biocement: building with bugs

A lot of energy goes into manufacturing cement, which is a key ingredient in concrete. Since concrete is widely used in just about every country, strategies to reduce its embodied energy could significantly reduce greenhouse gas emissions related to the construction of buildings, bridges and other large-scale infrastructure. World Watch estimates that production of cement accounts for 5% of human-caused carbon emissions.

One approach to reduce embodied energy in concrete is to replace some of the cement with fly ash, which is a byproduct of coal-fired electric power generation. It's cheap and abundant, and also reduces the amount of water needed to make concrete.

Or, if you prefer the high-tech route, recent research has opened up an alternative.

Last year Murdoch University researchers [link requires site registration] developed new biotechnology capable of producing sandstone within hours, which could potentially revolutionise aspects of the construction industry. Bacterial solutions 'cement' material together by building up calcium carbonate or calcite, and strengths exceeding conventional concrete can be tailored to suit the application. Dutch funders GeoDelft are interested in using it for the construction of dykes, but there are many other applications.

From July this year, the Australian government is funding another research project, called "Carbonate Binding: An Ecologically Sustainable Alternative to Cement", to be carried out at the University of New South Wales:

Carbonate binding is a frontier technology that promises a new generation of advanced materials for applications in construction. Precast concrete accounts for a large and increasing portion of total concrete usage. Precast materials made by carbonate binding would offer several advantages over conventional precast concrete. The energy savings of a low temperature process with negligible greenhouse gas emissions would contribute immensely to the goal of an environmentally sustainable Australia. The reduced hardening period would offer substantial increases in productivity to manufacturers.

Using crystal growth on calcite particles for binding is not exactly new: organisms in coral reefs and elsewhere have been using carbonate binding for millenia. It's the attempt to harness the process that provides an opportunity to reduce the energy required to maintain and expand our human-built environment. If this can be done without significantly changing construction methods, then it should be relatively easy to adopt this approach. It remains to be seen whether it can be used on a large scale.

More info:

• Easy reading: For a great summary of embodied energy in different building materials, have a look at this Australian guide aimed at helping homeowners make decisions that will reduce the energy impacts of house construction or renovation. It also explains, in straightforward language, how embodied energy is calculated and why it's important.
• Slightly technical: If you like pretty pictures and mild intellectual stimulation, here are some photographic examples of carbonates.
• Highly technical: A detailed analysis of the use of fly ash as a replacement for cement in concrete.
• Off the chart: You might need a PhD to follow this explanation of how the creatures living in coral reefs rebuild their homes after a disturbance, using carbonate binding.