Tuesday, 12 May 2015

Rammed Earth Strength Test Results

Welcome to our blog that follows up with our cylinder ramming test results.  The test cylinders we were ramming have been crushed by Levelton Consultants in Langford BC. 
Read on to view the results from the consultants and my opinions on what the implications are for building with rammed earth.

These compression results are comparable to concrete.  While we do not have data for other strength properties such as tensile strength it is fair to say that by using proper mix designs and implementation, rammed earth will perform as well as concrete in compression scenarios.  Interestingly, rammed earth that has a high compressive strength is generally very dense, and because of this it will weather well when exposed to the elements.
The technologies that were developed for the craft of working with concrete such as anchoring, sealing, adhesives, admixtures, mortaring, sawing, drilling, and even hanging a picture, all work just as well with rammed earth.  I believe rammed earth is the only truly green building technology that can piggy back on this huge inventory of tools and techniques developed by the concrete industry.
I will now break down the mix so we can see what modern rammed earth contains.  The mix designs  that were tested contain mostly subsoil aggregates and sand from locations that are less than 25 miles from the building site.  The binder that holds the rammed earth together is a combination of cement powder and fine particles and clay present in the sand and aggregates.  Replacing Portland cement in the mix with greener CSA cement is an ongoing fascination of mine.  While CSA is more expensive than Portland cement it has many advantages over Portland cement.  CSA cements are stronger than Portland cement.  CSA requires less heat energy during manufacturing.  Less heat means a savings in the amount of greenhouse gases produced during manufacturing.  Also in the mix are recycled blast furnace by-products and pozzolans.   By including hydro-phobic admixtures we can limit moisture migration in the structure as well as “rising damp” from the footing into the living space.

Sand and aggregate
Gravel Pit
Structure and strength of the mix
Local, inorganic, cheap, abundant, durable
Cement distributor
Binder to “glue” mix together
Less than ½ of that required for concrete
Blast furnace slag
Cement replacement
Redirects landfill bound by-product, replaces virgin Portland cement powder
SBA proprietary admixture
SIREwall of Saltspring Island BC
Repels water
Prevents rising damp and moisture migration
Crystalline admixtures
Promotes internal crystalline growth to mitigate unwanted moisture
Prevents rising damp and moisture migration

In conclusion, rammed earth can be very strong, especially in compression loading scenarios such as load bearing walls.  This strong rammed earth is also able to withstand the elements.  The materials in rammed earth are abundant and available locally which eliminates a lot of the transportation required for other building materials.  Rammed earth can “piggyback” on a lot of existing concrete practices and technologies.  Specific admixtures in the rammed earth repel moisture and prevent moisture migrating upwards or through the walls into living spaces.
Thanks for following this blog on mix design and the strength of rammed earth and be sure to check in next time for a blog about redesigning the flat roof into a really cool metal roof with hidden gutters and drainage.

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