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Q. What is the minimum reinforcement for crack-width control, and how is design accomplished using fiber? A. Reinforcement for crack-width control in concrete slabs typically involves steel bars, wire mesh, or macrofibers to manage cracks caused by shrinkage, thermal stresses, or other nonstructural factors. Fibers are commonly used to control these cracks, with minimum dosages specified for different fiber types. For steel fibers, the minimum dosage is typically 15 to 20 lb/yd³ (9 to 12 kg/m³), while for synthetic macrofibers, it is approximately 3 to 4 lb/yd³ (1.8 to 2.4 kg/m³). These minimum dosages are sufficient to control shrinkage and thermal stress-induced cracks. In addition to crack control, higher dosages of fibers can enhance the bending moment capacity and flexural toughness of the section after cracking, providing further structural benefits. Design professionals can refer to ACI 544.4R for detailed guidance on incorporating fibers into designs for crack-width control and structural applications. References: ACI 544.1R, ACI 544.4R Topics in Concrete: Concrete Fundamentals, Fiber Reinforced
Q. What is the minimum reinforcement for crack-width control, and how is design accomplished using fiber?
A. Reinforcement for crack-width control in concrete slabs typically involves steel bars, wire mesh, or macrofibers to manage cracks caused by shrinkage, thermal stresses, or other nonstructural factors. Fibers are commonly used to control these cracks, with minimum dosages specified for different fiber types. For steel fibers, the minimum dosage is typically 15 to 20 lb/yd³ (9 to 12 kg/m³), while for synthetic macrofibers, it is approximately 3 to 4 lb/yd³ (1.8 to 2.4 kg/m³). These minimum dosages are sufficient to control shrinkage and thermal stress-induced cracks.
In addition to crack control, higher dosages of fibers can enhance the bending moment capacity and flexural toughness of the section after cracking, providing further structural benefits. Design professionals can refer to ACI 544.4R for detailed guidance on incorporating fibers into designs for crack-width control and structural applications.
References: ACI 544.1R, ACI 544.4R
Topics in Concrete: Concrete Fundamentals, Fiber Reinforced