Pine Sawmill Waste-Derived Graphene Derivatives for Cementitious Composites

Graphene oxide (GO) and reduced graphene oxide (rGO), synthesized from pinewood waste biomass through a pyrolysis-temperature-controlled route at 450, 600, and 900 °C, were investigated for their influence on the hydration behavior, microstructure, and mechanical performance of cementitious composites at both cement paste and concrete scales. The graphene materials synthesized from biochar in this work are designed as replacements for conventionally synthesized GO and/or rGO from graphite, offering comparable performance while enabling production from renewable sources at an accessible cost. Comprehensive material characterization confirmed the successful formation of partially layered carbon structures. Incorporation of GO and rGO, which are synthesized from biochar by referring to BCGO and BCrGO, respectively, into cement pastes at a fixed dosage (0.05% by weight of cement (BWOC), used as an additive) resulted in accelerated hydration kinetics and enhanced development of hydration products without the formation of additional crystalline phases, indicating refinement of the hydration process rather than alteration of cement chemistry. Microstructural analysis revealed strengthened Si-O-Si and Si-O-Ca bonding environments, accompanied by a denser and more homogeneous cementitious system. Microphotographic observations further confirmed improved interfacial bonding between hydration products and graphene materials. At the concrete scale, the addition of GO and rGO at varying dosages (0.05 and 0.5% BWOC) as concrete additives resulted in consistent improvements in mechanical performance. Compressive strength increased by up to 10%, while flexural and tensile strengths improved by about 9% from all mixes. The most pronounced property enhancement was observed in the modulus of elasticity, with up to 55% enhancement. Concrete density, pH, and Poisson's ratio remained essentially unchanged, indicating improved mechanical properties without compromising ductility or chemical stability. These findings highlight the potential of renewable biochar-based GO and rGO as high-performance additives at the desired pyrolysis temperature, capable of enhancing mechanical and microstructural performance without compromising essential cementitious properties.