Advanced Self-Healing Asphalt Reinforced by Graphene Structures: An Atomistic Insight

Summary

Graphene-modified asphalt nanocomposite has shown an advanced self-healing ability compared to pure asphalt. In this protocol, molecular dynamics simulations have been applied in order to understand the role of graphene in the self-healing process and to explore the self-healing mechanism of asphalt components from the atomistic level.

Abstract

Graphene can improve the self-healing properties of asphalt with high durability. However, the self-healing behaviors of graphene-modified asphalt nanocomposite and the role of incorporated graphene are still unclear at this stage. In this study, the self-healing properties of pure asphalt and graphene-modified asphalt are investigated through molecular dynamics simulations. Asphalt bulks with two crack widths and locations for graphene are introduced, and the molecular interactions among asphalt components and the graphene sheet are analyzed. The results show that the location of graphene significantly affects the self-healing behaviors of asphalt. Graphene near the crack surface can greatly accelerate the self-healing process by interacting with the aromatic molecules through π-π stacking, while graphene at the top area of the crack tip has a minor impact on the process. The self-healing process of asphalt goes through the reorientation of asphaltene, polar aromatic, and naphthene aromatic molecules, and the bridging of saturate molecules between crack surfaces. This in-depth understanding of the self-healing mechanism contributes to the knowledge of the enhancement for self-healing properties, which will help to develop durable asphalt pavements.

Introduction

Deterioration under daily vehicle loadings and variant environmental conditions, and the aging of asphalt during service result in degradation or even structural failures, i.e., cracking and raveling, which can further weaken the durability of asphalt pavements. The inherent response of asphalt to repair micro-cracks and voids automatically helps it recover from damages and restore strength¹. This self-healing capability can considerably extend the service life of asphalt, save costs on maintenance, and reduce the emission of greenhouse gases^2,3. The self-healing behavior of asphalt gen....

Protocol

1. Build the atomistic models

1. Open the Materials Studio software to create five 3D atomistic documents and rename these documents as graphene, asphaltene, polar aromatics, naphthene aromatics, and saturates, respectively.
2. Build the graphene model by creating the unit cell of graphene sheet in the 3D atomistic document using the Sketch Atom option.
3. Construct the final structure using the Supercell option in the Build > Symmetry menu. Define the size of the graphene sheet as 40 Å x 40 Å, which is larger than the asphalt chains and the crack width.
4. Build and pack th....

Results

The contour of atom number
The contours of the atom number of pure asphalt and graphene-modified asphalt models in the yz plane are shown in Figure 3, where the color bar from blue to red exhibits atom numbers varying from 0 to 28. Figure 3a-c illustrates the contour of the atom number of the structures with 15 Å crack width in pure asphalt and asphalt nanocomposites modified by graphene at the crack .......

Discussion

The critical steps within the Protocol part are as follows: step 1.4 - Build and pack the four types of asphalt molecules; step 1.5 - Build the asphalt structure with the crack; step 2.3 - Achieve the equilibrium; step 2.4 - Perform the self-healing process. These steps indicate the most cohesive and important contents of the protocol. To create the desired shapes of the inserted crack, the packing process is modified compared to the normal packing in Materials Studio. The crack shape is created and filled inside the sim.......

Materials

Name	Company	Catalog Number	Comments
Atomistic models of asphalt and graphene/Materials Studio	BIOVIA	Materials Studio 8.0	The atomistic models are built for molecular dynamics simulations.
Large-scale Atomic/Molecular Massively Parallel Simulator Package	Sandia National Laboratories	lammps-stable20	The equilibrium is achieved under NPT ensemble, and the atomistic models get self-healed.
OVITO	Materials Science Department of Technische Universität Darmstadt, Germany	ovito-basic-3.1.0-win64	The self-healing behaviors of the atomistic models are visualized.
Origin	OriginLab	Origin 2018 64Bit	The contours of the atom numbers of the trajectory are drawn and analyzed.