Steel base metal laps or welding electrode surfaces were coated using graphene suspensions with various concentrations, and then the steel plates were welded using the shielded metal arc welding process. Microstructural observations showed that the addition of graphene to the weldment significantly refines the microstructure and promotes the formation of fine acicular ferrite. The results of mechanical testing indicated that with lower concentrations of graphene in the weldment, both the strength and ductility improve, but the hardness remains unchanged in comparison to the unreinforced weld metal. However, reinforcing with a higher concentration of graphene gives rise to the significant enhancement of the hardness and strength without deterioration of the ductility.
To develop a more reactive pozzolan for supplementary cementitious materials (SCMs), the co-calcination of kaolinite and limestone was investigated for its contribution to hydration of blended cement. Kaolinite (with ~50 wt% quartz impurity) was calcined at 700·°C, and a mixture of kaolinite and limestone was calcined at 800 °C. These activated SCMs were added to ordinary Portland cement (OPC), replacing ca. 30 wt% of the OPC. The compressive strength of these blended cement paste samples was measured after 28 and 90 days, while the hydration products and microstructural development in these blended cement pastes were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results revealed that adding free lime to OPC, together with metakaolin, led to enhanced compressive strength. The compressive strength of this new blended cement paste reached 113% and 112% of the compressed strength of pure OPC paste after 28 and 90 days of hydration, respectively. Furthermore, this study showed that the improvement was due to the increased consumption of Portlandite (CH), the formation of calcium aluminosilicate hydrate (CASH), and the reduction of porosity in the sample containing free lime and metakaolin.
PVA matrix composite films reinforced with graphene oxide (GO) and reduced graphene oxide (rGO) nanoplatelets are prepared by water‐solution processing. The structure and properties of the composites are investigated by field‐emission scanning electron microscopy, Raman spectroscopy, Fourier‐transform infrared spectroscopy, differential scanning calorimetry, and dynamic mechanical analysis. The results indicate a 22% improvement in the storage modulus and a 12°C increase in the glass transition temperature by the addition of only 0.5 wt% rGO into the PVA. The enhancement of the mechanical and thermal properties of the composite films is attributed to the hydrogen bond barrier and molecule movement restriction effects. The higher amount of the hydrogen bonds in the PVA/rGO composite compared to the PVA/GO sample cause its higher thermal stability and mechanical performance.
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