Chapter Two: Construction

Denmark

Pavements must be in relatively good condition before they are considered candidates for overlay with PA. They must have very few defects with no rutting, for example, because treatments are thin. In Denmark, quiet pavement systems have been used only in experimental locations, not as a routine measure.

All projects (coarse and dense graded) are low bid, but a 5-year warranty is included in all bids. The contractor must correct any defects at the end of this time. New construction contracts are being considered that give a contractor a designated amount of money annually to maintain a project over a 15-year period. If the contractor does a good job and no maintenance is required, the contractor keeps the money. If maintenance is more than the allocation, the contractor is required to maintain the project out of its pocket. This concept applies to all warranty conditions, not just noise.

Once a new concept or product has been evaluated, the researcher turns over the details to the Standards Committee (under the Ministry of Transport), which is composed of academia, contractors, etc. The Standards Committee takes the product and draws up the standards.

The contractor tests state samples—30 to 40 projects per year with a mobile test lab as a check. No penalties are assessed for failure to achieve the design noise criteria. The Danes run a noise-absorption test on test specimens and on in situ pavement, but they question the usefulness of this test. No specialized construction equipment, training, or inspection techniques are required.

The Netherlands

More than 65 percent of the national highway system has been surfaced with PA. Two-layer (Twinlay) mixes are used primarily on high-speed rural areas, and single-layer mixes are proposed for lower-speed urban areas.

Construction of the two-layer system should be placed “warm-on-warm”—not allowing cooling of the first layer and eliminating the tack coat. Conventional construction requires the use of tack coat between layers when placing warm on cool. The contract requires use of insulated truck beds and covered (tarped) beds. Although the mixes are designed at 25 percent air voids, the target on the roadway is 20 percent. The first noise measurements are taken 8 weeks after construction using the CPX procedure. The reference for noise reduction is dense asphalt concrete (DAC). The initial reduction is about 5 to 6 dB for the two-layer system on high-speed facilities, and about 3 to 5 dB on low-speed (30-to-55 km/h) roadways. The pavement life or durability for PA mixes is about 8 to 10 years, compared to 10 to 12 years for DAC. The pavement warranty covers durability, but not noise. Over the pavement life, the acoustical durability is about 4 dB. The loss in acoustics is because of clogging and raveling. Including both skid resistance and noise reduction under the 3-year warranty period is under consideration for the 2005 construction season.

Figure 9. Construction of the rollable road.

Figure 10. Construction of the ModieSlab (two-layer porous concrete).

France

France has established a noise database of some 289 SPB measurements. PA using the 0/6-mm aggregate size is the quietest pavement at 71 dB (69 to 74). The next quietest is the 0/10-mm size at 74 dB (69 to 78). The 0/14-mm size is 75 dB (74 to 76). For comparison, the reference pavement is a 0/10-mm dense-graded mix that measures 78 dB (74 to 82), and chip seals that measure 78 dB. It is assumed that when the noise increases on a PA mix, the pavement has clogged, but there is no supporting data. The French have stopped using the 0/14-mm mixes for surfacing because of a lower skid and decreased performance for noise reduction. The French begin noise measurements 2 to 3 months after construction, and have found an increase of 1 dB after 1 to 6 years of service. New pavements are expected to maintain a maximum noise level of 75 dB during the life of the pavement. If the noise level exceeds 75 dB, some type of corrective action is required.

A number of factors are used to select a contractor. Although low bid is an important consideration, other factors may include work history, qualifications, and technical expertise. The final selection is based on a combination of these considerations. Some projects have a 10-year guarantee on the total structure. The contractor is responsible for any structural failure (alligator cracking or any other distress that indicates a failure at depth in the pavement structure). This guarantee does not include normal wear of the surface course.

The thin mixes are used for most maintenance work. To begin laydown operations, the temperature must be higher than 5 degrees Celsius (C). Tack coat is considered essential between layers and is always required. The service life of these mixes is 10 to 14 years. Skid performance and noise reduction are much better for the 0/6-mm mixes, and these mixes do not clog as rapidly in urban (slow traffic speed) areas. The French do not attempt to clean porous mixes because they have not found the pressure wash and vacuum system to be effective.

Porous mixes were first used 15 years ago for spray reduction and to some extent for smoothness. However, the mixes were found to be rut resistant, skid resistant, and noise reducing. Porous mixes are not used at crossroads or other areas where severe turning actions are encountered. The primary failure mode for porous mixes is raveling. Raveling has been associated with gap grading, and 7 to 10 percent sand mortar is now used to resist raveling.

The French run a permeability test on mix specimens in the lab and in the field. Field test results cannot be predicted based on the lab results. A significant difference in noise level has also been noted using the same mixes and same contractor. By adding 1 to 2 percent rubber, a 1-dB noise reduction has been measured for the porous mixes as well as the thin mixes. Experimental sections have been placed using lightweight aggregates for skid resistance and noise reduction, and so far the tests look good. A test is being devised to quantify spray reduction.

Italy

The Italians began recycling PA mixes in 1996 using the hot-in-place process. They favor the Martex AR 2000 and the Marini ART 220 for recycling (see figure 11). During the hot-in-place recycling operation, the contractor conducts drainage tests that consist of filling a large tube (attached and sealed to the pavement surface) with water (figure 12). The amount of water that flows into the pavement over a 10-second interval is measured (procedure is similar to a falling head permeability test). A calculated flow rate of 20 liters per minute is considered good. If the flow rate does not achieve this value, the approach taken is not clear. One technician stated that the test would be run again, while one manager indicated that the amount of virgin material added to the recycled mix would be adjusted to achieve the desired permeability.

Figure 11. Recycling a porous pavement in Italy.

Figure 12. Permeability testing of recycled mix.

United Kingdom

“Traffic uses the same amount of energy in the first year as the total amount of energy used for construction.”—Robert Dudgeon, Highways Agency

Projects are awarded differently, depending on the system of financing. About 10 percent are awarded on the basis of design-build-maintain-and-operate concessions for 30 years. In these cases, proposals submitted are reviewed and weighted 80 percent on technical merit and 20 percent on cost. Other projects are design-build and handover. The main contractors are often partnered with material suppliers, and the surfacing product used is proprietary. Material specifications for such products are developed and owned by the contractor. The British are moving to performance-based specifications for paving materials to ensure a competitive market. The contractor is responsible for providing a quality control system.

The British have also implemented a procurement process referred to as early contractor involvement (ECI), in which the contractor is selected before a final design is complete. This process has reduced project conception-to-delivery time from 10 to 7 years and has reduced the contractor’s perceived risk (which is hoped to reduce project costs).

The British experimented with PA in the 1980s for spray reduction. They later discovered the noise-reduction benefits, but found durability problems because of raveling. One extremely hot summer destroyed many of the existing PA mixes laid in the United Kingdom, so they turned to thin surfacings in the 1990s. To meet U.K. skid-resistance requirements, development work with existing formulations for thin surfacings was needed to improve performance. A number of products met this requirement in 1996 through modification of their mix formula. Contracts now require the use of quiet pavements but allow the contractor to select from an approved list of more than 30 products (primarily thin surfacings).

The products are warranted to maintain their quality for 3 years, but longer warranty periods are being considered. Also, no incentives exist for developing products that exceed the minimum requirements. For example, a product that achieves a 5-dB reduction is not given any more credit than one that achieves the minimum 2.5-dB reduction. (A new class of higher noise-reduction performance is being launched in late 2004 to cover an emerging number of products that can now provide the extra benefit.) Thin-surface mixes are the primary quiet pavement technology now used in England. The primary failure mode is raveling. The mixes are subjected to a wheel-tracking test and warranted for 2 to 4 years.

Early use of exposed concrete pavements (Whisper Concrete 1993) proved to be successful, but current policy dictates that any concrete pavement must be covered with a HAPAS-approved quiet pavement mix. Forty percent of new roads are CRCP with a thin- surface lift, and 60 percent are constructed with concrete base. Porous concrete was never used in Britain because of excessive cost and the required construction techniques (must be placed wet-on-wet and use specific polymers).