Macro-Synthetic Reinforcement Family
Synthetic Steel Fiber
MICHEM Synthetic Steel Fiber is a macro-synthetic reinforcement family designed for concrete applications where post-crack load transfer, toughness and distributed crack control are more important than plastic-stage microfiber performance alone. The product should be selected by residual concrete performance, fiber geometry, dosage, mixing behavior and project design requirements—not by the phrase “synthetic steel” or by fiber tensile strength in isolation.
Material Definition
“Synthetic steel fiber” describes a reinforcement role—not a metallic material
The name can create confusion.
Synthetic steel fiber is not steel wire made from a different process. It is a market-facing term used for engineered synthetic macrofibers intended to perform some of the reinforcement functions traditionally associated with steel fibers, especially after a concrete crack has formed.
Fine polypropylene microfibers are normally selected for plastic shrinkage and settlement cracking while concrete is fresh. Macro-synthetic fibers are larger reinforcement elements evaluated mainly after cracking, when fibers crossing a crack continue transferring force between the two sides of the matrix.
For a microfiber, the first question may be how effectively the product reduces plastic-shrinkage cracking.
For a synthetic steel fiber, the more important questions are:
- What residual load can the fiber-reinforced concrete carry after cracking?
- At what crack opening or beam deflection is that residual capacity measured?
- How stable is the result across batches and fiber orientations?
- What dosage is required in the customer’s actual concrete?
- Can that dosage be mixed, pumped, placed and finished reliably?
- Is the intended application structural, nominal-reinforcement, crack-control or toughness driven?
Engineered Post-Crack Bridging
Polymeric macrofibers bridge crack interfaces to provide residual flexural strength and toughness.
Post-crack load transfer is the core performance mechanism
Before cracking, the cementitious matrix carries most tensile stress. Macro-synthetic fiber does not necessarily raise first-crack strength dramatically; its more important role begins after a crack forms.
Fibers crossing the crack bridge the two faces and transfer force through bond along their embedded length. As opening increases, fibers stretch, debond, pull out or rupture. The combined response creates residual load capacity.
This is why compressive strength alone is a poor qualification metric. A concrete can show little compressive-strength change yet develop a much more useful post-crack load-deflection response.
Pullout behavior can be as important as rupture strength
Controlled pullout can be beneficial because energy is consumed as the fiber debonds and slides through the matrix while the crack continues opening. Embossed, twisted, wavy, hooked or hinged geometries are all ways of managing anchorage.
Too little bond gives weak residual capacity; excessive anchorage can promote difficult mixing or premature rupture. Two fibers with similar tensile strength and length can therefore produce very different beam-test results. Geometry is part of the mechanical design.
Performance Qualification
Fiber tensile strength is important—but it does not equal concrete residual strength
A fiber TDS may report tensile strength, but a high tensile-strength number does not guarantee high residual performance in concrete. The fiber first has to mobilize that strength.
If the bond to concrete is weak, the fiber can pull out too easily. If the bond is too aggressive relative to the fiber strength, premature rupture may occur before enough pullout energy is dissipated. If the fiber is poorly oriented relative to the crack, only part of its capacity is mobilized. If the mixing process causes bundling, the effective number of fibers crossing the crack can fall sharply.
Residual performance therefore depends on several interacting variables:
| Variable | Why it matters |
|---|---|
| Fiber tensile strength | Defines one limit of the fiber’s load-carrying capacity |
| Elastic modulus | Influences how quickly fiber stress develops as a crack opens |
| Length and aspect ratio | Affect anchorage and crack-bridging potential |
| Surface geometry | Controls mechanical bond and pullout resistance |
| Fiber dosage | Changes the number of effective bridges across cracks |
| Orientation | Determines how efficiently the fiber crosses the critical crack plane |
| Concrete strength | Changes bond and pullout behavior |
| Mixing and placement | Affect dispersion and orientation |
| Crack width / deflection | Determines which stage of fiber response is being measured |
This is why supplier comparison should move quickly from fiber-property data to concrete beam or panel performance.
Grade Architecture
Standard-strength and high-strength grades should be separated by performance evidence
MICHEM’s website architecture divides the Synthetic Steel Fiber family into Standard-Strength Synthetic Steel Fiber and High-Strength Synthetic Steel Fiber subpages. That distinction should use controlled product data; “high strength” must not become a synonym for “better.”
Standard-Strength Synthetic Steel Fiber
A standard-strength grade can be the correct solution when it already meets the required residual performance at an economical dosage.
Project selection should consider residual concrete performance, dosage efficiency, bond behavior, workability and cost rather than defaulting to highest tensile strength.
High-Strength Synthetic Steel Fiber
A higher-strength grade becomes valuable when the project needs a higher performance envelope, better dosage efficiency or a different structural response and the concrete test data confirm that benefit.
A higher fiber tensile strength may be relevant, but must be supported by confirmed concrete beam test data under specific project conditions.
The parent page should explain this selection framework, while the two subpages should provide grade-specific data from approved MICHEM technical documents. Until those documents are confirmed, no numerical boundary between “standard” and “high” strength should be invented.
Reinforcement Comparisons
Synthetic Steel Fiber versus Polypropylene Microfiber
The two products may both be synthetic, but they solve different crack stages.
| Selection question | PP Monofilament Microfiber | Synthetic Steel / Macro-Synthetic Fiber |
|---|---|---|
| Main crack stage | Plastic / very early age | Hardened post-crack stage |
| Main function | Plastic shrinkage and settlement crack control | Residual strength, toughness and crack-width control |
| Typical fiber size | Fine microfiber | Larger macrofiber |
| Key test logic | Plastic-shrinkage comparison | Load-deflection or residual-strength testing |
| Structural design role | Usually limited | Can be considered when supported by engineering design |
| Main procurement risk | Poor dispersion | Selecting by fiber strength instead of concrete residual performance |
A project can use both functions when required: microfiber for early plastic cracking and macrofiber for post-crack performance.
Synthetic steel fiber versus steel fiber
Macro-synthetic and steel fibers can both create post-crack capacity, but they do so with very different material properties.
Steel has a much higher elastic modulus than common polymeric macrofibers. This means steel fibers generally develop stress with less elongation as a crack begins to open. Macro-synthetic fibers can require greater deformation before mobilizing comparable tensile force.
That difference influences the shape of the residual load-deflection curve.
Published comparative studies show that steel and macro-synthetic fiber reinforced concretes can produce substantially different post-crack responses even when both are described as structural FRC. Steel fibers may provide higher toughness more efficiently in some mixtures, while macro-synthetic fibers can still produce useful residual capacity when properly designed and dosed.
Synthetic macrofibers also offer a different durability profile because polymeric fibers do not undergo steel corrosion.
Do not compare steel and synthetic systems by equal kg/m³. Their densities and mechanical properties are too different. Compare required residual concrete performance, then evaluate installed cost, handling, durability and constructability.
Corrosion resistance is useful—but it is not a substitute for structural qualification
One attraction of macro-synthetic reinforcement is the absence of steel corrosion.
This can reduce concerns about rust staining from exposed fibers and eliminate corrosion of the polymer fiber itself. Research reviews report good durability of synthetic fibers in aggressive environments compared with corrosion-sensitive steel fibers crossing open cracks.
However, “non-corrosive” does not mean “structurally equivalent.” Durability and residual mechanical performance are separate qualification questions and both must be verified.
For long-service-life infrastructure, consider sustained tensile stress across cracks. Polymeric fibers are viscoelastic materials, and research on macro-synthetic FRC shows that creep and time-dependent pullout can become relevant under sustained post-crack loading.
Where long-term cracked-section capacity is a design requirement, short-duration beam strength alone may not be enough. The structural engineer should use the applicable design method and long-term performance evidence for the selected fiber system.
Compliance Frameworks
Testing Standards & Classification Codes
Standards classify the performance of the complete fiber-reinforced concrete system rather than isolated fiber names.
ASTM C1609 is more useful than a standalone fiber tensile-strength comparison
ASTM C1609/C1609M evaluates flexural performance of fiber-reinforced concrete under third-point beam loading. The test identifies first-peak and peak behavior and, importantly for macrofiber applications, residual strengths at specified beam deflections. Toughness can also be determined from the area under the load-deflection curve.
This makes the test much closer to the real engineering question than fiber tensile strength alone. A macro-synthetic fiber is intended to keep carrying load after the concrete matrix cracks. ASTM C1609 measures the behavior of the complete fiber-reinforced concrete specimen through that transition.
The result still depends on concrete mixture, fiber dosage, specimen preparation and distribution. Compare candidates in a controlled reference mix; do not transfer residual-strength numbers between unrelated concretes or approve a fiber solely from TDS tensile strength.
ASTM C1116 classifies the finished fiber-reinforced concrete
ASTM C1116/C1116M covers fiber-reinforced concrete delivered with the ingredients uniformly mixed. Synthetic fiber-reinforced concrete is classified separately from steel, glass and natural-fiber reinforced concrete.
The phrase “synthetic steel fiber” does not convert the product into a steel-fiber category. If the fiber is synthetic, the relevant FRC classification remains synthetic. Uniform mixing is also fundamental, and post-crack applications should be accepted against residual-performance requirements rather than compressive strength alone.
ASTM D7508 may be relevant when the selected grade is polyolefin
ASTM D7508/D7508M covers polyolefin chopped strands for use in concrete and includes requirements related to properties such as tensile strength, cut length and other fiber characteristics, together with the relationship to ASTM C1116 Type III synthetic FRC.
Reference ASTM D7508 for a MICHEM grade only if current product documentation confirms that its chemistry and product form fall within the standard’s scope.
EN 14889-2 is the European polymer-fiber framework
For European specifications, EN 14889-2 covers polymer fibers for structural and non-structural use in concrete, mortar and grout. The framework addresses fiber characteristics such as polymer type, geometry, dimensions and tensile-related properties, and distinguishes applications where fibers are intended to contribute to load-bearing capacity.
Where a project requires EN conformity or declared structural performance, the selected MICHEM grade must be supported by current product documentation and the required test evidence. Do not infer EN compliance from the product-family name.
Engineering Rheology
Dosage Optimization, Workability & Fiber Dispersion
Ensuring that specified fiber quantities translate into effective crack bridging on the jobsite.
Dosage should come from required residual performance—not from a generic kg/m³ number
Macro-synthetic fiber dosage is often discussed in kilograms per cubic metre. That is convenient for batching, but it is not a universal performance language.
The same dosage can produce different residual strength in two concretes because aggregate grading, paste content, concrete strength, fiber orientation and workability change the number and effectiveness of fibers crossing the crack.
Different fiber geometries also have different mass per unit length and anchorage behavior.
Start dosage selection with the required residual-strength or toughness target. Test several dosages in a representative mixture and identify the lowest level that meets performance with acceptable production behavior. A brochure dosage is a starting point; the project dosage is an engineering result.
Workability loss must be solved without destroying the mix design
Macro-synthetic fibers can reduce slump and increase the apparent cohesiveness or harshness of fresh concrete. The effect grows as fiber dosage, length and total surface area increase.
A field crew may respond by adding water. That is risky because extra water changes water-to-binder ratio, bleeding, strength and shrinkage.
Qualify the fiber together with the complete concrete rheology: paste volume, aggregate grading, superplasticizer, addition sequence, mixing time, slump, pump pressure and finishing. A high beam result has little value if the mix cannot be placed commercially.
Dispersion and orientation control the effective reinforcement
Fiber dosage tells you how much material entered the mixer. It does not tell you how many fibers crossed the critical crack.
Post-crack capacity depends strongly on fiber distribution and orientation. Research comparing steel and macro-synthetic FRC has found a direct relationship between the number of fibers crossing the crack and the residual tensile response.
Mixing, placement direction, pumping and element geometry can all influence orientation, especially in thin or sprayed elements. Qualification should reproduce the real production process as closely as practical.
Application Domains
Sector-Specific Implementation
Specific engineering criteria across flooring, shotcrete, and precast applications.
Slabs, pavements and industrial floors
Synthetic steel fiber is often screened for slab and pavement systems because distributed reinforcement can provide post-crack toughness throughout the concrete volume. Before reducing mesh or bars, define what the original reinforcement was doing—shrinkage control, structural moment resistance, concentrated-load support or crack-width control—then specify the residual FRC performance needed to replace that function.
Shotcrete and tunnel applications
Macro-synthetic fibers can be attractive in sprayed concrete because reinforcement is distributed throughout the mix and does not require placing a conventional mesh before every application. Shotcrete adds pump, hose, rebound and orientation effects, so qualification should represent the actual spraying process. Do not transfer a cast-concrete dosage directly into shotcrete without confirming in-place performance.
Precast and infrastructure elements
Precast producers may use macro-synthetic FRC where toughness and manufacturing efficiency justify it. Any benefit from reduced reinforcement handling depends on tightly controlled dosing, mixing and periodic concrete performance verification.
Engineering Protocol
A practical supplier-qualification workflow
Start with the engineering requirement rather than the catalog: application, element geometry, concrete strength, residual-flexural target, crack-width or deflection criterion, exposure, placing method and applicable design standard.
Review the approved fiber TDS, then prepare a controlled reference concrete. Test several dosages while keeping binder, aggregates, water-to-binder ratio and admixtures stable. Record fresh behavior and run the required post-crack test such as ASTM C1609 or the specified European method.
Select the dosage that meets residual performance without unacceptable mixing, pumping or finishing penalties, then confirm it at production scale and with representative raw-material variation.
Diagnostic Guide
Common troubleshooting patterns
Identify and resolve common field, testing, and structural discrepancies.
Fiber tensile strength is high but beam residual strength is low
Check fiber bond, dosage, orientation and dispersion. The individual fiber may be strong without being effectively mobilized in the concrete.
The concrete becomes difficult to pump
Review fiber dosage and geometry, aggregate grading, paste volume, admixture system and mixing sequence. Do not solve the problem with uncontrolled water addition.
Residual-strength results show high scatter
Inspect fiber distribution, specimen casting direction, mixing consistency and the number of effective fibers crossing the crack. FRC results can be sensitive to orientation.
Synthetic fiber is being compared with steel by kg/m³
Stop the mass-only comparison. Compare residual concrete performance and installed system cost.
A project wants to replace reinforcing steel
Require an engineered design and applicable performance evidence. The product name “synthetic steel fiber” is not sufficient authorization to remove conventional reinforcement.
Short-term performance is good but the element carries sustained post-crack load
Review creep and long-term cracked-section requirements. Polymeric fiber systems can show time-dependent deformation that needs to be considered in structural applications.
Procurement Verification
What MICHEM specifications should be confirmed before ordering
MICHEM’s product architecture includes Synthetic Steel Fiber with dedicated Standard-Strength and High-Strength subcategories.
The currently retrievable project sources do not provide enough approved grade-level data to publish one definitive numerical specification table on this parent page. For that reason, this page does not invent an unverified:
- polymer type
- grade code
- fiber length
- equivalent diameter
- aspect ratio
- tensile strength
- elastic modulus
- elongation
- density
- recommended dosage
- residual flexural-strength value
- packaging
- shelf life
Those fields should come from the current approved MICHEM/TenaBrix TDS for the selected grade. The Standard-Strength and High-Strength pages should then explain their specific performance windows using controlled source data rather than creating a generic “higher number is better” ranking.
Engineering & Specification FAQ
Frequently Asked Questions
What is synthetic steel fiber?
It is an engineered synthetic macrofiber intended to provide distributed post-crack reinforcement functions in concrete. The name does not mean the fiber is made of steel.
What is the difference between synthetic steel fiber and polypropylene microfiber?
Microfiber mainly targets plastic-stage shrinkage and settlement cracking. Synthetic steel or macro-synthetic fiber is selected primarily for post-crack toughness and residual load capacity.
Can synthetic steel fiber replace steel fiber, mesh or rebar?
It can be considered in engineered applications only when the project design, applicable standards and verified residual concrete performance support the substitution. Equal mass dosage or the product name alone is not sufficient.
Is higher fiber tensile strength always better?
No. Residual concrete performance also depends on bond, geometry, orientation, dosage and concrete properties.
What is the best test for structural macro-synthetic fiber?
ASTM C1609 is widely used to measure post-crack flexural behavior and residual strengths. The applicable project may instead require an EN beam test or another specified method.
Does synthetic macrofiber corrode?
Polymeric macrofibers do not undergo steel corrosion, which can be useful in aggressive or appearance-sensitive environments. Mechanical performance still requires separate verification.
Why can the same dosage produce different residual results?
Concrete strength, fiber orientation, distribution and the number of fibers crossing the crack all affect the result, so dosage must be qualified in a representative mixture.
What information should I provide for a MICHEM synthetic steel fiber recommendation?
Provide the application, element dimensions, concrete strength, existing reinforcement concept, required residual-performance standard, exposure environment, pumping or shotcrete process and any target for reducing conventional reinforcement.
Performance Summary
Select the fiber-reinforced concrete performance—not the fiber name
Synthetic steel fiber should be treated as an engineered macro-reinforcement system. The relevant performance begins when the concrete cracks.
At that point, geometry, bond, orientation, dosage and fiber material combine to determine how much load can continue crossing the crack and how the element deforms.
That is why the correct procurement sequence is: define the required residual performance, select the fiber family, verify the grade specification, test the complete concrete, and approve the dosage through the applicable engineering method.
Do not specify “synthetic steel” because the name sounds equivalent to steel. Specify the post-crack concrete performance the project actually needs.
Project Design & Testing Support
Submit your target residual flexural strength, slab/shotcrete specifications, or rebar replacement goals for engineering evaluation and beam-test verification.