June 15, 2011
The most expensive sentence in a steel fiber inquiry is "we need one ton of steel fiber". Until aspect ratio, tensile strength and dosage are fixed, no quotation can be compared.
Inquiries arrive every day that read: please quote steel fiber, we need one ton. It looks specific and is impossible to price, because steel fiber is not a product but a family of products. A 0.2 mm copper-plated micro wire and a 0.75 mm cold-drawn hooked wire can differ threefold in price and barely overlap in application. Put both behind one word and the factory can only guess, and the cost of guessing lands on site rather than on the quotation. An inquiry that works does not say steel fiber supplier China; it says industrial floor, 150 mm slab, replacing welded mesh, 25 kg/m3, ASTM A820 report required. The second one gets an answer the same day.
Aspect ratio is length divided by equivalent diameter. It decides whether the fiber can grip the matrix: too low and it pulls out with almost no friction, too high and it balls during mixing. Structural steel fiber normally sits between 40 and 80. Tensile strength is the second number: cold-drawn low-carbon wire runs 800 to 1150 MPa while copper-plated micro wire reaches 2850 MPa. These are not good and better, they are different jobs, the first for mass structures, the second for UHPC and thin walls. Dosage is the third, given as volume fraction or kilograms per cubic metre. 30 to 80 kg/m3 covers structural concrete; 90 to 268 kg/m3 is already UHPC territory.
Specifications often push aspect ratio upward as if the number alone meant performance. The opposite is true: the higher the ratio, the more the fibers interfere in the mixer, and past what the matrix and aggregate can accommodate they form balls. A ball is a defect, not reinforcement. Practice puts pumping and spraying below 60, precast and self-compacting mixes at 65 to 70, and anything above 80 only in ultra-high performance matrices where the aggregate is fine and the paste is viscous enough to let fibers separate. Ask how the concrete will be placed before asking for an aspect ratio.
Cold-drawn low-carbon wire fiber at 800 to 1150 MPa comes in 0.55, 0.75 and 1.0 mm diameters, 30 to 60 mm lengths, hooked at both ends. It is economical, consistent and widely compatible, from ordinary concrete to RPC. Copper-plated micro wire at 2850 MPa is only 0.2 mm in diameter with 6 to 20 mm lengths and aspect ratios of 30 to 100; it belongs in UHPC bridge decks, thin precast sections and precision elements. Using micro wire in a mass floor wastes money, and coarse wire simply will not fit a 30 mm wall. The first selection question is section thickness and clear cover, not strength.
Dosage is the number most often left vague on a quotation. Structural concrete uses 30 to 80 kg/m3, roughly 0.4% to 1.0% by volume; copper-plated micro wire in UHPC is recommended at 90 to 268 kg/m3, more than three times higher. One ton of fiber therefore covers 25 to 30 cubic metres of floor concrete but only 4 to 10 cubic metres of UHPC. Leave dosage out and the factory quotes the structural range, the unit price looks low, and the cost per cubic metre of concrete quietly doubles.
An inquiry that gets answered the same day usually has six lines: application (floor, shotcrete, precast, refractory), section thickness and clear cover, the specified tensile and flexural toughness values, dosage or volume fraction, the standard to be met (ASTM A820 or EN 14889-1), and packaging plus destination port. Add one line on whether a CE declaration is needed and the factory knows whether to run a certified batch. With those six lines, quotations converge from a threefold spread to within ten percent, because everyone is finally reading the same sheet. Write the application in the buyer's own words as well: steel fiber for concrete reinforcement, for industrial flooring, for tunnel shotcrete or for refractory linings. One fiber family can serve several of those, but the quotation changes with the wording, and so does the test report the factory attaches to it.
The failures in a spec sheet are rarely wrong numbers, they are misaligned units. A Chinese sheet states a dosage of 25 kg/m3; an English-speaking buyer converts at 1.685 and reads 42 lb/yd3, then replies with the single number 42, and the factory quotes 42 kg/m3 back. The price silently grows by 68 percent. Tensile strength carries the same trap: the factor between MPa and ksi is 6.895, so 1150 MPa is about 167 ksi, and one misplaced decimal becomes a tenfold error. Aspect ratio looks safest and still has a definition problem, because the denominator may be equivalent diameter or nominal diameter; for hooked wire it hardly matters, for indented and waved wire it moves the number by 15 percent. The robust fix is to print both unit systems on the sheet and state the conversion factors in the header. Net weight is the second recurring dispute: whether a 25 kg carton is gross or net shifts a full container by 400 kg. The third is the confusion between dosage and content, where dosage is kilograms added per cubic metre of concrete and content is the volume share in the finished product, two figures separated by the density of steel. Settle these conventions in the first email and every later technical clarification disappears.
A threefold spread on the same nominal specification is rarely fraud. It is usually three unstated differences. Raw material: cold-drawn low-carbon wire versus re-melted scrap gives a different order of strength consistency. Coating: true hot-dip copper versus cosmetic electroplating differs three to eight times in salt spray. Inspection: 28 in-line checks versus shipment sampling is a real cost difference. Write all three into the inquiry, ask for a batch report with the shipment, and the spread becomes explainable. To compare actual values, work from the model and measured data tables on the steel fiber product page rather than trading descriptions by email.
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Get a Free QuoteCopper-plated micro wire, cold-drawn hooked-end, glued in bundles, milled, 304 / 310S / 446 stainless and melt-extracted heat-resistant fiber, plus synthetic fiber for UHPC. Diameters from 0.2 to 1.0 mm, lengths from 6 to 60 mm, tensile strength from 700 to 2850 MPa, and dosage covering 0.5% to 2% by volume or 30 to 268 kg/m3. Production can follow ASTM A820 or EN 14889-1 with batch test reports, packed in cartons, jumbo bags or bulk, on EXW / FOB / CIF / DDP terms.
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