2008 Survey of European Composite Pavements (2010)

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12C H A P T E R 3 Two-Layer Concrete Composite Pavement SystemTwo-Layer Exposed Aggregate Concrete All two-layer concrete pavements observed during the trip included a top surface of exposed aggregate concrete (EAC). This surfacing has been used on concrete pavements since first employed by Belgian engineers in the 1970s (1). Gradually, this surface has become more popular among European countries. The Netherlands has used EAC since the early 1990s as a low- noise, high-friction, long-term surfacing on its jointed plain concrete pavements (JPCP). Germany built experimental sec- tions in the 1990s and has been specifying exposed aggregate texture in its concrete pavements since 2006. Austria has used and extensively developed EAC since 1990 (2). Various coun- tries, including those mentioned, have investigated the prop- erties of EAC on full-scale test sections constructed from the late 1980s onward (3–5). EAC typically is employed to provide texture and surfacing to reduce noise and increase friction. EAC has become the con- crete surface standard of choice in several European countries. Figure 3.1 shows an example of the surface texture in EAC. In countries that have adopted or are in the process of adopt- ing EAC on a large scale, the EAC texture has replaced other, older textures that are very familiar to American pavement engineers. One of the textures replaced by EAC is the longitu- dinal burlap (or jute) drag. Burlap texturing was the standard in Germany for more than 15 years, and during that time Ger- man pavement engineers observed the durability of this texture. The generally held opinion of burlap drag in both Germany and Austria is that it provides excellent noise reduction and friction in the first 5 years after construction (2, 6, 7); however, after this initial period, if the traffic volume is sufficiently high (Austrian engineers estimate this to be approximately 25,000 vehicles per day), the texture is eroded by traffic and the pavement loses some of its desired noise and friction qualities. Figure 3.2 shows an example of polishing in a 12-year-old longitudinal burlapdrag encountered by the R21 delegation on the A93 motorway near Kiefersfelden, Germany. Because the longitudinal burlap (jute) drag is not durable under long-term traffic, German pavement engineers no longer employ it in PCC pavements and are in the process of making EAC as the top layer for a two-layer JPCP the new standard for concrete pavements. The main justification for using EAC is that it makes for more durable, safer, and quieter pavements. While the noise- reduction capability of EAC has been only of recent interest to American pavement engineers (8), it has been the subject of several studies in Europe. Austrian studies found that EAC reduced pavement noise by 5 dB(A) over conventional con- crete surfacing (9). Other studies have noted that the EAC tex- ture does not lose its noise-reduction qualities as quickly as other popular surfaces do, including porous asphalt, dense- graded asphalt, and stone matrix asphalt (SMA) (10, 11). In addition to its noise-reduction properties, the texture of EAC is an effective method for increasing the friction of a concrete surface. Studies have shown the durability and fric- tion of EAC surfaces to be superior to longitudinal finishes, giving average values of 0.50 at 80 km/h and 0.60 at 60 km/h versus the required 0.30 and 0.38 using the Stuttgart device with blocked, PIARC (Permanent International Association of Road Congresses—World Road Association)-type wheel (2, 9). The friction numbers for EAC pavements have been shown to suffer very little reduction after 5 and 7 years (10). In addition, the R21 delegation’s Austrian hosts noted on many occasions that the application of studded tires on EAC surfaces “renews” and can sometimes improve the surface in terms of friction (though the studded tires do not help the surface in its noise-reduction capabilities). The noise-reduction and friction properties of the EAC texture result in part from the aggregates that are in the mix used for the layer that receives the EAC texturing. Recent research and years of engineering experience relayed to the

13Figure 3.1. An example of exposed aggregate texture (with maximum aggregate size of 8 mm) of a two-layer PCC pavement taken along the A1 motorway near Eugendorf, Austria.R21 delegation suggest that the most effective use of EAC is with a mix design that features a relatively small maximum aggregate size (at most 8 mm) with high-quality, durable, cubical aggregates that resist polishing (2, 4, 7). A later section of this report discusses the importance of aggregates in more detail. Although the EAC surface can be accomplished on a single- layer PCC pavement, most typically it is found in two-liftFigure 3.2. Loss of texture, especially noticeable in wheelpaths, in longitudinal burlap drag textured sections along A93 motorway (km 1.490–1.910) near Kiefersfelden, Germany.Figure 3.3. EAC texturing on a two-layer EAC PCC/PCC pavement.PCC/PCC pavements, wherein the lower lift contains a larger, lower-cost aggregate and the upper lift contains a smaller aggregate EAC that is very resistant to polishing. The EAC surface is obtained as shown in Figure 3.3: the finished pave- ment is first sprayed with a curing/retarding material, then the surface mortar is removed using a rotating wire brush to obtain the proper texture (usually two passes are required), and the finished, textured pavement is sprayed with a curing compound. The result is a high-quality ride surface that, as mentioned, has better long-term noise and friction characteristics than conventional texturing (longitudinal burlap drag or transverse/ longitudinal tining). The use of exposed aggregate textur- ing on European pavements was of particular interest to the R21 delegation, given this novel and widespread use of PCC/PCC. EAC Materials and Mix Design Accepted practices in all three countries use very similar materials in a two-layer EAC pavement. The following sub- sections discuss materials and mix designs as described to the delegation by its hosts in Europe and by the literature pro- vided to the delegation. Netherlands EAC The construction in 2000 of the full-scale EAC test sections along N279 was accomplished mainly to provide the Nether- lands with insight into noise reduction regarding the aggre- gate selection for the EAC top layer of the two-layer concrete composite. Dutch engineers desired, in addition to a size that optimized noise reduction, a durable aggregate that would prevent the pavement from losing its noise-reduction quali- ties over the course of being heavily trafficked.

14In constructing PCC pavements (either single-layer or two- layer composite) with EAC, the various pavements featured mixes that had aggregates of maximum aggregate size as small as 7 mm and as large as 22 mm. These aggregates were crushed gray quartzite, a high-quality, durable, hard stone (Figure 3.4), or a locally available crushed gravel. Furthermore, the aggregates were part of a gap-graded mix (one that uses only the finest and coarsest aggregates) or con- tinuous mix (one that has a full spectrum of sizes from fine to coarse). The full-scale test sections were examined for noise and skid resistance. Pavement engineers in the NetherlandsFigure 3.4. Top: A sample of gray quartzite, a high- quality aggregate used in EAC pavements, such as the N279 test sections in the Netherlands (12 ). Bottom: A hand specimen of diabase, an aggregate frequently encountered in EAC pavements along A1 in Austria (13).have concluded that a gap-graded 5/8-mm mix using gray quartzite performed best, both reducing noise and increasing skid resistance. Germany EAC Engineers in Germany were quick to point out that the gradation of the aggregate (e.g., maximum aggregate size, gap-graded) is important in achieving proper texture. The exposed aggregate layer typically is gap-graded with an 8-mm maximum aggregate size. The delegation inquired about any requirements on the shape of the aggregate and was informed that a certain shape is desired for the sake of workability and strength. The shape is measured using an index popular in Europe. The German hosts also were keenly aware of another measure of aggregate quality—PSV, or polished stone value. No demands on the type of aggregate used in EAC were men- tioned (outside of prevalent alkali–silica reaction concerns). Although the delegation was interested in the use of lower- quality aggregates and less cement content in the lower layer of a two-layer PCC pavement, the German hosts were unable to discuss this topic at length, because conservative German design and theory have prevented contractors from attempt- ing these kinds of “risky” lower layers. Both the top layer and lower layer of a two-layer PCC pavement in Germany use Type I cement, with slightly different cement contents and admixtures in each layer. The top layer uses superplasticizers for workability, whereas the lower layer uses none, to keep the mix relatively stiff for placement using two paving machines (for more information, see the A6 construction case study). It also should be noted that fly ash is not used in Germany and Austria. Although air entrainment and plasticizers are added to the top layer of EAC mixes, conventional wisdom in Germany is that fly ash is not necessarily helpful. Austria EAC In surveying pavement sections along the A1 motorway in Austria, the delegation noted that the EAC pavements that featured a particular dark aggregate appeared to be in excel- lent condition, given their age and the volume of traffic they had received. This aggregate was said to be diabase (also known as dolerite), which is an igneous rock that is similar in composition to basalt. A hand specimen of this aggregate is shown in Figure 3.4. The pavement experts in Austria were as adamant as their counterparts in Germany about the need for high-quality construction and high-quality aggregates to make a success- ful, durable two-layer EAC pavement. Typical mixes for the top layer use a gap-graded aggregate (30% of 0/1 mm, 70% of 4/8 mm). The aggregate for the 4/8-mm size is fairly cubical and is expected to be very durable.

15Austrian attitudes toward fly ash were similar to those in Germany. The Austrian hosts cited three main reasons for the lack of fly ash in Austria and Germany: 1) cement industry interests, 2) suspicion that fly ash may harm durability and make pavement more susceptible to freeze–thaw damage, and 3) fly ash quality is producer dependent. The Austrians prefer slag to fly ash, and they use as much as 32% slag in their PCC mixes. The PCC mix for the top layer is designed to have a higher strength content for the top lift, which ensures that smaller aggregates will stay in the cement paste–aggregate matrix, thereby creating a durable surface. The top layer has a water/cement ratio of 0.38 for the top lift and 0.41 to 0.42 for the bottom layer. Construction of EAC and Two-Layer Concrete Pavement Construction practices for two-lift PCC-over-PCC and EAC have varied during the past decade. At one time, the two-layer PCC pavement was placed at once using one slipform paver; however, this method has been replaced by a train of multiple, independent paving machines. In addition, there have been numerous innovations in the brushing techniques and the curing compounds and retardants used before and after the brushing process. The R21 delegation was able to spend a great deal of time on-site to observe the construction of two-layer EAC pavement, and a case study is appended to this section illustrating a construction project along the A6 motorway near Amberg, Germany. Netherlands On the basis of full-scale EAC test sections constructed along N279, Dutch engineers recommend texture depth of no more than 1.8 mm. The use of super-smoother in the paving process is recommended to help in noise reduction, although it is noted that super-smoother can further embed the aggre- gate near the surface and contribute to a loss of texture depth after brushing. Finally, because the layered construction had no influence on performance in terms of noise or friction, researchers in the Netherlands recommend that the cost of construction and selection of materials be left to the contrac- tor, provided certain performance measures are achieved (3). The delegation’s hosts in the Netherlands stressed the importance of having a technician carrying out quality-control checks for texture depth (using the sand patch test) at all times. They also emphasized the need for a knowledgeable contractor who understands when to initiate brushing. In addition, the Dutch find highly variable work for certain contractors and thus emphasize the need to know the contractor and the con- sistency of that contractor’s work, as consistency of texture is very important for successful EAC. Finally, given their experi-ence with testing several surface treatment compounds, the Dutch emphasize the careful selection of the retarding agent and curing compound used in the EAC process. Austria The delegation’s Austrian hosts stressed the need for two sep- arate paving machines in two-layer PCC construction to ensure consistent thickness of the layers. They also pointed to the dangers of vibrators and to the minimization of vibration to prevent the high-quality aggregates needed in the top layer from being dispersed into the lower layer. Overall, the Aus- trian researchers stated that two-layer PCC pavement pro- vides similar structural performance as an equivalently thick single layer at the same price, with the additional benefits of improved skid resistance and noise reduction due to the high- quality top layer. Austria has a great deal of experience with the recycling of concrete pavements. In the late 1980s, Austria undertook the long process of recycling PCC pavements that were more than 30 years old along the A1 motorway into new two-layer PCC pavements. This experience has led Austrian researchers to claim that the recycling concept is “an important innova- tion that is both economically and environmentally advanta- geous” (14). The R21 delegation was able to visit some of these recycled PCC pavements (featuring EAC texture) along A1 in Austria, and more details are provided in the case studies section of this report. As a result of their decades of experience with EAC, Aus- trian pavement engineers have gained considerable insight on the texturing process and the tests needed to evaluate texture (10, 15). The texture depth measurement that results from a sand patch test has been closely scrutinized in Austria. Assum- ing a maximum aggregate size of 8 mm, Austrian engineers recommend a narrow range of 0.8 to 1.0 mm. A texture depth below 0.8 mm will not provide adequately reduced noise; on the other hand, if texture depth is above 1.0 mm (with a max- imum aggregate size of 8 mm), the aggregate will become dis- lodged from the mortar either during the initial EAC brushing or later, when the pavement experiences traffic. Austria uses an additional metric for EAC texturing beyond the sand patch test. This additional test is the profile point test, which is a 5 cm × 5 cm test patch of texture. Within this patch, the pavement is required to have a certain number of visible aggregates, or “profile points.” Austrian researchers recommend a profile point count for a 25 cm2 test patch of approximately 60 for an 8-mm maximum aggregate size, and approximately 45 for an 11-mm maximum aggregate size (10). The aim of the profile point test is to ensure an optimal number of exposed aggregates so that the passing tire is mostly in contact with the aggregate tips, thereby allowing sufficient space between the tire and the mortar for drainage.

16A profile point count that is too high describes a surface that will not allow sufficient drainage between aggregates, and a low profile point count would allow the tire to contact too much of the mortar, resulting in a very noisy surface. Germany Much of the discussion about two-layer PCC construction with the delegation’s German hosts concerned the equipment used to construct two-layer pavements. In preparation for a survey of the construction site along the A6 motorway, Dr. Walter Fleischer of Heilit+Woerner GmbH in Munich detailed the equipment that his firm developed for two-layer construction. An important point for EAC texture discussed with the German pavement engineers is that, although there are sev- eral qualified contractors in Germany for the construction of PCC pavements (including two-layer PCC composites), there are only two contractors at this time capable of EAC texture (Ruboco and Heilit+Woerner). More details on the EAC tex- turing process are provided in the A6 construction case study. The delegation also discussed curing techniques for PCC pavements and learned that plastic sheeting has been aban- doned entirely by German and Austrian engineers because of the expense and unreliability in protecting the pavement dur- ing early age (first 72 hours). In the experience of both coun- tries, the plastic sheeting increases the heat of hydration, makes joint saw cutting difficult, and creates pockets of inconsistent moisture levels at the surface. Furthermore, the plastic cannot be reused and may embed itself locally in cured PCC. In short, plastic sheeting is viewed as expensive and dif- ficult to maintain (air bubbles between the sheet and the PCC create problems), and its only advantage is its resistance to effects from rain, should foul weather occur. Instead of plas- tic sheeting, curing compounds are applied immediately after placement, and water curing is used if possible and required. If exposed aggregate is constructed, a combination curing/ retarding compound is sprayed, and after the surface is brushed to achieve the texture, a curing compound is again applied as a precautionary measure. Construction Case Study: A6, Near Amberg, Germany As noted in Chapter 2, at the time of the R21 delegation’s visit, the A6 motorway in Germany was in the process of con- struction that would connect the two halves of A6, thereby allowing the roadway to run uninterrupted across Germany. The A6 construction project involved 21 km of two traffic lanes in each direction. The project was entirely EAC/PCC with exposed aggregate surfacing (or waschbeton, as it is known in German). Work began on the project in March 2004, and it was completed in September 2008.The project’s design specified a two-layer PCC pavement, with the layers constructed as “wet-on-wet,” or immediately after one another. Particulars of the design included the following: • PCC top: 5-cm PCC with crushed granite gap-graded (2/8 mm) with maximum aggregate size of 8 mm, 430 kg/m2, air content 5%, water/cement ratio 0.45. • PCC bottom: 25-cm PCC with river gravel, 350 kg/m2, air content 4%, water/cement ratio 0.4. • Base: 30-cm unbound aggregate (type and gradation unknown). • Subbase: 25-cm unbound local aggregate extracted from excavation for roadway and crushed on site; layer acts as a frost blanket. • Subgrade: Type unknown (delegation guess is class A-2), treated with cement to achieve modulus of 45 MPa. • Slab dimensions: Shoulder width 2.5 m; inner slab width 4.75 m; outer slab width 4.25 m. • Joints: 5 m between transverse joints; transverse and lon- gitudinal joints use bituminous hot seal; dowels are 25 mm in diameter, 50 cm in length; tiebars are 20 mm in diameter, 80 cm in length. On the day the R21 delegation visited the A6 construction site (May 13, 2008), the temperature was 26°C (78.8°F), and conditions were sunny and slightly windy. In part because of the weather, the site manager expected that more than 800 m of new two-layer PCC pavement would be placed and textured in the exposed aggregate style that day, well over the daily aver- age of 700 m per day. En route to the paving site, the delegation was impressed with the organization of the construction site. In addition to the meticulous subgrade, base, and drainage preparations under way (Figures 3.5 and 3.6), the contractor was able to take advantage of aggregates found on site during the process of excavating to clear for the roadway. These aggregates were crushed on site and used in the frost blanket subbase of the pavements. The two-layer PCC slab is placed with a train of three machines with an estimated total value of approximately 3 mil- lion euros. Each of the paving machines can be transported to and from the site in an International Organization for Stan- dardization (ISO) marine container. In addition, the pavers are modular and can accept several attachments, including a super-smoother, automated dowel inserter, or spray arm. The entire paving operation, including dump-truck opera- tors, crane-arm loader, spray tank, and other miscellaneous equipment, appeared to be working smoothly under the efforts of approximately 25 crew workers. The delegation noticed that a tanker truck directly in front of the first paver was liberally spraying the base layer in front

17Figure 3.5. Left: Site cleared for two lanes in each direction. Right: Stabilizing the subgrade with cementitious compound.Figure 3.6. Left: Frequent spraying of base layer in front of the first paver minimizes moisture loss in the lower layer of PCC to base. Right: Prepared, stabilized subgrade awaits frost blanket aggregate layer.

18of the slab with water (Figure 3.6). This practice saturates the base layer and minimizes the amount of moisture in the PCC lost to the base layer. The mix for the lower layer is dumped immediately in front of the first paving machine. The first paver in the paving train forms the lower layer of the two- layer PCC pavement (Figure 3.7). The delegation took partic- ular notice that string lines were established on both sides of the slab to guide the paving machines. It is apparent from the bottom photo in Figure 3.7 that the PCC mix being placed is stiff. This photo and Figure 3.8 show the use of an automated dowel inserter, which is attached to the back of the first paver. Two crew workers were required to insert the tiebars at regular intervals using a specialized tiebar inserter. The inset in Figure 3.8 is a comparison of the tiebar and dowel used in the pavement. The dowels were 25 mm inFigure 3.7. Front (top) and rear (bottom) views of the first paving machine, responsible for the lower of two PCC layers.Figure 3.8. Close-up of the rear of the first paving machine, which has an automated dowel inserter attachment. Inset: A tiebar and a dowel.diameter and 50 cm in length, while the tiebars were 20 mm in diameter and 80 cm in length. The next paving machine in line formed the top layer of the two-layer slab. This second paver was equipped with a super- smoother attachment. Front and rear views of the second paver are provided in Figure 3.9. The mix for the top layer of concrete was placed between the first and second pavers using a crane-arm loader. Dump trucks with the mix for the top layer positioned themselves parallel to and very near the slab so that the crane-arm oper- ator could lift the mix from the bed of the truck easily and place it directly in front of the second paver. This process is shown in Figure 3.10. The third and final machine, while technically capable of being a paving machine, was a finishing platform (Figure 3.11). The platform allows for last-minute finishing touches to be applied to the slab before it is sprayed with a curing compound and retarding agent. The finishing platform has a spray arm attached to accommodate spraying. The slabs were sprayed with a compound specifically designed to accommodate EAC texturing (Figure 3.12). This compound is a combination of curing compound and retard- ing agent, and the particular compound used on-site was man- ufactured by the Austrian company TAL. The retarding agent in the compound slows the hydration process in the mortar near the surface and prevents it from adequately bonding with the aggregates. This allows for the mortar to be brushed easily from the surface during the EAC texturing process. In addition to quality construction, the slab and mixes are regularly tested to ensure quality concrete. Hourly air content tests are conducted on both mixes, and strength cubes on both

19Figure 3.9. Front (top) and rear (bottom) views of the second paving machine, responsible for the upper of two PCC layers. Note the use of a super-smoother at the rear of the machine.mixes are conducted at least once per day. Cores are taken once per 1,000 m2 of paving. The cross-section in Figure 3.13 illustrates the result of a properly constructed two-layer PCC pavement: the high-quality, smaller aggregates in the top layer are segregated from the low-quality, larger aggregates in the lower layer. In discussing successful EAC texturing, the delegation’s hosts continually stressed two factors: quality construction and qual- ity aggregates. The final observation of the R21 delegation dur- ing its tour of the A6 construction site, then, was to observe the quality construction of an EAC texture. Although paving for the day began at 0800, brushing on this particular day did not begin until 1630. This falls in line with German experience, wherein brushing is said to begin anywhere between 7 and 20 hours after paving. Figure 3.14 shows the brushing equipment.From the discussions of the EAC texturing process with experts in Austria and Germany, the delegation was given the impression that the EAC process is very much operator dependent. The experience at A6 confirmed this. To determine when to begin brushing, the brush operator would hand broom sections at 10-m intervals every hour (Figure 3.15). This process allowed the operator to observe if the aggregate was moving in the mortar, if the aggregate resisted the broom and stayed embedded in the mortar, if the mortar was drying, how quickly the mortar was drying, and so forth. Once the hand-broom test indicated that the surface was ready for texturing, the operator would brush approximately 20 to 30 linear meters of a slab at a time using a small grader mounted with a large, machine-driven, steel-bristled, cylin- drical brush rotating clockwise (Figures 3.15 and 3.16). After completely brushing 20 linear meters of slab, the oper- ator would conduct more hand brushing tests in the regions that had been brushed once and in the 20 m beyond that region. Eventually, the operator would make a second pass over the original 20 m to achieve the desired texture (Figure 3.17). The process appeared to remove approximately 5 mm of mortar (Figure 3.18). Shortly after the second pass, a tractor equipped with a sprayer passes over the slab and applies a curing compound (the R21 delegation did not observe this step). Testing for the appropriate texture involves a sand patch test conducted four times per day on the first day of paving and once per day thereafter. These standards are less strict than elsewhere; in Austria and the Netherlands, frequent sand patch testing is conducted behind the operator to check for consistency of texture. In this particular case, the site manager chose to forgo this quality control check on this site, given the expertise of the brush operator. The EAC brushing is done to obtain a texture depth of 0.6 to 0.8 mm, though currently Germany has no regulations about texture depth. New specifications in development will require a texture depth of 0.6 to 1.1 mm. The R21 delegation did not observe joint saw cutting, but the site manager indicated that it follows brushing by approx- imately 2 to 5 hours, though these estimates are highly depen- dent on ambient conditions. Having observed the construction of the pavement from subgrade to texture, the delegation was able to view a few examples of a finished pavement awaiting lane markings, shown in Figure 3.19. Overall, the delegation learned much from the construction techniques on display. In addition to the observations already noted, the delegation noticed a lack of anecdotes about paving in subprime weather (rainy, for instance) when discussing previous projects with the contractor. In this sense, the dele- gation had the impression that our hosts were “fair-weather pavers,” in that they insisted on optimal conditions for paving.

20Figure 3.10. Use of loader to place top layer mix between lower- and top-layer paving machines. (a) (b) (c) (d)Figure 3.11. Left: Front view of the final machine in the paving train, the finishing machine. Right: A close-up of last-second touch-ups as the finishing machine continues along.

21Figure 3.12. Left: Rear view of the finishing machine with spray arm attachment. Right: View of placed two-layer PCC slab with combination curing compound and retardant sprayed on surface.Although it may be an incorrect assumption, it would explain in part the outstanding condition of many PCC pavements that were more than 20 years old encountered on the way to the A6 construction site. In addition to touring the paving, the delegation also visited the batching plant for the pavement construction (Figures 3.20Figure 3.13. Cross-section of completed two-layer PCC pavement. Smaller aggregates are in the top layer, and larger aggregates are in the lower layer.and 3.21). The batching plant on this day was located 3 km from the paving site. As with the paving machines, the batching plant was modular and portable and could be assembled from the contents of 13 ISO marine containers. The plant is designed for the construction of two-layer PCC pavements, and as a result, it batches both layer mixes simul- taneously in an organized fashion. It is as simple as one side of the plant being responsible for the upper-layer mix and its constituents, while the other side handles the lower-layer mix. The batching plant is able to supply trucks continuously with mix for the pavers. The minimum mix time for the upper layer was 60 seconds, and the minimum mix time for the lower layer was 45 seconds. The delegation noted a steady stream of trucks passing through the batching plant with no discernible delays or problems. Part of this efficiency resulted from preparation, as illustrated in Figure 3.22. Pavement Design and Condition Case Studies The following sections discuss the various two-layer PCC pavements reviewed by the R21 delegation in the Nether- lands, Germany, and Austria. These pavements contain a variety of interesting features, including EAC texturing. N279, Near Veghel, Netherlands The N279 sections were constructed in 2000 and currently are subjected to an average of 25,000 vehicles per day, 30% of which are commercial truck traffic. The sections originally were asphalt but were replaced with two-layer PCC to inves- tigate various exposed aggregate surfaces. Photos of some of these sections are shown in Figure 3.23.

22Figure 3.14. Left: A small grader with wire brush attachment for EAC texturing. Right: A close-up of wire bristles on brush.Two-layer construction was done with EAC as the top layer. The following was the design of this project: • 9 cm for top layer. This is crushed aggregate. A minimum thickness of 9 cm is required for production and construc- tion purposes (Figure 3.24). • 18 cm as lower-layer PCC (this can be varied for design). This aggregate does not need to be crushed. Separation of the wet- on-wet layers over time has never been observed. Photos of the 4/22-mm section in May 2008 are shown in Figures 3.25 and 3.26. The transverse joint is narrow and not sealed. The experimental features of this test site included the following (see Figure 3.24 for photos of four specific EAC surfaces):• Two aggregate types  Quartzite crushed  Dutch crushed gravel • Two gap-graded mixtures with 0/2 mm sand  4/8 mm (fine gradation)  11/16 mm (coarse gradation) Texture depth (sand patch method) varied from 1.1 to 1.8 mm for the 11/16-mm aggregate; the other textures were 1.8 mm. A new product was used that combined a retarding agent and a curing compound. This eliminated the need for plastic sheeting used before this. After 12 to 24 hours, the sur- face was subjected to steel wire brushing, which removed the surface mortar and exposed the surface aggregates to a desired texture depth, as stated previously. After brushing, the surfaceFigure 3.15. Left: Brush operator conducts hand brushing tests at regular intervals to determine when to initiate brushing. Right: First of two passes with brush to develop EAC texture.

23Figure 3.16. EAC texture after first pass of brush is shown in left half of photo. Unbrushed surface with compound still visible is shown in right half of photo.was then sprayed with a curing compound to complete the curing of the surface. They also used and recommended the super-smoother, which removed small surface unevenness, improving smoothness and reducing pavement/tire noise level. The full-scale sections of EAC on the N279 (Figures 3.27 and 3.28) resulted in valuable information regarding their construction and performance: • A maximum texture depth of 1.8 mm is recommended for these mixtures. • The smaller gradations of exposed aggregate types are preferred for reduced noise levels. • The fine quartzite aggregate with 5/8-mm gradation pro- duced the lowest noise for both cars and trucks. • The quartzite aggregate had better friction than the Dutch crushed gravel. • The friction level of EAC is comparable to that of brushed concrete (tined). • Use of a super-smoother behind the slipform paver leads to a lesser texture depth and has a positive effect on the noise level. • The noise level of one- and two-layer pavements with sim- ilar aggregates is comparable. A93, Between Brannenburg and Kiefersfelden, Germany The R21 delegation visited numerous pavement sections along A93 between Brannenburg and Kiefersfelden, Germany. The A93 motorway connects Munich to Innsbruck and is heavily trafficked, because it is considered a main connector to Italy. No specific average daily traffic figures were available, but theFigure 3.17. Top: Brush operator conducts more hand brushing tests at regular intervals to determine when to initiate second pass with brush. Bottom: Final of two passes with brush to complete EAC texture.Figure 3.18. Close-up of finished EAC texture on sections constructed on A6.

24Figure 3.19. Left: Finished two-layer EAC pavement. Right: Bituminous seal used for both longitudinal and transverse joints.delegation noted that traffic volume seemed particularly high during the surveys, and truck traffic seemed especially frequent. The A93 sections (except where indicated) are two-layer PCC/PCC originally constructed in 1995 or 1996. Their orig- inal design was (to the best of the knowledge of the delega- tion’s host for that day): • PCC top: 7-cm PCC with crushed quality aggregate and higher cement content than that of the bottom. • PCC bottom: 19-cm PCC with recycled PCC aggregate. • Base: Unknown, most likely 10- to 15-cm asphalt, 15- to 25-cm concrete-treated base (CTB), or 25+-cm crushed aggregate. • Subbase: Unknown; depending on base type, would be any- where from 30 to 50 cm of aggregate to provide required frost protection.• Slab dimensions: Unknown, though driving and passing slabs were of unequal widths, and the total width of both slabs was said to be 11 m. • Joints: 5 m between transverse joints; transverse and lon- gitudinal doweled joints use bituminous hot seal. In addition, all sections originally were textured with a longitudinal burlap drag, with the exception of a few sec- tions that acted as test sites for the use of longitudinal tin- ing or EAC. The delegation visited the A93 sections to investigate the various methods of texture rehabilitation used on these two-layer pavements. Many of the pavements had texture problems soon after construction. The delegation’s host has several hypotheses for these difficulties. Some sections (designated E through K in the following subsections) hadFigure 3.20. The concrete batching plant located near the A6 construction site is specifically designed for placement of two-layer PCC pavement.

25Figure 3.21. Top: Aggregate bins are double sided to accommodate aggregates for top-layer and lower-layer batches. Bottom left and right: Sand (0/2 mm) and crushed granite (4/8 mm) used as aggregates in the gap-graded, top-layer mix.degraded texture resulting from rain after placement. The main hypothesis was mortar difficulties: miscellaneous sand problems (sand is too calcite), high water/cement ratio, etc. The delegation’s observations agreed with the possibility of problems in the mortar. Following is a brief review of the pavement sections visited and any interesting details related to these sections. Note that these discussions assume unofficial section labels, for ease of discussion.Section A, Longitudinal Burlap Drag (Original Design), km 1.490–1.910 Section A was the first of many sections surveyed along A93 to illustrate polishing or wear in mortar. The shoulder was tex- tured, along with the remainder of the pavement, which revealed a nontrafficked version of the texturing (holds for all sections). In this particular case, the polishing of the longitudi- nal burlap drag was severe (Figure 3.29).

26Figure 3.22. Plates on the dash of all trucks (left) allowed the batch plant manager to deliver appropriate layer mixes quickly and efficiently.As discussed earlier in this report, Germany has more than 20 years of experience with longitudinal burlap drag, and during 15 of those years burlap texturing was the stan- dard for German pavements. Approximately 4 years ago, after years of observation, German pavement engineers concluded that burlap dramatically loses its noise reduc- tion and skid resistance after approximately 5 years, result- ing mostly from accelerated wearing of the burlap texture. The pavement shown in Figure 3.30 has received far more than 5 years of traffic, and it illustrates this wearing of the burlap texture into a highly polished surface that is both noisy and dangerous.Section B, Longitudinal Wide Tining (“American”), km 1.910–2.070, and Section C, Longitudinal Narrow Tining (“Spanish”), km 2.070–3.335 Sections B and C were the only sections along A93 originally constructed without the burlap drag texturing. These sections were textured with longitudinal tining in either a so-called American style or Spanish style. The only difference between the two styles seemed to be that the American style was slightly wider and the Spanish style was shallower (Figure 3.31). The tines were attached to the paver and, as a result, the stopping and starting of the paving train allowed the tines to settle intoFigure 3.23. Full-scale EAC test sections along N279 near Veghel, Netherlands.

27Figure 3.24. Different textures used in N279 test sections (top left, quartzite 11/16 mm; top right, quartzite 5/8 mm; bottom left, quartzite 5/8 mm; bottom right, Dutch gravel 4/8 mm).

28Figure 3.25. The 4/22-mm sections along N279 in the Netherlands.Figure 3.26. The texturing on the 4/22-mm sections along N279 in the Netherlands. Figure 3.27. A 5/8-mm section along N279 in the Netherlands.

29Figure 3.28. Texturing on a 5/8-mm section along N279 in the Netherlands.the pavement and create inconsistent, “wavy” depth. The tex- ture depth from the tines generally was shallower than the lon- gitudinal tining applied in the United States. Section G, Rehabilitated with Grooved Texturing, km 5.600–5.700, and Section K, Rehabilitated with Fine Diamond Grind, km 5.900–5.950 The construction on Sections G and K was marred by frequent rain. As a result, the original burlap texture wore quickly and had to be rehabilitated in 1999. Section G was rehabilitated with a grooved texture that has been applied in the United States. The grooved texture typically is used to eliminate hydroplaning and normally is applied on airfield pavements.Figure 3.29. Original burlap drag on A93, Section A (km 1.490–1.910).Figure 3.30. Significant polishing of burlap drag after 13 years of traffic on A93, Section A (km 1.490–1.910).Figure 3.31. Top: Longitudinal tining known as “American comb” (km 1.910–2.070). Bottom: “Spanish comb” (km 2.070–3.335).

30Figure 3.32. Left: Grooved texture on section along A93 (km 5.600–5.700). Right: Diamond-ground texture on another section of A93 (km 5.900–5.950).Although diamond grinding is not typically done in Europe because of the expense of the process, Germany has good experience with diamond grinds when they are used. While the grooved Section G looked to have its texture in good con- dition, the finely ground Section K had worn almost com- pletely in the wheelpath (Figure 3.32). Section M, Exposed Aggregate Concrete Pavement, km 7.440–8.600 Section M originally was constructed in 1995 and 1996 using an EAC texture. The aggregate gradation for the pavement was a continuous 0/8 mm. The delegation’s hosts for the A93 sur- vey did not know the aggregate in the top layer but claimed that it looked similar to the quartzite used in other EAC proj-ects on which they had worked. The delegation observed slight polishing (relative to the shoulder, which was also tex- tured), but overall the pavement looked to be in outstanding condition, given both its age and the amount of traffic it receives (Figure 3.33). The skid resistance measures for the pavement were said to be as good as they were shortly after construction. Section N, SMA Overlay, km 8.600–11.000 To rehabilitate the surface of Section N, a 3-cm layer of SMA was overlaid atop the original total 26-cm two-layer PCC pave- ment in 1995 and 1996. The SMA was a gap-graded mix with a maximum aggregate size of 8 mm. The SMA was paved in two 5.5-m passes over the PCC because of width restrictions on theFigure 3.33. Exposed aggregate section and texture (km 7.440–8.600).

31paver. The SMA-over-PCC was sawed and sealed over the PCC transverse joints and on longitudinal joints between the paving passes (and not over the longitudinal joints between the PCC slabs). The saw and seal work looked outstanding and of very high quality. The longitudinal joints between PCC slabs had propagated up through the SMA, between both the inner/outer slabs and the inner/shoulder slabs. The only significant mainte- nance conducted was placing a few patches at transverse joints where the SMA must have debonded from the PCC surface and cracked. These rectangular repairs can be seen in Figure 3.34. Section P, SMA Overlay, km 12.500–22.780 Section P originally had the same design as Section N (3-cm SMA over 26-cm two-layer PCC). However, because of reflec-Figure 3.34. Top: SMA over PCC in Section N (km 8.600–11.000). Bottom: Sections similar to Section N were reclaimed for EAC/PCC in new Section P (km 12.500–22.780).tive cracking in the SMA and a poor bond between the SMA and PCC layers, the old pavement was completely reclaimed in 2004 and used for the new Section P. The design of the reconstructed Section P is as follows: • PCC top: 5-cm PCC with crushed quality, gap-graded aggre- gate and higher cement content than that of the bottom. • PCC bottom: 21-cm PCC with recycled PCC aggregate from top and lower lifts of previous pavement. • Base: Crushed aggregate base of unknown thickness con- taining recycled SMA from previous pavement. • Subbase: Unknown composition and thickness. • Slab dimensions: Unknown, though driving and passing slabs were of unequal widths, and the total width of both slabs was said to be 11 m. • Joints: 5 m between transverse joints; transverse and lon- gitudinal joints use bituminous hot seal. The two-layer PCC pavement was finished with EAC tex- turing, as depicted in Figure 3.35. An interesting point about Section P’s reuse of the previ- ous pavement is that the previous pavement itself used re- cycled PCC aggregate in the lower of its two PCC layers. The recycling of concrete pavements has been common in Europe since the 1980s for several reasons, including the scarcity and expense of aggregates and the difficulties and cost of dump- ing old pavement material. In the late 1980s, Austria under- took the long process of recycling PCC pavements more than 30 years old (some with SMA overlays, as in Section P) into new two-layer PCC pavements. This experience has led Aus- trian researchers to claim that the recycling concept is “an important innovation that is both economically and environ- mentally advantageous” (14). A99, Near Ottobrunn, Germany The R21 delegation made a brief stop at a whitetopping proj- ect, the first of its kind in Germany, at an off-ramp for the A99 motorway near Ottobrunn. Although whitetopping is not relevant to R21, the project was notable for the R21 team because the panels used in the A99 project combined an EAC texture with a PCC mix design that included polypropylene fiber reinforcement (Figures 3.36 and 3.37). The panels in the A99 project were 14 cm thick and had dimensions of 2.6 m by 2.6 m. The PCC mix had a maximum aggregate size of 11 mm with gap-grading of 0/2 mm, 5/8 mm, and 8/11 mm. A1, Near Eugendorf, Austria The section at Eugendorf is a reconstructed two-layer PCC pavement with exposed aggregate texturing (Figures 3.38

32Figure 3.35. Texture close-ups in EAC sections and close-up of bituminous seal used on both transverse and longitudinal joints on A93 Section P (km 12.500–22.780).and 3.39). The original PCC pavement was recycled into the lower lift of the reconstructed pavement in 1993 and 1994. Particulars of the pavement design include the following: • PCC top: 4-cm PCC with diabase aggregate of maximum aggregate size 8 mm (gap-graded 0/8 mm). • PCC bottom: 21-cm PCC with recycled PCC aggregates of maximum aggregate size 32 mm. • Base: 5-cm asphalt. • Subbase: 25-cm cement-stabilized aggregate. • Slab dimensions: 3.75 m-wide driving-lane slab, 3.75 m- wide passing-lane slab, 3 m-wide shoulder; 5.5 m-long slabs. • Joints: 5.5 m between transverse joints; transverse and lon- gitudinal joints use preformed rubber seal with no bitumi- nous hot seal.In general, the Eugendorf section appeared to be in very good condition, given that the section has been exposed to heavy traffic (average daily traffic of 56,000, with 12% trucks) and 6 full months per year of metal snow plows and salting for 14 years. In addition, the pavement had to endure studded tires for 10 years. These conditions resulted in slight wear in the wheelpath, as shown in Figure 3.40. In the figure, the worn wheelpaths are lighter than the surrounding darker, lesser- trafficked portions of the driving lane. The noise level of the pavement was observed to be louder than expected (all observations are by ear and are not based on conclusive measurements) but still quieter than German sections because of the lack of a bituminous hot seal at the transverse joint that typically created a regular, faulting-like noise in the German sections. One likely explanation for the increase in noise is the presence of studded tires, which do notFigure 3.36. Left: Finished whitetopped ramp along A99. Right: A handful of polypropylene fibers included in PCC for the A99 project.

33Figure 3.37. Left: Close-up of the interesting combination of EAC and fiber reinforcement, which creates a “fuzzy” appearance. Right: One of the challenges of using fibers in PCC is the so-called clumping, made more visible in the A99 panels because of EAC.polish the pavement in the wheelpath so much as they roughen the texture and remove mortar. The Austrian hosts noted that studded tires in fact help the upkeep of the skid-resistance numbers, though they are a major contributor to a loss in noise reduction. The section showed very few distresses, and those that were apparent did not appear to be indicators of chronic problems in the pavement. The delegation’s host for this particular sec- tion oversaw the reconstruction of the section in 1993 and 1994 and relayed stories about early difficulties in the reuse of old PCC pavement in the lower PCC layer of the new two- layer PCC pavement. These stories only emphasized that Austria has two full decades of experience in the full-depth reclamation of old PCC into new two-layer PCC pavements,and as such Austria has many lessons to offer the United States as it works toward sustainable composite pavements. Furthermore, A1 near Eugendorf is an example that EAC texturing under extreme conditions can hold up for at least 14 years without any need for major rehabilitation. A1, Near Regau, Austria The section along A1 near Regau was included to provide an idea of the design and composition of the old two-layer PCC pavement that preceded the reconstructed sections along A1 being visited by the delegation. This section is shown in Figure 3.41 with the driving lane resurfaced with a thin asphalt layer. The passing lane shows the original PCC surface.Figure 3.38. Left: Traveling along the A1 motorway. Right: View of the Eugendorf section.

34Figure 3.39. The exposed aggregate texturing on the Eugendorf section.This section near Regau was interesting in that it had trans- verse joint spacing of 12.5 m, resulting in numerous mid-slab transverse cracking in the section slabs. The Regau two-layer section was constructed between 1963 and 1966. Its upper PCC layer is 6 cm thick with a maximum aggregate size of 22 mm, and the lower PCC layer is 16 cm thick with a maxi- mum aggregate size of 32 mm. A1, Near Vorchdorf, Austria The section at Vorchdorf is a reconstructed two-layer PCC pavement with exposed aggregate texturing (Figure 3.42). The original PCC pavement was recycled into the lower lift of the reconstructed pavement in 1999.Figure 3.40. The section at Eugendorf exhibited slight wear in the wheelpaths of the driving lane, resulting mainly from 14 years of regular salting and plowing and 10 years of studded tires.Figure 3.41. The old two-layer PCC Regau section, built in the 1960s, has a thin asphalt surface placed on the driving lane. The passing lane has the original concrete surface, which is more than 42 years old.The pavement design is similar to that of the Eugendorf section: • PCC top: 5-cm PCC with crushed gravel aggregate of max- imum aggregate size 11 mm (gap-graded 0/11 mm). • PCC bottom: 21-cm PCC with recycled PCC aggregates of maximum aggregate size 32 mm. • Base: 5-cm asphalt. • Subbase: 20-cm cement-stabilized aggregate. • Slab dimensions: 3.75-m-wide driving lane slab, 3.75-m- wide passing lane slab, 3-m-wide shoulder; 5.5-m-long slabs. • Joints: 5.5 m between transverse joints; transverse and longi- tudinal joints use preformed rubber seal with no bituminous hot seal.Figure 3.42. Traffic on the Vorchdorf section of the A1 motorway.

35The delegation observed that the condition of the pave- ment was worse than that of the Eugendorf sections, which were constructed 4 years before the Vorchdorf sections. Although there were no chronic distresses and the overall condition was relatively sound, the pavement exhibited noticeable polishing of aggregates in the wheelpath of the driving lane (Figure 3.43). As a result, the Vorchdorf sections were noisy. Given the similarities in traffic and design, the difference in performance was observed to be one of materials. An inspec- tion of the aggregates clearly indicated that the two pave- ments do not have the same aggregate in their upper layers: where the Eugendorf sections have the highly durable diabase, the Vorchdorf sections use a less-durable, locally available river gravel (Figure 3.44). The severity of polishing in the Vorchdorf sections made obvious the need for high-quality aggregates in the top layer, if EAC is to be applied. Along with notes on construction techniques, this was one of the more valuable lessons to be exported to the United States. In addition to lessons on pol- ishing and aggregates, the Vorchdorf sections had an un- textured shoulder, so the delegation was able to develop a feel for the relatively small amount of mortar that is removed in the EAC brushing process. The unbrushed shoulder also was encountered later on the Traun sections. A1, Near Traun, Austria The final sections reviewed along A1 were near the inter- section of A1 and A25 (Figure 3.45). These sections were reconstructed in 1994. The sections located after the merger of the two motorways receive slightly more than 100,000 vehicles per day. The design of the sections is similar to Eugendorf and Vorchdorf:Figure 3.43. The Vorchdorf sections showed noticeable polishing in the wheelpaths despite being only 9 years old.Figure 3.44. Exposed aggregate texture on the Vorchdorf section reveals top-layer use of crushed gravel with a maximum aggregate size of 11 mm.• PCC top: 5-cm PCC with diabase aggregate of maximum aggregate size 11 mm (gap-graded 0/11 mm). • PCC bottom: 20-cm PCC with recycled PCC aggregates of maximum aggregate size 32 mm. • Base: 5-cm asphalt. • Subbase: 25-cm cement-stabilized aggregate. • Slab dimensions: 3.75-m-wide driving lane slab, 3.75-m- wide passing lane slab, 3-m-wide shoulder; 5.5-m-long slabs. • Joints: 5.5 m between transverse joints; transverse and lon- gitudinal joints use preformed rubber seal with no bitumi- nous hot seal.Figure 3.45. View of the Traun section along A1. Note the lack of texture on the shoulder.

36Figure 3.46. Left: Unbrushed shoulder from a section along A1 near Traun, Austria. Right: EAC textured pavement from another section of A1.The condition of the Traun sections was very good. The pavement sections examined by the delegation showed no dis- tresses. Little polishing was observed in the wheelpath, an impressive observation given the age of the pavement and the conditions it experiences. The noise level was loud, but noise was difficult for the delegation to judge given the high volume of traffic experienced while reviewing the sections. It should be noted that the top layer used diabase, and the high-quality aggregate seemed to be performing well after 14 years of high- volume traffic. The Traun sections were again evidence that, provided that quality construction techniques are present, aggregate quality in the top lift is the second most important factor in an effective two-layer EAC pavement. The Traun sections had an unbrushed and untextured shoulder, so the delegation was able to develop a feel for the relatively small amount of mortar that is removed in the EAC brushing process. Figure 3.46 illustrates the significant tex- ture generated simply by removing mortar from the surface within anywhere between 7 and 20 hours of paving. Success Factors for Two-Layer EAC Composite PCC Pavements The R21 delegation left its tour of Europe impressed with the number and quality of two-layer PCC pavements visited. Furthermore, the delegation saw in EAC a potentially benefi- cial surfacing for American pavements. EAC texture currently is the surfacing used for bare concrete pavements in the three countries visited. It is the standard in Austria; it is becoming the standard in Germany (and is replacing Germany’s decades of experience with longitudinal burlap drag); and it is used on provincial highways in the Netherlands.The benefits of two-layer PCC with EAC texture are reduced noise, durable friction numbers, and improved smoothness. The two-layer method manages to reduce costs in circum- stances where high-quality aggregates are costly and in short supply. The concrete paver for the upper layer must be mod- ified to meet special requirements, including the orientation of the vibrators and the use of a super-smoother. The thick- ness of the upper layer ranged from 5 to 9 cm in the pavements visited by the delegation. Austria specifies a 5-cm minimum with experienced paving operations; Germany also uses 5 cm. The Netherlands uses a minimum 9-cm thickness for the upper layer. The thickness of the lower layer can vary to accommodate the structural design requirements. The two-layer EAC proj- ects visited were durable (over 18 years old in Austria), not requiring any additional maintenance. In short, the two-layer composite PCC pavement is a sustainable technology because of its durability, use of recycled concrete in the lower layer, lower maintenance costs, and limited use of high-quality aggregate in the thin upper layer. The delegation also established that laboratory tests and experiments must be performed using project aggregates to establish an optimum mixture for two-layer construction and EAC texturing. Particulars that deserve attention include the water/cement ratio and strength and durability (especially regarding the use of fly ash, which is common in the United States but not in Europe). There is also a need to cast slab specimens for determining appropriate textures and brush timing. In the lower-layer mix, the mixture should be stiff enough so that dowels and tiebars can be inserted behind the paver. Furthermore, the mix must be designed economically, using lower-cost materials to offset the cost of two-layer con- struction, but the lower layer must be of adequate strength as an important structural component of the pavement.

37The top-layer mixture should be more fluid than that of the lower layer because it requires minimal vibration. Fur- thermore, to be a safe, quiet roadway, it must contain high- quality, highly durable aggregate with an appropriate cubical shape. To achieve the EAC texture, a combination of curing compound and retarding agent rather than plastic sheeting is used, and it is applied immediately after the upper layer is placed. After brushing, the surface must again be treated with a curing compound, and frequent testing of the EAC texture is necessary to ensure an appropriate texture depth. The tim- ing and quality of surface brushing are critical to successfully reducing noise and increasing friction. According to the rec- ommendations of the delegation’s hosts, the maximum aggregate size in the upper layer should be 8 mm or less to minimize noise levels. Austria, on the basis of long-term measurements, has made its maximum aggregate size 8 mm and does not build 11 mm any longer because of distance from large projects. As indicated, the texture depth in Austria is specified to fall between 0.8 mm and 1.0 mm. All hosts of the delegation identified and reiterated two critical success factors for two-layer EAC composite PCC pavements. First, more than a typical single-layer pavement, the two-layer construction requires a consistent, quality effort. In addition to the use of two separate pavers, several small modifications were noted by the delegation (including the use of two string lines to guide the pavers) in observing the construction of a two-layer PCC pavement in Germany. In addition, the success of the brushing technique depends greatly on the experience of the construction crew, particu- larly the operator of the brush. For this technique to succeed in the United States, the delegation believes that the R21 proj- ect will need to “import” a knowledgeable EAC brushing expert when test sections are built. The second and final critical success factor is that the upper layer must involve a careful mix design and, most important, a high-quality aggregate of the appropriate shape and durability. The delegation noted that in all EAC pavements surveyed the quality of the aggregate was a major contributor to the overall condition and life span of the surfacing. This observation was confirmed by the engineers and researchers in Europe.References 1. Report on 2006 Tour of Long-life Concrete Pavements in Europe and Canada. FHWA-PL-07-027. Federal Highway Administration, 2007. 2. Sommer, H. Developments for the Exposed Aggregate Technique in Austria [Entwicklungen für das Waschbetonverfahren in Öster- reich]. Proc., 7th International Symposium on Concrete Roads, Vienna, Austria, Oct. 3–5, 1994. 3. Teuns, K. C. J. G., M. J. A. Stet, and W. van Keulen. Full-Scale Pavement Tests of Exposed Aggregate Concrete: Acoustical Aspects and Friction Characteristics. Proc., 9th International Symposium on Concrete Roads, Istanbul, Turkey, April 27–30, 2003. 4. van Keulen, W., and A. van Leest. The Acoustical Properties of Optimized Exposed Aggregate Concrete in the Netherlands. Proc., 9th International Symposium on Concrete Roads, Istanbul, Turkey, April 27–30, 2003. 5. van Leest, A., and W. van Keulen. The Structural Properties of Optimized Exposed Aggregate Concrete in the Netherlands. Proc., 9th International Symposium on Concrete Roads, Istanbul, Turkey, April 27–30, 2003. 6. Fleischer, W. Concrete for Heavily Loaded Modern Traffic Areas (part 1). Beton, Nov. 2003, pp. 536–538. 7. Fleischer, W. Concrete for Heavily Loaded Modern Traffic Areas (part 2). Beton, Dec. 2003, pp. 592–597. 8. Fults, K. Quiet Pavement Systems in Europe. FHWA-PL-05-011. Federal Highway Administration, 2005. 9. Stinglhammer, H., and H. Krenn. Noise Reducing Exposed Aggre- gate Surfaces—Experience and Recommendations [Lärmmindernde Waschbetonoberflächen—Erfahrungen und Empfehlungen]. Proc., 7th International Symposium on Concrete Roads, Vienna, Austria, Oct. 3–5, 1994. 10. Haider, M., J. Steigenberger, and H. Piber. Long-Term Performance of Low-Noise Concrete Pavements. Proc., 10th International Sympo- sium on Concrete Roads, Brussels, Belgium, Sept. 18–22, 2006. 11. Haider, M. Lärmemission von Fahrbahnoberflächen—Betonstraßen. Austrian Conference on Concrete Roads, Vienna, Austria, 2007. 12. Wikipedia. Quartzite. http://en.wikipedia.org/w/index.php?title= Quartzite&oldid=215845290. Accessed May 31, 2008. 13. National Park Service. Golden Gate National Recreational Area: Diabase FAQ. www.nps.gov/goga/forteachers/diabase-faq.htm. Accessed May 27, 2008. 14. Krenn, H., and H. Stinglhammer. New from Old: Recycling Concrete Pavements [Aus alt mach neu: Betondeckenerstellung in recycling- bauweise]. Proc., 7th International Symposium on Concrete Roads, Vienna, Austria, Oct. 3–5, 1994. 15. Steigenberger, J. Concrete Roads in Austria: The Newest Trends and Developments. Proc., International Concrete Roads Conference, Bratislava, Slovakia, 2003.