Development of chemical analysis protocols on the leaching compounds of forest- and agricultural wastes in cementitious environment: A case study of coir fibres

The present study established analytical protocols for the chemical analysis of leaching compounds of plant-based fibre materials in a cementitious environment. The leaching compounds of coir fibres (coconut fibres) were subjected to various solutions, including water, lime solution, and cement suspension. These solutions were soaked for durations of one hour and 24 hours, and the leaching compounds were subsequently identified and quantified. Two complementary methods were utilised for the identification and quantification of leaching compounds. Specifically, the application of enzymatic assays proved efficacious in quantifying the two predominant leaching compounds, formic and acetic acid. Gas chromatography coupled to mass spectrometry (GC-MS) was employed to identify a more extensive array of small molecules leaching from coir fibres in water and lime solution. A total of 23 compounds were detected using this approach. Consequently, formic acid was only detected in lime solution and cement suspensions at low concentrations (less than 4.3 mg/L). Conversely, the acetic acid concentrations in the lime solution and cement suspensions were found to be 503.2 ± 14.3 and 666.2 ± 16.8 mg/L, respectively, which were significantly higher than the formic acid concentration under equivalent conditions. Furthermore, the acetic acid concentration was found to be dependent on soaking time; from 1 hour to 24 hours, the concentration increased 2- to 4-fold. In addition to formic and acetic acid, other primary leaching compounds were identified by GC-MS, i.e., lactic acid (7.1-23.1 mg/L) and 4-hydroxybenzoic acid (13.5-49.8 mg/L), C5 sugar alcohol (4.8-14.1 mg/L), disaccharides (9.3-35.6 mg/L), C6 sugar alcohol (5.6-20.2 mg/L), C6 sugars (monosaccharides) (4.2-22.1 mg/L), quininic acid (1.3-8.0 mg/L). These compounds, in conjunction with acetic acid, were found to be the predominant leaching compounds and should be given primary consideration in further investigations.