Thoughts on the Engineering Industry

A blog covering engineering, technology and business topics

Concrete without Cement: Creative Usage of Other Materials in Concrete

Hello, I hope everyone is doing well. There isn’t anything new going on with me – just the usual stuff.  I am finally making progress on the graduation paperwork which is good.  It would be nice to officially finish my school stuff.  Today I want to talk to you about an article I read about a structure made with concrete mix that doesn’t use cement.

This is the link to the article: http://goo.gl/7z0B7f.

The building being discussed is the Global Change Institute (GCI) building for the University of Queensland.  In trying to achieve better sustainability, Hassel in collaboration Bligh Tanner, Arup, and Medland Metropolis has used a what they call a geopolymer precast concrete which replaces cement with fly ash.  The brand name for this mixture is called Earth Friendly Concrete (EFC) and was applied in 33 precast floor beams of the GCI building.  The mixture is comprised of sand, aggregate, and a binder containing blast furnace slag and fly ash.  The removal of cement greatly reduces the carbon dioxide emissions in the creation of the concrete as a whole.  In order to further increase their sustainability, hydroponic pipes were added to the floor beams as well to improve low energy and passive cooling modes.  Bligh Tanner’s director believes this will improve the carbon emissions created by the cement production, estimated to currently be 8% of the carbon emission in construction projects.  Before this, EFC has only been used in low level applications such as ground bearing pavements and masonry blocks.  The concrete also has faster curing times which decreases production and construction costs as well.  The different chemistry also has the following benefits: low shrinkage, low heat of reaction (reduces thermal cracks), 30% higher flexural tensile strength, and higher durability.

This sounds like a good innovation in concrete design in regards to carbon emission reduction.  Blast furnace slag and fly ash have been used a long time in the creation of concrete to improve cost and production efficiency since the most difficult material to create for concrete is cement.  Along with that, there is the benefit of making use of waste from steel production plants and coal fire power plants.  However, I worry about the lack of history with the usage of this material.  Over the lifetime of the structure, we don’t know how well the binder will hold up.  Also, there might be other issues with chemical reactions over time due to elements in nature.  It has taken lots of studies and years of observations with regular concrete to discover and address the chemical issues such as salt.  Upon further research, I have also read that concrete mixtures with fly ash has been shown to have higher occurrences of sulfate degradation.  In light of these unknowns, caution should be used in my opinion.

What is your opinion on this new concrete mixture? Have you heard or read about anything else like the innovations mentioned above?  I am also rusty on my chemistry in regards to concrete, is there anything else that needs to be considered in analyzing the possible chemical degradation issues? Thank you for your time and have a good week!

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