Abstract
The use of low-carbon and energy-efficient paving technologies is gaining worldwide acceptance in recent years as a means to encourage commitment towards more sustainable pavement management practices. However, there still remain some technical gaps regarding mix design procedures for the half-warm mix asphalt (HWMA) mixtures’ preparation and characterization in the laboratory. To this end, three different laboratory compaction methods (e.g., static load, Marshall impactor, and gyratory compactor) were selected and put into assessment to define the most suitable compaction test method for half-warm mix recycled asphalt (HWMRA) mixtures with 100% reclaimed asphalt pavement (RAP). Posteriorly, the effect of four-accelerated curing treatments (0, 24, 48, and 72 h) on the mixtures’ mechanical performance was investigated. Then, advanced mechanical characterization of the mixture performance was conducted to quantify the indirect tensile strength (ITS), stiffness modulus, rutting, and four-point bending (4PB) fatigue test. Thus, based on the authors’ findings, the HWMRA mixtures with 100% RAP and emulsified bitumen exhibited proper volumetric (e.g., air voids and density) and mechanical behavior in terms of moisture damage, ITS, stiffness modulus, rutting, and fatigue cracking. These findings encourage greater confidence in promoting the use of these sustainable asphalt mixes for their use in road pavements or urban streets.
Highlights
Over the last few decades, the transition from a high-consuming carbon and linear society to a closed-loop circular economy (CE) is gaining worldwide boost as a way to move towards more sustainable pavement management practices by positioning the use of greener disruptive production technologies at the top level of the agenda for sustainable development [1]
Materials 2019, 12, 1992 that has the potential to decrease the consumption of energy sources and the extraction of raw materials is the use of half-warm mix asphalt (HWMA) mixture with recycled asphalt pavement (HWMRA)
Despite the environmental and economic advantages offered by this technology, a large number of questions remain regarding their compactibility, namely since mix compaction occurs above the recycled binder’s softening point temperature (~ 85 ◦ C), the reclaimed asphalt pavement (RAP) aggregates tend to behave as black rock, implying a higher plastic deformation behavior of the recycled aggregates compared to the solid–rigid behavior expected from virgin aggregates used either in cold in-place (CIR) or hot in-place recycling (HIR) [6]; whilst some other authors reported that mixture compactibility improves as a result of the combination of half-warm temperatures and water content provided by the emulsion, which makes it possible to achieve a better quality of mixture in the field [7]
Summary
Over the last few decades, the transition from a high-consuming carbon and linear society to a closed-loop circular economy (CE) is gaining worldwide boost as a way to move towards more sustainable pavement management practices by positioning the use of greener disruptive production technologies at the top level of the agenda for sustainable development [1]. Materials 2019, 12, 1992 that has the potential to decrease the consumption of energy sources (i.e., fuel and gas-oil) and the extraction of raw materials is the use of half-warm mix asphalt (HWMA) mixture with recycled asphalt pavement (HWMRA). HWMA mixes offer many other potential benefits, such as lower energy consumption of up to 3–4 kg/ton—compared with both hot in-place recycling (HIR) and warm mix asphalt (WMA) [4] and decrease in carbon footprint emissions during mix production, by 30% of CO2 and 25% of SO2, in comparison with conventional mixtures [5]. Some authors stand up for the idea that, as the RAP aggregates are already covered by a thin-film layer of aged RAP binder, the moisture susceptibility is not expected to be worse than conventional HMA mixtures [12,13]; whilst some other authors asserted that mixtures with high RAP contents and at low temperatures showed lower load-bearing capacity and rutting performance values, likely as a result of lowering mixing and compaction temperatures [14,15]
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