High Performance Concrete Pavements Project Summary
Chapter 21. MINNESOTA 1 (I-35W, Richfield)
The Minnesota Department of Transportation (Mn/DOT) is reconstructing a portion of I-35W in the Minneapolis-St. Paul area (see Figure 58) using high-performance concrete pavement concepts. Located between I-494 and Highway 62 in Richfield (a suburb of Minneapolis), this project is being partially funded under the TE-30 program and is being designed for a 60-year service life (Rettner 1999).
Figure 58. Location of MN 1 project.
The benefits associated with a pavement that lasts for 60 years include reduced maintenance and user costs (Rettner 1999). However, such a pavement is also expected to have a higher initial cost. This project has the following objectives (Rettner 1999):
- Evaluate the cost/benefit of designing a pavement to last 60+ years with zero maintenance in a very high traffic volume environment.
- Evaluate the performance benefits of using a high performance concrete in an urban paving environment. The specific mix will be designed to have high durability using a number of design features, including:
- Low permeability.
- High air content.
- Well-graded aggregate.
- High-quality aggregate.
- Ground granulated blast furnace slag (GGBFS).
- Evaluate the durability of dowel bars clad in stainless steel compared to solid stainless steel dowel bars and assess their ability to perform satisfactorily for 60+ years.
- Evaluate the long-term performance of epoxy-coated dowel bars compared to stainless steel dowel bars.
- Evaluate the relative performance of 38-mm (1.5-in.) and 44-mm (1.75-in.) diameter dowel bars.
Project Design and Layout
The nominal pavement design for this project is a 340-mm (13.4-in.) thick JPCP with 4.6-m (15-ft) transverse joints. The slab thickness was developed based on a design traffic of 100 million ESAL applications over the 60-year design period. Tied concrete shoulders, 315-mm (12.4-in) thick, will be included with the expectation that they will carry traffic during construction or during future rehabilitation activities (Rettner 1999).
The existing sand base course beneath the original pavement is several feet thick and will be left in place for the new PCC pavement. It will be capped with 305 mm (12 in.) of select granular material, which in turn will be topped with a 100-mm (4-in.) thick, Class 5 dense-graded granular base to provide a paving platform for the new PCC pavement. No open-graded base or edge drains are being included in the design.
At least five different test sections were originally planned to be constructed as part of this project (Rettner 1999):
- Section 1 - JPCP containing a high-performance concrete mixture and 38-mm (1.5-in.) by 457-mm (18-in.) stainless steel dowel bars. This design will be constructed for 35 joints over five lanes (three driving, two shoulders) for a total length of 161 m (525 ft).
- Section 2 - JPCP containing a high-performance concrete mixture and 44-mm (1.75-in.) by 457-mm (18-in.) stainless steel clad dowel bars. This design will be constructed for 35 joints over five lanes for a total length of 161 m (525 ft).
- Section 3 - JPCP containing a high-performance concrete mixture and 38-mm (1.5-in.) by 457-mm (18-in.) stainless steel clad dowel bars. This design will be constructed over the rest of the mainline pavement project (approximately 2500 m [8,200 ft]).
- Section 4 - JPCP containing a high-performance concrete mixture and 38-mm (1.5-in.) by 457-mm (18-in.) stainless steel clad dowel bars. This will be constructed on all ramps except the bottom of the northwest exit ramp to CSAH 53. These ramps will be constructed to the same thickness (340-mm [12.4-in.]) as the mainline pavement.
- Section 5 - JPCP containing a high-performance concrete mixture and 38-mm (1.5-in.) by 457-mm (18-in.) epoxy-coated dowel bars. This will be constructed only at the bottom of the northwest exit ramp to CSAH 53. This ramp will be constructed to the same thickness (340-mm [12.4-in.]) as the mainline pavement.
Table 27 displays the experimental design matrix for this project. The section with epoxy-coated dowel bars is located on a ramp because of the desire for the entire length of the mainline pavement to last the 60-year design period without traffic disruptions that may be required for epoxy-coated dowel bars (Rettner 1999). Indications in Minnesota are that epoxy-coated bars may not last beyond 25 years without significant corrosion (Rettner 1999). In addition, a project being constructed immediately north of the current project includes epoxy-coated dowel bars and will also serve as a control section for this variable (Rettner 1999).
The high-performance concrete mix was used throughout the entire project for durability and longevity. The aggregate quality specifications were tightened so that only the most durable aggregate sources were eligible, including a stipulation limiting the amount of limestone to no more than 20 percent (Rettner 1999). In addition, a well-graded coarse aggregate was used for improved workability without the use of excessive amounts of water reducer. Other notable features of the concrete mix design include a higher specified air content (6 to 8 percent entrained) for increased freeze-thaw protection, the inclusion of ground granulated blast furnace slag for reduced permeability, a 28-day rapid chloride permeability of 2500 coulombs (which, according to ASTM C 1202, is a moderate level of permeability), and a water-to-cementitious-material ratio less than 0.40 (Rettner 1999).
|DIAMETER (IN.)||MAINLINE PAVEMENT||RAMP PAVEMENT|
|Stainless Steel Clad Dowel Bar||1.5||Section 3||Section 4|
|Solid Stainless Steel Dowel Bar||1.5||Section 1|
|Epoxy-Coated Steel Dowel Bar||1.5||Section 5|
These sections were constructed during the summer of 2000. However, there was considerable difficulty in obtaining the required number of stainless steel clad dowel bars from the manufacturer, and consequently several modifications to the original experimental design were made during construction. Most of the northbound and all of the southbound lanes were constructed with solid stainless steel dowel bars, and only a portion of the northbound lanes received stainless steel clad dowel bars. Furthermore, the outside shoulders were constructed with plastic-coated bars, and it appears as if the exit ramp that was to receive epoxy-coated bars will be also be constructed using plastic-coated bars. Finally, the inside shoulders will not be paved until the 2001 construction season.
State Monitoring Activities
Mn/DOT will monitor the performance of these pavement sections for a minimum of 5 years. Pavement distress surveys and ride quality measurements will be conducted every other year using standard Mn/DOT procedures (Rettner 1999). Load transfer efficiency will be measured on the outside lane using the Mn/DOT FWD on an every other year basis if traffic allows (Rettner 1999).
Some findings on the use of high performance concrete specifications and high performance materials in Minnesota were presented at the 2003 Annual TRB meeting. The following sections summarize some of the findings (Turgeon 2003; Rangaraju 2003).
Cement Paste Specification
The contractor elected to provide a mix containing 229 kg/m3 (384 lbs/yd3) cement and 123 kg/m3 (206 lb/yd3) GGBFS. This met all mix requirements including the RCP test. Typically contractors elect to use the 25 percent fly ash mixes under the standard specification. Fly ash is approximately half the cost of cement or GGBFS. The introduction of GGBFS to the paving process registered some complaints of a "sticky" mix from the finishers.
The mix was produced concurrently from two batch plants located at the same site, using the same mix design. This further aggravated the variability in the plastic air contents, which ranged from below 5 percent to over 10 percent. Upon completion of the project, price reductions were assessed for failing plastic air contents. Most price reductions related to tests results of around 6.0 percent, but some tests were as low as 4.0 percent.
The hardened air contents, as determined using ASTM C457, were determined for the top, middle, and bottom third of each sample. Results ranged from 6.7 percent to 15.7 percent, with an average value of 10.6 percent. Sixteen of the 26 hardened air contents were above the maximum allowable of 10.0 percent. Only one was below the range minimum of 7.0 percent. The cores were taken at random therefore they do not coincide with any of the plastic air tests taken. Even so, these results do not correspond well with the plastic air contents discussed previously. Further analysis of the linear traverse results showed the prevalence of small voids with diameters less than 100 microns. Few air voids are present in the 150 micron to 250 micron range. It has been theorized that the volumetric air meters used to determine plastic air contents are not efficient when measuring small bubbles, which could account for the test result differences. Small bubbles may be more susceptible to filling with secondary reaction by-products thus undermining the long-term void structure effectiveness. The ratio of entrapped to entrained air was determined to be acceptable; however this determination was not available until a few months after paving was complete.
The coarse aggregate supplied consisted of a low carbonate class C gravel. This material qualified for the full aggregate quality bonus. The contractor added "Safety Grit," No. 8 sieve to 9.5-mm (0.375-in.) sand, to the typical coarse rock and sand mixture to meet the denser gradation requirements.
The pavement was specified and constructed at a thickness of 340 mm (13.5 in.). The ability to finish the surface, avoiding edge slump deformation and meeting the low w/c ratio, were competing considerations that required the contractor's constant attention. The additional thickness added to the complexity of these issues.
The first paving was scheduled for fall 1999, but project conflicts delayed it until spring 2000. At that time, approximately 75 percent of the required quantity of stainless clad bars was available for installation. To keep the project on schedule, plastic-coated dowel bars of the same dimension were substituted and used in the shoulder. The opposing direction of traffic was paved in summer 2000, but sufficient stainless steel clad bars were not available. Consequently, the majority of this work used solid stainless dowel bars at a significant increase in cost.
Placement costs are primarily a factor of the complexity of the project and the pavement thickness. Projects that include long uninterrupted stretches of pavement are less costly to place since less time is spent mobilizing equipment and setting up. For thicker pavements, the larger volume of concrete needed to produce an equivalent area of concrete slows production, which leads to higher placement costs. Edge slump is also a more prevalent problem with thicker pavements. The placement bid price for the 340-mm (13.5-in.) pilot HPC project was $7.55/m2 ($6.31/yd2). Four projects let the same year with pavement thickness ranging from 254 mm to 267 mm (10.0 to 10.5 in.) had an average placement cost of $6.85/m2 ($5.72/yd2). The cost difference seems to be primarily due to thickness.
The two factors that greatly influence the structural concrete unit price are the project quantity and the ability of paving contractors to produce the material from their own mobile batch plants. Small quantity projects or projects without space to set up a portable batch plant require the paving contractor to purchase concrete from a local ready-mix supplier at a higher cost. Due to the confined location, the paving contractor purchased the 22,841 m3 (30,054 yd3) of concrete from a ready-mix supplier at a unit price of $97.40/m3 ($74.02/yd3). This unit price does not reflect any potential incentive / disincentives. Four similarly sized, non-HPC projects let that same year had the following quantities and unit bid prices for structural concrete: 13,824 m3 at $78.65/m3 (18,189 yd3 at $59.77/yd3 ); 19,838 m3 at $86.37/m3 (26,103 yd3 at $65.64/yd3); 40,806 m3 at $73.13/m3 (53,692 yd3 at $55.58/yd3); and 7,665 m3 at $116.18/m3 (10,085 yd3 at $88.30/yd3). The different quantities, aggregate availability, and project complexities make it difficult to make a direct assertion as to the added cost of the HPC specification. However, based upon feedback from the paving contractor, the added cost for the HPC structural concrete is approximately $13.00/m3 ($10.00/yd3).
The unit costs of the different types of dowel bars also varied considerably. The epoxy-coated dowel bar cost $5.20; the 38-mm (1.5-in.) stainless steel clad dowel bar $11.60; the 44-mm (1.75-in.) stainless steel clad dowel bar $14.30; and the solid stainless steel dowel bar $19.70. A 1.6-km (1.0-mi) long project consisting of two 3.6-m (12-ft) lanes and 4.6-m (15-ft) joint spacing requires 8,448 dowel bars, yielding a total dowel bar cost of $43,929.60 for the epoxy-coated dowels, $97,996.80 for the 38-mm (1.5-in.) stainless steel clad dowels, $120,806.40 for the 44-mm (1.75-in.) stainless steel clad dowels, and $166,425.60 for the solid stainless steel dowels. The annualized cost for a 60-year design using solid stainless dowels is significantly higher than the annualized cost of a standard 35-year design (ignoring user costs).
Point of Contact
Minnesota Department of Transportation
1400 Gervais Avenue
Maplewood, MN 55109
Ph: (651) 779-5535
Fax: (651) 779-5616
Rangaraju, P. R. 2003. Development of Some Performance-Based Material Specifications for Minnesota's High-Performance Concrete Pavement. Transportation Research Board Annual Meeting CD-ROM. Transportation Research Board, Washington, DC.
Rettner, D. 1999. I-35W High Performance Rigid Pavement Work Plan. Minnesota Department of Transportation, Maplewood.
Turgeon, C. 2003. Minnesota's High Performance Concrete Pavements, Evolution of the Practice. Transportation Research Board 2003 Annual Meeting CD-ROM. Transportation Research Board, Washington, DC.