High Performance Concrete Pavements Project Summary
Chapter 20. MICHIGAN 1 (I-75, Detroit)
The Michigan 1 project is located on I-75 (Chrysler Freeway) in downtown Detroit (see Figure 50). Built in 1993, this project came about as a result of an FHWA-sponsored tour of European concrete pavement design and construction practices in 1992. During that tour and a followup tour, one major observation of European concrete design and construction practices was the emphasis placed on the quality of the design, materials, and construction of the pavement, with less concern for higher costs or longer construction periods (FHWA 1992; Larson, Vanikar, and Forster 1993). The tours generated substantial interest in constructing a "European-type" concrete pavement to evaluate its constructibility and performance compared to conventional U.S. designs. This interest led to the selection of the 1.6-km (1-mi) test section on I-75 in Detroit (see Figure 50).
Figure 50. Location of MI 1 project.
The objective of this project is to determine whether innovative features of typical rigid pavement designs used in European countries can be applied cost effectively to conventional design and construction methods used for rigid pavements in the United States (Smiley 1995). The European pavement was constructed for the purpose of comparing the European design with conventional designs to demonstrate the applicability of certain European concepts to U.S. highway construction (Weinfurter, Smiley, and Till 1994).
Project Design and Layout
This project is located in the northbound lanes of I-75 and consists of two sections: a "control" section representing the Michigan Department of Transportation's (MDOT's) then-current standard concrete pavement design, and the European concrete pavement section incorporating several innovative design features (Weinfurter, Smiley, and Till 1994). The layout of these sections is shown in Figure 51, which also lists some of the key design features of each section.
Figure 51. Layout of MI 1 project.
The existing roadbed for the project lies within an approximate 7.6-m (25-ft) cut section (Weinfurter, Smiley, and Till 1994). The subgrade is predominately a silty clay material, which was required to be compacted to 95 percent of its maximum unit weight in accordance with Michigan's One-Point T-99 (Proctor) Test (Weinfurter, Smiley, and Till 1994).
These sections on I-75 contain three to four traffic lanes in each direction. In 1993, this portion of I-75 carried about 111,000 vehicles per day, including 11 percent heavy trucks (Smiley 1995).
Construction of the sections began in July 1993 and was opened to traffic in November of that same year (Smiley 1995). During the 1994 construction season, southbound I-75 traffic was detoured onto northbound I-75 while it was reconstructed. The entire I-75 reconstruction project was completed in October 1994.
Section 1 - Michigan Standard Pavement
The Michigan standard section is 2.1-km (1.3-mi) long and is located south of the European section. The cross section for the Michigan standard section is shown in Figure 52 (Smiley 1995). This is a 279-mm (11-in.) JRCP design with transverse joints spaced at 12.5-m (41-ft) intervals (Weinfurter, Smiley, and Till 1994).
Figure 52. Cross section for Michigan standard pavement (Smiley 1995).
The PCC mix used a higher quality coarse aggregate than standard so that the performance could be compared to the European section. A 100-mm (4-in.) permeable cement-treated base is located beneath the slab. The aggregates for the open-graded base were obtained by crushing the existing I-75 pavement and were stabilized with 6 percent cement (Weinfurter, Smiley, and Till 1994). A geotextile separator is located beneath the open-graded base and above the underlying 305-mm (12-in.) sand subbase (Weinfurter, Smiley, and Till 1994). Longitudinal collector drains (152 mm [6 in.] diameter) are located beneath both the inside and outside reinforced concrete shoulders. All traffic lanes in this section are 3.7 m (12 ft) wide.
Section 2 - European Pavement
The European pavement section is 1.6 km (1 mi) long and is located north of the Michigan standard section. It consists of a 254-mm (10-in.) JPCP that was placed in two lifts (see Figure 53 for the pavement cross section). The layers were placed "wet-on-wet" to ensure bonding between the top 64-mm (2.5-in.) concrete layer and the bottom 190-mm (7.5-in.) concrete layer. The same sources for cement and aggregate were used in the top and bottom layers, except that the course aggregate for the top layer was specified to be a 100 percent crushed basalt rock to provide resistance to polishing (Weinfurter, Smiley, and Till 1994). Conventional paving equipment was used for the placement of the two layers.
Figure 53. Cross section for European pavement (Smiley 1995).
The two-layer JPCP was constructed directly on a 152-mm (6-in.) lean concrete base (LCB) without the use of a bonding agent. Plane-of-weakness joints were sawed in the LCB at transverse and longitudinal locations to match those of the overlying JPCP slab and thereby prevent reflection cracking (Weinfurter, Smiley, and Till 1994). The joints were sawed to a depth of 61 mm (2.4 in.). A comparison of the specified concrete properties of the LCB, the top layer PCC slab, the bottom layer PCC slab, and the Michigan standard pavement is provided in Table 25 (Weinfurter, Smiley, and Till 1994).
|PORTLAND CEMENT CONCRETE PROPERTY||EUROPEAN PAVEMENT||MICHIGAN STANDARD PAVEMENT|
|TOP LAYER||BOTTOM LAYER||LCB|
|28-day compressive strength, lbf/in2||5,500||5,000||2,500||3,500|
|28-day flexural strength, lbf/in2||—||—||—||650|
|Maximum w/c (by weight)||0.4||0.42||0.7||0.5|
|Minimum cement content, lb/yd3||752||588||420||550|
|Maximum slump, in.||3||3||3||3|
|Air content, %||6.5 ± 1.5||6.5 ± 1.5||6.5 ± 1.5||6.5 ± 1.5|
LCB = lean concrete base
An exposed aggregate surface was specified for the top layer of concrete. This exposed aggregate surface provides surface texture and is expected to reduce noise levels. The exposed aggregate surface was produced through a patented process developed by Robuco, Ltd. of Belgium, consisting of the following steps (Weinfurter, Smiley, and Till 1994):
- Evenly spraying the surface with a set retarder within 30 minutes of the finishing operation.
- Covering the concrete surface with plastic waterproof sheeting (for a period of approximately 20 hours).
- Removing the sheeting and brushing the surface with a brushing machine.
- Placing a curing compound on the newly exposed aggregate surface.
Joint sawing operations were made through the protective sheeting prior to the brushing operation.
A 406-mm (16-in.) thick, nonfrost-susceptible aggregate subbase was placed directly on the subgrade, and longitudinal edge drains were installed beneath both the inside and outside PCC shoulders (Weinfurter, Smiley, and Till 1994). The outer lane consisted of a 4.1-m (13.5-ft) wide outer slab to reduce critical edge loading encroachments.
Transverse contraction joints were spaced at 4.6-m (15-ft) intervals and were designed to match those joints in the underlying LCB. Polyethylene-coated dowel bars, 32 mm (1.25 in.) in diameter and 508 mm (20 in.) long, were placed on chairs at the mid-depth of the composite slab and at the variable spacings shown in Figure 54 (Weinfurter, Smiley, and Till 1994).
Figure 54. Variable dowel spacings used on European pavement section
(Weinfurter, Smiley, and Till 1994).
The longitudinal and transverse joints were sealed with an ethylene propylene diene terpolymer (EPDM) seal (Weinfurter, Smiley, and Till 1994). Similar to conventional neoprene compression seals, these seals are placed without a lubricant/adhesive and require only a clean (but not dry) joint prior to installation (Weinfurter, Smiley, and Till 1994).
State Monitoring Activities
MDOT has been monitoring the performance of both sections since 1993. Performance data collected include surface distress, ride quality, surface friction, and tire noise levels (Weinfurter, Smiley, and Till 1994). Seasonal pavement deflection measurements are also taken periodically to identify any structural inadequacies that may develop in either pavement section (Weinfurter, Smiley, and Till 1994). Although limited performance monitoring continues, no formal reports have been prepared since 2000.
Initial Construction Findings
The construction of the European pavement section was accomplished without any major difficulties. Slower production rates were noted, much of which is attributed to an unfamiliarity with two-layer construction and exposed aggregate surfaces (Weinfurter, Smiley, and Till 1994). Among some of the specific recommendations for similar future projects include (Weinfurter, Smiley, and Till 1994):
- The saw cut depth for longitudinal joints in a two-layer pavement is recommended to be between 40 and 45 percent of the total pavement thickness. The saw cut depth for transverse joints is recommended to be between 25 to 30 percent of the total pavement thickness.
- The variable spacing of dowel bars in a basket assembly should be arranged such that the spacing between bars actually represents a standard "uniform" spacing but with selected bars missing. This will save on the costs associated with the fabrication of special dowel bar baskets.
- The top layer of the two-layer pavement should be designed no less than 70 mm (2.75 in.) thick in order to reduce the chance for poor consolidation and a thin surface layer to occur.
- The concrete mixture for the top layer should be revised to eliminate sand particles larger than 1 mm (0.04 in.). These coarser particles prevent the coarse aggregate in the mixture from "locking" together, which is needed in order to reduce noise.
- The environmental ramifications of the dust and slurry generated from the surface brushing operations must be clarified in the design stage. There was excessive dust generated during the brushing operation but fortunately the location was not near a residential area. Disposal of the slurry must meet all local regulations.
- Repair methods need to be developed for exposed aggregate surfaces when the texture depth is determined to be out of the specified range.
One-Year Performance Findings
In the first year after the construction of the pavement sections, distress surveys, skid testing, and noise studies were conducted. Results of those monitoring activities are given below (Smiley 1995):
- The first performance evaluation of the project was conducted in October 1994 just prior to the I-75 freeway being opened to normal traffic operations (the southbound lanes had been re-routed on the northbound lanes). Observations from that initial survey include:
- On the European pavement section, only one transverse crack was identified. A core retrieved over the crack indicated significant honeycombing. It was later determined in conversations with the construction project staff that the crack was likely a cold joint between old concrete and a botched attempt to patch fresh concrete that had been damaged by contractor paving equipment.
- Occasional surface popouts were noted throughout the European pavement section. The diameter of these popouts was normally between 25 and 50 mm (1 and 2 in.).
- The EPDM joint seals on the European pavement section appeared to be in very good condition, although there was occasional evidence of "camelback humping" on some of the transverse joints.
- The exposed aggregate surface of the European pavement section appeared to have lost macro-texture in the two inner lanes, where traffic was during most of 1994 when the southbound lanes were being reconstructed.
- On the Michigan standard pavement section, approximately 50 percent of the 12.5-m (41-ft) long panels contained transverse cracks, typical of JRCP designs. The cracks were tight and typically irregular in direction.
- Surface friction was measured on both sections in accordance with ASTM E-274. Tests were conducted in November 1993 and again in April 1994. Over that time, the overall average friction number for the European pavement section increased from 38 to 42, while the overall average friction number for the Michigan standard pavement section increased from 46 to 53.
- A traffic noise study was conducted in June 1994 on both the European pavement section and the Michigan standard pavement section. Both interior and exterior noise levels were recorded. The results from the study indicate that the exposed aggregate surface did not produce the expected reduction in noise levels that are perceptible to persons residing adjacent to the project or when traveling by car. One possible reason for this is that the exposed aggregate surface had too much macrotexture from the excessive spacing of the coarse aggregate particles.
Five-Year Performance Findings
A 5-year analysis of the performance of the two test sections was just recently completed (Buch, Lyles, and Becker 2000). This analysis included an evaluation of traffic, pavement distress, roughness, surface friction, and deflection data obtained on the sections from 1993 to 1998. An economic analysis of each section was also conducted. Summaries of these analyses are provided in the following sections.
Pavement performance is typically assessed in terms of how well the pavement stands up to traffic loading, which is generally expressed in terms of 80-kN (18-kip) equivalent single-axle load (ESAL) applications. However, because of variable commercial traffic levels and questionable vehicle classification data, the 5-year evaluation used total traffic volume as the basis for performance comparisons (Buch, Lyles, and Becker 2000). The cumulative total traffic volume (traffic in all lanes in one direction) for these sections is shown in Figure 55 (Buch, Lyles, and Becker 2000).
Figure 55. Cumulative total traffic volumes for MI 1 test sections
(Buch, Lyles, and Becker 2000).
Pavement distress surveys are conducted regularly on Michigan's highways as part of MDOT's pavement management activities. The condition of a pavement is reported in terms of a distress index (DI), which is computed based on the type, extent, and severity of distress. Data from 1995 and 1997 showed a DI of 0 for the European pavement section, indicating a distress-free pavement well below the rehabilitation trigger value of 50 (Buch, Lyles, and Becker 2000). The 1995 and 1997 DI values for the Michigan standard pavement section are 1 for both years, also suggestive of a pavement in very good condition (Buch, `Lyles, and Becker 2000).
MDOT has monitored the roughness of these pavement sections using an inertial profiler. International Roughness Index (IRI) values computed from the measured profiles are shown in Figure 56 as a function of total traffic (Buch, Lyles, and Becker 2000). The European pavement is noted to be slightly rougher than the Michigan standard pavement, but overall the smoothness levels have remained fairly constant. It should be noted that IRI values less than 1.3 m/km (80 in./mi) are considered to be smooth (Buch, Lyles, and Becker 2000).
Figure 56. Computed IRI values for MI 1 test sections
(Buch, Lyles, and Becker 2000).
Deflection testing on the test sections has been performed twice: once in November 1993 and once in April 1995 (Buch, Lyles, and Becker 2000). The 1993 measurements were taken during daylight hours prior to the pavement being opened to traffic; the 1995 measurements were taken at night because of lane closure restrictions (Buch, Lyles, and Becker 2000). An FWD using a 4000-kg (9000-lb) load was used to conduct the testing.
Table 26 summarizes the results of the FWD testing. It is observed that the magnitude of the maximum mid-slab deflections are less for the European pavement than for the Michigan standard pavement, which is not surprising given the strong base and thick subbase located beneath the European pavement slab. However, it is surprising that the load transfer efficiencies for both sections are as low as they are for such new pavements, and that the most recent LTEs for the European pavement are less than the Michigan standard pavement. One possible reason for this is the wet weather conditions that had preceded the April 1995 testing, which may have contributed to warping of the slabs (Buch, Lyles, and Becker 2000).
|TEST PROPERTY||TEST LOCATION||EUROPEAN PAVEMENT||MICHIGAN STANDARD PAVEMENT|
|NOVEMBER 1993||APRIL 1995||NOVEMBER 1993||APRIL 1995|
|Average maximum mid-slab deflection||Outside lane||1.30 mils||1.41 mils||1.99 mils||2.05 mils|
|Lane left of outside lane||1.37 mils||1.32 mils||2.13 mils||2.07 mils|
|Inside lane||1.27 mils||1.33 mils||2.28 mils||2.07 mils|
|Average transverse joint load transfer efficiency||Outside lane||77%||59%||68%||70%|
|Lane left of outside lane||79%||62%||72%||70%|
Friction numbers measured for these test sections are shown in Figure 57 (Buch, Lyles, and Becker 2000). The friction numbers for the Michigan standard pavement section are higher than those of the European pavement section, which is somewhat unexpected because of the exposed aggregate surface. Both sections show an initial increase in friction number, which is most likely due to the wearing off of the curing compound (Buch, Lyles, and Becker 2000).
Figure 57. Computed friction numbers for MI 1 test sections
(Buch, Lyles, and Becker 2000).
Economic Analysis of Pavement Sections
It was expected that the European pavement section would cost more to construct than the Michigan standard pavement, but the result would be a longer-lasting concrete pavement. A cost analysis showed that the European pavement cost about 234 percent more to construct than the Michigan standard pavement (Buch, Lyles, and Becker 2000). However, it should be noted that the European pavement was a demonstration project that was constructed as part of an "open-house" conference, so the costs are not representative of a conventional paving project.
An economic analysis was conducted to compare the life-cycle costs (LCC) of the European and Michigan standard pavements. This required several assumptions regarding future performance, future maintenance cycles, and future rehabilitation schedules. Based on the analysis, it was determined that the European pavement is not competitive with the Michigan standard pavement. However, the calculations are theoretical in the sense that the projected time to maintenance and rehabilitation activities are based on MDOT estimates (Buch, Lyles, and Becker 2000). In addition, the construction costs of the European pavement may not be representative since it was a demonstration project. Nevertheless, the extrapolated data suggest that in order for the European pavement to be competitive, it can cost no more than approximately 17 percent more than the Michigan standard pavement (Buch, Lyles, and Becker 2000).
Point of Contact
Michigan Department of Transportation
8885 Ricks Road
P.O. Box 30049
Lansing, MI 48909
Buch, N., R. Lyles, and L. Becker. 2000. Cost Effectiveness of European Demonstration Project: I-75 Detroit. Report No. RC-1381. Michigan Department of Transportation, Lansing.
Federal Highway Administration (FHWA). 1992. Report on the 1992 U.S. Tour of European Concrete Highways. FHWA-SA-93-012. Federal Highway Administration, Washington, DC.
Larson, R. M., S. Vanikar, and S. Forster. 1993. U.S. Tour of European Concrete Highways (U.S. TECH), Follow-Up Tour of Germany and Austria - Summary Report. FHWA-SA-93-080. Federal Highway Administration, Washington, DC.
Smiley, D. L. 1995. First Year Performance of the European Concrete Pavement on Northbound I-75 - Detroit, Michigan. Research Report R-1338. Michigan Department of Transportation, Lansing.
Weinfurter, J. A., D. L. Smiley, and R. D. Till. 1994. Construction of European Concrete Pavement on Northbound I-75 - Detroit, Michigan. Research Report R-1333. Michigan Department of Transportation, Lansing.