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Development of Sustainable (Hot and Warm Recycled) Porous Asphalt Mixtures through Laboratory and Field Investigation
Full text linkI conglomerati bituminosi drenanti sono ampliamente utilizzati come strati di usura autostradali grazie ai benefici apportati in termini di riduzione del rumore veicolare e il miglioramento delle condizioni di sicurezza in caso di pioggia. Nonostante i numerosi vantaggi, tali strati sono caratterizzati da una durabilità limitata a causa dell’elevato numero di vuoti che li rende più suscettibili a sgranamento e danni legati alla presenza d’acqua. Di conseguenza, i lavori di manutenzione autostradale sono spesso effettuati su strati drenanti, il che comporta l’accumulo di grandi quantità di materiale fresato (RAP). Allo stesso tempo, occorre considerare che solo gli aggregati vergini sono attualmente utilizzati per la produzione di miscele drenanti a causa delle loro delicate proprietà volumetriche. Al fine di promuovere l’uso di fresato anche in miscele drenanti è necessario che il RAP proveniente da strati di usura aperti sia stoccato separatamente dal resto e ri-utilizzato in tali strati. La prima parte del presente lavoro consiste in un’estesa ricerca sperimentale volta alla valutazione delle prestazioni meccaniche e di durabilità di miscele drenanti in cui i materiali vergini sono stati parzialmente sostituiti da materiale fresato proveniente esclusivamente da vecchie pavimentazioni drenanti.
Occorre altresì considerare che la sostituzione di aggregate vergini con materiale fresato implica l’utilizzo di temperature di produzione maggiori a causa della presenza di bitume invecchiato. Ciò comporta un maggiore consumo di energia e, quindi, maggiori costi di produzione e problemi ambientali legati all’emissione di gas dannosi. Quest’ultimo aspetto sta diventando cruciale dal momento che gli impianti di produzione si trovano sempre più spesso vicino ad agglomerati urbani; soluzioni urgenti sono quindi necessarie per risolvere sia il problema energetico che quello ambientale senza dover ridurre l’uso di materiale fresato nelle miscele. Una possibile soluzione è l’uso di additivi WMA (Warm Mix Additives) al fine di ridurre le temperature di produzione senza comprometterne la lavorabilità né la compattabilità delle miscele. In questo senso, la seconda parte del presente lavoro descrive l’indagine effettuata per valutare la possibilità d’impiego di vari additivi WMA per la produzione a temperature ridotte di miscele drenanti contenenti 15% di RAP.Nowadays, porous asphalt (PA) mixtures are extensively used as motorway surface layers due to their benefits in reducing traffic noise and improving safety during wet conditions. Despite these advantages, PA layers are characterized by limited durability due to the high air void content that makes them more susceptible to ravelling and water damage. As a consequence, maintenance processes in the motorway network are often performed on PA layers leading to a considerable amount of milled material. Moreover, only the use of virgin aggregates is currently allowed in PA mixtures in many countries due to their low durability and delicate volumetric properties. In order to promote the use of Reclaimed Asphalt Pavement (RAP) also in the PA layers, milled material coming from old PA mixtures needs to be stockpiled separately and re-used in PA courses. Given this background, the first objective of this research is to evaluate the feasibility of including milled materials coming from old PA layers as partially substitution of virgin materials without compromise pavement performance.
Furthermore, it must be taken into account that the substitution of virgin aggregates with RAP requires the use of higher production temperatures, due to the presence of aged bitumen. This implies significant energy consumption and, thus, higher production costs as well as environmental issues related to harmful gasses emission. The latest aspect is becoming crucial since most of the production plants are located near urban agglomerations. Urgent solutions are needed in order to solve the energetic and environmental issues without reducing the use of recycled materials. In this sense, the use of Warm Mix Additives (WMA) can represent a valid solution since it allows significant reduction in production temperatures without compromising the workability and compactability properties of asphalt mixtures. In the second part of this experimental study, the feasibility of using different WMA additives available on the market were analyzed involving PA mixtures prepared with 15% of RAP
Characterisation of warm recycled porous asphalt mixtures prepared with different WMA additives
No full textThe 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 Evaluation of Asphalt Concrete Modified by Polyolefins Through Dry and Wet Process
No full textAbstractPolymer modification in road paving applications enables significant improvement in road service life as regards main distresses such as rutting, fatigue and thermal cracking. Polymer modification can be performed through a dry or wet process, and it may lead to mixtures with different mechanical properties depending on the modification process employed. In this context, this paper presents a laboratory investigation concerning the effect of a polyolefinic additive (PO) on the mechanical response of asphalt concrete produced by dry and wet process. Mechanical characterization consisted of wheel tracking tests at 40 and 60°C for rutting resistance analysis and semi-circular bending tests at 10°C for cracking behaviour analysis. Results showed higher rutting resistance of PO modified asphalt concretes (AC) compared to the control mixtures, but they were found to be more temperature sensitive denoting a penalized rutting response at higher temperature. PO modified ACs also showed higher fracture toughness and reduced fracture energy. In particular, the dry process seems to guarantee an ability of deformation such as better endurance of cracking propagation with respect to the mixture produced by the wet process
Influence of polymer modification on asphalt binder dynamic and steady flow viscosities
No full textAsphalt pavement performance such as rutting, crack initiation and propagation as well as fatigue behaviour are substantially affected by the rheological properties of the bitumen. In this sense, the use of polymer modification in road paving applications has been growing rapidly over the last decade as it allows significant enhancements in bitumen properties with consequent improvement in road service life. In fact, the use of polymer modified bitumens (PMBs) leads to pavements characterized by higher resistance to rutting and thermal cracking and lower fatigue damage, stripping and thermal susceptibility. This paper presents a laboratory investigation concerning the effect of polymer modification on the flow behaviour of bitumens. Two different polymers, an elastomer and a plastomer, were used as bitumen modifying agents at three different percentages (2%, 4% and 6% by bitumen weight). Oscillatory mechanical analysis as well as viscosity measurements under steady state conditions were performed taking into account different testing parameters such as temperature, loading frequency and shear rate. The results confirm that the rheological properties of PMBs are strongly influenced by polymer nature and polymer content. The bitumen viscosity on the dynamic domain was combined with that in the steady-state domain, confirming the applicability of the Cox–Merz relationship for the plain bitumen and the PMBs with low polymer content. Finally, the Cross and the Carreau models were found to be suitable to fit the steady state and the dynamic results in order to determine the viscosity function of the investigated bitumens
Fatigue rheological characterization of polymer-modified bitumens and mastics
No full textFatigue 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 com- position. 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
Laboratory Study to Evaluate the Influence of Reclaimed Asphalt Content on Performance of Recycled Porous Asphalt
No full textRoad-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
Adhesion properties of warm recycled mixtures produced with different WMA additives
No full textEco-friendly, cost-saving and sustainable pavements have become a priority goal due to increased costs of raw materials and strict environmental regulations. To address these challenges, the use of Reclaimed Asphalt Pavements (RAP) and Warm Mix Asphalt (WMA) technologies is becoming more and more frequent in the asphalt industry.
Adhesion properties and water susceptibility are major concerns associated with the use of WMA mixtures due to the reduced production temperatures that alter the interaction at the bi-tumen-aggregate interface. The materials response significantly varies depending on WMA technology as well as mixture type.
In this sense, this study focused on the evaluation of both open and dense graded mixtures in-cluding RAP and three different WMA additives (organic wax, chemical additive and zeolite). Hot Mix Asphalt (HMA) mixtures were also prepared for comparison purposes. Since raveling (loss of aggregates from the surface layer) is strongly related to the adhesion properties between binder and aggregates, raveling performance were measured by means of Cantabro tests and correlated to the adhesion properties evaluated through Bond Bitumen Strength (BBS) tests. Tests were performed in dry and wet condition in order to assess the water susceptibility.
Results showed that the type of WMA technology may influence mixture performance especial-ly when subjected to water conditioning. However, RAP aggregates within both open and dense graded WMA mixtures significantly limited the negative effects of reduced production tem-peratures in terms of adhesion and water resistance. Only the chemical WMA additive guaran-teed performance comparable to HMA, particularly in terms of water susceptibility
Performance assessment of in plant produced warm recycled mixtures for open-graded wearing courses
No full textSustainable 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 (130çC) 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
Use of reclaimed asphalt in porous asphalt mixtures: Laboratory and field evaluations
No full textMaintenance 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, reliable techniques allowing the use of RA in new PA mixtures are needed. In this research study, the use of coarse RA from old PA as aggregate in new PA mixtures was evaluated. Because a previous laboratory study demonstrated that the use of 15% of RA aggregates in PA mixtures seems possible (or even recommendable) as long as an accurate mix design with adequate binder contents is performed, new laboratory and field evaluations on recycled PA mixtures with15% of RA aggregates were carried out. On one hand, cyclic coaxial shear tests (CASTs) were performed under both dry and water-submerged conditions in order to evaluate the simultaneous effect of traffic and water exposure. On the other hand, a comprehensive laboratory experimental program for assessing acceptability, durability, fracture resistance, and water sensitivity was carried out on materials taken from the field during the construction of a full-scale trial section. Moreover, drainage properties of surface layers were measured along such a trial section. Overall test results demonstrated that including 15% of selected coarse recycled aggregates into porous asphalt mixtures does not compromise performances and durability of both asphalt-plant and laboratory produced mixtures. It was demonstrated that recycled mixture with 5.25% of total binder content and prepared by accurate mix design can perform as well as (or even better than) standard PA mixture in terms of workability, acceptability, abrasion resistance, repeated loading resistance, fracture propagation resistance, moisture sensitivity, and water drainability
Aging effects on recycled WMA porous asphalt mixtures
No full textNowadays, the use of reclaimed asphalt pavements (RAP) is often combined with Warm Mix Asphalt (WMA) technologies with several benefits in terms of environment, cost and mechanical performance. Concerns still exist related to in-service and aging characteristics of warm recycled mixtures since WMA technologies have been developed over the last decade and hence long term performance data are not available yet. The objective of this experimental study is to evaluate the aging effect on recycled porous asphalt (PA) mixtures produced at reduced temperatures using different WMA additives (organic, chemical and zeolite) and including 15% of RAP. In this sense, long term aging was simulated in the laboratory on compacted specimens by means of the Viennese Aging Procedure (VAPro). Rheological properties of the extracted bitumen samples were measured in order to evaluate possible links between bitumen and mixtures performance. As far as mixtures are concerned, stiffness tests were carried out before and after aging, whereas fatigue resistance was evaluated on long term aged mixtures to compare long term performance of HMA and WMA porous asphalt. Mixtures as well as bitumens results showed that the lower aging process that WMA mixtures undergo during production affects mixtures stiffness at the beginning of service life. Only the presence of the organic additive increases the stiffness of WMA bitumens and mixtures due to the crystalline network structure that forms in the bitumen. On the other hand, extensive long term aging effects were measured in case of WMA mixtures. Nonetheless, overall fatigue results showed that long term fatigue performance of WMA mixtures are not significantly affected compared to HMA regardless of WMA additive types
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