Aneesh Boravkeaneesh.boravke.uk

Projects04In progress

Individual Project: Thermal Resistance of Concrete for Jet Landing Pads

My final-year individual project, looking at how concrete stands up to jet exhaust heat on landing pads.

Module
FEEG3003
Year
Year 3, 2026–27
Supervisor
Dr Ye Li (Construction Materials)
Labs
Cast and cured in the LSTL (Boldrewood), tested at the TSRL
Full title
Enhancing the Thermal Resistance of Concrete Landing Pads under Jet Exhaust: A Combined CFD–FEA and Experimental Study

1 · The question

Vertical-landing jets slowly damage their landing pads, and repairs are expensive. I’m testing whether a stronger top layer, not fully bonded to the concrete beneath, can take the heat damage and then be replaced on its own, instead of digging out the whole pad. Cheaper, longer-lasting pads matter for military operations now, and possibly for commercial VTOL later.

1.1 · Why it matters

The F-35B hovers and lands vertically, so the UK flies it from carriers and from RAF Marham, where it lands on purpose-built concrete pads. During a vertical landing the exhaust hits the pad at around 900 °C and close to the speed of sound. Ordinary airfield concrete is expected to crack and flake on the first landing, so pads use special heat-resistant concrete, and even that wears: the top few millimetres are ground off after a few hundred landings.

A published modelling study found the damage stays in those top few millimetres. That suggests a layer of better concrete about 2 cm thick on an ordinary slab could do much of the job of a far more expensive full-depth pad. Earlier experiments heated concrete either once at high temperature or many times at low temperature; rapid, repeated heating close to real landing conditions hasn’t been tested. That’s the gap I’m testing.

2 · What I’m testing, and why

The plan is to heat small concrete cubes from one face only, the way jet exhaust hits a pad, and compare four mixes. Each mix tests one idea:

  • M0 Control. Plain fine concrete, 10 mm maximum aggregate, no fibre. The baseline, and the mix I expect to be most prone to spalling.
  • M1 PP fibre + fly ash. About 25% Class F fly ash and polypropylene fibre at about 1.8 kg/m³, close to the recipe in the US Air Force pad guidance (ETL 14-4).
  • M2 UHPC. Ultra-high-performance concrete: cement, silica fume, fine sand and superplasticiser at a water/binder ratio of about 0.18, with steel fibre at about 2% by volume plus PP fibre.
  • M3 Top layer. A 30 mm M0 base with a 20 mm UHPC top, cast wet-on-wet on the same day. This is the replaceable-top-layer idea.

The specimens are 50 mm cubes, slightly smaller than a Rubik’s cube: 32 main cubes, eight per mix, plus up to 10 trial cubes. Per mix, 3 stay unheated as references, 3 are tracked through the heating cycles, 1 is instrumented with thermocouples and 1 is a spare.

3 · Method (planned)

  1. Cast one mix per day in the Large Structures Testing Lab (LSTL) on a vibrating table.
  2. Demould at 24 h, then water-cure for 28 days at 20 ± 2 °C.
  3. Air-dry until the mass changes by less than 0.1% in 24 h.
  4. Cycle 0 baseline: mass, ultrasonic pulse velocity (UPV) and photos.
  5. Heating: each cube sits in a ceramic-fibre board holder so heat only enters through the top face, like jet exhaust on a pad. Hot insertion into a furnace at 1200 °C, a 3 minute hold, then air-cooling.
  6. Checkpoints after cycles 1, 3, 5 and 10: mass, UPV, photos, a crack map, and the M3 interface.
  7. Thermocouples in the instrumented cube: A 10 mm below the heated face and B at the centre, with the probes bent into an L so the last stretch runs along an isotherm.
  8. Micro-CT scans at the University’s µ-VIS centre of four heated cubes, one per mix.
  9. Crush the tracked and reference cubes on the same day, giving residual strength as a percentage of unheated.
Heat in through the top face only furnace at 1200 °C, hot insertion, 3 min hold, then air-cool A B 50 10 25 isotherms (flat) thermocouple probes, bent into an L A: 10 mm below the heated face B: centre ceramic-fibre board holder 50 mm concrete cube dimensions in mm Section, not to scale
Fig. 2: Section through a 50 mm cube in its ceramic-fibre board holder, heated through the top face only, with thermocouples A (10 mm below the heated face) and B (centre). Section, not to scale.

4 · Simulation (planned)

  • A simplified CFD model of the jet impinging on the pad, checked first against a cold validation case, then a hot-jet case (ANSYS Fluent).
  • FEA and parameter sweeps of the heated slab (ANSYS).

5 · Timeline

Planned, subject to safety approval. Items move to done as they happen.

  1. 14 Oct 2026Project Plan presentationDone
  2. 23 Oct 2026Project Plan (M1) submittedDone
  3. Nov 2026Trial cast and trial heatingPlanned
  4. Nov 2026Main cast over four daysPlanned
  5. 27 Nov 2026Interim Report (M2)Planned
  6. Dec 2026 to Jan 202728-day cure, then air-dryingPlanned
  7. Late Jan to Feb 2027Cycle 0, then 10 heating cycles; CT scansPlanned
  8. Early Mar 2027Crush tests; full draftPlanned
  9. 23 Apr 2027Final Report (M3)Planned
  10. w/c 24 May 2027Poster (M4)Planned