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When pervious concrete pavement was first constructed in Belgium, it was found to exhibit undesirable durability in freezing weather. Subsequently, polymer additives were used along with higher cement content. The result was a significant improvement in the service life.13, 16 A policy that is currently being pursued in Japan is to replace all pavements with pervious systems due to their safety and riding comfort. To change over their existing concrete pavements to a pervious system, the preferred option is thinbonded pervious concrete overlays.16 Laboratory simulation tests have demonstrated that pervious concrete pavements can resist rutting and have a higher wear resistance to tire chains than porous asphalt. Since 1993, Japan’s Public Works Research Institute (PWRI) has been developing a new low-noise pavement that is referred to as “Porous Elastic Road Surface” (PERS). Potential noise reduction levels in Equivalent Noise Level (Leq) exceed 10 dBA. PWRI has already solved several of the problems with PERS such as insufficient adhesion between the pavement and the base course, low skid resistance, and poor fire resistance. PERS was first constructed on Japan’s National Highway Route 46. However, noise reduction levels measured in the field were less than expected due in part to the small size of the construction area. The noise reduction levels measured at the site are lower than those measured at the PWRI test facility. The noise reduction effect of PERS was found in the 1/3-bandwidth frequency of 800 Hz and over.17 In a separate study, pervious concrete pavements were evaluated in Japan with two experimental concrete sections, 200 mm (7.9 in) in thickness. When compared to dense asphalt pavements, they displayed noise reductions of 6 to 8 dBA for dry surfaces and 4 to 8 dBA for wet surfaces. This study was conducted with cars traveling at speeds from 40 to 75 km/h (25 to 45 mph). For heavy trucks, noise reduction values were 4 to 8 dBA and 2 to 3 dBA for dry and wet surfaces, respectively.18 One disadvantage of using pervious concrete pavements is the clogging of the pavement’s pores. The pores clog over time due to depositions in the voids of dirt and dust from the road surroundings, from wear of the pavement itself, and from tires.13, 16 2.3 Noise Reduction Technologies For the purposes of this research study, a pavement noise technology may be a part of the process, equipment, or machinery that is used to apply the paving material to the road surface. It does not include paving materials. 2.3.1 Pavement Texturing Pavement texturing can be designed and built into a pavement or placed upon hardened concrete pavement by equipment. The National Concrete Pavement Technology Center at Iowa State University (ISU), FHWA, ACPA, and other organizations have partnered to conduct a multi-part, seven-year Concrete Pavement Surface Characteristics Project.16 Part 1, Task 2, of the ISU-FHWA project, addressed the noise issue by evaluating conventional and innovative concrete pavement noise reduction methods in Europe and the U.S. 1 6 In the U.S., conventional concrete pavement surface options for controlling tire-pavement noise fall into two categories:16 • Conventional texturing (performed while concrete is still in a plastic state) o Drag textures (including artificial turf and burlap drag) o Tined textures (including transverse and longitudinal) • Diamond grinding (performed on hardened concrete pavement) A brief definition is provided for each category along with examples and outcomes of field studies or applications that relate to pavement noise reduction. A summary of the pavement texture options presented in this subsection is provided in Table 5 on page 23. 2.3.1.1 Drag Texturing Broomed surface textures are created by dragging a handheld or mechanical broom along the surface of the pavement, creating a ridged surface. This texture typically consists of 1.5 to 3mm deep (0.06 to 0.12 in.) grooves, either longitudinal or transverse to the centerline of the roadway. Artificial turf drag surfaces are similarly created by dragging an inverted section of artificial turf along the surface of the pavement. This technique often employs a device that controls the time and rate of texturing, most commonly a construction bridge that spans the pavement. Grooves of 1.5 to 3 mm (0.06 to 0.12 in.) in depth are typically created. Burlap drag (also known as Hessian drag) texturing is created by dragging moistened, coarse burlap across the surface of the pavement, typically creating grooves with depths between 1.5 and 3 mm (0.06 and 0.12 in.). Studies have shown that dragged textures are sufficient for roadways with speeds below 72 km/h (45 mph). More recent pavement evaluations in Minnesota have concluded that the use of drag texturing results in comparable noise levels and surface friction to conventional HMA pavements. The required texture depth specification in Minnesota is reported to be 1.0 mm (0.04 in.)16 According to Cackler et al.,16 the majority of concrete highway systems in Germany are finished using a burlap drag texture. The burlap drag finish provides adequate friction and minimizes air pumping. However, the frictional characteristics of the pavements often decrease due to pavement wear. Use of larger sand particles may increase the texture life by up to six years. The larger sand on the other hand may also reduce the concrete’s workability. Drag texturing techniques may provide a less costly and often quieter pavement than other alternatives. Measures should be taken to ensure adequate friction, both initially and during the service life. This can be achieved by selecting materials and mixes with improved wear resistance. 1 7 2.3.1.2 Tined Texturing Transverse tining is the most common texture on high-speed road and highway pavements in North America.19 It is produced by a mechanical device equipped with a tining head (metal rake) that moves laterally across the width of the paved surface. For smaller areas, a hand rake is often used. Optimal dimensions vary from 10 to 40 mm (0.4 to 1.6in) spacing for random tines with no more than 50% above 25 mm (1.0in), 3 to 6 mm (0.12 to 0.24in) tine depth, and 3 mm (0.12in) tine width.14,19 Skewing of tines has been found to reduce tire-pavement interaction noise. Favorable friction qualities of transverse tining are particularly pronounced in wet weather conditions. Deep macrotexture is capable of reducing the water film thickness resulting in reduced potential for hydroplaning. Depending on the properties of the concrete mixture, transverse tining can provide beneficial frictional qualities over the life of the pavement. Transverse tining has also been known to exhibit undesirable noise emissions due to the interaction between the pavement and vehicle tires. Noise emissions from transverse tined textures depend on tine spacing, depth, and width. A study conducted by WIDOT in 2000 concluded that wider and deeper transverse tine textures often produce greater noise.15,16 A 1977 Minnesota DOT (MDOT) report to the state legislature discussed the testing of different anti-skid groove spacings on PCC pavement. By changing the spacing from 1.5 to 1.0 inch, roadside noise levels were reduced 2.5 to 4.0 dB.20 Using results from a Wisconsin study, MDOT was able to reduce its spacing to 0.75 inch achieving a further reduction of 1.5 to 3.5 dB and an overall reduction of 4.0 to 7.5 dB. Wisconsin and Minnesota also conducted noise studies on different types of bituminous pavements that resulted in even greater noise reductions. Although no details are available about the data collection process or the data analysis, it is assumed that transverse tining was the texturing process applied to the PCC pavement in this study. Uniform transverse tine spacings typically range from 12.5 to 25 mm (0.5 to 1 in). “Wheel whine” is often associated with uniformly spaced tines. While the dBA level of a tined surface may not necessarily be higher than other texturing methods, the tonal nature of the whine makes this pavement texture objectionable to many. To help mitigate the tonal qualities, random tining is recommended. A broad range of random tine spacings, between 10 to 76 mm (0.4 to 3 in.) has been reported to reduce noise emissions. In situations where concrete finishing conditions are unfavorable (e.g., objectionable weather conditions and lack of equipment control), random spacings of 10 to 51 mm (0.4 to 2 in.) are recommended. The FHWA has recommended two random tining patterns, averaging 13 mm and 26 mm (0.52 in. and 1.04 in.), respectively.16 The shorter spacings have been recommended to mitigate the high noise levels reported by some states that have tried or adopted random spacings. 1 8 Skewing of transverse tining involves forming the grooves at an angle, rather than perpendicular to the centerline. This is a complementary method that has demonstrated benefits related to tire-pavement noise while providing the friction commonly associated with transverse tined pavements. Research by Cackler et. al. identified a skew with a recommended longitudinal-to-transverse ratio of 1:6.16 Longitudinally tined textures are constructed in a manner similar to that of transverse tining, except that the tining device is moved longitudinally along the direction of paving. Although longitudinal tining is not used as frequently as transverse, it has been used extensively in some states, including California. Longitudinal tining is commonly reported to exhibit lower noise characteristics thereby increasing its popularity and use. However, some transportation agencies have been cautious to use this texturing technique because the data shows longitudinally tined surfaces to have lower friction numbers when compared to transversely tined pavements, all else being equal. One possible explanation of this may be the shape of the grooves with respect to the traction forces of the tire (compared to transverse tining). It should be noted, however, that longitudinal tining on horizontal curves has been shown to prevent vehicle skidding and thus improve safety.16 Some DOTs report that if adequate crossslope exists, the differences between the surface drainage on transverse and longitudinal tining are minimal. Research shows that the long-term effectiveness of longitudinally tined surfaces is impacted by the design of the pavement mix. Data have shown that longitudinally tined pavements should contain a minimum of 25% siliceous sand to improve the level and durability of the friction capacity. The WIDOT study further concluded that among all of the concrete pavements evaluated, those with longitudinal tining provided “the lowest exterior noise while still providing adequate texture”. When the texture is properly designed and constructed, longitudinally tined pavements can achieve friction characteristics and durability comparable to either transversely tined concrete pavements or dense-graded HMA pavements.16 Volpe assisted California DOT in a comparison of three PCC test sections: longitudinal tining, burlap dragged, and broomed tining. Volpe also assisted ADOT in comparing uniform longitudinal tining, uniform transverse tining, and randomly spaced transverse tining. Their findings showed that the quietest surface treatments were CA burlap dragged, CA broomed, and AZ uniform longitudinal tining.11 2.3.1.3 Diamond Grinding Diamond grinding is a technique that removes a thin layer of hardened concrete pavement using closely spaced diamond saw blades. The diamond saw blades are stacked side-by-side and generally remove between 3 and 20 mm (0.12 and 0.8 in) from the surface. The blades are gang-mounted on a cutting head and can generate 164 to 197 grooves/m (50 to 60 grooves/ft). Although diamond grinding has traditionally been used to rehabilitate existing pavements by restoring smoothness, it has also been found to 1 9 reduce tire-pavement noise and restore pavement friction. The grinding procedure results in the development of macrotexture. Furthermore, directional stability is more easily controlled, making diamond grinding more appealing to drivers than longitudinal tining. In one study conducted to compare transverse tining to longitudinal diamond-grinding, test sections were constructed and evaluated for safety, noise, and other pavement characteristics.20 Diamond grinding was used to remove a thin layer of the concrete surface. In some cases, thin fins of concrete were left behind and were subsequently broken off by a blade. Each grinding head consisted of 166 saw blades, 3.18 mm (0.125 in.) separated by spacers with a thickness of 2.67 mm (0.105 in). It has been reported that the key variables of diamond grinding are cutting blades, cut depth, equipment horsepower, and the properties (e.g., hardness) of the aggregates used. In a 2001 study by Burgé, Travis, and Rado, the grinding rate was approximately 0.6 lane-km (0.4 lane-mi.) per day In addition, there was a specified minimum curing time of seven days before grinding. KDOT conducted a study in 2004 and concluded that smaller blade spacings led to reduced noise levels.16 The study concluded that the longitudinal ground pavement was quieter than the transversely tined pavement by 2 to 5 dBA (measured on the side of the road).16 When noise measurements were conducted a year later, there was no real change in noise levels. When comparing different vehicle types, the ground surface led to a 5-dBA noise improvement for light trucks and automobiles, and a 2-dBA improvement for medium and heavy trucks. The lower noise reduction for larger vehicles is believed to be due to differences in the noise emission source; larger vehicles generate a greater percentage of noise from the engine and exhaust systems (as compared to tire-pavement noise emissions).16 Prior to making a decision on a pavement surface technology, the percentage of heavy vehicles should be considered in determining overall effectiveness of surface treatments. Several states, including Arizona, California, New Jersey, North Dakota, and Virginia have experience with tined and textured surfaces of PCC pavements in addressing roadway noise. A partnership has been formed between California and the Western States-ACPA on the I-280 pavement rehabilitation project in San Mateo County. Noise from old longitudinally tined pavement will be compared to noise from a PCC pavement with diamond grinding, a PCC pavement with texture grinding, and a PCC pavement overlain with 30 mm (1.17 in) of OGFC.20 Noise measurements will be made for three to five years to assess the longevity of noise reduction benefits. The 2005 European scanning team recommended investigating and optimizing diamondgrinding blade configurations to enhance the noise-reducing properties of existing concrete surfaces in noise-sensitive locations. To achieve noise reduction texture should always be negative (pavement depressions). Positively textured pavements, such as chip seals, increase noise. Positive texture is the magnitude of texture that exists above a planar surface (the riding surface). Positive texture almost always produces greater noise with increasing texture depth. Chippings on concrete or exposed aggregate surfaces could be considered the extreme case of positive texture. 2 0 Negative texture refers to the magnitude of the texture that exists below a planar surface. A longitudinally grooved pavement would represent a negative texture. Negative textures do not “interfere” with the tire, resulting in less vibration and noise than a positive texture. Therefore, the effect of negative texture is different from the effect of positive texture.21 This is another reason why texture depth alone cannot be used to correlate noise across different pavement types. 2.3.1.4 Exposed Aggregate Concrete (EAC) EAC was discussed in the previous section as a concrete pavement treatment that is usually applied using a two-layer “wet on wet” paving process. It is the combination of aggregates used in the top layer that determine its surface characteristics and texture. Texture depths, curing solutions, and concrete finishing techniques are used to determine the best combinations for optimal performance. During the 2005 FHWA scanning tour, UK transportation officials reported that they experimented with EAC finishes and found thin-layer quiet surfacings to be more cost effective. Belgium uses EAC pavements and SMAs. Both have been optimized for noise. The porous surfaces provide a slightly better noise benefit than SMA and EAC, but officials believe that the latter provides a better blend of durability and noise reduction. The Dutch province of Noord-Brabant conducted a study intended to further determine the surface characteristics of EAC pavements. Various aggregates, texture depths, curing solutions, and concrete finishing techniques were used in the study to determine the combinations that provided optimal performance. Two Dutch aggregates, Dutch stone and Graukwartsiet, were used in the study. The Graukwartsiet possessed a higher polished stone value than the Dutch stone aggregate. Several texture depths were evaluated. The standard depth was considered to be one-quarter of the maximum aggregate size. Different retarding agents were evaluated, including lemon, acid solutions, and various combinations of retarding agents and curing compounds. One- and two-layer paving systems, as well as a super smoother (finisher) were also evaluated in the study.16 Several key measurements and observations were made after construction. Texture depth was found to be affected by the use of a super smoother, which resulted in a maximum texture depth of 1.8 mm (0.07 in). When not used, texture depths were not as great, with values commonly between 1.1 and 1.6 mm (0.04 and 0.06 in). The super smoother was shown to produce positive effects in regards to noise emission, possibly due to a reduction in megatexture. The selection of the retarding agent did not appear to make a difference on the results. It was concluded that lower noise levels were measured when smaller maximum aggregates were used. A Swedish Study tested several concrete and HMA pavements for abrasion resistance, friction, and noise under heavy traffic. The test sections were constructed with exposed aggregates in the surface on both jointed plain and continuously reinforced concrete pavements. Two different maximum aggregate sizes were used in the design of the 2 1 concrete pavements, 8 and 16 mm (0.31 and 0.63 in). Noise was measured using the close proximity (CPX) method. In comparison to the HMA pavements constructed on the same job, initial tests revealed that the EAC pavements with 16 mm (0.63 in) and 8 mm (0.31 in) stones provided noise levels that were 1.0 to 1.5 dBA and 3.0 to 3.5 dBA lower.16 The noise emissions of the 16 mm (0.63 in) EAC and HMA sections were found to be identical after one year. However, the 8 mm (0.31 in) EAC section actually produced quieter noise levels after a year. Three years after construction, the noise levels from all of the pavements had deteriorated. Also of interest was that during the winter season concrete pavements produced noise levels about 1 dBA higher than the HMA pavements. 2.3.1.5 Pervious Concrete Pavements Pervious concrete pavement was also discussed in the previous subsection as a pavement treatment. A relationship between sound absorption and aggregate size was identified in the research. In one study, a pavement with decreased aggregate size exhibited improved sound absorption. A combination of #4 and #8 aggregates in the mixture exhibited improved acoustic absorption characteristics when compared to straight gap grading. A Belgian study reported sound reduction using pervious concrete as well, with a 5 dBA decrease using a pervious concrete pavement with only 19% porosity.16 Durability is commonly regulated by the interface of the two concrete layers and the presence of pores. Once ice forms at the entrance of small pores and water is unable to move, damage occurs very quickly. In pervious concrete, freezing tends to originate at the top of the pavement and infiltrate into the lower depths of the layer. Differences in the properties of the pervious and dense concretes can lead to stress concentrations at the interface. The damage may take the form of an adhesion loss between the pervious concrete and the conventional concrete. To combat this problem, continuous maintenance and cleaning can be conducted to help preserve and restore the pavement’s acoustical performance. Double-layer pervious concrete has also been demonstrated as a possible solution where a top lift with smaller aggregates is placed over a larger stone mix. The resulting system may help to minimize infiltration of debris that causes clogging. The added cost of constructing pervious concrete pavement must be taken into consideration. The long-term effectiveness of this technique is still under debate. In one report by the Belgian Road Research Centre it is noted that compared with a conventional concrete 22 cm (8.7 in) thick a 4 cm (1.6 in) pervious concrete laid over 18 cm (7 in) of conventional concrete has associated extra costs estimated at 40%”. However, no significant cost difference was found with an equivalent structure including porous asphalt. The cost of constructing quiet pervious concrete pavements in New Zealand has been reported at US $132 per m² (US $111 per sq. yd.). In the United States, pervious concrete projects have been reported to cost 40% more.16
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