SCC and the traditional concrete mixes had compressive strengths that exceeded the specified strength of 8000 psi (55 MPa) at 28 days. All the precast box beams were erected on the Stalnaker Run Bridge on October 5, 2009.
Bridge construction continued through October, and the bridge opened to traffic at the beginning of November 2009. After its completion, WVU researchers installed a solar-powered, long-term monitoring system to continuously record in-situ strain measurements from all the prestressed concrete box beams and the caissons. These include measurements from concrete embedment strain gages as well as foil strain gages mounted directly to the prestressing strands and caisson reinforcement.
The authors would like to acknowledge the support from the FHWA and West Virginia Department of Transportation during this project. Particularly, we greatly appreciate the valuable technical assistance and guidance of Mr. Jimmy Wriston and Mr. Mike Mance of West Virginia Division of Highways and Mr. Chien-Tan Chang and Mr. Myint Lwin of FHWA.
1. Utah Department of Transportation, “Portland Cement Concrete,” UDOT Standards and Specifications, 2008 Edition, Section 03055.
2. Kentucky Transportation Cabinet, “Method for Approval of Using Self Consolidating Concrete (SCC),” Kentucky Method 64-320-08, Revised 03/08.
3. Illinois Department of Transportation, “Self-Consolidating Concrete for Cast-In-Place Construction,” BDE 80152, 2005.
4. New Jersey Department of Transportation, “SCC for Drilled Shafts,” NJDOT Standard Specifications for Road and Bridge Construction, 2007, Section 903.06.01.
5. Brown, D., Schindler, A., Bailey, J., Goldberg, A., Camp III, W., and Holley, D., “Evaluation of Self-Consolidating Concrete for Drilled Shaft Applications at Lumber River Bridge Project, South Carolina,” Transportation Research Record, No. 2020, 2007, pp 67-75.
6. Sweet, J. and Chen, R. H. L., “Evaluation of SCC Mix Designs for Moderately- and Heavily-Reinforced Members using West Virginia Aggregates,” Challenge and Barriers to Application SCC-2008 – Proceedings of the Third North American Conference on the Design and Use of Self-Consolidating Concrete, Center for Advanced Cement-Based Materials (ACBM), Evanston, IL, November 2008, pp.1-6.
7. Sweet, J. G. and Chen, R. H. L., “Self-Consolidating Concrete for Caisson Construction in Stalnaker Run Bridge Replacement, West Virginia,” Transportation Research Board 90th Annual Meeting, Paper #11-4155, Washington, D.C., January 2011.
Further information about this project is provided in Reference 7 or may be obtained by contacting the second author at email@example.com or 304-293-9925.
Reinforcement cage being Reinforcement protruding from the lowered into place. tops of the three SCC caissons after completion.
HPC Bridge Views, Issue 68, July/Aug 2011