Trucking Pre-Swollen Gel 60 km: Paying to Move Water by the Tonne

Eight truck movements, 20 tonnes each, 60 km of highway, to deliver the equivalent of one tonne of dry powder. The haulage bill came to 1,440 and the water arrived warm, partly evaporated and half of it in the bottom of the tipper. The job was a 2-hectare slope stabilisation where the hydroseeder could not handle dry powder feed, so the crew had decided that pre-swollen gel was the only option. It was not the only option, but it was the most expensive one.

Swollen gel is roughly 150 times its dry weight. That single ratio should govern every logistics decision about it, and yet contractors routinely plan to move wet gel because it feels easier at the mixing end.

The arithmetic of moving water

One tonne of dry polymer at 250 g/g in site water becomes about 250 tonnes of gel, allowing for drainage losses. A tipper carries 20 tonnes, so a single tonne of dry product is 12 to 13 loads. At 180 per load for a 60 km round trip, that is roughly 2,200 in freight against 60 to 90 per tonne to move the dry bags. The wet route costs 20 to 30 times more per effective kilogram.

Then there is what happens on arrival. A tipper is not a sealed tank. In summer, the top 200 mm of a load dries into a skin, and the material that slumps against the tailgate loses water as it sits. By the time the last load is placed, the solids content has drifted, and the dose in the last hectare is 10 to 20 percent lower than the first, which is exactly the error nobody measures.

When wet gel is the right answer

There are legitimate cases. If the mixing plant cannot handle dust, or if the site has no water supply and no tanker access, pre-swelling at a depot and delivering in a sealed tanker can be the only workable route. Short distances change the maths: under 5 km, with a 10 cubic metre tanker and a pump, the freight is negligible and the labour saving at the mixing end is real.

The other case is small volumes. For 50 kg of dry product on a 3-hectare hydroseeding job, pre-swelling in an IBC at the depot and delivering one tanker load is simpler than installing a dust-controlled mixing station. The cost per kilogram is high, but the absolute number is small.

If you do it, control three things

• Seal the load. A tanker or a lined, covered bin, not an open tipper. Evaporation is not the main loss; skinning and contamination are.
• Mix to a known solids content, 0.6 to 0.8 percent by weight, and record it at loading and at discharge with a simple cup-and-scale check.
• Deliver within 24 hours. Swollen gel held in a warm tank for three days goes anaerobic, smells, and loses structure; the viscosity drops and the material no longer suspends in a slurry.

Do not store swollen gel in an IBC in direct sun for a week and expect it to behave. We have seen a tank of gel turn to a sour, watery sludge in five days at 38 °C, and the crew then dosed it as if it were full strength, which put the application 40 percent under target on a slope that failed in the first storm.

The cheaper alternative most crews miss

Dry powder can be fed into a hydroseeder if you add it correctly: fill the tank two-thirds with water, start the recirculation, and add the powder through the eductor at the rate the venturi can pull, not in one dump. It takes 6 to 8 minutes for 25 kg. The dust is controlled by keeping the bag below the water surface as it empties. That is the method that removes the need for the eight trucks.

If dust is the real obstacle, a 200-litre drum with a lid and a water ring solves it for the price of a day’s hire. The mixing methods and the recommended slurry concentrations are set out on our SAP powder application pages, including the eductor feeding rate for hydroseeders.

Before the next slope job, calculate the freight per effective kilogram both ways and put the number in the tender. The decision usually makes itself once the haulage is on the same page as the material cost.