APPENDIX G—AGENCY AND INDUSTRY SURVEYS

INTRODUCTION

The research team developed and conducted an online survey of highway agencies and pavement industry personnel to identify successful practices for limiting damage of asphalt and composite pavements due to the presence of water. The agency survey was sent to all US highway agencies and Canadian Provincial Governments (total of sixty-three agencies). The industry survey was sent to the state asphalt and concrete associations, the American Concrete Pavement Association, the Asphalt Emulsion Manufactures Association, the Asphalt Interlayer Association, the Asphalt Recycling and Reclaiming Association, the FP² for Pavement Preservation, the Geosynthetics Material Association, the International Slurry Surfacing Association, the National Asphalt Pavement Association, and the National Center for Pavement Preservation (total of seventy-three industry personnel). Agency survey questions are shown in Appendix B and industry survey questions are shown in Appendix C.

AGENCY SURVEY RESULTS

A total of thirty-nine highway agencies (response rate of 62 percent), including five Canadian Provinces and thirty-four SHAs, responded to the agency survey. The research team made multiple attempts to increase the agency response rate by email notifications and personal outreach, with the above results.

The survey requested agency personnel to respond to a variety of questions related to their experience with water-related damage issues, geometrics, pavement design, drainage design, construction, preservation, and rehabilitation. The following provides a summary of key survey findings (a complete list of survey responses is provided in Appendix D).

General Information

Agencies were asked to provide their assessment of which distress/condition types tend to indicate damage due to the presence of water. A number of agencies also indicated that while damage may not be initially caused by water, distress tends to become more severe in the presence of water. A summary of agency-identified asphalt and composite pavement distresses due to the presence of water is provided in Figures G-1 and G-2, respectively. The majority of respondents indicated that pumping, stripping, and potholes were the primary distress types that indicate damage due to water in new construction, rehabilitation, and preservation of asphalt pavements (Figure G-1). Alligator cracking, heaving, raveling, and delamination were also identified as distress types that tend to indicate damage in asphalt pavements due to the presence of water.

Similarly, for composite pavements, the majority of respondents indicated that pumping, stripping, and potholes indicated damage in composite pavements due to the presence of water (Figure G-2). A number of respondents also indicated that delamination, patching, and raveling were indicators of water-related damage in composite pavements.

Agencies were asked to identify the methods used for assessing pavement damage due to the presence of water. Figure G-3 illustrates the identified water-related pavement damage assessment methods. The majority of agencies (twenty-eight) indicated that damage assessment is predominantly conducted through pavement coring, asphalt laboratory testing (17 responses), notification by agency personnel (14 responses), and pavement condition assessment (14 responses).

In order to determine the extent of pavement damage due to the presence of water, agencies were asked to indicate whether water-related pavement damage was (1) not an issue, (2) an issue, or (3) an issue in the past, but current agency specifications and practices have minimized the damage. Table G-1 provides a summary of agency responses in relation to premature failure or accelerated distress in new construction, rehabilitation (rehab), and preservation (pres) of asphalt and composite pavements due to the presence of water.

Of the responding agencies, 16 indicated premature failure or accelerated distress due to the presence of water in new asphalt pavements, while only one agency indicated an issue with new composite pavement construction (only 14 agencies indicated construction of new composite pavements). Twenty-three agencies indicated issues in asphalt pavement rehabilitation treatments and 14 agencies indicated issues in composite pavement rehabilitation treatments. Finally, 14 agencies indicated issues in asphalt pavement preservation treatments and eight agencies indicated issues in composite pavement preservation treatments. Nine agencies indicated that water-related premature failure or accelerated distress had been an issue in the past; however, these issues have been minimized due to specification or process changes. These responses are further illustrated in Figures G-4 and G-5 for asphalt pavements and composite pavements, respectively (note: values shown indicate the number of responding agencies).

Table G-1. Agencies’ experience with damage due to water in asphalt and composite pavements.

Agency	Asphalt Pavements			Composite Pavements
	New	Rehab	Pres	New	Rehab	Pres
Alabama DOT
Alaska DOT&PF
Alberta Transportation			―			―
Arizona DOT
California DOT
Colorado DOT
Connecticut DOT
Florida DOT
Hawaii DOT
Idaho TD
Indiana DOT
Kansas DOT
Kentucky TC
Maine DOT
Manitoba I&T
Maryland SHA
Michigan DOT			―	―	―	―
Minnesota DOT
Mississippi DOT
Missouri DOT
Nebraska DOR
Nevada DOT
New Brunswick DOTI
New Jersey DOT
New York State DOT			―
Ohio DOT
Oklahoma DOT
Ontario MOT
Oregon DOT
Pennsylvania DOT
Saskatchewan MHI
South Carolina DOT
South Dakota DOT
Tennessee DOT
Texas DOT
Virginia DOT
Washington State DOT
West Virginia DOH			―
Wisconsin DOT

= Water-related damage not an issue—no premature failures or accelerated distress.

= Water-related damage an issue—premature failures or accelerated distress.

= Water-related damage a past issue, now minimized by current practice.

= new composite pavements are not constructed.

― = no response.

The nine agencies that indicated water-related damage had been minimized due to current practice include Idaho, Indiana, Minnesota, Mississippi, Nevada, New Jersey, Oklahoma, Pennsylvania, and South Carolina. The current practices and procedures for these nine agencies (and others who indicated no issues with damage due to the presence of water) will be considered for use as case studies or agency examples in the guidelines.

Agency practices that have helped to minimize premature failure or accelerated distress are summarized in Tables G-2 and G-3 for asphalt and composite pavements, respectively.

Table G-2. Summary of agency practices for mitigating pavement damage due to moisture.

Table G-3. Summary of agency practices for mitigating damage in composite pavements due to the presence of moisture.

Table G-4 summarizes agency responses to the types of drainage features used by roadway functional classification. As expected, the predominant drainage features used by the majority of agencies are roadside ditches, followed by curb and gutter, underdrains, and daylighted bases. The less common drainage design features from the responding agencies include the use of fin drains, permeable friction courses, and cement-treated permeable bases.

Table G-4. Agency drainage feature utilization by functional classification.

Note: values shown represent number of responding agencies.

Agencies were asked to indicate if a drainage design checklist was used to assist the designer in determining if and when special designs are warranted for mitigating existing water or potential water problems. Three agencies, the Florida DOT, the Maryland SHA, and the New Jersey DOT indicated that a checklist was used (see Appendix E).

Practices for Addressing Freeze-Thaw Conditions

Figure G-6 illustrates agency responses to practices for addressing freeze-thaw conditions. Of the agencies that indicated freeze-thaw conditions exist, the primary practices include increasing the aggregate base layer thickness (17 agencies), placement of a non-frost-susceptible material over the existing subgrade (14 responses), minimizing the percent passing the No. 200 sieve in the

aggregate base course (13 responses), and imposing spring load restrictions (11 responses). Additional agency practices include adding a Styrofoam layer (Colorado DOT), stabilizing the subgrade (Nebraska DOR and Ohio DOT), including drainage (New York State DOT), and applying a seasonal factor to the subgrade resilient modulus value in the pavement design process (Pennsylvania DOT). It should be noted that many agencies employ multiple methods to mitigate pavement damage due to freeze/thaw conditions. For example, Washington State DOT indicated the use of all six methods, while Idaho TD, Maine DOT, Indiana DOT, and Manitoba I&T indicated using five of the six methods to mitigate freeze-thaw damage.

Practices for Addressing Weak Soils

Figure G-7 provides a summary of agency practices for addressing weak soil conditions. The primary practices include removing and replacing weak soil with higher quality material (twenty-eight responses), placing a geosynthetic between the subgrade soil and the base layer (twenty-four responses), increasing the aggregate base layer thickness (twenty-four responses), and stabilizing the subgrade layer (twenty-two responses). As with freeze-thaw mitigation, agencies may include multiple methods for minimizing damage due to weak soils.

Practices for Addressing High or Perched Water Tables

Twenty-three agencies indicated having practices for addressing high or perched water tables, which include installing edge drains, increasing the depth of roadside ditches, and installing culverts (Figure G-8). Nine agencies indicated that high or perched water tables are typically not a concern.

Agencies provided several additional practices, including adding subdrains or underdrains (six agencies), asphalt base (one agency), dry wells (one agency), French drains (one agency), drain rock (one agency), and increasing the pavement structural thickness (one agency).

Materials

Agencies responded to a number of questions related to material properties for aggregate base, asphalt- and cement-treated permeable base, geosynthetics, and asphalt materials. Table G-5 provides a summary of agency responses related to base materials; additional details (e.g., property values) are provided in Appendix D. Of the responding agencies, a majority (twenty--

one agencies) indicated the use of permeable aggregate base or a separator layer, 15 agencies indicated the use of asphalt-treated permeable base, and nine indicated the use of cement-treated permeable base. For all base types, predominate material specifications include L.A. Abrasion, non-plastic materials, and sodium sulfate soundness. For asphalt- and cement-treated permeable bases, the majority of agencies also indicated the use of maximum aggregate size and percent asphalt/cement.

Table G-5. Agency permeable base material specifications.

Note: values shown represent number of responding agencies.

Agencies indicated a variety of uses for geosynthetic materials. As shown in Figure G-9, these include subgrade separation (twenty-one agencies), subgrade stabilization (16 agencies), base reinforcement (14 agencies), drainage systems (12 agencies), and overlay stress absorption and reinforcement (seven agencies).

In relation to asphalt materials, agencies were asked to provide information related to predominant asphalt surface material type, test type for quantifying material moisture susceptibility, and the type of additive used to mitigate moisture-related damage. The following summarizes the responses.

• Predominate asphalt mixture type used by responding agencies include (see Figure G-10):
  • – Dense-graded (thirty-two responses).
  • – Open-graded (nine responses).
  • – Gap-graded (six responses).
• Tests for moisture susceptibility used by the responding agencies include (see Figure G-11):
  • – AASHTO T 283 (thirty-three responses).
  • – ASTM D4867 (six responses).
  • – AASHTO T 324 (five responses).
  • – AASHTO T 340 (one response).
• Asphalt mixture additives used by the responding agencies include (see Figure G-12):
  • – Liquid anti-strip (thirty-five responses).
  • – Dry or hydrated lime (twenty-six responses).
  • – Lime slurry (four responses).
  • – Lime slurry and marination (four responses).

Construction

Table G-6 summarizes responses on methods for accepting subgrade preparation, drainage, permeable aggregate base/separator layer, asphalt- and cement-treated permeable base, and asphalt mixtures.

Table G-6. Agency construction-related requirements.

Maintenance and Preservation

Figures G-13 through G-15 illustrate the agency responses for maintaining drainage features and preserving asphalt and composite pavements to minimize damage due to the presence of water. In total, thirty-one responses were received in regard to maintaining drainage features and preserving pavements to minimize damage due to the presence of water.

Figure G-13 illustrates that the majority of agencies maintain drainage features through cleaning ditches and removing culvert debris (twenty-four responses each), mowing and cleaning ditches (twenty-one responses), and repairing or replacing defective components (20 responses). A number of respondents also indicated pipe inspection (16 responses), mowing around outlet pipes (16 responses), and unplugging outlets, filters and drains (15 responses) as drainage maintenance activities. The fewest responses included deepening ditches (ten responses), drainage system video inspection (six responses), and flushing edge drains (six responses).

For asphalt pavement preservation activities, the majority of responses indicated the use of crack sealing (twenty-nine responses), chip sealing (twenty-two responses), and thin asphalt overlays (20 responses) (Figure G-14). A number of responses included the use of microsurfacing (17 responses) and surface seals (14 responses). For the purpose of this survey, surface seals were defined as fog seals, sand seals, and scrub seals.

Although the response rate is slightly lower, the pavement preservation activities for composite pavements are ranked in the same order as the asphalt pavement preservation activities (Figure G-15). Agencies indicated that crack sealing is one of the more prevalent preservation activities on composite pavements (twenty-four responses). Chip seal, thin asphalt overlay, and microsurfacing applications on composite pavements are conducted by half of the responding agencies, and ten agencies indicated the use of surface seals.

Rehabilitation

A summary of agency responses for asphalt pavement rehabilitation treatments for mitigating damage due to the presence of water is shown in Figure G-16. Of the thirty agencies responding to this survey question, the predominant responses included milling followed by an asphalt overlay (twenty-eight responses), pavement reconstruction (twenty-three responses), and an asphalt overlay (16 responses). Seven agencies indicated the use of cold in-place recycling and retrofit edge drains, two agencies indicated the use of an unbonded concrete overlay, two agencies indicated the use of milling, asphalt overlay, and sawing and sealing, and only one agency indicated using an asphalt overlay and sawing and sealing.

The majority of agencies (20 responses) indicated milling followed by an asphalt overlay as an effective treatment for mitigating damage to composite pavements due to the presence of water (Figure G-17). Reconstruction, retrofitting edge drains, and asphalt overlays received nine to 11 responses, and the remaining treatments had less than three responses each.

The final survey question asked respondents to identify which pavement and drainage features they considered to be the most effective in mitigating pavement damage due to the presence of water. Feature effectiveness was based on a scale of 1 to 5, with 5 being effective and 1 being ineffective in limiting pavement damage. A summary of agency responses on pavement and drainage feature effectiveness is provided in Table G-7. Agencies indicated that the most effective (based on the sum of responses indicating an effectiveness ranking of 4 and 5) pavement and drainage features for mitigating damage due to the presence of water include asphalt mixture additives, asphalt mixture aggregate quality, pavement drainage design, and asphalt mixture air voids/in-place density.

Table G-7. Agency assessment of drainage and pavement feature effectiveness.

Notes:

– Values shown represent number of responding agencies.

– Effectiveness is rated on a scale of 1 (ineffective) to 5 (effective).

INDUSTRY SURVEY RESULTS

A total of 12 industry members (out of seventy-three, for a response rate of 16 percent) responded to the industry survey. Responses were received from nine asphalt industry members and three concrete industry members. As with the agency survey, the research team made several attempts to increase the survey response rate through email notifications. Unfortunately, no additional responses were received. A summary of industry survey results is provided in the following discussion (a complete list of survey responses is provided in Appendix F).

Drainage and Pavement Feature Effectiveness

Industry members were asked to identify the effectiveness of various drainage and pavement features in minimizing the presence of water in asphalt and composite pavements. Feature effectiveness was based on a scale of 1 to 5, with 5 being effective and 1 being ineffective in limiting pavement damage. Figure G-18 presents the industry responses that have a feature effectiveness ranking of 4 or 5. Industry members indicated that asphalt permeable base (nine responses) was an effective feature, followed by aggregate permeable base, ditches, and open-graded friction courses (six responses each), and curb and gutter and edge drains (five responses each). Industry members also identified cement-treated permeable base as the least effective feature.

Effectiveness of Drainage Systems

Next, industry members were asked to rate the effectiveness (on a scale of 1 to 5) of drainage systems in removing water from the roadway. Specifically, industry members were asked to rank the effectiveness of aggregate trenches, edge drains, underdrains, and fin drains. Figure G-19 illustrates industry responses on drainage systems’ effectiveness. As in Figure G-18, the number of responses illustrated in Figure G-19 indicate the sum of responses received with a ranking of 4 and 5. While the results of the industry survey indicated that edge drains and underdrains were more effective than fin drains and aggregate trenches in removing water from the pavement structure, very few of the industry responses indicated that these drainage systems were effective in removing water from the pavement structure.

Practices for Addressing Weak Soils

Industry members were asked to identify methods that are effective in reducing the impact of weak soils on pavement performance. A summary of responses is shown in Figure G-20. All industry members indicated that removing and replacing weak soils with higher quality material or stabilizing weak soils (12 responses each) are effective measures in reducing pavement damage due to weak soil conditions. In addition, increasing the aggregate base thickness (nine responses) and placing a geosynthetic between the weak soil and the base layer (eight responses) were also effective methods for addressing weak soils. Only three industry members indicated increasing the asphalt layer thickness and only two industry members indicated increased the concrete layer thickness (for composite pavements) as effective methods for minimizing damage due to weak soil conditions.

Figure G-20 also includes the results of the agency responses on methods of addressing weak soil conditions (for all comparison plots, agency responses have been normalized to the number of industry responses for comparison purposes). As shown, there is a strong agreement between agency and industry responses on the top four methods; however, the order of method ranking is slightly different between the two survey results. Agencies and industry ranked remove and replace with high quality materials and increase the aggregate base thickness in the same order, but industry ranked stabilizing the weak soil higher than placing a geosynthetic, which was opposite of the agency ranking. Both surveys were in agreement on the rank order for increasing the asphalt or concrete layer thicknesses.

Practices for Addressing High or Perched Water Tables

The assessment of the effective methods for addressing high or perched water tables by the responding industry members indicated that installing edge drains (seven responses) and deepening roadside ditches (six responses) were slightly more effective than installing culverts (five responses) (Figure G-21). Three of the industry members indicated that high or perched water tables were typically not a concern. Additional comments included adding course aggregate drains and adjusting roadway profiles (during the design phase) to account for high or perched water tables. As shown in Figure G-21, the industry rank order of effective methods for addressing high or perched water tables is the same as the agency responses.

Effective Use of Geosynthetics

Figure G-22 summarizes the industry ranking of effective uses for geosynthetic materials. Industry members indicated that geosynthetics were effective in drainage systems (eight responses), separating subgrade soil from the base layer (seven responses), and subgrade stabilization (seven responses). Industry members ranked the use of geosynthetics as base reinforcement (two responses) and as an overlay stress absorption/reinforcement layer (one response) considerably lower than the other three uses. In comparison, agencies indicated a slightly different rank order for geosynthetic uses, ranking drainage systems lower than that of the industry members.

Construction

Similar to the agency construction-related questions, industry members were asked to respond to a series of questions related to construction of drainage systems, and subgrade, base, and asphalt layer placement. The following provides a summary of industry construction-related responses:

• The appropriate timing for drainage system installation is prior to pavement construction (eight responses). However, three responses indicated that placement should be at the edge of the outside shoulder, while five responses indicated that placement should be at the pavement/shoulder edge. The majority of responding agencies (twenty-one responses) indicated that the preferred location is at the pavement/shoulder edge.

• The drainage system installation should be verified by flushing the system (two responses), conducting a video survey (two responses), conducting a visual survey or taking cores (one response), ensuring good inspection during installation (one response), and verification is not required (one response).

• The effective methods for measuring subgrade compaction requirements are shown in Figure G-23. The majority of the industry responses included monitoring subgrade compaction through in-place density (ten responses), proof rolling (eight responses), and monitoring moisture content (five responses). None of the industry members indicated the number of passes as an effective measure for monitoring subgrade compaction. The agency ranking of the effective methods for measuring subgrade compaction is similar to those of the industry responses.

• The industry’s assessment of effective methods for controlling placement of aggregate base/separator layers is shown in Figure G-24. The ranking includes aggregate gradation (nine responses), layer thickness (eight responses), permeability/drainability (six responses), in-place density (four responses), and number of passes (one response). The rank order of agency responses was similar to that of the industry, except agencies did not identify permeability/drainability as an effective measure for monitoring aggregate base/separator layer placement.

• The industry responses for effective methods for controlling placement of asphalt-treated permeable base, as well as comparison to agency responses, are provided in Figure G-25. Aggregate gradation (nine response) had the highest number of responses followed by layer thickness (eight responses), binder content (seven responses), permeability/drainability (six responses), compaction temperature (five responses), and in-place density (four responses). Placement temperature and number of passes had two and one responses, respectively. Interestingly, the rank order identified by the industry is different than the agency responses. The highest-ranking methods according to agency responses were layer thickness, binder content, in-place density, placement temperature, and number of passes.

• The industry responses for the methods for controlling placement of cement-treated permeable base are shown in Figure G-26. The highest number of responses include aggregate gradation (six responses), layer thickness, cement content, and permeability/drainability (five responses), and curing method (four responses). In-place density and number of passes had two and one response, respectively. The highest ranked agency responses included layer thickness, aggregate gradation, and curing method.

• Figure G-27 summarizes industry responses for methods to control placement density of asphalt mixtures. The highest ranked method identified by the industry responses

• included the nuclear density gauge, followed by cores and non-nuclear density gauges. Agency responses indicated a somewhat different result in that coring was rated as more effective than nuclear density gauge testing for controlling asphalt mixture placement.