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OCR for page 38
38 Estimated network-level savings of $8,400,000 per Fly ash additives had twice the total amount of crack- year could be realized if strategies other than con- ing compared with emulsionlime slurry sections. ventional HMA are used (Maurer and Polish 2008). Fly ash additives had longitudinal cracking in one or Savings are achieved for FDR projects when the patch- both wheel paths compared with little or no cracking ing level is below 15% to 20% (PCA 2005). in emulsionlime slurry sections (Thomas et al. 2000). An Arizona study by Mallela et al. (2006) evaluated Additional cost savings are obtained by using less fuel the performance of 17 CIR projects: (energy) and by reducing disposal costs on recycling proj- CIR with double chip seal provided good performance ects (PCA 2009). Figure 31 summarizes the savings in con- for up to 20 years when traffic was below 5,000 AADT. struction zone traffic, use of new materials, disposal costs, Overlays of 50 to 75 mm (2 to 3 in.) provided excel- and fuel consumption. lent performance for at least 7 years (maximum age of projects in study). Life expectancies reportedly used in life-cycle cost assessments included CIR life of 13 years in Pennsylvania (Cuelho et al. 2006), 12 to 20 years in Pennsylvania (with overlay) (Cuelho et al. 2006), 17 to 25 years in Iowa (Lee and Kim 2007a), 18 to 22 years in Iowa when constructed on poor soil support (<5,000 psi) (Heitzman et al. 2007), 26 to 34 years in Iowa when constructed on good soil support (5,000 psi) (Heitzman et al. 2007), 10 to 18 years for Arizona CIR with consistently more reliable performance if a 2- to 3-in. HMA overlay is used with the CIR (Mallela et al. 2006). FIGURE 31 Potential reduction in construction zone traffic, FDR performance characteristics were not specifically use of new materials, disposal volume, and fuel consumption separated out in the literature because this process provides (based on PCA 2009). only a stabilized base for the new HMA surface. Perfor- mance-related characteristics such as in-situ or laboratory Life-cycle costs are commonly achieved by increasing the base modulus are typically used in the structural design. service life of the pavement. The length of time a given pro- cess will delay the progression of pavement distresses and Research conducted by the Ontario MTO (Kazmierowski the deterioration of the overall pavement condition needs to 2008) compared the performance of CIR and FDR projects be estimated when evaluating the potential reduction in life- over 11 years of service (Figure 32). This research indicates cycle costs. The following life-cycle-related performance that slightly more improvement can be achieved using FDR information was found in the literature. than CIR. This is expected given that FDR addresses defi- ciencies in all pavement layers. However, after about 8 years HIR performance characteristics have been reported as of performance, the FDR showed significantly slower losses in ride quality (i.e., IRI) and pavement condition. Heater-scarified sections showed that the appearance of distresses had the following annual rates of progression: A well-designed experimental approach to evaluating the International roughness index (IRI) increases of 15 progression of pavement distresses and the overall decline in./mi annually, in the pavement condition index for in-place recycling Rutting increases of 1.5 mm (0.06 in.) annually, methods is needed to provide reliable life-cycle cost and life Fatigue cracking increases of 22.3 m 2 (240 ft2) expectancy guidance. annually, Transverse cracking increases of 2 m (6.5 ft) annu- ally, and BARRIERS Longitudinal cracking increases of 30 m (97 ft) annually (Shuler and Schmidt 2008). Both agencies and contractors were asked to indicate what they considered to be barriers that limit the use of in-place CIR performance characteristics have been reported as recycling methods (Figure 33). Agencies identified the lack of mix designs most frequently. Both agencies and contrac- Kansas DOT showed that CIR sections with tors identified the frequently encountered barriers as