Jose L. Concha

Technical lignin represents an abundant industrial by-product with significant potential for valorization into sustainable functional materials. In this study, Kraft lignin was selectively converted into phenolic-rich bio-oils through optimized slow pyrolysis and subsequently upgraded into a bio-based antioxidant additive for asphalt binders. Pyrolysis conditions were optimized using a factorial design combined with response surface methodology, exploring temperatures between 400 and 600 °C and heating rates from 5 to 25 °C.min−1. The resulting bio-oils exhibited high phenolic selectivity (> 90 wt.%), with guaiacol, 4-methylguaiacol, and 4-ethylguaiacol as the main components, demonstrating strong antioxidant activity. Optimization indicated maximal phenolic yield at 542 °C and 12 °C.min−1. Upgrading of the optimized bio-oil through distillation enabled the removal of water and light volatile compounds, yielding a phenolic-rich bio-additive with preserved antioxidant activity. Incorporation of bio-additive into asphalt binders significantly enhanced resistance to oxidative aging, reducing the carbonyl index by 25% and increasing aromatic content by 49%. The anti-aging performance was mainly associated with the high guaiacyl-type phenolic content. These results reveal a sustainable route for the valorization of technical lignin into high-value bio-based additives and provide a promising strategy for the development of renewable materials for more durable and resilient pavement infrastructure.

This study investigates the rheological and chemical effects of waste tire pyrolytic oil (TPO) and its encapsulation (POC) as rejuvenators for asphalt binders. Driven by the need for sustainable and effective strategies to Recycle Reclaimed Asphalt Pavement (RAP), we investigated the use of TPO in two forms: as a liquid additive and as polymer capsules. The capsules, made in a 1:5 mass ratio (one part polymer, five parts TPO), were assessed through two methods: rheological tests (dynamic modulus and phase angles) and chemical composition analysis (carbonyl and sulfoxide indices). The binders underwent three aging levels: unaged, primary aging (RTFO), and secondary aging (PAV). Five liquid TPO dosages (1%, 2%, 4%, 6%, 9% by weight) and three encapsulated TPO dosages (6%, 9%, 12% by weight) were tested. Results show that TPO reduces stiffness, increases viscous response, and lowers aging indices, with higher dosages enhancing the effect. Quantitatively, 9% liquid TPO restores PAV-aged binder to near-unaged conditions, suitable for RAP recycling, while 4% release from POCs achieves rejuvenation comparable to RTFO-aged binders, enabling self-healing applications. The estimated release of TPO from POCs during mixing was 20–40%, ensuring a gradual softening effect. These findings highlight the potential of TPO and POC in enhancing asphalt durability and recycling.

This study investigates how recycled metal fibres from End-of-Life Tyres (ELTs) affect both microwave heating efficiency and crack healing properties in dense asphalt mixtures. The aim is to improve tyre recyclability by using their fibres in asphalt and exploring their self-healing potential with microwave heating. To achieve this, four dense asphalt mixture designs were studied in the laboratory. Each mixture used the same aggregate gradation and bitumen content, but with three different percentages of metallic fibres by binder volume (i.e., 1.5%, 2.5%, and 3.5%), along with an asphalt mixture without fibres serving as a reference material. The microwave heating properties of the asphalt mixtures and their individual components (i.e., aggregates and bitumen) were measured at six different heating times, ranging from 10 to 60 s. Based on the microwave heating results, the cracking and subsequent self-healing properties of the mixtures were evaluated by exposing them to microwave radiation at three heating times: 30, 40, and 50 s. The main results indicated that adding metallic fibres to facilitate microwave heating of the asphalt mixture is unnecessary because healing can be triggered predominately through the aggregates used. Unlike previous studies, it was observed that the healing level of asphalt mixtures, both with and without metallic fibres, increases with the accumulation of crack-healing cycles. Finally, it was determined that the advised microwave heating time for laboratory-sized mixtures, with or without fibres, is 40 s.

The growing need to enhance our road infrastructure has driven the development of several innovative techniques in recent years. Among these advancements, encapsulated rejuvenator solutions for extrinsic self-healing asphalt have emerged as a significant topic of interest. This paper evaluates the effect of optimised capsules containing vegetal oil as a biorejuvenator on the physical, mechanical, and self-healing properties of dense asphalt mixtures. In this study, previously optimised polynuclear alginate-based capsules were synthesised using vibrating jet technology with 5% wt. calcium chloride and a biopolymer-to oil mass ratio 1:7. Optimised capsules were incorporated into the asphalt mixture at concentrations of 0.125% wt., 0.25% wt., and 0.5% wt. Their spatial distribution within the asphalt mixtures was evaluated using an alternative method to CT scans, which utilised machine learning-based image analysis of the core asphalt samples. The main findings of this research are as follows: (1) a uniform distribution of capsules was achieved throughout the asphalt mixture, although clustering was observed at higher concentrations. (2) The capsules successfully survived the asphalt manufacturing process, and mechanical tests highlighted the adhesive properties of the alginate encapsulation material. (3) Asphalt samples with 0.125% wt. capsules exhibited mechanical performance comparable to samples without capsules; however, this content did not significantly enhance their self-healing properties. In contrast, self-healing capabilities were significantly enhanced with a capsule content greater than or equal to 0.25% wt.; however, this enhancement slightly affected some physical–mechanical properties of the dense asphalt mixture.

This study aimed to determine an optimal dosage of sunflower oil (i.e., Virgin Cooking Oil, VCO) as a rejuvenator for asphalt self-healing purposes, evaluating its effect on the chemical (carbonyl, and sulfoxide functional groups), physical (penetration, softening point, and viscosity), and rheological (dynamic shear modulus, and phase angle) properties of long-term aged (LTA) bitumen. Five concentrations of sunflower oil (VCO) were used: 1%, 2%, 3%, 4%, and 5% vol. of LTA bitumen. VCO was encapsulated in alginate biopolymer under vibrating jet technology using three biopolymer:oil (B:O) mass ratios: 1:1, 1:5, and 1:9. The physical, thermal, and mechanical properties of the capsules were studied, as well as their effect on the physical properties of dense asphalt mixtures. The main results showed that an optimal VCO content of 4% vol. restored the chemical, physical, and rheological properties of LTA bitumen to a short-term ageing (STA) level. VCO capsules with B:O ratios of 1:5 presented good thermal and mechanical stability, with high encapsulation efficiency. Depending on the B:O ratio, the VCO capsule dosage to rejuvenate LTA bitumen and asphalt mixtures varied between 5.03–15.3% wt. and 0.24–0.74% wt., respectively. Finally, the capsule morphology significantly influenced the bulk density of the asphalt mixtures.