The mechanical performance of recycled cardboard kraft fibres within cement and concrete composites

Abstract

Global population growth around the world requires significant infrastructure and building developments. The building and construction industry uses excessive quantities of virgin resources for those developments as well as contributing to the waste generated from the residential and commercial sectors. A contemporary solution is required to reduce these negative environmental impacts. In this study, the mechanical properties of cement composites containing kraft fibres (KFs) derived from waste cardboard was experimentally investigated. KFs and metakaolin (MK) were integrated within concrete samples as a cement substitute material. The compressive, flexural, and tensile strength was determined on three mix designs containing 5% raw KFs, 5% surface modified KFs, and matrix modified concrete specimens. Silica fume (SF) was applied to the fibre walls as fibre modification to lower the alkaline zone around the fibre within the cementitious matrix. 5% MK was used as a partial cement substitute to lower the alkaline level of concrete samples. All KF concrete specimens exhibited lower compressive strength properties. However, MK modified samples exhibited the highest tensile strength of 11 MPa. Fibre modified samples had stronger compressive and tensile strength of 20 and 9 MPa, compared to raw KFs. However, raw KFs exhibited a higher flexural strength of 2.5 MPa. The compressive, tensile, and flexural strength of the control were 25, 10 and 2.6 MPa, respectively. Scanning electron microscopy (SEM) observations demonstrated sufficient SF adhesion on the fibre walls, while the energy dispersive x-ray spectroscopy (EDS) observations showed efficient dispersion of all composite materials.