1,721,030 research outputs found
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
Mechanical behaviour of cement-bitumen treated materials containing different amounts of reclaimed asphalt
No full textCold recycling techniques have become one of the main sustainable solutions in road construction and maintenance. The use of reclaimed asphalt (RA) as a constituent material for bound mixtures offers two main advantages: it eliminates problems concerning disposal and it allows natural resources to be preserved. Among the most widespread recycled mixtures, the use of cement–bitumen-treated materials (CBTM) for subbase courses has rapidly increased over the last 10 years. This paper deals with the influence of RA content on the mechanical characteristics of CBTM. Several mixtures were produced by combining different dosages of binders (cement and bituminous emulsion) and RA contents. The behaviour of recycled mixtures was evaluated and compared in terms of indirect tensile strength, water sensitivity and stiffness modulus. In addition, the effects of temperature on the stiffness properties were investigated. Experimental results showed that the RA content did not significantly affect the compactability and the strength properties of CBTM. The presence of RA determined an increase in mix deformability and thermodependence, but the effect can be inhibited by increasing cement dosage. The findings offer good prospects for increasing the use of RA and encourage administrations to employ this material as an effective construction solution
Characterization of the three-dimensional linear viscoelastic behavior of asphalt concrete mixtures
No full textMechanistic-empirical pavement design methods typically require the identification of the complex Young’s modulus and Poisson’s ratio for the characterization of bituminous layers. However, since in small deformation the frequency-dependent shear and bulk responses of an isotropic body are decoupled, the complex shear and bulk moduli are generally considered fundamental response functions. The objective
of this study was to perform the experimental characterization of the three-dimensional response of asphalt mixtures in the linear viscoelastic domain, through the simultaneous measurement of the complex moduli E⁄, K⁄ and G⁄ and the complex Poisson’s ratio m⁄. The testing program consisted of cyclic compression and cyclic tension–compression uniaxial tests on cylindrical specimen, with the measurement of
both axial and transverse strain. In particular, frequency sweeps were carried out at temperatures between 0, and 40 C and at axial strain levels between 15 and 60 le. Experimental results highlighted that, for the tested mixture, the time–temperature superposition principle was applicable to both the bulk and shear response, and consequently to the axial response. E⁄ and G⁄ showed very similar trends in terms of both stiffness moduli and loss angle, whereas K⁄ values highlighted smaller frequency dependence. The time–temperature superposition principle was also applicable to m⁄ whose master curves can be qualitatively described using the local approximation to the Kramers–Kronig relations. Results suggest that the simultaneous assessment of bulk and shear response may be a useful tool for the performance characterization of asphalt mixtures
Experimental study of bitumen emulsion–cement mortars: mechanical behaviour and relation to mixtures
No full textCold bitumen emulsion mixtures are ecofriendly
materials for road pavement construction.
Portland cement and other supplementary cementitious
materials are added to the mixtures to improve
their performance. In bitumen emulsion–cement
(BEC) mixtures, the two binders affect the mechanical
behaviour and the curing process. In this research,
BEC mixtures are considered as multiphase composite
materials consisting of a mortar matrix and coarse
aggregate inclusions. The main objectives are to
identify the composition of BEC mortar phase and to
compare mixtures and mortars throughout the curing
process. Starting from two BEC mixtures containing
80% reclaimed asphalt, eighteen mortars were manufactured
by changing their water and air voids
content. Then, two design composition were selected
to analyse the curing process by monitoring indirect
tensile strength (ITS), indirect tensile stiffness modulus
(ITSM) and moisture loss. Results showed that
the short-term ITS of mortars (1 day of curing)
increased by reducing their water and their air voids
content. During curing (from 1 to 28 days), the
mechanical properties (ITS and ITSM) of mixtures
and mortars increased in a similar way. Unique
relationships were identified between mortar and
mixture properties, regardless of bitumen to cement
(B/C) ratio, curing time and curing condition. In terms
of predictive behaviour, the design composition
slightly underestimated mixture stiffness and overestimated
mixture strength
Verifica strutturale di pavimentazioni stradali in cubetti di pietra eseguita con analisi FEM
No full textIndagine sperimentale sulle possibilità di impiego stradale dei materiali provenienti dalle attività di recupero dei rifiuti di costruzione e demolizione di opere civili
No full textPermanent deformation behaviour of unbound recycled mixture
No full textNowadays, the use of recycled waste materials in road construction and rehabilitation processes aimed to
preserve non-renewable resources and to solve management problems related to the expansion of landfills
become a promising engineering solution. The current paper deals with the feasibility of using material
from construction and demolition wastes (C&D) as aggregate for unbound layers (base and/or
subbase) of road pavements. In particular, the permanent deformation behaviour of a recycled C&D mixture
under repeated triaxial loading was investigated and compared with that of two natural granular
mixtures selected as reference materials. An analytical model, proposed by the authors, was used to
describe the long-term permanent strain accumulation of materials. The results, in addition to showing
the ability of the model to predict change in mechanical behaviour depending on the different nature of
materials, highlight how the C&D mixture performs better under specific stress and moisture conditions
compared with traditional materials. Finally, the results obtained in this study not only provide a practical
approach for ranking granular materials for pavement with regard to their rutting potential but also
promote the use of C&D materials as a sustainable and effective alternative to traditional aggregates
Low-temperature tensile behaviour of asphalt binders: Application of loading time–temperature–conditioning time superposition principle
No full textThermal cracking of bituminous layers is one of the main modes of failure for asphalt pavements. This
distress is highly related to the rheological properties of asphalt binders. The purpose of this study
was to investigate the low-temperature behaviour of asphalt binders by performing Direct Tension Tests
(DTTs) according to Superpave specification. The DTT results were analyzed and compared in terms of
trend of stress–strain curve instead of conventional failure stress or failure strain values. Through the
analysis of stress–strain diagram, it was possible to evaluate the effects of temperature, elongation rate
and conditioning time on the rheological properties of binders. Particular attention was paid to the conditioning
time variable as it was observed that the stiffness of the binder changes with time when it is
stored isothermally at low temperature due to the physical hardening phenomenon.
To this end, a modified superposition effects principle, which also includes the conditioning time in
addition to the temperature and elongation rate variable, has been proposed. Finally, this principle
allowed the authors to find an analytical model capable of describing the rheological properties of asphalt
binders as functions of the three considered test variables
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