Investing in a Steel Fibre-Reinforced Concrete Warehouse Floor? You Need to Read This First!
October 22, 2024
Tim Walker, Managing Director at Face Consultants Ltd (New Zealand), explores how marketing promises about steel fibre-reinforced concrete floors (SFRC) sound great but could leave you vulnerable to real-world performance issues.
Many SFRC warehouse floor designs promise cost reductions but, in reality, compromise the safety and longevity of your floor.
By adopting a transparent, peer-reviewed approach using guidelines like the UK Concrete Society TR34, warehouse floors perform consistently, deliver on their promises, and very likely save you from costly repairs in the future.
Key Points to Take Away From This Article Include:
- Transparency in Design: Avoid proprietary models that lack transparency. Instead opt for open-source guidelines like TR34 to ensure your SFRC floors are designed using proven, peer-reviewed principles.
- Be Aware of Safety Margin Cuts: Suppliers may cut safety margins in ways that aren’t obvious. Make sure your floor designs account for real-world conditions like uneven slab thickness and inconsistent fibre distribution.
- Benefits of Independent Design Standards: Proprietary designs lock you into specific suppliers. Instead, use independent design standards to access a global supply chain and reduce costs without sacrificing safety.
- Design Performance Responsibility: Some suppliers provide SFRC floor designs but deny responsibility for their performance. Ensure you have an independent review to avoid liability in the long term.
- Real-World Performance: Look for designs that account for site variability, not just lab conditions. This ensures the longevity and durability of your floors in demanding industrial settings.
Cracks in the Story: Cutting Through the Marketing Spin in Steel Fibre-Reinforced Floors
In most concrete structure design, conventional reinforcement like rebar and mesh are treated as engineering commodities.
They’re based on transparent, well-documented design principles, and material properties such as those found in national codes like NZS3101 that are rigorously and independently developed and tend to stand the test of time.
However, when it comes to steel fibre-reinforced concrete (SFRC), floors the situation is different.
SFRC is often marketed with bold claims about reduced costs, increased durability, and innovative design – claims that are backed by proprietary design models and suspicious lab results rather than proven engineering principles.
This marketing-driven approach leaves clients vulnerable to designs that look great on paper but struggle in the real-world.
The answer is simple:
SFRC should be treated just like conventional reinforcement, relying on open, peer-reviewed design standards like UK Concrete Society TR34 to ensure consistency, transparency, and performance in the field.
The Risks of Proprietary SFRC Models: Why Engineering-Driven Solutions Are Essential for Industrial Floors
Unfortunately, in many corners of the world, SFRC has been turned into a marketing-driven product rather than an engineering driven one.
Suppliers frequently push proprietary design models that reduce safety factors to achieve thinner, cheaper slabs. These black-box models might seem attractive from a cost perspective, but they often fail to account for the reality of site conditions, where variations in concrete quality, fibre distribution, and slab thickness can lead to significant performance issues.
Using Open-Source Guidelines Like TR34 to Reduce Risks in Industrial Floor Design
By treating SFRC like an engineering commodity, as we do with traditional reinforcement, we can eliminate the opacity and risk that currently surrounds its use.
Open-source guidelines like TR34 ensure that SFRC designs are based on proven, peer-reviewed principles rather than marketing hype, making them more reliable for long-term industrial applications.
As well as reducing risk, clients will typically benefit from material cost savings.
By divorcing a design from a “proprietary solution” you can access a robust global supply chain and competitive procurement for fibres. This drives down cost at the expense of supplier margins, not at the expense of factors of safety or risk being transferred to the client. It also allows clients to lock in a design for a floor early in the project life cycle without needing to commit to a certain brand of steel fibre – allowing them to maintain competitive tension.
Proprietary Design Models: The Black Box Risk
Steel fibre suppliers often promote their proprietary design models as cutting-edge or innovative solutions, claiming they can optimise slab designs with thinner, lighter constructions.
But what these models don’t reveal is how safety margins are often cut in sneaky ways to make their solutions more competitive.
This leaves clients with floors that might meet specifications on paper – but don’t account for the variability of real-world conditions.
Take the issue of slab thickness.
We survey a lot of floors around the world, and it is common to see differences within the +/-15 mm from datum range at the slab surface. Furthermore, if sub-base preparation is not well controlled the slab can be thinner than anticipated in locations where the sub-base is high.
On top of variability of slab thickness, inconsistent fibre distribution during mixing can exacerbate these weaknesses, leaving the floor vulnerable to cracking and premature wear.
The Dangers of Misleading TR34 Safety Factor Claims in SFRC Floor Designs
Open-source guidelines like TR34, by contrast, offer transparent, peer-reviewed design processes that take these real-world conditions into account.
They provide robust safety factors that ensure the floor will perform as expected, even when site conditions aren’t perfect. This transparency is crucial for ensuring long-term durability, especially in demanding industrial environments.
I should add:
Watch out for suppliers presenting proprietary designs using “TR34 safety factors” – this is often code that they are trying to misrepresent a proprietary design.
For instance:
they might choose TR34 safety factors but use a different “proprietary” material strength assumption or “innovative” yield line model that makes their solution thinner. This approach is common amongst some very large and well-known steel fibre suppliers and is a covert way of cutting safety factors without making it obvious to the client or their engineer.
This can also make it hard to make ‘apples to apples’ comparisons between competing design and build bids.
It begs the question:
is a contractor cheaper because they are more efficient and productive, or have they just reduced safety factors in a sneaky way to save on material costs?
In the latter case, they can be cheating the client by offering a riskier solution than was asked for.
How Steel Fibre Suppliers Manipulate Loading Specs to Lower Costs
Another trick we sometimes see from steel fibre suppliers is the creative use of loading specifications.
Suppliers might assume larger-than-standard racking baseplates, wider gaps between back-to-back legs, or greater distances from joints – all intended to reduce slab thickness and make their solution look more competitive.
While this makes the designs look more cost-effective, they fail to account for real-world conditions where such assumptions might not hold true.
Lower Steel Fibre Dosage Claims: Pushing the boundaries
The construction industry has had a rough patch of late, creating a “race to the bottom” in terms of steel fibre designs in full force.
One way this manifests is through SFRC suppliers promoting lower fiber dosages than they previously considered sufficient.
At the moment we are seeing suppliers claim that as little as 15 kg/m³ or 20 kg/m³ of steel fibres will provide sufficient reinforcement for jointless industrial slabs on grade. Often this figure is based on the minimum quantity, or close to the minimum quantity, to satisfy “spacing theory”.
Spacing theory refers to the optimal distribution of steel fibres within the concrete matrix to achieve effective reinforcement.
The concept is centred on ensuring that there are enough fibres in the concrete, positioned in such a way that they are close enough to prevent crack formation and growth. Although using a minimum fibre dose from spacing theory has merit for some applications, such as in combination with conventional reinforcing in elements like beams, it is problematic in jointless steel fibre floors.
De-Risking Slab Durability with Traditional Steel Fibre Dosages
While spacing theory may play out in the controlled environment of a lab or in textbooks and produce sufficient Fr values and crack control, it doesn’t always translate to the realities of a construction site.
Issues such as inconsistent fibre distribution, or inaccurate batching/dosing of fibre, coupled with reduced slab thickness versus design, and other quality issues like poor concrete compaction can mean poor crack resistance in serviceability, and overall reduced slab performance.
That’s not to say that all slabs built with lower dosages of steel fibre will fail …
… but there is a greater risk of a serviceability issue due to these real-world factors, and more traditional dosages of steel fibre – closer to 30-40 kg/m3 can de-risk this, often with little to no significant impact to cost.
Are Low-Dosage SFRC and Hybrid Floor Designs Designed to Fail?
Additionally, there is often a lack of long-term performance data for low-dosage SFRC solutions or new approaches to industrial floors such as combined SFRC and mesh designs that are restrained and designed to crack.
This uncertainty is concerning.
While conventional reinforcement methods are supported by decades of real-world data, these low-dosage fibre solutions are still largely untested beyond about 5 years of service life, meaning clients may end up carrying the risk in the future.
When SFRC designs are based on marketing promises or a competitive “race to the bottom mentality” rather than real-world data, some floors are going to fail to live up to expectations.
Emphasising New “Technical Features” – The Flooring Marketing Game
In an effort to stand out, some suppliers push fibres with higher tensile strength, unique shapes, or extreme aspect ratios—none of which are necessary for typical industrial flooring applications. It’s akin to buying a high-performance sports car when all you really need is a reliable work truck.
Take higher tensile fibres, for example:
While they sound impressive, in normal-strength concrete they don’t offer any meaningful advantage. Similarly, fibres with higher aspect ratios are marketed as superior but often cause more harm than good, making surface finishing more difficult and increasing the risk of exposed fibres on the surface – something we are seeing in NZ at the moment with a push by some suppliers to use 80/60 aspect ratio fibres instead of the more traditional 65/60 fibres that have been used in flooring.
In reality, industrial flooring doesn’t need flashy extras.
What’s most important is an even distribution of fibres at an appropriate (i.e. not minimum) dosage that meets the performance requirements, without unnecessary bells and whistles.
Misrepresentation of Residual Flexural Strength: The Safety Net That Doesn’t Always Catch
Residual flexural strength, or post-crack strength, is a major benefit of SFRC that allows efficient slab on grade design.
The idea is that once a crack forms, the steel fibres will bridge the gap and continue to provide load-bearing capacity. As part of the steel fibre marketing arms race, we have seen trends to very high residual flexural strengths from certain fibre manufacturers – results that cannot be replicated in independent labs, or with sampling and testing of real-world concrete on site.
By being able to market higher residual flexural strengths compared to competitors, the supplier can attempt to justify thinner slab designs or lower dosages of fibres.
Tactics we have seen in support of “pumping up” these values include making sure fibres align perpendicular to the cracks that form in a beam test in the laboratory or using concrete mix designs that are in no way close to those used in real-world conditions.
Relying too heavily on these laboratory residual strengths can result in designs that are under-engineered.
Interestingly you can see trends in manufacturer data sheets where they have progressively quoted higher and higher residual strengths over the last 10 years – for a product that is the same shape, aspect ratio, and tensile strength.
The Risks of Proprietary SFRC Solutions and the Benefits of Open-Source Guidelines
The challenges of site variability — uneven slab thicknesses, inconsistent mixing, and the unpredictability of site conditions — are often glossed over by suppliers pushing proprietary SFRC solutions. But these real-world issues can have a major impact on performance.
Proprietary SFRC designs often trim these safety factors to create thinner slabs that look good on paper but don’t hold up on site.
The result?
Floors that crack, wear, and degrade faster than anticipated, leading to costly repairs and downtime.
By relying on open-source design guidelines like TR34, and using realistic residual flexural strengths, clients can ensure that their SFRC floors are designed with real-world tolerances in mind. This transparency eliminates the guesswork, providing confidence that the design will perform as expected, even in less-than-ideal conditions.
Understanding Design Ownership: Who Is Truly Responsible for Your Flooring Project?
A key challenge when working with steel fibre-reinforced concrete (SFRC) is the ambiguity around design ownership.
Frequently, suppliers offer design reports to assist clients, but these reports are filled with disclaimers that shift responsibility away from the supplier, leaving the client or their engineers holding the final accountability for the design’s accuracy and long-term performance.
For instance, one major multinational steel fibre supplier provides a very detailed design report with engineering calculations that are heavily caveated.
The fine print reveals that the design is supplied as an accommodation to the client, based solely on data provided by the client, and the supplier does not independently verify the inputs.
While the design may look complete, the supplier clearly states that they are not acting as a project engineer or architect, and the calculations should be fully verified by the client’s own project team.
Even more concerning, the supplier shifts the entire risk of performance failure onto the project user.
The report disclaims any warranty for the accuracy or completeness of the design, the software, or the recommendations, leaving clients exposed to liability if the design does not perform as expected.
Essentially, these reports provide preliminary guidance that requires thorough review by a suitably qualified engineer to ensure it meets the specific project’s requirements and standards.
This practice often causes confusion, as clients may incorrectly assume that the supplier’s design is ready to implement without further scrutiny.
However:
relying on these designs without independent verification could lead to significant liability if something goes wrong down the line.
Conclusion: Bring SFRC Back to Basics
Steel fibre-reinforcement can be treated as an engineering commodity in a similar manner to conventional reinforcing.
The focus should be on transparent, peer-reviewed design guidelines that take real-world conditions into account.
Marketing hype and proprietary design models have no place in an industry where long-term performance and reliability are critical.
A lot of the current practice we are seeing in New Zealand and Australia is the opposite of this – suppliers are competing by racing to the bottom with leaner and leaner designs, transferring risk to customers and preserving their margins.
Often this translates into a very small saving on construction costs that could result in bigger long-term maintenance bills.
In my experience, the owner or tenant of the property can be left footing those bills because by the time performance issues start to rear their head the contractors and suppliers have received their retention money and moved onto other projects.
Open-source guidelines like TR34 offer the framework needed to ensure that SFRC floors perform not just in the lab, but in the demanding, variable conditions of real-world industrial sites. By adopting these principles, and ensuring appropriate residual flexural strength values are used, clients can avoid the pitfalls of over-promising and under-delivering, ensuring that their floors are built to last.
Even though the designs may appear more expensive on paper, there is often very little difference in cost, and because they open clients up to a more competitive procurement process for steel fibre it’s possible to achieve cost savings while having a lower risk design.
It’s time to cut through the marketing spin and focus on what really matters: sound engineering, transparent design, and floors that deliver on their promises.
With that in mind, here are my 5 key recommendations for building owners and consultants wanting to de-risk their fibre-reinforced slabs:
- If specifying slabs for D&B – make sure you issue a detailed specification with very clearly defined loads, expectations around minimum fibre dose and type/shape, and insist on the use of an independent design model like TR34 4th Edition and realistic/real-world Fr values.
- Look out for contractors submitting designs and excluding key information – such as design method, steel fibre type/dosage, and design loads – if this information isn’t available or there is resistance to providing it, that should immediately ring warning bells.
- When comparing proposed designs from different contractors/suppliers, proceed with caution if one is offering a slab that is significantly cheaper, thinner or has a lower fibre dosage than other options.
- Ask who has ultimate responsibility as the designer of the slab. Can the contractor/supplier provide truly independent design review? Are there get-out-of-jail-free tags and clauses buried in their offer or design documentation that transfer risk to the client?
- Talk to Face Consultants – whether its for general advice, floor design, or taking care of the whole process from specification to construction monitoring – Face Consultants are the global experts in industrial floors.
For any inquiries or to explore the best options for your steel fibre-reinforced flooring project, please don’t hesitate to get in touch using the form in the link below.
https://face-consultants.co.nz/contact/
Tim Walker
Tim Walker is the Director of Face Consultants (NZ) and CoGri Limited (NZ). He has two decades of experience in the industry and provides the link between the Logistics Industry and Property and Construction; matching the requirements of one with the capabilities of the other.Contact Tim and his team today or follow us on LinkedIn:
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