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6 under the same traffic conditions. However, when increased a key part of the treatment selection framework/process pre- traffic loadings are applied, the pavement with the greater load sented later in this document. will deteriorate faster. This can be illustrated with perfor- mance curves showing that the time for treatment application Climate/Environment is reduced for pavements with higher traffic volumes. While the correct treatment application time depends on Climatic conditions impact preservation treatment usage in several factors, it is generally agreed that preservation treat- at least two ways: determining construction timing and affect- ments should be applied during the period when the pavement ing treatment performance. While the applicability of many is in good condition. Accordingly, surveying existing condi- of the treatments might not be affected by differences in cli- tions to determine whether the pavement is in good condition mate (such as ultra-thin friction courses for HMA-surfaced is an important part of the treatment selection process. pavements or diamond grinding for PCC pavements), some The selection of the correct type of preservation for dis- treatments, especially those using asphalt emulsions, can only tressed pavements generally depends on the location, density, be applied in limited temperature and humidity conditions. and magnitude of the distress. For instance, where a surface Climate can directly affect curing time, which in turn impacts treatment cannot be applied to a PCC pavement, such as a treatment feasibility and opening to traffic on high-volume heavily trafficked urban roadway, diamond grinding is often roadways. For example, slurry seals require several hours, performed to improve rideability. Resealing of joints in PCC warmer temperatures, and direct sunlight to break and cure pavements is done wherever poor sealing or lack of sealing is effectively; in environments where these conditions cannot be evident. On HMA-surfaced roadways, if transverse cracking assured and traffic cannot be kept off the pavement, a slurry is frequent but there is not a high degree of edge deteriora- seal is not an appropriate treatment. tion, a surface treatment such as a chip seal or slurry seal may In addition to temperature and climate considerations be the best preservation strategy. If the transverse cracks are during treatment placement, preservation treatments can low to moderate in frequency and have progressed to a point experience differential performance in different climates. For of high edge deterioration, then crack repair or patching may example, although thin HMA overlays are used successfully be necessary. If cracks are moderate in density and have little in all climatic regions, they are susceptible to thermal crack- deterioration, effective treatment can be accomplished by ing, which can be more pronounced in colder climates. The crack sealing or filling. Extensive longitudinal cracking in the performance of ultra-thin HMA overlays is particularly lim- wheel path is indicative of a structural problem, which makes ited in cold climates because of the thermal cracking issue and the pavement a poor candidate for preservation treatment. the challenges in achieving adequate density on thin lifts. While crack sealing is primarily performed on newer pave- Cold-applied (emulsion-based) treatments must be placed ments with fairly narrow cracks, crack filling is most often during the day and in warm temperatures, while treatments reserved for more worn, older pavements with wider, more constructed with hot asphalt binder can be placed at night and randomly occurring cracks. in cooler temperatures. Generally, the construction season Thin HMA overlays can be used on all types of roadways in runs from May to September to take advantage of the warmest good to fair condition for functional improvements. Such over- months for the northern States (Gransberg 2005). Good per- lays are particularly suitable for high-traffic-volume roadways formance of chip seals is related both to favorable climatic in urban areas, where longer life and relatively low-noise sur- conditions during placement and also to favorable climatic faces are desired. Similarly, slurry seals do not usually perform conditions during the weeks following placement. A major well if the underlying pavement contains extensive cracks cause of pavement failure is weather-related, such as when (Morian et al. 1998). rain or extreme temperatures occur shortly after construction Tables 2.5 and 2.6 reflect the state of the practice for treat- (Croteau et al. 2005). Some thin surfacings are also more ment use by transportation agencies based on existing pave- susceptible to damage from certain types of snow plowing ment surface conditions. In these tables, extensive use means techniques and certain plow blades. that two-thirds or more of the highway agencies reported From agency-provided responses on preservation prac- using a particular treatment to address a certain pavement tices, information was obtained that permitted the catego- deficiency. Moderate use represents use by between one-third rization of practices according to climate region, which in and two-thirds of the agencies, while limited use represents turn could be evaluated to determine whether their treatment use by less than one-third of the agencies. The results pre- use was at least partially driven by climatic factors. For the sented in these tables were combined with the application three climatic regions identified--deep-freeze (northern-tier best practices information contained in the literature to for- states, freezing index [FI] >400), moderate-freeze (middle- mulate a decision matrix for identifying feasible treatments tier states, 50 < FI 400), and no-freeze (southern-tier states based on existing pavement condition. The decision matrix is and portions of coastlines, FI 50)--the general practice for
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Table 2.5. Treatment Usage on HMA-Surfaced Roadways According to Pavement Condition Pavement Distress Surface Distressa Treatment Raveling Oxidation Bleeding Smoothness Friction Noise Light Moderate Heavy Crack filling N/A N/A N/A Limited N/A Limited Extensive Moderate Limited Crack sealing N/A N/A N/A Limited N/A Limited Extensive Moderate Limited Slurry seal Extensive Extensive Limited Limited Limited None Moderate Limited None Microsurfacing Moderate Moderate Limited Moderate Moderate Limited Extensive Moderate Limited Chip seals Moderate Extensive Limited Limited Moderate None Extensive Extensive Limited Ultra-thin bonded wearing course Moderate Moderate Limited Moderate Extensive Limited Extensive Moderate Limited Thin HMA overlay Extensive Moderate Moderate Extensive Moderate Limited Extensive Extensive Limited Cold milling and overlay Extensive Moderate Moderate Extensive Moderate Limited Extensive Extensive Moderate Ultra-thin HMA overlay Moderate Moderate Moderate Moderate Moderate Limited Extensive Moderate Limited Hot in-place HMA recycling Moderate Moderate Limited Moderate Moderate Limited Extensive Moderate Moderate Cold in-place recycling Limited Limited Limited Moderate Limited Limited Moderate Extensive Extensive Profile milling None None Limited Extensive Moderate Limited Moderate Limited None Ultra-thin whitetopping Limited Limited Limited Moderate Limited Limited Moderate Moderate Limited Note: Extensive = Use by 66% of respondents; Moderate = 33% to 66% usage; Limited = <33% usage. a Various forms of cracking.