Papers by Keyword: Fresh Concrete

Abstract: This study evaluated the combined effect of recycled glass powder (RGP) and nanosilica on the fresh-state properties of concrete. Mixtures were prepared with partial cement replacements of 10%, 15%, and 20%, incorporating nanosilica at 1.5 % by cement weight. The control mixture (RGP-0) does not include nanosilica, allowing comparison with the additive-containing mixtures. Results showed that RGP-10 improved workability, achieving a slump of 22.6 cm compared to 7.0 cm for RGP-0, while RGP-15 and RGP-20 exhibited only slight reductions in fluidity. Air content decreased in RGP-10, RGP-15, and RGP-20, with values of 1.6 %, 1.9 %, and 1.7 %, respectively, compared to 2.3 % in RGP-0, indicating that the mixtures with RGP and nanosilica develop a denser matrix with reduced void formation. Additionally, nanosilica accelerated early hydration, raising the initial temperature by up to 3.5 °C in RGP-20 without affecting workability. These findings demonstrate that moderate cement replacement with RGP and nanosilica can produce more stable, homogeneous, and sustainable concretes, providing useful insights for designing mixtures with improved fresh state performance.

Abstract: 3D Concrete Printing (3DCP) technology, compared to traditional monolithic construction, gives a possibility to increase the workspeed and reduce the manual laborproportion, reduce material consumption and also improve the architectural appearance of buildings being erected. At the same time, more stringent requirements are imposed on the material for 3D printing in terms of rheological characteristicscontrol, strength developmentkinetics, interplay adhesion and some other parameters than for conventional ready-mixed concrete. Therefore, to ensure the mass application of technologies for additive construction production using concrete as printing ink, it is necessary to develop a regulatory and technical base, including the development of standard test methods to determine the operational properties of this typeofmaterials. The article examines the main trends in the management of the materials’properties for construction 3D printing based on cement binders and describes the principles of building a system for standardizing materials for 3D printing construction in Russia, which was developed with the participation of the authors of this article.

Abstract: This paper presents the possibility to utilize the 3D printing technology in civil engineering field specifically for concrete structures. Since this technology is booming last years and spreads in different fields of industry, the tools to analyse structures in such a way is important. Many research groups worldwide try to develop cement-based material suitable for 3D printing so that it might be used for civil engineering structures. Moreover, this technology brings necessity to check the safety of the structure at early ages of concrete. Therefore, the modelling and simulation of the digitally printed concrete structure would be of great help for such effort. The software tool that enables simulation of digitally printed concrete structure using a nonlinear FEM analysis is presented. ATENA is well established tool for such analyses of civil engineering structures made of concrete. The new module for digital printing simulation is developed as an additional feature of ATENA software. The 3D extrusion technology is supported. The paper describes the whole procedure how to model and analyse such structures and stress out all the differences compared to analyses of structures produced by traditional manner. The structure itself is modelled as usual in FE software, whereby based on velocity of printing head the time of printing, i.e. production of each element is calculated. It is later used to activate the elements during analysis and it also influence the material behaviour, such as shrinkage, strength etc.

Abstract: In this paper, the phenomenon in which the fluidity drops significantly once the concrete, which is a problem in the construction work, is called “stiffness”, and the hypothesis of the occurrence mechanism was hypothesized based on a microscopic image of cement paste. Then, author developed a chemical admixture (stiffness reducing agent) that suppresses the aggregation of cement particles and verified the effect through various tests. In the verification test, author tried to quantify the stiffness of concrete by a simple test called the vane shear test. Also, through various construction performance tests, author confirmed the possibility of stiffness affecting the construction work.

Abstract: The paper is based on dynamic modeling research and experimental results obtained for freshly compacted concrete under stationary vibration. Thus, computational relationships and laws for vibration parameters and dissipated energy will be presented. In correlation with the dissipated energy, it will be evidenced by the evolution of the compaction degree and the resistance of the concrete depending on the vibration duration. It is noted that significant correlations have been established between the displacement curve of the dissipated energy and the loop hysteresis area for several vibration frequencies specific to the dynamic compaction regime

Abstract: In order to let fresh concrete react with carbon dioxide sufficiently, the carbon dioxide was added to mixing concrete. The study used three water cement ratio (0.55, 0.65, 0.75), three CO₂ pressures (0.2, 0.4, 0.6 MPa), and two CO₂ concentration (50% and 100%) to make concrete samples, and observed the effect of carbon dioxide adsorption in the above parameters. Finally, the compressive strength and carbonation degree of concretes were tested after three curing time (7, 14 and 28 days). The research showed that concrete could be more efficient to absorb carbon dioxide by using this pressure method. The results found that the mixing concrete react with carbon dioxide in a short time, and shorten the initial setting time of concrete. But this method would greatly reduce the workability of concrete after mixing with carbon dioxide and it might be enhanced by water or superplasticizer. The bond of cement matrix might cut down after reacting with carbon dioxide. Based on the above, the compressive strength of concrete which was mixed with carbon dioxide would be impaired. The proposed CO₂-mixing method has the capacity to uptake 9.5% carbon dioxide based on water cement ratio and CO₂ pressure.

Abstract: Part of free water in fresh concrete bleeds out and results in problems of hardened concrete. In order to explore the determinant factors to control bleeding process and effecting mechanism, a series of mix samples in various water-to-cement ratios and sand ratios for different slump requirements were prepared to test their bleeding rates. Then the parameters to control bleeding process of fresh concrete and their influencing factors were investigated by regression analysis. The results reveal that percent volume of powder in mix (β_p) and the ratio of powder to voids between sand particles (p/v) are key factors to control bleeding speed, and p/v also controls the dormant time of bleeding. The sand ratio influences the bleeding process by changing the value of p/v. Both β_p and p/v have their critical values and optimum ranges. When p/v=0.78~0.87, the bleeding can be regulated to Late-Slow type with the least harm to properties of hardened concrete.

Abstract: Water-cement ratio is an important parameter of concrete quality. Rapid measurement of fresh concrete water-cement ratio can effectively monitor the on-site concrete quality management and play a great role in quality control. We study the variation of fresh concrete resistivity with the aid of electrodeless cement concrete resistivity meter, and discuss the impact of water-cement ratio under different varieties of cement, mineral admixture, chemical admixtures conditions on fresh concrete resistivity. We establish the relationships between fresh concrete resistivity and water-cement ratio based on the law of Portland cement initial hydration resistivity. The studies show that: fresh concrete resistivity is most vulnerable to the changes of water-cement ratio; there is a correlation between the law of fresh concrete resistivity and water-cement ratio; according to the fresh concrete resistivity variation, we can quickly identify water-cement ratio, cement and other parameters.

Abstract: Currently in concrete technology a lot of materials were introduced to improve the quality and properties of concrete. Additional materials include the use of steel fibers into the concrete mix. With the used of steel fibers, it can enhance the strength of the concrete. In this research, two parameters will be investigated which is the volume friction of the steel fiber and the length of the steel fiber. End-hooked steel fiber with the length of 33 mm and 50 mm and the percentage of steel fiber 0.5 %, 1.0 % and 1.5 % used in this research. The size of the mold used is 100 mm x 100 mm x 100 mm. The characteristics during the fresh concrete were also investigated by conducting the slump test, compaction test and vebe test. All the samples has been cured in the water for 7^th, 14^th and 28^th days for the compressive strength test. Based on result, it was concluded that the optimum percentage of steel fiber in this report was 1.0 % for the end-hooked steel fiber with 33 mm length which provided the highest compressive strength at 28 days.

Abstract: It has been reported that, depending on the material used, batches of concrete having the same slump value behave differently when vibrated. It is therefore to be expected that batches of concrete having the same slump value and containing the same amount of powder will have different properties depending on the material used. However, these batches of concrete are treated as concrete of the same quality since, at present, no alternative test method has yet been established as a substitute for the slump test. This study proposed new simplified experimental methods for vibration properties of fresh concrete. By using these methods, the vibration characteristics of fresh concrete containing fly ash (FA) and containing a large amount of cement were exhibited.