Material Properties
Strain hardening, the most coveted capability of HPFRCCs, occurs when a material is loaded past its elastic limit and begins to deform plastically. This stretching or ‘straining’ action actually strengthens the material. This phenomenon is made possible through the development of multiple microscopic cracks, opposed to the single crack/strain softening behavior exhibited by typical fiber-reinforced concretes. It occurs in HPFRCCs as several fibers slip past one another.
One aspect of HPFRCC design involves preventing crack propagation, or the tendency of a crack to increase in length, ultimately leading to material fracture. This occurrence is hindered by the presence of fiber bridging, a property that most HPFRCCs are specifically designed to possess. Fiber bridging is the act of several fibers exerting a force across the width of a crack in an attempt to prevent the crack from developing further. This capability is what gives bendable concrete its ductile properties.
Listed below are some basic mechanical properties of ECC, or Engineered Cementitious Composite, a specific formula of HPFRCC, developed at the University of Michigan. This information is available in Victor C. Li's article on (ECC)- Tailored Composites through Micromechanical Modeling. The first property listed, the ultimate tensile strength of 4.6 MPa, is slightly larger than the accepted tensile strength of standard fiber-reinforced concretes, (4.3 MPa). More notable, however, is the extremely high ultimate strain value of 5.6% when compared to most FRC's ultimate strain values ranging in the few hundredths of a percent. The first crack stress and first crack strain values are significantly low compared to normal concrete, both the result of the multiple crack phenomenon associated with HPFRCCs.
| ECC Material Properties | |
|---|---|
| Ultimate Tensile Strength ( σCU ) | 4.6 MPa |
| Ultimate Strain ( εCU ) | 5.6 % |
| First Crack Stress ( σfc ) | 2.5 MPa |
| First Crack Strain ( εfc ) | .021 % |
| Modulus of Elasticity ( E ) | 22 GPa |
Read more about this topic: High-performance Fiber-reinforced Cementitious Composites
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