Papers by Keyword: Cement-Based Materials

Abstract: The conductivity of cement-based materials is usually poor, and this material is not a common conductive material. However, with the rapid development of Internet of Things technology in recent years, the rise of smart cities has brought more and more opportunities and needs, and conductive cement-based materials have emerged. Conductive cement-based material is a new type of composite material. The conductive material is added to the cement-based material to reduce its resistance and enhance the conductive properties of the material. The material can not only be applied to the construction of smart cities, such as smart street lamps and smart roads but also can be widely used in buildings, public transportation, and other fields. In the study of conductive cement-based materials, the size and shape of conductive materials have a direct impact on the electrical conductivity of cement-based materials. This is because the dispersion of the conductive material has a significant effect on the conductivity, and the size and shape of the conductive material can determine its dispersion. Secondly, in the application environment of cement-based materials, factors such as humidity and cracks may affect electrical conductivity. Therefore, to ensure the stability and reliability of conductive cement-based materials, a large number of experimental studies are needed to optimize the dispersion and shape of conductive materials and to understand the performance of materials in different environments. The research of conductive cement-based materials is of great significance to the construction of smart cities in the future. This conductive material has great application prospects, which can not only improve the intelligent level of urban infrastructure but also bring more social and economic benefits.

Abstract: This article presents the results of a study on the effect of carbon nanosized additives on the structure and properties of cement-based materials. The use of a carbon black dispersion as an alternative to an expensive dispersion of carbon nanotubes is proposed. Based on the experimental data, it is proven that the introduction of carbon black particles into the composition of the cement matrix in an amount of 0.2% by the weight of cement leads to an increase in strength of the cement stone, in both compression and bending, by 21% and 8%, respectively. This increase is compatible with the results obtained when cement matrix was modified with a dispersion of carbon nanotubes.IR spectral and thermal analysis of the modified cement matrix, as well as the study of its microstructure, confirm the formation of a dense net of cement hydration products, including low-basic calcium silicate hydrates and secondary nanosized globular thaumasite formations that contribute to the compaction of the material structure and the following increase in strength.

Abstract: Concrete carbonation serves as one common durability issues in reinforced concrete structures at present. In order to understand the carbonation mechanism, many methods were developed by previous researchers for the characterization of concrete carbonation. For example, Phenolphthalein spraying method, Thermo-gravimetric analysis (TGA), X-ray diffraction, Fourier Transform Infrared Spectroscopy (FTIR), Mercury intrusion porosimetry (MIP), etc.. In this paper, all existed carbonation methods were summarized, and, based on the parameter (pH value inside pores, microstructure, chemical composition, etc. ) each method focuses, the function behind method was elaborated. Finally, this paper discussed the pros and cons of current methods, and further developing directions were proposed.

Abstract: 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.

Abstract: In recent years, more and more attention has been paid to the effect of stray current on the properties of cement-base materials in subway engineering. In the actual service process, reinforced cement-based systems suffer from various erosive conditions, the degradation mechanisms in reinforced cement-based systems due to the combined effects of stray current and environmental multi-factors have been a serious problem in civil engineering for many years. This paper reviews the research achievements on the properties of cement-based materials under the multi-factor coupling conditions such as stray current and soft water, chloride ion, sulfate, stress, freezing and thawing cycle and so on. Furthermore, the improvement of cement-based materials on stray current resistance is also generalized in it. Prospects of cement-based materials for durability under environment multi-factor coupling actions are also presented.

Abstract: Based on the theory of ecological resources recycling, the effects of matrix quality, surface treatment method, soaking time, age after treatment and fluosilicate cation on hardening cement based materials were investigated by using the byproduct of phosphate fertilizer production namely fluosilicate as the surface treatment agent of cement-based materials and changing different surface treatments. The results showed that the permeation capacity of surface hardener solution , the wear resistance and surface hardness of cement-based materials were significantly improved by the treatments of surface sanding and oven drying. Both surface spraying and submerging methods can promptly increase the hardening effect by more than 20%, manifesting as the rapid improvement of wear resistance in 1 day and the maintenance of that in 7 days. The effective spraying amount and soaking time were 100g/m²-200g/m² and 6 h, respectively. The fluosilicate surface hardener exhibited better hardening effect than the silicate surface hardener for those matrix materials with different quality, especially for the matrix materials with low compactness. The magnesium fluosilicate displayed the best hardening effect. Besides, the mechanism of fluosilicate and silicate surface hardeners were discussed and compared. The results show that the fluosilicate surface hardener produced crystals and colloids by reacting with cement hydrates to fill the void and improve the compactness, other than the silicate surface hardener which produced calcium silicates by reacting with cement hydrates. As a result, the hardness and wear resistance of cement-based materials are improved, but also the probability of a potential alkali-aggregate reaction is substantially reduced.

Abstract: A Negative pressure sensing set-up for capillary pressure test was designed and used for testing the capillary pressure of cement-based materials, cement pastes of water-cement ratio 0.30 was adopted, and the factors that may affect the measured values such as hardness of water tube, gas volume in the set-up, gas content in water, test depth, bleeding of cement pastes was studied. The results shows that the accuracy of the measured value is very large impacted by the air volume in the set-up and by the hardness of water tube, the capillary pressure at different depths could be affected by the external environment and the bleeding of cement pastes. According to the test results, methods for measuring the capillary pressure of cement-based materials were proposed, and some other recommendations that help to improve the test accuracy were given.

Abstract: By combining the three-point bending beam test with theoretical derivation, the elastic modulus, fracture toughness, surface energy and the maximum defect size permissible under certain working stress of ultra-high strength cement-based materials were obtained. The fracture properties were studied with the water to binder ratios (W/B) from 0.18 to 0.14. Test results showed that the ultra-high strength cement-based materials are quasi-brittle and the net bending strength of specimen decreased substantially when there was a notch. The elastic modulus of ultra-high strength cement-based materials can be up to 74.0 GPa, obviously higher than that of ordinary cement-based materials, showing greater elastic deformation resistance. Moreover, with decrease of W/B ratio, the compressive strength, fracture toughness, critical strain energy release rate as well as the maximum defect size permissible under certain working stress of ultra-high strength cement-based materials increased significantly, indicating that the anti-cracking ability increased with the decrease of W/B ratio.

Abstract: The development of the city traffic and its increasing traffic flux are the signs of the development of the society, but causing a serious pollution on the city's ecological environment. Cement hydration reactions are needed to generate Ca (OH)₂, C-S-H gel, and AFt, as well as other hydrated products. Meanwhile, heavy metal ions are contained and fixed in a cement paste under physical encapsulation, absorption, isomorphous replacement, and double decomposition. This paper mainly discusses the impact of hydration environment on the adsorption law of materials adsorbing heavy metal ions and the adsorption mechanism under different pH values and temperatures, analyzing specific reasons from the perspective of micro-structure. Through the analysis it can be seen that, in addition to zinc ions, the cement-based materials’ capacity of adsorbing heavy metal ions increases as the pH value and the temperature increase. Micro-structure analysis shows that cement-based materials’ main adsorption methods are different when pH values are different.

Abstract: In this paper, a device for pore solution extraction from cement-based materials was presented, The relevant Factors of Efficiency of Pore Solution Extraction and the effects of squeezing pressures on the chemical concentrations of pore solutions were studied. The results shows, the efficiency of pore solution extraction can be effected by pressure values, squeezing duration, pressure maintaining time; A low rate of pressures loading is suitable for early-age cement pastes, and long-term samples can take larger rate; 30 minutes loading time can be adopted for specimens with all the different ages; no significant differences were observed regarding the chemical composition (Na and K) of the pore solution extracted between 300 and 900MPa.