Bottle bank grit proves its usefulness

Grit made from 100% recycled bottle bank glass tested over two days at shipyard to demonstrate its advantages over high pressure water in cleaning steel and preparing vessels being painted and coated.

A grit blast medium has sailed into the spotlight following a series of successful trials at a Gravesend shipyard, which demonstrated the medium's advantages over high pressure water in cleaning steel and achieving a suitable surface profile in preparation for vessels being painted and coated.

Grit made from 100% recycled bottle bank glass was tested over two days at Thames Shiprepair Service as part of a wider series of trials commissioned and funded by Wrap (the Waste and Resources Action Programme) and managed by the Shipbuilders and Shiprepairers Association (SSA).

Founded in 1940, the company, one of the last remaining shipyards on the Thames, handles between 25 to 30 large projects each year, servicing coastal, short sea vessels and London's passenger and freight maritime fleet.

Vessels entering the shipyard typically require a thorough cleaning to remove iron oxides, rust, oil, grease, dirt, old paint and other surface contaminants.

Cleaning also tackles corrosion caused by soluble salts in the air and water - a major problem in the marine industry, which can lead to premature paint failure if not removed.

Paul Huseman, Managing Director at Thames Shiprepair Service, said: "Being based where we are means we have an additional environmental responsibility and this limits our options for using abrasives, usually the fastest and most thorough means of cleaning, descaling, deburring and removing oxides".

"For this reason, we used high pressure water cleaning carried out by a subcontractor but, while effective, this had proved expensive and inflexible".

"We would frequently have to wait more than a week for the subcontractor to come out".

"When we were approached by the SSA and Wrap, we were happy to participate in the trials of recycled glass grit, as until now there has been no suitable alternative we could use near a watercourse".

Performed by Newcastle University's research team, a series of smaller tests on steel plates at the yard led to a full scale trial involving the blasting of a mooring barge.

Heavily corroded, the barge's hull was blasted in different sections by three types of cleaner: with recycled glass as a dry medium; with water added to form a wet mixture; and by high pressure to allow a direct comparison with the shipyard's normal practice.

The results of the trials indicated recycled glass grit could achieve similar results to high pressure in terms of productivity.

The ability of Thames' staff to perform the blasting themselves highlighted additional cost and time benefits.

Huseman said: "By bringing this function in house we will be able to grit blast whenever required, helping to improve turnaround times and our service to clients".

In addition to representing a more sustainable use of resources, recycled glass grit's main benefits over conventional blast media are that it is non-toxic, inert and does not cause respiratory or environmental problems.

Unlike some traditional media, it does not contain crystalline silica or heavy metals and so can be used in public places and environmentally sensitive areas, such as watercourses.

Glass grit is also free of chlorides and salts that can corrode clean surfaces so its use delays gingering of steel, and - through spent media being classified as a nuisance dust, rather than hazardous waste - can provide lower disposal costs.

And, in contrast to most conventional abrasives, recycled glass does not have to be imported, meaning shorter delivery times for blasting companies and potential environmental benefits through less energy being used in transportation.

Tom Dougherty, Director of SSA, said: "We're delighted Thames Shiprepair Service is now looking at how it can implement the use of recycled glass grit in its operation".

"These trials form part of a wider programme which has been running since April 2005 in controlled conditions at a number of yards around the country and we're encouraged by the results produced".

"Recycled glass has been proved to achieve a comparable surface profile to conventional abrasives, such as metal slags, olivine and garnet, and is as easy to use across a range of applications".

"The trials have also revealed the medium represents a commercially viable alternative, taking into account its cost and the surface area that each tonne of material can treat".

Full scale trials are also talking place with end-users, including the Ministry of Defence, BP and Exxon.

"The results of these trials will have implications for a wide range of industry sectors which use grit blasting widely to clean, descale, deburr and remove oxides and other surface contaminants," said Bronnie Allen, Materials Development Manager (glass) at Wrap.

"Recycled glass grit has been proved in the USA to clean masonry, renovate equipment and restore woodwork effectively, among other applications".

"These trials have proved the operational and commercial benefits of using glass grit in the marine industry and we hope specifiers and contractors will now use it more widely".

"We're delighted with the positive initial response we have had from these professionals and are very hopeful glass will become the blasting medium of choice across a range of sectors in the future".

The widespread use of recycled glass will assist the UK in meeting its target under the European Union packaging directive, which says 60% of glass must be recycled by 2008.

Preliminary data for 2005 indicates that 50% was achieved.

Recycled glass is available manufactured to BSI PAS 102 specifications, setting standards in terms of colour, contamination limits, particle size requirements and appropriate test methods, guaranteeing a consistent, high quality product.

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