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An Engineer's Dream

An Engineer's Dream

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    Conventional concrete breaks under flexural loading (above), while ECC merely bends under even higher pressure.

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    A mix design for ECC and regular concrete. In ECC, there are no coarse aggregates. Instead, very fine sand, fly ash, and microfibers are included.

In the example mix design below, no coarse aggregates are used. Instead very fine sand, fly ash, and microfibers are included in the mix. The amount, type, and size of these ingredients are tailored to match the requirements for synergistic interaction during excessive loading as described above.

As an example, the PVA fiber is especially tailored with specific length, diameter, strength, stiffness, and a surface coating to allow its gradual release so that premature fiber fracture is prevented. The resulting composite system develops a “give” at high tensile stress, which translates into a ductile yielding behavior not unlike that of the plastic yielding in ductile steel. The unique metal-like behavior of ECC in tension allows this material to meet demanding mechanical and durability requirements in structures.

Ideal for repairs

In addition to new structures, ECC has also been used in repair projects. These projects have demonstrated that the tensile ductility of ECC contributes to resistance to cracking and/or delamination often seen in failed concrete repairs.

This performance is consistent even after several years of freezing and thawing weathering cycles in cold climates. Recent experiments in the laboratory suggest that ECC can serve as an excellent concrete cover in protecting steel reinforcement from corrosion.

The cost of ECC is currently about three times that of normal concrete per cubic yard. However, a number of commercial projects in Japan and Australia have already demonstrated that initial construction cost savings can be realized when ECC is used through smaller structural member size, reduced or eliminated steel reinforcement, elimination of other structural protective systems, and/or faster construction offered by the unique fresh and hardened properties of ECC. When long-term cost and environmental impacts are accounted for, the advantages offered by ECC over conventional concrete become even more compelling.

ECC is a field-ready ductile concrete that has the potential to significantly contribute to the enhancement of infrastructure sustainability, durability, and safety. The material is currently emerging in the repair, manufactured product, precast, and ready-mix markets, as well as the bridge, pavement, agriculture, housing, and building industries.

— Victor C. Li is the E. Benjamin Wylie Collegiate Chair, Professor of Civil and Environmental Engineering, and Professor of Materials Science and Engineering at the University of Michigan, Ann Arbor. E-mailvcli@umich.edu.

For more information, visit http://ace mrl.engin.umich.edu, andwww.engineeredcomposites.com/.

The University of Michigan's Center for Professional Development offers Fundamentals of Bendable Concrete, a course developed and delivered by Victor C. Li, Dec. 5–7 in Ann Arbor. For more information or to register, visit http://cpd.engin.umich.edu or telephone Becky Erskine at 734-615-5698.