# Life Cycle Assessment for the Production Phase of Nano-Silica-Modified Asphalt Mixtures
## 2 Literature Review and Definitions
### Nanomaterials and their Application as a Modifier in Asphalt Mixtures  
Nanotechnology is an emerging technology and is regarded as a key enabling technology due to its numerous associated benefits to many areas of society. Nanotechnology is defined as the use of very small particles of materials (either by themselves or by their manipulation) to create new large materials [24]. The author added that nanotechnology is not a new science or technology, but an extension of the science and technology that has been in development for many years, and is used to examine nature at an ever-smaller scale. Ref. [25] defines nanomaterials as those physical substances with at least one dimension between 1 and 150 nm (1 nm = 10\({}^{-9}\) m). With reference to the European Commission's recommended definition of nanomaterials, Ref. [26] defines nanomaterial as a \"natural, manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1-100 nm\({}^{\prime\prime}\). The application of nanomaterials in the field of construction is growing rapidly. Ref. [27] mentioned that nanotechnology is a rapidly expanding area of research where novel properties of materials manufactured at the nanoscale can  
Figure 1: Structure of LCA study. be utilized for the benefits of constructing infrastructure. Although some nanomaterials are already being used in the concrete industry, their application as a modifier in asphalt binder has attracted more interest recently. Several experimental studies have been conducted to determine the effect of nanomaterials, especially nano-silica on the properties of asphalt mixtures. Nano-silica materials are used as additives which are applied in small percentages by weight of the asphalt binder to improve the rheological and other properties of asphalt mixtures. Ref. [7] investigated the characteristics of asphalt binder and mixture containing nano-silica and found that the addition of nano-silica has a positive influence on different properties of the asphalt binder and mixture. [PERSON]. [28] also studied the effect of nano-silica and rock asphalt on rheological properties of modified bitumen. In their study, [PERSON]. [29] found that the inclusion of nano-silica reduces the rutting susceptibility of nano-modified asphalt mixtures. [PERSON]. [30] studied laboratory evaluation of composed modified binder and mixture containing nano-silica/rock asphalt/SBS. In a similar experimental study, [PERSON]. [31] found that increasing the percentage of nano-silica increases the Brookfield Rotational Viscosity (RV). [PERSON]. [32] worked on the application of nano-silica to improve asphalt mixture self-healing. In another study, [PERSON]. [33] investigated the effect of nano-silica on thermal sensitivity of hot-mix asphalt. Nano-silica increases the strength or durability of asphalt mixture [34; 35]. [PERSON]. [36; 37; 38; 39; 40] also made similar studies on the effect of nano-silica on asphalt binder and mixtures. Table 1 summarizes the review of previous studies on the characterization of asphalt binder modified with nano-silica. Regarding the cost of using nanomaterials, [PERSON]. [41] provides the prices for almost all nanomaterials based on the quantity required. For example: precipitated calcium carbonate Nanopowder, 50 nm (100 g = $45, 1 kg = $85); nano-silica nanopowder, 60-70 nm (100 g = $55, 1 kg = $155); titanium oxide Nanopowder, 20 nm (100 g = $165, 1 kg = $468); zinc oxide Nanopowder, 80-200 nm (100 g = $58, 1 kg = $168). While some nanomaterials may seem costly, others may be cheap. However, on a large scale, an extensive economic analysis is required to determine the optimum cost for each nanomaterial based on the quantity required.