Aluminium vs Plastic Crane Mats: The Bending Test

The rig applies a 3-point load through a 500mm x 500mm steel plate, 30mm deep. We chose that plate size deliberately — it simulates the ground-bearing footprint of a mobile crane outrigger foot, so we're loading the mat the way a real job does: not a broad load spread evenly across the whole panel, but the small, hard, concentrated contact patch a mat actually meets on site. That's the honest test of a crane mat — can it take a load applied over roughly a quarter of a square metre in its centre and spread that load sideways, so the ground under its full footprint shares the burden, or does it simply bend around the load like a diving board?

We ran three progressively higher loads through that same plate — 1 tonne, 2.25 tonnes and 3.5 tonnes. At each load we tested an ALIMATS aluminium mat and a competing UHMW-PE plastic mat under identical rig conditions and measured the vertical deflection at the loaded point for each. The two products weren't identical in footprint or depth — a genuinely like-for-like panel wasn't available from the competing manufacturer — so we've recorded the exact dimensions and weight of each mat at every stage alongside its deflection figure, both in the narrative below and in the results table.

Across all three loads the pattern was consistent, and stark. In Test 1 we applied 1 tonne through the steel plate onto a UHMW-PE plastic mat measuring 1.8m x 0.6m, 50mm deep, weighing 52kg and manufacturer-rated for 54 tonnes. It deflected 102mm. The ALIMATS aluminium mat we tested alongside it — 1.74m x 0.58m, 60mm deep, weighing 38kg — deflected 2mm.

In Test 2 we raised the load to 2.25 tonnes on the same single-layer mats. The UHMW-PE mat deflected 328mm — more than three times its Test 1 deflection, off little more than double the load. The ALIMATS mat deflected 3mm.

Test 3 set out to answer a fair follow-up question: would doubling the plastic mat's thickness close the gap? We stacked two of the 50mm UHMW-PE mats to 100mm overall and tested them against a single-layer 60mm ALIMATS mat at 3.5 tonnes. The doubled-thickness plastic mat deflected 161mm. The single-layer ALIMATS mat deflected 8mm.

We'll be fair to the plastic mat. It's rated for 54 tonnes, and at no point across these three loads — every one a small fraction of that rating — did it crack, split or show any sign of structural failure. Compressively, it held up exactly as its manufacturer's rating says it should. This test isn't evidence that the mat is unsafe, or that its SWL rating is false. It demonstrates a different property altogether — stiffness, not strength — and the two are not the same thing.

This is where load triangulation matters. A mat that stays rigid under a point load transmits that load down through its full footprint at a shallow, even spread — the ground under the whole mat shares the pressure, which is the entire point of specifying a mat in the first place. A mat that deflects heavily stops doing that. Instead of a flat panel in full contact with the ground, it becomes a shallow bowl, bending hardest directly beneath the load and bearing less and less toward its edges. The load path narrows — it triangulates — down through a cone of material far closer in width to the loaded plate than to the mat's stated footprint.

Put a number on it. The UHMW-PE mat has a footprint of 1.08 square metres (1.8m x 0.6m); the steel plate applying the load covers 0.25 square metres (500mm x 500mm). At 102mm of deflection, the ground isn't experiencing anything like the pressure you'd calculate by dividing the load across that full 1.08 square metres — it's experiencing something much closer to the bare outrigger foot pressing almost straight into the ground, exactly the concentrated point loading the mat was specified to prevent. That gap between the footprint printed on the spec sheet and the footprint actually doing the work is the on-site consequence of low stiffness — and it's precisely what a headline SWL rating cannot show you.

There's one more thing worth being straight about, and it cuts against the plastic mat, not in its favour. Bending test rigs — ours included — are typically set up with a compressible layer beneath the test mat, commonly a foam such as Ethafoam, rather than a fully rigid steel or concrete base. That's partly practical: it protects the rig and the mat, and it isolates the reading to the mat's own deflection rather than transmitting shock through into the rig frame. But it has a real effect on the numbers.

On a compressible base, some of a flexible mat's apparent give is shared between the mat bending and the foam compressing beneath it — the yielding base takes up stress that, on a genuinely rigid subgrade, would have nowhere to go except into further bending of the mat itself. So a compressible test base flatters a flexible mat's real-world deflection, because the base is doing some of the absorbing work the mat would otherwise have to do alone.

Which means the 102mm, 328mm and 161mm figures recorded on our own rig, if anything, understate how much that mat would flex on a fully rigid subgrade. It's also why we'd tell anyone comparing published deflection or SWL data between suppliers to ask one blunt question first — what surface was your test rig sitting on? Two mats tested on two different bases are not being compared like for like, however close their headline numbers look on a data sheet.

This test sits inside a broader, well-established engineering picture. For stiffness — resistance to deflection, which is what governs load spread — the hierarchy across common mat and ground-protection materials runs steel, then aluminium, then timber, then nylon, then polyethylene. For raw compressive strength — the load a material bears before it yields or crushes — the order shifts: steel, then aluminium, then nylon, then polyethylene, then timber.

The telling detail is that timber and the two polymers swap places between the two lists. Timber's fibrous grain resists bending deflection reasonably well up to a point, even though it will eventually crush or split under enough raw compressive overload — so it out-performs nylon and polyethylene on stiffness despite ranking behind them on compressive strength. Nylon and UHMW-PE are genuinely tough and wear-resistant, but they're low-modulus materials — inherently more flexible — so they show visible elastic deflection under a concentrated point load long before they're anywhere near their compressive limit.

Aluminium sits second on both lists at once — behind steel on strength and behind steel on stiffness, but ahead of everything else on both counts, at a fraction of steel's weight. Strong enough not to fail, stiff enough not to bend appreciably, light enough to handle by hand — that combination is the whole engineering logic behind building ALIMATS from 6005A aluminium alloy, and it's why the deflection figures in this test look the way they do.

The practical takeaway is simple — don't accept a headline SWL figure on its own when you're comparing crane mats. Ask for deflection data at stated test loads to sit alongside it, and ask what surface that data was gathered on, for the reasons set out above. Two mats can carry an identical rated tonnage on paper and spread that load nothing like equally in practice — and spreading the load, not merely surviving it, is the entire reason you specify a mat in the first place.

ALIMATS is our patented modular aluminium crane mat system, built from 6005A alloy, with SWL ratings up to 80 tonnes across the range, independently verified with input from a Fellow of the Institution of Structural Engineers and comfortably rated for use under cranes up to 150 tonnes. We hire and sell it across the UK with 24/7 delivery from our base in Little Eaton, Derbyshire — and the deflection data in this test is exactly the kind of evidence we'd tell you to ask any supplier for, ourselves included.