New Methods for the Quantification of Deleterious Material Content in PGA

ABSTRACT Recycled glass can be transformed into processed glass aggregate (PGA) and used as a construction material. However, the presence of deleterious materials such as metal, food remnants, plastic, and paper, and a lack of reliable methods to determine the deleterious material content (DMC) have limited its widespread adoption. The current baseline method for determining DMC is visual classification, which involves manually identifying and separating pieces of deleterious material. This visual method is tedious and unreliable. Therefore, this study introduces a new, straightforward, and reliable testing method to quantify DMC in PGA using a combination of magnetic separation and thermal volatilization (protocol 1). In addition, density separation with water is coupled with manual separation and Fourier Transform Infrared Spectroscopy (FTIR) to detect plastics if the determination of plastics content in PGA is desirable (protocol 2). These protocols were validated on lab-manufactured PGA made using clean glass crushed into fine aggregate and adding known amounts of deleterious materials. Protocol validation demonstrated that DMC could be determined when paper, food residue, ferrous metals, and plastics are present. When PGA was prepared with a 2 % DMC, the measured value was 1.901 +/− 0.046 %. Subsequently, the testing protocols were applied to PGA samples with unknown amounts of DMC obtained from three different recycling facilities within the northeastern United States. These samples had DMC from 0.415 +/− 0.014 % to 2.952 +/− 0.113 %. Further, density separation was shown to provide a conservative estimate of plastic contamination in recycling facility PGA, with 9 of 10 samples having higher masses of floated material than plastic contamination determined through FTIR. Results demonstrated that protocol 1 is reliable for DMC determination and is operator independent. Protocol 2, albeit time-consuming, reliably quantifies plastic content. These protocols have the potential for routine application to ensure PGA meets allowable limits for deleterious materials.