Sustainable Construction with Concrete: Is it Possible?

The Ecological Footprint of the Cement Industry

Procedia Economics and Finance found that the embodied energy in the materials used to build homes produces more greenhouse gasses than the emissions associated with the annual "use-phase emissions." Despite advances in the energy-efficiency rating of dwellings, the energy needed to build the home usually outstrips any potential efficiency gains related to the house's operation. The study discovered that the concrete used in building new homes is responsible for the largest share of emissions. 

The International Energy Agency estimates that cement production is alone responsible for upwards of 7 percent of global carbon dioxide emissions. Thus it makes the cement industry a significant contributor to global warming. In addition, cement production has an annual growth rate of 2.5% percent. It is estimated to grow from 2.55 billion tons in 2006 up to 4.4 billion tons by 2050. Without meaningful and far-reaching changes in how cement is produced, it is safe to say that the cement industry will continue to be a significant contributor to global warming.

Recycled Concrete

The United States produces around 317 million tons of construction and demolition waste each year; a large percentage of that waste is from concrete. While discarded concrete fills large amounts of landfill space, today, 38 states use recycled concrete as a sturdy road base. In Germany, 89% of concrete demolition waste is recovered and recycled. Cement cannot be separated from the concrete. But, by pulverizing concrete, it is possible to create a useful aggregate for future construction projects. Thus it will limit the need for mining other raw materials and reduce the stress on landfills around the country.

Carbon Negative Cement

Negative carbon cement is still a work in progress. But, promising companies are working toward developing cement technologies that can capture more carbon than they emit. One innovative company, Novacem, developed an alternative to traditional Portland cement. Whereas Portland cement is made from quicklime, the proposed carbon-negative cement product would be manufactured from magnesium oxide. This compound can absorb carbon dioxide from the air with the addition of water to the cement powder.

Novacem claimed that their product achieves cost and performance parity with traditional cement options. Not only does it pull carbon dioxide from the air, but it also purportedly uses much less CO2 during the process of manufacture. Whereas limestone has to be heated to 2,600 degrees Fahrenheit for cement production, magnesium oxide can be prepared for cement at 1,300 degrees. Novacem was purchased by an Australian mystery company, which they felt needed $50-100M in investment before going to market.

Recycled Plastic as a Reinforcing Agent

The vast majority of concrete used in construction requires some reinforcing agents. Steel rebar is the most commonly used product for this purpose. Steel production is an energy-intensive process that is also responsible for large amounts of greenhouse gas emissions. In Australia, students from James Cook University came up with an alternative reinforcing product that could potentially replace the need for steel.

They manufactured recycled polypropylene fibers from industrial plastic waste into reinforcing agents mixed with Portland cement. By replacing steel with this recycled plastic product, they reportedly achieved 90 percent savings on the overall CO2 emissions associated with steel reinforcements.

Earth-Friendly Concrete

The Australian company, Wagners, has created what they term an "Earth-Friendly" Concrete product. This cement alternative uses absolutely no Portland cement. Instead, it utilizes a geopolymer binding system. It is 100% sourced from two typical industrial waste by-products: blast furnace slag (from iron production) and fly ash (from coal-fired power plants). Wagners claim that the total carbon emissions associated with this cement alternative reduce carbon dioxide emissions up to 90 percent compared to Portland cement. Also, it has a much lower embodied energy rating because it is sourced from industrial waste products.

This earth-friendly concrete has moved beyond the planning stage. Over 51,000 square meters of heavy-duty pavement has been constructed at the Brisbane West Wellcamp airport for taxiing runways. Wagners report that close to 9,000 tons of CO2 emissions were avoided using earth-friendly concrete instead of Portland cement for this project.

Bottom Line

As technology continues to advance, more and more cement alternatives should continue to emerge. These new options will allow builders and homeowners to continue to enjoy the structural advantages that cement and concrete offer while also vastly reducing traditional cement's ecological footprint.