Recycled glass powder as an alternative to fly ash in non-proprietary UHPC: A comparative study of resource-efficient design, mechanical and durability properties

Fly ash (FA) is one of the preferable supplementary cementitious materials used in the design of resourceefficient ultra-high performance concrete (UHPC). Recent changes in energy production have led to a reduced availability of FA which increases the need to find an alternative replacement. One suitable, innovative, and sustainable pozzolan with higher consistency in material properties is recycled glass powder (RGP), produced from 100% post-consumer glass. To fill the knowledge gap whether RGP is a suitable alternative to FA in nonproprietary UHPC, this research emphasizes the comparative investigation of material properties of UHPC using FA versus RGP. The comprehensive material characterization and analysis included workability, mechanical behavior such as compressive strength, single fiber pull out and direct tensile behavior, static elastic modulus, and long-term strength. Durability properties included electrical surface resistivity and freeze-thaw resistance. In addition, a comparative analysis for their resource-efficiency and service life was also performed. The results were compared to two commercial UHPCs, available in the United States. This research showed that UHPC with RGP can be designed to achieve comparable mechanical and durability properties as UHPC with FA. Compressive strength up to 176 MPa (25.5ksi) were obtained without the use of special treatment, at current material cost of about US$1145/m3 with 2% of fiber volume fraction of steel fibers. Over time, the compressive strength of UHPC with RGP increased by 15%, resulting in more than 200 MPa (29.0ksi) after three years. Both UHPCs designed with either FA or RGP showed strain-hardening under direct tension with maximum tensile strength of about 14.8 MPa (2.1ksi). Both the UHPC with RGP and FA achieved electrical surface resistivity of more than 870k Omega x cm and 822k Omega x cm in 28 days and relative dynamic modulus of 102% after 600 freeze-thaw cycles that ensure long term durability with design service life of 364 and 344 years respectively.