Geotechnical properties of paper recycling waste streams

This paper studies two waste streams of the paper recycling industry for potential use in geotechnical applications. Namely, de-inking paper sludge from the secondary treatment stage, and paper sludge ash (PSA) obtained from the incineration of this sludge. Salient geotechnical properties of the statically compacted sludge before and after stabilisation with lime or PSA are presented. Tests include shear box testing, uniaxial compressive strength (UCS) testing, 1-D swelling and compression in oedometric conditions, p-wave velocity measurements using a Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT), and filter paper testing to determine water retention characteristics. The volume changes of the untreated sludge were found to be considerable in all above tests; however its shear strength at a highly compacted state was overall adequate. Chemical stabilization of the sludge was effective in reducing volume changes. The PSA was also assessed as a silt soil stabiliser. As geomaterial stabiliser, PSA was found to have a similar or better performance than lime. Overall the results are encouraging and indicate that it is possible to use paper industry waste in geotechnical applications.