A Scottish company has found the concrete evidence it was looking for after successful trials showed recycled glass could replace primary aggregates in the manufacture of higher value blocks.
Fife-based concrete block manufacturer, Brand & Rae, received funding from the Scottish Executive through WRAP (the Waste & Resources Action Programme) to carry out commercial scale trials at its main plant at Russell Mill, Springfield, Cupar and a mobile plant at Bonnyrigg, near Edinburgh.
The six-month trial, involving the manufacture of 75,000 concrete blocks at both sites, confirmed that crushed recycled glass can be used as a replacement for primary aggregates in the manufacturing process and, in certain cases, blocks containing recycled glass perform better than conventional ones in terms of strength and performance in adverse weather conditions.
They also conclusively showed that this use of recycled glass represents a commercially viable and environmentally friendly alternative to the continued exploitation of primary aggregate sources, such as sand.
Glass materials for the Brand & Rae trials were provided by Viridor MacGlass, also located at Bonnyrigg.
Trials at the Bonnyrigg site tested blocks traditionally used in standard or cavity wall construction produced on a mobile concrete block making system. At the company’s Russell Mill site, lightweight, paint and masonry grade blocks were produced on a static plant, enabling comparisons between the two methods.
The Bonnyrigg trials found that the optimum percentage of recycled crushed glass in place of primary aggregates is 30 per cent. This is the percentage at which strength is at a maximum and drying shrinkage is at a minimum. The lower the drying shrinkage, the less prone a concrete block is to crack.
At Russell Mill, the trials concluded higher levels of replacement glass can be achieved at a static plant. The findings showed that, as the glass levels increased, the strength of the manufactured blocks improved. Up to 80 per cent of recycled glass was used as a direct alternative for natural aggregates without any detrimental effect on performance or handling. The best outcome for drying shrinkage was found to be 45 per cent replacement glass.
Commenting on the trials, Gary Bell, Managing Director of Brand & Rae, said: "The company has been delighted to be a partner in these operational trials. The advantages have been clearly demonstrated through better strength and lower drying shrinkage. We have already commenced production at Bonnyrigg of a block containing 30 per cent glass.
“Through the increased use of a range of recycled materials, Brand & Rae hopes to assist the public sector in achieving its targets in the coming years.
“We are committed to producing and marketing this type of concrete block and more glass needs to be made available for this application. We could potentially use as much as 65,000 tonnes per annum.”
The tests revealed a number of environmental benefits, including reducing the amount of cement and natural aggregates required, which provides substantial fuel savings and reduces the road miles travelled.
Mr Bell added:
“As the production of the blocks does not require the glass to be sorted into colours, this allows for the local use of green glass bottles, of which there is a surplus, and precludes the need for expensive sorting equipment, should the local market not have a glass manufacturer.”
Andy Dawe, Materials Section Manager (Glass) at WRAP, said:
“This major series of operational trials are a great example of getting real value out of the materials the public is recycling, which is indicative of the work that WRAP is doing in the UK.
“The tests have succeeded in their aim of proving the commercial and performance benefits – as well as the considerable environmental advantages – of using recycled glass in a range of industrial and construction products, including bricks and tiles, grit blasting, and water filtration media.” Mr Bell presented the results of the Brand & Rae trials at the British Glass and WRAP organised GlassAction Day, held recently at Tankersley Manor in Barnsley, South Yorkshire.