Owner: New York State Department of Transportation
Engineer: New York State Department of Transportation Office of Structures
Contractor: Lancaster Development Inc. – Richmondville, NY
Ready Mix Supplier: Cranesville Block Company – Amsterdam, NY
Lightweight Aggregate Producer: Norlite Corporation – Cohoes, NY
In the fall of 2010, the New York State Department of Transportation (NYSDOT) opened its first overhead Single Point Urban Interchange (SPUI). The $41.9 million interchange carries Route 7 over Interstate 87 (Exit 6) in the Town of Colonie. The bridge it replaced was 51 years old and had beam and bearing deterioration. Some beams had been impacted by trucks due to a clearance that was below the standard by 1’-10”. Temporary measures were instituted by adding planking under the bridge to prevent falling debris from damaging passing vehicles.
When designing the new structure, NYSDOT had the following four objectives in mind:
Four designs were taken into consideration, including cloverleaf, flyovers, diamond and the SPUI. The advantages with the SPUI were that the major points of conflict occur at one location. Traffic movements pass utilizing one intersection and one signal system that controls the ramp and through movements. This design would increase vehicle capacity at the interchange from seven to nine lanes.
The bridge was constructed in two stages in order to maintain all existing movements with Exit 6 remaining open and to reduce vehicle diversions and construction durations while minimizing the effects to the surrounding businesses. In 2009, the bridge foundations and walls were constructed in front of the existing abutments and a single center pier replaced two existing piers, leaving more room for two additional travel lanes for the possible future expansion on I-87.
In 2010, the steel girders and decks were set in two phases keeping travel lanes open for traffic flow. NYSDOT required a pre-pour meeting for all parties that were involved in the placement of the concrete decks. During the meeting, it was agreed upon that a trial batch would be conducted with a NYSDOT representative present one week prior to the first concrete deck placement to verify high performance lightweight concrete mix results. The desired slump was 5”, entrained air of 6.5% and a fresh unit weight less than 118 pound per cubic foot with a minimum strength of 4000 psi. The concrete placement method involved using a telescopic belt conveyor.
|
Material |
Pounds Per Cubic Yard (SSD) |
|
Cement |
500 |
|
Fly Ash |
135 |
|
Microsilica |
40 |
|
Fine Aggregate |
1300 |
|
Lightweight Aggregate |
826 |
|
Water |
32.4 Gallons |
|
Retarder |
27 Ounces |
|
Water / Cement Ratio |
.40 |
|
Air Entrainment |
5 – 8 Percent |
|
Slump |
3 – 5 Inches |
|
Plastic Wet Weight |
118 PCF Max |
Concrete placements utilized two telescopic belt conveyors on site that were placed at each end of the bridge deck. The high performance lightweight concrete was placed in five placements for a total of 1273 yards. It consisted of four placements of approximately 400 yards and one closure placement. The telescopic belt conveyors on average discharged nine yards of concrete in less than three minutes. The high performance lightweight concrete was not specified for its twenty-five percent reduction in weight but for its reduced cracking properties because of the geometry of the bridge. During the second placement, Jeff Kenyon with Lancaster Development, the prime contractor on the project, was quoted as saying, “I wish all HP concrete finished like this.” Jeff noted the ease of finishing the fresh concrete surface, the consistency of the high performance lightweight concrete, no water issues and not having to temper the concrete loads. The total project was completed in 2011 and has eased traffic congestion at this interchange. Several other intersections in New York are currently looking at the SPUI design.
