Mechanistic Properties of Field and Laboratory-Produced Warm Mix Asphalt Mixtures from Manitoba, Canada
AuthorPorras-Alvarado, Juan Diego
Civil and Environmental Engineering
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Warm Mix Asphalt is a generic term that refers to a specific group of technologies used to produce asphalt paving mixtures at lower temperatures than traditional Hot Mix Asphalt. There are many WMA technologies being used, foaming, organic, and chemical based technologies, and it is believed that others will soon enter the market. The concept and use of warm mix asphalt is becoming more popular in the asphalt industry. The promise of reduced energy consumption, reduced emissions, and a more workable product is very appealing to an industry pressured by environmentalists. However, the use of WMA may come with some potential issues as well. Lower production temperatures may result in softer asphalt due to the reduced oxidative aging. While poorly dried aggregates may create issue with moisture damage. The evaluation of field projects is necessary to determine the real benefits that this technology can offer. The present research analyzed the mechanistic performance of field and laboratory-produced mixtures from the Manitoba PTH-14 project in Canada. The project was constructed in summer of 2010 and consisted of a side by side HMA control section and three WMA sections in which the Advera, Evotherm 3G and Sasobit technologies were used. This study evaluated the resistance of field and laboratory-produced WMA mixtures in terms of their resistance to moisture damage, resistance to permanent deformation, resistance to reflective cracking and to fatigue cracking. Moisture damage was evaluated using Indirect Tensile Strength and |E*| property under multiple freeze-thaw cycles. The resistance to permanent deformation was analyzed conducting repeated loaded triaxial testing. Furthermore, the fatigue cracking and reflective cracking were studied using the flexural beam fatigue and the TTI Overlay Tester, respectively. For the field-produced mixtures all met the minimum unconditioned ITS criterion of 65 psi at 77F and the minimum indirect tensile strength ratio of 80% after 1 F-T cycle. While comparable TSR and |E*| ratios were observed for the mixtures after 1 F-T cycle, the WMA-Sasobit exhibited lower resistance to moisture damage when assessed after 3 F-T cycles. Except for the WMA-Sasobit, the WMA mixtures showed similar or higher resistance to reflective cracking when measured using the TTI overlay tester when compared to the HMA-control mixture. All WMA mixtures exhibited similar resistance to permanent deformation in the FN test at the LTPPBind 50% reliability temperature (118F) when compared to the HMA control section. However, none of the mixtures (including the HMA) met the proposed flow number criterion for warm-mix asphalt. When tested in the FN at the effective pavement temperature (92F), a different ranking for the mixtures resistance to rutting was detected. For the field-produced mixtures all met the minimum unconditioned ITS criterion of 65 psi at 77F; however, the minimum indirect tensile strength ratio of 80% after 1 F-T cycle was not met by the WMA mixtures. Highly stiffness reductions were detected for the WMA mixtures after been subjected to F-T cycling, for both TSR and |E*| ratio results. Except for the WMA-Sasobit, the WMA mixtures showed similar resistance to reflective cracking when measured using the TTI overlay tester when compared to the HMA-control section. HMA and WMA-Sasobit presented a higher resistance to permanent deformation when compared to WMA-Advera and WMA-Evotherm.The comparison between the results from the field and laboratory-produced mixtures exhibited differences in performance. The field-produced mixtures presented higher stiffness values when compared to the laboratory-produced mixtures. For this reason a conditioning difference between laboratory protocols and plant production procedures is suggested. Additionally, from the performance data a different conditioning protocol should be further study for each type of additive. The results exhibited adhesion problems between the asphalt binder and the aggregates that resulted in moisture damage for the laboratory-produced mixtures. A revision for the additives incorporation in laboratory protocols should be further assessed to determine the best way possible to simulate plant procedures.The continuous field monitoring for performance of the various sections will help in assessing any proposed criterion as well as the effectiveness of WMA mixtures in cold weather areas such as Manitoba. Additionally, this data will provided important information of real long term performance that can be compared to the laboratory performance testing of field-produced mixtures.