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29 of the old asphalt surface. Care is needed when the surface TABLE 30 is milled before pulverizing because the remaining pave- COMPARISON BETWEEN DIFFERENT TYPES OF BITUMEN APPLICATIONS (based on Wirtgen 2004) ment layer has to support the pulverizing equipment (Jahren et al. 1999). The second step prepulverized the remaining Factor Bitumen Emulsion Foamed Bitumen asphalt concrete layers to a depth of 12 in. Four percent lime Crushed rock Crushed rock was applied, repulverized, and allowed to mellow for 24 h. Aggregate Types Natural gravel Natural gravel The second admixture, which was 6% fly ash, was blended Applicable RAP, cold-mix RAP, stabilized into the lime-treated material. Water was added to the mix, RAP, stabilized Marginal (sands) which was compacted immediately. The stabilized base was Bitumen Mixing 320°C to 356°F then completed using 4 in. of new HMA. 68°F to 15°C Temperature (before foaming) Aggregate Tempera- Ambient (cold) Ambient (cold) ture During Mixing QUALITY MANAGEMENT PROGRAM Moisture Content 90% of OMC minus 65% to 95% of opti- During Mixing 50% of emulsion content mum moisture content Inspection Partial coating of Type of Coating of coarse particles and Coating of fine Aggregate cohesion of mix FHWA (2005a,b) has developed pocket-sized guides for HIR and CIR processes. These guides provide a useful checklist Construction and Compaction Ambient Ambient for agency inspection staff. Temperature Rate of Initial The checklist for HIR project inspection includes infor- Slow Medium Strength Gain mation for Modification of Yes Unsuitable Binder · Preheaters, Emulsion type · Milling/scarifying units, (anionic, cationic) Half-life · Additive or admixture system, Important Parame- ters of Binder Residual bitumen Expansion Ratio · Mixing unit/spreader, Breaking time · Paver (repaving), and Curing · Rolling. Initial compaction can be accomplished with a sheep's foot The checklist for CIR project inspection includes infor- roller. An additional water truck may be needed (additive/ mation for stabilizer dependent) to provide sufficient moisture con- tent for optimum density. Once the pulverized materials · Milling, crushing, and mixing; are mixed and the initial compaction completed, the profile · Additives and mixtures; is restored using a standard motor grader. The FDR surface · Pick-machine and paver; and can be broomed to remove any loose particles before open- · Rolling procedure. ing to traffic. Quality Control and Quality Assurance When more than one admixture is used in the FDR activi- ties, admixes are typically added sequentially (Harris 2007). Quality management programs are used to ensure that contrac- For example, one project in Delaware County, Ohio, placed a tors meet or exceed the project requirements (specifications) and limefly ash FDR section by first milling and removing 4 in. include systematic management throughout the process from FIGURE 26 Typical equipment in CIR recycling train (based on FHWA 1997; ARRA 2001).
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30 FIGURE 27 Flow chart of activities for FDR projects (based on FHWA 1997). FIGURE 28 Typical equipment used for FDR reclamation trains (based on FHWA 1997; ARRA 2001; Wirtgen 2004).
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31 quality planning, quality control (QC), quality assurance (QA), · Short-term performance before surface course is and quality improvement (Miron et al. 2008). Areas of concern placed. to agencies, as noted in the ARRA Basic Asphalt Recycling Manual (2001), are summarized in Table 31. Aspects associated Recommendations for QC approaches found in the litera- with QC (process control) and QA were evaluated in the survey. ture include emulsion testing to determine the percentage of residue from distillation (Thompson et al. 2009). Field- testing recommendations include depth measurements, TABLE 31 compaction monitored with nuclear density gauge (direct SUMMARY OF POINTS OF CONCERN FOR MONITORING transmission), and moisture content verified before overlay PROCESS CONTROL AND ACCEPTANCE OF IN-PLACE (CIR and FDR). RECYCLED MIXES Project Topics of Concern to Agencies HIR CIR FDR Contractor QC programs include field technician train- Heating of the existing pavement X ing; validation of mix design properties, material proper- Blue or black smoke emissions from heating unit X ties, and density; and documentation of application rates. Scorched or charred pavement surface X Acceptance Excessive temperature variation across the mat X Existing surface sufficiently softened for The acceptance of the project by the agencies includes a scarification X number of approaches: Treatment depth X X X Addition of additives (type and quantity) X X X · Construction of acceptable test strip (establishing Additives thoroughly mixed X X X rolling patterns, optimum moisture and dry density requirements, acceptable equipment); Placement of recycled mix X X X · Measurements of one or more of the following: den- Adequate temperature for compaction X sity, thickness, profile deviations, material properties, Excess moisture removed X X X material quantities, and mix properties. Compaction of recycled mix X X X Materials testing noted in the written responses include Surface appearance (need consistency) X X X emulsion testing, residual binder testing (penetration), and Grade and cross slope X aggregate gradations. Mix properties evaluated by agencies Recycled Mix Properties of Concern to Agencies cover a wide range of tests such as binder content, indirect Gradation of final mix X X X tensile strength, Hamburg rut testing, moisture sensitivity (boiling water, TSR), and other standard HMA tests (e.g., Asphalt content of final mix X X X volumetrics). Recovered binder properties X X X In-place density X X X SemMaterials recommends that QC/QA testing for FDR Recycled mix strength properties X X X projects include the following: Uniformity of compaction X X X · Asphalt emulsion: residue from distillation, oil distil- late by distillation, sieve test, and penetration;. Process control is a contractor program that is intended to · Added rock or dry additive: provide a uniform final product and consists of evaluations Confirmation of quantity and type used in mix during preconstruction and construction. Survey responses design, indicate that contractors use a range of process control Minimum material size, options, including Moisture content before emulsion. · QC technician on the job (about one-third of contractors), Suggestions for QA testing and parameters were found · Real-time mix design adjustments for variable existing in the literature and included 97% of the laboratory density pavement materials, or 92% to 98% of the theoretical maximum specific grav- · Verification of density (compaction), ity. Thompson et al. (2009) summarized a range of require- · Verification of gradations, ments, including · Mix design property verifications, · Monitoring and verification of applications rate, · Density · Verification of moisture content, 97% of laboratory density (laboratory-compacted · Verification of indirect tensile strengths, and samples, nuclear density, and moisture),
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32 92% to 98% of theoretical maximum density · Greater minimum resilient modulus of 837 to 1,034 (In-Place Recycling Conference 2008), MPa (120 to 150 ksi) (SemMaterials). Maximum dry density and optimum moisture con- tent (Franco et al. 2009); Lane and Kazmierowski (2005a) noted that the Ontario · Dry Marshall stability, minimum, of MTO uses the following for both QC and QA testing: Greater than 5.56 kN (1,250 lb) (Caltrans; for EE), Greater than 4.44 kN (1,000 lb) (IowaDOT, at · Indirect tensile strengths, minimum, of 300 to 350 kPa 100°F); (43 to 50 psi; dry) and 150 to 175 kPa (22 to 25 psi; wet) · Indirect tensile strengths, minimum, of for CIR with expanded asphalt; 241 to 276 kPa (35 to 40 psi; dry) and 138 to 173 kPa · Target density of 96.0% of job mix formulas, with no (20 to 25 psi; wet) (SemMaterials); result below 95.0%; Dry indirect tensile strengths of 300 to 345 kPa (43 · Moisture content of less than 2.0%, with no sublot to 50 psi; dry) and 150 to 175 kPa (22 to 25 psi; wet) value above 3.0%. (Ontario MTO); · Retained TSRs of QC/QA programs include measurements of density, Greater than 70% (SemMaterials; Caltrans), moisture content, recycling layer depth, verification of mate- Greater than 50% (Ontario MTO; foamed asphalt); rial properties, and performance-related mix testing.