Environmental optimization of concrete sidewalks in urban areas

Jordi Oliver-Solà, Alejandro Josa, Joan Rieradevall, Xavier Gabarrell

Research output: Contribution to journalArticleResearchpeer-review

33 Citations (Scopus)

Abstract

Background, aim, and scope: New neighborhoods and cities are built in both developing and developed countries worldwide. Given this urbanization context and current global environmental threats, the concept of sustainability will, in the long term, succeed or fail in cities. To succeed, we need to provide life-cycle-based data aimed at improving the environmental performance of new urban developments and redevelopments. This study discusses the installation criteria for three specific types of sidewalk; these criteria are currently based exclusively on economic and social factors, leading to design uniformity. This study also provides a comparative life cycle assessment (LCA) of these three types of concrete sidewalks and identifies potential redesign solutions. If sidewalk design were adapted to specific usability requirements, the environmental impact factors associated with sidewalks, and therefore cities, would be significantly optimized and reduced. Materials and methods: Although a wide range of materials and constructive solutions are available for sidewalk paving, this study focuses on three very common concrete-based systems with different functionalities in terms of traffic, surface characteristics, and maintenance (i.e., interlocking blocks, continuous concrete layer, and slabs set on a 10-, 12-, and 15-cm-thick concrete base). These systems are analyzed from a life cycle perspective. The impact assessment method used was CML 2 Baseline 2000; input data were provided by the City of Barcelona and other local municipal councils in Catalonia, Spain as well as by local producers. Results: In terms of main findings, this study provides a comprehensive description and inventory of the sidewalk systems under study. According to the LCA, the slab system has the highest environmental impacts; this happens to be the most widely used sidewalk type in the area studied, mainly due to aesthetic concerns and the imperatives of maintaining underground urban services. Regardless of the thickness of the concrete base, the slab system has the highest impact in all categories compared with the other two sidewalk types. However, when the slabs are set on 10 cm of concrete, performance approaches that of the continuous concrete system (with the difference ranging from 3.4% to 6.3%, depending on the impact category); this system is very convenient when maintenance work on underground urban services is required. The interlocking block system, which has the lowest structural capacity, reduces environmental impacts in all categories by 73.8% compared with the highest impact system (i.e., slabs plus a 15-cm concrete base). However, the interlocking block system is limited to areas in which vehicular traffic is prohibited. Nevertheless, there is a high potential for environmental impact reductions when this system is used in places where high structural capacity is not required. The highest environmental impacts of the various sidewalk types are associated with the use of cement (accounting for approximately 24% to nearly 77% of the total impact, depending on the impact category and the sidewalk system used); other impacts have origin in site-to-site transportation of materials, installation, and removal of slabs and continuous concrete layers. Aggregates, which are the materials used in larger quantities in concrete, have a negligible effect on the environmental impact (less than 10% in the categories where its effect is most pronounced). In contrast, the contribution of admixtures, which are used in much smaller quantities, exceeds 10% in the abiotic depletion category. Discussion: The redesign of sidewalks using environmental criteria and adjusting the sidewalk types to functions fulfilled can bring important benefits. Using a linear regression of the characterization results based on the weight of cement in each system, Pearson's coefficient of regression is greater than 0.99 for all impact categories. Therefore, the content of cement is a key factor in determining the environmental impacts of each sidewalk type. Conclusions: In certain high-traffic areas, e.g., when a sidewalk is located between a roadway and a parking garage entrance or when a sidewalk must to be dug up frequently to access underground service networks (in a process known as 'trenching"), the sidewalk must be reinforced and surface damage must be concealed. In such cases, the environmental impacts may be justified. However, sidewalks have multiple uses, and in many cases, their structural requirements are not excessively rigorous. Therefore, the systematic application of the slab system exacerbates urban environmental impacts. Restricting the use of concrete sidewalks with high structural capacity to street sections that actually require them could reduce environmental impacts by up to 73.8% in pedestrian-only areas. Recommendations and perspectives: In light of these findings, attention should be paid to the appropriate selection of sidewalks in urban developments and redevelopments based on street function. In addition, the use of materials containing cement should be optimized, local suppliers should be selected, and sidewalks should be designed to facilitate dismantling and reutilization of their components, especially when frequent access to underground networks is required. © 2009 Springer-Verlag.
Original languageEnglish
Pages (from-to)302-312
JournalInternational Journal of Life Cycle Assessment
Volume14
DOIs
Publication statusPublished - 1 Jun 2009

Keywords

  • Blocks
  • Cement
  • Cities
  • Civil engineering
  • Ecodesign
  • LCA
  • Pavement
  • Public space
  • Slabs

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