Influence of mineral fillers on the rheological response of polymer-modified bitumens and mastics

AbstractThe rheological properties of the bituminous components (bitumen and bituminous mastic) within asphalt mixtures contribute significantly to the major distresses of flexible pavements (i.e. rutting, fatigue and low temperature cracking). Asphalt mixtures are usually composed of mastic-coated aggregates rather than pure bitumen-coated aggregates. The purpose of this study is to investigate the effects of mineral fillers on the rheological behaviour of several polymer-modified bitumens (PMBs) through laboratory mixing. A neat bitumen and two types of polymers (elastomeric and plastomeric) were used to produce PMBs, and two fillers with different minerals (limestone and basalt) were selected to obtain mastics. The dynamic shear rheometer (DSR) and bending beam rheometer (BBR) were used to characterize the rheological properties of PMBs and mastics. In particular, multiple stress creep recovery (MSCR) tests were performed to evaluate the rutting potential at high temperatures, whereas BBR tests were carried out to investigate the low temperature behaviour of these materials. BBR results for unmodified mastics show that the increase of stiffness is similar regardless of the filler type, whereas results for polymer-modified mastics indicate that the degree of stiffening depends on the combination of filler/polymer types. MSCR results show that adding filler leads to a reduced susceptibility of permanent deformation and an enhanced elastic response, depending on the combination of filler/polymer types. Overall results suggest that a physical–chemical interaction between the filler and bitumen occurs, and that the interaction level is highly dependent on the type of polymer modification

Green manuring as sustainable management for southern Italy extensive cultivated areas

In the extensively-managed agricultural areas of Sicily, rainfall is often so limited that economically effective annual productions are not feasible. Bare fallow, the most extreme dry-farming technique, seems to be, under such conditions, the only suitable strategy. The introduction in these cropping systems of an annual legume to put early into the soil, as an alternative to bare fallow, may represent a technique able not only to prevent soil erosion, but also to improve the low soil organic matter reserves, with a direct benefit on the following yields and on the whole environment. The trial was aimed to verify the bioagronomical and qualitative behaviour of durum wheat managed under different cropping systems. Results, heavily influenced by very low rainfall (320 mm), stressed the extraordinary productive response of durum wheat cultivated after the green manure legume

Influence of polymer modification on asphalt binder dynamic and steady flow viscosities

Asphalt 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

Experimental characterization of high-performance fiber-reinforced cold mix asphalt mixtures

Maintenance of existing road pavements assumes increasing interest as the traffic growing produces a faster deterioration of road infrastructures compromising safety and pavement serviceability. In order to guarantee long-lasting pavement repairs, maintenance activities and products must be optimized in terms of both achieved performance and curing times to reach a proper pavement serviceability. This research project focuses on the experimental characterization of a high-performance cold mix asphalt mixture reinforced with three types of fibers (cellulose, glass–cellulose, nylon–polyester–cellulose) dosed at two different contents (0.15% and 0.30% by the aggregate weight). Such materials were investigated at different curing times (1, 7, 14, 28 days) and conditions (dry and wet). Laboratory tests (Marshall, Indirect Tensile, Abrasion and Compactability) usually employed for hot mix asphalts were considered, adjusting the testing procedures taking into account the specific characteristics of cold mixes. Results showed that the mix with 0.15% cellulose fibers provides similar (for curing times of 14 and 28 days) or even higher performance (for curing times within 7 days) than the standard mixture (without fibers). Finally, the last two mixtures were compared with two cold mix asphalt mixes available on the market. The cellulosefiber- reinforced material and the standard one showed enhanced performance, allowing the conclusion that they can be more successfully used in maintenance activities

Verifica prestazionale di materiali impiegati per la realizzazione di segnaletiche orizzontali

Road marking functional retraining is a maintenance operation that more and more often involves road pavement management. These maintenance operations, extended to the whole road network, become very expensive both for direct costs and for indirect costs due to traffic slowing down. Road marking noticeably influences road safety. On the subject, some studies show that the decrease of accident risk is strongly connected with typical road marking characteristics as right visibility (day-time and night-time), suitable adhesion level and durability compatible with road network management. The Standard UNI EN 1436/98, according to the provisions of the Italian Road Code, fixes the principles to control road marking performances through the service life concept. It mainly depends on the frequency of vehicular passing, on the traffic variety, on the pavement characteristics and on the particular climatic conditions. However, it ignores engineering aspects tightly connected with the material life. In this sense, the above-mentioned Italian Road Code and the relative Regulations underline the need to characterize road marking as a material and not only as a “furniture”. The present work shows the results of an experimental study carried out on a trial section. The characteristics of 6 different materials (3 solvent paints and 3 waterborne paints) were studied to evaluate both photometrical and adhesion properties employing the Standard provisions. Through direct comparisons and periodic monitoring, it has been possible to estimate, on two different pavement surfaces, the material life and the effects of environmental conditions on required performances

Improved durability of recycled porous asphalt

Porous asphalt mixtures are extensively used as highway surface layer due to their benefit in improving skid resistance and reducing spray and splash effects during wet conditions. Moreover, porous asphalts (PA) are also oriented towards the reduction of road traffic noise thanks to enhanced sound absorption capabilities. Nevertheless, the limited durability of porous asphalt layers leads to frequent maintenance and rehabilitation activities. In this study, the use of course reclaimed asphalt (RA), obtained by milling old porous surface layers, as aggregate in new PA mixtures was evaluated. Preliminary, Binder Bond Strength tests on coated and uncoated basalt aggregate substrates showed encouraging results in terms of adhesion properties between unaged polymer modified bitumens and substrates coated with aged bitumens, simulating RA aggregates. Thus, five porous asphalt mixtures prepared with 15% course RA aggregates and different total binder contents were studied in the laboratory. A reference PA mixture containing only virgin aggregates was also investigated for comparison purposes. Indirect tensile strength tests, particle loss (Cantabro) tests, semi circular bending (SCB) tests and repeated indirect tensile tests were carried out in both dry and wet conditions in order to evaluate acceptability, durability, fracture resistance and water sensitivity of recycled mixtures. Results showed that recycled porous asphalt mixtures can perform as well as (or even better than) reference one. In particular, recycled mixtures at equal or higher binder contents than the reference mixture demonstrated an improvement in moisture resistance and durability

Experimental characterization of high-performance fiber-reinforced cold mix asphalt mixtures

Maintenance of existing road pavements assumes increasing interest as the traffic growing produces a faster deterioration of road infrastructures compromising safety and pavement serviceability. In order to guarantee long-lasting pavement repairs, maintenance activities and products must be optimized in terms of both achieved performance and curing times to reach a proper pavement serviceability. This research project focuses on the experimental characterization of a high-performance cold mix asphalt mixture reinforced with three types of fibers (cellulose, glass–cellulose, nylon–polyester–cellulose) dosed at two different contents (0.15% and 0.30% by the aggregate weight). Such materials were investigated at different curing times (1, 7, 14, 28 days) and conditions (dry and wet). Laboratory tests (Marshall, Indirect Tensile, Abrasion and Compactability) usually employed for hot mix asphalts were considered, adjusting the testing procedures taking into account the specific characteristics of cold mixes. Results showed that the mix with 0.15% cellulose fibers provides similar (for curing times of 14 and 28 days) or even higher performance (for curing times within 7 days) than the standard mixture (without fibers). Finally, the last two mixtures were compared with two cold mix asphalt mixes available on the market. The cellulosefiber- reinforced material and the standard one showed enhanced performance, allowing the conclusion that they can be more successfully used in maintenance activities

Performance Evaluation of Cold Recycled Mixture Containing High Percentage of Reclaimed Asphalt

Cold recycling of asphalt pavements proved to be an effective maintenance and rehabilitation technology for both environmental and economic reasons. Nevertheless, the use of cold-recycled (CR) asphalt mixtures requires a careful assessment of their mechanical properties, especially when they are designed to replace traditional hot-mix asphalt concrete (AC) mixtures. In this study, the potential use of a CR asphalt mixture as base course of an Italian motorway was evaluated. The studied mixture was produced in a central plant employing high-reclaimed asphalt (RA) content and used to construct two experimental sections along an in-service Italian motorway. In particular, a special mixing procedure, involving the use of water vapour and bituminous emulsion, was tested. A third experimental section was constructed with the same layer thickness using the AC mixture currently used in rehabilitation projects, incorporating 30% of RA. Volumetric properties, stiffness, resistance to permanent deformation and fatigue behaviour of mixtures were investigated by performing tests on samples cored from the three test sections and on laboratory-compacted samples. Results of the mechanical tests showed that CR mixtures provide lower stiffness modulus and lower resistance to repeated loading, but better resistance to permanent deformation when compared with AC. This behaviour can be explained due to the presence of cementitious bonds that reduce thermal sensitivity and viscous response

Performance Optimization of Warm Recycled Mixtures

Warm Mix Asphalt (WMA) technologies are becoming popular due to their ability to reduce mixing and compaction temperatures compared to the conventional hot mix asphalts (HMAs), with remarkable advantages of environment and costs. Moreover, WMA is considered as one of the most promising technology for increasing the re-use of Reclaimed Asphalt (RA) within the mixture although its effectiveness in recycling issues require more dedicated research activities. This paper describes a laboratory investigation aimed at optimizing a dense graded asphalt mixture for wearing course, produced with WMA technology and including up to 30% of RA. WMA mixtures were prepared by using two contents of a plain bitumen, two contents of RA and one chemical additive. A recycled HMA containing lower RA content, according to technical specifications currently applied in Italy, was selected as reference mixture. Strength and stiffness properties, water sensitivity, rutting and cracking resistance were investigated on shear gyratory compacted specimens. The result analysis on stiffness, rutting and fracture properties indicated the possibility to produce suitable WMA mixtures with higher RA contents without penalizing their performance compared to the reference one