High Performance Concrete Pavements Project Summary
Chapter 25. MISSOURI 1 (I-29, Rock Port)
As part of the TE-30 program, the Missouri Department of Transportation (MoDOT) constructed an experimental unbonded concrete overlay in 1998. Located in the southbound lanes of I-29, just west of Rock Port (see Figure 72), the overlay includes test sections of conventional unbonded overlays, steel fiber-reinforced overlays, and polyolefin fiber-reinforced overlays, all with varying thicknesses (MoDOT 2000).
Figure 72. Location of MO 1 project.
The overall objective of this study is to compare the performance of fiber-reinforced unbonded concrete overlays to that of conventional unbonded concrete overlays (MoDOT 2000). The addition of the fibers to the concrete mix is expected to increase the service life of the overlay by increasing the "toughness" and post-cracking behavior of the concrete (Mindess and Young 1981). Toughness is defined as the total energy required to break a specimen, and the addition of fibers gives concrete a considerable amount of apparent ductility before ultimate failure of the specimen (Mindess and Young 1981).
Project Design and Layout
This project, constructed in 1998, consists of eight test sections, each 762 m (2500 ft) long (MoDOT 2000). Of the eight test sections, three sections incorporate steel fibers in the concrete mix, three sections incorporate polyolefin fibers in the mix, and two sections use a conventional concrete mixture. The layout of these test sections is illustrated in Figure 73 (MoDOT 2000).
Figure 73. Layout of MO 1 test sections (MoDOT 2000).
All of the test sections are unbonded concrete overlays placed over an existing 229-mm (9-in.) jointed reinforced concrete pavement (JRCP) that has 18.7-m (61.5-ft) transverse joint spacing (MoDOT 2000). A 25-mm (1-in.) asphaltic interlayer treated with white curing compound was used to isolate the concrete overlays from the underlying pavement (MoDOT 2000).
Based on a laboratory evaluation of fiber-reinforced mixes conducted by the DOT, and on the recommendations of the fiber manufacturers, two fibers were selected for the I-29 project (MoDOT 2000):
- 50-mm (2-in.) 3M polyolefin fibers. The fibers are straight with an aspect ratio (length/diameter) of 79 and were applied at a dosage rate of 14.8 kg/m3 (25 lb/yd3).
- 60-mm (2.4-in.) Dramix steel fibers. These fibers have hooked ends to promote bonding, an aspect ratio of 75, and were applied at a dosage rate of 44.5 kg/m3 (75 lb/yd3).
Each of the fiber-reinforced sections are differentiated by slab thickness, with thicknesses of 229 mm (9 in.), 152 mm (6 in.), and 127 mm (5 in.) included in the study. Furthermore, within each fiber-reinforced test section, four subsections with variable joint spacings (4.6 m [15 ft], 9.1 m [30 ft], 18.3 m [60 ft], and 61 m [200 ft]) are also included. The two control sections for the project are a 229-mm (9-in.) unbonded JPCP with 4.6-m (15-ft) transverse joints and a 279-mm (11-in.) unbonded JPCP with 4.6-m (15-ft) transverse joints. The experimental design matrix for the project is provided in Table 38.
|UNBONDED OVERLAY PORTLAND CONCRETE CEMENT|
|CONVENTIONAL||Steel Fiber||Polyolefin Fiber|
|5-in. Slab Thickness||15-ft Joint Spacing||Section 7||Section 8|
|30-ft Joint Spacing||Section 7||Section 8|
|60-ft Joint Spacing||Section 7||Section 8|
|200-ft Joint Spacing||Section 7||Section 8|
|6-in. Slab Thickness||15-ft Joint Spacing||Section 6||Section 5|
|30-ft Joint Spacing||Section 6||Section 5|
|60-ft Joint Spacing||Section 6||Section 5|
|200-ft Joint Spacing||Section 6||Section 5|
|9-in. Slab Thickness||15-ft Joint Spacing||Section 1||Section 2||Section 3|
|30-ft Joint Spacing||Section 2||Section 3|
|60-ft Joint Spacing||Section 2||Section 3|
|200-ft Joint Spacing||Section 2||Section 3|
|11-in. Slab Thickness||15-ft Joint Spacing||Section 4|
Paraffin-treated, epoxy-coated steel dowel bars were included in all test sections. The 279-mm (11-in.) test section contained 38-mm (1.5-in.) diameter bars whereas the rest of the test sections contained 32-mm (1.25-in.) diameter bars. Transverse joints were sealed with a hot-poured elastic sealant.
State Monitoring Activities
MoDOT is monitoring the performance of these sections annually for a minimum of 5 years, with additional monitoring thereafter conducted as appropriate. Data collection activities include pavement distress surveys, roughness measurements, surface friction testing, and FWD testing.
During construction, the properties of the materials were monitored. The fiber-reinforced concrete overlay mix had a w/c of 0.39 and utilized a limestone coarse aggregate with a 13 mm (0.5 in.) top size (MoDOT 2000). Nonuniform distribution of the fibers was observed, particularly for the polyolefin fibers (MoDOT 2000). Mixing times were increased, batch sizes were decreased, and the order of mixer loading was altered to address this concern, and these seemed to increase the uniformity of the fiber distribution in the concrete (MoDOT 2000).
Initial finishing of the overlays used a burlap drag, but this was later changed to an unweighted carpet drag because it was found that the fibers became caught in the burlap such that some fibers and aggregate were pulled from the top layer of the overlay (MoDOT 2000). In lieu of the conventional transverse tining texturing method, the final surface texture was established by diamond grinding the overlay 21 days after construction for smoothness and rideability (MoDOT 2000). Following grinding, profilograph readings averaged less than 0.17 m/km (11 in./mi) (0 blanking band), resulting in a smoothness bonus for the contractor (MoDOT 2000).
The in-place construction costs for these pavement sections are shown in Figure 74 (MoDOT 2000). This figure shows that the initial cost of the fiber-reinforced sections is higher than the cost of the conventional sections (the cost of furnishing the steel fiber concrete and the polyolefin fiber concrete was $56.22 and $71.77 more per m2 [$47 and $60 more per yd2], respectively, than the conventional concrete).
Figure 74. Relative cost of MO 1 test sections (MoDOT 2000).
Preliminary results/findings are based on the first 2 years of performance monitoring of these test sections. After nearly 2 years of service, the overall performance of these sections was good, although a few of the sections performed poorly (MoDOT 2000). In particular, the thin 127-mm (5-in.) sections, both steel and polyolefin reinforced, exhibited a large amount of transverse cracking. In addition, the 152-mm (6-in.) steel fiber-reinforced section also showed significant transverse cracking. Figure 75 summarizes the cracking data collected up to 1999 on these test sections (MoDOT 2000).
Figure 75. Transverse cracking on MO 1 test sections (MoDOT 2000).
Most of the transverse cracks that had developed were not located above joints or cracks in the existing pavement, so they did not appear to be reflective cracks (MoDOT 2000). In fact, most of the cracks on the thin steel fiber-reinforced sections were parallel to and located within 0.3 m (1 ft) of the transverse joints, whereas the cracks in the thin polyolefin fiber-reinforced sections were located away from the joints near mid-panel (MoDOT 2000). Because of the problems of the cracking and subsequent spalling, the test sections 7 and 8 were replaced with full-depth concrete in 2000.
Four general conclusions are drawn from the performance data collected up to 1999 (MoDOT 2000):
- The steel fiber-reinforced test sections exhibited more transverse cracking than the polyolefin fiber-reinforced test sections.
- The longer panels exhibited more cracking than the short panels.
- The thinner overlay sections exhibited more cracking than the thicker sections.
- Cracks that had developed in the steel fiber-reinforced test sections were tighter than those in the polyolefin fiber-reinforced test sections (3 mm [0.12 in.] vs. 6 mm [0.25 in.]).
Although no formal reports have been developed since the 2000 summary, MoDOT has provided additional performance data for inclusion in this report (Chojnacki 2004). Cracking surveys were conducted in December 2003 on these test sections, and the results are shown in Figure 76 (Chojnacki 2004). These data have been combined with the previous data to produce Figure 77.
Figure 76. Transverse and longitudinal cracking on MO 1 test sections (Chojnacki 2004).
Figure 77. Transverse cracking on MO 1 test sections.
In 2003, joint repairs were performed at several locations where transverse cracks existed near joints and spalling had occurred. The deteriorated areas were replaced with a full-lane-width concrete patch at least 1.8 m (6 ft) long. The patches were tied at one end with 19-mm (0.75-in.) epoxy-coated tie bars and doweled at the other end with 19-mm (0.75-in.) epoxy-coated dowel bars (Chojnacki 2004).
Point of Contact
Missouri Department of Transportation
1617 Missouri Boulevard
P.O. Box 270
Jefferson City, MO 65102
Chojnacki, T. 2004. Performance Data from MO1 Test Sections. Missouri Department of Transportation, Jefferson City.
Mindess, S., and J. F. Young. 1981. Concrete. Prentice-Hall, Inc., Englewood Cliffs, NJ.
Missouri Department of Transportation (MoDOT). 2000. Test Sections - Unbonded Concrete Overlay. Internal Technical Summary. Missouri Department of Transportation, Jefferson City.