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50 TABLE 33 SURVEY RESULTS ON FIELD QC/QA PRACTICES Specification Quality Management System U.S. Canada Content Analysis Inspection Responsibility? Agency 28 6 18 Consultant 0 1 0 Contractor 0 1 0 Use of Independent Lab to Verify Job Mix Formula? Yes 3 0 0 No 21 8 18 Do not know 4 0 0 Field Sampling/Testing? Yes 20 5 10 No 5 3 8 Do not know 3 0 0 Field Testing Responsibility Agency 15 3 15 Consultant 5 0 0 Contractor 0 2 0 Not specified 0 0 3 Source of Field Acceptance Tests? Source/pit 2 2 10 Stockpile 15 4 6 While transferring to nurse units 1 0 0 Before entering the mixing machine 1 1 0 Do not know/not specified 3 1 4 developing the job mix formula to the microsurfacing contrac- QUALITY OF MICROSURFACING WORKMANSHIP tor. This changes the classic QC/QA relationships. NCHRP Synthesis 376: Quality Assurance in Design-Build Projects As with all paving contractors, microsurfacing contractors bid (Gransberg et al. 2008) found that shifting design responsibility their projects based on a calculated rate of production. If the from the owner also shifts some of the traditional QA respon- contractor does not complete the number of lane-miles each sibility. Therefore, one would expect to see some level of in- day that its bid is based on, then the contractor's profit is at volvement of the contractor in the QA as well as the QC process risk. When this happens, the tendency to speed up to catch up and a higher use of contractor test results in the QA program. becomes almost overwhelming, possibly causing a deepening disregard for the quality of the workmanship. Therefore, it is Table 33 illustrates the output from the survey and content important to both the agency and the contractor that unnec- analysis with regard to the division of responsibilities between essary delays and/or interruptions in production be minimized the agency and the contractor. It shows that all U.S. and most if possible. The construction of test strips discussed in chap- Canadian agencies retain the traditional inspection responsi- ter six is a good technique to alleviate technical differences bilities. However, only three agencies in the entire sample of opinion as to what constitutes acceptable quality before require independent verification of the job mix formula based the contractor begins full-scale production. Another tool that on test results. All U.S. agencies also retain the traditional is often used is inspection checklists that both the agency's role with regard to performing their own field tests with either inspector and the contractor's QC manager have to allow agency personnel or a consultant retained on the agency's both parties to check and verify that important details have behalf. This is not the case in Canada, where two of five agen- been accomplished before starting production. A copy of one cies assign that task to the contractor. Agencies in Australia such checklist authored by the FHWA (2010) is contained in and New Zealand use performance-specified maintenance Appendix C. contracts, which make construction testing less important than in a traditional construction or maintenance contract (Manion and Tighe 2007). Quality Assurance Focus QA theory advocates identifying those areas that are of par- Laboratory Testing Practice ticular concern before starting construction and jointly address- ing them in a preconstruction meeting (Austroads 2003b). The Table 34 is a summary of the microsurfacing-related labora- ISSA Slurry Systems Inspector's Manual (2010a) contains a tory tests that were identified in the survey and the content list of preconstruction meeting objectives, which includes a analysis. No conclusions or effective practices can be drawn discussion of QC/QA issues. The Minnesota DOT's micro- from this analysis. Therefore, it is presented for information surfacing specification (2009) echoes the need for this type purposes only. of conference and prescribes a "Pre-Paving Meeting" of
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51 TABLE 34 SURVEY RESULTS ON LABORATORY QC/QA TESTING PRACTICES Specification Total Test U.S. Canada Content Occurrences Analysis Residual Asphalt Content 18 6 18 42 Sand Equivalent 17 3 12 32 Wet-Track Abrasion Test ISSA TB 100 15 4 11 30 Wet Stripping Test ISSA 114 12 5 10 27 Softening Point 14 5 7 26 Penetration 12 5 8 25 Mix Time Test ISSA TB 113 12 4 9 25 Classification Test ISSA TB 144 11 4 8 23 Modified Cohesion Test ISSA TB 139 11 4 6 21 Loaded Wheel Test ISSA TB 109 9 3 7 19 Abrasion Resistance 9 2 6 17 Lateral Displacement Test ISSA TB 147 7 5 5 17 Soundness 11 1 4 16 Cure Time Test ISSA TB 139 6 2 3 11 Tests for the Presence of Clay 6 2 2 10 Percent Sodium Sulfate Loss (resistance to freeze/thaw) 6 0 4 10 Compatibility of Aggregate with Binder 5 3 2 10 Set Time Test 4 1 3 8 Consistency Test ISSA TB 106 3 1 1 5 TTI Mixing Test 1 0 1 2 similar nature to the one discussed in the ISSA manual. The box be outside the line of the pavement and edge boxes National Highway Institute's Pavement Preservation Treat- be used when shoulders are covered. ment Construction Guide does a thorough job of synopsizing · Uneven Mixes and Segregation: Poorly designed main areas of microsurfacing workmanship quality concern microsurfacing mixtures or mixtures with low cement as listed here. content or too high a water content may separate once mixing in the box has ceased. This leads to a black and · Longitudinal Joints: Longitudinal joints may be over- flush looking surface with poor texture. Separated mixes lapped or butt jointed. They can be straight or curve may lead to "false slurry," where the emulsion breaks with the traffic lane. It is important that overlaps not be onto the fine material. In such instances delamination in the wheel paths nor exceed 75 mm (3 in.) in width. may occur, resulting in premature failure. These types · Transverse Joints: Transverse joints are inevitable when of mixes can be recognized as nonuniform and appear working with truck-mounted batch systems; every time to set very slowly. a truck is emptied a transverse joint is required. Transi- · Smoothness Problems: Microsurfacing mixtures follow tions at these joints must be smooth to avoid creating a the existing road surface profile and thus do not have the bump in the surface. The joints must be butted to avoid ability to significantly change the pavement's smooth- these bumps and handwork be kept to a minimum. The ness. However, when using stiffer mixes, the spreader main difficulty in obtaining a smooth joint occurs as the box may, if incorrectly set up, chatter or bump as the microsurfacing machine starts up at the joint, particu- material is spread and produce a washboard effect. The larly when working with microsurfacing that is difficult chattering may be reduced by making the mixture slower to work by hand and breaks quickly. Some contractors to set, adjusting the rubbers on the box, or adding weight tend to over wet (add too much water) the mix at start- to the back of the spreader box. ups, leading to poor texture and scarring at the joints. · Damage Caused by Premature Reopening to Traffic: Starting transverse joints on roofing felt can eliminate It is important that the microsurfacing build sufficient these problems. cohesion to resist abrasion resulting from traffic. Early · Edges and Shoulders: Sealed edges and shoulders can stone shedding is normal, but not to exceed 3%. If a be rough and look poor. This occurs more often with mixture is reopened to traffic too early it will ravel off microsurfacing applications that break quickly, making quickly, particularly in high stress areas. It is important them harder to work by hand than slurry seals. For micro- that the mixture develops adequate cohesion before it is surfacing, it is important that handwork be kept to a opened. Choosing the right time to reopen a surface to minimum. It is important that the edge of the spreader traffic is based largely on experience. However, a general