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Several studies have applied recycled aggregates (RA) in road layers and demonstrated appropriate results. In general, RA can be one of two types: recycled concrete aggregates (RCA) or mixed recycled aggregates (MRA), each of which has lower density, higher water absorption, and lower mechanical strength than natural aggregates (NA). Alumina waste (AW), obtained from the process of aluminum refinement, could be mixed with RA in order to improve its properties, such as compaction and bearing capacity, for application in road construction. Few studies have investigated the use of AW with RA in civil constructions. This paper presents the results of a laboratory study of different materials based on the addition of AW to RCA and MRA. In the experiment, the mechanical behaviors and microstructural properties of RCA, MRA, and mixes of RCA or MRA with AW were compared. Different specimens of unbound recycled mixtures demonstrated increased resistance properties, and the formation of new cement hydrated particles was observed in these novel mixtures. The properties of the mixtures of RCA and MRA with AW suggest that these recycled materials can be used in unbound road layers to improve the long-term mechanical behavior.

The application of mixed recycled aggregates (MRA) and recycled concrete aggregates (RCA) in road works has been studied intensively over the last two decades. One of the properties that has not been studied enough is the self-cementing capacity of recycled aggregates (RA), which favours improving the bearing capacity of compacted recycled aggregates. This research aims to analyse the variables that influence the self-cementing of recycled aggregates, both concrete and mixed. Elaborating recycled aggregate is carried out by crushing the material in a treatment plant which favours self-cementing. In this research part of the recycled material is crushed again in the laboratory in order to produce a better self-cementing process when the material is crushed and used in a short period of time. One of the causes for which the bearing capacity is improved is the appearance of old unhydrated cement particles, which can favour residual setting in the medium-term. In this work two series with different treatments, based on crushing and sieving part of the material, were studied to determine the influence of these changes on the bearing capacity: a series called All-in-one (AO) with a particle size of 0–20 mm, which includes coarse fraction (C) and fine fraction (F) and a second series, called Fine (F), which only include fine fraction with a particle size of 0–4 mm. In both series different samples of RA were processed by sieving, crushing and compaction in different ways. In addition, natural aggregate samples were studied to compare with recycled ones. The results show that the influence of the treatment in the material, mainly crushing and fresh compaction, as well as particle size, significantly improves the loading capacity of recycled aggregates.

This paper presents the results of a research study whose main objective was to analyze the environmental benefits derived from a cleaner production technology for manufacturing asphalt mixes. This study measured polluting emissions during the construction of two consecutive stretches of highway on which a hot mix and a half-warm mix were spread. Combustion gases (CO, NO x , O 2 , CO 2 ), total organic carbon (TOC), particles, volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs), were measured during the manufacturing of hot and half-warm asphalt in plant and also during the spreading and compaction processes. The results obtained in this research project show that for the same manufacturing and spreading conditions, the half-warm mix asphalt (manufactured at less than 100 °C) is a cleaner production technology and can be considered more environmentally friendly since it considerably reduced polluting emissions.

The cold in-place recycling (CIR) of asphalt pavements is a technique for pavement rehabilitation that uses 100% of the milled or reclaimed asphalt pavement (RAP) from a deteriorated road surface at ambient temperature, and which does not heat any of the mix components. Consequently, CIR has the advantage of reducing gas emissions into the atmosphere. It also cuts fuel consumption since there is no need to transport RAP to an asphalt plant or to convey the mix from the plant to the paving site for spreading and compaction. Nevertheless, one of the weaknesses of this technique is the design of the job mix formula since the densities of laboratory test specimens are generally higher than the densities of the samples obtained at the worksite. As a solution for this problem, we designed an in-laboratory compaction procedure capable of manufacturing test specimens, whose density closely approximated the density of the material at the worksite. For the purposes of our research, we selected three CIR roadwork projects carried out in 2009 in southern Spain. These sites provided the RAP and the emulsion for the laboratory work in our study. It was thus possible to validate the compaction method designed in our research by comparing the dynamic modulus values of pavement cores extracted at the worksite with the values of cores taken from the laboratory specimens. The results obtained validate the new compaction procedure designed in this study.

The use of crumb rubber modifier (CRM) in bituminous mixes made by the dry process is not as widely used as the wet process. Nonetheless, this process has advantages, such as the potential to consume larger quantities of crumb rubber, thus resulting in greater savings in energy and natural resources. This research study contributes to the further development and evolution of the dry process through the analysis of the effect of the digestion time (the contact time between the crumb rubber and the bitumen) and the quantity of crumb rubber on the mix design properties. The results of the study showed that the digestion time had no influence on the selection of the optimal binder content or on the compaction of the mixture. In contrast, the digestion time was found to have an impact on the mechanical performance of the mix. In this respect, an increase in the quantity of crumb rubber contributed to a corresponding increase in the amount of bitumen needed, and also caused the mix to become less compact. This study showed that a crumb rubber percentage of less than 1% of the total weight of the mix and a digestion time of 90 min produced the best results.

One of the most common road pavement pathologies is caused by water action. The presence of moisture causes a reduction in aggregate-binder adhesion in the mix as well as in the internal cohesion of the bitumen. This leads to problems such as pot holes, aggregate peeling, stripping, etc., which eventually lead to the structural failure of the pavement. Currently, there are numerous laboratory tests that analyze the susceptibility of bituminous mixes to moisture, providing a qualitative or quantitative evaluation. This study analyzes the performance of bituminous mixes in different experimental conditions. For this purpose, a comparative study of two laboratory tests was carried out. The tests differed in mix compaction method, the conditioning of the test specimens, and the type of load applied. The results obtained showed that in these tests the conditioning temperature had a greater impact on mix performance than the temporal duration of the conditioning process. Furthermore, the application of tensile stress was found to be more suitable for studying moisture susceptibility since mixes were found to be more sensitive to this type of load.