Properties of Foamed Asphalt for Warm Mix Asphalt Applications (2015) / Chapter Skim
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Pages 23-52
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23 A Laboratory Binder Study Several binders from six different producers and eight refinery locations were collected and used to investigate the influence of certain variables on their foaming characteristics using the test methods and metrics described in Chapter 2.
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Binder ID Grade Producer N6 64-22 A N7 70-22 T6 64-22 B Y6 64-22 C (1st shipment) Y62 64-22 (2nd shipment)
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25 Figure 3-5. ERmax and k-value for binder N6 in the Wirtgen foamer at 1.0% and 3.0% water content.
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26 The following observations can be made based on data presented in Figure 3-8: • As discussed in the previous subsection, different binders clearly have different ERmax values at the same water content. This finding was consistent with foams produced using both foaming units.
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27 Figure 3-11. Bubble size distribution of binder A6 foamed in the Wirtgen foamer with 3.0% (left)
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28 WMA, and additives F1 through F3 were alkaline products manufactured with the specific objective of enhanced foaming. The additives were combined with heated binder to a temperature of 284°F to 320°F (140°C to 160°C)
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29 Figure 3-20 presents a series of pictures of the surface of the Wirtgen foamed binder samples with and without additives after 5 s of being dispensed in a 1-gallon container. Both the foamed binder sample with W1 and the sample with no additive had clear, shaped bubbles on the surface, and the difference between these two samples was not significant.
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Figure 3-20. Surface of the foamed binder 5 s after foaming in the Wirtgen foamer: (a)
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31 ERmax at 1.0% water content with and without additives, the FI values were distinctly larger than the ones obtained for the binder with no additives or the binder with additive W1. The SAI and FI values at 60 s are illustrated in Figure 3-23.
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32 A.1.6. Water-Bearing Additives (Zeolite)
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33 that was observed approximately 10 to 15 minutes after starting to mix. This normalization also incorporates the increase in volume due to the addition of the zeolite particles, which was approximately 2.0%.
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34 water from the foaming process. The error bars in this figure indicate the high and low values for the weight loss.
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35 m-value at low temperatures were similar to the S and m-value of base binders.
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36 to deliver a certain mass of water at different pressures. In this study, the selected binder temperature and pressure were 320°F (160°C)
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38 Figure 3-32. PTI foamer; (a)
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39 characteristics of N6 and O7 with 1.0% and 3.0% water contents from the three foaming units.
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40 the Wirtgen foamer, only 30 and 60 s are reported because after 60 s the binders had very small and uniform bubble sizes. In addition, O7 with 3.0% water content in the Wirtgen foamer had a very turbulent expansion and collapse that did not form any distinguishable bubbles, and thus the results are not included in Figure 3-38.
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41 2. The difference in bubble size seemed to be more pronounced at 3.0% water content versus 1.0% water content.
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42 temperatures for foamed WMA and HMA as well as the control HMA are summarized in Table 3-8. The comparison of workability and coatability by foamed WMA versus HMA was used to verify whether the foaming process produced WMA mixtures with better workability and coatability characteristics as compared to the control HMA.
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43 WMA mixtures and as compared to the control HMA for binder N6 and O6. However, there was relatively little difference for binder Y6.
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44 WMA production temperature, which was approximately 25°F lower than the recommended production temperature. Thus, it may be advantageous to increase the temperature for foaming polymer-modified binders.
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45 HMA for each foaming water content (i.e., 1.0%, 2.0%, and 3.0%)
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46 change in ERmax with added water and were thus considered ideal candidates to assess changes in mixture workability after the inclusion of liquid additives. Besides the additives listed in Table 3-2, a fourth additive was considered for this part of the study (henceforth labeled W2)
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47 As was observed during the comparison of laboratory foamers (Section 3.A.3) , binder foam produced in the Wirtgen foamer had the largest ERmax values, while that produced in the PTI foamer had the lowest ERmax values for three foaming water contents.
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49 observed for 1.0% and 2.0% water contents, while the opposite trend was shown for 3.0% water content. SAI values exhibited a gradual reduction with the elapsed foaming time, which was mainly attributed to the collapse of the binder foam.
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50 better mixture workability and coatability characteristics were shown for foamed mixtures at three different foaming water contents as compared to the control HMA, as indicated by lower maximum shear stress values and higher CI values. In addition, the selected optimum foaming water content for the foamed mixture produced in the Accufoamer was 2.0%, which was able to produce a foamed mixture with the best workability and coatability characteristics as compared to the HMA control.
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51 the average MR stiffness value of three replicates, and the error bars represent ±1 standard deviation from the average value. As illustrated in Figure 3-53, equivalent MR stiffness was achieved by the control HMA, the foamed mixture produced by the Accufoamer (at 2.0% water content)
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52 Figure 3-56. HWTT LCSN and LCST results for foamed mixtures produced in different laboratory foamers versus the control HMA.
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