Frequently asked questions and answers

You are here

For cast-in-place SFRC when is internal vibration used and when is form vibration used?

For cast in place, internal vibration is the most used option to consolidate the concrete.

Form vibration is generally used in the precast industry. When steel fibre concrete is cast into form work a small amount of vibration of the forms helps keep the fibres from touching the forms and thereby from being visible when the forms are removed. For example, during casting of steel fibre reinforced precast structures, the forms are vibrated to consolidate the concrete. This action results in an almost fibre free surface of the structures. So allowing a short period of form vibration in the all cast-in-place structures, in addition to internal vibration where possible, will provide the best finished surface.

Are there any problems associated with casting SFRC against a water proof membrane?

No failures of the plastic liner due to fibre punctures have ever been identified. The abrasion from sharp aggregates during placement of the concrete poses just as big of a threat to the liner as do the steel fibres. After placement the fibres tend to move around and re-orient themselves during vibration which relieves any pressure of an individual fibre on the liner created during placement. Many projects using SFRC are constructed with cast-in-place and sprayed shotcrete directly in contact with water proof membranes.

Is the concrete electrically conductive and does this lead to a risk of electrical shock?

Typical steel fibre reinforced concrete contains less than 0.5% vol. steel fibres and hardly more than 0.75% vol. Those fibres are discontinuous and not connected to each other. Tests only show a slight decrease in electrical resistivity due to the addition of steel fibres. However, the resistance to current flow is still substantial. Effects from moisture content and aggregate composition are much more dominant than the addition of steel fibres.

Can macro-synthetic Fibres act as a structural concrete reinforcement method?

Macro Polymer fibres can NOT act as structural reinforcement of concrete because: 
  • The Young's Modulus is insufficient to reinforce
  • The Young's Modulus creates large crack openings or big deformations
  • Polymer fibres creep
  • Polymer fibres melt at 165°C

What is a structural fibre?

The ISO standard 13.270 mentions the following: Steel fibres are suitable reinforcement material for concrete because they possess a thermal expansion coefficient equal to that of concrete, their Young's Modulus is at least 5 times higher than that of concrete and the creep of regular carbon steel fibres can only occur above 370 °C.

What is the main design standard for FRC concrete?

Model Code 2010 edited by Fib is consider at the reference design standard. 

Can we use the Fib Model Code for all type of fibres?

Fibre materials with a Young’s modulus which is significantly affected by:
  • time and/or
  • thermo-hygrometrical phenomena are not covered by this Model Code.

What are the main performance criteria according to this Fib Model Code?

The residual strength indices which are of greater importance, according to Fib Model Code 2010, are:
  • Value fR1 (CMOD = O.5mm) is used for the verification of Service Limit State.
  • Value fR3 (CMOD = 2.5mm) is used for verification of the Ultimate Limit State 

Which testing standard is used in the Fib Model Code to get the material properties?

The EN 14651 is a test developed specifically to characterize FRC. This is a three point bending test on a notch beam. 

What is the minimum performance required according to MC 2010?

Fibre reinforcement can substitute (also partially) conventional reinforcement at ultimate limit state if the following relationships are fulfilled:
  fR1k/fLk > 0.4;      fR3k/fR1k > 0.5