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57 Engineered Performance Specifications 100% 81% 67% In a previous NCHRP synthesis, a performance specification 80% 49% was defined as "how the finished product should perform over 60% time" (Chamberlain 1995). Specification of design life expec- 40% tations is an effective means of determining long-term chip seal performance. The most prominent example of a chip seal 20% performance specification is Transit New Zealand's, Notes 0% for the Specification of Bituminous Reseals (P17) (2002). The Bleeding Raveling Bleeding and philosophy behind this specification is that the texture depth Raveling after a 12-month inspection is the most accurate indication of FIGURE 58 Most common distress modes identified by the performance of the chip seal for its remaining life. The survey respondents. New Zealand specification contends that "the design life of a chip seal is reached when the texture depth drops below 0.035 in. (0.9 mm) on road surface areas supporting speeds greater than 43 mph (70 km/ h)" (Notes for the Specifica- Quality of design, tions . . . 2002). The deterioration models developed in New Quality and consistency of construction, Zealand have directed the P17 specification to require the fol- Quality and consistency of materials, lowing minimum texture depth 1 year after the chip seal is Environmental conditions, and completed, using Eq. 4. Traffic conditions. Td1 = 0.07 ALD log Yd + 0.9 (4) Visual Surface Ratings where Chip seal performance is commonly measured through a sys- Td1 = texture depth in 1 year (mm), tem that provides for visual rating of the chip seal's condition. Yd = design life in years, and Visual rating of chip seal performance by apparent distress ALD = average least dimension of the aggregate. modes is justified because these distresses generally determine The entire specification is based on the assumption that chip the life of a chip seal. The role that aesthetics play in the chip seals fail as a result of bleeding (Notes for the Specifications . . . seal process also makes objective decision making difficult. 2002). Within the specification, noise or aesthetic factors are The idea that the road should look good after it is completed the only reasons for specifying a maximum texture depth. The is an important driver of chip seal performance perception final acceptance is based on the achievement of the required (Gransberg et al. 1998). Visual performance assessment is texture depth, without any significant chip loss. More on the irreplaceable, even though it is inherently subjective. There- detailed methodology behind New Zealand's performance- fore, agencies should ensure that experienced personnel are based specification can be found in Appendix D. employed to make these assessments. Furthermore, there is evidence that technical vocabulary for chip seal performance is considerably variable within a state, let alone on national and QUALITATIVE PERFORMANCE INDICATORS international levels. One can see how establishing any objec- tive metric to assist inspection forces based on visual assess- It must be noted here that although the measurement of ment is problematic (Gransberg et al. 1998). skid resistance is common throughout North America, the researchers could find no instances where public highway agencies were using skid numbers to directly evaluate the Visible Chip Seal Distress performance of chip seals. Skid numbers, however, were used as trigger points for making the decision to apply a new Chip seals generally deteriorate as a result of binder oxida- chip seal on a road. Therefore, the only true form of chip seal tion, wear and polishing of aggregate, bleeding, and aggre- performance measure identified among the North American gate loss (Sprayed Sealing Guide 2004). These processes are survey respondents was the rating of visual distresses that expressed graphically in the Austroads chips seal distress materialize during the design life of the chip seal. Figure 58 model (Figure 59). Performance evaluation pertaining to shows the distress modes that survey respondents commonly surface appearance, reflective cracking, aggregate loss, and identified in their chip seals. texture loss can all be subjectively observed and rated based on their extent and severity of distress. As evident from the It is obvious that raveling and bleeding are widespread dis- both the survey responses and confirmed in the literature tresses. The literature review shows that chip seal perfor- review, bleeding and raveling are the most common distresses mance is generally a function of the following factors (Elmore found with a chip sealed surface (Benson and Gallaway 1953; et al. 1995a and b): Holmgreen et al. 1985).

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58 FIGURE 59 Chip seal distress model (adapted from Sprayed Sealing Guide 2004). Bleeding Raveling Bleeding is normally distinguished by black patches of excess Raveling is the loss of aggregate from the chip seal's surface. binder appearing on the surface of the chip seal (Gransberg Such chip seal surfaces have a very irregular appearance, et al. 1998). In other words, a bleeding surface has a smooth because the surface is not completely covered by the aggre- and slick appearance where the aggregates are less visible. gate, as shown in Figure 61a and b. Raveling occurs when Figure 60a and b illustrates this condition. Bleeding is caused the bond between the aggregate and binder fails, causing the by either an excess of binder in proportion to the aggregate or aggregate to become displaced from the binder. Raveling is where the aggregate is forced to achieve levels of embedment most common in areas outside of the wheelpaths where embed- beyond the design embedment depth (Sprayed Sealing Guide ment is lowest (Senadheera and Khan 2001). 2004). Such distress is usually observed in the wheelpaths where the repetitive load cycle of tires causes subsequent embedment of aggregates. Bleeding problems are generally Defects associated with high binder rates and nonuniform aggregate gradations, and bleeding is accelerated by high temperatures In addition to the distresses that form from the deterioration (Gransberg et al. 1998). During hot weather, underlying asphalt of the chip seal over time, two common defects need to be layers may soften to a point that these aggregate particles may mentioned: poor construction and placing a chip seal on a penetrate into the underlying binder, leaving excess asphalt on structurally inadequate pavement. Such defects commonly the surface (Senadheera and Khan 2001). cause the chip seal to fail before its planned service life. (a) (b) FIGURE 60 (a and b) Results of excess binder--Bleeding in wheel paths.

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59 (a) (b) FIGURE 61 (a and b) Results of aggregate loss--Raveling. Streaking, also known as drilling, is the formation of alter- Ohio Visual Evaluation Method nating lean and heavy lines (streaks) in the chip seal that result from a failure to apply the binder uniformly across the road's For integration into Ohio's Supplemental Specification 882, surface (Senadheera and Khan 2001). Streaking, shown in Chip Seal with Warranty, the state has established the fol- Figure 62, is mostly an aesthetic problem, but it can reduce lowing performance criteria for chip seal construction, as the design life of the chip seal when aggregate loss begins to detailed in Table 13. This table is a particularly useful way to take place. quantify the subjective nature of visual distress assessment by demanding remediation of the distress when the illustrated Rutting on the pavement surface is the result of deformation extent of severity is met. in the layers of the pavement's structure (Senadheera and Khan 2001). It is directly related to the structural strength of the In addition, the Ohio DOT prescribes the following chip underlying material. As one can see from Figure 63, chip seals seal acceptance criteria: will not benefit a pavement susceptible to rutting; these pave- ments need rehabilitation or reconstruction. Additionally, seal- Finished surface has minimal tears and binder streaking. Joints appear neat and uniform without buildup, uncovered ing a rutted pavement will likely cause the ruts to be flooded areas, or unsightly appearance. with binder and fail as the result of bleeding in a very short time. Longitudinal joints have less than a 2 inch (50 mm) overlap. FIGURE 63 Rutting (Asphalt Surface Treatments--Construction FIGURE 62 Streaking (Senadheera and Khan 2001). Techniques 1988).