# Practical Application of Sustainable Road Structure: Mechanical and Environmental Approach
## 1 Introduction  
Sustainable road construction is within the interest of both practitioners and researchers for past decades. The recently published NCHRP guidebook [1] summarizes current technical achievements and typical practices implemented in order to improve ecological footprint of road constructions. One should take into account that economic viability of innovative technical solutions has to be proofed before they will be implemented in practice. As stated by [PERSON] et al. [2] in the paper dealing with greenhouse gas (GHG) emission monitored during road construction projects, several elements are found to contribute to the variation in CO\({}_{2}\): the technical standards of road (e.g., traffic, lane width), current structure condition (e.g., foundation, pavement), materials selection and construction technique as well as drainage and structures (type, number, etc.). The construction of a road is an energy- and resource-intensive process, releasing large amounts of emissions to the environment and resulting in the depletion of natural resources. Therefore, road construction is a sector where measures need to be taken in order to reduce the energy demand and environmental impact, and, in particular, to reduce the use of raw materials with cost-effective measures. At present, potential measures with sound sustainability, including alternative binders, low temperature mixtures, the use of high rates of reclaimed asphalt (RAP) and a wide use of recycled materials, are not widely implemented, regulated, and harmonized within road construction and a wholesale shift touse of these types of materials has yet to occur. A recent study by [PERSON] [3] proved high performance in low, medium and high temperature of asphalt mixture with up to 50% or RAP and bio-origin binder. Using waste materials in pavement construction will improve sustainability but one should take into account pavement durability, including moisture resistance. The long-term aging of asphalt will further reduce the moisture resistance of asphalt pavements. [4]. Another finding in the sustainable road technologies was presented by [PERSON] [5] who proved that asphalt mixtures produced below 100 \({}^{\circ}\)C, the so-called half-warm foamed bitumen, are ecologically friendly and demonstrated high durability. According to the research presented by [PERSON] [6] optimization factors responsible for bitumen foaming process (pressure, bitumen temperature and water content) allow to reduce bitumen temperature retaining required foaming parameters. A rather untypical solution was presented by [PERSON] [7] where oil sludge was used to substitute part of the bituminous binder in the asphalt mixture incorporated up to 4% in asphalt mixture). A strengths, weaknesses, opportunities, and threats (SWOT) analysis was applied to assess asphalt mixture with crumb rubber [8]. The applied analysis underlined the environmental aspects of this technology, especially in the city areas. In order to assess various technical solutions as more or less sustainable, the road life cycle should be taken into account. Moreover, not only construction but also maintenance techniques play a vital role in life cycle sustainability analysis. The sustainability of a developed road pavement can be assessed throughout the life cycle analysis (LCA) as well as life cycle cost analysis (LCCA). The LCA is an environmental assessment method, widely used in the construction and infrastructure projects, that allows to compare the environmental performance of the conventional (baseline) with alternatively developed scenario. The life cycle cost analysis allows to quantify the total costs occurred within the whole life cycle of a normalized 1 m\({}^{2}\) of road pavement. Although the LCA is a strong tool helping to increase the environmental effect of road construction, some highway agencies still do not take a full account of LCA implementation of road renovations projects [9]. Some researchers employed fuzzy logic expert systems for such assessment [10].