Paved Skin: Sidewalks and Light-Weight Traffic Road Pavement

Table 22.1 shows the environmental impact of conventional designs of concrete, asphalt and granite sidewalks to support pedestrian and light-weight traffic in cities. The design solutions have different service lives: 15 years for asphalt and 45 years for concrete and granite. However, the GWP of each sidewalk changes according to the variability of the service life of the constructive solutions. The shorter the service life, the higher the number of maintenance and removal operations (top-layer replacement) to restore the serviceability of the sidewalks during the period of analysis (50 years). Thus, two maintenance scenarios were considered, e.g., high and low maintenance rates. During this time frame, the most environmentally friendly pavement design is the concrete top-layer, which had a GWP 6 % and 28 % lower than asphalt and granite, respectively.

However, the environmental performance of pavements strongly depends on their service life and a sensitivity assessment was conducted for a range of lifespan from 5 to 45 years. When the same service life is considered for the three solutions (i.e., lifespan is equivalent under certain exposure conditions), asphalt becomes the

Table 22.2 Global warming potential (GWP) (kg of CO2 eq.) of a natural gas network design for a time frame of 50 years for low and high density scenarios

Urban density

Neighborhood

Buildings

Dwellings

Waste treatment

Total

Low

6290

905

1160

866

9221

High

6290

30,000

75,100

4030

115,420

best practice: in urban areas with a high renovation rate of sidewalks and lightweight traffic pavements (≤15 years), asphalt is recommended for both sidewalks and light-weight traffic pavements: in contrast, concrete is the most suitable option in urban areas with a low renovation rate of sidewalks (>40 years), whereas asphalt has a maximum lifespan of 15 years and a high renovation rate is unfeasible. In general, granite sidewalks are less environmentally due to the high resource intensive manufacture of granite tiles (Mendoza et al. 2012a, b, 2014a).

Gas Network

Table 22.2 shows the environmental impact of natural gas distribution networks for low and high density neighborhood scenarios. Contrary to other elements, the gas network only considers a standard constructive design – i.e., HDPE (high density polyethylene) pipes for medium-pressure gas distribution – and instead of multiple materials, scenarios compared urban densities. The studied system is a standard local neighborhood. The scenarios considered recreate one low density detached house neighborhood (4 dwellings) and a high density Mediterranean neighborhood (24 dwellings). The assessment includes the network in the neighborhood (100 m), the elements of the gas distribution in the buildings and the dwellings, and the waste treatment of the materials. The results show that the distribution of the environmental load between subsystems changes radically according to urban density. This means that in low-density areas the neighborhood network is the subsystem that gives raise to most impact (68 %), while in high-density neighborhoods the building and dwelling subsystems are those that are responsible for more than 95 % of the GWP (Oliver-Solà et al. 2009a, b). For the purpose of our study, the impact of the neighborhood network was considered in the profile of the street (see Table 22.5).

 
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