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Purposes For improving the mechanical properties of GO incorporated cement paste, two types of nano-silica (crystalline and amorphous) and coal-bearing metakaolin (CMK) were used seprately to improve GO dispersion in cement paste. Methods UV-vis spectrophotometry was used to investigate the effects of ultrasound time and different dosages of amorphous nano-silica (ANS) and crystalline nano-silica (CNS) on the dispersion of GO in saturated calcium hydroxide solution. The effects of different particle materials on GO dispersion were characterized by using compressive strength results. The dehydration and decomposition processes of various phases of hydration products were observed by thermogravimetric (TG) analysis, and the effect of adding different particle materials and GO on the pore structure of cement paste was analyzed by mercury intrusion porosimetry (MIP). Findings According to UV-vis spectroscopic study, when the contents of ANS and CNS were 2% and 1.5% by weight of cement, respectively, GO dispersion in saturated Ca(OH)2 solution is improved greatly. Compared with two nano-silicas, CMK is more effective to improve the compressive strength of GO incorporated cement paste. At the age of 28 d, the flexural strength and compressive strength of the cement paste incorporated with 4% CMK and 0.03% GO are 26.93% and 30.41%, respectively, higher than those of a plain cement paste sample. The results of TG and MIP tests showed that the pozzolanic reaction of CMK can effectively refine the pore structure of cement paste, improve GO dispersion, and enhance the bonding between hydration products and GO, which is the main reason why CMK can effectively improve the mechanical properties of GO incorporated cement paste.

Carbon fibre, steel fibre and graphite were used as conductive fillers to prepare cementitious materials with excellent electrothermal properties. The electrically conductive cementitious materials with different volume dosages were analysed through compressive and flexural strength, electrochemical impedance spectroscopy and temperature rise tests. An equivalent circuit model was established to study the electrically conductive heat generation mechanism in the electrically conductive cementitious composites. The results indicate that the mechanical properties of cementitious composite materials with a ternary conductive phase are better than those of pristine cementitious materials because the fibrous filler improves their mechanical properties. However, the incorporation of graphite in the material reduces its strength. Introducing fibrous and point-like conductive phase materials into the cementitious material enhances the overall conductive pathway and considerably reduces the electrical resistance of the cementitious material, enhancing its conductive properties. The volume ratios of carbon fibre, steel fibre and graphite that achieve an optimal complex doping in the cementitious material were 0.35%, 0.6% and 6%, respectively. This was determined using the mutation point of each circuit element parameter as the percolation threshold. In addition, at a certain safety voltage, there is a uniform change between the internal and surface temperatures of the conductive cementitious material, and the heating effect in this materialis is considerably better than that in the pristine cementitious material. [ABSTRACT FROM AUTHOR]

To explore the effects of the introduction order of calcium sources and the bacteria-to-calcium ratio on the microbially induced calcium carbonate precipitation (MICP) product CaCO3 and to achieve the regulation of CaCO3 crystal morphology, the mineralisation products of MICP were compared after combining bacteria and calcium at ratios of 1/9, 2/9, 3/9, 4/9, 5/9, and 6/9. A bacterial solution was combined with a urea solution in two calcium addition modes: calcium-first and calcium-later modes. Finally, under the calcium-first addition method, the output of high-purity vaterite-type CaCO3 was achieved at bacteria-to-calcium ratios of 2/9 and 3/9; under the calcium-later addition method, the output of calcite-type CaCO3 could be stabilised, and the change in the bacteria-to-calcium ratio did not have much effect on its crystalline shape. [ABSTRACT FROM AUTHOR]

Exploring cheap and efficient cocatalysts is particularly important for a photoanode during photoelectrochemical (PEC) water splitting. Herein, we demonstrate that composite CoOx/CuO cocatalyst could efficiently enhance the oxygen evolution activity of BiVO4. The onset potential of BiVO4 shifts negatively from 0.42 to 0.38 V vs. the reversible hydrogen electrode (RHE), and the photocurrent of BiVO4 increases from 0.42 mA cm−2 to 1.58 mA cm−2 at 1.23 V vs. RHE, which increases by about 3.76 times. It was confirmed by subsequent electrochemical and physical characterization that the charge separation and injection efficiency were improved, and the IPCE was also improved. Systematic studies indicate that composite CoOx/CuO cocatalyst exhibits better performance than the single CoOx or CuO cocatalyst for promoting the separation of electron‐hole, and accelerating the surface water oxidation reaction. [ABSTRACT FROM AUTHOR]

Photocatalytic removal of hexavalent chromium (Cr(VI)) based on semiconductor is important under visible light for environment and energy. Herein, a visible light-responsive heterojunction composed of molybdenum disulfide and zinc indium sulfide was synthesized through a simple one-pot hydrothermal method to ensure full contact between the two components to efficiently improve the Cr(VI) reduction. The MoS2/ZnIn2S4 composites build heterojunctions between MoS2 and ZnIn2S4 to inhibit recombination of photogenerated holes and electrons and provide the reaction sites to trap photogenerated electrons to participate in the reduction of Cr(VI). The highly efficient reduction of Cr(VI) was obtained by adjusting the proportion of molybdenum disulfide. It demonstrates that the 0.5 wt% MoS2/ZnIn2S4 composite microstructures show the highest degradation rate of 0.1989 s−1 under visible light irradiation, 1.7 times of bare ZnIn2S4. Moreover, the MoS2/ZnIn2S4 showed excellent stability during photocatalytic recyclable processes. This work encourages researchers to remove Cr(VI) by constructing effective heterojunction structures. [ABSTRACT FROM AUTHOR]

In order to study the effects of fibers and secondary curing on strength of C60 high performance concrete (HPC) subjected to high temperature, a simulated fire test was performed on a C60 HPC specimen mixed with polypropylene fibers, steel fibers, and hybrid fibers (polypropylene fibers and steel fibers). Two groups of experiments were designed separately until the specimen cools down to 20 °C, one for direct loading and the other for loading after 14 days of standard curing. Then the com pressive strength and split tensile strength were determined. The test results show that the compressive strength and split tensile strength of C60 HPC decreases with the increase of the fire temperature. Compared with the concrete with single kind of fibers or without any fibers, the one with mixed fiber can significantly reduce the damage at high temperature. Compressive strength and splitting tensile strength of C60 HPC can be picked up a certain extent after the secondary curing. [ABSTRACT FROM AUTHOR]

To know the variation of mechanical properties of steel after different high temperatures with different cooling methods, the yield strength, tensile strength, elongation percentage, shrinkage percentage of HRB400 steels with three types of cooling methods including spray cooling, nature cooling, furnace cooling were evaluated. Nondestructive infrared thermography technique was used to analyze the infrared thermal image of steels after high temperature with different cooling methods. Experimental results indicated that the mechanical properties were related to the temperature and cooling methods. The mechanical properties of the furnace cooling and natural cooling were similar, while water cooling changes was intense The average temperature rise was increased with the fire temperature of steel. The cooling method had little effect on the infrared average temperature rise of the post-fire bars below 700 °C, while water cooling had a greater impact on infrared temperature rise above 700 °C. Based on experimental data, the fitting formula of relationships among the average temperature rise of infrared, the fire temperature, the ratio of yield strength ratio, tensile strength ratio were developed. The results can be used to evaluate the bearing capacity of HRB400 steel after fire. [ABSTRACT FROM AUTHOR]