The concrete industry is constantly looking for innovations, better performance and ways to lower its carbon footprint. Surprisingly, cement production accounts for about 5% of the total CO2 emitted in the atmosphere around the world.
Another way to look at it is that each ton of cement produced outputs a ton of CO2. Much of it comes from the high melting temperature (2500°F) and from the process of decarbonation of limestone. So to lower the carbon footprint, the industry would have to either change the cement production process or to use less cement in concrete mixtures. Much research has been done around the world in finding ways to dispose of industrial byproducts like fly ash or silica fume and use them in making concrete. So much that these are now commonly found in most concrete mixtures. What other material can be recycled into cement?
Meet recycled glass
In the US, only 33% of the glass products is being recycled and only 40% of the glass that is collected is actually recycled. Part of the reason may be that glass recycling is still costly due to transportation and color sorting. Crushed glass in large particles (larger than 75µm) produces an expansive gel that results in concrete cracking, so the particle size must be finer than 75µm to not create an alkali silicate reaction. When this happens, mortar durability is increased. The only exception to this is the use of large glass particles in making concrete kitchen counter tops. These are becoming very popular as they combine cost saving, green practices, beautiful and unique results.
A better solution is glass powder as it has been found to improve concrete’s compressive strength and durability. Another great discovery was the water reducing effect of glass powder, leaving more water to improve the cement’s workability.
Michigan State University has been conducting extensive research in their labs on the use of glass in concrete on their campus. They have managed to replace about 20 percent of the cement used to produce concrete by milled, or finely ground glass. The resulting concrete becomes lighter but has the same appearance with regular concrete, maybe a little lighter in color. More research is underway to test all variables needed to make this new element a standard in the industry. To read more on this, two papers were published on the durability of the mixture, one in the Journal of Solid Waste Technology and Management, and the other in the Journal of Construction and Building Materials of Michigan State University.
The American Journal of Engineering Research (AJER) conducted workability test, density test and compressive strength test on waste glass powder in concrete. They also found that glass powder does increase the workability, density and compressive strength of concrete. Read the complete report here.
Europe and India have also successfully spearheaded research in this emerging field. The study conducted by Dr. G.Vijayakumar, Ms H. Vishaliny and Dr. D. Govindarajulu at Pondicherry Engineering College, in Pondicherry India, had the following very positive conclusions:
“Replacement of glass powder in cement by 20%, 30% and 40% increases:
- the flexural strength by 83.07%, 99.07% and 100% respectively.
- the compressive strength by 19.6%, 25.3% and 33.7% respectively.
Glass powder concrete increases the compressive, tensile and flexural strength effectively, when compared with conventional concrete. Very finely ground glass has been shown to be excellent filler.” The complete report can be read here*
The Centre of Sustainable Development in Quebec, Canada was an early adopter of powder glass in concrete, which allowed them to reach a LEED Platinum certification. They simultaneously managed to reduce the amount of concrete used and the amount of glass dumped in landfills.
It is still too early to know whether or not glass can be used for shotcrete applications. Not enough testing and research has been done on wet or dry mix shotcrete. However, promising results were discovered in early findings for dry mix on rebound and reinforcement of bar encapsulation in the placement phase.
Stay abreast on new technologies and the latest research with United Equipment Sales. With over 40 years in the industry and all things concrete, we can help you on your next concrete job, solve challenges and find you a great deal on concrete pumps.
Recipe for success: Recycled glass and cement
Glass Powder Utilization in Concrete Production from the European Journal of Applied Sciences
Studies on Glass Powder as Partial Replacement of Cement in Concrete Production
Performance of Using Waste Glass Powder In Concrete As Replacement Of Cement from the American Journal of Engineering Research