Characterization of chemically treated waste wood fiber and its potential application in cementitious composites

Abstract

In recent years, the utilization of various fibers in cementitious composites gained remarkable popularity worldwide. Unlike well-known fibers, this study focused on examining the incorporation of waste wood fiber (WWF) assorted from construction and demolition sites into the cementitious matrix. In the first stage of the study, alkali-treatment of the WWF was carried out with different concentrations of sodium hydroxide (NaOH) solution (i.e., 1.0 M, 2.0 M, 2.5 M, 5.0 M, 10.0 M) and treatment durations (i.e., 2 h, 4 h, 6 h, 12 h) to eliminate impurities and enhance fiber properties and fiber-matrix compatibility through surface treatment. To investigate alkali-treatment efficiency, microstructural analyses were conducted on the untreated and alkali-treated WWFs by Scanning Electron Microscopy and Fourier Transform Infrared Spectrophotometer measurements. Afterward, physical and mechanical performance assessments were conducted by water absorption test, compressive and four-point bending tests on the WWF-incorporated cementitious composites to monitor the compatibility behaviour of the WWF-matrix interface. Microstructural examinations showed that after the alkali treatment, impurities (i.e., painting, hemicellulose, lignin, etc.) on the WWF surface were successfully removed; however, higher alkali concentrations (beyond 5.0 M) and longer treatment duration (after 6 h) lead to deterioration, fragmentation, and a more heterogeneous structure due to the degradation of long cellulosic chains of WWF. Four-point bending test results showed that the flexural strength capacity of 2.5M-2 h-WWF-composite was 7.9 MPa, which was higher than untreated WWF-composite and plain mortar by 34.7% and 39.8%, respectively. Furthermore, the 2.5M-2 h treated WWF composite had the highest compressive strength of 46.3 MPa, which was higher than plain mortar, and the untreated WWF composite by 6.4% and 21.5%, respectively. The elimination of impurities such as painting, lignin, hemicellulose, and other inorganic compounds at the optimal alkali treatment concentration and time increases the WWF surface area and strengthens the fiber-matrix interface adhesion, resulting in a stronger matrix-WWF interface connection and an increase in load-carrying capability. The study's findings are believed to encourage the usage of alkali-treated WWF in cementitious matrix with improved mechanical performance and high waste upcycling.