engineered cementitious composites

ECC incorporates super fine (100 microns in diameter) silica sand and tiny polyvinyl alcohol-fibres covered with a very thin (nanometer thick), slick coating. ECC has a strain capacity of 3%, regular concrete has a strain capacity of 0.1%.

ECC: a ductile concrete that does not use coarse aggregate and does include a coated network of fine polymer fibres within the cement that allow it to slide under stress, so no irreparable breaches, just thousands of fine cracks, dusted with cement, that self-repair with water.  

Engineered cement composites were developed at the University of Michigan by Victor Li in the early 1990s.  Although fibre reinforcement comes in many modes; the ECC uses micro-scale (10 micron) fibres that actually bond the cement within the concrete. They introduce a plasticity that allows the concrete to deform rather than break. In a paper by Victor Li, the abstract states: Engineered Cementitious Composites (ECC) is a material micromechanically designed with high ductility and toughness indicated by multiple micro-cracking behavior under uniaxial tension.

Neat.  Apparently ECC is of great use in bridge repairs where there is an incompatibility between old concrete under stress and new normal concrete patched in, which is both shrinking and calcifying at a different rate, introducing weakness at the old/new interface.  ECC's flexibility – its internal slipperiness – does not allow it to shrink and crack.  And in  2003 in Japan where most of the applications seem to be, it was sprayed in a 20mm layer over 600m2 of the aging, cracking, leaking and spalling Mitaka Dam.

To add to all of this wonderfulness is that its life cycle costs are lower than conventional concrete (tested on bridge deck systems: agency costs – material, construction, and end-of-life costs, plus social costs – emissions damage costs from agency activities, and vehicle congestion, user delay, vehicle crash and vehicle operating costs. These costs were estimated across all life-cycle stages (material production, construction, use, and end of life) over a 60-year analysis period.)

At 40 times lighter than conventional concrete, and with its bendiness, clearly it is headed towards earthquake zones, which perhaps is why it is well-deployed in Japan.  Life cycle costs can be misleading: although over a 60 year period it might be less expensive than ordinary concrete construction, I'll bet those little polyvinyl alcohol fibres with their slidey nano-coating cost a bundle, and are inaccessible to most of the people so devasted, and so regularly, by earthquakes.