PVA fibers have been used for over ten years in Japan for tunnels and erosion control. PVA fibers have several unique characteristics that make it popular for shotcrete. First, the fibers can be used like steel fibers, eliminating the high labor costs required to hang rebar and welded wire mesh. Second, the soft fibers do not plug as easily as steel fibers. In addition, they cause much less wear and tear on the equipment. When spraying, operators worry less about rebound in their eyes or elsewhere. And when the concrete is cured, there are no sharp fibers sticking out to injure workers. After curing, there is no chance of unsightly rusting, a particular problem for retaining walls, drainage culverts and erosion control.
One environmental advantage that PVA fibers have over the lightweight plastic fibers like polypropylene is its heavier weight. The density of PVA fibers is 1.3, compared to about .91 for polypropylene. It is important in many mines to filter the fibers out of the equipment and the environment. This is done in water, so the fiber must be heavier than water so that it sinks out. Even nylon and acrylic, with a density of 1.1 can be a problem in some mines as the dirty recycled water they use has a density of about 1.1 or 1.15.
And unlike synthetic fibers like polypropylene, only carbon dioxide and water are produced when PVA fibers are burned. PVA fibers also provide a "sacrificial" fiber, allowing water vapors to vent during a fire, reducing the chance of explosive spalling.
Finally, there are no health problems with PVA. If burned, they produce only carbon dioxide and water.
For structural shotcrete with no steel reinforcement, we recommend 13 to 22 lbs of fiber per yard, (10kg/m3 to 13kg/m3 of RF4000/30mm) to ensure a long, crack-free service life. Mines with a short service life often use low dosages of fibers; the above recommendation is for permanent structures.
Our smaller PVA fibers can also be sprayed. The size of the fiber is related to the maximum size of the aggregate in the mix. Please call to discuss your requirements. |
|
PVA-reinforced shotcrete is widely used for repair of concrete damaged by cracking and spalling.
Elimination of steel reinforcement allows for quick application and design flexibility.
Tunnels reinforced with PVA fibers are safer, less expensive and easier to build. |
