In Vietnam, the current amount of thermal ash (fly ash and bottom) remains nearly 100 million tons, causing great environmental and social impacts. The recycling and reuse of this source of waste is an effective solution towards sustainable development. The paper introduces the results of study on some properties and particle size distribution of aggregate from thermal ash, Duyen Hai factory for refractory concrete. Particle composition is calculated and selected according to the density of particle size arrangement with the maximum number of points of contact. The continuous particle size distributions of thermal ash is calculated by Andersen’s formula with Dmax = 5 mm. The bulk density and porosity of the particle mixture corresponding to the vibrating modes is determined. By the experimental planning method (Design of experiments - DoE), the optimal aggregate particle composition was determined with the calculated value of n = 0.387 and the vibration time of 90 s gives the maximum bulk density of 1313.17 kg/m3 and the smallest actual porosity is 34.69%.
This study aimed to investigate the effect of heat treatment on the physico-mechanical and microstructure properties of cement pastes containing fly ash (FA) and silica fume (SF). Portland cement (OPC) has been partially replaced by 5% SF and 20, 30, 40 and 50 wt.% FA. After curing, the hardened cement pastes were dried at 100°C for 24 hours, subjected to thermal treatment at the rate of 5°C/min, and heated at temperature of 200, 400, 600, 800, 1000°C for 2 hours, then cooled to room temperature in air. Finally, their bulk density and compressive strength were determined. X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods and were used for identification of the changes in the microstructure of the cement matrices. The results showed that the cement pastes containing 80% OPC + 5% SF + 15% FA is the optimum mix which gives a higher compressive strength and lower bulk density loss. Moreover, this optimum binder has the formation of inner fibers and crystalline needle like Wollastonite, Gehlenite which is responsible for the reduction in compressive strength loss from 800 up to 1000°C.
This paper presents an environmentally friendly and efficient method to prepare graphene from graphite, in there a high-powered ultrasonic vibration device is used to separate graphite into graphene in a liquid. During exfoliation, ultrasonic waves provide mechanical energy to break Vander Walls bonds in order to split graphite layers into graphene. Graphene was prepared by the exfoliation of graphite layers in distilled water with Tween 80 surfactant and then the solvent was vibrated at high power for 1 to 5 hours. The obtained results show that high-frequency ultrasound is a powerful tool to break Vander Waals bonding forces between adjacent layers in graphite. The SEM and ZetaSizer distribution results show that with the average size of 931 nm, 419 nm, 411 nm, 408 nm, 317 nm, the ultrasound time is 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours, respectively. The TEM and Raman results show that the graphene material has a thickness of about 3 nm corresponding to the number of layers less than 10 as low-layer graphene. These results show that high-frequency ultrasonic waves not only reduce the average size, but also separate graphite layers, forming graphene.
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