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Sustainability of Concrete



Although sustainability is a popular term, it remains an ill-defined and vague concept in the construction industry. Sustainability is not equivalent to recycling, something we are accustomed to performing daily by separating glass, plastic, and paper from other refuse. Even with the best recycling programs, it is sometimes difficult to understand the cost-benefits of these efforts.

There is no straightforward, simple definition of what sustainability means to the construction industry. Further, there are few tools or even metrics available to help decision makers specify one construction material over another in relation to sustainability. One reason for this is the sustainability of concrete, the most widely used material in the world, is still a difficult concept to quantify.

Most sustainability or green voluntary certification programs attempting to qualify sustainable materials have focused primarily on energy, material and water conservation; indoor environmental quality; and site selection and development. While these are all important aspects of sustainable building design and construction, lifecycle does not appear to be an integral part of this definition.

A ‘greener’ concrete is available with calcium sulfoaluminate (CSA) cement. This rapid-setting cement requires burning mixtures of limestone, bauxite, and gypsum at lower temperatures than portland cement—approximately 1482 C (2700 F) for portland cement versus 1232 C (2250 F) for CSA cement.

This lower burning temperature reduces the amount of energy and carbon dioxide emissions associated with portland cement production. CSA cement also requires less limestone, the primary source of carbon dioxide released during the chemical sintering process. CSA clinker is also easier to grind, which reduces the energy needed during the milling process.

Quantifying sustainability

When selecting a building material—asphalt, portland concrete, or CSA concrete—sustainability should be easily quantifiable. One method for assessing the sustainability of a construction material could be to divide its lifecycle by the amount of non-renewable resources required in its manufacturing process.

Using this method, a Sustainability Index would be defined as:

 Sustainability Index (S) = Lifecycle /Resources

“Lifecycle” refers to the durability of concrete, in years. It is linked to fatigue life and other material properties such as shrinkage, cracking, and porosity. “Resources” refers to the quantity of non-renewable resources used in concrete manufacturing (such as, but not limited to, carbon footprint). Finally, the Sustainability Index, as defined above, can have the unit of [yd3*years/ton-CO2].

In this equation, sustainability is tied not just to resources used but also to lifecycle. If the lifecycle of one-cubic meter of concrete were infinite, it would be sustainable. However, if the entirety of our planet’s resources were required to manufacture the same amount of concrete, it would not be sustainable. The Sustainability Index helps to quantify the sustainability of producing and using one cubic meter of concrete in simple, measureable terms.

This straightforward index can help rate the sustainability of various materials and mix designs and helps decision makers choose materials consistent with stated sustainability goals. The Sustainability Index brings lifecycle into the equation, and a greater lifecycle decreases the burden on resources.

CSA cement can play an important role in improving the sustainability of construction materials, mostly because its chemistry and materials science differ from the well-established standards of portland cement. It can play a significant role in the sustainability of concrete technology from the perspective of raw materials use, energy demand, carbon footprint, and pavement longevity.



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