Shorter steel fibres would be better in order to ease the mixing process and achieved the desired workability. Using steel fibres with a length of 50 mm or 60 mm would result in lower workability and possible poor dispersion within the matrix.

Long steel fibres will impart hindrance to the flowability in SCC. Moreover, the fibres may get obstructed in between the reinforcement bars and cause blockage in the path of concrete flow. It is advisable to use short steel fibres of around 10 mm to get good results.

The papers I have read regarding this matter use steel fibers with maximum length of 35 mm, because as you referred, long fibers affect the flowability of SCC. However, it is unclear to me how much the concrete flow would be obstructed if you use 50 or 60 mm long steel fibers.

You will find out that depending on the fibre thickness and its length (aspect ratio) there will be blockage. Using the L-box will confirm this. However, I think when the length of the fibre is not more than 20mm, which is smaller than the minimum horizontal spacing between bars as in American and British codes, while the thickness or diameter of fibres allows flowability, required w/c ratio of about 0.4, flexibility of the steel fibres, it will suffice. Thank you.

No please. I just could not check out the details right now, but it (fibre length) should not be more than 20mm for steel fibres, while that of plastics may be up to 35mm also depending on its thickness, since they are flexible. Look at how it is: aspect ratio is length of fibre divided by thickness or diameter of fibre. Minimum horizontal spacing between bars is thickness of aggregate + 5mm = 25mm, while that of vertical spacing is a spacer bar of 16mm for normal concrete.. That of SCC should be lower or else it will clog the system due to low flowability. I hope this meets your aspiration, even without a laboratory test. I am very busy now reviewing some international and local journals, I would have given you a better explanation, but I hope this suffices you. Thank you.

Dear Mr Lasica

it is without any problems possible to use long fibres (50 to 60 mm) in Self-compacting fibre concrete. For this, I can refer you to my PhD-Thesis from the year 2006 (TU Delft), there you can find examples.

Hello

it is possible to use long steel fiber into SCC. It is true that the long fiber can hinder the flow. However, with right composition of superplasticizer and enough trial mixing, it is possible to achieve high flow concrete. You can refer to my last research paper.

DOI: 10.1016/j.conbuildmat.2020.119963

It should be noted that my research was the investigation on the bending capability of beams with no reinforcement.

The resulting concrete will be too porrous and cause degradation of the steel fibres. We are talking about optimized structural concrete that gives the professional both structural safety and economy in construction and in service of the resulting structural member. Thank you.

Dear Sir

To my knowledge there is not much research available explaining length of "Steel fiber"" and workability, also it depends on several other factors including your aggregate quality and mix design