Methods and Practices on Reduction and Elimination of Asphalt Mix Segregation (2015)

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47 chapter three SURVEY RESULTS DESCRIPTIONS, DETECTION, RESPONSIBILITY, AND TRAINING Descriptions Well-defined descriptions of segregation are important so that agency field staff and contractors have a consistent basis for detecting segregation. Segregation descriptions also help narrow the list of potential areas to target for reducing segre- gation. The first survey question collected information about how segregation is described by each agency or industry rep- resentative (Table 10). Question 1: Your agency considers an asphalt mix to be segregated when there are (Choose all that apply.) The most frequently selected descriptions of segregation are those used to define end-of-truck, random, and longitu- dinal segregation. The majority of respondents also included the description for fine aggregate segregation. Approximately one-third of the respondents also considered the newer and less commonly used descriptions as types of segregation observed in their state. ➢ Segregation is more than just localized areas of pave- ment with coarse texture. Other types of non-uniformity during construction include areas of cooler tempera- tures and evidence of poorly mixed additives or quanti- ties of binder that have drained off of the aggregate. ➢ Clear descriptions of all forms of segregation are to be developed so that field staff can consistently detect segregation. Detection Various methods can be used to detect segregation. The visual and infrared methods are the most commonly used and reported in research studies. Other methods with the potential for detecting segregation include ride quality immediately after construction and monitoring density during or after construc- tion with GPR. Methods that are considered useful for detect- ing segregation were determined with Question 10 (Table 11). Question 10: How are areas of segregation asphalt mix detected? (Choose all that apply.) Almost all of the respondents reported using visual exami- nation to detect segregation. In addition to visual examination, some measurement of temperature differences using infrared guns, infrared cameras, or infrared sensor bars were also used to detect segregated areas. “Bumps” or ride quality (i.e., profilers, profilograph) were frequently used by seven agencies. This may reflect states that have ride quality requirements for the acceptance of the final project, and ride quality is strongly influenced by construction practices that also minimize or eliminate segregation. GPR and a combination of GPR and infrared sensor bars were not selected as methods to detect segregation. ➢ Visual examination alone, or in conjunction with, tem- perature measurements are the most common methods for detecting segregation. ➢ Some form of ride quality measurement is considered as a method for detecting segregation by 15% of the agencies. Responsibility for Detecting Segregation Field inspectors are responsible for detecting and enforcing segregation specifications. Question 2 was included in the survey to determine who performs the field inspections on behalf of the agency (Table 12). Question 2: Does your agency typically perform field inspection of paving projects with agency staff or with consultants? (Choose all that apply.) The majority of agency projects are inspected by agency staff, although some agencies use some combination of agency and consultant staff for field inspection. In one case, as much as 75% of the field inspections are undertaken by consultants. In another case, only 2% of the state’s projects are inspected by consultants. ➢ Field inspection, which is the main method for visually detecting segregation, can be the primary responsibil- ity of agency staff or some combination of consultants and agency staff. ➢ Training is important so all of the field inspection staff have a consistent understanding of: – What definitions of segregation are used. – What causes each type of segregation. – Where to concentrate on detecting segregation before it is returned to the back of the paver.

48 TABLE 11 METHODS FOR DETECTING SEGREGATION (Question 10) Survey Choices Choice of Method(s) Agency (N = 48) Industry (N = 19) % n % n Visual examination 98% 47 100% 19 Infrared thermometer (gun) 24% 11 57% 11 Infrared camera 21% 10 13% 2 Infrared temperature sensors (e.g., Pave-IR) 13% 6 22% 4 Inertial profiler—full size 5% 3 4% 1 Bump detection software for profiler 5% 3 4% 1 Inertial profiler—light weight 3% 1 4% 1 Profilometer (California) 0% 0 13% 2 Ground penetrating radar (GPR) 0% 0 0% 0 Combination of infrared temperature sensors and GPR 0% 0 0% 0 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 10 DESCRIPTIONS OF SEGREGATION (Question 1) Survey Choices Description(s) Agencies (N = 48) Industry (N = 19) % n % n Common Descriptions for End-of-Truck, Random, and Longitudinal Segregation Localized areas of coarse texture in the finished mat 95% 46 100% 19 Longitudinal “streaks” of coarser-texture mix in center of mat behind the paver (e.g., under gear box, at screed extensions) 88% 42 71% 13 Longitudinal “streaks” of coarser-textured mix on one or both sides of mat behind the paver 75% 36 68% 13 Localized areas of very fine texture in the finished mat (smoother surface than uniform textured areas) 68% 32 57% 11 Newer and Less Common Descriptions for Temperature and Additional Forms of Mix Segregation Localized areas of hotter or cooler temperature mix behind the paver 38% 18 45% 9 Transverse sections of cooler temperature mix (e.g., after changing trucks, paver stops) 38% 18 39% 7 Localized “clumps” of fibers and/or binder or other mix additives 30% 14 32% 6 Localized areas of binder-rich (e.g., “fat spots”) in the finished mat 28% 13 42% 8 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. Training and Certification Programs Training of the field and construction staff is important for consistent segregation detection and for identifying the most successful practices for reducing segregation. Ques- tion 19 collected information about the content of existing asphalt plant and field technician certification programs (Table 13). Question 19: Indicate topics that are covered in asphalt plant and/or field technician certification programs (all levels) in your state. (Choose all that apply.) Almost half of training and certification programs contain a section on the identification of segregated mix; however, less than one-third of the respondents believe this training helped reduce segregation. More respondents believe training that

49 TABLE 12 FIELD INSPECTION RESPONSIBILITIES (Question 2) Survey Choices Inspection Staffing Agencies (N = 48) Industry (N = 19) % n % n Agency Staff 86% 48 97% 18 Consultant 44% 23 65% 12 Percent Split When Both Agency and Staff Personnel Perform Inspections % Agency/% Consultant Split When Both Are Used for Inspection 25%/75% 1 No information on percent split included 50%/50% 2 60%/40% 2 65%/35% 1 70%/30% 1 80%/20% 1 90%/10% 2 95%/5% 1 98%/2% 1 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. Survey Choices Included in Program Helps Reduce Segregation Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Aggregate Production and Handling Stockpiling of aggregates 54% 26 45% 9 44% 21 35% 7 Loading cold feed bins 44% 21 39% 7 42% 20 34% 7 Material Properties, Field Sampling, and Identification of Segregation Properties of component materials 60% 29 45% 9 17% 8 23% 4 Random sampling 54% 26 39% 7 17% 8 19% 4 Identification of segregated mix 50% 24 45% 9 29% 14 13% 2 Asphalt Plant Calibration and Quality Control Plant calibration 44% 21 42% 8 19% 9 32% 6 Quality control charts 48% 23 32% 6 15% 7 26% 5 Asphalt Plant Production Heating 38% 18 32% 6 13% 6 23% 4 Blending 38% 18 32% 6 23% 11 26% 5 Drying 38% 18 32% 6 13% 6 19% 4 Mixing 44% 21 26% 5 23% 11 26% 5 Loading haul trucks 54% 26 39% 7 38% 18 26% 5 Mix Transport, Mix Transfer, and Rolling Transportation to job site 46% 21 32% 6 23% 11 26% 5 End dump transfer to paver 46% 22 32% 6 31% 15 29% 6 Loading material transfer device 50% 22 32% 6 38% 18 26% 5 Roller operations 50% 22 42% 8 8% 4 19% 4 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 13 TECHNICIAN TRAINING PROGRAMS (Question 19)

50 covers stockpiling aggregates, loading cold feed bins, load- ing haul trucks, and transferring mix from the haul trucks to the paver is more useful for reducing segregation than train- ing on the detection of segregation. Topics related to asphalt plant production equipment and practices tend to be less frequently included in training or cer- tification programs, although there are a number of key areas of the production process that have a significant impact on segregation. ➢ Training programs may help reduce segregation by: – Explaining how segregation occurs in each part of the production process. – Linking each topic to segregation descriptions and successful practices for reducing or eliminat- ing segregation. TESTING Once segregation is detected, additional testing may be con- ducted to determine if mix properties do not meet the speci- fication requirements. Two questions were included in the survey to collect information about current practices for addi- tional testing in segregated areas. Roadway Density Testing Question 12 elicited information about how any additional roadway density testing was conducted (Table 14). Question 12: If density testing (other than standard ran- dom sampling) is conducted after segregation is identified, indicate how the testing is done. (Choose all that apply.) Both nuclear and non-nuclear density gauges are used in a variety of ways. Single point measurements, pairs of den- sity tests, and longitudinal density profiles are used more frequently than skewed or transverse density profile testing. Gauges are not always calibrated with core properties. ➢ Both nuclear and non-nuclear gauges are used in a variety of ways for additional roadway density testing in segregated areas. ➢ Gauges are not always calibrated with cores. Laboratory Testing Standard QC/QA testing can be used to determine if the mix in potentially segregated areas meets the specification require- ments (Table 15). Question 13 collected information on labo- ratory test methods used when testing potentially segregated samples. The selection of the appropriate test method is impor- tant so that segregation is not under- or over-estimated. Question 13: If cores and/or loose mix are obtained for laboratory testing (other than for standard random sampling) after segregation is identified, indicate the testing which is completed on the potentially segregated mix. (Choose all that apply.) The most frequently used density test was AASHTO T166. This method is quick and simple; however, the uncoated sam- ple can absorb significant amounts of water when testing seg- regated mix. When this happens densities are overestimated, which can lead to erroneously accepting a lot or sublot with out-of-specification materials. Methods that seal the samples before testing can be used to test segregated mixes; however, this was used only 13% of the time, at best. Gradations and asphalt content are determined by sepa- rating the mix back into the individual material components (i.e., asphalt and aggregate). The method used to separate the asphalt from the aggregate portion of the mix can bias the test results. If gradations are determined after burning off the Survey Choices Nuclear Gauge Non-Nuclear Gauge Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Single point on pavement 15% 7 10% 5 10% 5 6% 3 Skewed longitudinal density profile 8% 4 4% 2 4% 2 0% 0 Pair of single points, one each in uniform and non-uniform textured areas 10% 5 10% 5 8% 4 8% 4 Longitudinal density profile 13% 6 10% 5 6% 3 4% 2 Transverse density profile 4% 2 4% 2 0% 0 0% 0 One or more cores taken for gauge calibration 4% 2 13% 6 4% 2 6% 3 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 14 ROADWAY DENSITY TESTING (Question 12)

51 asphalt in the ignition oven, the heat may fracture aggregate particles, which can make the gradation appear less coarse (less segregated). Any moisture retained in the internal aggre- gate voids turns to steam as the oven heats up, which can also fracture the particles. Calibration samples are required to fac- tor out aggregate damage during ignition oven testing. It can be noted that only 35% of the respondents elected to answer this question; the lowest number of responses for any survey question. This may indicate a limited understanding of laboratory testing by construction staff and contractors. A better understanding of the limitations of test methods by field staff and, conversely, a better understanding of the impact of out-of-specification materials on test results would be useful for material engineers. ➢ Laboratory density testing may need to coat (seal) samples before testing to avoid underestimating density changes resulting from segregation. ➢ When determining aggregate gradations for poten- tially segregated samples after ignition oven asphalt content evaluation it is important to account for any aggregate fracturing resulting from heating. ➢ Obtaining better understanding of testing limitations by field staff is important for accurate estimates of mix property changes resulting from segregation. Performance-related testing, such as moisture sensitivity and rutting, can be included in the mix design of the proj- ect. The most common tests evaluate the indirect tensile strength of the mix before and after moisture conditioning (AASHTO T283) and rut testing (e.g., Hamburg loaded wheel test). None of these performance tests were identi- fied as being frequently used to assess changes resulting from segregation. ➢ Performance-based testing is not frequently used to evaluate rutting, fatigue, tensile strength, or permeabil- ity of segregate mixes. SPECIFICATIONS A total of 21 agency respondents documented specific segregation-related specification sections or special provi- sions (Table 16). • Thirteen agencies base their detection of segregation on the visual observations of field inspectors, resident engineers, or district engineers. • Eight agencies use visual inspection to detect segrega- tion with no additional testing requirements outside of standard QC/QA of random samples. Survey Choices Cores Loose Mix Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Density Test Methods Density testing (AASHTO T166) 27% 13 29% 6 0% 0 6% 1 Density testing, paraffin coating (AASHTO T275) 0% 0 6% 1 0% 0 6% 1 Density testing, parafilm wrapped (ASTM D1188) 2% 1 6% 1 0% 0 0% 0 Density testing, vacuum sealed (AASHTO T331) 13% 6 6% 1 0% 0 6% 1 Gradation and Asphalt Content Test Methods Gradation, after ignition oven 21% 10 10% 2 10% 5 16% 3 Gradation, solvent-extracted aggregate 6% 3 10% 2 6% 3 10% 2 Asphalt content, ignition oven (AASHTO T308) 13% 6 6% 1 6% 3 16% 3 Asphalt content, solvent extraction (AASHTO T164) 6% 3 10% 2 10% 5 6% 1 Performance-Related Test Methods Indirect tensile strength, dry (AASHTO T283) 2% 1 6% 1 0% 0 6% 1 Tensile strength ratio (AASHTO T283) 4% 2 % 1 0% 0 6% 1 Permeability 2% 1 6% 1 0% 0 6% 1 Rut testing 2% 1 6% 1 0% 0 6% 1 Fatigue testing 0% 0 0% 0 0% 0 0 0 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 15 RESULTS FOR QUALITY CONTROL/QUALITY ASSURANCE TESTING (Question 13)

GA 400.3.06.E http://www.dot.ga.gov/doingbusiness/ Materials/Documents/provision400.pdf X X X X X X X Case I (Random Segregation) Case II (Regular Intervals of Segregation) Case III (Longitudinal Streaks) IA 2.53.G.4 http://www.iowadot.gov/erl/current/CM/ content/CM%202.50.htm X Testing cores at option of engineer Pay factor on visual inspection S t a t e S p e c i f i c a t i o n W e b s i t e V i s u a l I n s p e c t i o n T e m p e r a t u r e T e x t u r e C o n s t r u c t i o n R e q u i r e m e n t s D e n s i t y ( i n - p l a c e ) T e s t i n g ( c o r e s ) L e v e l s M e a s u r e m e n t R a n g e M T V R e m i x i n g ( g e n e r a l ) O t h e r C o n s t r u c t i o n R e q u i r e m e n t s A s p h a l t C o n t e n t G r a d a t i o n D e n s i t y A i r V o i d s V M A V F A F i n e s t o B i n d e r AK 409.04 http://www.arkansashighways.com/standard_ spec/2014/Division%20400.pdf X 10°F SA X X AL ALDOT 389-98 http://www.dot.state.al.us/conweb/doc/ Specifications/2012%20DRAFT%20Standard %20Specs.pdf X AZ 406-5 http://www.azdot.gov/docs/business/2008- standards-specifications-for-road-and-bridge- construction.pdf?sfvrsn=0 G CA 39-1.05 http://library.constantcontact.com/download/ get/file/1101788399873-201/SS_39_D01-27- 11_v6+_2_.pdf X CO 401 (revision; 2-3-2011) http://www.coloradodot.info/business/design support/construction-specifications/2011- Specs/standard-special-provisions/sections- 200-500-revisions/401ts.docx/view X >25°F T X FL 330-9.2 http://www.dot.state.fl.us/specificationsoffice /Implemented/SpecBooks/2014/Files/ 2014eBook.pdf X X TABLE 16 SUMMARY OF SURVEY RESPONSES AND REVIEW OF SPECIFICATION DOCUMENTS SPECIFICALLY IDENTIFIED BY RESPONDENTS

LA 502.08(b) http://wwwsp.dotd.la.gov/Inside_LaDOTD/ Divisions/Engineering/Standard_Specifications/ Standard%20Specifications/2006%20Standard %20Specifications%20for%20Roads%20 and%20Bridges%20Manual/09%20- %202006%20-%20Part%20V%20-%20 Asphaltic%20Pavements.pdf X X ME 401.201(d) http://maine.gov/mdot/contractors/ publications/standardspec/docs/ ss_combined.pdf X X X X X X X Based on QA pay factors MI 503.03.N http://mdotcf.state.mi.us/public/ specbook/2012/ X Heavy (based on testing cores) MN S-1 (Draft) http://www.dot.state.mn.us/materials/icdocs/ 2016_QualityManagement_SP2014-54.1_ 01.03.14.pdf X ≤25°F good >25°F and ≤50°F moderate 50°F severe MO 403.13.2 http://www.modot.org/business/standards_ and_specs/Sec0403.pdf X X- LP Max. density range; max. density drop ND 408.04.H http://www.dot.nd.gov/manuals/environmental/ 2008-Vol01.pdf X NJ 902.02.04 http://www.state.nj.us/transportation/eng/ specs/2007/spec900.shtm X S t a t e S p e c i f i c a t i o n W e b s i t e V i s u a l I n s p e c t i o n T e m p e r a t u r e T e x t u r e C o n s t r u c t i o n R e q u i r e m e n t s D e n s i t y ( i n - p l a c e ) T e s t i n g ( c o r e s ) L e v e l s M e a s u r e m e n t R a n g e M T V R e m i x i n g ( g e n e r a l ) O t h e r C o n s t r u c t i o n R e q u i r e m e n t s A s p h a l t C o n t e n t G r a d a t i o n D e n s i t y A i r V o i d s V M A V F A F i n e s t o B i n d e r KS 602.4.e http://www.ksdot.org/burConsMain/ specprov/2007/602.pdf BP X- SA Max. density range; max. density drop TABLE 16 (continued) (continued on next page)

OK 411.03.F http://www.okladot.state.ok.us/c_manuals/ specbook/oe_ss_2009.pdf X >10°F T X OR 745.6 http://www.oregon.gov/ODOT/HWY/SPECS/ docs/08book/08_00700.pdf X PA 409.03(h) (3) ftp://ftp.dot.state.pa.us/public/Bureaus/design /Pub408/Pub%20408%20Chg%207/ Sections/409.pdf X X X X X Potentially segregated >0.610-mm texture difference WA 5-04.3 (10)B2 http://www.wsdot.wa.gov/publications/ manuals/fulltext/M41-10/SS2014.pdf X >25°F SA X T = transverse; SA = surrounding area; LP = longitudinal profile; BP = best paving practices; G = general wording; VFA = voids filled with asphalt; VMA = voids in mineral aggregate. S t a t e S p e c i f i c a t i o n W e b s i t e V i s u a l I n s p e c t i o n T e m p e r a t u r e T e x t u r e C o n s t r u c t i o n R e q u i r e m e n t s D e n s i t y ( i n - p l a c e ) T e s t i n g ( c o r e s ) L e v e l s M e a s u r e m e n t R a n g e M T V R e m i x i n g ( g e n e r a l ) O t h e r C o n s t r u c t i o n R e q u i r e m e n t s A s p h a l t C o n t e n t G r a d a t i o n D e n s i t y A i r V o i d s V M A V F A F i n e s t o B i n d e r OH 401.15 http://www.dot.state.oh.us/Divisions/ ConstructionMgt/OnlineDocs/Specifications/ 2013CMS/400/401.htm X <25°F T X TABLE 16 (continued)

55 • Six agencies use temperature measurements in their specifications: – Three agencies (Minnesota, Ohio, and Oklahoma) define segregation based solely on temperature difference. • Three agencies (Arkansas, Colorado, and Washington) use temperature differences to identify areas for further testing. • One agency (Pennsylvania) uses measureable texture changes to identify areas for further testing. • One agency (Arizona) addresses segregation with word- ing to minimize segregation, but does not provide spe- cific directions on how to identify or what to do when segregation is observed. When further testing is required, five agencies use in-place density testing to determine if the non-uniform areas fail to meet specification-defined limits or ranges. Five other agen- cies require additional laboratory testing of cores. Incentives/Disincentives Comments from the agency respondents regarding incentives and disincentives included the following: • Remove and replace is an effective disincentive to obtain corrective action to minimize segregation (12 agencies). • “Suspend operations” for quick resolutions to non- uniformity (two agencies). • Pay adjustments for less severe levels of non-uniformity with the remove/replace option for the most severe non- uniformity (two agencies). • Use of a pay factor disincentive of 5% (one agency). Contractor comments included similar incentives/ disincentives: suspend operations, remove and replace, and percent within limits applied before remove and replace is required. One respondent indicated that the time required for identification, testing, and analysis was actually a sig- nificant disincentive because it can result in construction delays and delay penalties. Another contractor noted that its state had only a disincentive ($10/yd2), with no opportu- nity for incentives; a less subjective method of segregation would be appreciated so that incentives could be included with the disincentive. Advantages Agency respondents noted the following as advantages to their current segregation specifications: • Provides defined steps for the identification and testing of non-uniform mix/work (seven agencies). • Includes the ability to reject unacceptable mix/work (six agencies). • Allows the inspector to use a broad interpretation of “seg- regation” to reject non-uniform mix/work (two agencies). • Forces contractor “best practices” (one agency). • Length of time specification has been in use so every- one knows what to expect (one agency). Contractors reported that the advantages of their state’s segregation specification were: • Encourages the use of effective practices (e.g., use of MTV and no stopping). • Ensures that everyone is aware of the (potential) problem. • Quantifies segregation. • Produces pavements with more uniform densities and smoother ride quality. Disadvantages Agency respondents reported the following disadvantages with their state’s segregation specification: • Subjective specification (12 agencies). • Too much time to test for segregation (four agencies). • No severity level is included (two agencies). • Specification may pass pavement that looks like it may be segregated (one agency). • Cannot be used on previously constructed pavement sec- tions (one agency). • Required equipment not always appropriate for low- volume roadways (one agency). • Contractor complaints about cost of equipment (one agency). Contractors reported disadvantages such as: • Definitions of segregation were subjective. • Central laboratory testing of potentially segregated areas can have a turnaround time of 20 days (or more) and is not useful for daily project QC. • Slows down production. • Additional equipment costs for the contractor. • Poorly trained inspectors, lack of understanding of seg- regation, coarse texture as a result of handwork being defined as segregation. Dispute Resolution Of the agency respondents who provided an answer to this question, ten indicated that very little time was spent on dis- pute resolution. Two agencies noted decreases in time spent on dispute resolution once the specification was amended to require the use of material transfer machines and devices. Other responses included: • Less than 0.5% of the time • 120 person-h/year

56 • 6 times/year • 30% per week during the paving season • Handled at the district level rather than the state level. Contractors noted that very little time is spent on dispute resolution because most “differences of opinion” are addressed in the field. Desired Changes in Segregation Specification Agency respondents believed that the following segregation options would improve their current specification: • Less subjectivity in either (or both) segregation defini- tions and segregation measurements (eight agencies). • Implement temperature measurements (six agencies). • Smaller tolerances for one or more of the following: “pattern segregation” mix property changes, air voids, and number of patches before requiring removing and/or replacing (three agencies). • Defined levels of severity for specific corrective actions (two agencies). • Better guidelines for removing and/or replacing, along with a better definition(s) and measurements (one agency). • Add a segregation test method (one agency). • Require at least one core for testing (one agency). • Mandatory, rather than optional, testing for temperature differences (one agency). Contractor’s indicated the following changes would be desirable: • Less subjectivity • Use Pave-IR technology • Focus on incentives rather than disincentives • Better control of mix gradations • Enforcement of current specification(s) • Use permeability testing in the laboratory to identify potential damage to pavement since stripping (moisture damage) and freeze/thaw cycles are major causes of deterioration. Summary of Segregation Specification Comments • Both agency staff and contractors agree that pay factors and requirements for removal and replacement are great motivators for minimizing segregation. However, con- tractors would like to see the same level of emphasis that is put on incentives placed on disincentives. • Both agency staff and contractors agree specifications that encourage the use of effective practices in plant and placement operations are considered advantages. • Although not stated in the same way, both agency staff and contractors noted that the use of effective practices to minimize segregation has the additional advantages of increasing mat density uniformity and improving ride quality. PAVEMENT DISTRESSES IN SEGREGATED AREAS Segregation is responsible for significant loss of pavement life throughout the country. Question 25 is used to document agency and industry experience about the particular types of distresses that are seen more frequently in segregated areas compared with non-segregated areas (Table 17). Question 25: Based on experience, indicate the type(s) of individual pavement distresses which occur in segregated areas. (Choose all that apply.) Potholes, raveling, and longitudinal raveling are more fre- quently seen in segregated areas of the pavement than in the surrounding pavement. The loss of ride quality (i.e., a rougher ride) in segregated areas is frequently observed by about one- third of the respondents. Raveling is followed in quick succession by longitudinal cracking and fatigue cracking. This concept is supported by respondents noting that longitudinal cracking and fatigue cracking either in or between the wheel paths also occurs more frequently in segregated than non-segregated areas. Reflective cracking, which is cracking initiated by under- lining joints or cracks, was not influenced by segregated mix in the surface layer. Progression of these segregated-related distresses is the source of the loss of pavement life resulting from segre- gation, but are also the least likely to be documented dur- ing traditional network pavement condition surveys. This is because the impact of localized areas of distress(es) are “averaged” using various pavement management system algorithms into the percentage of the roadway with each dis- tress and the perceived impact of each distress on the useful life of the pavement. Twenty-one agency respondents provided responses about the ability of their current pavement condition survey pro- cedures to adequately capture the intermittent nature of segregation-related distresses and these are summarized as follows: • Current procedures are not sensitive enough to evaluate cyclic distresses (nine agencies). • Agency does not specifically track segregation-related distresses (four agencies). • Not sure (four agencies). • Texture has been used, but not routinely (one agency). • International Roughness Index and video are used to con- firm raveling (one agency). • Formal monitoring of interstate roadways is conducted (one agency).

57 • Emerging distresses are evaluated as part of warranty programs (one agency). • Walking survey is conducted for a sample 500-ft section (one agency). • Additional monitoring is done once raveling is detected (one agency). ➢ Intermittent potholes and raveling are the most fre- quently observed distresses in segregated areas of the pavement. ➢ Higher roughness (decreased ride quality) is frequently expected in segregated areas. ➢ Additional distresses seen in segregated areas include intermittent longitudinal and fatigue cracking. ➢ Current pavement condition survey procedures do not adequately capture the intermittent nature of segregation-related pavement distresses. REDUCING SEGREGATION DURING DESIGN, PRODUCTION, AND PLACEMENT Mix Designs Segregation can be reduced or encouraged by choices of grada- tions, asphalt (binder) type, and asphalt content. An additional question was included in the survey to explore the segrega- tion potential of mixes with high recycled asphalt-containing material contents. Recycled materials are typically more variable because of the range of sources of materials, differences in the recy- cled material densities, methods for pre- and post-removal processing, and the lack of consistent QC testing plans of recycled material stockpiles. All of these factors can influ- ence the consistency of the final asphalt mix gradation and Survey Choices Frequently Higher Than Non-Segregated Areas Same as Rest of Pavement Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Raveling, Stripping, Potholes Raveling 52% 25 45% 9 0% 0 6% 1 Longitudinal raveling (e.g., at joints, auger gear box, locations of screed extensions) 35% 17 23% 4 2% 1 0% 0 Raveling along construction joints 40% 19 26% 5 2% 1 0% 0 Potholes (patched or unpatched) 46% 22 39% 7 0% 0 0% 0 Ride Quality Roughness 35% 17 39% 7 0% 0 0% 0 Rutting Depressions in wheel paths (e.g., rutting in low density areas) 8% 4 13% 2 19% 5 6% 1 Cracking Longitudinal cracking in wheel path(s) 25% 12 26% 5 6% 3 6% 1 Fatigue cracking in wheel path(s) 21% 10 19% 4 13% 6 6% 1 Longitudinal cracking, non-wheel path, non- reflective cracking (e.g., at joints, auger gear box, locations of screed extensions) 17% 8 3% 3 6% 3 6% 1 Longitudinal fatigue cracking in only one wheel path (e.g., screed extension location) 17% 8 13% 2 4% 2 6% 1 Transverse cracking 8% 4 6% 1 21% 10 13% 2 Reflective cracking 0% 0 6% 1 17% 8 13% 2 Miscellaneous Distresses Shoulder drop-off, shoving, etc. 4% 2 13% 2 15% 7 6% 1 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 17 PAVEMENT DISTRESSES IN SEGREGATED AREAS (Question 25)

58 asphalt content, which also influence the segregation poten- tial of the mix. Gradations and Mix Type The literature review found that segregation can be reduced by using mixes with smaller maximum aggregate sizes. Little information was found in the literature concerning the segrega- tion potential of stone matrix asphalt (SMA), porous asphalt, and ultrathin wearing course. Question 14 collected informa- tion on these topics (Table 18). Question 14: Based on your experience, indicate the ten- dency of the following aggregate gradations to segregate. (Choose all that apply.): Agencies believe that dense mixes with maximum aggre- gate sizes of 12.5 mm or larger occasionally or frequently seg- regate. Industry representatives believe segregation decreases with decreases in the maximum size of aggregates. All respon- dents agree that mixes with 9.5-mm maximum aggregate size are not likely to segregate. Written comments included dense mixes with 37-mm (1.5-in.) maximum size aggregates and a generic designation of “big rock asphalt base” mixes as likely to segregate. The use of 12.5 mm or smaller maximum size gradations rarely segregate. SMA, porous asphalt, and ultrathin wearing course grada- tions are considered to have some potential for segregation. SMA and porous asphalt mixes often have a larger percent- age of coarser aggregates and higher asphalt contents, which implies that segregation is a separation of asphalt from the aggregates. When there is not enough surface area to “hold” the asphalt, the asphalt drains off of the aggregate. Respon- dent comments indicated that they were less familiar with the segregation potential of these mixes than with dense-graded mixes. ➢ Segregation can be reduced by reducing the maximum size aggregate in the gradation. – 9.5 mm and smaller maximum aggregate size grada- tions are not likely to segregate. ➢ SMA and porous asphalt mixes occasionally segregate (asphalt drains down). Binders (Asphalt) Different types of binders and mixes designed for asphalt con- tents either with higher or lower contents can influence the ability of the binders to “stick” the aggregate particles together (i.e., asphalt film thickness) (Table 19). Question 15: Based on your experience, indicate the impact of various binders on the tendency of mixes to seg- regate. (Choose all that apply.) The only binder-related mix that frequently segregates is one with low asphalt content. Base courses or asphalt- stabilized layers are examples of mixes typically designed with low asphalt contents. In this instance, the segregation potential is related to the asphalt low film thickness that fails to provide sufficient binder to hold the aggregate particles together. Mixes with high asphalt content, and modified and unmodified binders occasionally segregate. There is a trend Survey Choices Frequently Segregates Occasionally Segregates Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Dense-Graded Mixes Dense mix, 25-mm (1-in.) max. agg. size 19% 9 26% 5 15% 7 50% 10 Dense mix, 19-mm (3/4-in.) max. agg. size 15% 7 16% 3 38% 18 45% 9 Dense mix, 12.5-mm (1/2-in.) max. agg. size 0% 0 4% 1 38% 18 36% 7 Dense mix, 9.5-mm (3/8-in.) max. agg. size 0% 0 0% 0 6% 3 14% 3 Other Types of Mixes SMA gradations 0% 0 0% 0 14% 7 23% 4 Porous asphalt gradations 0% 0 6% 1 8% 4 14% 3 Ultrathin wearing course 0% 0 0% 0 4% 2 5% 1 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. Max. agg. = maximum aggregate; min. agg. = minimum aggregate. Boxed values highlight the impact of decreasing maximum aggregate size on the tendency of the mixes to segregate. TABLE 18 TYPICAL ASPHALT MIX GRADATION AND MAXIMUM AGGREGATE SIZES IN USE (Question 14)

59 for warm mix asphalt (WMA) mixes to have a somewhat lower expectation of segregation; however, agency respon- dents selected the “don’t know” choice from 30% to 48% of the time. ➢ Low asphalt content mixes can frequently segregate. Recycled Materials Variability in recycled material particulate sizes and asphalt content has the potential to increase the segregation potential of the asphalt mix (Table 20). Question 16 collected infor- mation about the respondent’s experiences with increasing segregation because of increasing RAP and/or RAS content. Question 16: Based on your experience, indicate the impact of recycled materials used in your mixes to increase the tendency to segregate. (Choose all that apply.) Mixes with recycled material contents are not likely to fre- quently segregate. Mixes with 10% or less RAP are consid- ered to “occasionally segregate” by no more than 13% of the respondents. Mixes with RAP contents of greater than 10% have more potential to occasionally segregate. It is interest- ing to note that industry representatives consider mixes with more than 10% RAP or with some RAS content to be more susceptible to segregation. It is likely that the lack of wide- spread and long-term use with high RAP and/or RAS content can skew the interpretation of the survey results. One agency’s comment drew attention to a potential cause of segregation in mixes with a higher percentage of recycled materials: We have done some limited production of higher RAP mixes (20%). Because we count all RAP asphalt toward the total asphalt content, we have suffered from some dry mixes with higher RAP contents. We have not realized that some RAP asphalt never remixes and that some of the RAP asphalt stays “locked-up” in the RAP and cannot contribute to the overall required asphalt content. Therefore, the measured asphalt content really isn’t the true “working asphalt” content and we end up with drier mixes that segregate easily. That is, the low film thickness that occurs when the asphalt in the recycled material is not fully incorporated in the total Survey Choices Frequently Segregates Occasionally Segregates Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n High asphalt content mixes 0% 0 0% 0 10% 5 23% 4 Modified binder mixes 2% 1 1% 1 17% 8 19% 4 Unmodified binder mixes 2% 1 0% 0 13% 6 23% 4 Warm mix asphalt (WMA) 0% 0 0% 0 8% 4 13% 2 Low asphalt content mixes 15% 7 23% 4 27% 13 32% 6 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. Boxed values highlight (1) WMA mixes to have less of a tendency to segregate than other mixes, and (2) the increased tendency of low asphalt mixes to have the most tendency to segregate. TABLE 19 USE OF ASPHALT BINDER TYPES AND ASPHALT CONTENTS (Question 15) Survey Choices Frequently Segregates Occasionally Segregates Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n RAP mixes, 10% or less 0% 0 0% 0 13% 6 5% 1 RAP mixes, 10% to 25% 0% 0 0% 0 27% 13 25% 5 RAP mixes, greater than 25% 4% 2 3% 1 19% 9 20% 4 Recycled asphalt shingles 0% 0 3% 1 8% 4 20% 4 Combination of RAP and shingles, 10% or less 2% 1 3% 1 4% 2 25% 5 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 20 USE OF ASPHALT-CONTAINING RECYCLED MATERIALS (Question 16)

60 asphalt binder content of the mix ends up producing uninten- tionally lean mixes that in turn produce mixes that are more likely to segregate. ➢ If higher percentages of asphalt-containing recycled materials unintentionally result in low effective asphalt contents (i.e., low film thickness), then the segregation potential of the mixes may increase. ➢ Future research studies might investigate the segrega- tion potential of mixes with high recycled material con- tent and allowable percentages of replacement binder ascribed to these materials. Material and Mix Production Two questions (17 and 18) collected information about the frequency of use of specific equipment, operations, and train- ing. Information was also collected about the respondent’s assessments of each option to help reduce segregation. Aggregate Production The selection of equipment used to move aggregate during the construction of stockpiles and the skills of the loader operator can significantly reduce segregation (Table 21). Question 17: Indicate the typical use of aggregate pit/ quarry equipment and practices and the potential impact on coarse or fine aggregate segregation. (Choose all that apply.) Both agency staff and industry representatives agree that the use of radial, telescoping stackers helps reduce segrega- tion when constructing aggregate stockpiles. The literature also indicates radial stackers with telescoping capabilities are the most effective option for building stockpiles. However, radial stackers (telescoping or fixed) are typically larger- sized equipment, which are used in larger aggregate pit and quarry operations and may be a factor in the lower usage. The more labor-intensive practice of constructing stock- piles with trucks, dozers, and fixed conveyors likely reflect stockpiles commonly built in locations with limited areas for stockpiles, such as at hot mix plants. Higher percentages of personnel-dependent processes make the skills of the loader operators more important to the overall reduction of segrega- tion in asphalt mixes. Slightly less than half of the agency respondents frequently use technician training, but not certification programs for equipment operators. Approximately one-third of the indus- try representatives believe that both training and certification programs can help reduce segregation. Because the skills of the loader operator can impact the level of segregation in the stockpiles, more emphasis on training and certification programs can be helpful for controlling segregation. Loader operator skills are particularly important if aggregate produc- tion and asphalt plant operations are combined at one location, because the same equipment operators can be responsible for both building the stockpiles and loading the cold feed bins. ➢ Segregation in the aggregate stockpiles can be reduced by skilled loader operators. – Stockpiles are much more likely to be built using fixed location conveyors and truck/dozer methods, but are also methods that are more dependent on the skills of the loader operator to prevent segregation. Survey Choices Frequently Used Helps Reduce Segregation Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Equipment Truck dumps/dozer stockpile construction 38% 18 23% 4 17% 8 10% 2 Fixed location conveyors 29% 14 26% 5 4% 2 3% 1 Radial stackers 17% 8 16% 3 17% 8 16% 3 Radial, telescoping stackers 13% 6 10% 2 25% 12 29% 6 Practices Technician certification programs 44% 21 29% 6 8% 4 29% 6 Equipment operator certification programs 6% 3 6% 1 8% 4 26% 5 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 21 AGGREGATE PIT/QUARRY EQUIPMENT AND PRACTICES (Question 17)

61 ➢ Loader operator certification programs are useful for reducing segregation during aggregate stockpile construction. Asphalt Plant Characteristics and Practices Segregation in a batch plant can be introduced into the mix because of a build-up of fines or coarse aggregate in the #1 hot bin and introduced at several points at drum mix plants. Infor- mation on the range of options currently used for equipment and practices that can reduce segregation was collected with Question 18 (Table 22). Question 18: Indicate the typical hot mix plant equip- ment and practices used in your state. (Choose all that apply.) The number of cold bins available at the asphalt plant dic- tates the number of stockpiles that can be used to produce the mix gradation. More stockpiles allow for more stock- pile and gradation options, stockpiles with narrower ranges of particle sizes, tighter control of the job mix formula, and help keep the overall aggregate gradations well-blended. The majority of the respondents frequently use four or more cold feed bins. Approximately one-third of the industry respon- dents believe that the use of four or more cold feed bins helps reduce segregation. Although batch plants are still in use in most states, drum mix plants are used more frequently. Industry representatives indicated that counterflow drums are used somewhat more frequently than parallel flow drums. About one-third of these respondents also use kickback flights in the drum to help increase aggregate drying and mixing times. The lower percentage of responses from the agencies may be because this drum characteristic is not easily observed during production. Kickback flights help reduce segregation by ensuring that a uniform asphalt film thickness is obtained and help reblend the mix to minimize any segregation that may occur in the drum. Fixed plows at the discharge point are used, but not frequently. Survey Choices Frequently Used Helps Reduce Segregation Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Aggregate Cold Feed Bins Cold feed bins, 3 or fewer 19% 9 6% 1 2% 1 3% 1 Cold feed bins, 4 or more 52% 25 58% 11 19% 9 29% 6 Plant Type Batch plants 10% 5 6% 1 8% 4 0% 0 Drum mix plants 56% 27 58% 11 10% 5 20% 4 Drum Characteristics Parallel flow drums 33% 16 23% 4 4% 2 3% 1 Counterflow drums 31% 15 39% 7 6% 3 10% 2 Kick back flights in drum 13% 6 29% 6 13% 6 20% 4 Fixed plow at drum exit 6% 3 10% 2 4% 2 3% 1 Silos Silo loading batcher 38% 18 45% 9 19% 9 35% 7 Load out accomplished in multiple drops 52% 25 55% 10 29% 14 39% 7 Training Plant technician certification programs 38% 18 16% 3 13% 6 30% 6 Cold feed bin loader operator skills/training programs 4% 2 48% 9 13% 6 25% 5 Plant equipment operator certification programs 6% 3 23% 4 6% 3 20% 4 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 22 ASPHALT PLANT CHARACTERISTICS AND PRACTICES (Question 18)

62 Almost half of the industry respondents use silo batchers that help reduce segregation. Noticeably fewer agency respon- dents noted a frequent use of silo batchers or believe this equip- ment reduces segregation. More than half of all respondents use multiple drops to load haul trucks and about one-third believe this helps reduce segregation. More than one-third of the agencies use plant technician training programs; however, significantly fewer believe this training program can help reduce segregation. Less than 20% of the industry representatives noted that plant techni- cian training is used; however, more than one-third believe this training helps reduce segregation. The differences between agency and industry respondents are likely the result of how technician test results are used; that is, agen- cies use testing for acceptance and contractors use the results for process (quality) control. One interesting obser- vation is that industry representatives are more likely to believe training and certification programs are important for reducing segregation. ➢ Segregation can be reduced when – Four or more cold feed bins are used at the asphalt plant. – Drum mix plants use kickback flights. – Silo batchers are used. – Haul trucks are loaded with multiple drops. – Training and certification programs are used for asphalt plant technicians, loader operators, and asphalt plant operators. Mix Transport and Mix Transfer Segregation that occurs during asphalt mix production can be perpetuated and enhanced, or significantly reduced, by how the asphalt mix is transferred to the paver. Asphalt mix that is segregated in the truck and deposited directly into the paver hopper appears as end-of-truck segregation in the finished pavement. Question 20 collected information about the type of haul trucks typically used on state projects and whether the respondents believed that the choice of the type of haul truck influences segregation (Table 23). Question 20: Indicate the type(s) of haul trucks used in your state. (Choose all that apply.) Agencies are more likely to use (see) a range of haul truck types on state projects. End dumps are the most frequently used; however, approximately one-third of the agencies see belly dumps and approximately one-sixth see live bottoms on state projects. State projects are typically larger projects that can benefit from transporting large amounts of mix at one time. Industry responses reflect more regional and local agency projects that have a wider range of project sizes, lengths, traf- fic levels, individual project constraints, and smaller budgets than those overseen by state agencies. About 10% of the agency respondents believe that larger capacity haul trucks can help reduce segregation. This may be a reflection of the how the mix is transferred to the paver when either belly dumps or live bottom trucks are used. Belly dumps deposit mix in a windrow and windrow eleva- tors can help reblend the mix as it is placed in the paver hopper. Live bottom truck bed designs that funnel the mix down and horizontally out the back can also help minimize segregation. An additional benefit from using these types of trucks is that they do not have to be raised to transfer the mix. This implies that areas with height restrictions are more easily accessed. ➢ Belly dumps and live bottom haul trucks may help reduce segregation, but this may actually be because of how the mix is transferred to the paver. Survey Choices Frequently Used Helps Reduce Segregation Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n End dumps 43% 20 58% 11 0% 0 0% 0 Transfer dumps (pups) (i.e., end dumps with extra trailer) 4% 2 0% 0 0% 0 0% 0 Bottom dumps (belly dumps) 31% 15 3% 1 10% 5 3% 1 Live bottom (flow boys) 15% 7 0% 0 13% 6 3% 1 Mixed types of trucks on single project 8% 4 10% 2 0% 0 0% 0 Quad axle dump trucks 2% 1 0% 0 0% 0 0% 0 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 23 USE OF TYPES OF HAUL TRUCK (Question 20)

63 ➢ End dump haul trucks are the most frequently used truck types but the choice of truck type depends on the size of the project physical limitations (e.g., height constraints), and the mix of truck types in the contractor’s fleet. Information about mix transport practices that may reduce temperature segregation and how mix is transferred to the paver was collected with Question 21 (Table 24). Question 21: Indicate the mix transport and transfer equipment and practices used in your state (Choose all that apply.) Tarps are used to minimize flying debris and help slow temperature loss. At least half of the respondents frequently use tarps on haul trucks; however, fewer than one-quarter believe tarps actually help reduce (temperature) segregation. Less than 20% of the respondents use insulated truck beds. One-third of the respondents use MTDs and also believe that this equipment helps reduce segregation. Because belly dumps are used approximately one-third of the time on state projects, about the same percentage indicated the use of wind- row elevators. At most, one-quarter of the agency respondents remove spills between the haul truck and paver, a practice that is considered likely to reduce segregation. Industry frequently removes spills, but does not always consider this a practice that can help reduce segregation. ➢ Temperature segregation can be reduced by using insulated truck beds. – Tarps may help, but may more likely be used to pre- vent flying debris. ➢ MTDs help reduce segregation. – Windrow elevators are not considered as effective at reducing segregation. ➢ Removing spillage of mix between the haul trucks and paver is a good practice that may help reduce some forms of segregation. Pavers Paver equipment and paving practices can either reduce or increase segregation, particularly longitudinal segregation (Table 25). Information about paver equipment and opera- tions currently in use was collected with Question 22. Question 22: Indicate the typical paver equipment and practices used in your state. (Choose all that apply.) Front of the Paver Older paver designs that use conveyors to move the mix from the hopper to the screed are still used on more than half of the pavers. Newer designs that replace conveyors with a pair of twin augers are now used about one-third of the time. The twin augers help pull mix from the entire paver hopper as well as reblend the mix as it moves back to the screed. Eliminating the conveyors may help reduce longitudinal segregation when Survey Choices Frequently Used Helps Reduce Segregation Agency (N = 48) Industry (N = 19) Industry (N = 19) % n % n % n % n Haul Truck Characteristics During Transport Tarps 50% 24 55% 10 23% 11 10% 2 Insulated truck beds 17% 8 10% 2 19% 9 10% 2 Heated truck bodies 0% 0 0% 0 0% 0 0% 0 Mix Transfer from Truck to Paver Material transfer device 31% 15 35% 7 29% 14 35% 7 Material transfer device with remixer 31% 15 32% 6 31% 15 35% 7 Windrow elevator (if windrow paving is used) 27% 13 3% 1 10% 5 10% 2 Baffle in truck bed around hydraulic lift 10% 5 3% 1 4% 2 6% 1 Removal of spillage between end dump and paver 23% 11 31% 6 25% 12 15% 3 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. Agency (N = 48) TABLE 24 HAUL TRUCK CHARACTERISTICS AND MATERIAL TRANSFER UNITS (Question 21)

64 coarser aggregate particles roll off the edges of the conveyors or are fractured under the conveyor belts. The conveyor belt configuration has also been linked to early occurrences of top-down cracking that aligns with the edges of the conveyor belts; the newer paver designs may also reduce this type of distress. Although none of the respondents indicated that they fre- quently flip the paver wings, approximately one-third noted that this practice is still occasionally used (28% to 33%). The use of material transfer units helps minimize this practice, because the surge bin in the hopper prevents this practice. Back of the Paver Screed extensions either front or back and with or without auger extensions are used about 40% of the time. Only the use of the auger extensions can reduce segregation. About the same percentage of pavers still have gear boxes in the center of the screed. From one-quarter to one-third of the pavers in use can bal- ance the flow of mix so that both sides of the screed augers receive the same volume of mix. The literature review indi- cated that keeping a uniform volume of mix across the screed can significantly reduce segregation and dragging of the screed because one or both augers are starved for mix. However, only 10% of the respondents believe that an option for variable flow is important to reducing segregation. The potential benefit of this equipment option could be explored more thoroughly in future studies. There is currently a limited use of temperature differences to adjust paving operations. Agency respondents, more than industry, believe this is useful for reducing segregation. ➢ Segregation can be reduced with the use of: – A pair of twin augers to move mix from the hopper to the screed.  The benefit of this design could be investigated in future research studies. – Auger extensions are used when screed extensions are deployed. ➢ Additional research is essential to determine if the use of balanced mix flow across the screed augers reduces segregation. – The literature review identified this feature as ben- eficial, but the survey results do not confirm the literature. Compaction Several documents found in the literature review acknowl- edged the potential for sound compaction practices and Survey Choices Frequently Used Helps Reduce Segregation Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Front of Paver Hopper, slat conveyor(s) 65% 31 58% 11 13% 6 15% 3 Hopper, twin augers 29% 14 20% 4 15% 7 20% 4 Paver operator folds wings between each load 0% 0 3% 1 6% 3 10% 2 Back of Paver Screed extensions, front of screed 40% 19 15% 3 2% 1 10% 2 Screed extensions, back of screed 38% 18 39% 7 0% 0 10% 2 Auger extensions 38% 18 42% 8 25% 12 20% 4 Spread auger, gear box 46% 22 42% 8 6% 3 10% 2 Spread auger, outboard motor 6% 3 3% 1 2% 1 3% 1 Use of variable mix distribution to balance flow to augers 23% 11 35% 7 10% 5 10% 2 Use of mix temperature information to make adjustments to paver operation 6% 3 10% 2 17% 8 10% 2 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 25 PAVER EQUIPMENT AND OPERATIONS (Question 22)

65 aggressive compaction to minimize low density in mix or temperature segregation (FHWA 2002; Gilbert 2005). How- ever, no specific studies were found to substantiate these observations. Question 23 was included to collect informa- tion on typical compaction practices for breakdown, inter- mediate and finish rolling, and the possibility for improved durability with various combinations of rollers (Table 26). Question 23: Indicate typical roller types used in your state. (Choose all that apply.) Over half of the respondents use steel wheel vibratory rollers for breakdown rolling. Agencies use steel wheel vibra- tory rollers as the intermediate roller about twice as often as pneumatic rubber tire rollers. Industry representatives use both types about equally. This difference in use is likely a reflection of the wider range of project sizes and traffic volumes repre- sented by the industry responses. Industry representatives are slightly more convinced than the agencies that an intermediate steel wheel vibratory roller can help improve the durability in segregated areas. About one-quarter of the agencies believe that the use of inter mediate pneumatic rubber tire rollers can help improve durability; however, significantly fewer industry representatives agree. Steel wheel rollers are commonly used as the finish rollers, but are not considered to improve durability in segregated areas. ➢ Steel wheel vibratory rollers are commonly used as the breakdown roller. – There is no consensus on whether they can improve the durability in segregated areas. ➢ Pneumatic rubber tire rollers are used as the interme- diate rollers about one-quarter of the time. – There is no consensus on whether they can improve the durability in segregated areas. Survey Choices Frequently Used Helps Improve Durability of Segregated Mix Agency (N = 48) Industry (N = 19) Agency (N = 48) Industry (N = 19) % n % n % n % n Breakdown Rollers Breakdown, steel drum, vibration 65% 31 55% 10 23% 11 16% 3 Breakdown, steel drum, no vibration 15% 7 10% 2 10% 5 0% 0 Breakdown, pneumatic 4% 2 0% 0 15% 7 3% 1 Intelligent compaction unit 2% 1 0% 0 6% 3 3% 1 Intermediate Rollers Intermediate, steel drum, vibration 42% 20 29% 6 10% 5 16% 3 Intermediate, steel drum, no vibration 8% 4 6% 1 8% 4 0% 0 Intermediate, pneumatic 27% 13 23% 4 25% 12 13% 2 Finish Rollers Finish, steel drum 67% 32 55% 10 6% 3 10% 2 Not all respondents answered all questions. Responses for “occasionally used,” “rarely used,” and “don’t know” not shown; multiple answers were allowed. TABLE 26 COMPACTION EQUIPMENT (Question 23)