Rammed Earth Testing - Small Samples

The decision on using Rammed earth for our house was dependant on the suitably of the soil on site (see material selection for the reasoning behind this). I had a strong suspicion that the soil could work from seeing the way the footpaths in the around here set into firm smooth surfaces with the passage of people and animals. The paths do not erode easily nor do they swell of crack with the cycle of wet and dry.  It is one of the qualities that makes mountain biking so enjoyable here in Rwink.   Further down the valley the soils are clay heavy and get stick when they are wet, then crack if they dry too quickly.

Earth Sample with metal tube rammer, showing the wood plug blocking the end, and the black pvc tube as a mold.

To investigate the suitability of the soil, I followed a few of the usual tests, many of which are well outlined in David Eatons Rammed Earth House. To begin with, a bucket-sized sample was taken from an existing hole on site and a simple sample mold was constructed from 50mm pvc pipe and a steel tube. The initial samples showed promise, but the mold was difficult to release. Paper and plastic sleeves were both tried as aids to remove the samples but as you can see from the image, there was a lot of damage.  After finding some pipe clamps in Kigali, the mold now has a split and can be used to produce full height samples.

From Left to Right: Hand molded ball, the first rammed sample showing extensive deformation from getting stuck, and then progressing toward the samples that were rammed using sleeves to help with releasing from the mold.

Even in their damaged state, the samples developed great strength after only a day of curing, and by the end of a week they were as hard as Sydney sandstone. This was good enough to try again with a larger sample.  Rammed Earth Testing - Large Sample