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Texturing of Concrete Pavements (2009)

Chapter: Chapter 6 - Texture Selection Process

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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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Suggested Citation:"Chapter 6 - Texture Selection Process." National Academies of Sciences, Engineering, and Medicine. 2009. Texturing of Concrete Pavements. Washington, DC: The National Academies Press. doi: 10.17226/14318.
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81 Selecting a texture for a concrete pavement requires an understanding of the particular needs and requirements of the facility and matching the friction and noise qualities of the tex- tures to those needs (ACPA, 2000). Such needs and require- ments vary substantially, because even short stretches of high- way may present different features, situations, and settings that affect highway user safety and the quality of life of persons residing in the vicinity of the highway. Friction demand, for instance, is affected by factors such as traffic characteristics (i.e., speed, volume, and composition), highway alignment (i.e., vertical and horizontal), and highway geometric features affecting vehicle maneuvers (e.g., presence of turn lanes, cen- ter lanes, interchange ramps, intersections, and driveways). Similarly, highway setting (urban versus rural), right-of-way dimensions, adjacent land use (e.g., residential, commercial, agricultural), terrain, and traffic characteristics determine the need for noise abatement consideration. When selecting a texture, it is paramount that safety, in the form of minimizing the potential for wet-weather crashes caused by inadequate friction, hydroplaning, or splash/spray, take precedence over designing for all other surface charac- teristics (e.g., noise, rolling resistance, tire wear, and fuel consumption). Although speed and cross-slope are considerations for assuring safety, micro-texture and macro-texture must be controlled to improve friction and reduce the potential for hydroplaning and splash/spray. Effective micro-texture typ- ically provides adequate surface friction on dry pavements at all speeds and on wet pavements at slower speeds, whereas macro-texture is typically required to provide adequate fric- tion in wet conditions at high speeds (Hoerner et al., 2003). Pavement micro-texture is primarily governed by the surface properties of the aggregate particles comprising the pave- ment surface course, while macro-texture is determined by either the texturing method of the surface course or by the mix properties (shape, size, and gradation of aggregate) (AASHTO, 2008). Although increased macro-texture (i.e., higher MTD) gener- ally results in better surface drainage and thus improved friction and hysteresis, the increased size and number of asperities cause greater excitations in vehicle tires which leads to increased noise at the pavement–tire interface. Thus, trade-offs between friction and noise must be considered. Because friction and noise are both functions of texture, and texture changes over time (depending on durability under the effects of traffic, use of snowplows, and environment), the selec- tion process must consider both initial and long-term perfor- mance qualities. Both micro-texture (aggregate) and macro- texture (mix and texturing) durability properties are critical. Also, issues such as texture constructability and relevant agency and contractor experience are important. These factors, as well as material costs (aggregates and mixes) and texturing opera- tional costs, all affect the cost-effectiveness of textures. Texture Selection A logical, rational process must be used for determining the type of texture needed for a particular highway project. Such a process involves gathering and reviewing all available critical information about the project, identifying any poten- tial constraints/limitations (both internally and externally) in terms of available resources/technologies and performance/ cost expectations, developing alternative feasible solutions, and determining the most economical and practical alternative. Figure 6-1 illustrates the process for identifying pavement surface texturing options at the project level. This process uses key information about the project to establish target levels for friction, noise, and other surface characteristics (Step 1). The target levels are then combined with information on available (locally or otherwise) aggregate types and contractor experi- ence with texture construction, to identify feasible texturing options (Steps 2 and 3). The cost of each texturing option (both initially and over the life-cycle of the pavement) then is estimated, and the results are evaluated carefully with respect C H A P T E R 6 Texture Selection Process

82 to the overall functional and structural design and perfor- mance of the pavement (Step 4). Steps 2 and 3 in the process cover the identification of fea- sible texture options, based on (1) the minimum friction lev- els required for safety over the life of the pavement and (2) any maximum noise levels allowed by statute (wayside noise for adjacent residents or businesses) or desired (interior noise). Information gleaned from the literature and derived from the analyses of data collected on existing test sections serves as the basis for these two steps. Friction requirements stipulated in Step 2 should conform with guidelines established and pre- sented in the Guide for Pavement Friction (AASHTO, 2008). This four-step process covers both new construction/ reconstruction and rehabilitation projects. Steps 1 and 4 are essentially the same for each type of project; Steps 2 and 3 dif- fer depending on the textures involved. Step 1—Project Information Gathering For each highway project, information pertaining to the needs and expectations of friction, noise, and other related surface characteristics must first be gathered. Such infor- mation includes • Climatic Conditions—Establishing a higher threshold level of friction (and thus requiring greater amounts of texture) may be necessary for locations with increased probability of wet-weather conditions (FHWA, 2005), particularly if only polish-susceptible aggregates are available. Because wet roads have been shown to be slightly louder (1 to 4 dB(A) at the wayside) than dry roads (Sandberg and Ejsmont, 2002), consideration should be given to locations with urban settings. • Highway Alignment—Increased friction demand associ- ated with horizontal and vertical curves is often addressed through increases in the horizontal radius of curvature, inclusion of or increases in curve super-elevation, and/or reductions in longitudinal grades. However, the alignments for some projects (particularly, those in which the existing alignment will be kept) may preclude taking these mea- sures. In lieu of posting reduced speed limit signs, specify- ing a pavement surface with increased texture depth may be a viable solution. Highway alignment, particularly the char- acteristics of curves, affects noise. If speed is not reduced, sharp horizontal curves will have a pronounced effect on far-field noise experienced at the interior of the curve. Also, because of the need for greater engine power emission dur- Step 1—Project Information Input Highway Features/Environment (vehicle maneuvers) Available Aggregates (incl. Perf Characteristics) Highway Alignment (vertical, horizontal) Design Traffic Characteristics (amount, composition) Climatic Conditions Design Speed Highway Setting & Adjacent Land Use Contractor Experience Agency Experience & Policies Step 2—Friction Analysis Step 4—Selection of Preferred Texture Target Friction Levels Friction/Texture Matrix (Identification of Candidate Textures) Feasible Texture Options Noise Regulations & Preferences Target Noise Levels Noise/Texture Matrix (Identification of Candidate Textures) Feasible Texture Options Consideration of Other Surface Characteristics Economic Considerations Preferred Texture Alternative Step 3—Noise Analysis Figure 6-1. Flowchart for texture selection process.

83 ing uphill climbs and the likelihood of increased downhill vehicle speeds and downhill truck engine breaking, steeper grades will result in increased vehicle noise. • Highway Features/Environment—Highway geometric fea- tures and environment influence traffic flow and thus fric- tion. Traffic flow is defined largely by the level of interacting traffic situations (e.g., entrance/exit ramps, access drives, unsigned/unsignalized intersections), the presence of con- trolled (signed/signalized) intersections, the presence of specially designated lanes (e.g., separate turn lanes at inter- sections, center left-turn lanes, through versus traffic lanes), the presence and type of median barriers, and the setting (urban versus rural) of the roadway facility (AASHTO, 2008). • Design Speed—The design traffic speed will influence both friction and noise. As speed increases, the level of friction decreases, reaching a minimum at approximately 60 mi/hr (96 km/hr) (FHWA, 2005). Also, as Figure 6-2 shows, pavement–tire noise and total vehicle noise increase with increasing speeds, with pavement–tire noise increasing by about 2 to 3 dB(A) per 10-mi/hr (16-km/hr) speed increase (Rasmussen et al., 2007a). At speeds above typical city speeds (>30 to 35 mi/hr [>48 to 56 km/hr]), pavement–tire noise is the dominant source in the overall noise produced by vehicles. • Design Traffic Characteristics—Both traffic volume and composition affect friction and noise as follows: – The higher the traffic volume, the greater the number of driving maneuvers (per segment of highway), which increases the risk of accidents, especially in high-speed areas (NCHRP, 2009). Pavements with higher traffic volumes may require greater amounts of texture to pro- vide a higher level of friction (FHWA, 2005). Higher traffic volumes also result in increased noise because of the additional vehicles and by a change from point source to line source noise (Rasmussen et al., 2007a). – Pavements with higher percentages of trucks may war- rant the consideration of increased texture to account for (1) stopping distances of trucks, (2) steering capabil- ities of trucks, and (3) friction levels produced by truck tires (NCHRP, 2009). Because of its large propulsion system and numerous tires, the typical heavy truck is more than 10 dB(A) louder than a typical passenger car. Also, if trucks constitute more than 10% of the traffic stream, they will likely dominate the overall noise level (Rasmussen et al., 2007a). Step 2—Feasible Textures Based on Friction Requirements With consideration of all relevant project information, an assessment can be made to determine the level of friction required over the life of the new or rehabilitated pavement and the types of textures that can provide the friction requirements. The friction design categories identified in the Guide for Pave- ment Friction (AASHTO, 2008) for individual segments with specific alignment characteristics, highway features/environ- ment, traffic level, and travel speed can be used to define fric- tion demands. Feasible textures for each segment or for the entire project can be identified (based on the segment with the highest overall friction demand). Table 6-1 identifies five possible friction design categories, A through E, in which “A” represents the highest level of fric- tion demand and “E” represents the lowest. The table can be used to establish the level of friction required for both new construction/reconstruction and rehabilitation projects. For the selected friction design category for the project (or one for each individual segment), feasible textures can be iden- tified by selecting combinations of micro-texture and macro- texture that will satisfy the required friction based on the IFI model (AASHTO, 2008). DFT(20) or British Pendulum Num- ber (BPN) can be used as surrogates for micro-texture and MPD or MTD for the macro-texture component. The micro-texture and macro-texture values should reflect long-term, residual values that account for the polishing or wearing characteristics of the aggregate and the surface mate- rial and its texturing. These characteristics include the aggre- gate polished DFT(20) or BPN values (known as polished stone values [PSVs]) and reduced value of MPD or MTD of the mixture, depending on the strength and durability of the mix and texture, and the anticipated environment. The equations presented in Chapter 3 can be used to deter- mine MPD for a required friction level F(60) and the expected long-term micro-texture friction DFT(20). MTD also can be determined based on the required friction F(60) and the expected long-term micro-texture DFT(20). Figure 6-3 Figure 6-2. Speed effects on vehicle noise sources.

84 provides a means for selecting pairs of DFT(20) and MTD that will satisfy the following friction ranges: Friction Design Category F(60) Range A ≥36.0 B 32.0 to 35.9 C 28.0 to 31.9 D 24.0 to 27.9 E 20.0 to 23.9 For instance, if F(60) must be at least 32 (friction design category B) and the long-term value of DFT(20) is estimated to be 60, then a texture with a long-term MTD of 0.026 in. (0.65 mm) would be needed. Or, if F(60) must be at least 24 (category D) and the DFT(20) is 50, then MTD of 0.02 in. (0.52 mm) would be needed. Table 6-2 provides typical ranges of MTD for newly con- structed textures based on values reported in the literature and on field measurements made in this study. Also listed in this table are corresponding ranges of MTD that reflect the typical levels of wear experienced by each texture. These val- ues can be used with information on friction requirements and long-term micro-texture (DFT(20)) to identify feasible textures for a project. The friction–texture plots shown in Figure 6-3 and the macro-texture information provided in Table 6-2 have been used to identify feasible textures based on friction requirements. Table 6-3 identifies suitable general texture types for new con- crete pavements with anticipated specific long-term DFT(20) 0.0 0.5 1.0 1.5 2.0 2.5 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 IFI F(60) M TD , m m DFT(20)=80 DFT(20)=75 DFT(20)=70 DFT(20)=65 DFT(20)=60 DFT(20)=55 DFT(20)=50 DFT(20)=45 DFT(20)=40 DFT(20)=35 ABCDEDesign Friction Ranges 0.65 0.52 Figure 6-3. MTD versus F(60) and DFT(20). Low Traffic1 Moderate Traffic1 High Traffic1Degree of Driving Difficulty due to Highway Alignment Issues Degree of Driving Difficulty due to Highway Features/ Environment Low/ Moderate Speed2 High Speed2 Low/ Moderate Speed High Speed Low/ Moderate Speed High Speed Low E E D C C B Low High4 E D D C B A Low D D C B B A High3 High4 C C C A A A A = highest friction demand, E = lowest friction demand 1Traffic Designations: 3Project contains multiple locations with considerably tight horizontal curves (with possibly inadequate super-elevation) and/or steep vertical grades. 4Project contains a considerable number of geometric design features that will increase the number of driving maneuvers and make the driving environment more difficult. Low (ADT2-way < 5,000 veh/day) High (ADT2-way > 25,000 veh/day) Moderate (5,000 ≤ ADT2-way ≤ 25,000 veh/day) 2Speed Designations: Low/Moderate (≤ 45 mi/hr [≤ 72 km/hr]) High (> 45 mi/hr [> 72 km/hr]) Table 6-1. Friction design categories.

85 Texture Type Typical MTD for Newly Created Textures, mm Typical MTD for Aged/Trafficked Textures, mm New Pavement Burlap, Broom, and Standard Turf Drags 0.35 to 0.50 0.30 to 0.45 Heavy Turf Drag 0.50 to 0.90 0.40 to 0.80 Transverse and Transverse Skewed Tine 0.60 to 1.25 0.50 to 1.15 Longitudinal Tine 0.60 to 1.25 0.50 to 1.15 Longitudinal Diamond Grind 0.70 to 1.40 0.50 to 1.25 Longitudinal Grooving 0.80 to 1.50 0.70 to 1.40 EAC 0.90 to 1.60 0.75 to 1.50 Porous PCC 1.20 to 2.50 0.90 to 2.25 Restoration of Existing Pavement Longitudinal Diamond Grind 0.70 to 1.40 0.50 to 1.25 Longitudinal Grooving 0.80 to 1.50 0.70 to 1.40 Shotblasted PCC 1.00 to 1.50 0.80 to 1.40 HMA (dense-graded fine) 0.40 to 0.75 0.30 to 0.70 HMA (dense-graded coarse) 0.60 to 1.20 0.50 to 1.10 Ultra-thin Bonded Wearing Course 1.00 to 1.75 0.80 to 1.50 1 in. = 25.4 mm Table 6-2. Typical ranges of macro-texture for new and aged surface textures. General Texture Type Friction Design Category Long- Term DFT(20) Range Burlap, Broom, Std Turf Drag Heavy Turf Drag Tran Tine Long Tine Long Diamond Grind Long Groove EAC Porous PCC >80 70 to 80 60 to 70 50 to 60 40 to 50 A (F(60)>36) 30 to 40 >80 70 to 80 60 to 70 50 to 60 40 to 50 B (F(60)>32) 30 to 40 >80 70 to 80 60 to 70 50 to 60 40 to 50 C (F(60)>28) 30 to 40 >80 70 to 80 60 to 70 50 to 60 40 to 50 D (F(60)>24) 30 to 40 >80 70 to 80 60 to 70 50 to 60 40 to 50 E (F(60)>20) 30 to 40 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Table 6-3. Identification of textures for new concrete pavements based on friction requirements and expected long-term micro-texture.

86 values, and Table 6-4 indicates suitable options (including thin asphalt treatments) for re-texturing existing concrete pave- ments to enhance surface friction characteristics. Tables 6-3 and 6-4 were developed for aged/trafficked sur- faces, the upper end of the MTD ranges listed in Table 6-2, and the upper end of each DFT(20) range. Although this table illustrates texture possibilities, detailed analyses of friction must be performed to ensure that each viable texturing option meets the established friction requirement(s). Concerning the identification of feasible texturing options for friction, the following items should be noted: 1. Polished DFT(20) values depend on the type and quality of the aggregate used in the surface mixture. Aggregates that exhibit the highest levels of polish resistance and resistance to wear typically are composed of hard, strongly bonded, interlocking mineral crystals embedded in a matrix of softer minerals (Folliard and Smith, 2003; Liang, 2003). 2. The relationship between BPN and DFT(20) is expressed by the following equation (Henry, 2000): 3. Consideration could be given to adjusting the minimum F(60) friction design values based on climatic conditions (e.g., values should be increased for locations with high wet-pavement times). 4. The IFI F(60) friction value is fairly closely aligned with FN40S values, particularly for lower texture depths. For the ranges of F(60) < 50 and MTD ≤ 0.04 in. (MTD ≤ 1 mm), there is less than 3% difference between F(60) and FN40S BPN DFT 20 Eq. 6-1= × ( ) +57 9 23 1. . General Texture Type Friction Design Category Long- Term DFT(20) Range Long Diamond Grind Long Groove Shot- Abrade Thin HMA Overlay (Fine Mix) Thin HMA Overlay (Coarse Mix) Ultra-Thin Bonded Wearing Course >80 70 to 80 60 to 70 50 to 60 40 to 50 A (F(60)>36) 30 to 40 >80 70 to 80 60 to 70 50 to 60 40 to 50 B (F(60)>32) 30 to 40 >80 70 to 80 60 to 70 50 to 60 40 to 50 C (F(60)>28) 30 to 40 >80 70 to 80 60 to 70 50 to 60 40 to 50 D (F(60)>24) 30 to 40 >80 70 to 80 60 to 70 50 to 60 40 to 50 E (F(60)>20) 30 to 40 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Table 6-4. Identification of textures for restoration of existing concrete pavements based on friction requirements and expected long-term micro-texture.

87 and 3 to 5% difference for the range F(60) < 50 and 0.04 in. < MTD ≤ 0.08 in. (1 mm < MTD ≤ 2 mm). Thus, FN40S can provide a general indication of the F(60) design levels. 5. The textures identified in these tables are based solely on assumed long-term friction needs. Consideration of costs, constructability, and experience may dictate elimination of specific textures from consideration. Step 3—Feasible Textures Based on Noise Requirements and Preferences There is no nationally recognized requirement for the max- imum level of noise (either at the source or at a point on the wayside) that can be generated by a highway pavement. How- ever, Code of Federal Regulations (CFR) Title 23, Part 772, governs the amount of overall wayside noise that can be pre- dicted to occur for projects to qualify for federal cost sharing. This CFR does not restrict the use of noise-reducing pavement (Bernhard and Wayson, 2005). In this step, the qualitative noise level categories presented in Chapter 5 are considered. These categories can be fitted to various conditions/scenarios defined by traffic speed, volume, and composition; facility setting (urban versus rural); and adjacent land use. Metropolitan projects in noise-sensitive areas (e.g., residences, parks, and hospitals) and having higher traffic speeds and volumes (trucks and overall) will require lower levels of exterior noise, thereby narrowing the number of texturing options. Projects in rural settings, on the other hand, will not be as demanding of limits on exterior noise, thereby resulting in more texturing options. Table 6-5 lists target initial exterior noise levels for untraf- ficked highway projects, based on the forecast traffic charac- teristics and the noise-sensitivity of the adjacent environ- ment. Only qualitative noise levels A, B, and C are included in this table because all textures can be designed and con- structed to meet at least level C requirements. Low-speed facil- ities (<35 mi/hr [<56 km/hr]) are not included in Table 6-5 because pavement–tire noise at low speeds is secondary to propulsion/engine noise; texture selection in these instances will be more rudimentary. The noise levels given in the table are representative of those generated at the source by a vehicle traveling at 60 mi/hr (96 km/hr); noise characteristics at other speeds (e.g., the moderate category) are proportional to those for 60 mi/hr (96 km/hr). Unless otherwise desired, feasible textures can be identified on the basis of exterior, at-the-source noise target levels. The data collected in this study show a general relationship between the noise measured at the source and the noise measured inside the vehicle. If lower interior noise levels are required for a proj- ect, then a lower target level should be selected as the basis for the identification of feasible textures. Once a target noise level has been established to meet the exterior noise requirements and/or interior vehicle noise preferences of the project, the noise–texture alternatives in Tables 6-6 and 6-7 can be used to identify candidate textures for new construction/reconstruction and restoration proj- ects, respectively, on the basis of noise. The selection involves determining the general textures suit- able for the desired target noise level (A, B, or C). These are des- ignated by checkmarks () under the appropriate target noise level column (or multiple columns for some textures). More specific applications of each general texture can then be evalu- ated, based on the favorable noise characteristic provided by the particular features of the texture, as illustrated by arrows that stretch across a particular target level or multiple target levels. Textures spanning target levels A and/or B are also can- didates for target level C; however, higher costs or other factors may eventually preclude them from being feasible options. Identifying specific textures that satisfy both the friction and noise target levels requires iteration of Steps 2 and 3 because texture features (i.e., the texture produced by drag devices) and dimensions (i.e., groove spacings, depths, and widths) Low Traffic1 Moderate Traffic1 High Traffic1 Noise-Sensitivity of Adjacent Land Use Traffic Speed Low % Trucks2 High % Trucks2 Low % Trucks High % Trucks Low % Trucks High % Trucks Moderate 4 C C C C C B Lo w 3 High 4 C C C B B B Moderate C C B A B A High 3 High C B A A A A A = low noise, B = fairly low noise, C = moderate noise. 1Traffic Designations: Low (ADT2-way < 5,000 veh/day). Moderate (5,000 ≤ ADT2-way ≤ 25,000 veh/day) 3Adjacent Land Use: Low (rural undeveloped or urban developed with non-critical zoning designations [e.g., industrial, commercial]), High (urban partly or fully developed with critical zoning designations [e.g., residential, parks, schools, hospitals]) 4Traffic Speed Designations: Moderate (35 to 45 mi/hr [56 to 72 km/hr]) High (>45 mi/hr [>72 km/hr]) High (ADT2-way > 25,000 veh/day) 2Truck Volume Designations: Low (≤ 15 percent). High (> 15 percent) Table 6-5. Target levels for exterior noise.

88 Candidate Textures by Target Noise Level General Texture Specific Texture Features/Dimensions A B C Remarks Long Drag Burlap Broom or standard turf Heavy turf Greater texture depth provided by heavy turf drag will generate more noise, but will also yield higher friction. Uniform spacing highly prone to creating objectionable tonal spikes. Use on high-speed facilities should be carefully considered. Wider spacing (>0.75 in. avg.) Wider average spacing prone to generating greater overall noise. Tran Tine (Uniform Spacing) Shallow grooves (<3.2 mm) Standard grooves (3.2 mm) Deep grooves (> 3.2 mm) D eeper grooves will generate more noise than shallower grooves, in part because deeper grooves are normally wider and because more mortar is displaced creating additional positive texture (ACPA, 2006). Variable spacing can significantly reduce or remove tonal spikes, but overall noise likely to be same or greater, partly due to increased tine spacing used to create variable pattern (ACPA, 2006). Wider spacing (>1.25 in. avg.) Wider effective average spacing prone to generating greater overall noise. Tran Tine (Variable Spacing) Shallow grooves (<3.2 mm) Standard grooves (3.2 mm) Deep grooves (> 3.2 mm) See above comment. Combination of skewed and variable grooves can effectively eliminate tonal issues and have been shown to reduce overall noise. Wider spacing (>1.25 in. avg.) Wider effective average spacing prone to generating greater overall noise. Tran Skewed Tine (Variable Spacing) Shallow grooves (<3.2 mm) Standard grooves (3.2 mm) Deep grooves (> 3.2 mm) See above comment. Straight grooves Meandering grooves At the sacrifice of some friction, straight grooves generate a little less noise than meandering grooves. Constructability of longitudinal meander tine is low. Wider spacing (>0.75 in. avg.) Preliminary indications suggest that noise may be reduced using narrower tine spacings. Long Tine Shallow grooves (<3.2 mm) Standard grooves (3.2 mm) Deep grooves (> 3.2 mm) Deeper grooves will generate more noise than shallower grooves, in part because deeper grooves are normally wider and because more mortar is displaced creating additional positive texture (ACPA, 2006) Wider spaces (>0.11 in.) Conventional wisdom holds that narrower spacings produce less noise than wider spacings. However, data from this study show conflicting results. Research by others suggests that the profile of the fins produced by the grinding operation are more of a factor (ACPA, 2006). Long Diamond- Grind Shallow grooves Deep grooves For a fixed spacing, shallower grooves will yield lower texture depths, which generate less noise. Wider spacing (0.75 in. std.) Increased groove spacing results in lower overall noise. Long Groove Shallow grooves Deep grooves Increased groove depth results in greater overall noise. Research from other countries indicates low levels of noise can be successfully achieved with these textures. However, experience with their use in the U.S. is very limited (only one EAC site was tested in this study). Careful consideration should be given before accepting either as a feasible option. EAC & Porous PCC Shallow texture Deep texture Increased depth results in greater overall noise. ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Narrow spacing (≤ 0.75 in. avg.) Narrow spacing (≤ 1.25 in. avg.) Narrow spacing (≤ 1.25 in. avg.) Narrow spacing (≤ 0.75 in. avg.) Narrow spacers (≤ 0.11 in. avg.) Narrow spacing (≤ 0.50 in.) ✓ Table 6-6. Identification of textures for new concrete pavements based on noise requirements (and/or preferences).

89 largely determine the texture depth (MTD or MPD), which directly influences the amount of friction and noise that can be expected. Chapter 2 presented examples of texture depth associated with different tine dimensions. This information can serve as a starting point in estimating texture depth, which can then be used to evaluate friction (along with the properties of the expected aggregate) and noise. Step 4—Selection of the Preferred Texturing Alternative The last step in the texture selection process involves evalu- ating the adequacy of feasible textures with consideration of other important surface characteristics, such as splash/spray, fuel consumption and rolling resistance, and cost-effectiveness. Consideration of Other Surface Characteristics Because of the implications to highway safety through bet- ter visibility, consideration must be given to the splash/spray and other surface characteristics. • Splash/spray—Increased macro-texture facilitates sur- face drainage and results in decreased splash/spray inten- sity and duration, thus improving visibility (Pilkington, 1990). – A porous structure (e.g., porous PCC) through which water can be drained vertically and then run off later- ally through the road, rather than on its surface, is the optimum surface for splash/spray. – Splash/spray is less significant on transverse-tined pave- ments than on longitudinal-tined pavements (Kuemmel, et al., 2000), due to the better surface drainage provided by the lateral channels. – Less splash/spray is developed on transverse-tined pave- ments than on dense-graded asphalt (FHWA, 1996b). • Driver perceptions of handling. – Longitudinal-tine spacings greater than 0.75 in. (19 mm) are particularly objectionable to drivers of small vehicles (FHWA, 1996b). – Motorcycle drivers report a perception of instability on longitudinally grooved roads (FHWA, 1980). – Narrower grooves (e.g., 0.1 in. versus 0.125 in. [2.5 versus 3.2 mm]) reduce the vehicle tracking influence (ACPA, 2006). • Rolling resistance/fuel consumption—Roads with high levels of micro-texture and macro-texture result in in- creased rolling resistance and, subsequently, increased fuel consumption. • Tire wear—Both micro-texture and macro-texture con- tribute to tire wear, with micro-texture contributing more significantly to such wear. Candidate Textures by Target Noise Level General Texture Specific Texture Features/Dimensions A B C Remarks Wider spacing (>0.11 in. spacers) Conventional wisdom holds that narrower spacings produce less noise than wider spacings. However, data from this study show conflicting results. Research by others suggests that the profile of the fins produced by the grinding operation are more of a factor (ACPA, 2006). Long Diamond- Grind Shallow grooves Deep grooves For a fixed spacing, shallower grooves will yield lower texture depths, which generate less noise. Standard spacing (0.75 in.) Increased groove spacing results in lower overall noise. Long Groove Shallow grooves Deep grooves Increased depth results in greater overall noise. Shot- Abrade Shallow texture Deep texture Increased depth results in greater overall noise. Thin HMA Overlay Fine Dense-Graded Mix Coarse Dense-Graded Mix Fine mixes have more sand-sized particles which results in decreased texture depths and, subsequently, lower overall noise. Ultra- Thin Bonded Wearing Course Fine Mix (0.1875-in.) Coarse Mix (0.375-in.) Fine mixes, characterized by a smaller top-size aggregate, will have decreased texture depths and, subsequently, lower overall noise. ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Narrow spacing (≤ 0.11 in. spacers) Narrow spacing (≤ 0.50 in.) Table 6-7. Identification of textures for friction restoration of existing concrete pavements based on noise requirements (and/or preferences).

90 • Light reflection/retro-reflection and glare—High levels of macro-texture help break up possible water levels in the wheel tracks (Sandberg, 1998). Economics The final assessment of feasible textures involves costs— both the initial cost of constructing the texture and its long- term or life-cycle cost. Rough estimates of the unit costs asso- ciated with constructing the various texturing options on new concrete pavements and re-texturing options for existing pavements are provided in Chapter 2. Examination of the costs associated with new textures indicates a substantial dif- ference in cost between traditional formed textures (drags and/or tines) and the more labor- and technology-intensive cut textures (ground or grooved), exposed aggregate textures, and porous concrete. For re-texturing, there appears to be a basic cost advantage to shot-abrading over grinding, grooving, and thin resurfacing with asphalt mixes. However, depending on the depth of diamond grinding and the hardness of the aggregate (which affects spacing), grinding costs could be equal to or less than alternatives. The initial costs provided in Chapter 2 can be used as part of a pavement evaluation strategy that considers the design life and projected maintenance and rehabilitation activities. Life-cycle cost analysis (LCCA) techniques, such as net pres- ent value (NPV) and equivalent uniform annual cost (EUAC), may be used to identify the texture(s) with the lowest life- cycle costs. Example Application of Texture Selection Process This section provides an example to illustrate the application of the texture selection process. The example given is for a proj- ect involving the reconstruction (using PCC) of a four-lane freeway with the following features: • The project is located in a suburb of a large city in a wet non- freeze climate (annual precipitation >55 in. [1,400 mm]). • The land adjacent to the highway facility is mostly a mix of professional buildings and residential subdivisions. • The current two-way ADT is approximately 35,000 veh/day and, although there are occasions of congested traffic flow, most of the time, traffic is in free flow condition at the posted speed limit of 55 mi/hr (89 km/hr). • The percentage of heavy commercial trucks that use the facility is estimated to be 12 percent. • The freeway has partially controlled access, with inter- changes every 1 to 1.5 miles (1.6 to 2.4 km). • The terrain is mildly flat; there are no major horizontal curves. • The fine aggregate to be used in the concrete mix is a blend of natural and manufactured sand, and the coarse aggregate is crushed limestone. Historical data on the polishing char- acteristics of the blended fine aggregate indicate a long-term DFT(20) of 60 is expected. • Grinding or grooving of the pavement post-construction is not permitted; there is no local experience with porous concrete and EAC. • Tire whine complaints were reported in the recent past and should be avoided. Steps 1 and 2: The information in Table 6-1 indicates that the project is best represented by friction design category B. The IFI F(60) minimum friction level for this category is 32, but because of the wet environment, a minimum friction of 36 would be desired. For this value and the long-term DFT(20) value of 60, and considering the exclusion of cer- tain texturing methods, Table 6-3 indicates that transverse tining, transverse skewed tining, and longitudinal tining are the most feasible options. Step 3: Because the project is in a noise-sensitive environ- ment and considering the project’s traffic characteristics, Table 6-5 indicates that the selected texture must reduce exte- rior noise to the 100 to 102 dB(A) range (qualitative noise level A). Table 6-6 shows that, of the three friction-based fea- sible textures, only longitudinal tining with certain features/ dimensions will meet the criteria—specifically, narrowly spaced grooves of shallow or standard depth. Based on information provided earlier in Table 2-2, 0.75-in. (19-mm) spaced longitudinal tines with shallow groove depths can be expected to provide an MTD value of about 0.03 in. (0.8 mm). For this value and the long-term DFT(20) value of 60, Figure 6-6 indicates that this texture just barely meets the minimum IFI F(60 ) = 36 criterion. A standard-depth longitu- dinal tine with slightly higher MTD value would better satisfy this criterion. Thus, both textures would be considered as the final feasible options and would be evaluated for other surface characteristics and economics in Step 4. Texture Construction Specifications and Practices Appendix F, available on line at the TRB website, contains sample guide specifications for the following selected group of concrete textures that provide good friction and noise charac- teristics on high-speed pavements: • Heavy turf drag • Transverse skewed variable tine • Longitudinal tine • Longitudinal diamond grind • Longitudinal groove.

91 Successfully constructing these textures requires great attention to detail to both the materials production and con- struction processes. Good QC procedures combined with a statistically based QA program will help ensure that the as-built texture provides the friction and noise characteristics for which it was designed. Therefore, when specifying the depth of grooves and/or texture depth (as measured by the sand patch method, CT Meter, or other texture devices), it is important to account for the expected loss of macro-texture over time/traffic. Important considerations in constructing the selected textures successfully follow: Mix Workability—For drag and tine textures, uniform con- crete slump that is not too dry (workable mix) must be main- tained throughout the paving process. Slight adjustments to the mix (within the limits of specified concrete mix), such as increasing the slump, adjusting the sand content, or adding a retarder, may be required to achieve the desired workability. Texturing Operations— • Drag and tine equipment (preferably a tine and cure machine) should allow the operator to maintain a consis- tent distance behind the paving and finishing operations, apply the proper amount of pressure (uniformly over the width of the paving) on the drag and/or tine assemblies, hinge the tine rake to optimize the angle of tine insertion, and have the capability to water-mist the surface. • Drag and tine operators should be capable of monitoring texturing characteristics closely and making proper adjust- ments in response to site conditions (e.g., changes in mix consistency, rapid drying of the mix due to high winds and/or temperatures, delays in the paving and finishing operations, and buildup of mortar on the drag and/or tines). Timing of the texturing operation is critical: texturing too early may result in grooves filling up with mortar or surface tearing, and texturing too late may result in reduced groove depth (Iowa DOT, 2007). • For heavy turf drags, the potential for significant mortar build-up and release should be considered because this can influence the surface profile and increase roughness. • The speed of diamond grinding operations will be influ- enced by the hardness of the aggregate and the depth of cut. Grinding of pavements with extremely hard aggregate (e.g., quartzite) requires more time and effort than projects with softer aggregate, such as limestone (Correa and Wong, 2001). Curing and Protection—For drag and tine textures, imme- diate application of curing compound or membrane following the texturing operation is essential to achieve good pavement surface durability. If the pavement cures too quickly, the mor- tar forming the texture ridges will not set properly, its durabil- ity will be reduced, and its friction (and noise) properties will be diminished more quickly (FAA, 2004). Generally, curing compounds can be applied earlier for longitudinal dragging and tining operations than for transverse tining operations. Quality Control (QC)—Continuous evaluation and mea- surement of groove dimensions created by tining will help identify and correct deviations from the design profile. Random checks of depth may be made using a tire tread depth gauge or similar tool together with visual checks of the amount of mortar deposited on the surface by the tining operation and the straightness and width of the grooves; deeper tine pene- trations generally result in more ragged and widened (at the top) grooves. Quality Assurance (QA)—Groove and/or texture depth measurements on hardened concrete should be made to deter- mine compliance with texture specifications. The measure- ments should be made at random locations throughout a paving run (or lot) at the earliest possible time following the tex- turing operation. The surface at the locations of testing should be wire brushed or lightly scraped with a steel straightedge to remove all mortar deposits that could affect the measurements. Structural Design Considerations—Because diamond grind- ing generally reduces slab thickness by 0.19 to 0.25 in. (4 to 6 mm), it can influence the cracking potential of a concrete pavement. This is particularly true if the grinding is performed shortly after construction to serve as the initial surface texture. Research has indicated that a 0.25-in. (6-mm) reduction in slab thickness can result in roughly a 30% reduction in fatigue life (Rao et al., 1998). Thus, where diamond grinding is to be used as the initial texture, measures should be considered to offset this effect (e.g., increased thickness or strength requirements). Diamond grinding of an older pavement has less effect on fatigue life because of the strength gain with time (typically 20% higher than the design strength).

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 634: Texturing of Concrete Pavements explores a recommended process for determining the type of concrete pavement texture that may be used for a specific highway project. The process considers the effects of texture type on friction and noise characteristics.

Appendixes A through F contained in the research agency’s final report are available online. The appendixes provide detailed information on the literature review, test results, and data analysis, as well as a sample specification for texture.

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