Recycling of contaminated waste glass in ultra-high performance concrete: Impurities impact

The feasibility of recycling clean waste glass in construction products has been demonstrated. However, the direct utilization of contaminated waste glass from consumed beverage glass bottles may negatively affect the performance of concrete. This study aimed to investigate the effect of impurities in waste glass on the properties of ultra-high-performance concrete (UHPC). Washed and unwashed waste glass powder and sand were used as cement and river sand substitutes, respectively. Light particles, clay and fine silt, organic impurities and aluminium content in waste glass were determined. The results showed that the use of washed waste glass powder (W-WGP), washed waste glass sand (W-WGS) and unwashed waste glass powder (U-WGP) had a limited negative effect on the compressive strength of UHPC. In contrast, the use of unwashed U-WGS significantly decreased the compressive strength of UHPC due to the presence of impurities (e.g., paper and metallic aluminium). However, the impurities in the unwashed waste glass could positively reduce the autogenous and drying shrinkages of UHPC. The metallic impurities reacted with an alkaline solution to generate gases, resulting in the expansion of the matrix and reduction of autogenous shrinkage at the early stage. X-ray CT and microstructural images indicated that expansion resulting from the U-WGS caused cracks in the matrix and degraded the interfacial zone between the U-WGS and the paste. However, the incorporation of waste glass did not induce any alkali-silica reaction expansion in UHPC due to its low water-cement ratio and dense structure. The UHPC prepared with 30 % U-WGP as a replacement for cement was found to achieve satisfactory performance and lower carbon emissions.