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Sustainability | Certification | Green Concrete | Sustainability Committee | Building Codes

 

Green Building Rating Systems, EPDs and Concrete

 

Sustainable rating systems such as LEED, Greenglobes, and Envision are developed to provide independent assessment standards that evaluate the performance and sustainability of buildings and infrastructure. While each rating system may favor certain strategies over others, there are similarities when evaluating building materials. Three measurements of materials predominate: Reduced embodied energy and carbon footprint (often stated as Global Warming Potential (GWP) in units of CO2 equivalents); reduced resource depletion (including increased recycled content); and transparency in reporting environmental impacts.

Reduce Embodied Energy and Carbon Footprint

 

Embodied energy and carbon footprint calculations consider the following:

 

- Pre-use Phase - Initial embodied energy involved in the acquisition, processing, manufacturing and transportation of building materials during the construction phase calculated within the boundaries of Cradle-to-Gate (factory gate) or Cradle-to-Site (factory gate to construction site);

 

- Use Phase - Maintenance, repair, restoration, refurbishment or replacement of materials, components or systems during the structure’s life span;

 

- End-of-life Phase - Demolition energy in the destruction, removal, and recycling of building materials.

 

For the past several decades, embodied energy and carbon footprint in building materials has been studied by researchers interested in the relationship between building materials, construction processes, and their environmental impacts.  As the life span of the structure increases, the ratio of the initial embodied energy to total energy decreases and becomes less significant in comparison. Therefore, efforts to minimize embodied impacts must consider strategies to increase durability and service life. The embodied energy and carbon footprint of a concrete mixture generally decreases in inverse proportion to its cement content. For example, it is estimated that for every 1% replacement of cement with fly ash, the embodied energy of concrete is reduced by approximately 0.7% (Marceau, 2007). Similar reductions can be assumed for other supplementary cementitious materials (SCMs) such as slag cement and silica fume, although to a lesser degree. The reduced portland cement content in High Volume Fly Ash (HVFA) concrete mixtures and other mixtures with high volumes of other SCMs offers considerable benefit toward reducing the embodied energy and carbon footprint of concrete.

Reduce Resource Depletion
 

The global population currently stands at seven billion people, and is predicted to rise to more than nine billion by 2050. The growing middle class, especially in China, will drive demand for consumer goods and infrastructure, not to mention the energy needed to produce them, to levels unheard of in human history. This economic development is hampered by limited natural resources of an effectively closed system like planet Earth.

Depletion is not a process of simply "running out" of a resource, but instead is a complex process of technological change and adaptation. This adaptation can leads to development of new resources, which are often lower quality, more costly to process, or more difficult to access. Green rating systems attempt to stem this depletion of materials within a broad context of resource conservation strategies. These typically include:

 

- Reduced Construction and Demolition Debris

- Material Reuse

- Recycled Content

- Regional Materials

- Encourage use of rapidly renewable materials

- Sustainably sourced materials

While much attention today is being focused on climate change, the other pressing issue of resource depletion has taken a back seat since the early days of promoting reuse, reduce and recycle. Fortunately, the use of fly ash and other industrial byproducts such as slag cement and silica fume, concrete can address both of these concerns. SCMs not only reduce carbon footprint but also conserve resources since they can replace a portion of the cement in concrete which requires considerable natural resources and energy to produce.

Transparency of Reporting Environmental Impact
 

There is a movement towards transparency in reporting the environmental impact of building materials and products through the use of Environmental Product Declarations (EPDs), a science-based, comprehensive disclosure of a product's environmental impacts based on a Life Cycle Assessment (LCA). EPDs are rapidly becoming the key component of the material selection process in sustainable rating systems, particularly in the building sector.  The EPD declares environmental impact measures such as:

 

- Primary Energy Consumption
- Resource Depletion (e.g. Water Use)
- Global Warming Potential
- Ozone Depletion
- Acidification
- Eutrophication
- Photochemical Ozone Creation/Smog

The focus on transparency also helps disclose to the end user about chemicals or hazardous materials they should be concerned with and if raw materials are extracted in an environmentally sustainable way. Generally, the use of SCMs helps reduce the environmental impacts of concrete and those reductions will be reflected in an EPD.

References


Marceau, M. L., Nisbet, N.A. and VanGeem, M.G. (2007). Cycle Inventory of Portland Cement Concrete, Portland Cement Association, Skokie, IL, 2007.

 

NRMCA Sustainability Initiatives

NRMCA EPD Program

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Sustainability Related Courses

 

Sustainability | Certification | Green Concrete | Sustainability Committee | Building Codes

 


 

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