Joe Neuer of Neuber Concrete, Kimberton, Pa., takes exception to the National Ready-Mixed Concrete Association's P2P program (which aims to change the specification of concrete mixes from prescription- to performance-based) when it comes to slab-on-ground mixes.
As a concrete contractor who specializes in high tolerance and super flat floors, I usually found the owner and general contractor to be ecstatic with the finished product on the day I poured and finished my floors. I would, in most cases, get paid in a timely manner. But about half the time, anywhere from 6 months to a year later, the floors would show excessive curling, cracking, shrinkage, and sometimes joint rocking. I was beside myself trying to figure out what to do to get the long-term characteristics of my flatwork to be similar to the day I poured it.
Narrow-strip concrete placements are the industry standard for narrow-aisle, defined-traffic warehouse slabs. To meet the tight flatness tolerances, usually Fmin 50 to 100, contractors perform narrow-strip construction by setting edge forms 14 to 20 feet apart and striking off the concrete with a vibratory truss screed.
