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

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

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

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

Comparison of energy and environmental performance between warm and hot mix asphalt concrete production: A case study

The use of additives to produce warm bituminous mixtures in asphalt pavements gives the possibility to decrease temperatures with positive implications on energy consumption, and on emissions of greenhouse gases and airborne pollutants. This study investigates the changes in energy and environmental performance of an asphalt plant switching from hot to warm asphalt concrete production. A full-scale trial section was constructed in an Italian motorway with recycled bituminous mixtures containing SBS polymer modified bitumen. Reference hot mix asphalts (HMAs) mixed at 170 °C were compared with warm mix asphalts (WMAs) mixed at 130 °C with different chemical additives. Calculations and analysis were performed considering three production phases during which the production technologies (HMA and WMA) and the mixture types varied in temperatures, mixing duration, and quantity of virgin materials employed. Energy performance was calculated through values provided by the asphalt plant operator and thermodynamic equations. Emissions of CO2 were calculated based on energy consumption and emission factors reported in the literature for the Italian energy mix. Airborne pollutants were measured at the stack of the dryer drum. The results showed that for each mixture type, a reduction of 40 °C in the production temperature corresponds to 15% lower thermal energy values for the drying/heating of the aggregates, with consequent lower consumption of fuel oil. The drying/heating of aggregates for WMA lead to lower emissions of particulate matter, NOx, and VOCs compared to HMA

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

Advanced Testing and Characterization of Interlayer Shear Resistance

The performance of multilayered pavement systems depends strongly on interlayer bonding. To guarantee good bonding, tack coats (also called bond coats) are usually applied at various interfaces during pavement construction or overlay. The effectiveness of the tack coat can be assessed with the use of several devices arranged by different laboratories to evaluate interlayer shear resistance. This paper shows how interlayer shear resistance may be evaluated through the Ancona shear testing research and analysis (ASTRA) device. ASTRA results, expressed in units of maximum interlayer shear stress (τpeak) highlight the effects of various influence parameters such as type of interface treatment, curing time, procedure of specimen preparation, temperature, and applied normal load. Moreover, this paper compares the τpeak results obtained by two different shear test devices: the ASTRA tester designed and developed in the Polytechnic University of Marche (Italy) and the layer-parallel direct shear tester created by the Swiss Federal Laboratories for Materials Testing and Research. The two test methods provide different but comparable results showing the same ranking of shear resistance for different interface treatment

Mechanical characterization of environmentally friendly mixtures

Nowadays, road traffic is the main cause of urban pollution. Owing to the primary importance of this problem two different environmentally friendly mixtures were considered: the first to reduce traffic noise and the second to mitigate atmospheric pollution. The anti-noise mixture is a dense-graded HMA in which 27% volume of mineral aggregates was replaced with expanded clay. The second mixture, which should mitigate air pollution, is an open-graded asphalt concrete partially filled with a cement mortar containing a photocatalytic agent (titanium dioxide). In order to properly use these mixes for road applications the evaluation of specific mechanical performance is required. In particular, the Authors show the laboratory characterization of the mixtures in terms of stiffness modulus, fatigue life and rutting comparing them with dense-graded and open-graded wearing courses, respectively

Comparing the field and laboratory curing behaviour of cold recycled asphalt mixtures for binder courses

The cold recycling of reclaimed asphalt (RA) for the rehabilitation of end-of-life pavements is becoming very common. Cold recycled asphalt mixtures (CRAMs) are characterised by a curing time, required to reach the material design mechanical performance. Since the laboratory simulation of the long-term field curing is not yet a standardised procedure, a CRAM was laid as binder course in a full-scale trial section that was monitored for more than two years. The comparison between field curing and oven-curing in laboratory at 40◦C was performed by carrying out indirect tensile stiffness modulus (ITSM), indirect tensile strength (ITS) and complex modulus tests, as well as measurements of the air voids content. The evolution of the ITSM as a function of the curing time (field/oven-curing) was obtained for both gyratory specimens and cores taken from the trial section at different time periods. Results showed that the material stiffness development can be accelerated with a small effect on its long-term value if oven-curing is applied a few days/weeks after compaction. A linear relationship was found between the ITS measured on the cores and their air voids content. Finally, the complex modulus tests confirmed that CRAMs provide an intermediate behaviour between asphalt concrete mixtures and cement-bound mixtures