2008 Survey of European Composite Pavements (2010)

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38C H A P T E R 4 Asphalt Surfaced Composite Pavement SystemSeveral European countries have built thin, high-quality asphalt surfacing on newly placed concrete pavements for many years (1). Two main types of asphalt surfaces were identified during the surveys, although other types (particularly micro- surfacing) also have been placed successfully: • Porous asphalt. The surfacing in the Netherlands included both one- and two-layer porous asphalt. The one-layer porous was 5 cm, and the two porous layers were 2.5 and 4.5 cm thick. The porous asphalt surface was constructed over continuously reinforced concrete pavement (CRCP) and has produced excellent results for up to 10 years of per- formance. This design is the standard in the Netherlands. Other countries known to build this type of design include the United Kingdom, France, Belgium, and Italy. • SMA. The stone matrix asphalt (SMA) surfacing in Germany ranged from 2 to 4 cm thick and included a high-quality aggregate and polymer modified binders. These composite pavements were sawed and sealed at transverse and longitu- dinal joints when placed over jointed plain concrete pave- ment (JPCP). Beginning in the early 1990s, SMA has been placed on JPCP, and more recently (2007–2008) it has been placed over CRCP to reduce reflection cracking. This SMA surfacing is now the standard in Germany. Italy has constructed many miles of CRCP with a porous asphalt concrete (AC) surfacing. This design has existed on the ring road around Rome since the early 1990s and carries heavy traffic. About every 7 to 10 years, the porous AC needs to be milled off and replaced because of clogging from fines or other problems. The total structural design life is 40 years. A cost comparison conducted in the 1990s of the composite AC/CRCP versus the conventional semi-rigid pavement with an AC surface over lean concrete or concrete-treated base (CTB) shows the following, where R equals the ratio of cost of composite versus the conventional (1): • Construction cost: R = 1.3 • Maintenance: R = 0.3• User costs: R = 0.55 • Total life cycle costs: R = 0.87 This chapter includes the R21 research project’s May 2008 survey results for thin, high-quality asphalt surfaces over concrete that were observed in the Netherlands and Germany. Netherlands Composite AC/CRCP Projects Noise has been a big issue in the Netherlands for at least two decades. This is especially true in urban areas where highways are near houses. The Netherlands has built several major proj- ects in the past 10 years using porous asphalt surfacing over CRCP and has considerable confidence in this design. The fol- lowing projects are among those visited on this and other occasions: • A12, west of Utrecht, 1998 • A76, Southern Netherlands, 8 km, 1991 • A5, Schiphol Amsterdam Airport, 5 km, 2000 • A50, Eindhoven, 35 km, 2004–2005 • A73, Province of Limburg, between Venlo and Echt- Susteren, 42 km, 2007 The challenge is how to provide low noise and good fric- tion, as well as reduced splash and spray. The Netherlands believes that porous asphalt over CRCP provides a good solution. Exposed aggregate (small stone, 4/8 mm) is approximately equal in noise quality to a dense AC mixture. The two look sim- ilar, and one may be confused regarding which is which. How- ever, porous AC provides < 3 dB(A) than cross-tined PCC. Porous AC usually fails from raveling over CRCP. No reflection cracking has occurred for this design. The Netherlands expects 8 to 10 years of life from the porous AC surface but expects

39overall porous AC/CRCP to be a “perpetual” pavement, where only the surface needs to be replaced over time as needed. Porous AC mixtures and layering used in the Netherlands include the following: • Single semi-porous AC layer: 2.5 to 3 cm, 14% air voids (called semi-porous) in porous AC surface course. No mod- ified asphalts used in Limburg Province, but they are used on national highways. • Double porous AC layers: Surface semi-porous AC layer plus elastic stress absorbing interlayer (SAMI). • Triple AC layers: Semi-porous AC surface, elastic layer, more porous AC layer (25% air voids) directly on PCC to provide drainage. Dense AC is 7% air voids. It is expected that porous AC/PCC will require more main- tenance. They expect to mill off the top semi-porous layer and replace when needed—about every 8 to 15 years, mainly because of raveling. A12 AC/CRCP Composite Project This project was surveyed in May 2008. The survey consisted of walking along portions of the project that could be accessed safely and observing the pavement from the outer shoulder, noting all types of distress and taking photographs. The project is located west of Utrecht on the A12, in the southbound direction between km 64.36 and 67.66 (this is just before exit 19) (2–4). The highway consists of three lanes in the southbound direction and inner and outer shoulders. This proj- ect is a typical heavily trafficked freeway with controlled access that carries a large volume of auto (100,000 vehicles per day in 1998) and truck traffic between Arnhem and Utrecht. This free- way is one of the main routes into Germany (Figure 4.1). The design of this porous AC over CRCP is given as fol- lows (2–4): • Porous AC surfacing. • 250-mm CRCP. • Mean as-constructed strength of concrete: 57 MPa at 90 days. • 60-mm AC dense-graded base layer. • 256-mm AGRAC subbase layer. • 261-mm sand sublayer. • Subgrade. The various moduli of these layers are provided in Table 4.1. The following observations were made regarding the visual condition of the pavement: • Overall condition was very good. • Smoothness: Ride rating was “very good,” or about 4.0 on a scale of 0 to 5.Figure 4.1. A12 between Utrecht and Ede, Netherlands, May 2008.• Raveling of the porous asphalt friction surface layer (Fig- ure 4.2). This layer had been in service for 10 years. The raveling was not excessive but likely will necessitate that the surface layer be replaced within about 2 to 3 years. • The measured noise level was not known, and a current measurement would be useful. It appeared to have relatively low noise during the drive to the site. The raveling of the porous asphalt surface was somewhat discernible. A photo taken on the shoulder showed considerable fines infiltrating the porous AC surface (Figure 4.3). • No clear transverse reflection cracking was observed from the underlying CRCP. There were slight indications in sev- eral locations, but even after 10 years no distinct transverse cracking existed (Figure 4.4). There was no longitudinal cracking either, except possibly in one location that may have been out of the project limits. A73 Porous AC/CRCP Composite Pavement Project The A73 is a 42-km, four-lane divided freeway with inner and outer shoulders. This project is a heavily trafficked freeway with controlled access that carries a large volume of traffic (truck traffic consisted of 7,000 trucks per day in one direction in the first year). The project is located in the south Netherlands Province of Limburg to connect the city of Venlo, via Roer- mond, to the existing A2 highway near the community of Echt-Susteren. The recently completed A73 is shown in Figures 4.5 and 4.6. This project, completed in 2007, was surveyed in May 2008. Discussions were held concerning the design, materials, and construction. The R21 delegation then performed a visual

40Parameter Design Objective Actual Realized Thickness sand subgrade 250 mm 261 mm E-modulus sand subgrade 100 MPa >200 MPa k-value subgrade 0.045 N/mm3 ∼0.070 N/mm3 Thickness lean concrete base 150 mm Not realized E-modulus base 9.000 MPa - Thickness AGRAC base 250 mm 256 mm E-modulus AGRAC base Not designed 4.000 MPa Composed k-value 0.118 N/mm3 ∼0.160 N/mm3 Thickness asphalt interlayer 60 mm Approximately 60 mm E-modulus asphalt interlayer Unknown 7,500 MPa Thickness concrete 252 mm nonreinforced 250 mm min./261 mm average Strength class concrete C45 C57 average Table 4.1. Summary of A12 Design and As-Constructed Pavement Propertiessurvey consisting of driving and walking along portions of the project that could be accessed safely, observing the pavement from the outer shoulder and on off-ramps, and noting any distress and taking photographs. This two-layer porous asphalt surfacing over CRCP com- posite pavement consists of the following structure: • 2.5-cm porous asphalt 4/8 mm (modified with polymer). • 4.5-cm porous asphalt 6/11 mm (modified with polymer). • 25-cm CRCP with 0.7% reinforcement (at exits, lanes are bare 32-cm CRCP).Figure 4.2. Raveling of porous AC surfacing in the outer lane wheelpaths of the A12 motorway.• Concrete quality of the pavement: C35/45. • 6-cm dense asphalt base course with E-mod of 400 N/mm2. • Granular subbase with an E-mod of 400 N/mm2. • Sand layer of 500 mm with an E-mod of 100 N/mm2. • Subgrade has a k-value of 0.036 N/mm3 (E-mod 75 N/mm2), sand and gravel with good grading curve. No transverse steel was used. Longitudinal steel was lapped. Transverse supports for the steel were placed at 20-degreeFigure 4.3. Close-up of the porous asphalt surface of the A12 motorway. Note fines infiltrating the porous asphalt surface on the edge of the traffic lane.

41Figure 4.4. A12 motorway between Utrecht and Ede after 10 years in service.angles from perpendicular to eliminate any possibility of trans- verse cracking over the transverse steel supports (Figure 4.7). Transverse supports served as tiebars. Plastic inserts were used for longitudinal joints. They were placed at 10 cm deep, or 40% of the 25-cm slab thick- ness. This provided for an effective depth to form the longi- tudinal joint. The paving was 12 m wide and consisted of two lanes and two shoulders, as illustrated (for another similar project) in Figure 4.8. The CRCP surface was textured longitudinally with burlap drag. No curing compound was applied. Thin, whole plastic sheets were used to cure the PCC for 7 days (which reducesFigure 4.5. Completed A73 composite AC/CRCP motorway in the Netherlands, May 2008.Figure 4.6. Double-layer porous AC surface of the A73 motorway, recently opened to traffic.the brushed texture). A tack coat of 0.2 kg/m2 emulsion was applied twice because of the texturing. The CRCP was cracked at about 2- to 3-m spacing. The transverse cracking in the CRCP ramps is shown in Figure 4.9.Figure 4.7. A73 CRCP reinforcing steel. The transverse supports are placed at a 20-degree angle from transverse perpendicular.

42Figure 4.8. Paving of CRCP motorway in the Netherlands.Some additional details of the design of this AC/CRCP pave- ment are as follows: • Design life: 40 years. • Annual number of traffic days/year: 270. • Average daily traffic (averaged over 7 days per week), heavy traffic in one direction: 7,000 initially.Figure 4.9. Transverse cracking on the unsurfaced A73 CRCP.• Annual growth in traffic: 2.5%. • Tire types that will be used on the road:  Type of tire: 30% single, 30% double, 40% wide tire.  The wander of the traffic across the traffic lanes and over the longitudinal joints: ▪ Merge lane: 2% of traffic, 94% lateral wander. ▪ Heavy traffic lane: 93% of truck traffic, 92% lateral wander. ▪ Fast lane: 5% of truck traffic, 92% lateral wander. ▪ 1% of traffic on the shoulder edge and 5% over the longitudinal joints. The truck axle load distribution (single, tandem, and tridems) are given in Table 4.2. It is planned to remove and replace the top 2.5 cm of porous AC as needed over time (perhaps every 7 to 8 years). Filling of the voids with fines also may be needed, which would increase the pavement/tire noise level. The quality of construction was believed to be very good. Terminal anchors. Four are used at bridges with 7-m spac- ing center to center. They are 1.5 m deep from top of CRCP. The visual condition of the pavement was found to be as follows: • Smoothness: Ride rating was “very good,” or about 4.8 on a scale of 0 to 5. • The porous asphalt friction surface layer was just opened to traffic and was in excellent condition.Single, Percentage Tandem, Average of Heavy Load Tridem Axle of Axle Loaded Class Load (kN) Load (kN) Highway 1 20–40 30 20.26 2 40–60 50 30.72 3 60–80 70 25.98 4 80–100 90 12.46 5 100–120 110 6.45 6 120–140 130 2.67 7 140–160 150 1.00 8 160–180 170 0.31 9 180–200 190 0.12 10 200–220 210 0.03 Maximum axle load [kN] 210 Number of axles per truck 4.0 Table 4.2. Axle Load Distribution of All Types of Axles

43Figure 4.10. A ramp end on the A73 showing the unsurfaced CRCP.• The noise level of the surface appeared to be very low. We observed the noise level of vehicles driving off the exit ramp from the porous AC onto the bare, transversely tined CRCP at end of the ramp (Figure 4.10). There was a signif- icant noise increase on the bare CRCP. • No transverse reflection cracking or any other kind of cracking was observed from the underlying CRCP. • The bare CRCP was observed on off-ramps. It was spaced at about 2 to 3 m, but longer at the free ends of the ramps. The cracks were tight and typical of cracks of newly con- structed CRCP. • Overall condition was excellent, and the delegation’s hosts stated that the construction quality was excellent on this project. SMA/JPCP AND SMA/CRCP, Germany A11 Motorway SMA/JPCP, Near Berlin Germany has built SMA surfaces over a few JPCP since 1992– 1993, when a section was built on the A11 near Berlin. This particular section was not visited on this trip, but it included the following design and construction details, which are similar to the project on the A93 built in 1995–1996 (5) (Figures 4.11 and 4.12): • 4-cm SMA surfacing with crushed gravel and a polymer modified bitumen for a binder. The bitumen content was 6.4% and air voids were 5.96%. • Adhesion layer (tack coat) consisting of a polymer modi- fied bitumen emulsion was placed and fine gravel was placed on top to prevent damage from truck tires.With permission of ISCP. Figure 4.11. German adhesion tensile strength test between SMA and the JPCP slab surface (5).• Transverse joints were cut into the SMA/JPCP and sealed with bitumen soon after placement of the SMA. • 26-cm JPCP doweled transverse joints at 5 m. • 15-cm cement treated or lean concrete base course. • 25 cm of a granular frost protection layer. An adhesion tensile strength test was conducted in the field, as shown in Figure 4.11, that showed a range of 0.59 to 0.87 N/mm2, which met the German standard ofWith permission of ISCP. Figure 4.12. Sawed and sealed joints on the A11 near Berlin in 1993 (5).

440.50 N/mm2. A small area of pavement that was not covered with the fine granular material to prevent damage was noted to have been disturbed by truck tires, and the tensile strength at this location was much lower than that achieved with the fine granular material. After 15 years of heavy truck traffic, the SMA/JPCP section on the A11 was still performing well. B56 Highway SMA/CRCP Recently, additional testing has been conducted using a spe- cial low-noise SMA over CRCP. Figure 4.13 shows the grain size, binder, and air void content, which is 9% to 11% by vol- ume for the B56 highway. Note that the field void content was specified as 10% to 15%. A93 Motorway SMA/JPCP, South of Munich One of the oldest German projects was built in 1995–1996 south of Munich on the A93. This project was surveyed by the R21 research team in May 2008, and photos of the pavement are shown in Figures 4.14 through 4.18. The design consisted of the following: • 3-cm SMA surface. The SMA was paved in two 5.5-m passes over PCC because of the width of the paver. It is notWith permission of ISCP. Figure 4.13. Details of the low-noise SMA used in 2007 in Germany (5).known if an adhesive layer (tack coat) was applied to the PCC surface prior to placement of the SMA, as was done on the A11 described. • Saw and seal on transverse joints (over PCC transverse joints) and on longitudinal joints (between paving passes) looked very good after 13 years, with the exception of those that were patched. • 26-cm JPCP with 5 m doweled joint spacing over a 15-cm lean concrete base. References 1. Darter, M. I. Report on the 1992 U.S. Tour of European Concrete Highways. FHWA-SA-93-012. Federal Highway Administration, 1993. 2. Van der Ven, D., K. P. Drenth, R. J. Dekkers, and L. Houben. Mon- itoring Program CRCP Highway Pavement: Interim Performance Evaluation. Proc., 7th International Conference on Concrete Pave- ments, International Society for Concrete Pavements, Orlando, Fla., 2001. 3. Dekkers, R. J., and D. van der Ven. 10 Years Monitoring the A12. Technical Report. KOAC-NPC, Netherlands, 2006 (in Dutch). 4. Dekkers, R. J., and W. F. Stas. Monitoring the A12. Asfalt nr. 3. Netherlands, Sept. 2000 (in Dutch). 5. Holler, F. Continuously Reinforced Concrete Pavement with SMA Coating—The Composite Structure for the Challenges of the Future. Proc., 9th International Conference on Concrete Pavements, International Society for Concrete Pavements, San Francisco, Calif., 2008.Figure 4.14. A93 motorway in Germany showing SMA over JPCP with sawed and sealed joints after 13 years of heavy truck traffic.

45Figure 4.15. A93 SMA over JPCP with sawed and sealed transverse and longitudinal joints. Note patch placed in wheelpath of transverse joints.Figure 4.16. A93 SMA/JPCP motorway near Munich, with sawed and sealed longitudinal and transverse joints.Figure 4.17. A93 motorway showing transverse sawed and sealed joint in SMA over JPCP after 13 years of heavy traffic. In center of photo, note longitudinal joint that is also sawed and sealed.Figure 4.18. Close-up of A93 SMA surface and transverse sawed and sealed joint over JPCP after 13 years of heavy traffic. Some transverse joints required patching for unknown reasons.