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Q. How should the appropriate fiber be selected for a specific application, and how is fiber dosage determined? A. The selection of fibers should be based on the primary purpose of their addition. If the main concern is controlling early-age cracking due to plastic shrinkage, synthetic microfibers are typically preferred. On the other hand, if the goal is to enhance post-crack ductility and toughness, macrofibers—either steel or synthetic—are more suitable. Fiber dosage is determined based on the required performance for a specific application. Performance-based tests, such as those measuring residual strength or toughness, help evaluate whether a particular fiber type and dosage achieve the desired mechanical properties. For plastic shrinkage crack reduction using microfibers, the crack-reduction ratio (CRR) is often specified, and the required dosage is determined based on ASTM C1579 data. For hardened concrete properties using macrofibers, dosage is selected to meet post-crack performance criteria, such as equivalent flexural strength or strength ratio (ASTM C1609/C1609M) or energy absorption capability (ASTM C1550). Concrete mixtures may need adjustments to achieve the desired workability, pumpability, and finishability. Following the fiber manufacturer’s recommendations ensures optimal results. Additionally, environmental conditions and exposure should be considered—for instance, synthetic fibers are preferred over steel fibers in situations where corrosion is a concern. References: ACI 544.1R, ACI 544.2R, ACI 544.9R Topics in Concrete: Concrete Fundamentals, Fiber Reinforced Concrete, Design of Concrete, Testing of Concrete
Q. How should the appropriate fiber be selected for a specific application, and how is fiber dosage determined?
A. The selection of fibers should be based on the primary purpose of their addition. If the main concern is controlling early-age cracking due to plastic shrinkage, synthetic microfibers are typically preferred. On the other hand, if the goal is to enhance post-crack ductility and toughness, macrofibers—either steel or synthetic—are more suitable.
Fiber dosage is determined based on the required performance for a specific application. Performance-based tests, such as those measuring residual strength or toughness, help evaluate whether a particular fiber type and dosage achieve the desired mechanical properties. For plastic shrinkage crack reduction using microfibers, the crack-reduction ratio (CRR) is often specified, and the required dosage is determined based on ASTM C1579 data. For hardened concrete properties using macrofibers, dosage is selected to meet post-crack performance criteria, such as equivalent flexural strength or strength ratio (ASTM C1609/C1609M) or energy absorption capability (ASTM C1550).
Concrete mixtures may need adjustments to achieve the desired workability, pumpability, and finishability. Following the fiber manufacturer’s recommendations ensures optimal results. Additionally, environmental conditions and exposure should be considered—for instance, synthetic fibers are preferred over steel fibers in situations where corrosion is a concern.
References: ACI 544.1R, ACI 544.2R, ACI 544.9R
Topics in Concrete: Concrete Fundamentals, Fiber Reinforced Concrete, Design of Concrete, Testing of Concrete