By Bob Humer, P.E. and John Davis
One of Nevada’s busiest freeways is I-15 that runs through Las Vegas. It is the connection of the industries and sea ports in Southern California with the rest of the nation.
It carries more than a quarter million vehicles per day with 11 percent being trucks. A 5.5 mile stretch running north from the I-15/US95 interchange to Craig Road consisted of a deteriorated concrete pavement in need of reconstruction and widening.
In order to expedite delivery of the project, the Nevada Department of Transportation (NDOT) decided to contract this out as a design/build (D/B) paving project.
“It was the first D/B project that NDOT has let,” says Ryan Mendenhall, Construction Manager for Las Vegas Paving. “North Corridor Constructors (NCC), a joint venture, was the winning bidder. CH2M was the primary designer and Las Vegas Paving was the primary paver. It was a major partnering effort with the state, the city and the contractor.”
NCC recently completed the five year freeway design-build project on I-15, north of Las Vegas, in half the time. “The design/build concept was proposed to get the job done quicker,” says Las Vegas Construction Manager Randy Rosenberg. “The contractor’s proposal came in months ahead of schedule and NDOT was pleased with that.”
NDOT’s request for proposal was open to bids from both PCC concrete and asphalt contractors. NCC was chosen based on: least cost, project design, the ease of construction, delivery time and least disruption to traffic.
“Compared with our traditional design and construction time, NDOT and NCC completed the project 18 months to two years earlier than if standard project procedures had been used,” says Darin Tedford, Principle Materials Engineer for NDOT. “NDOT was primarily interested in the sequence, the critical path and the contractor’s construction management plan.”
Early on when NDOT started this unique project, Dean Weitzel (retired NDOT Materials Engineer) and Sohila Bemanian (retired NDOT Pavement Design Engineer) were key persons involved with developing the project concepts, the pavement structural design approval and the initiative to add additional pavement performance criteria. The Request for Proposal (RFP) was done by the project manager, Jeff Hale (NDOT).
This $242 million project included 15 new bridges, excavations for roadway realignment, lane additions, a new median, desert landscaping and extensive utility work typically associated with such a project. The biggest effort went into the new bridge designs using precast girders. This was a change to the normal NDOT bridge designs that are mainly cast in place girders. All were constructed without interrupting traffic on this busy national route.
Three aspects of this project were unique for the NDOT:
- It was their first design/build paving project.
- It was their first long-life asphalt pavement project.
- It was their first project with performance requirements in mix design and QA.
Mix designs were Hveem method based, while the field produced mixes had to meet strict performance test requirements equal to or better than the performance tests for the mix design mixes. The performance tests included: the Asphalt Pavement Analyzer (APA), fatigue testing (AASHTO T321) and the Repeated Load Triaxial (RLT) test.
Crack/seat was used on the old PCC pavement in preparation for the new asphalt pavement structure. A total of 430,944 tons of mixes were placed, using PG 76-22NV, AC-30 and AC-20 binder grades for the different lifts. Work progressed six days a week, 24 hours per day with double shifts. The project started in September of 2007. By September 2009, more than 1,000,000 man hours were used, without accidents. This was remarkable for such a large and complicated project, while paving in live traffic.
This project widened a 5.5 mile stretch of I-15 and replaced 15 bridges, in a heavily traveled urban area on the north side of Las Vegas. From the I-15/US-95 interchange (locally referred to as “the Spaghetti Bowl”) to the Lake Mead interchange, I-15 was widened from 6 lanes to 10 lanes. The stretch from Lake Mead Blvd. to Craig Road was widened from 4 lanes to 8 lanes.
The existing pavement structure was 8 inches of plain jointed concrete on 5 inches of Cement Treated Base (CTB). The existing PCC was in poor condition and the cement treated base was deteriorated. Reconstruction or a major rehabilitation such as crack and seating or rubblizing was considered necessary. High ground water and ground water seepage was observed in several locations.
Where crack and seating was applicable, a saturated paving fabric was incorporated as a stress relief layer. The total project had to be finished with a ? inch layer of Plantmix Bituminous Open-graded Surface (PBOGS) as a wearing surface on all flexible pavements.
Long-life design/build (pavement design requirements): ?? All pavement sections had to be designed and constructed to perform for no less than 35 years.
- The existing sub-grade was very poor with R-values varying from 10 to 12.
- The heaviest traveled section had to be designed for 103.7 million ESALs.
The final structural thickness design called for:
- 2 inches Type 3 leveling course with AC-20 binder, then
- 8 inches of ¾ inch Type 2C dense-graded mix with AC-30 binder, then
- 4.5 inches of ¾ inch Type 2C dense-graded mix with PG 76-22NV (polymer modified) binder, followed by the ¾ inch open-graded surface wearing course.
The designed total thickness of 12.5 inch dense-graded plus ¾ inch open-graded was used for all mainline paving as well as the outside shoulders. The leveling course and saturated paving fabric was only included where crack and seating took place. A total of 40,000 square yards of paving fabric were used.
The inside shoulders were constructed with 4 inch of Type 2C mix with PG 76-22NV type binder, placed on 16 inches of aggregate base. A total of 405,662 tons of dense-graded and 25,282 tons of open-graded mix were placed on this project.
Performance based mix design and QA
NDOT’s standard Hveem mix design was modified with the additional requirement that the maximum rut depth of the mix at the optimum binder content under the Asphalt Pavement Analyzer (APA) at 140¿F should not exceed 0.16 inch.
The weekly quality assurance (QA) samples had to meet the following requirements:
- They could not exceed the 0.16 inch rut depth at 140¿F under the APA.
- The fatigue life of the field mix at 70¿ F and a strain level of 500 microns by AASHTO T321 had to be equal or better than the fatigue life of the mix design mixture.
- The rutting life of the field mix at 158¿ F using the Repeated Load Triaxial Test (RLT) as described in NCHRP Report 465, with 30 psi confining pressure and 45 psi deviator stress, had to be equal or better than the rutting life of the mix design mixture.
If the field mixtures did not meet the three QA requirements, paving operations would have to be suspended and corrective actions taken.
Three hot mix plants were involved in this project (Loan Mountain, 5th Street and the Race Track Plants). All the aggregates came from the APEX quarry, about 10 miles north of Las Vegas. The Race Track Plant produced most of the tonnage for this project. Crack and seating of the old PCC and widening and excavation for realignment were major parts of the pavement rehabilitation. Excavation on section 4 (the northern most of the four sections) started in April of 2008, and was completed by January of 2010.
The Hveem S-values, air voids and all the performance tests came in as required. With a few exceptions, all gradations and binder contents also met the project specifications.
“Planning and planning meetings, collaboration with state and city officials, partnering with them were key factors in the success of the project,” says Mendenhall. “We did studies to find out what could be done and how to do it efficiently. We were able to choke down traffic. The state played a huge part and took a small gamble.”
NDOT’s Tedford agrees that planning was a key part of the project. “Not only careful planning before the project, but there were coordination meetings with the contractor every two weeks during the project.”
“We implemented traffic control to eliminate traffic disruption,” says Mendenhall. “We did multiple detours, cut the lanes to two in each direction and constructed bridges in half the time. We used 17 miles of concrete barriers and completed the project under heavy traffic with a tight right-of-way and no big detours.”
What significantly cut the project delivery time, were three factors, according to Rosenberg:
- By having the project divided in four sections, construction could start after all aspects of the first section were designed. This allowed design and construction efforts to follow in sequence.
- Nine of the 15 bridges were constructed with pre-cast girders. This allowed for demolition of the old bridge and completion of the new bridge each time in approximately 4 weeks.
- Major time savings came from innovative traffic control. After completion of the widening projects and new shoulders, all traffic was shifted to one side of the freeway, with two lanes open for each direction of traffic. This allowed 24 hours per day work to progress on the closed side of the freeway, and it kept construction away from live traffic.
Mendenhall sees this big project as a landmark success. “It was the most successful set of projects that Las Vegas Paving has been involved in. Although it was huge in scope and cost, it was well planned and well executed.”
Mendenhall says that it took a team—state, city and contractor—and a close partnership between them, to deliver such a vast project. “We had over one million working man hours without an accident. It was a success in every aspect—planning, partnering, quality and safety.” “This was an outstanding project that was the result of hard work and dedication of an outstanding team,” concluded Joe Schroeder, Project Manager for NCC.
Bob Humer is a Senior Regional Engineer for the Asphalt Institute in Los Angeles. He has 30+ years in asphalt technology and mixture design and evaluation.
John Davis is a contributing editor for Asphalt magazine.