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ethics/ lighter side

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On the use of polypropylene fibers (Fibermesh being a specific company) as
temperature and shrinkage crack control in concrete, that is all we specify.
Anywhere WWF is used ONLY for this type of crack control, not for flexural
reinforcement, we have been specifying fibermesh. This is always for slabs
on grade, exposed or to be covered, interior and exterior. The reason being
after input from contractors, field supervisors, inspectors, and other
engineers, is that WWF is never placed correctly. As it comes out in rolls,
usually sitting on the site corroding away, and when they finally place it,
it is a wavy mess. I believe ACI recommends that for PROPER placement, it
should be placed at 1.5" from the top of the slab. From what I have
gathered, the WWF is usually placed on the grade, not on chairs, and when
the concrete is being poured a guy walks around pulling it up into the
concrete using a rake... not very exact, and not at 1.5", and probably not
doing what it needs to do. In fact, if it comes into contact with the earth,
which it always does, is that not just a path for the moisture to travel
through? In the end, does it not do more damage to the slab then help? I
believe so. Also, there is no room for error when they add fibers at the
plant, and the shrinkage reinforcement is evenly placed at every conceivable
angle throughout the slab. I would love to hear from other engineers or
contractors on their use of this type of product in lieu of WWF and any
issues positive or negative. Keep in mind that this is mainly for southern
climates with little regard to freeze/thaw cycles. Also the regular
placement of expansion and control joints are assumed. I do not know very
much about steel or nylon fibers.

Andrew Kester, EI

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