Transport Research International Documentation (TRID)

Generation and characterization of wear particles from ferrochrome containing asphalt

Fri, 07 Aug 2026 08:36:54 GMT

Ferrochrome slag is a byproduct of high carbon ferrochrome alloy production and has promising material properties for use as aggregate in asphalt wearing courses. However, concerns remain regarding chromium-containing particle emissions during asphalt pavement wear. This study investigates the wear behaviour, particle size distribution, and elemental composition of wear particles generated from asphalt mixtures containing ferrochrome slag. Eight SMA11 and SMA16 asphalt mixtures with different combinations of slag and granite (as aggregate and filler) were prepared and tested using Tröger and Prall abrasion methods. Airborne particles were measured with Aerodynamic Particle Sizer (APS) and Scanning Mobility Particle Sizer (SMPS), and elemental composition was analysed with X-ray fluorescence (XRF). Prall and Tröger results show that ferrochrome slag provides wear resistance comparable to the reference material (with granite from Skärlunda as aggregate and filler), despite mixtures not being optimized for slag-specific density or porosity. All mixtures generated particles across a broad size spectrum. Tröger abrasion resulted in coarser particles due to loss of the finest particles during dry collection, while Prall testing yielded finer fractions because particles were collected in water. Airborne PM10 concentrations were similar for all mixtures, and ultrafine particles (<100 nm) were emitted regardless of aggregate type. Elemental analysis of filters (total suspended fraction), collected wear particles from the Tröger apparatus (coarse fraction), and the fine fraction (PM2.5. revealed the presence of chromium in slag-containing materials. Chromium was also detected at low levels in the granite samples, likely due to abrasion of the steel needles in the Tröger apparatus. While chromium was clearly present in the generated wear particles, its oxidation state was not determined. Overall, the results indicate that ferrochrome slag can be used in asphalt wearing courses without increasing airborne particle emissions compared with conventional asphalt pavement. Further investigations on chromium speciation, leaching of fine fractions, and field-scale validation are recommended to ensure environmental and health safety. However, the results are based on laboratory experiments conducted under controlled conditions and although the methods are designed to simulate real studded tire wear, emissions and particle characteristics may differ under actual road conditions.

Unmodified Bitumen in SMA: A Sustainable and Cost-Effective Approach

Mon, 27 Jul 2026 11:16:39 GMT

Stone Matrix Asphalt (SMA) is a Hot Mix Asphalt (HMA) mixture consisting of a discontinuous aggregate gradation characterised by a high coarse aggregate content (between 70 and 80%), a high percentage of binder (typically between 6 and 7%) and a filler content as high as about 10%. SMA has an aggregate skeleton which imparts high strength and rutting resistance to the mixture. The high binder content though provides the mixture with durability, it also drains through the void spaces in the aggregate skeleton during production, transportation and placement of the mixture in the field. Hence, to reduce the drainage of bitumen and bitumen mortar, the SMA guidelines suggest using a modified bitumen or pelletised cellulose fibres in the mixture when a conventional bitumen such as Viscosity Graded (VG 30) is used. However, the production of cellulose fibres is not only expensive but also requires trees to be cut since cellulose is obtained from plant sources leading to deforestation. Due to the high cost of Polymer Modified Bitumen (PMB), the SMA mixtures prepared with the modified bitumen are also expensive. Hence, the present study focuses on the laboratory evaluation of SMA mixes using a conventional Viscosity Graded bitumen (VG 40) without the use of pelletised cellulose fibres. The results indicated that the susceptibility of mixtures to drainage of binder and/or binder mortar was within the permissible limit of 0.3% by weight of the mixture. The mechanical and moisture susceptibility tests conducted on compacted specimens indicated that the performance is comparable to that of the mixtures prepared using PMB. Further, it was noted that only the grades of bitumen softer than VG 40 required cellulose fibres to reduce drain-down. The study also revealed a reduction in cost due to not using cellulose fibres with VG 40 bitumen or modified bitumen, which makes it more environmentally friendly and sustainable.

Influence of Fillers in Performance of Cold Mix Asphalt Using Reclaimed Asphalt Pavement Material

Tue, 21 Jul 2026 09:49:16 GMT

The present research investigated the influence of different fillers on the performance of cold mixtures using 50% and 100% Reclaimed Asphalt Pavement (RAP) materials in place of virgin aggregates stabilized with bitumen emulsion for the sub-base layer. Bitumen emulsion is a two-phase system in which water, bitumen, and one additive are added to enhance its formation and stabilization. Soft water (having a calcium amount of less than 75 ppm) is used to make an emulsion of bitumen. In the research, three different fillers, cement, fly ash, and Stabil road, were used at various dosages (1, 2, and 3% of dry aggregate weight) with cold recycled mixes to enhance the performance of mixes. Fillers are used to achieve higher strength and resistance to water damage. The results show that the 50% RAP define mixes have more stability and resilient modulus than CM and 100% RAP mixes with the same curing temperature, which depends on aggregate gradation and filler characteristics.

Binary blended filler of spent fluid catalytic cracking (FCC) catalyst (ECat) and limestone for asphalt mixtures

Wed, 15 Jul 2026 09:23:58 GMT

The asphalt industry faces significant challenges regarding long-term durability, sustainability, with urgent need for decarbonisation. This study focuses on the reuse of a spent catalyst from the fluid catalytic cracking (FCC) unit, known as equilibrium catalyst (ECat), as a constituent of the binary-blended filler with limestone for asphalt mixtures. Since 2019, ECat has been officially classified in Portugal (to the authors’ knowledge, the only country) as a by-product eligible for use in construction materials, supporting its potential valorisation. A comprehensive chemical, geometrical, and physical characterisation revealed that ECat’s aluminosilicate-based composition with an exceptionally high specific surface area promotes a high bitumen number and a high Rigden Voids value. These properties enhance filler-bitumen affinity and mastic cohesion, but cause early stiffening when ECat fully replaces conventional filler. Asphalt mastics incorporating 15–30% ECat-limestone blended filler achieved a balance between stiffness and workability while meeting technical and normative thresholds; 15% is recommended to avoid excessive stiffening. Statistical analyses identified bitumen number, Rigden voids and absorption capacity as dominant predictors of mastic behaviour, enabling predictive models for filler optimisation. ECat allowed a reduction in bitumen content up to 10% without compromising the mechanical behaviour of asphalt mixtures while improving their functional performance. Overall, ECat improves high temperature performance and filler-bitumen interaction, offering a potential scalable circular-economy solution for ECat; field-scale mixture testing and long-term ageing assessments are recommended before widescale implementation.

Performance evaluation of asphalt mixtures and mastics containing precipitated calcium carbonate filler: Fatigue resistance at intermediate temperatures

Mon, 29 Jun 2026 09:20:07 GMT

Fatigue cracking remains a primary structural distress in asphalt pavements, necessitating the exploration of high-performance modifiers to enhance durability. This study investigates the multi-scale fatigue behavior of asphalt mixtures and mastics modified with Precipitated Calcium Carbonate (PCC) filler. A comprehensive experimental program was conducted, employing Indirect Tensile Fatigue (ITF) tests for mixtures and Linear Amplitude Sweep (LAS) tests for mastics at various PCC replacement levels (0%, 35%, 70%, and 100%) and temperatures (10 °C and 20 °C). To explore the potential underlying mechanisms, cohesive and adhesive bond strength tests were performed. Results indicate that the incorporation of PCC can extend the fatigue life of both asphalt mastics and mixtures while reducing their stress sensitivity. Phenomenological modeling suggests that increasing PCC content tends to optimize fatigue parameters at both scales; for instance, the fatigue slope (K2) of the mixtures shifted toward zero (e.g., from −1.252 to −1.014 at 10 °C), reflecting a trend toward enhanced structural robustness. Simultaneously, LAS test results revealed an improvement in mastic fatigue endurance across the replacement levels, with statistical validation via t-tests supporting the significance of these performance gains (p-value < 0.001). Mechanistically, strong second-order polynomial correlations (R2 > 0.96) were observed between cohesive/adhesive bond strengths and the fatigue endurance of both mastics and mixtures. The high specific surface area of PCC particles is thought to promote physicochemical interactions with the bitumen, potentially pinning micro-cracks and increasing the energy threshold for crack propagation. Notably, a strong correlation (R2 = 0.9572) was identified between mastic and mixture fatigue lives, suggesting that mastic-scale testing may serve as a valuable preliminary screening indicator for evaluating bulk mixture fatigue trends. This research suggests that PCC holds promise as a effective and sustainable modifier for potentially extending the service life of pavement structures.

Effects of Inert and Active Fillers and Their Physicochemical Properties on Asphalt Mixture Performance

Wed, 24 Jun 2026 10:29:07 GMT

The primary objective of this study is to assess the impact of various inert and active fillers, along with their physicochemical properties, on the laboratory performance of asphalt mixtures. To achieve this objective, various fillers, including active fillers derived from industrial wastes, are sampled, processed, and evaluated. Two state-approved asphalt mixes, a stone matrix asphalt (SMA) and a surface mixture, were selected. For each selected filler, the study characterizes its physical and chemical properties and its influence on the mixture’s laboratory performance against major distresses, specifically, rutting, durability, moisture resistance, and cracking. Results indicate an acceptable correlation between the physical and chemical characteristics of the fillers and the performance of the mixes prepared with these different filler materials. Concerning laboratory-mixed performance, mixes containing industrial fillers, particularly fly ash and steel slag, exhibit better rutting and cracking performance than the control mixes for SMA and surface mixes. In relation to durability, the control mix and steel slag appear to enhance the durability of the surface mixtures. SMA, on the other hand, consistently demonstrates robust performance across filler types. For moisture-damage resistance, the tensile-strength ratio is higher for the different industrial filler materials, especially fly ash and steel slag, than for the control filler. In summary, this study recommends using fly ash and steel slag powder as replacements for mineral fillers in asphalt mixtures. These industrial waste-derived fillers are found to outperform conventional fillers while allowing the reuse of industrial waste in the road infrastructure.

Evaluation on wide-temperature rheological properties and compatibilization of polyphosphoric acid-modified asphalt mastic

Tue, 23 Jun 2026 13:52:11 GMT

Polyphosphoric acid (PPA)-modified asphalt provides cost-effectiveness and performance advantages, making it well-suited for stone mastic asphalt (SMA) mixtures. However, the performance and interactions of the modified asphalt mastic in the mixture require further investigation. This study investigates the wide-temperature rheological properties and interactions of PPA-modified asphalt mastics with a high filler-to-binder ratio, considering asphalt source (Shell 70# and DH 70#), fiber type (lignin fibers (LF) and basalt fibers (BF)). The rheological characteristics were examined using a dynamic shear rheometer, and the interactions in the PPA-asphalt-filler-fiber system were analyzed using Cole-Cole, Han, and Van Gurp-Palmen (vGP) plots. Mechanisms of PPA and fiber interaction were explored through microscopy and infrared spectroscopy. The results showed that PPA forms a strongly modified mastic system with DH 70# (asphaltene content 20.7%). The Jnr3.2 decreases by 43.6%, indicating improvement in high-temperature performance. In contrast, Shell 70# exhibits only weak modification; its Jnr3.2 even increases by 2.7%. PPA improves the fatigue life of asphalt mastic, particularly at low-strain. BF further enhances the fatigue life across the entire-strain. However, LF exhibits a positive effect only in the strongly modified system. Meanwhile, fibers (particularly BF) reduce the low-temperature stress relaxation capacity. In addition, PPA improves the compatibility of the asphalt–filler system. However, the fibers fail to provide further benefits and instead intensify high-temperature heterogeneity in weakly modified system. Esterification reactions may occur between PPA and LF. However, PPA has reacted with the asphalt binder. As a result, system interactions are dominated by physical adsorption, ultimately leading to heterogeneous structure.

Study on the Cracking Potential of Emulsion Treated Base Layer Mixes Using the Concepts of Fracture Energy and Post Peak Slope

Tue, 23 Jun 2026 13:51:05 GMT

Emulsion Treated Base (ETB) is a base stabilization technique in which aggregates are coated with a bituminous emulsion, imparting flexibility to the material. In conventional pavement design, ETB is assumed to fail primarily through permanent deformation, and therefore the provision of a crack relief layer is generally not considered necessary. However, when designers have flexibility in selecting the proportions of constituent materials, certain ETB combinations may exhibit a tendency to fail through cracking rather than rutting. This study evaluates the factors influencing the cracking resistance of ETB mixes using fracture energy and post-peak slope as key performance indicators. Results indicate that fracture energy increases with higher emulsion content, active filler content, incorporation of Reclaimed Asphalt Pavement material (RAP) and greater compaction effort, suggesting improved particle bonding. Conversely, the post-peak slope increases with higher cement content and compaction effort, indicating a greater susceptibility to cracking. It was observed that ETB mixes with 50% RAP and higher emulsion content are more prone to rutting, while mixes with higher cement content and compaction effort are more likely to crack. The study recommends that ETB mixes prone to cracking should be designed based on fatigue criteria, and the inclusion of a crack relief layer should be considered in such cases.

From performance to environmental benefits: recycling solid waste for low-carbon pavements

Wed, 20 May 2026 09:10:36 GMT

Recycling solid waste as fillers in asphalt mixtures offers a sustainable approach for low-carbon pavements. This study evaluated five common solid wastes as mineral filler alternatives through integrated performance, environmental safety, and life cycle assessments (LCA). Results showed that steel slag (SS), iron tailings (IT), and waste cement (CE) fillers notably enhanced rutting, moisture, and fatigue resistance, with SS exhibiting 20% lower fracture energy than limestone filler in low-temperature cracking. Leaching tests confirmed heavy metal levels were well below regulatory limits, indicating minimal environmental risk. In a Guangdong highway case, SS, CE, and IT fillers reduced rehabilitation interventions from five to three over 40 years, while desulfurization gypsum (DG) reduced them to four. LCA revealed SS, IT, and CE fillers decreased all environmental impact categories by over 32%, with CE achieving the greatest reductions in human health, ecosystem, and resource impacts. This framework supports sustainable pavement engineering using solid waste.

Comparative Performance of Asphalt Binders and Sulfur-Waste Mixes Containing SBS and ABS Polymers

Fri, 15 May 2026 09:18:20 GMT

This study explored the use of sulfur waste (SW) as a mineral filler in hot mix asphalt (HMA) modified with styrene-butadiene-styrene (SBS) and acrylonitrile-butadiene-styrene (ABS) polymers to enhance the asphalt’s performance and sustainability. A series of laboratory tests were conducted, including Marshall stability and flow, indirect tensile strength (ITS), Kim test, semicircular bending (SCB), and others, to evaluate the mechanical and rheological properties of the modified asphalt mixtures. The results showed that the addition of SBS and ABS significantly improved the viscosity, stiffness, and resistance to deformation at both high and low temperatures, with SBS offering better high-temperature performance, making it suitable for heavily trafficked roads. ABS, on the other hand, provided a more cost-effective solution for areas with moderate climatic conditions. In addition, the modified mixtures exhibited enhanced moisture resistance and fracture resistance, demonstrating better durability compared to the control mixture. Life-cycle cost analysis further confirmed the economic advantages of using SW with SBS and ABS, reducing asphalt production costs. In conclusion, SBS is recommended for high-traffic, high-temperature regions, while ABS is more suitable for cost-sensitive projects or moderate climates, offering a balance between performance and cost.

Comparison of hot and warm asphalt mixture workability with different types of filler

Thu, 14 May 2026 17:04:33 GMT

The study aims to determine the impacts of using the WAM pavement by adding the Sasol wax Sasobit to asphalt pengrade 40-50 widely used in paving. The amount of Sasobit added (1% to 3%) by weight of asphalt. Physical and rheological tests have been used to determine the optimum content of Sasobit that will enhance the local asphalt to withstand the high temperatures in summer in Iraq. The results showed that the optimum content is 3% by weight of asphalt. This percentage was used to produce a WAM mix with different fillers of hydrated lime, limestone, and cement. Asphalt mixtures with hydrated lime for HMA and WAM have lower torque values and are more workable than other types of fillers while mixtures with limestone filler have a high torque and less workable than others. Sasobit additive reduces the mixing temperature by about 12-15 °C and compaction by about 13 °C.

Mechanical and electromagnetic performance assessment of magnetite-modified asphalt mixtures for electrified pavement applications

Mon, 11 May 2026 08:50:45 GMT

The integration of wireless power transfer (WPT) systems into pavements requires materials that enhance electromagnetic coupling while maintaining structural performance within standard durability limits. This study evaluates AC16 asphalt mixtures incorporating synthetic magnetite (Fe₃O₄) as a filler at 0–100 % volumetric replacement of calcium carbonate, with the objective of identifying magnetite contents that enhance WPT efficiency without compromising key mechanical performance criteria. Electromagnetic performance was first assessed using a resonant double-coil setup at 85 kHz. Magnetite improved inductive coupling, with received power increasing up to + 17.6 % relative to the air-gap baseline and power transfer efficiency rising by + 2–3.5 %. Mechanical performance was subsequently evaluated through Marshall stability, volumetric properties, resilient modulus, indirect tensile strength ratio (ITSR), and rutting resistance. At 50 % magnetite substitution and 4.6 % bitumen content, mixtures achieved a resilient modulus of approximately 6100 MPa, air voids close to 4 %, and ITSR values slightly above 100 %, attributed to reduced interconnected porosity and improved filler packing after moisture conditioning. Rutting resistance improved markedly, with rut depth reduced to 1.74 mm, although the wheel-tracking slope (0.08 mm/1000 cycles) remained slightly above the Spanish specification limit. Overall, the results demonstrate that magnetite-modified asphalt mixtures can enhance inductive power transfer while maintaining mechanical performance compatible with electrified pavement applications.

From hazardous waste to sustainable filler: Synergistic use of treated spent cathode carbon and basalt fiber in asphalt mixtures

Fri, 01 May 2026 14:33:17 GMT

Spent cathode carbon blocks (SCCB), a by-product of aluminum electrolysis, are considered hazardous waste because they contain toxic substances like fluoride and cyanide. Traditional treatment methods pose a risk of environmental pollution. To achieve reliable and large-scale recycling and utilization of SCCB, this paper utilizes physicochemical synergistic harmless treatment of spent cathode carbon powder (SCCP) to prepare gel-encapsulated spent cathode carbon (PSC), PSC is used as a filler to replace part of limestone powder (LP), and basalt fiber is introduced as a modifier. Microscopic analysis, pavement performance, and environmental tests were conducted to evaluate its feasibility in road engineering, and analysis of variance (ANOVA) was employed to statistically analyze the performance differences among different treatments. The results show that PSC surfaces contain numerous grooves and pores, which bond well with asphalt. When the PSC replacement ratio is 50 %, the overall pavement performance of the asphalt mixture reaches the optimal level. However, all PSC replacement ratios exert a negative impact on the low-temperature cracking resistance of the asphalt mixture, and this adverse effect can be effectively mitigated by the incorporation of basalt fiber. After synergistic treatment, the fluoride ion leaching concentration of PSC is significantly reduced to 8.207 mg·L⁻¹ , and the fluoride ion leaching concentration of the corresponding asphalt mixture is less than 10 mg·L⁻¹ , both of which meet the environmental standards. This study proposes a sustainable approach to the resource recovery of SCCB, facilitating the safe recycling of hazardous materials and contributing to sustainable environmental development.

Experimental investigation and multi-scale Mori–Tanaka modeling of viscoelastic asphalt mastic with imperfect interfaces

Fri, 20 Mar 2026 14:47:52 GMT

Asphalt mastics, comprising asphalt binder and mineral filler, play a critical role in determining the performance of asphalt mixtures. This study examines the viscoelastic behavior of mastics composed of two asphalt binders and three fillers (gabbro, quartz, and hydrated lime) with varying particle sizes. Repeated Creep and Recovery Tests (RCRT) were conducted to evaluate the influence of filler type and concentration on mastic strain response. Then, a modified multi-scale Mori–Tanaka model was successfully employed to predict the viscoelastic properties of the mastics. The model parameters were found to be influenced by the filler type and size, as well as by imperfections at the binder–filler interface. Results show that mastics containing hydrated lime exhibit higher moduli, particularly at high filler content (40% by volume), with significantly lower final strain in RCRT compared to those with gabbro or quartz. This enhanced performance is attributed to the high surface area of hydrated lime and its chemical interactions with the asphalt binder, which promote the formation of a network structure within the mastic. While the proposed model effectively captures the physical interactions in asphalt mastics, it requires further refinement to account for the additional influence of chemical reactions between fillers, such as hydrated lime, and the asphalt binder.

Performance grading and mechanistic design method of base course incorporating RCP and RCA stabilized with asphalt

Fri, 20 Mar 2026 08:41:00 GMT

With the rapid growth of construction and demolition waste (C&DW), its resource utilization has become an important research direction in road engineering. Although the application potential of recycled concrete aggregate (RCA) and recycled concrete powder (RCP) in road base courses has gained attention, the synergistic use of RCA and RCP in asphalt-stabilized base courses still lacks systematic performance evaluation methods and corresponding design theory. Furthermore, the absence of a scientific classification system tailored to different road grades results in insufficient guidance for material selection in engineering practice. To address these issues, this study first established a three-tier classification system for recycled mixtures based on performance grade (PG) through multi-scale testing and principal component analysis. Subsequently, leveraging KENLAYER mechanical simulations, a corresponding performance-graded mechanistic design (PGMD) method was proposed. Results indicate that RCP as a filler significantly enhances the high-temperature performance and deformation resistance of the mastic. The RCP75 mastic demonstrated lower temperature and frequency sensitivity, along with a broader applicable temperature range. The RCA60 mixture exhibited optimal performance in high-temperature stability and moisture stability, with improvements of 91.8 % and 6.9 % respectively, achieving a PG value of 0.878 and a Grade I rating, meeting the technical requirements for high-grade highway base courses. Based on these findings, a thickness design equation and nomogram for the base course were developed using PG and the number of axle load repetitions (Ne) as variables, balancing structural reliability and material economy. This study provides theoretical support and design methods for the standardized and high-value application of construction solid waste in high-standard road base courses.