12 SPRING/SUMMER 2022 TOWARDS SUSTAINABLE PAVING Summer 2021 Field Trials One major benchmarking experiment/project was planned and developed for the 2021 paving season. The experiment included two RPM 12.5 mm dense-graded surface mixtures (SM-12.5 P1 and SM-12.5 P2) alongside two typical VDOT control dense-graded mixtures (SM-12.5 D and SM-12.5 E). The first RPMmixture featured the use of a complex arrangement of polyethylene-based polymers designed for the extension and enhancement of asphalt binders used in road surfaces at a rate of 5% by total weight of the employed asphalt binder (herein referred to as “P1”). The second plastic trial featured the use of polyethylene terephthalate-based plastomeric amorphous polymers designed to improve the overall performance at a rate of 3% by total weight of the employed asphalt binder (herein referred to as “P2”). The RPMmixtures were designed to meet the agency’s specifications in terms of gradations and volumetric properties. Both RPMmixtures included 15% RAP and were produced using a PG64S-22 asphalt binder. The mixtures were produced following typical contractor practices. The only difference is that the plastics were added to the mixtures following a “dry process.” The plastics were introduced at the RAP collar behind the flame at the target rates using carefully calibrated fiber feeders to ensure a consistent flow of plastic. They were then mixed with the hot aggregates prior to introducing the asphalt binder as shown in Figure 1. The RPM mixtures were produced at a temperature range of 320 to 330°F. About 700 tons of RPM asphalt mixtures per each recycled plastic product were produced and were placed in the field in a 1.5-inch single lift over the course of 1-mile long adjacent stretches on Old Stage Road in Chester, Richmond, Virginia. The first few tons of RPM mixtures with plastic P1 were produced at a relatively lower temperature (~290 to 300°F) which resulted in the initial roller pattern and control strip not meeting the density specifications. This could be due to the slight increase in stiffness of produced asphalt mixtures when recycled plastic particles were included. To account for that, the production temperature of asphalt mixtures at the plant was increased to 320 to 330°F. As △ continued from page 11 As much as we care about diverting plastics and any other material coming from various waste streams (tire rubber, RAP, glass, etc.), we also care about including these materials in a very responsible manner that would guarantee good performance. Figure 1. (a) feeder machine used for plastic P1, (b) feeder machine used for plastic P2, (c) Polyethylene (PE)-based plastic P1, and (d) Polyethylene Terephthalate (PET)-based plastic P2. (c) (a) (b) (d)
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