Mechanical enhancement of natural-curing geopolymer via shear-exfoliation graphene addition for sustainable paving blocks

The compressive strength and surface hardness of fly-ash based geopolymer paving block composites (GPBC), fabricated in a room temperture curing process (natural curing), have been successfully improved with the addition of low-cost liquid shear-exfoliation graphene (LSE-G) additives.The incorporation of LSE-G represents a breakthrough enabling natural-curing geopolymer composites to compete with conventional geopolymer materials while being easier and more economical to produce, making them suitable for small-scale production by local communities.Natural-curing GPBC was synthesized by mixing coal fly ash, sand, Na 2 SiO 3 , NaOH, and LSE-G solution with concentrations of 20 mg/ml, 40 mg/ml, and 80 mg/ml.The GPBC were characterized using compressive strength tests, Vickers hardness, water absorption tests, Raman spectroscopy (RS), scanning electron microscopy-EDX Spectrum (SEM-EDX), and transmission electron microscopy (TEM).Raman spectroscopy analysis indicated that LSE-G was well-distributed within the geopolymer matrix.The addition of LSE-G up to a concentration of 40 mg/ml increased compressive strength of geopolymer composite to 21.83 MPa (a 23.4% increase) and surface hardness to 122.5 Hv (a 6.15% increase).However, higher concentrations led to a decline in both parameters.SEM analysis revealed a denser and more compact geopolymer composite structure when LSE-G was added, with a reduction in porosity by 26.80%, which also resulted in a decrease in water absorption by 10.71%.EDX analysis supported the RS results, showing that LSE-G was homogenously incorporated into the composite matrix.TEM analysis explained that adding LSE-G up to a certain limit could enhance the density and compactness of the material.LSE-G has proven to be an effective and promising additive for improving the mechanical properties of natural-curing geopolymer paving block composites.