1. Introduction
Brazil has witnessed two major catastrophes in the last decade due to the rupture of iron ore tailings containment dams. On 5 November 2015, the Fundão dam collapsed, resulting in the spillage of over 50 million cubic metres of mining waste into the Rio Doce [
1]. Four years later, in 2019, the tailings dam of Córrego do Feijão, located in Brumadinho, Minas Gerais, collapsed. This tragedy led to the loss of over 250 human lives and the spilling of approximately 12 million cubic metres of ore tailings into the Paraopeba River and nearby areas [
2].
These events caused a significant loss of human life, extensive environmental degradation, and social and economic losses, and were associated with mining activities that exert adverse effects on the ecosystem [
3]. According to the National Mining Agency [
4], there are 928 registered mining waste containment dams in Brazil, of which 252 have a high associated damage potential (DPA). This indicator is related to the potential damage caused by eventual dam rupture, and it is determined by the construction and conservation characteristics of the dams. Of the dams, 51 are classified as high-risk according to the categorical risk index (CRI).
Mining waste obtained at different stages of the mining process comprises materials with favourable granulometry (sandy tailings) from a geotechnical perspective and materials with unfavourable or deficient characteristics, such as fine-grained tailings, which are referred to as fine tailings or slimes [
5].
Apaza et al. [
6] evaluated the incorporation of sandy tailings composed of quartz minerals (88%) and haematite (9%) as aggregates from the iron-ore-refining process in cold asphalt microsurfacing. The results were satisfactory, and the iron ore waste did not present any chemical, environmental, mineralogical, or physical restrictions that would affect its use as aggregates in microsurfacing mixtures.
Due to the intrinsic environmental risks associated with the mineral exploitation process, Rybak et al. [
7,
8] conducted an investigation based on the experience of the Russian mining industry. The scholars proposed a process capable of eliminating harmful accumulated waste, recovering the precious metals contained in these residues, and using the remaining waste as a landfill material in the form of an aggregate or binder. The experimental results suggested a potential use of landfill material waste, which could prevent disasters resulting from the collapse of abandoned galleries and protect the environment against toxic pollution.
Conversely, fine-grained tailings consisting of silt and clay fractions are typically plastic and highly compressible materials, as described by Lima [
9]. These characteristics limit their potential for direct reuse. However, their utilization in the production of calcined aggregates for pavement is a promising alternative, as assessed by Sultan [
10]. In this study, the results indicated that regardless of whether they were untreated or stabilized with cement or asphalt, mining wastes exhibited suitable engineering characteristics to be harnessed as alternative materials in pavement construction.
In this scenario, various approaches emerged that aimed at the reutilization of waste materials originating from mining. However, regarding their applications in road construction, the utilization of mine tailings has not yet been extensively explored. Additionally, there is a significant gap in the legislation specifically addressing this issue, as explained in Ref. [
11].
In addition to the aforementioned alternatives, there is a concern regarding the use of industrial waste that is in line with the principles of waste-free mining [
12,
13]. Rybak et al. [
3] confirmed that this phenomenon is feasible through the systematic and integrated use of mineral resources, improving the efficiency in the development of mineral deposits and the economic effects resulting from the prevention of environmental impacts.
Numerous scholars have evaluated the use of waste materials in engineering as a sustainable approach for aggregating production. An example is the work of Fan et al. [
14], who investigated the use of ashes from municipal solid waste incineration (MSWIBA) and calcined clay as ecologically friendly artificial aggregates (EFAAs). With a compressive strength exceeding 30 MPa at 28 days, concrete produced using this artificial aggregate showed low toxicity, low energy consumption, and low CO
2 emissions, making it suitable for use in construction. However, the use of coal ash waste as a substitute for fine aggregates in lightweight concrete could reduce the strength when subjected to acidic environments, as observed in the work of Ghazali et al. [
15]. Nevertheless, when properly thermally treated with an appropriate burning plan, the fluxing elements present in the waste could confer satisfactory strength to the aggregates, as concluded by Cabral et al. [
16]. These authors obtained low-cost aggregates through the calcination of clayey soils, making them suitable for use as pavement materials.
Regarding calcined aggregates, the Brazilian Army (EB) was a pioneer in the production of artificial calcined clay aggregates in Brazil. The use of these materials in pavement construction became significantly important due to the challenges faced by the EB’s engineering corps regarding the scarcity of rock deposits in the northern region of the country [
17].
The topic was addressed by Batista [
18], who evaluated the use of calcined clay aggregates in asphalt mixtures for pavement in the Amazon region. It was concluded that the results of the resilience modulus using calcined clay produced at a temperature of 900 °C for 30 min demonstrated the technical feasibility of using the aggregate in asphalt mixtures for pavement, differing from the values obtained for the region soil.
The results were corroborated by Silva et al. [
19], who indicated that the application of sintered calcined clay aggregates (SACCs) in asphalt concrete mixtures for road pavement was a good alternative to natural granular aggregates in regions where these materials are scarce. The tests performed under cyclic loading indicated that the performance of SACC in AC50/70 asphalt concrete mixtures was comparable to that of traditional aggregates. Additionally, the study showed that the use of SACC could reduce the carbon footprint of asphalt concrete production.
Santos [
20] investigated the use of calcined clay aggregates as coarse aggregates in asphalt coatings, considering a firing temperature of 900 °C and firing time of 15 min. A comparison of the results for asphalt mixtures using rolled pebbles (commonly used in the Amazon region) and calcined clay aggregates showed that in certain aspects, such as permanent deformation, the mixture with calcined clay presented better results, better adhesion among its components, and consequently, higher mechanical resistance than the asphalt mixture containing pebbles. Moreover, increasing the firing temperature of the synthetic aggregates resulted in a reduction in asphalt cement consumption due to the transformation from the crystalline to the amorphous phase [
21], indicating a strong possibility of using this aggregate as an alternative material for pavement in the region.
In addition to the surface layers, studies have been developed to assess the suitability of using calcined clay aggregates in other pavement layers. A noteworthy study conducted by Barbosa et al. [
22] verified the viability of two soils in Acre: one to produce calcined clay aggregates, and another to produce soil–aggregate mixtures as the pavement base. The calcined aggregates were subjected to firing temperatures of 900 °C, 1000 °C, and 1100 °C, and all met the established limits of the present regulations for use as base materials for pavement. Regarding the addition of calcined aggregates to the soil–aggregate mixture, it was found that a proportion of 30% (by dry weight) was sufficient to promote the granulometric stabilization of the lateritic soil deposit used.
Cabral [
23] proposed his own methodology for producing calcined clay, establishing parameters for the acceptance of the clay used by adjusting the final quality of the calcined aggregate. In summary, his methodology recommended the use of clays with a plasticity index (PI) higher than 15% and a granulometry preferably falling within regions B, C, or D of the Winkler diagram.
Other scholars have investigated the thermal behaviours of pavements composed of artificial aggregates. Yinfei et al. [
24] studied the use of materials with phase change properties in asphalt pavements and how the granulation of lightweight aggregates (LWAs) could affect cooling performance. The results indicated that the granulation characteristics of LWAs significantly impacted the latent heat storage capacities of asphalt mixtures. Khan et al. [
25] investigated the use of LWAs in asphalt mixtures and the base and subbase layers as a strategy for reducing frost damage in flexible pavements. The data indicated that the use of LWAs in asphalt mixtures and in the base and subbase layers could significantly reduce frost penetration in the subgrade and exhibit lower conductivity and diffusivity and higher specific thermal capacity values than conventional asphalt mixtures.
In other branches of the construction industry, scholars have indicated that the use of structural concrete with lightweight artificial aggregates could offer significant advantages in terms of weight reduction, improved thermal and acoustic insulation, and reduced energy consumption and CO
2 emissions during production [
26]. However, there are also some limitations and challenges associated with the use of these aggregates, such as the need for pretreatment of aggregates, reductions in mechanical strength and durability in certain cases, and the lack of standardization and regulations for the use of alternative materials.
As stated above, although there is a significant body of research on the use of mining waste to produce artificial aggregates for pavement, it is important to note that this subject requires further study. This phenomenon occurs due to the diverse nature of the waste characteristics, making accurate characterization essential for ensuring its proper application.
According to Segui et al. [
11], utilizing mining waste as a construction resource offers dual advantages: the preservation of natural resources and the mitigation of the environmental repercussions of mining. However, the extensive implementation of mining waste in road construction is still in its infancy, largely due to a lack of comprehensive regulations. This gap arises from the multitude of exploited rock types, the heterogeneity of tailings, mining residues, and potential valuable byproducts earmarked for valorisation, alongside distinct environmental considerations.
Therefore, the aim of the present study is to evaluate the utilization of calcined aggregates produced from fine mining waste (sludge) as an alternative material for pavement construction that meets the criteria for selecting pavement materials established by the present standards in Brazil. The following hypothesis is presented in this study: the production of calcined aggregate from fine mining waste is a technically viable alternative in pavement construction.