Life cycle assessment of granite application in sidewalks

Sidewalks are important built areas for promoting environmental sustainability in cities since they support walking as a zero emission form of transportation contributing to protect the environment and the health of individuals. However, sidewalk management is typically focused on assessing their suitability for users without applying any environmental criteria on the infrastructure design. The paper aims to quantify the environmental impact that sidewalks can contribute to the urban space if no environmental criteria are applied in sidewalk design. This study focuses on the environmental assessment of a very common sidewalk system found in cities to support pedestrian and light motorized traffic for over 45 years. The constructive solution consists of granite slabs (top layer) fixed on a mortar layer (3-cm thick) that is settled on a base of concrete (15-cm thick). The life cycle methodology was employed to conduct the environmental assessment of the system. The results are compared with the environmental outcomes of a sidewalk system that has the same function but is paved with concrete slabs to identify the environmentally optimal sidewalk design. The impact assessment method was CML Baseline 2001, and the inventory data were compiled from manufacturers associations, local authorities, and literature review. Construction materials have the highest environmental impact (48-87%) in the sidewalk life cycle, where the granite top layer is the first contributor, although the amount of granite in the sidewalk system represents the 30% of the total weight of the construction materials used. A granite sidewalk has from 25% to 140% higher impact than a concrete one. The energy required to produce slabs is the key factor that characterizes the environmental impact of granite. Electricity and diesel consumption in stone cutting and moving represent over the 70% of the environmental burden of granite. The transportation of granite slabs is also relevant to the environmental impact. The use of imported granite could account for up to 76-177% of the total environmental impact of the sidewalk life cycle. Although granite is a natural material, using granite slabs as flooring material is not an environmentally suitable alternative over using concrete ones for paving sidewalks. The results have shown that if no environmental criteria are applied during sidewalk design and management, urban planners may be unconsciously contributing to an important environmental burden on the built environment. The ecodesign is a strategic opportunity to promote environmentally suitable urban infrastructures that contribute to promote urban sustainability in cities. Energy efficiency techniques, water management and well-considered transportation management should be developed and implemented in the granite industry to minimize the environmental impact of using it for paving. Additionally, further research is needed to quantify the environmental performance of other construction materials used in sidewalk construction in order to identify the best environmental alternatives and design improvements by optimizing the use of materials to the sidewalks functions.