As recently published at the MDPI Research Portal, scholars have investigated the performance of asphalt modified with waste tire rubber powder and surface organic layered double hydroxides, with the aim of improving road pavement durability and supporting more sustainable use of tire recycling materials. The study, published in Gels, used rubber powder produced from waste truck tires together with surface organic layered double hydroxides to modify 70# matrix asphalt. The research found that the composite modified asphalt showed improved high-temperature deformation resistance, low-temperature crack resistance, elastic recovery and UV aging resistance compared with matrix asphalt and rubber powder modified asphalt alone. The findings add to ongoing research into rubberized asphalt, crumb rubber and advanced modifiers that can help expand higher-value applications for recycled tire materials in road engineering.

Research focuses on sustainable pavement materials

The study was conducted by researchers from North China University of Water Resources and Electric Power, Southeast University, Chang’an University, Dalian University of Technology and other institutions. The authors said traditional asphalt pavement materials can soften and deform at high temperatures, while long-term ultraviolet exposure and oxidation can contribute to cracking. To address these issues, the study combined rubber powder from waste tires with surface organic layered double hydroxides, or SOM-LDHs, which are known for UV-blocking and anti-aging properties.

Rubber powder content optimized through response surface method

The researchers used the Box-Behnken response surface method to optimize the preparation parameters for the composite modified asphalt. The three main variables were rubber powder content, SOM-LDHs content and shear temperature, while the response indicators were penetration, ductility and softening point. The optimum formulation was determined as 21.7% rubber powder, 4.8% SOM-LDHs and a shear temperature of 160 °C.

The study found that rubber powder content had a stronger effect than SOM-LDHs content and shear temperature on penetration, ductility and softening point. According to the authors, the optimized composite modification improved the overall road performance of asphalt by enhancing flexibility, deformation resistance and high-temperature stability.

Composite modified asphalt showed stronger aging resistance

The research used rotating film oven testing and accelerated ultraviolet aging to assess thermo-oxidative and UV aging performance. After aging, the composite modified asphalt showed lower mass loss and viscosity ratio, along with a higher residual penetration ratio, indicating improved anti-aging performance. In the UV aging test, the surface of the matrix asphalt showed more visible deterioration, while the RP/SOM-LDHs composite modified asphalt had more uniform crack distribution and narrower cracks.

The authors attributed the improved aging resistance to the combined action of rubber powder and SOM-LDHs. Rubber powder can form a network structure within asphalt, while the layered structure of SOM-LDHs can help shield ultraviolet light and slow oxygen penetration into the asphalt matrix. This combination helped reduce photo-oxidative aging and improved the durability of the modified asphalt material.

High-temperature deformation resistance improved

Dynamic shear rheometer testing showed that the complex shear modulus of the RP/SOM-LDHs composite modified asphalt was higher than that of matrix asphalt and rubber powder modified asphalt at the same test temperature. After aging, the complex shear modulus of the composite modified asphalt increased by 27.35%, indicating stronger resistance to shear deformation.

The study also reported that the rutting factor of the composite modified asphalt reached 79.86 kPa at 46 °C after short-term aging. The phase angle decreased by 11.83% after UV aging, which the authors said indicated improved elastic recovery and resistance to permanent deformation. These results suggest that the composite asphalt could offer better rutting resistance under high-temperature road conditions.

Low-temperature crack resistance also enhanced

Low-temperature bending rheology tests showed that, in the range from −18 °C to −24 °C, the creep stiffness of the composite modified asphalt was about 30% lower than that of matrix asphalt, while the m-value increased by about 15%. Lower creep stiffness and higher m-value indicate improved stress relaxation and reduced risk of low-temperature cracking.

The researchers also used a multi-stress creep recovery test at 64 °C. Under 3.2 kPa stress, the strain recovery rate of the composite modified asphalt reached 78.5%, while unrecoverable creep compliance was as low as 0.18 kPa−1. The study said this performance was better than both matrix asphalt and single rubber powder modified asphalt, showing improved elastic recovery and deformation control.

Microscopy showed interaction between rubber powder and SOM-LDHs

Scanning electron microscopy showed that SOM-LDHs nanoparticles were distributed on the rough surface of rubber powder particles and acted as nanoscale physical crosslinking points between the rubber phase and asphalt matrix. The researchers said this structure improved the integrity and thermal stability of the composite asphalt system.

Atomic force microscopy further showed that the surface roughness of RP/SOM-LDHs composite modified asphalt was reduced by 60.42% compared with matrix asphalt. The study found that rubber powder was the main factor reducing the internal honeycomb-like structure of asphalt, while SOM-LDHs further filled voids and helped create a more ordered and compact asphalt microstructure.

FTIR and GPC tests supported anti-aging findings

Fourier transform infrared spectroscopy indicated that rubber powder modification did not create new characteristic absorption peaks compared with matrix asphalt, suggesting that rubber powder and asphalt mainly interacted through physical mixing rather than chemical reaction. After aging, the carbonyl and sulfoxide index growth rates were lower in the composite modified asphalt than in matrix asphalt, supporting the conclusion that SOM-LDHs helped inhibit UV-related oxidation.

Gel permeation chromatography showed that asphalt molecular weight increased after aging, but the growth rate was lowest for the RP/SOM-LDHs composite modified asphalt. The researchers linked this to the combined effects of rubber powder and SOM-LDHs, including physical restriction of molecular movement, UV shielding and reduced oxygen diffusion. The results indicated improved aging resistance and more stable molecular structure after modification.

Study points to applications for rubberized asphalt

The authors concluded that RP/SOM-LDHs composite modified asphalt can improve high-temperature deformation resistance, low-temperature crack resistance and UV aging resistance. They said the optimized formulation provides a possible route for developing more durable road materials that use recycled tire rubber in combination with nanoscale modifiers.

The study is relevant to tire recycling and rubberized asphalt markets because it demonstrates another potential high-value use for rubber powder recovered from end-of-life tires. While the research remains laboratory-based, it supports broader efforts to expand applications for crumb rubber and recycled tire materials in road construction, sustainable pavement design and circular economy infrastructure.

Further research planned

The authors noted several limitations, including insufficient characterization of dynamic chemical processes and the absence of some control groups, such as SOM-LDHs-only and untreated-LDHs-only formulations. Future work is expected to include dynamic light scattering, rheological time sweeps, in-situ microscopy, molecular simulation, interfacial analysis, FTIR peak deconvolution and additional factorial testing.

The researchers also plan to examine the influence of different shear temperatures and separate the individual and combined effects of rubber powder, SOM-LDHs, untreated LDHs and coupling agents. This future work could help clarify the mechanisms behind network formation, aging resistance and performance improvement in composite modified asphalt.

To read the full study, proceed MDPI Research Portal.