Marco Pasetto

Experimental evaluation of high performance base course and road base asphalt concrete with electric arc furnace steel slags.

The paper presents the results of a laboratory study aimed at verifying the use of two types of electric arc furnace (EAF) steel slags as substitutes for natural aggregates, in the composition of base course and road base asphalt concrete (BBAC) for flexible pavements. The trial was composed of a preliminary study of the chemical, physical, mechanical and leaching properties of the EAF steel slags, followed by the mix design and performance characterization of the bituminous mixes, through gyratory compaction tests, permanent deformation tests, stiffness modulus tests at various temperatures, fatigue tests and indirect tensile strength tests. All the mixtures with EAF slags presented better mechanical characteristics than those of the corresponding asphalts with natural aggregate and satisfied the requisites for acceptance in the Italian road sector technical standards, thus resulting as suitable for use in road construction.

Laboratory investigation on foamed bitumen bound mixtures made with steel slag, foundry sand, bottom ash and reclaimed asphalt pavement

The paper describes an experimental investigation on foamed bitumen bound mixtures for road pavements, with the aggregate matrix entirely composed of industrial by-products, such as steel slags, foundry sand, bottom ash and reclaimed asphalt pavement. The study consisted of a laboratory analysis of the physical and leaching properties of the single recycled granular materials considered, followed by mechanical characterisation of the foamed bitumen bound mixtures, in terms of indirect tensile strength, stiffness modulus and permanent deformation tests. The mechanical tests were also performed in wet conditions, in order to investigate the moisture sensitivity of the mixes.

Synthesis of standards and procedures for specimen preparation and in-field evaluation of cold-recycled asphalt mixtures

The use of recycled asphalt (RA) materials in pavement rehabilitation processes is continuously increasing as recycling techniques, such as cold recycling (CR), are being utilised in increasing magnitude and greater awareness for use of recycled materials and consideration of sustainable practices is becoming common in the construction industry. The focus of this paper is on developing a state of the art and state of the practice summary of processes used for classification of RA as well as the curing and specimen preparation practices for cold-recycled asphalt mixtures. A variety of topics were explored through an exhaustive literature search, these include RA production methods, definition of RA materials, stockpiling practices, industrial operations, specimen curing and preparation practices and in-field evaluation of cold-recycled rehabilitation. This paper was developed through efforts of CR task group (TG6) of RILEM Technical Committee on Testing and Characterization of Sustainable Innovative Bituminous Materials and Systems (TC-237 SIB).

Geocomposites against reflective cracking in asphalt pavements: laboratory simulation of a field application

Asphalt pavements often suffer reflective cracking phenomena. Crack appearance at the road surface leads to several detrimental effects, including the loss of watertightness. Geocomposites, such as grid-reinforced bituminous membranes, represent an efficient method against reflective cracking since they combine improved tensile properties of grids and stress-relieving effects of membranes. Moreover, membranes allow pavement waterproofing. This paper presents laboratory and field studies carried out to investigate the reflective cracking resistance of geocomposite-reinforced asphalt systems. The study is based on a real-scale field trial constructed along an in-service motorway. Five geocomposites were taken into account and the possible use of a tack coat and application on a milled surface were also evaluated. Interface shear tests were carried out both on field cores and on laboratory-made samples. Moreover, pre-notched laboratory specimens were subjected to specifically developed simulative tests through the Wheel Tracking equipment. Experimental results clearly showed that a proper selection and application of optimised grid-reinforced bituminous membranes can significantly enhance reflective cracking resistance of asphalt pavements.

Resistance to Permanent Deformation of Road and Airport High Performance Asphalt Concrete Base Courses

The paper discusses the results of a laboratory investigation aimed at analyzing the rutting susceptibility of high performance asphalt concretes, made with three different bituminous binders and four types of artificial and recycled aggregates (steel slags, glass wastes, municipal solid waste incineration bottom ash and coal ash), used in partial substitution of the natural limestone. The experimental study has been focused on the characterization of the physical-mechanical properties of the marginal materials, as well as on the volumetric mix design and the permanent deformation evaluation (by means of Creep Recovery Tests, Repeated Load Axial Tests, Wheel Tracking Tests) of bituminous mixtures for road and airport asphalt concrete base courses. Because the requisites for acceptance in the Italian Specifications and Standards have been satisfied and given the positive mechanical performance (indirect tensile strength at 25°C on dry and wet samples up to 1.27 MPa and 1.07 MPa respectively), it has been verified that the marginal aggregates investigated can be used as substitution of the lithic materials in the base courses, also with very high content (up to 70% on the weight of the aggregates).

Rheological Characterization of Warm-Modified Asphalt Mastics Containing Electric Arc Furnace Steel Slags

The environmental sustainability of road materials and technologies plays a key role in pavement engineering. In this sense, the use of Warm Mix Asphalt (WMA), that is, a modified asphalt concrete that can be produced and applied at lower temperature, is considered an effective solution leading to environmental and operational benefits. The environmental sustainability of WMA can be further enhanced with the inclusion of steel slag in partial substitution of natural aggregates. Nevertheless, such innovative material applied at lower temperatures containing warm additives and steel slag should be able to guarantee at least the same performance of traditional hot mix asphalts, thus assuring acceptable mechanical properties and durability. Therefore, the purpose of this study is to investigate the rheological behaviour of bituminous mastics obtained combining a warm-modified binder and a filler (material passing to 0.063 mm) coming from electric arc furnace steel slag. To evaluate the influence of both warm additive and steel slag, a plain binder and limestone filler were also used for comparison purposes. Complex modulus and permanent deformation resistance of bitumens and mastics were assessed using a dynamic shear rheometer. Experimental results showed that steel slag warm mastics assure enhanced performance demonstrating promising applicability.

Fatigue performance of asphalt concretes with RAP aggregates and steel slags

The results are presented of an experimental investigation and a theoretical study on the fatigue behaviour of asphalt concretes, determined by the four-point bending test, according to the EN 12697-24 Annex D standard. The testing was performed on bituminous mixtures, with Reclaimed Asphalt Pavement (RAP) aggregates and Electric Arc Furnace (EAF) steel slags, used at different proportions (up to 70% of the weight of the aggregates), in partial substitution for natural limestone. Fatigue life was evaluated by means of the conventional approach, related to a 50% reduction in the initial stiffness modulus, as well as using more rational concepts, related to the macro-structural damage condition of the mixtures, in terms of dissipated energy and damage accumulation. With respect to the control mixture with limestone aggregates, the asphalt concretes with RAP aggregate and EAF slags presented improved fatigue properties and delayed macro-crack initiation.

Effect of Warm Mix Chemical Additives on the Binder-Aggregate Bond Strength and High-Service Temperature Performance of Asphalt Mixes Containing Electric Arc Furnace Steel Slag

Warm Mix Asphalt (WMA) is a modified asphalt concrete, obtained by using organic, chemical or foaming additives, which can be produced and compacted at lower temperatures (100–140 °C). The environmental sustainability of WMA can be enhanced with the inclusion of steel slag in substitution of natural aggregates. Given this background, this paper illustrates an experimental research aimed at characterizing WMA containing steel slag. Rheological tests were carried out on asphalt binders in order to investigate the effect of the WMA additive on high-service temperature properties. Then, the bond strength between asphalt binders and aggregates (limestone and steel slag) was investigated. Finally, compactability and permanent deformation resistance of the studied mixtures were also evaluated. Results mainly showed that, regardless the presence of steel slag, the studied additive allowed adequate mixing and compaction at lower temperatures, improving the bond strength between binder and aggregates without affecting permanent deformation resistance of asphalt mixes.

Fatigue Characterization of Asphalt Rubber Mixtures with Steel Slags

The paper discusses the results of a laboratory testing concerning the fatigue properties of asphalt rubber mixtures (by wet process), made with Electric Arc Furnace (EAF) steel slags (up to 93% of the weight of the aggregates). The experimental trial analyzed different bituminous mixtures, i.e. Stone Mastic Asphalt (SMA), base course and wearing course concretes, by means of the four-point bending test, according to EN 12697-24 Standard Annex D. The purpose was to evaluate the fatigue resistance of the mixtures, considering the dissipated energy approaches, which allow consistent material parameters to be identified, indicative of the damage accumulated in the asphalt mixes. Both aged and unaged samples were tested, in order to investigate the ageing effects. The asphalt rubber mixes presented better fatigue behaviour than the reference mixtures made with conventional or polymer modified bitumen.

Cold Recycling of Reclaimed Asphalt Pavements

Pavement engineers have in front of them multiple challenges linked to addressing issues related to social development and society’s expanding needs. One of the most substantial of these issues is perhaps how to effectively rehabilitate and/or maintain the existing road network while preserving and sustaining limited natural resources. The re-usage of existing pavement materials to reconstruct/rehabilitate our future pavements is the solution that is now more and more selected by the different road administrations around the world. However, upon closer inspection, one can find many areas and details, not negligible issues, that are simply extensions of HMA technology (i.e. mix design process in cold recycling) or empirical arrangements; in particular RAP still does not have an internationally recognized classification. So SIB – TG6 decided to develop a classification protocol of RAP, depending on its intended application. The objective has been followed by considering the procedures generally utilized to classify the natural aggregates: tests able to identify the main components (i.e. the geometrical and mechanical properties of aggregates and the characterization of recovered bitumen for RAP) and provide information on their behaviour under specific conditions, near to real life usage (e.g. the Los Angeles test for aggregates gives an idea of the potential behaviour of aggregates under the action of a roller compactor). The following sections illustrate and explain the actions of the TG in order to achieve the goals outlined above: the review of current standards, the protocol designed to classify RAP and the round robin tests carried out to validate the protocol.