Emiliano Pasquini

Laboratory characterisation and field validation of geogrid-reinforced asphalt pavements

In order to improve the mechanical properties of pavements, reinforcement systems can be employed in asphalt layers. However, the presence of a grid at the interface causes an interlayer de-bonding effect. Moreover, a real challenge is related to the proper in situ installation of grids. The present research aims to evaluate the effectiveness of pavement rehabilitation with fibreglass geogrids. To this purpose, a real-scale field trial was constructed and monitored through Falling Weight Deflectometer measurements. Interface shear tests and flexural tests were also carried out on double-layered samples prepared in the laboratory reproducing real-scale field trial characteristics. Moreover, shear tests were also performed on in situ cored specimens. Results mainly showed that a proper installation of the reinforcement is fundamental in order to obtain suitable test results and good pavement performance.

Use of Reclaimed Asphalt in Porous Asphalt Mixtures: Laboratory and Field Evaluations

AbstractMaintenance and reconstruction of road pavements involve the production of huge amount of discarded material, such as reclaimed asphalt (RA), every year. As a consequence, issues related to RA stockpiles and disposals are dramatically increasing. At the same time, the growing importance of environmental and economic matters has led researchers and engineers to promote reusing milled materials rather than using valuable and nonrenewable natural resources (bitumen and aggregates). Road pavement maintenance and construction usually involve the use of porous asphalt (PA) mixtures, in particular in the case of motorways and highways. In fact, PA mixtures are widely employed as pavement surface layer thanks to their ability in reducing traffic noise and enhancing safety in wet conditions. In this sense, the reuse of RA into PA should be strongly encouraged. Unfortunately, technical specifications adopted in many countries do not allow any recycled materials in porous asphalt surface layers yet. Thus, re...

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.

Laboratory Study to Evaluate the Influence of Reclaimed Asphalt Content on Performance of Recycled Porous Asphalt

Road-pavement maintenance and rehabilitation are more frequently performed on porous asphalt (PA) surface layers because of their inherent low durability. Such activities lead to the production of a considerable amount of reclaimed asphalt (RA), mainly from PA layers and from the heavy use of virgin non-renewable natural resources, because of the fact that the use of RA is not usually allowed in PA. In this sense, the use of milled materials from old PA wearing courses in new PA layers promotes an important cycle of re-use that should be encouraged. The experimental study aims to investigate the performance of recycled PA mixtures prepared by partly substituting virgin aggregates with selected coarse RA from a milled PA wearing course. A reference PA mixture (without RA) and six recycled PA mixtures prepared with two amounts of RA (20 % and 25 %) and three total binder contents (5.25 %, 5.50 %, and 5.75 %) were investigated in terms of compactability, durability, and water resistance. In this sense, indirect tensile strength (ITS) tests, particle loss (Cantabro) tests, semicircular bending (SCB) tests, and repeated indirect tensile tests were carried out in both dry and wet conditions. Moreover, compactability properties of the reference PA mixture and the recycled PA mixtures were compared. Results showed that recycled PA mixtures with 20 % and 25 % of RA can perform as well as the reference PA mixture in terms of moisture resistance and durability if an accurate mix design is performed. The optimum total binder content was found to increase as the amount of RA increases, because of the fact that a prominent part of the aged binder acts as “black aggregate.” Finally, on the basis of a performance-based equivalence principle, a reliable approach for a practical method able to predict the amount of “re-activated” binder within the RA is proposed.

Optimization of geocomposites for double-layered bituminous systems

In order to improve pavement service life, reinforcement systems can be employed in asphalt layers. In this regard, geocomposites obtained by combining geomembranes with geogrids represent a promising option because they should allow both waterproofing and improved mechanical properties of asphalt pavements. However, the presence of reinforcement may cause an interlayer de-bonding effect that negatively influences overall pavement strength. Given this background, the present research aimed at evaluating the effectiveness of pavement rehabilitation with geocomposites in the laboratory. In particular, the present experimental study intended to implement new products by selecting the optimum combination among different geomembrane compounds, reinforcement types, reinforcement positions and interface conditions. The laboratory investigation was preliminarily organized to perform interface shear tests by means of the ASTRA apparatus. Then, on the basis of the results of the previous phase, the more promising configurations were selected to be further evaluated by means of the three-point bending tests. Specimens were obtained from double-layered slabs compacted in the laboratory. The results presented in this paper enabled the preliminary tuning for the selection of optimized composites to be submitted, in the near future, to performance-related dynamic tests and in situ monitoring of real scale trial sections.

Resilient behaviour of unbound granular materials through repeated load triaxial test: influence of the conditioning stress

The present paper reports the results of a laboratory investigation aimed to investigate the resilient behaviour of unbound granular materials (UGMs) for pavement unbound layers under repeated triaxial loading. The first part of research was focused on the effects of stress history, in terms of loading conditioning phase and stress paths, on the resilient response of the investigated UGM. The obtained results highlighted that the samples that experienced several stress paths after an initial stress conditioning showed reduced resilient moduli as well as higher stress dependency of the resilient properties as compared with samples not subjected to any specific stress history. The second part of research aimed to evaluate the influence of the conditioning stress level on the resilient modulus. The results showed poorer resilient characteristics along the several stress paths as the selected conditioning stress increases. Whereas, a sort of “loading memory effect”, resulting in a similar mechanical behaviour, can be recognised as a similar stress state between conditioning phase and subsequent stress path is considered. The study confirms the high dependency of the resilient response of UGM on the stress condition and in particular, the main role of conditioning confining pressure on the stable mechanical behaviour of these materials is highlighted. Finally, a simplified approach that would allow the intrinsic resilient properties of UGM to be predicted for a specific combination of conditioning stresses and stress paths is proposed.

Advanced Characterization of Clear Chip Seals

Chip seals are widely used throughout the world for the construction and preventive maintenance of asphalt pavements because they are recognized as cost-effective solutions able to improve skid resistance while creating a waterproof surface. On the other hand, chip seals are often affected by early stone loss because of several, not always easily manageable, material-related and traffic-related factors. It is, therefore, in the interest of researchers to develop scientific methods able to predict the aggregate retention performance of chip seals. Given this background, in the present paper, a performance-based evaluation of chip seals with regard to aggregate retention properties is carried out through a laboratory test based on the Ancona shear testing research and analysis equipment. In this study, a chip seal prepared with a clear emulsion derived by emulsifying a synthetic clear binder was analyzed and compared with two traditional chip seals manufactured with a plain cationic bituminous emulsion and a styrene butadiene styrene polymer-modified asphalt emulsion, respectively. Specifically, six chip seals obtained by combining the three selected emulsions with two types of aggregates (crushed limestone and basalt) were tested at three different temperatures. Moreover, a rheological characterization of emulsion residues was also carried out through the dynamic shear rheometer and the binder bond strength adhesion tester. Results mainly showed that the investigated clear synthetic emulsion can be successfully used for the construction of clear chip seals in combination with aggregates of different mineralogy.

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.

Mix design and preliminary validation of sustainable asphalt concrete manufactured with electric arc and ladle furnace steel slags

In the manufacture of carbon steel in Spain and Italy, there is a prevalent process known as “the electric cycle”, which involves melting scrap in an Electric Arc Furnace (EAF) and then refining the steel in a Ladle Furnace (LF). In this process, the main residues generated are two types of slag: the EAF Slag and the LF Slag. The excellent properties of EAF slag are well known and guarantee its successful use as a coarse aggregate in the manufacture of bituminous mixtures. On the other hand, research and application concerning the use of LF slag in asphalt mixtures are still at an early stage notwithstanding such slag has appropriate particle size and promising chemical features to be used as fine aggregate and/or filler. In this research, a rational approach to manufacturing dense graded asphalt concrete exclusively with steel slag aggregates is developed, not using any natural aggregate and thus providing sustainable (and high-performance) asphalt mixes. The design of this mix involves using EAF slag as coarse aggregate and LF slag as fine aggregate and filler. A laboratory test program was organized to accomplish this objective based on the evaluation of different bituminous mixtures incorporating these slags. Such mixtures were designed according to the Marshall procedure and then compared with a reference material (manufactured with conventional aggregates). In particular, natural filler, fine aggregate and coarse aggregate of the reference mixture were progressively replaced by the corresponding slag in order to highlight the contribution of the different fractions. The laboratory study was carried out by performing different tests analysing mechanical behaviour, durability and moisture susceptibility. The results arising from this preliminary research show that, although some refining may be done in the mix design, a sustainable asphalt concrete manufactured entirely with steel slag aggregates can be successfully achieved.

Life-cycle assessment of road pavements containing marginal materials: Comparative analysis based on a real case study

The Life-Cycle Assessment (LCA) is a standardized procedure generally used, in Italy, in industrial engineering to evaluate the economic-environmental efficiency of production processes. LCA is aimed at optimizing the design, with special emphasis on environmental sustainability. Also in the construction sector, LCA has recently gained a fundamental role as a quantitative measurement tool able to take into account correctly the environmental and economic benefits achievable adopting different alternatives (most of them uncommon) based on the entire service life, maintenance and end-of-life procedures included. As far as pavement engineering is concerned, the use of marginal materials (such as, for example, reclaimed asphalt pavement, crumb rubber, slags, etc.) is becoming of strategic importance due to the decreasing availability of virgin natural resources and the consequent increasing public consciousness addressed to environmental protection and preservation. In this regard, the LCA applied to road pavements constructed using marginal aggregates probably represents the only effective tool able to evidence the crucial aspects on which the design choices should be based, taking also into account longterm parameters. Given this background, the present research illustrates one real case study of LCA analysis applied to asphalt pavements of a motorway. The use of industrial by-products (i.e. steel slags) instead of natural mineral aggregates is considered. Comparative evaluation of different scenarios has been carried out using specifically developed spreadsheets. The research study demonstrates that LCA is able to highlight potentialities and issues related to the different analyzed scenarios, representing a valid tool for designers and decision-makers. Moreover, the obtained results contribute to enlarge the worldwide database about the implementation of LCA for pavements. 1.2 The standards for LCA methodology Life Cycle Assessment is defined and described in ISO 14040 and ISO 14044 (ISO 2006a, b) standards. LCA framework (Fig. 1) can be divided in the following steps: 1) goal and scope definitions; 2) inventory collection and analysis; 3) environmental impact assessment; 4) obtained results interpretation. ISO standards describe in detail principles, framework, requirements and guidelines for the LCA, including: a) the goal and scope definition of the LCA; b) the life cycle inventory analysis (LCI) phase; c) the life cycle impact assessment (LCIA) phase; d) the life cycle interpretation phase; e) reporting and critical review of the LCA; f) limitations of the LCA; g) relationship between the LCA phases; h) conditions for use of value choices and optional elements. However, these standards do not state specific prescriptions to perform a LCA or defined methodologies for the specific LCA phase. Further, LCI phase can be performed separately from a specific LCA study, because LCI inputs/outputs introduction and quantification are not closely linked with the specific product or service evaluated with the LCA. Figure 1. Life Cycle Assessment framework (from the ISO 14040 (ISO 2006b)). 1.3 LCA in road engineering The attention addressed to the minimization of impacts related to the construction inclusion in the environment defines a general trend concerning the study of ecological characteristics throughout the different infrastructure project hypothesis (from design to maintenance, from use to end-oflife). LCA can be applied to several civil engineering sectors, such as the transport infrastructure one. In this sense, many researchers already ventured in LCA implementation to evaluate the environmental impacts connected to transport infrastructures, facing the most important problems related to the material type and its transport, that strongly represent onerous items in road construction and maintenance (Jullien et al. 2009, Santero et al. 2011, Azarijafari et al. 2016). The increasing expensiveness of road design (in terms of energy request and environmental impacts) involves the need to reduce work emissions and costs during its lifetime. In this sense, even more researchers, management and construction companies develop sustainable project and utilize LCA in decision procedures which affect several environmental aspects (such as impacts of different pavement types and materials). Also the decision-makers, with an accurate life cycle cost analysis, can use LCA to evaluate the project or policy impacts (Santero et al. 2011). Many studies evaluate the environmental issues and the effects on road construction, management/maintenance and rehabilitation. Amini et al. (2012) compared conventional and perpetual pavement (i.e. not requesting structural maintenance) and their different effects on environment and costs. Others researchers suggested to take into account the effect on the environment and infrastructure caused by road traffic (Zaabar & Chatti 2010, Santos et al. 2015a). For example, Bryce et al. (2014) evaluated through LCA the possibility to reduce the road maintenance activities considering the pavement damage and the related tire vehicles consumption (the surface type affects the vehicles pollution). Yang et al. (2015) assessed the use of Reclaimed Asphalt Pavement – RAP and Recycled Asphalt Shingle – RAS in partial substitution of virgin aggregates to check the different environmental impacts, considering also the vehicles fuel consumes as a function of the IRI index. Others authors studied LCA applied to road infrastructure materials. DeDene & Marasteanu (2012) examined the possibility to reduce production costs and harmful emissions of asphalt pavement with 15% of RAP. Butt et al. (2014) applied LCA to bituminous mixtures assessing the energy consumption and the environmental sustainability. In this case, the analysis of significant 1 Goal and scope definition 2 Life Cycle Inventory analysis (LCI) 3 Life Cycle Impact Assessment