Exposed-aggregate, polished concrete floors are in high demand, and the use of glass is an emerging trend used to create an aesthetically pleasing surface. The American Society of Concrete Contractors and the Concrete Polishing Council conducted a field study in late 2021 to evaluate installation techniques, troubleshooting and repair issues, and came away with a set of best practices and crucial considerations for mix design, placement, glass distribution and grinding and polishing.
Many commercial and residential owners looking to make a striking visual impact on guests often work with designers and innovative contractors alike to create an impressive moment for their home or business. A common request gaining popularity over the years has been the exposed-aggregate polished concrete floor. One of the emerging trends in this segment has been the use of glass.
The American Society of Concrete Contractors and Concrete Polishing Council identified the need for a “best practices standard” for the surface broadcast of glass aggregate on concrete flatwork.
A field study, performed in late October 2021, was meant to evaluate: various installation techniques; how to deal with adverse conditions, and; the troubleshooting of and repair of common issues found on polished concrete projects utilizing broadcast glass aggregate.
While evaluation and testing confirmed many best practice techniques, the study revealed key considerations regarding the practice involving mix design, placing, finishing, and more.
The main difference between a mix design specific to embedding glass into the surface, as compared to a standard mix design used to produce a power troweled Class 7 or 9 industrial floor slab, is the consideration of Alkali-Silica Reactivity (ASR).
When using crushed glass, ultimately polishing the surface and when exposed to moisture, a reaction can occur forming a gel that is expansive and thereby potentially creating pop-outs.
Unfortunately, there is no way of predicting how fast or slow ASR will occur. The industry has had good success using pozzolanic materials such as Type F fly ash, metakaolin, and granulated blast furnace slag to help mitigate this reaction in several ways.