1,354,302 research outputs found
Experimental characterization of asphalt for an elasto-visco-plastic constitutive model.
No full textThis paper describes a range of uniaxial creep tests that have been undertaken for a
proprietary polymer modified asphalt, the procedure used to determine the parameters
required for an elasto-visco-plastic constitutive model.
Uniaxial compressive creep testing and creep recovery testing have been undertaken
over a range of temperatures and stress conditions. Procedures used to determine the
model parameters from the test data are detailed and parametric equations are developed
to describe the model parameters as functions of the test conditions. Particular attention
is given to the determination of the parameters related to visco-plastic flow and damage
accumulation at high strain levels. The model has been implemented in to the CAPA-
3D Finite Element (FE) program and preliminary verification has been undertaken
Experimental validation of a fractional model for creep/recovery testing of asphalt mixtures
No full textPrediction of asphalt mixtures’ behavior during their service life is a challenge due to its complexity and
sensitivity to environmental and loading conditions. It has been proved that, when subjected to loading
conditions comparable with most pavement operating conditions, asphalt mixtures behave as linear
visco-elastic (LVE) materials. Traditionally the LVE behavior of bituminous material is modeled via
creep/recovery functions. In the past, several rheological models constituted by elastic and viscous elements
arranged in series or in parallel (analogical models) have been proposed and specified for both
bitumen and asphalt mixtures. The corresponding constitutive laws always involve first order derivatives
of time with exponential type solutions but problems in setting parameters arise when both the creep
and recovery behavior have to be modeled. In this paper it is shown that experimental creep data follow
a power decay law, rather than an exponential one. As a consequence, a simple fractional model is here
proposed for predicting creep/recovery behavior of asphalt mixtures with a small number of parameters
and low computational efforts with respect to the classical analogical models. The proposed model is
then calibrated by a best fitting procedure on experimental data from creep and creep/recovery tests carried
out on asphalt mixtures under different load and temperature conditions
The end of the road?
No full textRoad traffic has grown more than 80% since 1980 – as a result roads have deteriorated more quickly than could have been envisaged. Britain’s road network is one of the country's largest national assets.
Professor Andy Collop from the Department of Civil Engineering describes the research taking place in Nottingham Transportation Engineering Centre and the improvements such knowledge can make to road materials, structures and sustainability
Experimental Characterization of High Performance WAM-Foam Trial Sections
No full textThis study aims to evaluate the feasibility of using warm asphalt mixes for high performance pavements on the basis of a complete mixture characterization. In this work WAM Foam technology is studied by introducing a soft binder and a hard foamed bitumen at different stages during mixing. This results in lower production temperatures which is beneficial both in terms of energy consumption and air emissions. By proper selection of the two binders, a high-performance mixture was produced (Greenfalt®) which was used on a heavy trafficked high-speed road in Italy. The paper describes results of tests that were carried out on laboratory and field compacted specimens taken from experimental trial sections as well as results of Falling Weight Deflectometer (FWD) tests carried out on the same sections. The results show good performance in terms of stiffness, fatigue life and resistance to permanent deformation
Fundamental characterisation of reclaimed asphalts: the importance of testing homogeneous specimens
No full textThis study highlights the importance of defining appropriate specimen manufacturing procedures when assessing the fundamental properties of reclaimed asphalt mixes for further modelling purposes. Two gyratory compactor procedures were used: the first leading to specimens with a non-uniform air voids distribution and the second tailored to obtain homogeneous specimens. The study was performed by using three SMAs incorporating up to 30% of reclaimed asphalt but designed to have identical properties. A detailed characterisation of the loose mixes and binders, a X-Ray CT micro-structural study of the manufactured specimens and a further mechanical characterisation showed that testing nonhomogeneous gyratory specimens leads to a significant overestimation of the mechanical properties of asphalt mixes. This study has been developed within the FP7 project ReRoad
Indirect Tensile versus Two Point Bending Fatigue Testing
No full textThis paper describes a comparison between an indirect
tensile fatigue method and the currently preferred
European standard two-point bending, trapezoidal
fatigue test. A study was undertaken using both tests to
determine the fatigue properties of a standard UK
asphalt mixture at two temperatures of 10 and 30 8C.
The fatigue life, in addition to using the traditional 90%
reduction in initial stiffness, was also computed using a
fatigue failure point based on the transition between the
quasi-stationary phase (associated with a uniform
stiffness decrease and the development of micro-cracks)
and the failure phase (associated with localised crack
propagation). This fatigue failure point, determined by
taking the peak of the product of loading cycles and
stiffness versus loading cycles, was also converted into an
alternative form used to determine the fatigue failure
point for the indirect tensile fatigue test. Separate
fatigue relationships were produced for the four
combinations of test method and temperature based on
the phenomenological initial tensile strain versus fatigue
life relationship. Although the indirect tensile fatigue test
produced shorter fatigue lives compared to the
two-point bending fatigue test, it was also possible to
combine all four fatigue relationships to produce one
unique fatigue function for the 20mm dense bitumen
macadam asphalt mixture
The end of the road?
No full textRoad traffic has grown more than 80% since 1980 – as a result roads have deteriorated more quickly than could have been envisaged. Britain’s road network is one of the countries largest national assets. Professor Andy Collop from the Department of Civil Engineering describes the research taking place in Nottingham Transportation Engineering Centre and the improvements such knowledge can make to road materials, structures and sustainability.
Manufacturing reclaimed asphalt test specimens using gyratory compactor
No full textThis paper presents a laboratory investigation aiming to provide a protocol that
allows to confidently using gyratory compaction for the production of reclaimed asphalt test
specimens. The presented investigation is part of a wider experimental programme aiming at
obtaining input parameters for modelling purposes. For this reason, it has been necessary to
define a quick and reliable and repeatable procedure to manufacture a high number of
specimens with a limited amount of material. Gyratory specimens were compacted by
targeting to densities defined in previous Marshall mix design and with the final aim of
obtaining specimens with a fixed and homogeneous distribution of air voids content. The
study has been developed by comparing results of two Stone Mastic Asphalt mixtures, a
control mix with virgin material and a reclaimed asphalt mix with 30% of RA. The mixtures
had almost identical air void contents, aggregate grading curves and the binders had similar
conventional binder properties. Homogeneity of air void distribution was investigated by X-ray
Computed Tomography (CT), image analysis techniques and buoyancy tests. Coring and
trimming of the compacted specimens were used to obtain the final test specimens with fixed
homogeneous properties. The study concluded that gyratory compaction is suitable to
produce homogeneous test specimens also for mixtures containing high amount of reclaimed
asphalt. Nevertheless final coring and trimming of the specimens are mandatory as well as
performing a preliminary investigation for each material consisting in the compaction, and the
further buoyancy tests, of few specimens having densities ranging from 100 to 90% of the
initial target. The presence of high percentage of RA did not present remarkable issues apart
making the compaction harder. This study has been developed within the FP7 European
Project Re-Road
Laboratory mix design of asphalt mixture containing reclaimed material
No full textThis paper presents a study on the production of asphalt test specimens in the laboratory containing reclaimed asphalt. The mixtures considered were stone mastic asphalt concrete mixtures containing up to 30% of reclaimed asphalt. Specimens were compacted to the reference density obtained from the Marshall mix design. Gyration compaction method was used for preparing specimens for the experimental programme, while coring and cutting methods and X-ray computed tomography (CT) were used to investigate the change in properties within the specimens and to validate the selected methodology.The study concluded that gyratory compaction is suitable to produce homogeneous test specimens also for mixtures containing high amount of reclaimed asphalt. Nevertheless, preliminary trials for each material are mandatory, as well as final coring and trimming of the specimens due to side effects
Mechanical characterization of dry asphalt rubber concrete for base layers by means of the four bending points tests
No full textThe mechanical characterisation of the asphalt concrete in terms of both the fatigue resistance and the stiffness modulus is necessary to use any design method of the flexible road pavements.
Even more the determination of these mechanical properties is necessary if the asphalt concrete investigated is an innovative material as a dry asphalt rubber concrete DARC (i.e. a bituminous mixture with rubber via dry process).
Such material is less known and investigated than the asphalt rubber concrete via wet process, even if its application implies peculiar economical and environmental advantages such as no specialized equipment or significant plant modifications and large quantity of recycled waste tires compared to the wet process.
This paper focused on the mechanical behaviour of some DARCs with different rubber content that varies within 0, 3.0% by weight of the aggregates; these materials are designed to the base layer of the flexible pavements.
In particular an experimental survey was carried out in order to determine the stiffness modulus of the DARCs by means of the four point bending test on prismatic specimens (UNI EN 12697-26:2004)
- …
