Q. What is the Round Determinate Panel (RDP) test?
A. click here to view

Q. What is “toughness”?
A. Toughness refers to the energy absorption capacity of a shotcrete panel while it is subjected to a load over a fixed displacement. It is measured in Joules and can be calculated as the area beneath the curve on a Load-Displacement plot.

Q. How do the RDP results compare to EFNARC square panel results?
A. The RDP result is multiplied by 2.5 to calculate the equivalent EFNARC square panel performance.

Q. How is it possible for synthetic fibres to replace steel fibres or mesh?
A. Technological improvements over the last decade have allowed synthetic materials to be designed and manufactured with specific characteristics. The principal characteristics for a concrete/shotcrete reinforcing fibre are the tensile strength and the fibre-concrete bond.

Q. How do the Barchip fibres achieve the bond with the concrete?
A. The fibres utilise the mechanical interaction that is formed between the raised embossing of the fibre and the concrete mass. Conceptually, this is the same concept as the raised welds on conventional steel reinforcing bar.
Additionally, there is a chemical coating on the fibre that ensures a chemical bond is also created with the cement paste.

Q. Why do synthetic fibres perform better than steel fibres in deforming ground?
A. As can be seen from the graph of the characteristic RDP plots, the synthetic reinforcement has greater load carrying performance at higher displacements. Thus, in deforming ground, the synthetic fibres will maintain the cracks tighter than steel fibres.

Q. Can synthetic fibres replace steel mesh?
A. As can be seen from the RDP plots above, the synthetic fibre plot closely follows the performance of the steel mesh over the first 12 mm. After this point, the mesh welds begin to fail and the synthetic fibre has better load carrying abilities.

Q. The Young’s Modulus of polypropylene is much lower than that of steel. Does this mean the synthetic fibres stretch more?
A. No. Conventional steel fibres utilise end-anchorage to achieve the bond with the concrete. This is typically achieved with a flattened or hooked end. As a consequence of the end-anchorage, all the elongation in a steel fibre occurs over the full length of the fibre. In contrast, the Barchip synthetic fibres use continuous anchorage with full-length embossing, which means that the fibre elongation occurs only across the width of a crack and a small portion of the embedded fibre.

Q. Is corrosion an issue?
A. [durability test page]

Q. What is the ratioof the dosages when comparing equivalent performance of steel and Barchip synthetic fibres?
A. Typically the ratio by weight varies from 6:1 to 8:1, depending on individual mixes and considering a high performing, hooked-end steel fibre. In terms of quantities of individual fibres, the numbers of steel and synthetic fibres are of the same order of magnitude.

Q. How should Barchip fibres be dosed or batched?
A. click here to find out

Q. How can I determine the appropriate dosage of Barchip fibres for my application?
A. In the case of an underground excavation, it is suggested that Barton’s modified Q-System is utilised to define the reinforcement category. The Ready Reckoner [link] will then allow a specific dosage to be selected.

Q. How can the fibre dosage and layer thickness be optimised?
A. Due to improvements in fibre performance in recent years, it is now possible to reduce the shotcrete layer thickness by increasing the fibre dosage without compromising the final shotcrete toughness. More details on this can be supplied by Elasto-Plastic Concrete engineers.

Q. How can I select the most economical fibre that suits my application?
A. The user is effectively purchasing energy absorption capacity, not kilograms of fibre, so the economic analysis must be done on the basis of $/J.

Q. What is the best way to specify the shotcrete reinforcement?
A. Specifications can be either performance-based (eg. 360 J on a standard RDP test) or recipe-based (eg. 8 kg/m3 of fibre X). It is our view that the former is preferable, as it ensures the designer considers what is desired from the shotcrete in terms of the performance and yet allows the contractor the flexibility to use whatever materials are currently available to meet the specification. With the increasing speed of technological improvements, it is not always possible for designers to be abreast of the latest materials. A recipe-based specification is self-defeating if the contractor uses the specified materials in a poor manner.

Q. How can I relate the displacement of the RDP test to a crack width or a ground movement in the field?
A. The standard displacement of the RDP test is 40 mm, which is equivalent to a 16 mm crack width at the bottom of the panel. Alternatively, this represents a 213 mm ground movement in the middle of a 4.0 x 4.0 m drive.

Q. Why are the panels tested at 28 days?
A. This is due to a historical convention that originated in the concrete industry. As the graph shows below, the toughness of a fibre can change over time as the UCS of the concrete increases. Depending on the application, the specifier should consider requesting QA tests at different time periods. For example, the early age toughness is more important for a mine where access may be required within a few days, while a traffic tunnel requires a minimum level of toughness over a period of decades.

Q. Can Barchip synthetic fibres be used for reinforcing concrete or shotcrete on an embankment?

A. Yes. Additionally, this is accompanied by the benefit of reducing the concrete consumption. Usually mesh can never be placed at a fixed distance from the rock due to the irregular contours of the final face and this always results in excessive concrete being placed to ensure adequate cover over the mesh. Through the use of fibres, the required thickness can be applied without the necessity of trying to cover poorly-positioned mesh.