Medway adopts pre-wet gritting, cutting salt use by 20%
VolkerHighways’ Medway highway maintenance contract has entered its second year of using pre-wet salt to grit our road network as an alternative to traditional dry salt.
Pre-wetted salt is a mixture of dry rock salt that has been coated with a liquid brine solution before being spread on the road surface, essentially making it wet salt which helps it cling to the surface and melt snow and ice more effectively compared to dry salt alone. As well as improving de-icing efficiency this also reduces salt usage.
The brine solution requires specialist equipment, a saturator to produce the brine solution, a storage tank to store the brine solution to be drawn-off as required and saddle tanks retrofitted to the gritting vehicles to dispense the brine solution over the salt at the spinner disc.
The brine solution is made by adding a large amount of marine white salt to the saturator's salt hopper manually. The rest of the process is automated. Fresh water flows through the salt to create the solution, which then moves into the dilution chamber, where the salinity is measured. Once the salinity reaches the target concentration of 24%, the solution is sent to the brine storage chamber before being transferred to the saddle tanks.
The dry rock salt is mined within the UK and transported to the depot. The last winter season (Oct 23 – Apr 24), which was a mild year (the UK’s fourth mildest year on record), the team used approx. 1,200t of dry rock salt. By using this technique, on average 20% less rock salt is used. This would equate to around 300t less rock salt used, reducing 11 lorry loads.
The pre-wet salt method is used on Medway’s eight gritting primary routes, totalling 437km and has already saved 200t of rock salt this winter season to date.
Further reducing the impact on the environment by using the earth’s natural resources, next winter season, the team plan to add a rainwater harvesting system that feeds the saturator system via filtered rainwater.
