Francesca Frigio

Use of Reclaimed Asphalt in Porous Asphalt Mixtures: Laboratory and Field Evaluations

AbstractMaintenance and reconstruction of road pavements involve the production of huge amount of discarded material, such as reclaimed asphalt (RA), every year. As a consequence, issues related to RA stockpiles and disposals are dramatically increasing. At the same time, the growing importance of environmental and economic matters has led researchers and engineers to promote reusing milled materials rather than using valuable and nonrenewable natural resources (bitumen and aggregates). Road pavement maintenance and construction usually involve the use of porous asphalt (PA) mixtures, in particular in the case of motorways and highways. In fact, PA mixtures are widely employed as pavement surface layer thanks to their ability in reducing traffic noise and enhancing safety in wet conditions. In this sense, the reuse of RA into PA should be strongly encouraged. Unfortunately, technical specifications adopted in many countries do not allow any recycled materials in porous asphalt surface layers yet. Thus, re...

Laboratory Study to Evaluate the Influence of Reclaimed Asphalt Content on Performance of Recycled Porous Asphalt

Road-pavement maintenance and rehabilitation are more frequently performed on porous asphalt (PA) surface layers because of their inherent low durability. Such activities lead to the production of a considerable amount of reclaimed asphalt (RA), mainly from PA layers and from the heavy use of virgin non-renewable natural resources, because of the fact that the use of RA is not usually allowed in PA. In this sense, the use of milled materials from old PA wearing courses in new PA layers promotes an important cycle of re-use that should be encouraged. The experimental study aims to investigate the performance of recycled PA mixtures prepared by partly substituting virgin aggregates with selected coarse RA from a milled PA wearing course. A reference PA mixture (without RA) and six recycled PA mixtures prepared with two amounts of RA (20 % and 25 %) and three total binder contents (5.25 %, 5.50 %, and 5.75 %) were investigated in terms of compactability, durability, and water resistance. In this sense, indirect tensile strength (ITS) tests, particle loss (Cantabro) tests, semicircular bending (SCB) tests, and repeated indirect tensile tests were carried out in both dry and wet conditions. Moreover, compactability properties of the reference PA mixture and the recycled PA mixtures were compared. Results showed that recycled PA mixtures with 20 % and 25 % of RA can perform as well as the reference PA mixture in terms of moisture resistance and durability if an accurate mix design is performed. The optimum total binder content was found to increase as the amount of RA increases, because of the fact that a prominent part of the aged binder acts as “black aggregate.” Finally, on the basis of a performance-based equivalence principle, a reliable approach for a practical method able to predict the amount of “re-activated” binder within the RA is proposed.

Fatigue rheological characterization of polymer-modified bitumens and mastics

Fatigue is one of the major distresses of flexible pavements and is mainly related to the rheological properties of the bituminous components of mixtures. In particular, bitumen and mineral filler create a blend called mastic that significantly influences the service life of asphalt pavements depending on its nature and composition. The purpose of this study is to investigate the effects of different polymer types and mineral fillers on the rheological behavior of a plain bitumen. Two types of polymer (an elastomer and a plastomer) were employed to produce polymer modified bitumens (PMBs) through laboratory mixing. Moreover, two fillers characterized by a different mineralogical nature (limestone and basalt) were selected in order to obtain several mastics. The dynamic shear rheometer (DSR) was used to study the fatigue behavior of all materials. Experimental data show that the effect of both polymer types is similar on mastics and bitumens as the presence of the elastomer leads to an improvement in fatigue life whereas the presence of the plastomer leads to a slight decrease in fatigue performance with respect to the plain bitumen, regardless of the mineral filler type. Moreover, the stiffening effect of mineral fillers was found to be significant regardless of filler mineralogy and bitumen type leading to a decrease in fatigue life with respect to bitumens. All mastics were less sensitive to the strain level applied as compared to the corresponding bitumens.

Characterisation of warm recycled porous asphalt mixtures prepared with different WMA additives

The use of Reclaimed Asphalt Pavement (RAP) into new asphalt mixtures and the reduction in the production temperatures by means of Warm Mix Asphalt (WMA) additives are two recognised solutions for sustainable pavements. Despite their environmental advantages, the reduced production temperatures of WMA mixtures may lead to rutting and moisture susceptibility issues. Such concerns need to be properly investigated, particularly in case of porous asphalt mixtures (PA) due to their low durability and high water sensitivity. The objective of this study is to evaluate the feasibility to reduce the production temperature of recycled PA including 15% of coarse RAP aggregates; three different WMA additives were selected (organic, chemical additive and zeolite) to produce PA mixtures at 130 °C. One HMA mixture was also prepared at 170 °C and an additional WMA mixture was prepared at reduced temperature without any WMA additive for comparison purposes. The experimental programme focused on compactability and durability properties of the PA mixtures. Results highlight the issues related to the reduced production temperatures of PA mixtures, particularly in terms of moisture susceptibility. Only the presence of the chemical additive in the mixture ensures adequate water resistance, although it does not guarantee short-term performance comparable to the HMA mixture.

Performance Assessment of Plant-Produced Warm Recycled Mixtures for Open-Graded Wearing Courses

Sustainable solutions, such as the combination of reclaimed asphalt pavement (RAP) as a partial substitution of virgin materials and warm-mix asphalt (WMA) additives to decrease production temperatures, represent the new research frontier in the asphalt industry. Specific investigations must evaluate the consequences of recycled WMA performance, especially in the case of open-graded (OG) mixtures, given that lower production temperatures can affect the adhesion properties and durability of those materials. This paper describes an experimental effort that involved OG mixtures produced in plant at warm temperatures (130°C) with two WMA chemical additives characterized by different compositions. In addition, an equivalent mixture (used as a control for comparison purposes) was produced at standard temperatures. Each material was prepared with a polymer-modified binder and 15% RAP. The main objective of the study was to characterize volumetric and mechanical properties of the investigated mixtures with particular attention paid to compactability aptitude and durability. To this end, gyratory-compacted specimens were subjected to several laboratory tests after dry and wet conditioning (i.e., indirect tensile strength, Cantabro test, semicircular bending, and repeated indirect tensile loading). Moreover, plant production of the investigated mixtures made it possible to evaluate the feasibility of large-scale processes. The WMA mixtures showed significant water susceptibility, although they guaranteed good compactability and satisfied mechanical acceptance requirements and international recommendations for raveling resistance in dry conditions. The chemical composition of the WMA additives was found essential to reduce the water damage. Surfactants and adhesion enhancers included within one of the investigated WMA additives ensured better water resistance than the other additive classified as a viscous regulator.