Evaluation of the Moisture Susceptibility of WMA Technologies (2014) / Chapter Skim
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51 This chapter presents overall findings from the three experiments described in the previous chapter, a summary of WMA performance compared to HMA, guidelines for evaluating WMA for moisture susceptibility during mix design and QA, and suggested research based on the results of this project. Findings WMA Laboratory Conditioning The following are findings from the results of the WMA laboratory-conditioning experiment that included evaluation of almost 250 LMLC specimens, onsite and offsite PMLC specimens, and PMFC cores from the Iowa, Texas, and Montana field projects: • MR results showed that the stiffness of LMLC specimens increased with higher conditioning temperatures and longer conditioning time and that WMA was more sensitive to conditioning temperature than conditioning time.
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52 • Equivalent dry MR stiffnesses between LMLC specimens with up to 2 weeks LTOA at 140°F (60°C) and PMFC cores at construction were shown for most Iowa and Texas mixtures, indicating the similar initial stiffness in the laboratory as compared to the initial field conditions.
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53 HMA and WMA mixtures from the different field projects in the context of these laboratory results, limited field performance data, traffic, climate, and materials is provided. The laboratory results were compared to common thresholds, including minimum 80% for TSR and MR-ratio, minimum SIP of 10,000 based on the Iowa specification, and minimum wet IDT strengths of 65 psi and 80 psi for mixtures with unmodified (Iowa)
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54 Discussion and Guidelines Figure 4-1 shows proposed guidelines for evaluating WMA for moisture susceptibility during laboratory mix design based on an analysis of the results of this project. If appropriate laboratory equipment is not available to fabricate LMLC specimens with the WMA technology, testing may be conducted on PMLC specimens fabricated on site or off site with minimal reheating from plant trial batch materials as shown in Figure 4-2 and Figure 4-3, respectively.
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55 grade or inclusion of RAP) ; or any combination of these modifications is then proposed prior to a second evaluation of the modified WMA with these same criteria.
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56 Figure 4-3. Proposed WMA moisture susceptibility evaluation for mix design or QA with offsite PMLC specimens.
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Aging Protocol (+antistripping) Conditioning/Testing Protocol Test Parameter Iowa Texas Evotherm Sasobit Evotherm Foaming LMLC STOA 2 h @ 240°F (116°C)
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58 result in both mixture types having adequate performance at the onset of freeze-thaw cycles and wet and cold days in the winter. The next step is to characterize any early-life weakness as compared to HMA and tie thresholds for laboratory test parameters to field performance.
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59 duce a stripping number (SN) and crack speed index that also incorporates IDT strength analysis and AV.
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