Laboratory investigation on chemo-rheological and mechanical properties of bio-asphalt materials for sustainable asphalt pavements

Al giorno d'oggi, uno dei principali interessi della società moderna è quello di sostituire quantità sempre maggiori di prodotti derivati dal petrolio, che è una fonte non rinnovabile in progressivo esaurimento. Negli ultimi decenni, l'uso di biomateriali ha acquisito un notevole interesse nel settore dell'ingegneria civile. In questo contesto, l'industria stradale è interessata a sviluppare nuove soluzioni "verdi", promuovendo i principi della sostenibilità e dell'economia circolare. Infatti, data la rapida crescita delle città e dei volumi di traffico, la domanda di materie prime per la costruzione e la manutenzione delle pavimentazioni è aumentata drasticamente, insieme al loro prezzo. Allo stesso tempo, non si possono trascurare le questioni ambientali legate alle emissioni di carbonio e di gas serra nell'atmosfera dovute all'uso di risorse non rinnovabili. Per questi motivi, i bio-leganti sono attualmente considerati una soluzione promettente per le pavimentazioni stradali flessibili. Essi sono definiti come leganti bituminosi in cui il bitume, che deriva dal processo di distillazione del petrolio greggio, è interamente o parzialmente sostituito da varie bio-risorse come rifiuti animali, bio-oli (legno, girasole, mais, soia), olio di scarto da cucina, lignina ecc. Attualmente, uno dei problemi principali è quello di garantire che i bio-leganti offrano buone prestazioni, almeno comparabili a quelle dei materiali convenzionali. Tuttavia, la conoscenza di tali materiali è ancora limitata in termini di prestazioni e, soprattutto, di durata nel tempo. Alla luce di queste premesse, la presente ricerca di dottorato (cofinanziata dall'azienda petrolchimica svedese Nynas AB) si propone di valutare scientificamente la fattibilità della parziale sostituzione del bitume con un bio-olio e diversi tipi di lignina derivanti da sottoprodotti della lavorazione del legno e della carta. A tal fine, è stato condotto un ampio programma sperimentale che prevedeva analisi chimiche e reologiche avanzate sui bio-leganti selezionati. Successivamente, gli stessi bio-leganti ottenuti in laboratorio sono stati impiegati per produrre bio-miscele, successivamente sottoposte a un'ampia campagna di caratterizzazione meccanica che ha incluso indagini a bassa, media e alta temperatura, prove di adesione con gli aggregati lapidei, suscettibilità termica, all’umidità e all'invecchiamento. Tutti i risultati ottenuti incoraggiano fortemente l'uso di questo tipo di bio-leganti, che possono rappresentare una valida alternativa ai bitumi tradizionali. Infatti, lo studio ha dimostrato prestazioni perfettamente comparabili o, in alcuni casi, addirittura migliori, suggerendo i potenziali vantaggi non solo dal punto di vista ambientale ed economico, ma anche da un punto di vista prestazionale.Nowadays, one of the main interests of modern society is to replace increasingly larger quantities of petroleum-derived products, which is a non-renewable source progressively depleting. In the last decades, the use of bio-materials has gained notable interest in the civil engineering sector. In this context, the road industry is interested in developing new “green” solutions, promoting sustainability and circular economy principles. In fact, given the rapid growth of cities and traffic volumes, the demand for raw materials for pavement construction and maintenance has dramatically increased, along with their price. At the same time, the environmental issues related to the carbon footprint and greenhouse gas emissions in the atmosphere due to the use of non-renewable resources cannot be neglected. For these reasons, bio-binders are currently considered a promising solution for flexible pavements. They are defined as bituminous binders in which bitumen, which derives from the distillation process of crude oil, is entirely or partially replaced with various bio-resources such as animal waste, bio-oils (wood, sunflower, corn, soybean), waste cooking oil, lignin etc. Currently, one of the main issues is to ensure that bio-binders offer good performance, at least comparable with that offered by conventional materials. However, the knowledge of these materials is still limited in terms of performance and, above all, durability over time. Given this background, this PhD research (co-financed by the Swedish petrochemical company Nynas AB), aims to scientifically evaluate the feasibility of partially replacing bitumen with a wood-based bio-oil and different kind of lignin deriving from by-products of wood pulp and paper industry. To this end, an extensive experimental program was carried out involving advanced chemical and rheological analysis on the selected bio-binders. Then, the laboratory-produced bio-binders were used to produce bio-asphalt mixtures, which were subjected to a wide mechanical characterization campaign, including low-, medium- and high-temperature investigations, adhesion with aggregates, thermal, moisture and aging susceptibility. Based on the overall findings, all elements encourage the use of such kind of bio-binders as a valid alternative to traditional bitumens. Indeed, the study demonstrate perfectly comparable, or, in some cases, even better performances were identified, while suggesting the potential benefits from technical, environmental and economic point of view

Performance assessment of asphalt mixtures produced with a bio-binder containing 30% of lignin

Lignin is one of major by-product from wood and paper industry. As natural biopolymer, it could be a valid alternative as bitumen replacement and/or modifier to enhance the relevant performance of asphalt mixtures, promoting concurrently environmental benefits. In this context, the study focused onthe effects of two different binders containing 30% of lignin (by weight) on the mechanical properties of bio-asphalt mixtures. Specifically, two different lignins were blended with two plain bitumens having different consistencies so obtaining two bio-binders with a similar consistency to that of a reference plain bitumen. The two bio-binders and the reference bitumen were used to produce in the laboratory three dense graded asphalt mixtures for binder courses according to the Italian Technical Specifications. The binder-aggregate adhesion, Indirect Tensile Strength, Stiffness Modulus, thermal susceptibility, fatigue resistance, and low-temperature cracking of mixtures were analysed in both unaged and long-term aged conditions. Overall, this investigation demonstrates that bio-mixtures containing lignin offer comparable results to the reference asphalt mixture. Moreover, the bio-asphalt mixtures exhibit a lower thermal susceptibility, as well as lower aging susceptibility. The findings of this research highly encourage the use of lignin as partial replacement of bitumen in asphalt pavements

Performance Assessment of Asphalt Mixture Produced with a Bio-Based Binder

Nowadays, the growing energy costs and pressing worldwide demand for petroleum-based products create a strong need to develop alternative binders deriving from green and renewable sources. Bio-binders (or bitumen added to bio-based materials) can potentially be a viable alternative for the production of bituminous mixture, promoting the circular economy as well as environmental sustainability principles without reducing the overall performance of the mixture. In this context, the current study focuses on evaluation of the effects of a bio-binder on the mechanical response of asphalt concrete (AC) produced with it. In particular, a 10% bio-oil deriving from a by-product of the paper industry has been blended with a conventional 50/70 penetration grade bitumen to obtain the bio-binder. Moreover, plain bitumen having the same consistency was chosen to produce a reference AC. Two dense-graded AC wearing courses were prepared in the laboratory according to Italian technical specifications. A mechanical characterization in terms of indirect tensile strength, indirect tensile stiffness modulus, fatigue response and permanent deformation resistance was performed on gyratory compacted specimens using both conventional and performance tests. In addition, aging and water sensitivity of the AC specimens were evaluated. Overall results highlight that the AC produced with the bio-binder did not show reduced mechanical properties and it was comparable to the reference AC regardless of aging and water conditioning. This highly encourages the use of bio-binder as a viable alternative in asphalt technology

Chemical and rheological analysis of unaged and aged bio-extended binders containing lignin

The use of alternative renewable sources to totally or partially replace bitumen is one of the most current challenges in the road pavement sector. The growing energy cost and environmental concerns lead to the necessity to find alternative solutions, by supporting at the same time sustainability and circular economy principles. Within this framework, this paper presents the application of a powder lignin, a natural bio-polymer deriving from by-products of wood pulp and paper industry, to replace part of bitumen. The bituminous blend consisting in 70% of bitumen and 30% of powder lignin (by weight) was made in laboratory through the use of a high shear stirring mixer, and a reference plain bitumen characterized by a similar consistency (i.e., same penetration grade) was used as comparison. Then, an extensive investigation on chemical and rheological properties of the bio-binder is presented. Fourier transform infrared spectroscopy (FTIR), saturates, aromatics, resins and asphaltenes (SARA), bending beam rheometer (BBR), frequency sweep tests and multiple stress creep recovery tests (MSCR) with a dynamic shear rheometer (DSR) were performed. Moreover, unaged, short- and long-term aging conditions were considered. Results indicated that powder lignin dominates the rheological behavior of the bio-binder and, from chemical analysis, it seems that it partially acts as a filler and partially as a binder. This would result in improved performances at both low and high temperatures, leading to a wider temperature range of performance grade (PG). Moreover, despite a stiffening effect is recognized, lignin also offers an antioxidant potentiality, reducing the aging susceptibility of the investigated bio-binder

Performance Analysis of Bio-Based Asphalt Mixtures Containing Lignin

Given the need to promote the circular economy and sustainability, one of the main current trends in road materials construction is to employ industrial residues and by-products deriving from renewable sources as extender, replacement or modifier of bitumen, obtaining the so-called “bio-binders”. As regards, lignin can represent a potentially attractive solution, because it is the most abundant natural biopolymer, available in large quantity and characterized by certain chemical similarity with bitumen. In this context, this study focuses on the evaluation of two dense-grade asphalt mixtures for binder layer made with bio-binders containing two different lignins, as partial replacement of bitumen. A preliminary phase allowed to optimize lignin content (30% by bio-binder weight) based on empirical test (i.e. dynamic viscosity, penetration and softening point tests) with the aim of maximizing the bitumen replacement and at the same time obtaining two bio-binders having a consistency similar to a reference plain bitumen. In the second phase, two bio-based mixtures were produced by using the before-optimized bio-binders in different attempt contents. After mixing, specimens were produced by means of a gyratory compactor at set gyrations. Then, the two lignin-based asphalt mixtures were compared with the reference mixture in terms of workability, Indirect Tensile Strength (ITS) and water sensitivity. Despite the bio-based mixtures revealed a slightly penalized workability, overall results showed that they are characterized by fully comparable performances to the reference one, allowing a reduction of the effective bitumen content

Analysis of Fatigue and Healing Properties of Conventional Bitumen and Bio-Binder for Road Pavements

The analysis of fatigue behavior of bituminous binders is a complex issue due to several time-temperature dependent phenomena which interact simultaneously, such as damage accumulation, viscoelasticity, thixotropy, and healing. The present research involves rheological measurements aimed at evaluating the fatigue behavior and compares the self-healing capability of two plain bitumen and a bio-binder obtained by partially replacing one of the plain bitumen with a renewable bio-oil. Healing potential was assessed by means of an experimental approach previously implemented for modified bitumen and bituminous mastic and based on the use of a dynamic shear rheometer (DSR). The effects of some variables such as bitumen type, bio-oil addition, and aging on the healing potential of binders were taken into account. Results showed that the above-mentioned method for healing analysis is also suitable for conventional and bio-add binders. Outcomes of the experimental investigation highlight that fatigue and self-healing are mainly dependent on binder consistency and also affected by aging. Finally, the addition of bio-oil may induce even better performances in terms of healing potential compared to conventional bitumen, especially in aged condition

Investigation of unaged and long-term aged bio-based asphalt mixtures containing lignin according to the VECD theory

In the near future, the world of civil and building engineering will be dominated by the advent of bio-materials. Even the road paving sector is involved in the transition towards more sustainable solutions, promoting at the same time environmental benefits and economic savings. Currently, one of the main goals is to ensure that bio-binders offer good performance, at least comparable with that offered by conventional materials. In the last decades, the exponential increase in traffic volumes has led to various types of asphalt pavement distresses, among which fatigue cracking is one of the most common. Within this context, this study presents the characterization of a bio-based asphalt mixture obtained by replacing 30% of bitumen with lignin, which was compared with a reference asphalt mixture containing a plain bitumen characterised by the same penetration grade. Laboratory produced and compacted specimens were subjected to complex modulus and cyclic fatigue tests with the Asphalt Mixture Performance Tester (AMPT). Both unaged and long-term aging conditions were investigated. The tests and the subsequent analyses were based on the simplified viscoelastic continuum damage (S-VECD) approach. Overall, the results showed that the presence of lignin led to a lower aging susceptibility, but also caused a slight reduction in fatigue life due to an increase in the material stiffness. Furthermore, the obtained results confirmed previous findings deriving from the study of the two binders and from the conventional characterization of the same asphalt mixtures as well