# Life Cycle Assessment for the Production Phase of Nano-Silica-Modified Asphalt Mixtures
## 1 Introduction  
Asphalt is the most widely used pavement layer in the world. It consists of a binding material called bitumen and crushed or natural aggregates. The mixture of these materials forms asphalt mixtures. Demand for paved roads exceeded the supply of lake asphalts in the late 1800s and led to the use of petroleum asphalts [1]. Asphalt is often used as a shortened form of asphalt concrete which is the material of choice in the pavement sector. In the United Kingdom and the rest of Europe, the term 'bitumen' is used as a synonym for the term 'asphalt binder' while 'asphalt cement' is often used in the United States [2]. Asphalt cement or bitumen is used to bind the aggregates together to provide the required strength and stiffness to transfer vehicular loads. In addition to its strength andstiffness, asphalt pavements offer a damping ability due to the viscous-elastic nature of the bitumen [3]. Consequently, asphalt mixtures are qualified to provide optimal driving comfort as well as flexible maintenance actions. Asphalt pavements are designed to provide maximum performance throughout the design life. Bitumen (asphalt binder) performs two functions: Binding aggregates together and protecting the aggregates from distortions. However, unlike concrete pavements, asphalt pavements experience deformations over short periods of time. This, coupled with increased traffic loads and extreme weather conditions have resulted in asphalt pavement authorities seeking alternative solutions to improve the resistance of the road pavements to the adverse effects of mechanical and environmental loading [4]. Currently, several additives and modifiers produced commercially are used to modify the properties of the asphalt binder. Ref. [3] stated that additives and other modifiers are added in asphalt mixtures to lower mixing and compaction temperatures. This was found to improve adhesion and increase resistance against cracking and rutting. Regarding the viscosity of bitumen, Ref. [5] studied the effects of asphaltene on rheological properties of diluted Athabasca bitumen. Nanotechnology and nanomaterials have recently attracted significant attention from the pavement industry. Nanomaterial application is considered to have the potential to improve asphalt binder properties. As mentioned by Ref. [6], the application of nanomaterials as asphalt modifiers is growing rapidly in popularity due to its unique characteristics that significantly improve the performance of asphalt binder. It has been shown in several studies that the addition of nano-silica in asphalt mixtures improve the oxidative aging property, increases resistance to the rutting effect, improves the rheological properties of asphalt mixture and decreases the interaction between asphalt molecules [7; 8; 9; 10]. In addition, [PERSON]. [11] investigated and found that increasing nano-silica content in asphalt mixtures decreases the ductility and temperature sensitivity of the asphalt mixture. It is becoming increasingly important to explore the full benefits of additives and modifiers on the long-term performance of asphalt pavements. With sustainability in mind, and also embracing the global effort to reduce the environmental impacts associated with these newly perforated materials, being able to make decisions and judge the benefits and environmental friendliness linked to the long-term pavement performance has become important. Consequently, having a life-cycle assessment (LCA) tools available to assess modified-asphalt materials on a life-cycle basis becomes necessary. Due to the concern of global warming and resource depletion, LCAs for different materials and products and systems have gained significant popularity with researchers. LCA studies can help to determine and minimize the energy consumption, use of resources, and emissions to the environment by providing a superior understanding of the systems [3]. LCA studies can help to consider different alternatives if the environmental performance of a particular material or product is not favorable.