This Small Business Innovation Research Phase I project aims to manufacture a masonry building block from materials that could radically improve the environmental profile of one of the most common construction products on the planet. The research will investigate the feasibility of using engineered alkali-activated soil blends to promote geopolymerisation in the presence of nanoaluminosilicates using a novel manufacturing process. The specific fine particle components, specifically clay minerals, micas and feldspars, are commonly found in soil and recycled materials from commercial aggregate and quarrying operations. The intellectual merits of the project include a deeper understanding of geopolymerisation in the presence of nanoaluminosilicates, the measurement of the structural capabilities of engineered soil blends composed of these materials under extreme compaction, and the ability to utilize a wide range of natural soil sources to produce durable, structurally-stable masonry products. The anticipated result is an environmentally-sustainable stabilized earth building block, with equivalent performance to traditional concrete blocks, but with a reduction in embodied energy by as much as 90% due to the total elimination of energy-intensive Portland cement binders.
The broader impact/commercial potential of this project is the potential to transform traditional cement-based masonry products on a global scale. The product will meet a clear market need for sustainable materials in both the US and global construction marketplace. The elimination of traditional ordinary Portland cement (OPC) in masonry blocks will provide valuable social and environmental benefits to the public in the form of reduced carbon dioxide (CO2) emissions, increased economic activity, and improved public health. Approximately 8 billion concrete blocks are manufactured in the US annually to support construction activities, requiring the use of 15 million metric tons (MMT) of OPC. The manufacture of this cement emits approximately 14 MMT of CO2, which represents 0.25% of the 6,000 MMT of industrial CO2 emissions overall in the US. The use of soil, a ubiquitous, innocuous and unlimited resource, as the principal component of stabilized earth mix designs, promises the possibility of sustainable cradle-to-cradle environmental performance over a full product life cycle. From an economic perspective, green construction, which is projected to reach $96-140 billion by 2014, is the fastest growing segment of the construction market, which itself is a key driver of the national economy.
The research performed by Watershed Materials, LLC during the SBIR Phase I Program has successfully demonstrated the feasibility of using commonly-occurring, natural aluminosilicates from recycled, quarried soil products to produce geopolymers that exhibit reliable mechanical performance without requiring the use of ordinary Portland cement (OPC) binders or supplemental cementitious materials (SCMs). The objective was to reduce the environmental impacts of manufacturing masonry blocks while achieving reliable mechanical performance. Concrete Masonry Units (CMUs), the technical term for a common concrete block, are ubiquitous unitized masonry building materials that contain between 10-16% cement by weight. In 2007, 8 billion CMUs were produced in the US, requiring the use of approximately 15.2 million metric tons (MMT) of cement. This represents approximately 30% of the 45 MMT contributed by the manufacture of cement for all uses in the US (US EIA, 2009). The leading method for reducing the environmental impact associated with concrete materials is to replace a portion of the OPC binder constituent with SCMs. Toxicity is the most pressing issue with respect to SCMs derived from industrial byproducts (Glazer et al. 2011,Qijun et al. 2005, Rankers and Hohberg 1991, Min-Hong et al. 2001), though inadequate supply of conventional SCMs in proximity to the greatest demand presents another problem (U.S. Geological Survey Cement, 2012, American Coal Ash Association 2010, World Steel Association 2010, ACI 234R-06 2006). Fly-ash availability around the country follows the same pattern as the distribution of coal-fired plants from which it is derived, resulting in uneven geographical availability; finally then, the widespread utilization of fly ash as an OPC substitute could effectively subsidize coal-fired electricity generation, which is currently responsible for 20% of the world’s total Greenhouse Gas (GHG) emissions, as fly ash is transformed from a liability to a co-product that can be sold at a profit (Oliver et al. 2012). The geopolymerization of aluminosilicates has been studied for over half of a century because of its potential to provide an alternative to OPC stabilization of concrete (Pacheco-Torgal et. al. 2008). Extensive literature explores the principal factors affecting the alkali activation of kaolin and metakaolin, the use of supplementary cementitious materials and, to a lesser extent, the application of feldspars and zeolite-type minerals to produce geopolymer concrete (Lemougna, 2011). By contrast, comparatively little information is available about the stabilization of soils with geopolymers, and minimal work has been done to date to investigate the use of geopolymer stabilizers in compressed soil systems (Cristelo, 2012). The NSF SBIR Phase I research conducted by Watershed Materials extends existing scientific understanding of metakaolin and fly-ash to explore the feasibility of using geopolymerization of aluminosilicates found in natural soils to produce a new class of environmentally friendly masonry building materials. The challenge of producing durable geopolymer materials using natural aluminosilicate minerals of low reactivity, in comparison to the SCMs typically required for effective geopolymerization, was overcome through both chemical and physical means: by promoting nucleation in the geopolymerization reaction (chemical), and through the application of proprietary dynamic compression (physical). Two types of nanoparticle additives, crystalline and amorphous, were found to be effective nuclei seeds in promoting geopolymerization. The addition of 4% wt. calcite (a crystalline aluminosilicate) and 0.25% wt. amorphous synthetic nano-aluminosilicate (having a silica-to-aluminum ratio of 2) rendered 60% and 80% compressive strength gains, respectively. Incorporating a dynamic compression component into the production of test specimens resulted in increases in density, reductions in absorption and significant increases in compressive strength greater than 25% for all mix designs and moisture contents tested. The combination of these two strategies lead to production of test specimens with compressive strengths of at least 1900-psi after 7 days of curing at 90oC, meeting minimum strength requirements of concrete blocks following ASTM standard C90-13. Two additional strategies were identified in the research for increasing the compressive strength of test specimens, allowing for the use of reduced curing temperatures (high-temperature curing being suboptimal in large-scale production applications). These strategies were: i) reducing the clay content of the mix design and ii) combining low moisture contents and proprietary dynamic compression techniques (resulting in increased densities). The resulting specimens experienced an increase in compressive strength (up to 2600 psi) and a decrease in water absorption (down to 9.7 pcf, well below maximum allowable absorption requirements for concrete masonry units following ASTM standard C90-13), while the curing temperature was reduced from 90oC to 65oC. This verification of the feasibility of achieving geopolymerization using natural aluminosilicates found in soils represents a significant finding, as it demonstrates a means of producing durable masonry products not only in the absence of ordinary Portland cement (OPC), but in the absence of supplemental cementitious materials or highly-reactive aluminosilicates (e.g. fly-ash. ground granulated blast furnace slag), replacing these energy-intensive, limited (and in some cases, potentially toxic) materials with abundant, inexpensive, natural resources.
