Sustainable Materials Development and Microstructural Tailoring

The goal of microscale research within this project is the development of new infrastructure materials which serve to maximize three sustainability indicators; social well being, economic performance, and environmental protection. The unique development process behind these materials is shown in the figure below. Schematically embodied below is the top portion of the integrated materials design framework for sustainable infrastructure (Process Loop “A”). This material design approach begins with an engineering and environmental evaluation of current raw material inputs and systematically replaces virgin components with industrial wastes or recycled materials. Once a small pool of acceptable replacement materials is defined which meet both mechanical and sustainability standards, microstructural tailoring of the material can proceed by engineering each material component, and the microscale interactions among them, for maximum composite performance. Finally, the finalized material properties are defined and matched with an appropriate infrastructure application demanding that exact mechanical performance, resulting in an efficient and sustainable use of materials for each chosen application.

Engineered Cementitious Composites (ECC)

While the above material development paradigm can be applied to nearly any infrastructure material, this study focuses on a unique cementitious composite called Engineered Cementitious Composites (ECC). This class of high performance fiber reinforced cementitious composites (HPFRCC) was developed using micromechanical design principles to achieve performance much higher than plain or conventionally reinforced concrete. Rather than forming cracks and loosing strength under tensile load, as in the case of concrete, ECC material performs similar to ductile metals like aluminum by strain-hardening, or “stretching” as higher load is applied. This allows ECC to be a very versatile component of many infrastructure applications, while proving very durable and extending the service life of infrastructure far beyond current expectations. The typical tensile load response for ECC material is shown below. For more information about ECC material, current applications and uses, or microstructural tailoring, please visit the Advanced Civil Engineering Materials Research Laboratory website at http://ace-mrl.engin.umich.edu/NewFiles/projects/env_proj.html

Green ECC Development

Using the materials development paradigm developed above, along with established micromechanical design guidelines, a number of new ECC mix formulations have been developed which incorporate significant amounts of industrial waste products. These waste products have displaced most of the virgin materials, making these ECC versions some of the most advanced sustainable infrastructure materials currently being developed. Waste materials which have been investigated thus far include waste fly ash from coal fired power plants, blast furnace slag, post consumer carpet fibers, waste foundry sand, shredded office machine waste, waste polystyrene beads. Each of these materials underwent preliminary micromechanical, chemical, and environmental impact analyses to determine if they were acceptable component materials for ECC. Following preliminary analysis, a number of these wastes, including fly ash, waste foundry sand, and post consumer carpet fibers, have undergone further micromechanical study. The outcome of these studies have resulted in highly tailored versions of ECC material which are perfectly matched to individual infrastructure applications depending on the required mechanical performance.

In addition to matching specific versions of green ECC material to current infrastructure applications, material selection charts, similar to those developed by Ashby, are also being developed. An example of one of these charts is shown below. This will allow designers to simply select a version of green ECC which maximizes sustainability indicators while still meeting all of the necessary engineering (i.e. mechanical and structural) demands of the infrastructure system. For more information specifically on Green ECC development within this NSF grant, please visit the MUSES portion of the Advanced Civil Engineering Materials Research Laboratory website at http://ace-mrl.engin.umich.edu/NewFiles/projects/env_proj.html

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