Carpet fiber recycling in regular-use concrete mixtures and associated life cycle analysis

Abstract

This paper reports the characterization of post-consumer carpet fibers and optimization of concrete mixtures containing high volumes (2.5% and 5% as compared to ≤ 2% reported in past work) of carpet fibers, in an effort to contribute to the efficient management of such wastes. This study identifies the different fiber types in a typical post-consumer carpet bale using Fourier transform infrared (FTIR) spectroscopy and the range of tensile strengths demonstrated by the fibers. In order to quantify the sustainability of concretes containing carpet fibers, a cradle-to-gate life cycle analysis is carried out. The results demonstrate that the use of carpet fibers along with fly ash helps reduce the CO2 emission potential by ∼ 12.5% compared to conventional concrete, in addition to saving critical land area that would otherwise be needed to dispose of the ever-increasing amounts of carpet waste. Notable reductions (of up to 10%) in other environmental impact categories (e.g., acidification, eutrophication, etc.) are also observed with respect to conventional concrete. Even with the additional energy required to process the fibers, the overall energy consumption to produce carpet fiber reinforced concretes is similar to that of conventional concretes. The conditions under which carpet fibers become an environmentally sustainable approach for concretes designed to achieve a particular compressive strength are also outlined. It is expected that this work will pave the way for the management and beneficial utilization of otherwise landfilled shredded carpets in concrete applications such as slabs-on-grade.