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Concrete
Published in A. Bahurudeen, P.V.P. Moorthi, Testing of Construction Materials, 2020
[IES 2019] Which of the following methods will help in reducing segregation in concrete? Not using vibrator to spread the concrete.Reducing the continued vibrationImproving the cohesion of a lean dry mix through addition of a further small quantity of water. 1, 2 and 31 and 2 only1 and 3 only2 and 3 only
Concrete Mix Design
Published in M. Rashad Islam, Civil Engineering Materials, 2020
Workability is the ease with which the concrete components can be mixed, transported, placed, compacted, and finished, with respect to a homogeneous condition. Sufficient workability in concrete is required for proper compaction, and prevents segregation of concrete, resulting in a strong and durable concrete. Increasing water content in concrete increases the workability of concrete. However, an increase in the water ratio causes a decrease in the strength of the concrete, and enhances the segregation. There are several ways of improving the workability without increasing the W/C ratio, such as: Use of smooth textured and round aggregates improves workability, as these types of aggregates can slide over one another very easily. Angular aggregates tend to interlock and are difficult to work with.Use of well-graded, fine aggregates provides better workability.Use of larger aggregates causes an increase in the workability.Decrease in the ambient temperature can increase the workability of concrete.Chemical admixtures, such as water-reducers, air-entraining superplasticizers, and workability agents, are often used to improve the workability of concrete.
Technogenic byproduct filler-based earthquake-resistant super concrete
Published in Vladimir Litvinenko, Advances in Raw Material Industries for Sustainable Development Goals, 2020
M.S. Saidumov, A.Kh. Alashkhanov, S-A.Yu. Murtazaev, T.S-A. Murtazaeva
As is commonly known, among the most important indicators of the quality of concrete mix for cast-in-situ construction is the ability of the concrete to retain the parameters of its workability (mobility, composition stability, etc.) for a long time. In this regard, the rheological and technological properties of concrete mixtures were studied, in particular their mobility, durability, ability to retain workability, water segregation (bleeding), segregation of concrete, etc. As can be seen from Table 3, the compositions studied and proposed in this work (special concrete compositions) based on filled binders and special additives are characterized by increased capacity to retain workability (8-10 hours). High rates of workability parameters preservation of concrete mixtures contribute to the production of an integral in-situ construction without the formation of “cold joints” in case of unforeseen circumstances associated with breakdown of equipment and tools, failure to supply the mixture, etc. And after the end of the inhibitory effect of the additive, these mixtures quickly gain strength at an early age (1-3 days), which increases the efficiency of form reuses and, as a result, drastically reduces the construction time, which is very important in modern cast-in-situ construction. For elements of the precast reinforced construction industry, such a feature of the proposed concrete formulations (high durability, rapid strength development, etc.) will slash the manufacturing time of constructions, and in some cases, partially or completely eliminate the cost of concrete steaming.
Challenges in the Analysis of Historic Concrete: Understanding the Limitations of Techniques, the Variability of the Material and the Importance of Representative Samples
Published in International Journal of Architectural Heritage, 2022
A lack of suitable grading is conducive to segregation, which in turn can result in the dense coarse aggregate particles settling to the bottom of the mix and fluid cement paste rising to the top (Neville and Brooks 2010). The effects of segregation on concrete heterogeneity should not be underestimated, particularly when selecting samples for analysis, as it has been found to result in a difference in cement content of as much as 100 kg/m3 between the top and bottom of concrete walls and columns (Skinner 1980).