Fibre reinforcement in greenhouse construction: pouring floors on sand

A greenhouse floor is almost always a monolithic concrete floor on sand: 10–15 cm of concrete on a compacted sand bed with PE film, poured in a single operation and power-floated by machine. Fibre reinforcement (2–6 kg/m³ of macro fibre) replaces the reinforcement mesh — corrosion-free under fertilisers and permanent moisture, and with no separate laying stage before the pour.

Concrete in the greenhouse: a load combination few sectors know

Dutch greenhouse horticulture has some of the largest continuous concrete floors and paths in the country: main paths hundreds of metres long, processing areas, ebb-and-flood floors and loading pits. That concrete has to endure a combination of loads rarely seen outside the sector:

• Chemical exposure — fertilisers, nutrient solutions (pH typically 5.5–6.2) and crop protection products land on the floor daily.

• Permanent moisture loading — irrigation water, condensation against the greenhouse roof and humidity that stays high all year round.

• Intensive, repetitive transport — pipe rail trolleys, pallet trucks, forklifts and, increasingly, harvesting and UV robots driving exactly the same routes day in, day out.

• Ground risks — settlement from subsidence and a falling water table, resulting in cracking and unevenness in floors and foundations.

For traditional steel reinforcement, that first combination in particular is a problem: as soon as the concrete cover cracks or is too thin, moisture and chemicals attack the reinforcing steel. How that mechanism works — and why fibres are immune to it — is explained in our article on corrosion of reinforcing steel. What the agricultural business faces outside the greenhouse (barn floors, silage clamps, slurry acids) is covered separately in fibre-reinforced concrete in the agricultural sector; this article is about the cultivation side: the greenhouse floor itself.

Pouring a greenhouse floor on sand: the build-up

Greenhouses generally stand on a levelled sand layer, and the floors and paths are poured directly onto it — a concrete floor on sand, without a separate foundation. The quality of that sand bed determines the end result just as strongly as the concrete itself. The build-up from bottom to top:

• Sand bed — 20–30 cm of clean sand, mechanically compacted in layers with a plate compactor or roller.

• Separating layer — 0.2 mm PE construction film with generous overlaps; without film the mixing water drains away into the sand and the concrete cracks prematurely on the underside.

• Concrete slab — 10–15 cm of fibre-reinforced concrete, depending on the loading, power-floated by machine straight away.

The full pouring sequence — from ordering the concrete with the fibres already in the mix through to curing — is set out in the complete guide to pouring fibre-reinforced concrete.

Concrete floor thickness on sand: guide values for the greenhouse

The thickness follows from the heaviest load that will ever come onto the floor, not the average. Practical values on a well-compacted sand bed:

• Concrete paths between the crop rows — 8–10 cm; pipe rail trolleys and pedestrians.

• Main path — 10–12 cm; harvest trolleys, pallet trucks and robot traffic.

• Main path with forklift traffic — 12–15 cm; including the route to and from the packing shed.

• Processing area and loading pit — 15–18 cm; forklifts, lorry docks and point loads from racking.

The minimum thickness of a concrete floor on sand is around 10 cm. A reinforcement mesh makes pouring thinner than that difficult: the mesh needs 20–30 mm of concrete cover on both sides and must be set at height — at 10 cm there is hardly any setting room left. Fibres have no cover requirement and sit homogeneously through the whole slab, which makes 10 cm reliably buildable. The full thickness table per application can be found in how thick should a concrete floor be.

Monolithic concrete floor: pouring and finishing in one day

Greenhouse floors and main paths are executed as a monolithic concrete floor: pouring, levelling and machine power floating in one continuous operation, producing a dense, wear-resistant top layer without a separate screed. For cultivation, that is more than a cost issue. A power-floated, flat surface is easy to keep clean and disinfected (hygiene is a cultivation precondition in horticulture) and automated transport systems and robots impose strict flatness requirements: every bump on the main path is a breakdown in the making.

Fibre reinforcement fits seamlessly into that way of working. The fibres are blended through the mix at the batching plant and arrive with the truck mixer; the pouring crew can start straight away, and with a correctly dosed macro fibre the power floating proceeds by machine as normal. Large areas can moreover be executed with fewer contraction joints — every joint is an obstacle for trolleys and robots and a dirt trap.

Ebb-and-flood floors: watertight under nutrient solution

The ebb-and-flood floor is the most demanding concrete application in the greenhouse. This cultivation floor is flooded a few centimetres deep with nutrient solution per cycle and drained again after 10–30 minutes; the water is collected and reused. That imposes three hard requirements:

• Watertightness — the nutrient water must not leak away into the subgrade; in practice, concrete with crack widths up to around 0.2 mm counts as watertight.

• Chemical resistance — the floor stands full of slightly acidic, salt-rich nutrient solution many times a week.

• Dimensional stability under falls — the floor must lie exactly to falls in both directions to drain without ponding, and keep doing so for decades.

Crack control here is therefore not aesthetics but functionality. Fibre reinforcement limits crack widths because millions of fibres per cubic metre bridge every incipient crack immediately — including in the top zone, where a reinforcement mesh never reaches because of the cover requirement. And because synthetic fibres are chemically inert, the risk of a hairline crack leading to rusting reinforcement and spalling concrete simply does not exist.

Pipe rail, harvesting robots and point loads

Internal transport in a modern greenhouse is almost entirely standardised around the pipe rail system: steel pipes between the crop rows carrying pipe rail trolleys and spray robots. The rails themselves rest on supports, but all the traffic converges on the concrete main path — and that is exactly where the governing loads arise.

A fully laden harvest trolley, a pallet truck with crates or a harvesting robot with its battery pack loads the floor not evenly but via small wheel contact areas: point loads returning to the same lanes day after day. Fibre-reinforced concrete distributes those repetitive loads through the full slab cross-section and thus slows fatigue cracking on heavily used routes. For heavy, concentrated loads — racking legs in the processing area, dock edges at the loading pit — a locally thicker slab or supplementary reinforcement remains a matter for the structural engineer.

Settlement and subsidence: the slab moves with the ground

Many greenhouse areas lie on settlement-prone clay and peat soils, and subsidence and a falling water table are increasing the likelihood of differential settlement. A concrete floor on sand behaves as a slab on an elastic bedding: if the subgrade drops locally, the slab has to bridge that gap. That is precisely the moment when reinforcement present everywhere in the cross-section counts. Fibres provide residual strength after cracking (demonstrable via the flexural strength test of EN 14651) and hold crack faces together, so a settlement crack stays controlled instead of growing into a stepped fracture — for robot traffic, the difference between carrying on and standing still.

No reinforcement can prevent settlement entirely; a carefully compacted sand bed and a realistic assessment of the subgrade remain the foundation under every greenhouse floor.

Worked example: m² of greenhouse floor per day, with and without mesh

Suppose: a new-build greenhouse with 3,000 m² of poured concrete — main path, processing area and loading pit. With traditional reinforcement mesh, a separate work stage precedes the pour: delivering the mesh, laying it out, connecting it with laps and setting it on spacers. With a crew of two, 400–600 m² per day is a realistic output; for 3,000 m² that means 5 to 7 extra working days before the first truck mixer can arrive — in a greenhouse that at that point is often already glazed, with all the internal transport of mesh through narrow paths that entails.

With fibre reinforcement that stage disappears entirely: the fibres are already in the concrete when it arrives. The crew lays the film, sets up the laser-guided screeding equipment and pours and floats 800–1,200 m² per day. The difference is therefore not just around a working week of lead time, but also: no steel to carry into the greenhouse, no cover errors that come back years later as rust damage, and no mesh sinking away during the pour. What that saves in euros is worked out sector-wide in the knowledge centre under applications and target groups.

Which fibre for which greenhouse floor?

For greenhouse floors, main paths and processing areas, the Wiking 4050 TR is the logical first choice: an acid- and alkali-resistant macro fibre made of polyolefin (dosage 2–6 kg/m³) that is insensitive to fertilisers, nutrient water and cleaning agents — and therefore the designated fibre for greenhouse floors under chemical loading. For structurally heavier applications, such as loading pits or floors with high point loads, the TwistR offers structural residual strength as corrosion-free floor reinforcement for horticulture: a 100% polypropylene macro fibre with a twisted structure that can replace traditional reinforcing steel in floors on sand.

Steel fibres are technically usable, but in the permanently damp, chemically loaded greenhouse climate, fibres at the floor surface can leave rust marks — for ebb-and-flood floors and visible floors, a synthetic fibre is therefore the safer choice. For the foundations of the greenhouse structure itself (wind loading, anchoring of columns), calculated traditional reinforcement generally remains the starting point; fibres play at most a supplementary role in crack control there. Always put structural choices to your structural engineer.

From greenhouse floor to haul road: fibres around the development

Fibre reinforcement does not stop at the greenhouse floor. Around a new-build greenhouse there is also yard paving, a loading area and, during construction, a haul road that has to carry heavy construction logistics for months. For the Tuindersweijde development in Obdam, Dura Vermeer built such a temporary haul road zero-emission with fibre-reinforced asphalt: 1,890 tonnes, designed for the heavy construction traffic of the entire project.

Planning a greenhouse floor, processing area or ebb-and-flood floor? Request a quotation with your floor area and loading and we will advise on fibre type and dosage — or use the selection guide to determine yourself which fibre suits your project.