Doctoral Thesis in Civil Engineering
Marisa Sofia Fernandes Dinis de Almeida
University of Beira Interior, Covilhã, Portugal
Technology of asphalt pavement recycling had its beginning in USA in the XX century,
in the late seventies. At that time was taking place the first petroleum crisis, and
construction companies had to take into account the influence of the rising cost of
bitumen and fuel used for the production and transportation of bituminous mixtures.
This, along with a shortage of natural aggregate that was increasingly felt, as well as
greater environmental awareness of people and the official authorities led to the
development of pavement recycling technology in the USA and across Europe.
In Portugal, asphalt pavement recycling started to be of interest in the last two decades,
due to increasing number of roads in need of rehabilitation. On the other hand, in order
to reduce the production of natural aggregates, it became necessary to incorporate and to
reuse recycled asphalt pavement (RAP) based on asphalt recycling technology.
In answer to these new challenges, there have been various paving techniques that are
very interesting solutions at the technical, economic and environmental level, thus
contributing to sustainable development. These techniques are based on reducing the
temperature of production with regard to conventional asphalt mixtures and
consequently reducing the energy consumption and CO2 emissions.
Among the different techniques of pavement recycling (made in situ or in plant, cold,
warm or hot production), this work concerns the warm-mix recycled asphalt (WMRA)
with bitumen emulsion in plant. It is a developing new technology, which has proved
very promising, both economically and environmentally. This technology allows to use
100% RAP and to reduce the energy consumption, since the recycled mixture is
produced at lower temperatures than hot asphalt mixes.
There are still several important gaps in knowledge that have limited the use of warmmix
recycled asphalt (WMRA) more generally, which relate mainly to insufficient
information about the recycled pavement performance. As such, it is intended with this
research to contribute to a better knowledge of this technique in order to promote its
implementation in Portugal.
Thus, this study looked at the most commonly used pavement recycling techniques,
comparing them and identifying the key benefits that are associated with reduction of
temperature in the production of recycled mixtures.
The present study explores the main asphalt mixtures design used in several countries,
as well as the different laboratory tests used to characterize the performance of
bituminous mixtures, as a basis for developing a novel design method for WMRA.
Thus, the work concerns the development of an experimental study of different WMRA
compositions produced in the laboratory and discussing the results obtained from its
It also presents an in situ case study of WMRA pavement, describing the properties of
materials used, the construction process adopted and the evaluation of their performance
by conducting various laboratory tests. It also presents an economical study comparing
different mix compositions, which demonstrates the advantages of the WMRA in
relation to conventional mixtures.
Finally, some recommendations are proposed regarding the production of warm-mix
recycling in plant, as well as a design method for the WMRA resulting from the
laboratory study done.