CIFE 2009-2010 Seed Project:
Sustainable Design and Manufacturing of Prefabricated Durable Infrastructure

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Our Built Environment Lacks Sustainability

The ongoing push for more sustainable living has the engineering world searching through each and every area of expertise for sustainably inefficient technologies to improve upon. Today's built environment presents such an opportunity. The United States commits billions of dollars each year to building projects that involve unacceptably high life cycle costs.  Not only do current practices waste building material and cause costly delays, but the resulting buildings lack durability.

Previous attempts at solving this problem took a small step in the right direction but did not do enough.  Current precast concrete technologies cut back on waste and on-site quality control issues because the elements are fabricated in a factory under strictly controlled conditions. These elements involve some degree of on-site concrete casting, however, which introduces waste and makes replacing of the elements very difficult. In addition, these prefabricated concrete members almost exclusively comprise traditional reinforced concrete technology which is notoriously undurable.

Placement of Precast Element
Placement of Precast Concrete Element

The answer to this problem clearly needs to involve a few important features. First, it must incorporate the same benefits of manufacturing current precast concrete technology elements. Second, it needs to develop an innovative method for placing the precast elements, such that the assembly is waste-free and allows easy repair.  Finally, the answer to the durablity problems of the built environment must address the durability of building elements themselves.  The answer that this project will investigate is the design and implementation of prefabricated, bolt-together concrete elements made from engineered cementitious composite (ECC).

ECC Bending Test
ECC Bending Test

Prefabricated, reusable, bolt-together ECC building elements provide a possible solution to the problems experienced with current building technology. These ECC elements would be manufactured in a factory environment, allowing for not just minimal waste and stringent quality control standards, but also for the development of a number of standardized shapes available for interchangeable use in many different projects. Bolt-together elements would take much less time than cast-in-place concrete to construct, and therefore cut down-time to a bare minimum period for hoisting and bolting elements. In addition, the bolt-together capacity of the members would allow for damaged elements to be easily replaced and potentially reused elsewhere, again with limited down-time. The ability to bolt together concrete sections is only possible through the use of ECC - a concrete material with a tremendous tensile strain capacity that allows the reversed loads experienced by a bolted member under structural forces. ECC also provides the individual elements (and therefore the entire structure) with greatly improved durability, which also arises from the tensile characterisitics of this material. These elements obviously have great potential, but their development requires the use of a framework that considers all of the levels of work that contribute to the ultimate goal of a more sustainable built environment.

SIMSS Paradigm
SIMSS Framework

The Sustainable Integrated Materials, Structures, and Systems (SIMSS) design approach focuses on all of the different factors that go into every level of a system and considers the influence of all of these factors when trying to improve upon the system. For example, an improvement in the material properties causes the durability of the elements to improve, which improves the durability of the system as a whole. This design philosophy also considers the sustainability of the options for the system design and, using the principles of Life Cycle Analysis, allows for a quantifiable ruling on whether a certain design decision is sustainable or not.

The cornerstone of this work will be Engineered Cementitious Composites (ECC) technology. ECC technology uses polymeric fibers and specifically tailored cement matrix cracking characteristics to produce a very ductile material. The material's tensile characteristics make it more like metals in this regard than other concretes.  At the same time, ECC uses mostly traditional concrete mix materials. Without this technology, the proposed work would not be possible.

Funding Agency:

Stanford University Center for Integrated Facility Engineering

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©2010 M. Lepech

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