The influence of Nano-SiO2 (NS) on the strength of high-performance concrete (W/B=0.24, W/B=0.29, W/B=0.34) has been studied in this paper. The results show that compressive strengths of concrete in both the early and later stage can be improved by adding Nano-SiO2 content. And the influence on the early compressive strength is greater than that on the later compressive strength. According to the results, 3%-5% Nano-SiO2can be used as the proper mixing ratio. X-ray diffraction, SEM (scanning electron microscope) and mercury injection experiment were used to analyze the action principle of Nano-SiO2 microscopically, the microscopic characteristics of concrete can be significantly improved through interfacial and filling effect effects so that the performance of concrete can be accordingly improved.
In this work, two type graphene were dispersed in aqueous solution via sonication, and graphene nanoplatelets (GP) and graphene oxide (GO) were characterized by means of ultraviolet visible spectroscopy (UV-vis), X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, the effects of different graphene (GP and GO) on mechanical properties and microstructure of cement-based materials were investigated via filed emission scanning electron microscopy (FESEM). The results suggested that the incorporation of GP and GO both improved the flexural and compressive strength of cement, and the GP had a more prominent impact on the strengths of cement, compared with GO. The flexural and compressive strength of cement increased up to 23.5% and 7.5% with 0.05 wt% GP, respectively. FESEM analysis indicated that the microstructure of GP-cement paste was similar to that of control sample without graphene, whereas, a few flower-like crystals were generated in GO-cement paste. This work could provide a new understanding for further researches of graphene-cement composites.
Kaolin is a material with broad sources and a low price. Metakaolin is made from kaolin which is calcined, finely ground at an optimum temperature of 750 being kept constant for 4 hours. High strength and performance concrete can be mixed from metakaolin as a substitute for equal mass cement. The influences of 5%, 10% and 15% metakaolin in substitution of equal cement masses were studied on the mechanical properties of high-performance concrete. The test results showed that the addition of metakaolin improved the cubic compressive strength, splitting tensile strength and flexural strength of HPC, among which the improvement in compressive strength was the most siginificant, and simultaneously, there was also an improvement in concrete toughness in a certain degree. The optimum content of metakaolin is 10% resulting in an increase of the cubic compressive strength of concrete by 8.3% correspondingly.
The microwave absorbing properties of multi-walled carbon nanotubes-reinforced cement-based composites (MWCNTs/CC) in the range of 2–18 GHz were investigated in this paper. MWCNTs with the addition of 0.08% by mass of cement were incorporated to cement mortar. It is shown that MWCNTs which act as microwave absorber reinforce the microwave absorbing properties of MWCNTs/CC. Two absorbing peaks of MWCNTs/CC appear in the range of 4–8 GHz, one lies in 4.9 GHz with the reflectivity of -29.1 dB and the other lies in 6.8 GHz with the reflectivity of - 19.2 dB, indicating that the absorbing properties of the composites are improved greatly.
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