Under the magnifying glass - The viability of crushed glass for roadbuilding
By now, the knowledge that motor vehicles cause a great deal of damage to the environment is almost ubiquitous. To combat this, the transportation industry has been a nearly constant source of environmental and economical innovation ranging from the removal of leaded fuel in the 1970s, to the development of Electronic Vehicles (EV’s) and hydrogen fuel cells today. What’s even more surprising, however, is that the roads that these vehicles ultimately drive on are more-or-less the same as they were over fifty years ago.
This may be about to change.
In September 2020, the NSW government announced that the use of recycled glass in asphalt base courses may now be up to 10%. This forms a substantial increase as the previous maximum was a mere 2.5% (Keyes, 2020). To put this into perspective, this will potentially equate to 234 million glass bottles being used in road bases over the next three financial years (Keyes, 2020). By implementing this new initiative, the NSW government aims to help ease some of the oversupply issues many recycling stations around Australia have been experiencing in recent years (Davis, 2017). This sounds like an excellent opportunity for Australia’s glass recyclers, but to see what it will mean for players in the pavement and asphalt biz, we’ll need to dig a little deeper.
At present, cost is the main reason for not utilising glass in massive quantities for the building of new roads. Crushed glass for road building in the US is sold at up to $60/Tonne (US) which far exceeds the cost of sand and gravel which is generally sold at $19/Tonne (US) (GHD, 2008). Add to this a large-scale supply crisis and massive production restraints from the recycling industry in Australia and this cost may be a lot higher (Davis, 2017). This is a lot of coin for little practical gain. But what if we direct our attention to smaller-scale projects?
Though the cost of crushed glass makes it difficult to justify it as a base-course ingredient, there are some very interesting results from the use of glass for resurfacing projects. Studies show that the use of crushed glass can increase skid-resistance values of the surface due to glass particles becoming more exposed through vehicular traffic. It has also since been proven that if crushed to smaller than 4.75mm granules, it will not have any adverse effects on tyre health or wear (Su and Chen, 2002). It has also been found not to have any significant negative affect on the rutting/breakdown of the road surface (GHD,2008).
Before we all get too excited, it should be noted that there are some caveats. During the 1960s, the Washington State government in the United States began allowing up to 40% crushed glass in asphalt mixes. It became apparent that perhaps this was too much as the pavement quickly began showing evidence of severe rutting and stripping. Although subsequent studies have determined that crushed glass can increase the longevity of pavement if used in proportions less than 20%, the potential risk of “over-doing” this method should still be considered (GHD, 2008). Additionally, due to the low cost, stockpiling of recycled glass can be common which may cause issues with supply; especially when considering that most recycling plants are already processing at full capacity.
The idea of using glass in pavement is clearly not a new idea, and it shows that the Pavement Industry in Australia has still a long road ahead, but still, it’s hard not to be swept up by optimism in these trying times.
NSW releases new recycled glass asphalt guidelines (wastemanagementreview.com.au)
Australia's glass recycling crisis: the industry responds (sustainabilitymatters.net.au)
Su, N. & Chen, J.S. (2002) “Engineering properties of asphalt concrete made with recyclable glass”, Resources, Conservation and Recycling, 35, Taiwan, pp 259 – 274, Wu, S et al, (2005) op cit.