Categories: Issue 60 March/April 2010

David W. Mokarem and Mohammad S. Khan, Professional Service Industries, Inc.

HPC was used in the superstructure of the Hickman Road Bridge, TN.
HPC was used in the superstructure of the Hickman Road Bridge, TN.  

In 1993, the Federal Highway Administration (FHWA) initiated a national program to implement the use of high performance concrete (HPC) in bridges. The program included the construction of one or more demonstration bridges in each of the FHWA regions and dissemination of the technology and results at showcase workshops. Nineteen bridges in 14 States were constructed. In addition to the joint state-FHWA HPC initiative, other states have independently implemented the use of HPC in various bridge elements.

The bridges are located in different climatic regions of the United States and use different types of superstructures. The bridges demonstrate practical applications of high performance concretes. Construction of these bridges also provided opportunities to learn more about the placement and actual behavior of HPC in bridges. Consequently, many of the bridges were instrumented to monitor their short- and long-term performance. In addition, concrete material properties were measured for most of the bridges.

Following completion of the HPC bridges, information about the 19 bridges was compiled into a single source.(1,2) The structural systems used in the 19 HPC bridges consisted of three types. Fourteen of the bridges consisted of precast, prestressed concrete beams with a full depth, cast-in-place concrete deck. Three of the bridges consisted of precast, prestressed concrete beams supporting precast, prestressed concrete deck panels with a partial depth, composite cast-in-place concrete deck. Two bridges consisted of adjacent precast, prestressed concrete box beams one with and one without a cast-in-place concrete deck.

Bridge Inspection
After the bridges had been in service for generally 5 to 10 years, they were inspected to assess and evaluate their in-service condition relative to the compiled data. These inspections included a visual survey and a detailed crack survey to document the number, length, and width of the transverse, diagonal, and longitudinal cracks on each deck. The crack densities were calculated from these surveys.

An in-depth analysis was performed on the concrete material properties for all the decks.(3) Analyses were made to compare the calculated crack densities to water-cementitious materials ratios (w/cm) and total cementitious materials content. These analyses were performed to determine the ranges and combinations of w/cm and cementitious materials contents that resulted in the least amount of cracking.

Conclusions
The following conclusions were drawn from the observations and analyses performed in this investigation:

  • The average crack density for all concrete bridge decks ranged from 0.003 to 0.74 ft/ft2 (0.01 to 2.43 m/m2) with an overall average of 0.12 ft/ft2 (0.41 m/m2).
  • The average crack density for 14 bridges with full-depth cast-in-place concrete decks ranged from 0.003 to 0.17 ft/ft2 (0.01 to 0.54 m/m2) with an overall average of 0.074 ft/ft2 (0.24 m/m2).
  • A w/cm between 0.35 and 0.40 resulted in an average crack density of 0.069 ft/ft2 (0.23 m/m2).
  • Cementitious materials contents between 600 and 700 lb/yd3 (356 and 415 kg/m3) resulted in an average crack density of 0.053 ft/ft2 (0.17 m/m2).
  • The measured compressive strengths for the cast-in-place decks ranged from 4000 to 8000 psi (28 to 55 MPa) at 28 days. There did not appear to be a correlation between 28-day compressive strength and crack density, although higher compressive strengths are generally expected to result in more cracking.(4)
  • The measured permeability values ranged from 320 to 5600 coulombs and were generally less than the specified values. All values except one bridge were in the very low to moderate ranges defined by AASHTO T 277.
  • There were no indications of alkali-silica reaction (ASR), sulfate attack, or other deleterious reactions.
  • No significant spalling or delamination was observed on the bridge decks; however, some spalling was observed along the edges of some of the cracks.
  • Observations from the Texas bridges indicated that bridge geometry influences the amount of concrete cracking, particularly when the bridge geometry results in torsional stresses from skewed supports.
  • When the structural system of the bridge included skewed supports, diagonal cracks developed near the supports.
  • When the structural system of the bridge included continuity over the supports, negative moment transverse cracks developed.
  • Observations from the bridge in Ohio showed that longitudinal reflective cracks occurred in the asphalt topping above the edges of the adjacent boxes.

Summary
From the data obtained from this study, a high performance concrete mixture with a w/cm between 0.35 and 0.40, cementitious materials content between 600 and 700 lb/yd3 (356 and 415 kg/m3), and appropriate construction practices, is expected to result in lower crack density. The associated rapid chloride permeability is expected to be in the low to moderate range for these mixtures. This average w/cm and cementitious materials content is reasonable and readily producible. These data show that if these types of concrete mixtures are produced, placed, and cured properly, they can aid in reducing the incidence of cracking in bridge decks.

The observations and analysis of collected data from the study indicated that the HPC in both decks and girders performed well. The measured properties of the HPC used in the bridges showed that the concrete met design specifications. In addition, field surveys on the individual bridge decks indicated that the material was performing well with no indication of deterioration due to material properties. The study demonstrated that HPC can be designed and fabricated in a cost effective and efficient manner to produce durable concrete bridges.

References
1. Russell, H. G., Miller, R. A., Ozyildirim, H. C., and Tadros, M. K., “Compilation and Evaluation of Results from High-Performance Concrete Bridge Projects, Volume I: Final Report,” FHWA, U.S. Department of Transportation, Report No. FHWA-HRT-05-056, October 2006, 178 pp.

2. Russell, H. G., Miller, R. A., Ozyildirim, H. C., and Tadros, M. K., “Compilation and Evaluation of Results from High-Performance Concrete Bridge Projects, Volume II: Appendixes,” FHWA, U.S. Department of Transportation, Report No. FHWA-HRT-05-057, October 2006, 303 pp.

3. Mokarem, D., Russell, H., and Khan, M., “High Performance Concrete Bridge Deck Investigation,” FHWA, U.S. Department of Transportation, Report No. FHWA-HRT-10-28, November 2009, 733 pp. Available as PB 2009-115497 at www.ntis.gov.

4. Browning, J. and Darwin, D., “Specifications to Reduce Bridge Deck Cracking,” HPC Bridge Views, May/June 2009.

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