Guest post by Alex Wright of Watershed Materials, the company who’s making geopolymer concrete blocks out of waste clay materials. We’ve covered their exciting development in two previous blog posts. This article focuses on their rammed earth block machine.
“Watershed Materials is pioneering a new machine platform to produce high strength masonry with less – potentially zero – cement from a wide range of aggregates including recycled or repurposed waste from quarries, mines, construction site excavation, and even recycled concrete. Until now, structural masonry has been made with one of two types of machines – either high production volume concrete block machines made by companies like Besser, Columbia, and Tiger or low production volume, relatively unsophisticated compressed earth block machines. Watershed Materials new masonry machine platform is intended to bridge the two and mass produce high quality, building code compliant masonry from natural aggregates and using far less cement.
High volume concrete block machines are designed with two goals – filling the molds evenly with the low slump concrete mix and then producing block as fast as humanly possible. The largest machine that Besser makes can crank out 3,240 block per hour. However, all of the strength of concrete block is provided by the cement content, so the manufacturing process has little to do with the final strength of a concrete block. Watershed Block’s masonry machine technology fundamentally changes this. The Watershed research team found that by applying intense compressive force in the manufacturing process, cement content could be reduced significantly. However, an entirely new machine platform would have to be designed, as the machine platforms used by concrete block manufacturers offer no compressive function.
Existing compressed earth block machines also apply compressive forces in the manufacture of low cement, natural aggregate masonry. However, Watershed Materials needed far more compressive force to produce block that could meet stringent building code requirements. Many traditional compressed earth block machines produce masonry with compressive forces between 400-800 psi. The ASTM C-90 specification for concrete block requires 2,000 psi. So improvements to the manufacturing process and the mix design were required to achieve that high level of quality.
With support of the National Science Foundation, Watershed Materials has redesigned from the ground up a new platform for making high strength masonry using natural aggregates and reduced cement content. The final performance of the masonry – including compressive strength, wet-dry durability, linear shrinkage and other factors – is determined by the manufacturing process itself as well as the control over the mix design of the input materials. In the manufacturing process, Watershed Materials has found that ultra high compaction [and high frequency vibration] has a significant impact on final performance. Variables in mix design require close attention to detail in the screening and analysis of input feedstock. When the two work together, beautiful, durable high performance masonry that meet US building codes can be manufactured with lowered cement levels.
Watershed Materials is also working on geopolymer mix design technology that will allow for zero cement masonry to be produced using the same machine platform. The geopolymer technology is not market ready, but early tests have indicated very high compressive strengths with no cement, no fly ash, no blast furnace slag, and no metakaolin. In place of these highly processed sources of silica, Watershed Materials has found a way to activate natural clay minerals as a source of silica for geopolymer reactions.
Watershed Materials masonry manufacturing machine platform is still in development but should be market ready next year. If you’re interested in being notified when the machine platform is developed, please fill out the second form on the contact page here: http://watershedmaterials.com/contact/
*It’s exciting to note that earth blocks by Watershed Materials could be a huge game changer, a very serious competitive threat to the concrete industry, because they use ultra low cost waste products like crusher fines from abandoned quarries. In comparison, concrete products use virgin mined aggregates that cost significantly more. Plus, we all know cement manufacture requires an enormous amount of energy for the kilning process. That energy doesn’t come cheap. It’s also a major cause of environmental damage. Watershed Materials earth blocks don’t require kilning or massive amounts of energy to manufacture. Combine these two advantages – lower cost raw materials and lower cost production – and it’s easy to see how they’re eventually going to be a major threat to the concrete industry. The tipping point is developing a machine that can produce block as fast as concrete block.