J. Heim, R.L. Vander Wal
Penn State University,
United States
Keywords: bricks, blocks, coal, plastic, construction, composite
Summary:
Advancing new markets for coal can enhance U.S. national defense security, bolster the nation’s energy and mineral security, enhance our nation’s environmental objectives and contribute to America’s economic prosperity. Given that the market price of coals is currently around ~$0.04/kg, there is a clear economic incentive to use available U.S. coals to derive high-value products from them. A preliminary cost model for CBBs projects a competitive price compared to clay and cementitious products (~ $1 - $2 per unit) while offering technical superiority. Coal or coal by-products can be incorporated into novel materials for the purposes of improving performance, decreasing costs, or both. Coal-derived composites can have mechanical, thermal, and electrical properties that can produce new types of building materials or produce superior versions of existing building materials. When compared to the current state of the art, coal-derived building materials should possess equivalent performance at a lower price or possess properties that are superior to existing building materials. This project evaluates the ability of coal-based bricks to compete on price and quality, identifying competitive strengths and limitations. Market attractiveness will be assessed based on market size, market growth rate, required attributes and competitive strengths of the coal-based bricks and blocks (CBBs). A useful attribute of thermoplastics as binders is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Advantages include low cost, availability, binding ability and processability. Tests demonstrate good compatibility between matrix and anthracite coal without requiring surface modification of the anthracite. Methods of fabrication using hot press molding and extrusion. Composites are evaluated according to a design-of-experiments (DoE) approach. DoE variables are a) relative weight fractions of binder and total coal fines, b) relative proportions of large versus small (milled) anthracite size fractions and c) additive percentage. CBBs are evaluated for compressive strength, modulus of rupture (flexure test) and water absorption per ASTM C67 with density by the Archimedes drainage method. Fractured interfaces are examined by SEM to resolve fracture dynamics and interior microstructure uniformity. These results serve to identify the binder and relative weight percentages for optimum strength, density and porosity – each assessed based on the DoE results. At each fabrication stage reference composites will be fabricated without coal (or carbon black) as reference points to assess property gains of the coal-based composite. CBBs possess strength comparable to clay-based bricks but are no permeability and are hydrophobic, hence resistive to degradation by freeze-fracturing and efflorescence. TEA analyzes both technical and economic details for the CBM bricks. Economic analysis includes capital and operating cost estimates over equipment service life. Notably CBBs do not require the high temperature calcination to produce cement, nor do they require the 3-day firing as do clay brick equivalents. Hence, they have a far lower projected energy cost and CO2 footprint. TEA analysis reflects this reduced energy cost while a comparative CO2 emission analysis quantifies the reduced environmental footprint to project economic advantage as dependent on a future carbon tax.