New York (state) changed forever in the early months of 2020, not just because of the COVID-19 lockdown. On 14th March 2020, the last coal power plant in New York closed, making a permanent and dramatic commitment to a sustainable future. 

New York State is not the first state to move away from coal production in the US and it won't be the last. Many experts have expressed their concerns regarding "nailing the coffin" in the state's concrete infrastructure supply chain because of uncertainty- but there is hope.

 In the US, it has become widely accepted and known that fly ash and slag are excellent alternatives for virgin material in cement mixes as supplementary cementitious materials (SCMs). Though this may be a victory for the environment and idle stores of the materials, it has become increasingly harder to access ash and slag for significant projects. 

In 2017 the National Precast Concrete Association (NPCA) reported that “fly ash availability has been significantly reduced.” Even suggesting that members reported, “For the most part, the situation has been, ‘Get in line and wait your turn’”. With an additional 52 plants due to close in the next 6 years, it may only get harder to access. 

This is when the US infrastructure supply chain began to turn to SCMs for more options. To have a lasting impact, the new material must be as chemically reliable as ash/slag are, be readily accessible, available in millions of tonnes a year, and must be able to be sourced at a low cost to concrete manufacturers.

... and one pozzolan has made the cut- Ground glass pozzolans (GGP). Made of glass from beer bottles and salsa jars, this SCM can be sourced at a low price because it is technically classified as waste material. It also has the advantage of the high, consistent amounts of silica found in engineered glasses. 

Understanding the significance of glass as a possible tool for the concrete industry, university labs such as Clarkson University’s Center for Advanced Materials Processing (CAMP) have been running tests on glass SCMs for years. This testing has provided a valuable understanding of glass SCM's performance in concrete.

To increase the speed at which this material may be processed and ready for use, KLAW Industries in the US have developed a new technologically advanced method. Using their technology, KLAW Industries can take any glass from the recycling system, remove unwanted materials, and make an ultra-pure GGP called Pantheon.

The company aims to use this pure material to solve the doubts and supply issues highlighted in the state of New York and later the whole country, lowering the cost and increasing the supply of SCMs for the nation. Through their advanced method, KLAW Industries will be able to source glass anywhere; a requirement if GGPs are going to fill the monstrous shoes of fly ash and slag.

Silica is the active ingredient in the beneficial reaction of SCMs. More silica means more strength, more chemical resistance, and overall, more durability. Test results of GGPs back this up. When compared to slag and fly ash in concrete core compression tests (AASHTO-T22), glass presents new and strong results when compared with ash/slag. These results are not the same for all glass pozzolans, but KLAW Industries believes they can beat slag in strength by 11% at a 20% cement replacement rate (in a 4,000-psi mix). As a bonus to the concrete manufacturers, glass SCMs can achieve this without changing the batching process at all.

Ground glass pozzolans are potentially the future of concrete infrastructure. With increased positive reviews and additional education,   
it may only be a matter of time before glass SCMs reach the acceptance needed to be used in large public infrastructure projects. What a win for the environment! 

To learn more about pozzolans and SCMs, click here.