Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 81
81 CHAPTER 6 Texture Selection Process Selecting a texture for a concrete pavement requires an Although increased macro-texture (i.e., higher MTD) gener- understanding of the particular needs and requirements of the ally results in better surface drainage and thus improved friction facility and matching the friction and noise qualities of the tex- and hysteresis, the increased size and number of asperities tures to those needs (ACPA, 2000). Such needs and require- cause greater excitations in vehicle tires which leads to increased ments vary substantially, because even short stretches of high- noise at the pavementtire interface. Thus, trade-offs between way may present different features, situations, and settings friction and noise must be considered. that affect highway user safety and the quality of life of persons Because friction and noise are both functions of texture, and residing in the vicinity of the highway. Friction demand, for texture changes over time (depending on durability under the instance, is affected by factors such as traffic characteristics effects of traffic, use of snowplows, and environment), the selec- (i.e., speed, volume, and composition), highway alignment tion process must consider both initial and long-term perfor- (i.e., vertical and horizontal), and highway geometric features mance qualities. Both micro-texture (aggregate) and macro- affecting vehicle maneuvers (e.g., presence of turn lanes, cen- texture (mix and texturing) durability properties are critical. ter lanes, interchange ramps, intersections, and driveways). Also, issues such as texture constructability and relevant agency Similarly, highway setting (urban versus rural), right-of-way and contractor experience are important. These factors, as well dimensions, adjacent land use (e.g., residential, commercial, as material costs (aggregates and mixes) and texturing opera- agricultural), terrain, and traffic characteristics determine the tional costs, all affect the cost-effectiveness of textures. need for noise abatement consideration. When selecting a texture, it is paramount that safety, in the Texture Selection form of minimizing the potential for wet-weather crashes caused by inadequate friction, hydroplaning, or splash/spray, A logical, rational process must be used for determining take precedence over designing for all other surface charac- the type of texture needed for a particular highway project. teristics (e.g., noise, rolling resistance, tire wear, and fuel Such a process involves gathering and reviewing all available consumption). critical information about the project, identifying any poten- Although speed and cross-slope are considerations for tial constraints/limitations (both internally and externally) assuring safety, micro-texture and macro-texture must be in terms of available resources/technologies and performance/ controlled to improve friction and reduce the potential for cost expectations, developing alternative feasible solutions, and hydroplaning and splash/spray. Effective micro-texture typ- determining the most economical and practical alternative. ically provides adequate surface friction on dry pavements at Figure 6-1 illustrates the process for identifying pavement all speeds and on wet pavements at slower speeds, whereas surface texturing options at the project level. This process uses macro-texture is typically required to provide adequate fric- key information about the project to establish target levels for tion in wet conditions at high speeds (Hoerner et al., 2003). friction, noise, and other surface characteristics (Step 1). The Pavement micro-texture is primarily governed by the surface target levels are then combined with information on available properties of the aggregate particles comprising the pave- (locally or otherwise) aggregate types and contractor experi- ment surface course, while macro-texture is determined ence with texture construction, to identify feasible texturing by either the texturing method of the surface course or by options (Steps 2 and 3). The cost of each texturing option the mix properties (shape, size, and gradation of aggregate) (both initially and over the life-cycle of the pavement) then is (AASHTO, 2008). estimated, and the results are evaluated carefully with respect
OCR for page 82
82 Step 1--Project Information Input Step 2--Friction Analysis Available Aggregates (incl. Perf Characteristics) Highway Features/Environment (vehicle maneuvers) Highway Alignment (vertical, horizontal) Design Traffic Characteristics (amount, composition) Target Friction Friction/Texture Matrix Levels (Identification of Climatic Conditions Candidate Textures) Design Speed Highway Setting & Adjacent Land Use Contractor Experience Feasible Texture Options Agency Experience & Policies Step 4--Selection of Preferred Texture Step 3--Noise Analysis Economic Consideration of Feasible Texture Noise Regulations & Considerations Other Surface Options Preferences Characteristics Preferred Texture Noise/Texture Matrix Target Noise Alternative (Identification of Levels Candidate Textures) Figure 6-1. Flowchart for texture selection process. to the overall functional and structural design and perfor- · Climatic Conditions--Establishing a higher threshold level mance of the pavement (Step 4). of friction (and thus requiring greater amounts of texture) Steps 2 and 3 in the process cover the identification of fea- may be necessary for locations with increased probability of sible texture options, based on (1) the minimum friction lev- wet-weather conditions (FHWA, 2005), particularly if only els required for safety over the life of the pavement and (2) any polish-susceptible aggregates are available. Because wet maximum noise levels allowed by statute (wayside noise for roads have been shown to be slightly louder (1 to 4 dB(A) adjacent residents or businesses) or desired (interior noise). at the wayside) than dry roads (Sandberg and Ejsmont, Information gleaned from the literature and derived from 2002), consideration should be given to locations with urban the analyses of data collected on existing test sections serves settings. as the basis for these two steps. Friction requirements stipulated · Highway Alignment--Increased friction demand associ- in Step 2 should conform with guidelines established and pre- ated with horizontal and vertical curves is often addressed sented in the Guide for Pavement Friction (AASHTO, 2008). through increases in the horizontal radius of curvature, This four-step process covers both new construction/ inclusion of or increases in curve super-elevation, and/or reconstruction and rehabilitation projects. Steps 1 and 4 are reductions in longitudinal grades. However, the alignments essentially the same for each type of project; Steps 2 and 3 dif- for some projects (particularly, those in which the existing fer depending on the textures involved. 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 Step 1--Project Information Gathering a viable solution. Highway alignment, particularly the char- For each highway project, information pertaining to the acteristics of curves, affects noise. If speed is not reduced, needs and expectations of friction, noise, and other related sharp horizontal curves will have a pronounced effect on surface characteristics must first be gathered. Such infor- far-field noise experienced at the interior of the curve. Also, mation includes because of the need for greater engine power emission dur-
OCR for page 83
83 ing uphill climbs and the likelihood of increased downhill the additional vehicles and by a change from point source vehicle speeds and downhill truck engine breaking, steeper to line source noise (Rasmussen et al., 2007a). grades will result in increased vehicle noise. Pavements with higher percentages of trucks may war- · Highway Features/Environment--Highway geometric fea- rant the consideration of increased texture to account tures and environment influence traffic flow and thus fric- for (1) stopping distances of trucks, (2) steering capabil- tion. Traffic flow is defined largely by the level of interacting ities of trucks, and (3) friction levels produced by truck traffic situations (e.g., entrance/exit ramps, access drives, tires (NCHRP, 2009). Because of its large propulsion unsigned/unsignalized intersections), the presence of con- system and numerous tires, the typical heavy truck is trolled (signed/signalized) intersections, the presence of more than 10 dB(A) louder than a typical passenger car. specially designated lanes (e.g., separate turn lanes at inter- Also, if trucks constitute more than 10% of the traffic sections, center left-turn lanes, through versus traffic lanes), stream, they will likely dominate the overall noise level the presence and type of median barriers, and the setting (Rasmussen et al., 2007a). (urban versus rural) of the roadway facility (AASHTO, 2008). Step 2--Feasible Textures Based on · Design Speed--The design traffic speed will influence both Friction Requirements friction and noise. As speed increases, the level of friction decreases, reaching a minimum at approximately 60 mi/hr With consideration of all relevant project information, an (96 km/hr) (FHWA, 2005). Also, as Figure 6-2 shows, assessment can be made to determine the level of friction pavementtire noise and total vehicle noise increase with required over the life of the new or rehabilitated pavement and increasing speeds, with pavementtire noise increasing by the types of textures that can provide the friction requirements. about 2 to 3 dB(A) per 10-mi/hr (16-km/hr) speed increase The friction design categories identified in the Guide for Pave- (Rasmussen et al., 2007a). At speeds above typical city ment Friction (AASHTO, 2008) for individual segments with speeds (>30 to 35 mi/hr [>48 to 56 km/hr]), pavementtire specific alignment characteristics, highway features/environ- noise is the dominant source in the overall noise produced ment, traffic level, and travel speed can be used to define fric- by vehicles. tion demands. Feasible textures for each segment or for the · Design Traffic Characteristics--Both traffic volume and entire project can be identified (based on the segment with the composition affect friction and noise as follows: highest overall friction demand). The higher the traffic volume, the greater the number Table 6-1 identifies five possible friction design categories, of driving maneuvers (per segment of highway), which A through E, in which "A" represents the highest level of fric- increases the risk of accidents, especially in high-speed tion demand and "E" represents the lowest. The table can be areas (NCHRP, 2009). Pavements with higher traffic used to establish the level of friction required for both new volumes may require greater amounts of texture to pro- construction/reconstruction and rehabilitation projects. vide a higher level of friction (FHWA, 2005). Higher For the selected friction design category for the project (or traffic volumes also result in increased noise because of 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 Figure 6-2. Speed effects on vehicle noise be determined based on the required friction F(60) and sources. the expected long-term micro-texture DFT(20). Figure 6-3
OCR for page 84
84 Table 6-1. Friction design categories. Degree of Degree of Driving Low Traffic1 Moderate Traffic1 High Traffic1 Driving Difficulty due to Difficulty due to Highway Low/ Low/ Low/ Highway Features/ Moderate High Moderate High Moderate High Alignment Issues Environment Speed 2 Speed 2 Speed Speed Speed Speed Low Low E E D C C B High 4 E D D C B A High 3 Low D D C B B A High 4 C C C A A A A = highest friction demand, E = lowest friction demand 1 Traffic Designations: Low (ADT2-way < 5,000 veh/day) Moderate (5,000 ADT2-way 25,000 veh/day) High (ADT2-way > 25,000 veh/day) 2 Speed Designations: Low/Moderate ( 45 mi/hr [ 72 km/hr]) High (> 45 mi/hr [> 72 km/hr]) 3 Project contains multiple locations with considerably tight horizontal curves (with possibly inadequate super-elevation) and/or steep vertical grades. 4 Project contains a considerable number of geometric design features that will increase the number of driving maneuvers and make the driving environment more difficult. provides a means for selecting pairs of DFT(20) and MTD that 24 (category D) and the DFT(20) is 50, then MTD of 0.02 in. will satisfy the following friction ranges: (0.52 mm) would be needed. Table 6-2 provides typical ranges of MTD for newly con- Friction Design structed textures based on values reported in the literature Category F(60) Range and on field measurements made in this study. Also listed in A 36.0 this table are corresponding ranges of MTD that reflect the B 32.0 to 35.9 typical levels of wear experienced by each texture. These val- C 28.0 to 31.9 ues can be used with information on friction requirements D 24.0 to 27.9 and long-term micro-texture (DFT(20)) to identify feasible E 20.0 to 23.9 textures for a project. The frictiontexture plots shown in Figure 6-3 and the For instance, if F(60) must be at least 32 (friction design macro-texture information provided in Table 6-2 have been category B) and the long-term value of DFT(20) is estimated used to identify feasible textures based on friction requirements. to be 60, then a texture with a long-term MTD of 0.026 in. Table 6-3 identifies suitable general texture types for new con- (0.65 mm) would be needed. Or, if F(60) must be at least crete pavements with anticipated specific long-term DFT(20) 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 2.5 2.0 MTD, mm 1.5 1.0 0.65 0.5 0.52 0.0 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Design Friction Ranges E C A D B IFI F(60) Figure 6-3. MTD versus F(60) and DFT(20).
OCR for page 85
85 Table 6-2. Typical ranges of macro-texture for new and aged surface textures. Typical MTD for Typical MTD for Newly Aged/Trafficked Texture Type Created Textures, mm 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 6-3. Identification of textures for new concrete pavements based on friction requirements and expected long-term micro-texture. Friction Long- General Texture Type Design Term Burlap, Broom, Heavy Long Category DFT(20) Std Turf Turf Tran Long Diamond Long Porous Range Drag Drag Tine Tine Grind Groove EAC PCC A >80 (F(60)>36) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40 B >80 (F(60)>32) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40 C >80 (F(60)>28) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40 D >80 (F(60)>24) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40 E >80 (F(60)>20) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40
OCR for page 86
86 values, and Table 6-4 indicates suitable options (including thin interlocking mineral crystals embedded in a matrix of softer asphalt treatments) for re-texturing existing concrete pave- minerals (Folliard and Smith, 2003; Liang, 2003). ments to enhance surface friction characteristics. 2. The relationship between BPN and DFT(20) is expressed Tables 6-3 and 6-4 were developed for aged/trafficked sur- by the following equation (Henry, 2000): 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 BPN = 57.9 × DFT ( 20 ) + 23.1 Eq. 6-1 illustrates texture possibilities, detailed analyses of friction must be performed to ensure that each viable texturing option meets the established friction requirement(s). 3. Consideration could be given to adjusting the minimum Concerning the identification of feasible texturing options F(60) friction design values based on climatic conditions for friction, the following items should be noted: (e.g., values should be increased for locations with high wet-pavement times). 1. Polished DFT(20) values depend on the type and quality of 4. The IFI F(60) friction value is fairly closely aligned with the aggregate used in the surface mixture. Aggregates that FN40S values, particularly for lower texture depths. For exhibit the highest levels of polish resistance and resistance the ranges of F(60) < 50 and MTD 0.04 in. (MTD 1 mm), to wear typically are composed of hard, strongly bonded, there is less than 3% difference between F(60) and FN40S Table 6-4. Identification of textures for restoration of existing concrete pavements based on friction requirements and expected long-term micro-texture. Friction Long- General Texture Type Design Term Long Thin HMA Thin HMA Ultra-Thin Category DFT(20) Diamond Long Shot- Overlay Overlay Bonded Wearing Range Grind Groove Abrade (Fine Mix) (Coarse Mix) Course A >80 (F(60)>36) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40 B >80 (F(60)>32) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40 C >80 (F(60)>28) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40 D >80 (F(60)>24) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40 E >80 (F(60)>20) 70 to 80 60 to 70 50 to 60 40 to 50 30 to 40
OCR for page 87
87 and 3 to 5% difference for the range F(60) < 50 and 0.04 in. ities (<35 mi/hr [<56 km/hr]) are not included in Table 6-5 < MTD 0.08 in. (1 mm < MTD 2 mm). Thus, FN40S because pavementtire noise at low speeds is secondary to can provide a general indication of the F(60) design levels. propulsion/engine noise; texture selection in these instances 5. The textures identified in these tables are based solely on will be more rudimentary. The noise levels given in the assumed long-term friction needs. Consideration of costs, table are representative of those generated at the source by a constructability, and experience may dictate elimination vehicle traveling at 60 mi/hr (96 km/hr); noise characteristics of specific textures from consideration. at other speeds (e.g., the moderate category) are proportional to those for 60 mi/hr (96 km/hr). Step 3--Feasible Textures Based on Unless otherwise desired, feasible textures can be identified Noise Requirements and Preferences on the basis of exterior, at-the-source noise target levels. The data collected in this study show a general relationship between There is no nationally recognized requirement for the max- the noise measured at the source and the noise measured inside imum level of noise (either at the source or at a point on the the vehicle. If lower interior noise levels are required for a proj- wayside) that can be generated by a highway pavement. How- ect, then a lower target level should be selected as the basis for ever, Code of Federal Regulations (CFR) Title 23, Part 772, the identification of feasible textures. governs the amount of overall wayside noise that can be pre- Once a target noise level has been established to meet the dicted to occur for projects to qualify for federal cost sharing. exterior noise requirements and/or interior vehicle noise This CFR does not restrict the use of noise-reducing pavement preferences of the project, the noisetexture alternatives in (Bernhard and Wayson, 2005). Tables 6-6 and 6-7 can be used to identify candidate textures In this step, the qualitative noise level categories presented for new construction/reconstruction and restoration proj- in Chapter 5 are considered. These categories can be fitted to ects, respectively, on the basis of noise. various conditions/scenarios defined by traffic speed, volume, The selection involves determining the general textures suit- and composition; facility setting (urban versus rural); and able for the desired target noise level (A, B, or C). These are des- adjacent land use. Metropolitan projects in noise-sensitive ignated by checkmarks () under the appropriate target noise areas (e.g., residences, parks, and hospitals) and having higher level column (or multiple columns for some textures). More traffic speeds and volumes (trucks and overall) will require specific applications of each general texture can then be evalu- lower levels of exterior noise, thereby narrowing the number of ated, based on the favorable noise characteristic provided by texturing options. Projects in rural settings, on the other hand, the particular features of the texture, as illustrated by arrows will not be as demanding of limits on exterior noise, thereby that stretch across a particular target level or multiple target resulting in more texturing options. levels. Textures spanning target levels A and/or B are also can- Table 6-5 lists target initial exterior noise levels for untraf- didates for target level C; however, higher costs or other factors ficked highway projects, based on the forecast traffic charac- may eventually preclude them from being feasible options. teristics and the noise-sensitivity of the adjacent environ- Identifying specific textures that satisfy both the friction and ment. Only qualitative noise levels A, B, and C are included noise target levels requires iteration of Steps 2 and 3 because in this table because all textures can be designed and con- texture features (i.e., the texture produced by drag devices) structed to meet at least level C requirements. Low-speed facil- and dimensions (i.e., groove spacings, depths, and widths) Table 6-5. Target levels for exterior noise. Low Traffic1 Moderate Traffic1 High Traffic1 Noise-Sensitivity of Traffic Low % High % Low % High % Low % High % Adjacent Land Use Speed Trucks2 Trucks2 Trucks Trucks Trucks Trucks Lo w 3 Moderate 4 C C C C C B High4 C C C B B B High 3 Moderate C C B A B A High C B A A A A A = low noise, B = fairly low noise, C = moderate noise. 1 Traffic Designations: Low (ADT2-way < 5,000 veh/day). Moderate (5,000 ADT2-way 25,000 veh/day) High (ADT2-way > 25,000 veh/day) 2 Truck Volume Designations: Low ( 15 percent). High (> 15 percent) 3 Adjacent 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]) 4 Traffic Speed Designations: Moderate (35 to 45 mi/hr [56 to 72 km/hr]) High (>45 mi/hr [>72 km/hr])
OCR for page 88
88 Table 6-6. Identification of textures for new concrete pavements based on noise requirements (and/or preferences). Candidate Textures by Target Noise General Specific Texture Level Texture Features/Dimensions A B C Remarks Long Drag Burlap Greater texture depth provided by heavy turf drag will Broom or standard turf generate more noise, but will also yield higher friction. Heavy turf Tran Tine Uniform spacing highly prone to creating objectionable tonal (Uniform spikes. Use on high-speed facilities should be carefully Spacing) considered. Narrow spacing ( 0.75 in. avg.) Wider average spacing prone to generating greater overall Wider spacing (>0.75 in. avg.) noise. Shallow grooves (<3.2 mm) D eeper grooves will generate more noise than shallower Standard grooves (3.2 mm) grooves, in part because deeper grooves are normally wider Deep grooves (> 3.2 mm) and because more mortar is displaced creating additional positive texture (ACPA, 2006). Tran Tine Variable spacing can significantly reduce or remove tonal (Variable spikes, but overall noise likely to be same or greater, partly Spacing) due to increased tine spacing used to create variable pattern (ACPA, 2006). Narrow spacing ( 1.25 in. avg.) Wider effective average spacing prone to generating greater Wider spacing (>1.25 in. avg.) overall noise. Shallow grooves (<3.2 mm) See above comment. Standard grooves (3.2 mm) Deep grooves (> 3.2 mm) Tran Combination of skewed and variable grooves can effectively Skewed eliminate tonal issues and have been shown to reduce Tine overall noise. (Variable Narrow spacing ( 1.25 in. avg.) Wider effective average spacing prone to generating greater Spacing) Wider spacing (>1.25 in. avg.) overall noise. Shallow grooves (<3.2 mm) See above comment. Standard grooves (3.2 mm) Deep grooves (> 3.2 mm) Long Tine Straight grooves At the sacrifice of some friction, straight grooves generate a Meandering grooves little less noise than meandering grooves. Constructability of longitudinal meander tine is low. Narrow spacing ( 0.75 in. avg.) Preliminary indications suggest that noise may be reduced Wider spacing (>0.75 in. avg.) using narrower tine spacings. Shallow grooves (<3.2 mm) Deeper grooves will generate more noise than shallower Standard grooves (3.2 mm) grooves, in part because deeper grooves are normally wider Deep grooves (> 3.2 mm) and because more mortar is displaced creating additional positive texture (ACPA, 2006) Long Diamond- Narrow spacers ( 0.11 in. avg.) Conventional wisdom holds that narrower spacings produce Grind Wider spaces (>0.11 in.) 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). Shallow grooves For a fixed spacing, shallower grooves will yield lower Deep grooves texture depths, which generate less noise. Long Groove Narrow spacing ( 0.50 in.) Increased groove spacing results in lower overall noise. Wider spacing (0.75 in. std.) Shallow grooves Increased groove depth results in greater overall noise. Deep grooves EAC & Research from other countries indicates low levels of noise Porous can be successfully achieved with these textures. However, PCC 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. Shallow texture Increased depth results in greater overall noise. Deep texture
OCR for page 89
89 Table 6-7. Identification of textures for friction restoration of existing concrete pavements based on noise requirements (and/or preferences). Candidate Textures by Target Noise General Specific Texture Level Texture Features/Dimensions A B C Remarks Long Diamond- Narrow spacing ( 0.11 in. spacers) Conventional wisdom holds that narrower spacings Grind Wider spacing (>0.11 in. spacers) 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). Shallow grooves For a fixed spacing, shallower grooves will yield lower Deep grooves texture depths, which generate less noise. Long Groove Narrow spacing ( 0.50 in.) Increased groove spacing results in lower overall noise. Standard spacing (0.75 in.) Shallow grooves Increased depth results in greater overall noise. Deep grooves Shot- Abrade Shallow texture Increased depth results in greater overall noise. Deep texture Thin HMA Overlay Fine Dense-Graded Mix Fine mixes have more sand-sized particles which results Coarse Dense-Graded Mix in decreased texture depths and, subsequently, lower overall noise. Ultra- Thin Fine Mix (0.1875-in.) Fine mixes, characterized by a smaller top-size Bonded Coarse Mix (0.375-in.) aggregate, will have decreased texture depths and, Wearing subsequently, lower overall noise. Course largely determine the texture depth (MTD or MPD), which A porous structure (e.g., porous PCC) through which directly influences the amount of friction and noise that water can be drained vertically and then run off later- can be expected. ally through the road, rather than on its surface, is the Chapter 2 presented examples of texture depth associated optimum surface for splash/spray. with different tine dimensions. This information can serve as Splash/spray is less significant on transverse-tined pave- a starting point in estimating texture depth, which can then ments than on longitudinal-tined pavements (Kuemmel, be used to evaluate friction (along with the properties of the et al., 2000), due to the better surface drainage provided expected aggregate) and noise. by the lateral channels. Less splash/spray is developed on transverse-tined pave- Step 4--Selection of the Preferred ments than on dense-graded asphalt (FHWA, 1996b). Texturing Alternative · Driver perceptions of handling. Longitudinal-tine spacings greater than 0.75 in. (19 mm) The last step in the texture selection process involves evalu- are particularly objectionable to drivers of small vehicles ating the adequacy of feasible textures with consideration of (FHWA, 1996b). other important surface characteristics, such as splash/spray, Motorcycle drivers report a perception of instability on fuel consumption and rolling resistance, and cost-effectiveness. longitudinally grooved roads (FHWA, 1980). Narrower grooves (e.g., 0.1 in. versus 0.125 in. [2.5 versus Consideration of Other Surface Characteristics 3.2 mm]) reduce the vehicle tracking influence (ACPA, Because of the implications to highway safety through bet- 2006). ter visibility, consideration must be given to the splash/spray · Rolling resistance/fuel consumption--Roads with high and other surface characteristics. levels of micro-texture and macro-texture result in in- creased rolling resistance and, subsequently, increased · Splash/spray--Increased macro-texture facilitates sur- fuel consumption. face drainage and results in decreased splash/spray inten- · Tire wear--Both micro-texture and macro-texture con- sity and duration, thus improving visibility (Pilkington, tribute to tire wear, with micro-texture contributing more 1990). significantly to such wear.