Fly Ash Additive to Brick mix

Submitted by pregusay on Mon, 09/09/2019 - 11:56

Do you have any experience using the residue coming from coal fired electric plants?
We have an abundance of that here in our area which are being thrown away.
And one of the big power plants has allowed us to take it for FREE.

Would that be a suitable material to use in making the interlocking bricks?

If so, what would be a good ratio to start with?

Submitted by geoffrey on Tue, 10/09/2019 - 00:25


That is a great question.  Anything that we can do to reduce the use of OPC (Ordinary Portland Cement) is useful for the health of the planet.  OPC production is very energy intensive and responsible for a lot of greenhouse gas emissions:

" A single industry accounts for around 5 percent of global carbon dioxide (CO2) emissions. It produces a material so ubiquitous it is nearly invisible: cement. It is the primary ingredient in concrete, which in turn forms the foundations and structures of the buildings we live and work in, and the roads and bridges we drive on. Concrete is the second most consumed substance on Earth after water. On average, each year, three tons of concrete are consumed by every person on the planet. "

Using fly ash can partially replace OPC and still give a concrete that is as strong as one made with 100% OPC. 

" Typically, 15 percent to 30 percent of the portland cement is replaced with fly ash . . .  "

There are many more advantages to fly ash concrete; read the linked article to learn more. The curing time needed might be longer.

It is also possible to make a lime-fly ash mix.  You can test the strength of your blocks with a compression tester from the CVBT.

Just a couple of additional notes on mix design:  Make your blocks as strong as necessary for the application.  Interior walls might not need any stabilization (addition of cement).  A one-story building doesn't need blocks as strong as for a two-story building. You might find some information on different standards in

Compressed Earth Blocks Standards (CDI - CRATerre-EAG, 1998, 144 p.)

We hope you'll post the results of your production and construction here.