What would you build a house with? A technical report published by ISTC claims that the ash produced from biomass gasification can become bricks and concrete. The result for cement companies, according to their report, could be a savings for nearly $155,000 per year in inputs and transportation costs (if 20% of their cement substituted the ash). The ash provider would also save just over $100,000 on landfill fees.
Coal ash is used as an input in brick and concrete making. It's high lime content and any unburned carbon in the ash add to the self-cementing and high temperatures needed to create building materials. Biomass conversion in the U.S. continues to grow (between 2002 and 2013 it grew 500%), as does the volume of the resulting ash.
It sounds good, and could be beneficial to many--especially because coal ash is the largest type of waste created in the U.S. Does biomass gasification-derived ash have unique properties that differentiate it from coal ash? Does it behave any differently?
Critics have charged that recycling of fly ash in concrete building materials is dangerous because it offers inferior structural capability and may result in indoor air contamination due to leaching chemicals or caustic reactions with other materials. Variances in the chemical composition of fly ash from different sources compounds the problem by making it difficult to assure the proper strength of the final concrete products.
According to the report, 5-18 percent BGA replaced clay and shale in brick-making, with the best results replacing 5-10 percent. The bricks were lighter in color and weight, but still met ASTM standards for compression strength. In other words, it's an acceptable substitute for coal ash. But what about the leaching problem?
Long ago, I remember hearing about fly ash being used in China for construction. The results weren't good. People abandoned their homes, I learned, because of the unexpected staining inside their homes due to the leaching. The ash also affected indoor air quality. This is still an issue that is ripe for innovation.
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