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Manual for Emulsion-Based Chip Seals for Pavement Preservation (2011)

Chapter: Chapter 8 - Quality Control

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Page 26
Suggested Citation:"Chapter 8 - Quality Control." National Academies of Sciences, Engineering, and Medicine. 2011. Manual for Emulsion-Based Chip Seals for Pavement Preservation. Washington, DC: The National Academies Press. doi: 10.17226/14421.
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Page 26

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26 Quality control is required to ensure desired performance. The following section describes procedures that should be followed to improve the likelihood of good performance for a chip-seal project. 8.1 Aggregate Sieve Analysis Aggregate gradation should be checked whenever there is potential for significant variation in the chip gradation. For example, if chips have been stockpiled near the project and there is sufficient quantity to supply the entire project, a com- plete gradation analysis before construction begins, and every 100 tons thereafter, should be adequate. Also, loader opera- tions at the stockpile can produce excess material passing the no. 200 screen and should, therefore, be monitored. Aggregate gradation should not deviate from the target design gradation by more than the following tolerances: Tolerance, Sieve ±, % 3⁄4 5 1⁄2 5 3⁄8 4 No. 4 3 No. 8 1 No. 200 0.5 When chips are supplied from multiple locations, sam- pling and testing for gradation should be done with more frequency, including checking each truck if high variability is suspected. Because a full sieve analysis may not be practical, hand sieving in the field using only the coarse aggregate screens can provide information on the suitability of the material or help determine if more laboratory testing is needed. 8.2 Moisture Content of System The moisture content of the chips should be measured at the beginning and the end of the day for (1) calculating aggregate spread rate and (2) determining when sweeping can be done and when traffic control can be removed. Moisture content can be determined by complete moisture evaporation from the chips using a forced draft oven or a microwave oven. By weigh- ing the chips before and after removing moisture, the moisture content (w) can be determined as follows: 8.3 Embedment Depth Measurement During Construction Embedment depth is usually determined during construc- tion by pulling several chips out of the binder and visually esti- mating the amount of embedment. This is difficult and often subjective even if chips have a very low flakiness index. There- fore, a new method is recommended of spreading a volume of 50 cm3 of glass beads over the surface of the embedded chips and measuring the diameter. During the chip-seal design, the relationship between glass bead diameter and aggregate embed- ment is determined. During construction the glass beads are spread on the pavement and the diameter measured. Embed- ment is then determined using the relationship between glass bead diameter and embedment from the design measurements. 8.4 Field Viscosity The viscosity of the emulsion should be checked for each transport load. This can be done in the absence of a field lab- oratory using a Wagner flow cup. Flow times of 20 to 70 s at 85 to 150°F for a 6-mm orifice or 10 to 60 s at 85 to 140°F for a 7.5-mm orifice have been found to provide satisfactory flow rates. If flow rates using a Wagner cup are not within these limits, the temperature of the emulsion should be checked to determine if emulsion temperature is the cause. If tempera- ture of the emulsion is not causing unacceptable flow rates, other causes should be investigated. w, wet weight dry weight wet weight % = − ×100 C H A P T E R 8 Quality Control

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 680: Manual for Emulsion-Based Chip Seals for Pavement Preservation examines factors affecting chip performance, highlights design and construction considerations, and explores procedures for selecting the appropriate chip seal materials. The report also contains suggested test methods for use in the design and quality control of chip seals.

Appendices A to J of NCHRP Report 680 provide further elaboration on the work performed in this project.

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