Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments (2017) / Chapter Skim
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5 C H A P T E R 2 This chapter presents the process for developing the proposed EPG specifications. The proposed specifications for performance-graded emulsion used in chip seal, microsurfacing, and spray seal treatments are presented in Attachments 1 and 2, respectively.
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6 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments 2.1.2 Distress Types in Asphalt Surface Treatments That Are Affected by Binder Properties Based on the literature review as well as information gleaned from communications with pavement preservation professionals, a list of key binder performance characteristics (or distresses) that relate to PST mixture performance was compiled.
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Results, Interpretation, and Applications 7 For this prioritization process, the research team considered only those distresses that relate directly to the binder material's performance. For example, reflective cracking was not considered a critical distress despite its common occurrence in chip seals, because it relates to the condition and integrity of the existing pavement structure and not to the performance of the asphalt binder.
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8 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments much to the binder's properties. The rutting potential in microsurfacing is related to the viscoplasticity of the residual binder at high temperatures.
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Results, Interpretation, and Applications 9 2.1.4.1 Fresh Emulsion Testing The properties of an emulsion during its storage, transportation, and construction have a major effect on the performance of asphalt surface treatments. Table 2.2 lists the test methods that were modified to evaluate the properties of fresh asphalt emulsions that affect the overall stability, constructability, and performance of PSTs in the EPG specification.
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10 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments over time (Redelius and Walter 2006)
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Results, Interpretation, and Applications 11 steel ball to roll 25 cm is used for the EPG specifications and is the minimum curing time to avoid the tracking of spray seal emulsion onto tires upon traffic opening. 2.1.4.2 Existing Emulsion Specification Tests Retained in the EPG Specifications Table 2.3 lists the existing AASHTO emulsion test methods for fresh emulsion and recovered residue that are retained in the proposed EPG specifications.
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12 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments requires a thin film that allows the residue to be recovered using a low curing temperature (60°C) and only 6 hours of curing time.
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Results, Interpretation, and Applications 13 Ultimately, rutting was identified as the critical high-temperature performance distress in microsurfacing treatments that relates to emulsion residue performance. The MSCR test for the microsurfacing binder EPG specifications follows the test used for chip seal bleeding characterization.
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14 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments where the performance modification was relevant to the test results, the poor-performing emulsion is highlighted in the results and analysis. For example, one supplier changed the emulsifier type and content of its standard emulsion such that the emulsion's demulsibility, defined as the ability to release water or the rate at which a liquid separates from an emulsion, approached 100% in order to produce an inferior product.
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Results, Interpretation, and Applications 15 After identifying the emulsions required for the development of the EPG specifications, the emulsions were allocated to individual suppliers. The individual suppliers were asked to fabricate only emulsions that they typically formulate and provide for in-service projects.
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16 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments 2.3 Performance-Graded Specifications Framework This section describes the conceptual framework of the EPG specifications in terms of the intended use of the EPG specifications, temperature grading concepts, traffic designations, binder grade designations, and overall conceptual development. 2.3.1 Intended Use of the EPG Specifications The EPG specifications provide specifications for performance-graded emulsions for use in chip seals, microsurfacing, and spray seals.
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Results, Interpretation, and Applications 17 include material property testing for critical distresses, such as fatigue and reflective cracking, which are related to the strength and integrity of the pavement structure. The only distresses addressed within these EPG specifications are those distresses that are not related directly to pavement structural integrity, are not the result of pre-existing pavement issues (e.g., rutting, cracking, etc.)
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18 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments High PG at 20 mm Depth Figure 2.3. Theoretical high-temperature performance grade map based on current HMA specifications.
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Results, Interpretation, and Applications 19 to be -18°C, the HMA low-temperature grade requirement is -22°C. The corresponding EPG low-temperature grade requirement if available low-temperature PGs were increased 3°C is -19°C.
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20 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments specification is acceptable, and using the HMA low-temperature grade requirement plus 3°C as the EPG low-temperature grade requirement is appropriate. 2.3.3 Traffic Designations for the EPG Specifications Because the performance of PSTs such as chip seals and microsurfacings depends upon the traffic conditions that the PST undergoes, the developed EPG specifications provide material test limits for grading binders according to the expected traffic.
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Results, Interpretation, and Applications 21 2.3.5 Underlying Concept and Outline for the Development of the EPG Specifications 2.3.5.1 Fresh Emulsion Concept Statistical analysis was conducted to develop the specification test limits for fresh emulsion properties under the assumption that the standard emulsions tested in this study represent a broad range of materials that perform acceptably in service. Both standard and poor-performing emulsions, as defined previously, were tested in developing these EPG specifications.
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22 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments 2.3.5.2 Residual Binder Concept For developing the specifications for residual binders, the relationship between each binder property measured for the proposed residual binder test method was compared against the mixture performance to which the binder property relates. Based on this relationship, the corresponding binder test limit could be determined to ensure that the target mixture performance was achieved.
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Results, Interpretation, and Applications 23 • Develop proposed EPG specifications. • Develop draft specifications for test methods used in the proposed EPG specifications.
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24 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Se pa ra tio n Ra tio Emulsion Number Unmodified Modified Outlier (a) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 S ep ar at io n R at io Emulsion Number Unmodified Modified 98% Reliability (b)
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Results, Interpretation, and Applications 25 Figure 2.10 and Figure 2.11 show examples of the specification limit determination for the sprayability and drainout constructability parameters that are applicable to chip seals and spray seals in the EPG specifications, respectively. A maximum limit for sprayability viscosity in chip/ spray seals in the EPG specifications ensures that the binder has a low enough viscosity value to ensure consistent output when sprayed through a nozzle during the emulsion application process.
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-200 0 200 400 600 800 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Vi sc os ity (c P) Emulsion Number Sprayability Unmodified Modified (a)
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Results, Interpretation, and Applications 27 distresses. The residual binder is the asphalt binder material that remains after all the water has evaporated from the asphalt material.
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28 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments Similar to the chip seal specimen fabrication process, the residual asphalt content and aggregate rate were held constant for all specimens (9% asphalt content was used in this case)
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Results, Interpretation, and Applications 29 material to higher levels of stress and strain than the DSR test used to measure G*
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30 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments obtained from DSR testing, has been recommended for binders used in chip seal treatments (Vijaykumar et al.
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Results, Interpretation, and Applications 31 The rut depth in microsurfacings was determined by measuring the difference in height between the wheel path and non-wheel path areas of the microsurfacing specimen that was subjected to MMLS3 loading (the processes for measuring bleeding and rutting performance are fully detailed in Appendix C)
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32 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments The MMLS3 test for multilayered seals represents harsher loading conditions than field traffic due to the accelerated loading rate used in MMLS3 tests that causes increased bleeding potential compared to field traffic (Lee 2007 and Adams and Kim 2013) , i.e., 80% bleeding under MMLS3 traffic loading does not equate to 80% bleeding under field traffic loading.
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Results, Interpretation, and Applications 33 volumes. Note that the binder Jnr values do not change with traffic volume.
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34 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments y = 13.126ln(x)
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Results, Interpretation, and Applications 35 no microsurfacing rut depth threshold value existed prior to this research, the 5-mm maximum rutting limit was derived from the fact that each applied MMLS3 wheel load is one-third of a typical dual wheel single-axle load (Lee 2003)
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36 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 R ut D ep th (m m)
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Results, Interpretation, and Applications 37 and the rut depth approaches an asymptotic depth, which was achieved for most mixtures at the medium traffic level. Therefore, one maximum Jnr limit will define acceptable performance for both high and medium traffic volumes for the microsurfacing EPG specifications.
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38 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments method and natural bond formation have on the correlation between bond strength and aggregate loss for chip seals. Initially in this study, the BBS test was conducted using the so-called residue on rock (ROR)
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Results, Interpretation, and Applications 39 at either 15°C or 25°C. The problem with the ROR curing method is that it does not accurately simulate the initial bond development and chemical interaction that occur between the fresh emulsion and aggregate when they are introduced during chip seal construction.
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40 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments Microsurfacing For intermediate temperatures, raveling and reflective cracking were identified as the most critical distress types in microsurfacing treatments. However, raveling of microsurfacing mixtures was determined to be driven by the chemical interaction between the emulsion and other mixture constituents (i.e., aggregate, cement, lime)
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Results, Interpretation, and Applications 41 Figures 2.26 and 2.27 present the correlations between these binder parameters and mixture performance where binder S(60) is compared to the low-temperature aggregate loss measured from Vialit tests of chip seal mixtures and fracture energy is measured from single-edge notched beam (SENB)
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42 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments 0 5 10 15 20 25 30 35 40 45 0.00 0.10 0.20 0.30 0.40 0.50 A gg re ga te L os s (% )
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Results, Interpretation, and Applications 43 Recommended Low-Temperature Parameter for EPG Specifications Fracture-mechanics-based and rheology-based residual binder properties were evaluated for both chip seal and microsurfacing low-temperature specifications. The strength of the correlation between mixture performance and binder properties was used to evaluate the appropriateness of the parameter for low-temperature specifications.
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44 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments increasing the temperature or decreasing the rate) , the excitation overcomes the forces of the material's microstructure, and hence, a tendency toward fluid behavior ensues.
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Results, Interpretation, and Applications 45 emulsion has been used successfully in -25°C regions on medium traffic roadways and meets this criterion, further validating its reasonableness. The medium traffic aggregate loss threshold was selected simply as the average of the high and low traffic thresholds.
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46 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments good agreement between the aggregate loss and G* values irrespective of the mixture test temperature (R2 = 0.86)
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Results, Interpretation, and Applications 47 the only emulsion evaluated that is currently used in a -25°C or colder region, and hence, the performance-grading results appear reasonable. 2.4.2.5 Critical Phase Angle Values and Dynamic Shear Modulus Test Limits for Thermal Cracking in Microsurfacing at Low Temperatures Trends in the test results were used to establish critical performance thresholds for microsurfacing fracture energy at low temperatures; Figure 2.35 presents the SENB test results.
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48 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments certain critical temperature. (Note that for CQS-1h-E, this critical temperature exceeds the range of temperatures considered in testing.)
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Results, Interpretation, and Applications 49 Low-temperature EPG (°C)
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50 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments Both CQS-1hP-E and CSS-1hP-D have a low-temperature EPG of -25°C. CSS-1h-L has a lowtemperature EPG of -19°C, and CQS-1h-E fails the specification at -19°C.
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Results, Interpretation, and Applications 51 grade. The EPG specifications have flexibility in that an EPG 67 (low)
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Existing Emulsion Name Proposed EPG Grade Fresh Emulsion Tests Residual Binder Tests Pass & Grade or Fail at Test Temp/ Traffic Level Emulsion Type Climate Traffic Level Storage Stability Rd < 2 Separation 0.5 |
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Results, Interpretation, and Applications 53 exhibit bleeding in the chip seal; indeed, none of the single-seal or triple-seal sections exhibited any signs of bleeding after over 1 year in service. At low temperatures, raveling due to binder fracture is the critical distress addressed in the EPG specifications.
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54 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments 2.6.2 Microsurfacing Short-Term Validation Microsurfacing field validation sections were constructed by the North Carolina Department of Transportation (NCDOT) in Forsyth County, North Carolina, in June 2013.
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Results, Interpretation, and Applications 55 b ca Figure 2.40. Microsurfacing cracks visible prior to the first winter following construction.
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56 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments Based on the cores, the existing pavement layer was determined to be 300-mm deep and was found to be composed of several HMA layers, an asphalt binder layer, and a concrete layer at the bottom. Each core was covered with an approximately 6.25-mm thick layer of microsurfacing.
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