The various approaches, established for concrete mix design, are not universal because design mixes are explicit to local climate, available materials, and type of exposure. The new-generation mix design method should be developed based on the performance criteria. The concrete strength obtained from the designed concrete mix and optimum cement content should not be considered as the only parameter for the suitability of the concrete mix. This study was carried to compare the proportioning of concrete mixes obtained by following procedures of Indian Standard (IS), American Concrete Institute (ACI) and British Standard (BS) of concrete mix design without the use of admixtures to validate for use in a moderate climate like Kashmir, India. The concrete mixes have been prepared with the necessary 28 days resistance in compression as “15 MPa, 20 MPa, 25 MPa, 30 MPa and 35 MPa”. The assessment of water-cement (w/c) ratio; cement, water, fine aggregate (FA) and coarse aggregate (CA) proportion was carried. The w/c ratio among all formulated mixes is significantly high in the BS method and low for IS method. The BS method uses less quantity and IS method uses the maximum quantity of cement. In addition, the ratio of total aggregate content (TAC) and the aggregate-cement ratio is higher in BS design method as compared to IS and ACI design methods. The aggregate content in ACI mix design appears to be consistent and it added to the relative high compressive strength. The specimens cast following BS guidelines failed to attain the target mean strength (TMS) due to a higher volume of aggregate content, high w/c proportion, less quantity of cement in the mix. The specimens cast by ACI and IS mix design upon compression testing showed higher results than the calculated TMS. The cost analysis per cubic meter of concrete revealed that IS and ACI mix proportioning are expensive than BS method. The IS procedure results in dense concrete followed by ACI procedure. It is expected that with a comprehensive investigation on selected design parameters concentrating more on local challenges, the present study will floor the way for the development and adoption of performance-based design mix selection for moderate climate.
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Construction sites may be exposed to crisis conditions during the casting process, resulting in delays of several hours and causing destruction of ready-mix concrete. This study suggests an experimental analysis of the possibility of using a specific ad ditional dose of retardant admixtures, which may be used to ready-mix concrete be fore the initial setting of the concrete occurs. The effect of this additional dose on concrete characteristics in terms of workability, setting time, and compressive strength is also being studied. To conduct this investigation, three types of retardant admixtures from three branded companies were used. In addition, a penetration re sistance experiment was conducted on the concrete to determine its setting time. The setting time of concrete was measured at different period intervals depending on when the additional dose of the retardant admixtures was added from the start of the concrete mixing. The results showed that concrete maintained proper workability for a period of more than five hours after using the additional dose of retarding ad mixtures. The additional dose of retarding admixtures not only delayed the concrete setting but also improved the compressive strength of the concrete. This implies that the use of an additional dose of retardant admixtures specifically tailored for ready mix concrete is an effective option to avoid the return of ready-mixed fresh concrete.
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Studies in the literature show that the physical and mechanical properties of concrete could be improved by the incorporation of different kinds of industrial waste, including waste tire rubber and tire steel. Recycling of waste is important for economic gain and to curb environmental problems. In this study, finely ground CuAl10Ni bronze is used to improve the physical and mechanical properties, and freeze-thaw resistances of C30 concrete. The density, cold crushing strength, 3-point bending strength, elastic modulus, toughness, and freeze-thaw resistances of concrete are determined. In addition, the Schmidt Rebound Hammer (SRH) and the ultrasonic pulse velocity (UPV) tests, which are non-destructive test methods, are applied. SEM/EDX analyses are also carried out. It is noted that a more compacted structure of concrete is achieved with the addition of bronze sawdust. Then higher density and strength values are obtained for concretes that are produced by bronze addition. In addition, concretes including bronze sawdust generally show higher toughness due to high plastic energy capacities than pure concrete.
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Dispose of waste rubberized tires become a dangerous problem around the world, represented a big serious risk to the sur-rounded environment. Many studies show that over 1000 million tires reach their expired date yearly and this figure is anticipated to be 5000 million tires by reaching 2030. A minor part of them is employed as recycled materials and the residual amount is stockpiled or buried. This paper aimed to successfully utilize the vast amounts of tire rubber waste existing currently in landfills. This paper represents a practical investigation of the ductility performance of the reinforced rubberized concrete beams. Thirteen reinforced concrete beams simply supported, with waste rubber tires mixtures vary from 0 to 8 percentage as aggregates replacements, were tested by mid-span load. Therefore, to examine the ductility performance of reinforced rubberized concrete beams, three sets of samples were made. In the first group, coarse aggregates in the concrete mix were replaced by different percentages of the waste rubber partials, while for the second group, crumb rubber was replaced for the fine aggregates, and for the third one, a mix of waste and crumbed rubber were replaced for both types of aggregates. Experimental results of rubberized specimens were also compared with that of the reference beam (without rubber replacement), the comparison results declare that concrete contains rubber particles is less ductile than conventional concrete.
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Non-destructive methods have many advantages over traditional test methods, especially since it does not damage the specimen, it can be used multiple times on the same specimen. These advantages also provide a great benefit in terms of following the property development in concrete as the same specimens are used which eliminates the variations related to the specimens. In this study, it is aimed to determine the damage amount of concrete produced with different binders by electrical bulk resistivity, resonance frequency, and ultrasonic pulse velocity methods. Firstly, concretes containing different binders were produced, and along with the mechanical properties, ultrasonic wave velocity, resonance frequency, and electrical resistivity values of the produced concrete were determined at the 7, 28, and 90 days. Besides, the specimens were subjected to gradually increased compressive loads and non-destructive methods were used to estimate the extent of damage on specimens. It was attempted to establish a relationship between the damage on concrete specimens and the results obtained by non-destructive methods. Consequently, the compressive strength, electrical resistivity, ultrasonic pulse velocity and resonance frequency values of all specimens increased with the advancing age. It was concluded that the resonant frequency method is more successful than other methods in estimating the amount of damage in concrete.
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Hediye YORULMAZ, Sümeyye ÖZUZUN, Burak UZAL, Serhan İLKENTAPAR, Uğur DURAK, Okan KARAHAN, Cengiz Duran ATİŞ
Hediye YORULMAZ, Sümeyye ÖZUZUN, Burak UZAL, Serhan İLKENTAPAR, Uğur DURAK, Okan KARAHAN,
... Devamını oku
It is known that nano-and microparticles have been very popular in recent years since their advantages. However, due to the very small size of such materials, they have very high tendency to agglomeration particularly for nanoparticles. Therefore, it is critical that they are properly distributed in the system to which they are added. This paper investigated the effects of dry particle coating with nano-and microparticles to solve the agglomeration problem. For a clear evaluation, paste samples were preferred to detemine the compressive strength. Nano-SiO2 and nano-CaCO3, microCaCO3 and micro-SiO2, also known as silica fume, were selected as particulate additives. It was studied by the addition of various percentages (0.3, 0.7, 1, 2, 3 and 5%) of nano-and microparticles in cementitious systems, replacing cement by weight with and without dry particle coating. Dry particle coating was made by using a highspeed paddle mixer. Portland cement and additive particles were mixed at 1500 rpm for 30 seconds in high-speed powder mixer designed for this purpose. The 3-day compressive strength of the cement-based samples to which particles were added at the specified rates was determined and the effect of the dry particle coating on the early strength was investigated. According to the results, it was observed that the production of paste with the dry particle coating technique gave higher compressive strength compared to the production of paste directly in early period. Especially with dry particle coating, compressive strength increased more than 100% in paste samples containing 0.3% nano-SiO2 compared to direct addition without coating.
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As for the communication between concrete and the particles, the surface shows Cl− shock and Na adsorption. With expanded particle focus, the solid adsorption capacity for Cl− is upgraded as a result of a detailed overview of the dynamic molecular simu lation studies examining the chloride diffusion coefficient. Different characteristics of the diffusion process, including molecular models, system-size effects, tempera ture, and pressure conditions, and the type of protection, are discussed. This paper focus on Molecular Dynamic Simulation to determine the diffusion coefficient of chlo ride ion and water molecules in concrete. The diffusion coefficient for NaCl salt ob tained 6.60178x$10^{-10}$$m^2$/s and the diffusion coefficient for $CaCl_2$ salt obtained 7.29305x$10^{-10}$$m^2$/s. So, the average chloride diffusion coefficient 6.9475x$10^{-10}$$m^2$/s. Diffusion coefficient obtained from graph 5.562x$10^{-10}$$m^2$/s. Diffusion coefficients for water molecules for NaCl solution are 6.125x$10^{-10}$$m^2$/s, 6.85x$10^{-10}$$m^2$/s, 1.044x$10^{-10}$$m^2$/s, 8.525x$10^{-10}$$m^2$/s, 6.25x$10^{-10}$$m^2$/s. diffusion coefficient of water molecules in CaCl2 solution are 4.5x10-10$m^2$/s, 6.725x10-10$m^2$/s, 1.254x10-10$m^2$/s, 7.725x$10^{-10}$$m^2$/s, 1.3x$10^{-10}$$m^2$/s. Average value obtained for water molecule diffusion are 4.545x$10^{-10}$$m^2$/s, 7.4062x$10^{-10}$$m^2$/s and 1.149x$10^{-10}$$m^2$/s. This diffusion of chloride effects the binding of water in concrete pore.
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Zeolite is of a significance for geopolymers as it is a natural precursor and does not require additional heat treatment for activation. However, aluminosilicates sourced from natural sources require additional handling for the best use of exploitation. In this study, geopolymers were synthesized by binary use of zeolite and fly ash as main binding material and sodium silicate and sodium hydroxide as alkaline activator. The influence of alkaline activator ratios and sodium hydroxide concentrations on the compressive strength and flexural strength of the zeolite-fly ash based geopolymers were studied. In this research, zeolite-fly ash based geopolymer mortars were pro duced by using 50% of natural zeolite (clinoptilolite) and 50% of C-type fly ash. Four different activator ratios ($Na_2SiO_3$/NaOH: 1, 1.5, 2 and 2.5) and two sodium hydrox ide molarities (10M and 12M) was utilized to activate zeolite and fly ash in order to determine the effect of these parameters on the mechanical strengths of the pro duced geopolymer mortars. The results indicated that as the alkaline activator ratio and NH molarity were increased the compressive strength of the zeolite-fly ash based geopolymers also increased. The maximum compressive and flexural strength values obtained after 28 days of curing were 20.1 MPa and 5.3 MPa respectively and corre sponds when used activator ratio of 2.5 and sodium hydroxide concentration of 12 molarity. The obtained results indicated that both the alkaline activator ratio and so dium hydroxide concentration affected the compressive and flexural strengths of ze olite-fly ash based geopolymer mortar specimens.
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The water utilized in concrete manufacture plays an important role within the concrete mix, beginning from controlling the process of hydration of cement, besides appropriate curing to achieve the required strength, not to mention controlling the workability and durability of the concrete structure. The utmost significant challenge for concrete technology is to improve the properties of concrete. Nowadays, the engineering field needs to produce structures in harmony with the concept of sustainable development through the utilization of high-performance materials with an ecofriendly impact that is produced at a low-cost. The magnetic water (MW) provides one of the utmost towards this objective. The cost of magnetizing water is low because of the simple instruments used and the cost can be adapted to the scale of the work. In the last two decades, a new technology, so-called MW technology, has been extended to use in concrete manufacturing. Therefore, currently, the researchers are interested in the use of MW in the manufacture of cementitious materials helping to rationalize the cement usage and reducing reliance on chemical additives that have a negative environmental impact. Consequently, this paper presents the effect of the magnetization process in the structure of water molecules, the main properties of water. Additionally, the effect of using MW on the fresh and mechanical properties, as well as the durability characteristics and performance of cementitious materials have been reviewed. Moreover, the factors that affect the magnetization process of water, which highlighted discuss in this study. The results revealed that using MW significantly enhances the flowability and the characteristic strengths of cementitious materials as well as the durability properties.
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The effect of high temperature on self-compacting concrete, which contains different amounts of fly ash, has been investigated. By considering the effect of concrete age and increased temperatures, the optimum fly ash-cement ratio for the optimum concrete strength is determined using experimental studies. Self-compacting concrete specimens are produced, with fly ash/cement ratios of 0%, 20% and 40%. Specimens were cured for 28, 56 and 90 days. After curing was completed, the specimens were subjected to temperatures of 20°C, 100°C, 400°C, 700°C and 900°C for three hours. After the cooling process, tests were performed to determine the unit weight, ultrasonic pulse velocity and compressive strength of the specimens. According to the experiment results, an increase in fly ash ratio causes a decrease in the compressive strength of self-compacting concrete. However, it positively contributes to self-compaction and strength loss at high temperatures. The utilization of fly ash in concrete significantly contributes to the environment and the economy. For this reason, the addition of 20% fly ash to concrete is considered to be effective.
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