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2.3.1.6 Innovative Pavement Texturing Solutions In his research on concrete pavement noise reduction methods, Cackler identified several innovative texturing solutions that were either being researched or were in experimental stage.16 • Stamping, Brushing, and Other Texturing Techniques: Other proposed alternative texturing techniques are proposed to conventional tining, but will be designed with better surface characteristic properties. • Sprinkle Treatment: This technique is similar to EAC and distributes partially embedded, small, polish-resistant stone chips on fresh concrete surface. This technique was previously used in the U.S. in the 1970s and 1980s; however, the equipment was rented from England, and therefore not available for widespread application. Equipment will need to be developed or purchased. • Shot Peening (or shotblasting): Special equipment is used to propel tiny steel shots onto the pavement surface. The shots make an imprint on the surface and remove a thin layer of mortar and aggregate, exposing coarse aggregate. An open porous surface texture is created increasing skid resistance and reducing noise levels. • Use of Helmholtz Resonators: Originally developed at the University of Göttingen in Germany, euphonic pavements were designed as “quiet tire/road combination” pavements, incorporating “Helmholtz resonators underneath a perforated but planed aluminum structure”. Helmholtz resonators are designed to absorb low frequencies, typically ranging between 100 to 250 Hz. Other potential texturing techniques identified by Cackler include:16 • Paving concrete that possesses inclusions (e.g., fiberglass, foam, and rubber particles) to increase acoustical absorption, • Application of acoustically absorptive materials for concrete shoulders (as opposed to traffic lanes), allowing for noise of all sources to be absorbed en route to the receiver and also reducing surface wear and clogging issues, • Quiet joint designs, addressing the significant factor of wheel “slapping” at the joints in overall noise levels, • Dimpling, waffling, or other innovative geometries of fresh concrete texture, • Textured profile pans, e.g. a corduroy pattern, for example, might be machined into the profile pan of a slip-form paver to construct a surface similar to that resulting from diamond grinding. 2 3 Table 5: Summary of Concrete Pavement Texture Options16 Texture Description Current Use and Perception Artificial turf drag Produced by dragging an inverted section of artificial turf from a device that allows control time and rate of texturing. Usually a construction bridge that spans the pavement typically produces 1/16 to 1/8 inch deep striations. Artificial turf drag textures have shown sufficient friction characteristics for many roadways, as well as reduced noise relative to many transversely tined pavements. Minnesota has used this type of texturing to reduce noise on high-speed roads. Burlap drag Produced by dragging moistened coarse burlap from a device that allows control of the time and rate of texturing, usually a construction bridge that spans the pavement; typically produces 1/16 to 1/8 inch deep striations. Burlap drag textures provide sufficient friction characteristics for many roadways, especially those with speeds less than 45 mph, and reduced noise relative to many transversely tined pavements. This texture is used on Germany’s high-speed Autobahn system. Transverse tining Produced by moving a mechanical device equipped with a tining head across the width of the paving surface laterally or on a skew. Consistent concrete mixture and constant forward movement of the paving train at a uniform speed is required for a consistent tining depth. For tined pavements, texture depth and groove width are important parameters in tire-pavement noise generation. Pavements with uniformly spaced transverse tining generally, but not always, exhibit undesirable “wheel whine” noise. Artificial turf or burlap drag texture precedes many projects. Longitudinal tining Achieved by a mechanical device equipped with a tining head (metal rake) pulled in a line parallel to the pavement centerline. For consistent tining depth, maintain a consistent concrete mixture and move the paving train forward constantly at a uniform rate of speed. Most projects precede with an artificial turf or burlap drag texture. Tined texture depth and groove width are important parameters in tire-pavement noise generation. Longitudinal tining is often quieter than transverse tining. Narrower time spacings might be used to reduce vehicle tracking and possibly reduce noise even further. Lateral stability of narrow-tired vehicles may also benefit from this. Diamond grinding Longitudinal, corduroy-like texture made by equipment using diamond saw blades gang-mounted on a cutting head. About 50 to 60 grooves/ft. are produced by the cutting head 1/8 to ¾ inch is removed from the pavement surface. Diamond grinding has traditionally been used to restore pavement smoothness, but has also been shown to reduce tirepavement noise and improve friction in the short term. Diamond ground pavements do not affect vehicle tracking as much as widely spaced longitudinally tined pavements. EAC pavement European practice includes applying a set retarder to the new concrete pavement and then brushing or washing away mortar to expose durable aggregates. Other techniques involve the uniform application of aggregates to the fresh concrete. Regarded as an effective method for reducing tire-pavement noise while providing adequate friction. Smaller aggregate sizes have been reported to provide larger noise reductions, while aggregates with a high polished stone value increase durability. Only one large-scale EAC pavement project has been completed in U.S. Pervious concrete pavement When used in highway applications, pervious concrete is typically used as a top layer (wearing course), providing both low noise emission and good drainage capacity. The pervious concrete typically overlays a conventional (dense) concrete pavement using a “wet-on-wet” process. Sound absorption increases with higher porosity levels for pervious concrete, and also results from smaller aggregate sizes. Use of pervious pavements for high-volume, high-speed facilities is still in its infancy and will require more testing. Regular maintenance and cleaning may be needed to prevent clogged pores and to preserve the pavement’s acoustical performance. Research on durability is ongoing in wet, hardfreeze areas