SteelX Rebar
The Technology

Twisted steel rebar.
Not steel fibre.

Steel fibre enhanced concrete is not a new concept — many shapes, lengths and tensile strengths have been added to concrete for decades, so many incorrectly assume SteelX is just ‘another’ steel fibre. The failure mechanism says otherwise.

Torsion, not friction
What it does to the concrete
Designing with it
Batching & mix design

Torsion, not friction

SteelX 5:25 is a Twisted Steel Reinforcement (TSR) with a unique ability to bond with concrete due to its twisted shape, providing a torsional anchorage that engages before the concrete fails and creates a true composite with the concrete.

Each piece bonds to the matrix over its full length and must untwist as it pulls out. That is significantly different from traditional steel fibres, where pullout is governed by friction.

The torsional pullout mechanism requires considerably more force — 2 to 5 times more than steel fibres — and remains consistent over roughly 80–90% of the embedded length.

Traditional steel fibre
SteelX TSR
Pullout governed by friction
Must untwist to pull out — torsion
Engages after a crack forms
Engages before the concrete fails
Bond at the hooked ends
Bonds over the full length of the strand
Baseline pullout force
2-5× the pullout force
No change to first crack strength
Increases modulus of rupture (MOR)
Force diagram of a SteelX 5:25 wire during pullout
FIG. 1 Force diagram of SteelX 5:25 wire being pulled from the concrete matrix — a torsion failure mechanism, not bending or friction.
Pullout load versus slip: twisted steel rebar slip-hardening compared with hooked-end fibre slip-softening
FIG. 2 Pullout load against slip. Twisted steel sustains load all the way to full withdrawal; a hooked-end fibre peaks early, then decays as the hook straightens. Curves are representative reconstructions from published test data, not digitised results.
Interactive — measured test data

Watch a strand untwist as it pulls out

Open full screen →

What it does to the concrete

Because of the superior bond, the material properties of the concrete itself improve before a dominant crack ever forms. That is proactive reinforcement — and it is measurable.

Before the crack
Proactive reinforcement
Material properties of the concrete improve prior to a dominant crack forming. Reinforcement begins at microscopic, water-tight crack widths invisible to the naked eye.
First crack
Higher modulus of rupture
SteelX increases the concrete's first crack strength, and the amount of strain the concrete can carry before a crack forms — TSR concrete is more ductile and flexible.
After the crack
Stable post-crack capacity
Once a dominant crack forms, SteelX holds a stable capacity across ~80-90% of the embedded length, so engineers can design with it just like rebar.
Durability
Tensile splitting strength
Testing shows meaningful improvement in tensile splitting strength even at relatively small dosages — real, tangible gains in long-term serviceability.

Tensile splitting data from a TSR product published in “Mechanical, durability and microstructural characteristics of ultra-high-strength self-compacting concrete incorporating steel fibers”, Amr S. El-Dieb, 1 April 2009.

Designing with it

Engineer resources →
Design software
Mi Concrete Design

Run your SteelX designs in McClay’s own design tool — work through reinforcement ratios and slab thickness, and get a SteelX dosage you can put on the drawings.

On site

Easiest product on the market to add, mix and record

Typically a mix design requires minimal to no alteration. A mix that performs well without SteelX will, in most instances, perform well with it. Complex jobs — jointless slabs, restrained elements, critical crack widths — get a free mix design review.

Request a mix design review →
If your plant is dosing it
In South East Queensland we dose SteelX on site at the truck — see on-site dosing. Elsewhere, or where a plant doses it, this is the sequence:
01
SteelX into the agitator. Load the total volume of SteelX directly into the agitator of the truck. The boxes are not soluble — don't load them.
02
80–90% of the water. Add 80–90% of the mix water and let the SteelX mix in the water for at least 30 seconds — 60 seconds for dosages of 15 kg/m³ or more.
03
Everything else. Add aggregate, sand, cement, other ingredients and the remaining water — aggregate first where possible.
04
Record it. Note the SteelX dosage on each batch ticket and record every batch on the SteelX Batching Register.
Download the method & register (PDF) →
Slump targets
Below 10 kg/m³ — 80–90 mm · 10–19 kg/m³ — 90–110 mm · 20–30 kg/m³ — 110–150 mm

Get a free analysis on your project

Send us your drawings and we’ll show you what comes out: the mesh, the rebar, the thickness, the weeks.