SmartFix40 - Accelerated Construction for 1-40
Through Knoxville, TN


May 30, 2008

June 1, 2009

I-40 Viaduct between James White Parkway and I-275
Before & after aerial photos taken by Aerial Innovations, courtesy of TDOT



Bridge deck photo courtesy of
Doug Brown, Harrison Construction Company

The need to widen Interstate 40 through the downtown area of Knoxville, TN was not a question, but how to do it safely and without greatly disturbing the community was. The interstate had been built in the 1960s and was no longer able to safely carry traffic through the area. However, the task of rebuilding this urban section of I-40 was very challenging. The Tennessee Department of Transportation (TDOT) visited the Indiana Department of Transportation to review their experience with accelerated construction of an interstate through downtown Indianapolis, which successfully utilized a total closure of the interstate for a short period of time to allow construction to proceed as quickly as possible.

Impressed with the lessons learned in Indiana, the concept for SmartFIX40 was developed by TDOT where the interstate through Knoxville would also be closed for reconstruction after alternate travel routes were upgraded. By utilizing the SmartFIX40 accelerated construction process, TDOT could speed up construction and rehabilitation of the roadway and bridges through a total road and bridge closure from May 2008 to June 2009. This allowed construction workers the time and space they needed to do their jobs quickly and safely without causing long-term inconvenience to motorists. It was estimated that this closure saved 2˝ to 3 years of traffic delays from construction if the project had been built using the traditional method of maintaining traffic as construction progressed.

The project was let in two contracts. The first was awarded in March 2005 with a bid of just over $85 million. This contract was focused on rebuilding some of the connecting roadways to allow for continued access to downtown when I-40 was closed. The second contract was let in March 2006 with a winning bid of about $104.7 million. The work in this contract was mostly related to the reconstruction of I-40. It included the section of the interstate that would be closed during construction.

A significant portion of the second contract was the rehabilitation and widening of Bridge 16, a four-lane viaduct just to the east of the I-40/I-275 interchange. The 21-span viaduct carried I-40 through a commercial district. The existing bridge consisted of continuous steel girders in two to four span units with spans varying from 37 ft to 109 ft. The deck was completely replaced while the existing substructure units and many of the existing girders were in good condition and could be reused. The existing span arrangement was retained with new columns and caps constructed at each end of the existing piers to support an eight-lane roadway, which was more than twice as wide as the existing structure. The bridge, which was 1672 ft long, was reconstructed using staged construction, so it was not part of the total roadway closure. Two major stages of construction were required, with a third stage consisting of placing a deck closure between the two halves of the structure.

During the design stage, the engineering firm responsible for the design of this structure, Wilbur Smith Associates, attempted to reuse the existing steel girders, which included some riveted steel girders and some rolled shapes with cover plates. Frank Bale, PE, the engineer in charge of the design, recalls that the use of lightweight concrete was considered for the deck to reduce the dead load on the existing girders and substructure units since TDOT now required a minimum deck thickness of 8 inches, while the existing normal weight concrete deck was 7 to 7.5 inches thick. However, even with the use of lightweight concrete, the designers eventually determined that it would be more cost effective to replace many of the existing girders. This was mostly because it was difficult to demonstrate that the existing girders would satisfy the requirements of current design specifications. The use of lightweight concrete for the new bridge deck was retained to make possible the reuse of the existing substructure units for the new structure.

The TDOT Standard Specifications include lightweight concrete for decks as “Class L” concrete. Therefore, a special provision was not required for lightweight concrete, as would be the case in most other states. A plan note for this bridge stated “Class “L” Concrete for bridge decks shall be in accordance with Section 604 of the Standard Specifications.” A footnote to the table in Section 604.03 of the Standard Specifications indicates that “The unit weight of air dried Class L Concrete (lightweight concrete) shall not exceed 115 lbs/cf as determined by ASTM C 567.” The table also requires lightweight concrete to have a minimum compressive strength of 4,000 psi, a minimum cement content of 620 lbs/CY, a maximum water/cement ratio of 0.40, a design air content of 6%, and a maximum slump of 8 inches. Requirements for lightweight aggregates are given in Section 903.19 of the Standard Specifications. Carolina STALITE coarse lightweight aggregate met all of these requirements, was listed on the TDOT qualified aggregate list, and was used for the lightweight concrete in Bridge 16.

The contractor that built this bridge, Charles Blalock & Sons, placed nearly 7,200 CY of lightweight concrete in the deck. All concrete was placed by pumping. There were several very large placements, all of which occurred during the dead of winter. According to Doug Brown of Harrison Construction Company, the lightweight concrete supplier for the bridge, this presented some challenges. However, he indicated that in spite of the difficult weather conditions, the lightweight concrete was placed “without any low breaks and no real problems.” He also said that “air entrainment is always a little difficult on a bridge deck, but not really any more with lightweight concrete than normal weight concrete.” Dale Dockery of Charles Blalock & Sons agreed, saying that Harrison Construction Company “did a super job with the consistency of mix.” Dale didn’t think they had any more difficulty finishing the lightweight concrete mix than a normal weight concrete mix. After the deck was completed, it was ground longitudinally for rideability and grooved transversely for skid resistance.

Bridge 16 was completed by the time that the rest of the downtown I-40 corridor was reopened to traffic in June 2009. At the opening ceremony, State of Tennessee Transportation Commissioner Gerald F. Commissioner Nicely said that this project was “the largest interstate improvement effort ever undertaken by the Tennessee Department of Transportation.” He added that as a result of this massive project, I-40 had been widened to six through lanes with four auxiliary lanes, 13 bridges were built or rehabilitated, 15 retaining walls and 3 noise walls were constructed, and 12 side roads and 7 new ramps were also constructed.
 

 

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