Saturday, September 5, 2009
We're two-thirds of the way through wall building, getting ready for the final piece of the tryptic this week. Things have been going just about as well as we could have hoped for. One of the especially fun parts of the experiment has been the success of our multiple conveyor delivery system.
In the recently old days, rammed earth was built by mixing on the ground with a tractor bucket and rototiller, then transporting the mixed material to the forms and shoveling out of the bucket. Starting in the late nineties, in an effort to speed up production, we began using mix augers for proportioning and blending. After that we started designing and building articulated conveyor belts for moving material and dropping it directly into the forms. Each project gave us an opportunity for subtle improvements to the system.
At Terra's house we introduced for the first time a rotating delivery conveyor that mounts to a hub in the center of the building. The mixing machine drops onto a first conveyor which then takes material to a second conveyor which reaches over the formwork to the center of the building. The rotating conveyor spins on a "lazy Susan" and rides along the top of the wall form to deliver material right to where it's needed. No shoveling!
The rate of delivery is adjusted to match the speed at which the rammers can compact the material. At Terra's we're using four men on rammers and placing about five cubic yards per hour. If we had more people on rammers, we could double the rate of production.
To be sure, the equipment adds to the capital investment required for wall construction, but it improves the uniformity of the mix, increases the rate of production, and adds credibility to the process for engineers and building inspectors.
The photos in this post illustrate the conveyors, the mixing machine, and the team of rammers laying down the mix behind the rotating delivery conveyor.