Asphalt mixtures known as “cold mixtures” are those whose bituminous binder is incorporated in the mixture in the form of bitumen emulsion (emulsion of bitumen in water), allowing the mixture to be produced and placed at ambient temperature. This type of mixtures can be produced either using “new” aggregates or using reclaimed asphalt pavement (cold recycled mixtures). Generally, the materials used in the production of asphalt cold mixtures are aggregates, bitumen emulsion and water. Water is used in order to provide a satisfactory degree of coating of the aggregates by the bitumen emulsion, to improve the mix workability and the layer compaction. The fact that no heating is necessary for the production and placement of asphalt cold mixtures provides some advantages to this technique in relation to the use of traditional hot mixtures: - Reduction of energy costs; - Reduction of emission of pollutants; - Possibility of using lower complexity asphalt plants, that can easily be installed next to the work site, providing: - Reduction of time and costs of materials transport; - Flexibility in using local aggregates. Furthermore, in situ asphalt cold recycling provides the following benefits: - Reuse and conservation of non-renewable natural resources, since the aggregate source is the existing pavement; - Waste materials reduction. However, after placing asphalt hot mixtures, the pavement can be trafficked almost immediately and the mixture presents the “final” characteristics for which it was designed. This is not the case for asphalt cold mixtures. In fact, after their placement in the pavement, cold mixtures firstly develop the so-called “curing” process. This is mainly because one of the main constituents of this type of mixtures is water, both added to the aggregate mixture and present in the asphalt emulsion. After the manufacture and placement of the asphalt cold mixture, the water starts being eliminated, mainly through the compression induced by the rolling compactors and later by evaporation. At the end of the curing process, a continuous cohesive film that holds the aggregate in place with a strong adhesive bond must be achieved (Asphalt Institute MS14, 1990). Therefore, cold mixtures will only present their “final” characteristics when the curing of the asphalt cold mixture is concluded, which can take several months. Nevertheless, there is an intermediate phase, before the curing is completed, when the pavement can already be trafficked, being necessary to ensure that no pavement damages occur that could compromise pavement performance, either in the short or in the long term. Curing of asphalt cold mixtures has a great influence on the evolution of the mixture properties and therefore on the performance of the entire pavement. Taking this into account, a research study was developed in the frame of a PhD thesis, under the theme “New techniques of pavement rehabilitation – Asphalt cold mixtures”. The main objectives of this research project were: - To evaluate the influence of curing on some mechanical properties of a selection of asphalt cold mixtures; - To evaluate the short and long term performance of the rehabilitated pavements; - To contribute to the development of analytical methods for the design for road pavements incorporating this type of materials. (Author/publisher)
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