September 1999

Wire mesh or steel rebar has long been used in concrete to improve tensile strength, stabilize adjacent slabs, and as a component of the grounding system for the control of stray voltage in animal facilities. In recent years there has been growing interest in the use of polypropylene fibers to improve the crack resistance of concrete. Polypropylene fibers are typically added to the concrete mix at a rate of about 1½ lb. ($6-$7) per cubic yard. While these fibers may be useful in some cases, polypropylene or similar fibers should be not viewed as a replacement for wire mesh or steel rebar.

Settling of poorly compacted fill and freezing and thawing of the sub-grade are a common cause of slab instability. Wire mesh is used to stabilize concrete by preventing cracks or joints from opening up or shifting vertically. Slab stability is important where materials are flushed or scraped and where pipes or heating cables are embedded. Fiber reinforcement has been shown to be useful in preventing small shrinkage cracks but is unlikely to provide the slab stability provided by wire mesh or steel rebar.

There are concrete applications around the farmstead where wire mesh or steel rebar may not be needed. Aggregate interlock and construction joints often provide adequate slab stability for sidewalks, basements, driveways and some pavements on a stable sub-grade. Fiber reinforcement may enhance concrete in these situations where wire mesh adds material and labor cost with little improvement in performance.

Fiber reinforcement can be used alone or with conventional reinforcement to enhance certain concrete properties, but it should not be used alone where wire mesh or steel rebar is needed to stabilize a slab.

Tim Harrigan

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