C-DRONE GUIDE · 7 SEPTEMBER 2026

Drone and hot-mix asphalt plant: ICPE heading 2521, mixing tower, silos and aggregate stockpiles

A hot-mix asphalt plant is thirty to forty metres of steel tower rising abruptly at the edge of a quarry or an industrial estate, a drying-and-mixing drum heating aggregates past 150°C, bitumen tanks held at temperature day and night, insulated hot-mix storage silos, a bag filter, a stack — and, all around it, stockpiles of aggregate and road millings that shift every week. Through the paving season the plant almost never stops : every hour of downtime is a truckload of asphalt not delivered to a site that is waiting for it. As a result the high points only ever get looked at from a distance, scaffolding is never on the table, and a lift cannot fit between the conveyors. Here is what a drone genuinely documents on this kind of site, what it never replaces, and the prices.

Published on 7 September 2026, reviewed on 11 September 2026 — regulations in force as of September 2026.

ICPE heading 2521: what the nomenclature actually says

Site vocabulary happily talks about « producing materials treated with hydrocarbon binders ». The French classified-installations nomenclature is narrower and more literal : heading 2521 is titled « Enrobage au bitume de matériaux routiers (Centrale d') » — bitumen coating of road materials — and that is the exact wording an asphalt plant is classified under, the one to use in a regulatory file. The heading reads in two paragraphs. Paragraph 1, « hot », falls under the registration regime with no capacity threshold : every hot-mix plant is caught, whether it produces 80 or 400 tonnes an hour. Paragraph 2, « cold », splits in two : capacity above 1,500 t/day under registration, capacity above 100 t/day but at or below 1,500 t/day under simple declaration.

That structure is recent. Decree no. 2019-292 of 9 April 2019, published in the Journal officiel of 11 April 2019, moved hot-mix plants from the authorisation regime to registration and removed the authorisation threshold — a simplification that also covered headings 2564 and 2565. General requirements for registered plants are set by the order of 9 April 2019 ; cold plants under declaration still fall under the order of 30 June 1997. One point the circular of 6 March 2007 had already settled : a hot-mix plant falls under heading 2521 alone and not under heading 2910 (combustion), because combustion there is part of processing the material itself.

The 9 April 2019 order deals explicitly with the temporary site plant, under the phrase « installations operating over a single period of twelve months or less » : for those, stack height is set at at least 13 metres for a capacity of 150 t/h or more, and at least 8 metres below that. A mobile plant set up for the duration of a major motorway job does not escape the framework : it enters it with rules of its own. The text also requires a general layout plan of the workshops and stockpiles showing the danger zones, including the bituminous-materials storage zone, safety devices on heated tanks (low-level detection and automatic heating shutdown), and dust-carryover measures on powdery stockpiles. The logic is close to, but not the same as, that of a ready-mix concrete batching plant under heading 2518 : same aggregate stockpiles, same conveyors, but here with a furnace, a hot binder and a stack on top.

Insulation, drum shell, stack: what a flight reads on the mixing tower

An asphalt plant stacks, over some thirty metres, a run of equipment almost none of which can be reached on foot : the cold-feed bins and their supply conveyors, the drying-and-mixing drum and its shell, the bag filter and its steelwork, the exhaust duct and stack, the hot-mix storage silos with their insulation, the bitumen tanks and their thermal lagging, the bucket elevator or reclaim conveyor, and all around them the access walkways and stairs whose gratings and handrails age in contact with dust and condensate. A photogrammetric flight plus a series of close manual-flight shots produce, in half a day, full coverage of that assembly with nobody climbing and no production stoppage.

Three readings come first. Insulation thermography to begin with : on a hot-mix silo or a bitumen tank held at temperature, a torn lagging panel, an open joint or a detached cladding sheet show up plainly on the thermal image. That is two problems in one — energy paid for and lost every operating hour, and an outer surface that can become burning hot to the touch, a few metres from a walkway the operators use. The logic is exactly the one detailed in our guide to pipe-rack and insulated piping inspection, applied here to vertical vessels. Then corrosion : rust spots on the filter steelwork, streaking under a duct connection, pitting on a silo skirt, paint breakdown on the drum shell — an optical zoom picks these up from a safe distance, as on the shell of an industrial rotary kiln inspected by thermography. Lastly the condition of the stack before the season restarts : crown, flanges, any guy wires, cage ladder, duct and paint condition.

Airborne thermal measurement on bituminous materials is nothing exotic. A team led by Naaga Viswanath Vedula published in 2024, in the journal Transportation Research Record, a drone thermal survey protocol applied to asphalt paving : eight sites tracked from 0 to 60 minutes after laydown, quantifying mat temperature differentials (Gini index, percentage of non-uniformity, coefficient of variation) and detecting locally segregated spots (see the study on Google Scholar). That work covers the downstream end, the paving job, not the plant ; but it validates an airborne thermal sensor's ability to render usable temperature differences on a bituminous product, provided flight height and emissivity are controlled. The same caution applies at a plant : bare steel, dirty lagging and light-coloured paint do not share an emissivity, and a raw thermal image is read as relative differences, not absolute degrees.

Aggregate and millings stockpiles: volumes, inventory and a record before dismantling

Around the tower, the yard holds the other half of the site's value : the aggregate bays by size fraction, the reclaimed asphalt stockpiles — millings from pavement planing — and sometimes fines or filler. These piles move constantly, blend at the edges of the bays and are poorly counted from the ground. A photogrammetric survey produces a 3D model and a volume per pile, repeated on the same flight plan month after month to give a comparable series : the method detailed in our guide to drone stockpile and volume measurement for quarries and civil works, directly transposable to an asphalt plant yard.

Recycling has raised the stakes. According to the environmental report published by Routes de France (2024 data, released June 2025), the average rate at which reclaimed asphalt is reintroduced into bituminous mixes, excluding emulsion mixes, reached 25.3%, against 23.7% in 2023. A pile of millings is no longer a nuisance waiting for disposal : it is a raw-material stock, with a balance-sheet value, a limited footprint on the yard and a real interest in being measured rather than eyeballed. A study by D. J. A. Davis and N. S. Guy, published in 2023 in the International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, compared three acquisition techniques on aggregate stockpiles — total station, terrestrial laser scanning and drone photogrammetry : the total station generally under-reports volumes and becomes impractical on fine materials, while the drone performs best at low altitude with a high overlap ratio (see the study on Google Scholar). In other words : the result depends on the flight plan as much as on the hardware, and a pile that is partly covered, backed against a bay wall or being loaded out during the flight remains a source of error no software recovers.

Two recurring uses round out the volume survey. First the photographic file for the environmental inspectorate : a dated orthophoto of the yard, showing the actual storage footprint and the condition of the containment areas and roadways, prepares a visit or supports a regulatory notification far better than a set of ground-level photos — the same periodic-coverage logic as in our guide to quarry 3D modelling for the annual production declaration. Then the record before dismantling a mobile plant at the end of a job : a full survey of the platform before demobilisation documents the footprint, the soiled areas, the concreted aprons and the state of the ground — a useful document when the site has to be reinstated, and a hard one to reconstruct once the modules have gone.

Who commissions this kind of mission, method and 2026 prices

These missions are commissioned by road-works contractors and their asphalt subsidiaries, operators of fixed and mobile plants, the QSE and maintenance departments preparing a season or a shutdown, integrated quarry operators running both the quarry and the plant on one site, and inspection bodies that need a visual baseline before committing to a detailed survey. The core argument is the same everywhere : through the season the plant is running ; shutdowns are short, planned to the day, and an inspection requiring scaffolding or a lift consumes exactly the resource the operator is short of. A drone surveys without climbing and without a full stop — provided site rules are respected.

The mission is prepared beforehand, never on the morning itself. As with any intervention on an industrial site with a prevention plan and coactivity, the briefing with the QSE manager sets the slots compatible with production, the movement of articulated lorries and loading shovels across the yard, any explosive-atmosphere zones classified around the fuel, gas or hot-bitumen tanks — the same precaution as on a hydrocarbon storage tank in an ATEX zone — and a take-off point clear of steam plumes and dust. Expect a hot, dusty environment loaded with bitumen fume : plumes disturb the thermal image, foul the optics and are best flown around rather than through. A pass over the feed belt conveyors usefully rounds out the tower survey.

The limits have to be stated plainly, because they shape the whole job : the drone documents and targets, it certifies nothing. It replaces neither the stack emissions measurements, which are the job of a qualified external body at the frequencies set by the order of 9 April 2019, nor the periodic inspections of pressure equipment, nor the electrical installation checks, nor an ultrasonic residual-thickness measurement on a corroded plate. Nor does it say whether lagging complies : it shows where it plainly no longer does. On a drum shell or a steel frame, it sorts — which points warrant physical access, and which can wait for the next shutdown.

Ranges observed in France in 2026, excl. VAT:

A travel charge applies beyond a 30 to 50 km radius, and recurring monitoring on the same flight plan is usually negotiated at a tapering rate. For an asphalt plant, a road-works subsidiary or a mobile-plant operator, request a quote stating the tower height, the hourly capacity, the number of silos and tanks to check, and the goal (season preparation, ICPE inspection file, stock inventory or a record before demobilisation).

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