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Technical : Properties : Mixing
Mix instructions for PVA fibers
1) After mixing the concrete, the desired volume of RF4000x30mm should be added gradually into the mixer over a period of 2 minutes. For large amounts, the rate of addition should be 22 lbs. per minute.
2) After adding the desired amount of fiber, continue mixing for at least an additional 60 seconds.
When working with a cement truck, add the fibers on site gradually, then add any admixtures that are normally added on site.
KURALON™ RECS 100L x 12mm (for mortar and concrete)
Mix cement and sand for 30 seconds. (Fly ash and silica fume could be added here as well.) Add water, superplasticizer and air entraining agent. Mix two minutes. Add fibers gradually and mix for an additional two minutes or more. (Check fresh sample for even distribution without clumping.)
KURALON™ REC 15 x 12mm (for mortar)
This fiber requires more careful mixing than other PVA fibers. High shear mixers are highly recommended. Biaxial, or planetary mixers are preferred. For test batches, the options include a drill with mixer attachment or Hobart/heavy-duty kitchen mixer with dough hook. If using a traditional mortar mixer, pre-wetting fibers can help with dispersion. (Mix with a small amount of the water already measured for use in the mortar.) In addition, Class D fly ash from 25% to 66% as a replacement for the equivalent weight of Portland Cement is recommended for mixing, workability, finishing and final product quality.
Mix cement and sand for 30 seconds. (Fly ash and silica fume--to replace 10% of cement--could be added here as well.) Add water, superplasticizer and air entraining agent. Mix two minutes. Add fibers gradually and mix for an additional three minutes or more. (Check fresh sample for even distribution without clumping.)
For PVA-ECC: (highest strength) refer to separate instruction sheet for mix design. Strain-hardening is optimized by use of an engineered mix design.
Quantities to use:
The RECS100x 6 or 12 are the preferred fibers for plastic and drying shrinkage crack control and can be used as structural fibers as well. Here are some guidelines:
Plastic shrinkage cracking 0.05 - 0.1% volume/ or between 1.1 lbs. and 2.2 lbs. per yard for mortar or concrete.
Plastic and drying shrinkage cracking 0.2% volume/0.12% by weight, or 4.4 lbs. per yard for mortar or stucco. 1.6 to 3 lbs. per yard for concrete, depending on aggregate size and mix design.
Structural reinforcement 0.5% to 2% volume or 0.3% to 1.2% by weight for mortar or stucco.
Sample mix design for structural stucco/mortar:
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Metric
Addition of fibers to mortar or concrete will cause a reduction in slump. To maintain consistent compressive strength, do not add water to improve workability. Any standard superplasticizer / water reducing agent such as methylcellulose should be used to attain the desired slump.
Studies have shown that replacing 15% of the Portland cement binder with fly ash improves the performance and workability of PVA fibers.
Precise mix designs and mixing instructions are available upon request.
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