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Put a sock on it

14 Oct 14 They say the simplest ideas are always the best, and what could be simpler than the Concrete Sock?

The Concrete Sock is held in place with a strong webbing strap and cam-buckle
The Concrete Sock is held in place with a strong webbing strap and cam-buckle

Operators of concrete truck mixers well understand the need to wash out the chute on their machines before leaving site following a delivery.

Failure to wash-out means that residual cement and aggregate will start dripping out of the vehicle’s back end, polluting the roads and potentially damaging other vehicles. But environmental concerns mean that, increasingly, washing-out on a customer’s site is not possible unless special facilities are available to collect and properly dispose of the surplus material.

These facilities – settlement tanks, pH correction filters and so on – tend to be expensive, too. So what to do? The simple answer is to put a Concrete Sock on the end of the chute. Any surplus concrete making its way out of the machine on the return journey is collected in the tough, flexible bag and can be properly disposed of – or even recycled - back at the batching plant. It’s amazing to think that such an obvious no-brainer took so long to dream up – but then the problem did not require a solution until quite recently.

The Concretesock’s inventor, civil engineer Karl Goff, got the idea after seeing the mess left on site by departing truck mixers. “There was always a snail-trail to the washout area,” he says. He conceived the idea of a simple bag to contain the residue while working in New Zealand.

It was only on his return to the UK that Karl, and his brother Dan Smith, decided that there was mileage in the idea. Although simple, the concept seemed to tick so many “must-have” boxes that they set up a company – called Concretesock – and produced a series of prototypes.

The breakthrough came in 2010, when Goff was working for Interserve on the Drift water treatment works granular activated carbon project for South West Water in west Cornwall.

The close proximity of a local watercourse and concern about possible pollution from high pH water associated with traditional site-based concrete washout skips persuaded Interserve to establish a zero-washout rule. Interserve also wanted to eliminate the costs associated with establishing and maintaining washout facilities, pH treatment units and waste disposal on site. After discussions with concrete supplier Bardon, Interserve decided to trial Goff’s idea. Goff later received a “Best Innovation” award from his employer.

The Concretesock is essentially a shallow bag made from tough tarpaulin, shaped to the profile of the mixer’s chute. It is attached firmly with a strong webbing strap and cambuckle which is tightened just behind the flange where the lower folding section of the chute articulates.

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“The first prototypes were very crude and we tried to fix them further up the chute but they only slipped down again. The final design only reaches about 50mm up the chute, but it fits so tightly that you can’t get it off unless you loosen the buckle,” says Goff.

The company now makes eight different designs to suit various types of mixer. Bardon found that the device enabled the recycling of all residual aggregate and the use of recycled water to clean the chutes back at the depot, while Interserve eliminated the need for costly and high pollution-risk concrete washout facilities on site. The original idea was simply to reduce the amount of mess, admits Goff. But he quickly began to realise that his invention (which he has now patented) offered numerous additional benefits.

Besides being cleaner and removing the problem from the customer’s site, the system significantly reduces water consumption and time – giving a quicker turn-around and maximising the driver’s ‘tacho’ time.

The only alternative system Goff can cite is the fitting of an additional washout tank to the truck itself, a bulky and expensive solution. However, he has already seen copy-cat versions of his design cropping up. Disappointingly, he says, one of the offenders was a major national that had previously provided a glowing testimonial for the Concretesock.

Getting the idea accepted by the industry has been a frustrating experience, admits Goff. Although the product has only been on the market for four and a half years, it has quickly attracted the attention of most leading main contractors but has yet to be widely adopted by the concrete suppliers.

“Part of the problem is that the concrete companies have always believed that waste is the customer’s responsibility. And the customers have usually accepted that,” he says. His strategy therefore is to apply gentle pressure on the suppliers via their customers: “We’re beginning to see Concretesock being written into contracts,” he says.

This article first appeared in the September 2014 issue of The Construction Index magazine. To read the full magazine online, click here.

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