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Practices for Unbound Aggregate Pavement Layers (2013)

Chapter: Appendix A - Questionnaire

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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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Suggested Citation:"Appendix A - Questionnaire ." National Academies of Sciences, Engineering, and Medicine. 2013. Practices for Unbound Aggregate Pavement Layers. Washington, DC: The National Academies Press. doi: 10.17226/22469.
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127 APPENDIX A Questionnaire SURVEY QUESTIONNAIRE NCHRP PROJECT 20-5 TOPIC 43-03 PRACTICES FOR UNBOUND AGGREGATE PAVEMENT LAYERS NCHRP TOPIC 43-03 SURVEY QUESTIONNAIRE February 2011 The Transportation Research Board (TRB) is preparing a Synthesis on “Practices for Unbound Aggregate Pavement Layers.” This is being done for NCHRP, under the sponsorship of the American Association of State Highway and Transportation Offi- cials (AASHTO), in cooperation with the Federal Highway Administration (FHWA). Granular aggregate base and subbase layers are very important in pavement construction and performance. Properly designed and constructed bases have the potential to improve pavement performance and longevity while also addressing today’s issues like the costs of other pavement materials, the need to save energy, and to reduce greenhouse gas emissions associated with the construction and reconstruction of pavements. A synthesis is being undertaken concerning the full range of unbound aggregate base and subbase issues for both flexible and rigid pavement systems. States have diverse specifications and construction practices for unbound aggregate pavement layers; sharing this informa- tion among the states will most likely lead to better design and construction practices. Information is being gathered through a literature review, survey of the members of the AASHTO Highway Subcommittee on Materials (including Canadian prov- inces), and selected interviews. Gaps in knowledge and current practices will be noted, along with research needs to address these gaps. This synthesis will ultimately provide information for harmonization of specifications (particularly on a regional basis) to ultimately benefit both states and material producers without adverse impacts on pavement performance. This questionnaire is being sent to State Departments of Transportation. Your cooperation in completing the questionnaire will ensure the success of this effort. If you are not the appropriate person at your agency to complete this questionnaire, please forward it to the correct person. Please complete and submit this survey by April 6, 2012. For questions, please contact our principal investigator: Erol Tutumluer, Ph.D. E-mail: tutumlue@illinois.edu Phone (217) 333-8637 Please identify your contact information. NCHRP will email you a link to the online report when it is completed. Agency: ____________________________________________________________________________________________________ Address: ____________________________________________________________________________________________________ City: ____________________________ State: ___________________________ ZIP: _____________________________ Questionnaire Contact: _______________________________________________________________________________________ Position/Title: ______________________________________________________________________________________________ In case of questions and for NCHRP to send you a link to the final report, please provide: Tel: ______________________________________________ E-mail: _______________________________________________

128 General: Use of Unbound Aggregate Base and Subbase Layers Please provide the contact information of the persons in your agency who directly deal with the material selection and char- acterization, as well as design and construction of unbound aggregate base and subbase layers for pavement applications. The consultants will contact the relevant personnel separately with specific questions. Material Selection and Characterization Name: _____________________________________________________________________________________________________ Position/Title: ______________________________________________________________________________________________ Address: ___________________________________________________________________________________________________ City: ____________________________ State: ___________________________ ZIP: _____________________________ Telephone: __________________________ ; E-Mail: _________________________; Fax: ___________________________ Pavement Design Name: _____________________________________________________________________________________________________ Position/Title: ______________________________________________________________________________________________ Address: ___________________________________________________________________________________________________ City: ____________________________ State: ___________________________ ZIP: _____________________________ Telephone: __________________________ ; E-Mail: _________________________; Fax: ___________________________ Construction of Pavements with Unbound Aggregate Layers Name: _____________________________________________________________________________________________________ Position/Title: ______________________________________________________________________________________________ Address: ___________________________________________________________________________________________________ City: ____________________________ State: ___________________________ ZIP: _____________________________ Telephone: __________________________ ; E-Mail: _________________________; Fax: ___________________________ 1. Is it common practice for your agency to incorporate unbound aggregate layers into the design and construction of pavement structures? (Note that this survey focusses on unbound aggregate layers in asphalt, concrete, and compos- ite pavements only, and does not include unbound aggregate layer applications in unsurfaced pavements and gravel roads.) � Yes � No If your answer to the above question is “No”, you do not need to complete this survey. Please include comments below regarding why your agency does not prefer to construct unbound aggregate layers as pavement base and subbase courses. ________________________________________________________________________________________________ ________________________________________________________________________________________________ ________________________________________________________________________________________________ 2. What types of unbound aggregate layers are commonly constructed by your agency? (Please check all that apply.) � Base course � Subbase course

129 � Open graded drainage layer � Pavement working platforms for subgrade stability applications 3. What types of pavement structures designed and constructed by your agency commonly incorporate unbound aggregate layers? � Flexible pavements (comprising hot mix or warm mix asphalt surface layer) � Rigid pavements (comprising portland/hydraulic cement concrete slabs) � Rehabilitated pavements (asphalt overlay over concrete, etc.) � Others such as composite pavements, inverted pavements, etc. (Please specify): 4. What primary functionalities of unbound aggregate layers are intended to serve in pavement systems designed and con- structed by your agency? (Please check all that apply.) � Dense graded base courses as primary structural layers � Open graded layers under rigid pavements for uniform support and providing drainage � Pavement construction platforms to protect weak subgrade layers from excessive rutting under heavy construction equipment loading � Others (please specify): Category 1: Material Selection and Construction Practices 5. How frequently does your agency check the acceptance of materials obtained from commonly used and/or approved aggregate sources? � Prior to the use on every major construction project � More than twice every year � Twice every year � Once every year � Less than once every year � Other (please explain): 6. What tests are used by your agency for evaluating quality aspects of virgin aggregate materials for pavement base and subbase applications? (Please check all that apply.) � Na2SO4/MgSO4 Soundness Test � Los Angeles Abrasion and/or Micro Deval Test � Sieve Analysis � Percent Deleterious Materials � Other (please indicate): ___________________________________________________________________ ___ 7. Does your agency permit the use of uncrushed aggregates in pavement base and subbase applications? � Yes � No � Other (please explain):

130 8. What is the maximum aggregate particle size (Dmax) in inches allowed by your agency in the following constructed unbound aggregate layers? � Dense graded base: � Dense graded subbase: � Open graded base as drainage layers: � Open graded subbase as drainage layers: � Other (please list below): 9. What is the maximum amount of fines (material finer than 0.075 mm or passing sieve No. 200) allowed by your agency for aggregates to be used for unbound aggregate base and subbase course applications? � Dense graded base (%): � Dense graded subbase (%): � Open graded base/subbase as drainage layers (%): 10. Does your agency specify different allowable percent fines (material finer than 0.075 mm or passing sieve No. 200) for aggregates having nonplastic and plastic fines? � Yes (please give the specified values below): � Base, Nonplastic (%): � Base, Plastic (%) � Subbase, Nonplastic (%): � Subbase, Plastic (%): � No 11. What is the maximum value of plasticity index (PI) allowed by your agency for the fines fraction of aggregate materials to be used in the following unbound pavement layers? � Dense graded base: � Dense graded subbase: � Open graded base as drainage layers: � Open graded subbase as drainage layers: 12. Does your agency have a list of approved aggregate types and sources for base and subbase course applications? � Yes (please reference document/website) � No � Other (please explain): 13. If you answered “Yes” to Question 12, does your agency frequently allow new materials into the list of approved aggregate types and sources for base and subbase course applications? � Yes � No � Other (please explain):

131 14. Does your agency have specific guidelines regarding the transportation and storage (stockpiling) of aggregate materials for base and subbase construction? � Yes (please reference document/website) � No � Other (please explain): 15. What is the maximum construction lift thickness for unbound aggregate layers permitted by your agency? � 6 in. � 8 in. � 10 in. � 12 in. � Other (please indicate): � No such restrictions 16. Does your agency allow the construction of multiple unbound aggregate layers placed on top of each other (e.g., dense graded base over an open graded drainage layer)? � Yes � No � Other (please explain): 17. If you answered “Yes” to the above question, do you separate the two unbound aggregate layers by any kind of constructed aggregate separation (i.e., filter) layer? � Yes � No � Other (please explain): 18. Does your agency allow the construction of unbound aggregate layers over or under pavement layers stabilized/treated with lime, fly ash, cement, or bitumen? � Yes � No � Other (please explain): 19. If you answered “Yes” to the above question, please give typical thicknesses of such constructed layers: • Thickness (in.) of stabilized layer • Thickness (in.) of unbound aggregate layer Category 2: Unbound Aggregate Base Characterization for Design 20. Who is responsible for testing/characterizing aggregate materials and providing input properties for the design of pave- ments with unbound granular layers? � Geotechnical/materials laboratory � University laboratory (under research subcontract) � Field engineer � Other (please indicate):

132 21. What laboratory tests are conducted by your agency for strength, deformation, and modulus characterization of unbound aggregates used in base and subbase course applications? (Please check all that apply.) � Strength index tests (e.g., CBR, Hveem stabilometer, etc.) � Triaxial shear strength tests � Repeated load triaxial tests for resilient modulus (standard tests such as AASHTO T 307, NCHRP 1-28, etc.) � Repeated load triaxial tests for permanent deformation behavior � Other (please indicate): 22. What field tests are conducted by your agency for strength, deformation, and modulus characteristics of in-service unbound aggregate layers? (Please check all that apply.) � Plate Load tests � Dynamic Cone Penetrometer (DCP) tests � Falling Weight Deflectometer (FWD) tests � Light Weight Deflectometer (LWD) tests � Soil Stiffness Gauge tests (e.g., GeoGaugeTM, etc.) � Other (please indicate): 23. How often are these laboratory/field tests conducted to characterize aggregate materials for use in granular base and sub- base layers? � Once on limited aggregate types/materials commonly used by the agency � On a project-need basis � Once on all agency-approved aggregate sources � At regular intervals on agency-approved aggregate sources to establish a database � Other (please indicate): 24. Is the structural contribution of open graded aggregate drainage layers taken into account in pavement thickness design by your agency? � Yes � No � Other (please explain): 25. What method is used by your agency to design pavements with unbound aggregate base and subbase layers? � 1972 AASHTO Design Guide � 1986 AASHTO Design Guide � 1993 AASHTO Design Guide � Mechanistic-Empirical Pavement Design Guide (MEPDG) � Agency-Specific Mechanistic Procedure: � Agency-Specific Empirical Procedure: � Other (please indicate): 26. What aggregate properties and/or characteristics are used as inputs for the design of pavements with granular base/subbase layers by your agency? (Please check all that apply.) � Percent passing sieve sizes (gradation) and/or maximum aggregate particle size � Particle shape and angularity (crushed or uncrushed)

133 � Compaction characteristics; i.e., optimum moisture content and maximum dry density � Shear strength properties (e.g., friction angle, CBR, etc.) � Resilient modulus � Other (please indicate): _______________________________________________ 27. What approach is adopted by your agency for assigning resilient modulus values to unbound aggregate base and subbase layers? � Modulus is not used in pavement design � Single modulus is assigned to the entire layer � Stress-dependency of aggregate layer modulus is considered during pavement design � Based on research by the International Center for Aggregate Research (ICAR), anisotropy (directional depen- dency) of aggregate layer modulus is considered � Other (please indicate): ______________________________________________ 28. How does your agency determine the resilient modulus of unbound aggregate materials for use in granular base and sub- base layers? � Resilient modulus testing in the laboratory � Empirical correlations with index properties like CBR, gradation parameters, etc. � In-place modulus measurement of constructed layers by deflection-based methods such as FWD, LWD, etc. � Other (please indicate): _______________________________________________ 29. Does your agency have special provisions for including new and/or locally available “marginal” aggregates in the thick- ness design of unbound base and subbase layers? � Yes � No � Other (please explain): ________________________________________________ Category 3: Compaction, Quality Control, and Field Performance 30. How are aggregate compaction characteristics established in the lab by your agency? � Drop-hammer based methods like the standard and modified Proctor tests � Static compaction methods � Vibratory compaction methods � Gyratory compaction methods � Kneading compaction methods � Other (please indicate): ________________________________________________ 31. List typical equipment used for placement and construction of unbound aggregate base/subbase layers in your state. (Please check all that apply.) � Dump truck � Material Transfer Device � Trucks and graders � Aggregate spreaders

134 � Other (please indicate below): 32. Please describe briefly the preferred method of placement and construction of unbound aggregate base and subbase lay- ers in your state. 33. How is moisture content of constructed/compacted unbound aggregate base and subbase controlled in the field? � According to quarry reported moisture content � Sampled during construction/compaction for laboratory testing � Measured through field testing using (please indicate): � Other (please indicate): 34. What is an acceptable variation from optimum moisture content for constructed/compacted unbound aggregate base and subbase allowed by your agency? 35. What is the primary approach used by your agency for evaluating degree of compaction and construction quality control of unbound aggregate base and subbase layers? � Gradation � Proof-rolling � Measurement of constructed layer density � Field measurement of constructed layer modulus � Continuous compaction control by means of Intelligent Compaction (IC) equipment � Other (please indicate): 36. If your answer to the previous question was “Measurement of constructed layer density,” what method is commonly used by your agency for measuring constructed layer densities in the field? � Nuclear density methods (ASTM D 2922/AASHTO T310 or T238) � Sand cone method (ASTM D 1556/AASHTO T191) � Balloon method (ASTM D 2167) � Oil or water method � Drive cylinder method (ASTM D 2937) � Rapid method (ASTM D 5080) � Electrical density measurement method (ASTM D 7698) � Other (please indicate):

135 37. Is it common practice for your agency to construct “test strips” to establish roller patterns and check for compaction density growth of unbound aggregate base and subbase layers? � Yes � No � Other (please explain): 38. If your answer to the above question was “Yes,” do you primarily use nuclear density measurement method for this purpose? � Yes � No � Other (please explain): 39. What is the primary mode of nuclear gauge operation used by your agency for density checks on constructed unbound aggregate base and subbase layers? � Direct transmission � Backscatter � Not applicable (nuclear density measurement not used) 40. If your agency uses the “drop-hammer based” methods to establish compaction characteristics of aggregates in the labora- tory, please circle and select all applicable options from the list below regarding the minimum compaction requirements in the field: Pavement Type Aggregate Layer Type Compaction Method Field Relative Compaction Flexible Base Standard Proctor 90% 95% 100% Other ________ Flexible Base Modified Proctor 90% 95% 100% Other ________ Flexible Subbase Standard Proctor 90% 95% 100% Other ________ Flexible Subbase Modified Proctor 90% 95% 100% Other ________ Rigid Base/Subbase Standard Proctor 90% 95% 100% Other ________ Rigid Base/Subbase Modified Proctor 90% 95% 100% Other ________ 41. If you selected “Other” as one of the responses to the above question, please specify the answer below (submit your answer in the format: Flexible Base-Standard Proctor-xx%) � 42. If your agency does NOT use “drop-hammer based” methods to establish compaction characteristics of aggregates in the lab- oratory, please specify the relative compaction requirements for the following unbound aggregate base/subbase applications: Pavement Type Aggregate Layer Type Field Relative Compaction Flexible Base 90% 95% 100% Other ________ Flexible Subbase 90% 95% 100% Other ________ Rigid Base/Subbase 90% 95% 100% Other ________ 43. If you selected “Other” as one of the responses in the above question, please specify the details below: �

136 44. Is there common interest among engineers in your agency to implement non-nuclear density measurement methods for construction quality control of unbound aggregate base/subbase layers? � Yes (please select all possible reasons): � Safety concerns � Nuclear certification too expensive � Nuclear certification too inconvenient � Non-nuclear methods provide better results � No � Other (please explain): 45. Has your agency ever participated in demonstration projects involving continuous compaction control of unbound aggre- gate base/subbase layers using Intelligent Compaction (IC) techniques? � Yes � No � Other (please explain): 46. Has your agency actively implemented IC techniques to construct in-service pavements with unbound aggregate base/ subbase layers? � Yes � No � Other (please explain): 47. If your answer to the above question was “Yes,” does your agency have a specification for continuous compaction control using IC techniques and construction of unbound aggregate base/subbase layers? � Yes � No � Other (please explain): 48. Does your agency implement modulus-based compaction control for the construction of unbound aggregate base/subbase layers? � Yes � No � Other (please explain): 49. If you answered “Yes” to the previous question, what method is used for measuring the field modulus of constructed unbound aggregate layers? � Falling Weight Deflectometer (FWD) � Light Weight Deflectometers (LWD) � Soil Stiffness Gauge (e.g., GeoGaugeTM) � Seismic testing such as the Portable Seismic Pavement Analyzer based on spectral analyses of surface waves � Other (please indicate):

137 50. If you answered “Yes” to question No. 46, what percentage of construction projects in your agency involve modulus based compaction control? � <10% � 10–30% � 30–60% � >60% 51. Does your agency use any non-traditional compaction technique (e.g., South African “slushing” technique) during the construction of unbound aggregate base/subbase? � Yes (please name the technique and give brief detail below) � No Comments: 52. Does your agency perform FWD tests to assess the structural condition of unbound aggregate base and subbase layers in existing in-service pavements? � Yes � No � Other (please explain): 53. If your answer to the previous question was “Yes,” what backcalculation program/software/approach does your agency use to determine granular base/subbase modulus from the FWD test results? (Please indicate below.) 54. What tests are commonly used by your agency to evaluate the field-performance of existing pavements with unbound aggregate base and subbase layers? (Please list all.) Category 4: Recycling Aggregates and Recycled Granular Materials Note: Recycled Granular Materials in this questionnaire refer to Recycled Concrete Aggregates (RCA) and Reclaimed Asphalt Pavement (RAP) materials only. 55. Does your agency commonly recycle unbound aggregate materials from base and subbase layers of existing pavements for application in new and rehabilitated pavement construction? � Yes � No � Other (please explain):

138 56. If your answer to the previous question was “Yes,” what tests are used by your agency for evaluating the quality of these recycled aggregates? (Please check all that apply.) � Na2SO4/MgSO4 Soundness Test � Los Angeles Abrasion and/or Micro Deval Test � Sieve Analysis � Percent Deleterious Materials � Other (please indicate): 57. What other tests are used by your agency to characterize recycled aggregates from existing base and subbase courses for acceptance and design? (Please list all.) � � � 58. Is the use of recycled aggregates from existing base and subbase courses incorporated into your agency specifications? � Yes � No � Other (please explain): 59. Does your agency allow contractors to use locally available “marginal or out of specification” aggregates for unbound aggregate base and subbase layer applications? � Yes � No � Other (please explain): 60. What other recycled granular materials are approved for use by your agency in unbound aggregate layer construction? (Please check all that apply.) � Reclaimed Asphalt Pavement (RAP) � Recycled Concrete Aggregates (RCA) � Other (please indicate): � None of the above (please skip to Category 5 of the survey) 61. What tests are used by your agency for evaluating the material quality of recycled granular materials (RCA, RAP, and/or others from question No. 58) for base and subbase applications? (Please check all that apply.) � Na2SO4/MgSO4 Soundness Test � Los Angeles Abrasion and/or Micro Deval Test � Sieve Analysis � Percent Deleterious Materials � Other (please indicate):

139 62. What other tests are used by your agency to characterize recycled granular materials (RCA, RAP, and/or others from ques- tion No. 58) for acceptance and design? (Please list all.) � � � 63. Does your agency have environmental concerns regarding the use of recycled granular materials (RCA, RAP, and/or oth- ers from question No. 58) in unbound aggregate base and subbase layers? � Yes � No � Other (please explain): 64. If your answer to the above question was “Yes,” what environmental issues is your agency particularly concerned about (e.g., leaching, etc.)? � � � 65. Does your agency require strength, deformation and modulus testing and characterization of recycled aggregates (from existing base and subbase courses) as well as recycled granular materials (RCA, RAP, and/or others from ques- tion No. 58)? � Yes � No � Other (please explain): 66. If you answered “Yes” to the previous question, are these characterization tests the same as those used for virgin aggregates? � Yes � No (please indicate below how the test methods are different) Comments: Category 5: Climatic Effects and Drainage 67. Are climatic effects on pavement subgrade performance a major concern for your agency? � Yes � No � Other (please explain): 68. If your answer to the above question was “Yes,” please check all factors that contribute to this concern: � Groundwater table (GWT) is often shallow (can be less than 5 ft deep) under the pavements � Native soils primarily fine-grained (e.g., silts, clays, etc.) and may get wet of optimum due to upward movement of moisture from GWT � In-service pavement subgrades are often under “wet of optimum” moisture conditions

140 � Seasonal fluctuations cause significant changes in subgrade soil properties � Subgrades stay frozen for extended periods (one month or longer) � More than 10 freeze-thaw cycles per year are experienced at the subgrade level � Spring thaw weakening and timing of spring load restrictions � Subgrade soils are primarily frost-susceptible (i.e., silty soils) 69. Are aggregate materials selected for use in granular base/subbase applications by your agency tested for climatic effects (e.g., soil water characteristic curve, freeze-thaw durability, suction characteristics of fines, etc.)? � Yes (please indicate the test types) � No � Other (please explain): 70. Does the pavement design procedure used by your agency consider the effects of climatic changes on unbound aggregate layer performance? � Yes � No � Other (please explain): 71. If your answer to the above question was “Yes,” what unbound aggregate layer properties are adjusted in your pavement design procedure to account for detrimental climatic effects on pavement performance? � Layer structural coefficients � Resilient modulus � Shear strength � Other (please indicate): 72. Are there different gradations specified by your agency for unbound aggregate applications targeting drainable vs. low permeability aggregate layers? � Yes � No � Other (please explain): 73. If drainage is one of the primary functions of your flexible pavement unbound aggregate base/subbase layer, what approach is adopted by your agency to facilitate the drainability of dense-graded base courses? � Limiting the maximum allowable percent fines (material passing sieve No. 200) � Increasing the maximum aggregate size � Adjusting the constructed layer gradation toward a more open-graded layer � Other (please explain): 74. Does your agency distinguish between crushed and uncrushed aggregate types while constructing open-graded drainage layers? � Yes � No � Other (please explain):

141 75. How is the effectiveness of an open-graded aggregate drainage layer measured by your agency? � In-situ permeability measurements � Laboratory tests to measure the permeability of aggregate samples � Empirical correlations to estimate the permeability from aggregate physical properties like gradation, dry density, specific surface, and void ratio (or porosity) � Other (please explain): 76. For pavement structures with aggregate drainage layers, is it common practice in your agency to include a filter layer underneath to protect the drainage layer from clogging? � Yes (open graded aggregates commonly used to construct the filter layer) � Yes (geosynthetics commonly used as the mode of filtration) � No (no extra layer constructed for filtration purposes) 77. How common is it for your agency to construct subsurface drainage systems like “edge-drains” under unbound aggregate base and subbase layers? � Yes, very common � Yes, for specific projects when required by the design � No, not common at all This is the End of Questionnaire Thank you for your Cooperation

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 445: Practices for Unbound Aggregate Pavement Layers consolidates information on the state-of-the-art and state-of-the-practice of designing and constructing unbound aggregate pavement layers. The report summarizes effective practices related to material selection, design, and construction of unbound aggregate layers to potentially improve pavement performance and longevity.

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