جستجوی مقالات مرتبط با کلیدواژه « Self-Compacting Concrete » در نشریات گروه « عمران »

As the industrial production of Self-Compacting Concrete (SCC) in the form of ready-mixed concrete faces challenges in different weather conditions, it is necessary to consider mixing, transportation, and casting to achieve the desired workability, mechanical, and durability properties. As a result of improper compaction and placement of SCC, a decrease in workability can result in failure to achieve the desired strength and durability. It was found that replacing mixing water with ice with 0, 10, 30 and 60% reduced the temperature of fresh concrete by approximately 1, 3, and 12°C compared to the control mix design after 110 minutes from the start of mixing. The superplasticizer amount and concrete properties were examined. After reducing the temperature of fresh concrete and maintaining its fluidity, the amount of superplasticizer decreased by 62.4%, and the result of its decrease with an increase in the amount of ice, increased the final production cost by 5.4%. In general, reducing the temperature of fresh concrete improved the rheological properties of SCC. When compared to the control mix design, the use of ice did not significantly alter the compressive strength, water absorption, and electrical resistance, except for a 17% increase in water absorption due to replacing 60% of the ice.

The present paper studies experimental research on the effects of fiber on the strain and the Poisson's ratio of self-compacting concrete (SCC). The experiment was carried out on 48 cubic concrete samples and 68 standard cylindrical samples of 4 different mixes with compressive strengths of 25, 28, 30, and 33 MPa. The percentage of fiber in the mixes increases from 0 to 12. Axial and lateral strains of the samples were calculated simultaneously, with respect to the stress exerted by uniaxial compressive loading. Having compared the stress-strain curves for axial and lateral strain, Poisson's ratios were calculated by taking the number of the loadings into account. One of the implications of the results was that the ratio of the inner area in lateral stress-strain curve to those in axial stress-strain curve relate to the square of Poisson's ratio in the same percent of fiber. At the end, with respect to the concrete's compressive strength and percentage of fibers, an integrated model was formulated for Poisson's ratio of fiber SCC under compressive loading. The results show that an increase in fiber (only 2%) causes a significant increase in Poisson's ratio (more than 5%) after the second compressive loading. Also, the third lateral strain provides maximum strength in all self-compacting concrete mixes.

Self-compacting concrete (SCC) is known for its outstanding characteristics such as superior mechanical and durability properties. Corrosion of rebar due to penetration of chloride ions in the reinforced concrete elements is of particular importance. Therefore, this issue in the SCC must be investigated. Pozzolanic materials could be used in the SCC to increase the resistance of concrete against chlorine ion penetration. In this research, effects of pozzolanic materials including micro silica, nano silica, fly ash, rice husk ash, as well as limestone powder on the mechanical and durability characteristics of self-compacting concrete placed in chloride environment have been studied. The results show that nano-silica increases the mechanical and durability characteristics of self-compacting concrete. Moreover, the SCC containing combination of nano-silica and pozzolanic materials has better properties than the one containing nano-silica.

Industrial steel fibers (ISFs) are the most widely-used fibers for the purpose of concrete reinforcement. The industrial production of these fibers is costly, and it contributes to Greenhouse gas emissions. The present study, therefor, aims to explore the ways in which these fibers can be replaced by recycled steel fibers (RSFs) made of scrap vehicle tires. To this end, the present study examined 13 mixtures containing different volume percentages (0%, 0.5%, 1%, 1.5%, and 2%) of ISFs, RSFs, and their combinations. The examinations included rheological properties of the fresh self-compacting concrete (J-ring, L-box, U-box, and V-funnel tests), mechanical properties of the hardened concrete (compressive, Brazilian tensile, and flexural strength tests), environmental characteristics (global warming potential (GWP)), and economic characteristics. Results showed that RSFs had a poorer performance than ISFs in terms of mechanical properties. The use of 2% ISFs increased the splitting tensile and flexural strengths by 114% and 82%, respectively, while the same amount of RSFs increased these parameters by 80% and 44%, respectively. On the other hand, RSFs showed better performance than ISFs in terms of rheological, environmental, and economic characteristics. Replacing ISFs with RSFs in mixtures containing 2% fibers could improve the rheological, environmental, and economic characteristics by 8%, 30%, and 65%, respectively. Finally, given the multi-criteria optimization results, RSFs were superior to ISFs in terms of rheological, mechanical, environmental, and economic characteristics.

Self-compacting concrete (SCC) containing fibers is a continuous compound, in which the fibers are dispersed throughout the concrete matrix and reduce shrinkage and microcracks. Furthermore, SCC properties such as filling capability and high efficiency produce a homogeneous mixture that could remove many problems of the conventional concrete. In this study, 10 mix designs were examined and tested, one of which was considered for the control sample and the other 9 designs included 0.25, 0.5, and 0.75 v/v% of steel, single-strand macrosynthetic (MEX 100), and carbon fiber reinforced polymer (CFRP) fibers. The rheological behavior of fresh SCC was investigated by the rheometer test as well as common tests used to determine the properties of fresh SCC, including slump flow, J-ring, L-box, U-box, and V-funnel tests. Then, the behavioral model of the hardened concrete was analyzed by tests determining mechanical properties such as compressive strength and modulus of elasticity. The results indicated adding fibers to fresh concrete reduced self-compacting and rheological properties of concrete; this effect became more visible with increasing the volume percentage of fibers, so that the greatest effect was observed in the design containing CFRP fibers. Results of mechanical properties of hardened concrete showed adding low volumes of fibers to SCCs improved some of these properties. However, using high volumes of fibers increased ductility and, thus, reduced compressive strength and modulus of elasticity in SCCs.

The use of waste glass aggregates as a substitute for fine natural aggregate and glass powder as a substitute for cement can have economic and environmental benefits. In this study, the behavior of self-compacting concretes containing waste glass aggregate (up to 600 kg / m3) and glass powder (up to 180 kg / m3) has been investigated. For this purpose, flowability, stability, and viscosity of self-compacting concrete in fresh state and compressive strength, electrical resistance, resistance to chloride ion penetration and scanning electron microscopy images in hardened state were examined. The results of experiments show that the use of waste glass can have a significant effect on the properties of fresh self-compacting concrete and can increase the use of superplasticizer and potential of bleeding and segregation. Also, by replacing cement with glass powder up to 40%, the results of compressive strength, electrical resistance and chloride ion penetration resistance tests were significantly improved. In this study, it was shown that with the simultaneous use of glass powder and glass aggregates up to one third of the concrete volume, desirable results can be achieved.

One Of the effective parameters in the final strength and durability of self-compacting concrete is post-fabrication curing. External Curing with water Supply and moisture retaining coating are commonly used despite the limitation of these methods. Internal curing is one of the main issues in the implementation of reinforced concrete and bulk concrete structures with much less restrictions, especially in high performance concrete. The aim of this study was to investigate the effect of internal curing of self-compacting concrete using superabsorbent polymers on mechanical properties and durability of concrete. These polymers absorb some water and gradually release it during the hydration process. Using this method, the curing process is performed more efficiently, not only on the surface but also in the depth of concrete elements. Two types of superabsorbent polymer powders based on sodium and potassium with two different amounts have been used in this research. Concrete samples at 7 and 28 days of age were subjected to compressive strength, electrical resistance, water permeability, thaw-freeze cycle and microstructure tests including SEM, XRD and XRF. Compressive strength of samples with internal curing increased by 11.4% compared to control samples. In terms of durability parameters, the samples with internal curing show a reduction of more than 100% in water permeability and 16.7% improvement in electrical resistance. The result of microstructural experiments showed an improvement in evolution of the hydration process by at least 2.4% and at most 8.3% due to internal curing.

Considering the low concrete resistance to cracking and high volume of aggregate used in it, this study has addressed the effects of increasing the volume of wavy steel fibers (0.15, 0.3 and 0.45%) and volume of coarse aggregates (30, 40, 50 and 60%) in relation to the total volume of aggregates on the properties of fresh, hardened self-compacting concrete as well as on the fracture mechanics. To this end, different tests were performed on: 1) fresh concrete (slump-flow, T-50, J-Ring, Sieve analysis and L-BOX tests), 2) hardened concrete (compressive strength, tensile strength and modulus of elasticity tests) and 3) fracture mechanics (Mode I fracture toughness test on ENDB specimens) using 108 cylindrical specimens. Results showed that increasing the coarse aggregate volume improves the rheological properties and increasing the wavy steel fiber volume reduces the efficiency and flowability of the self-compacting concrete, but improves the compressive strength in concretes containing 50 and 60% coarse aggregate volume. Increasing this volume, will slightly reduce the tensile strength of only the fiber reinforced self-compacting concretes containing 60% coarse aggregates. Increasing the coarse aggregate volume by 30 to 60% improves the modulus of elasticity of specimens containing a fixed fiber percent and increasing the volume of wavy steel fibers, at 30 and 40% coarse aggregate volumes, increases the fracture toughness (Mode I) of the self-compacting concrete specimens containing wavy steel fibers.

The durability of a concrete structure is highly dependent on the strength and permeability of the surface layer, as it is the surface layer that must prevent the entry of materials that can initiate or enhance the harmful effects on concrete. Sulfates are one of the most common destructive factors in concrete in most parts of Iran, especially in the southern regions of the country where concrete is exposed to seawater (which contains sulfate compounds). Also, the lack of compaction of the surface layer, due to the difficulty of vibration in limited spaces between molds and rebars and other accessories, is one of the main reasons for the poor durability of reinforced concrete structures exposed to environmental factors. Naturally, incorrect vibration results (worming, detachment, dehydration) have stronger negative effects on permeability and therefore durability. Self-compacting concrete with suitable properties is free from these defects and as a result, materials with less inconsistency and uniform permeability have less weaknesses for environmental harmful factors and, therefore, have better durability. Therefore, considering that the "torsion" test shows good sensitivity to surface changes of concrete, so in this study, using the "torsion" test, the effect of magnesium sulfate on the surface strength of self-compacting concretes has been investigated. In the "twist" test, a 5 cm diameter metal cylinder is glued to the surface of the test site using epoxy resin adhesive. Then, using a conventional hand-held tachometer, a torsion anchor is inserted into the metal cylinder to break the test object. The equipment used in the "twist" test is very cheap, simple and accessible compared to other corresponding tests. The damage from the "torsion" test is very superficial and minor, and by causing failure in the test object itself, it directly determines its strength. Self-compacting concrete mixing designs were studied by replacing 25, 35 and 45% cement with fly ash filler, and a conventional concrete mixing design as a control to study the effect of magnesium sulfate on the strength of self-compacting concrete. Self-compacting concrete tests including slump flow test, slump flow time of 50 cm, V-shaped funnel, V-shaped funnel increase time (5 minutes) and L-shaped mold were performed on self-compacting concrete acceptance criteria on self-compacting concrete mixing designs. . The results indicate that sulfated water not only does not have a negative effect on the surface strength of self-compacting concrete containing fly ash, but also provides better curing conditions for these samples. The use of fly ash also makes the magnesium sulfate solution a more suitable medium than ordinary water for the surface strength of self-compacting concretes. The process of obtaining surface strength in almost all self-compacting samples treated in magnesium sulfate solution is more than that in ordinary water. However, in the case of ordinary concrete, the process of obtaining the surface strength of all samples placed in magnesium sulfate solution is less. For self-compacting samples treated in magnesium sulfate solution, with increasing the percentage of fly ash, the surface resistance of 3 and 7 days decreases. But the 28-day surface resistance increases.

Despite the fact that in most operating conditions, concrete components, compaction and curing affect the performance of concrete, but premature failure of concrete structures due to problems with the durability of concrete structures also occurs a lot. Due to the lack of information on the effect of type and strength of aggregates on the durability of self-compacting concrete, in this article, using the tests of "friction transfer" and "drilled core" to investigate the effect of strength of different aggregates on the reliability of concrete Self-compacting has been exposed to sodium sulfate. 9 types of stones with the names of travertine, granite, basalt, andesite, marble, green stone tuff, crystal green tuff, rhyolite and limestone have been used to make self-compacting concretes. Compressive strength tests of self-compacting concretes cured with water and sodium sulfate solution were performed at ages 7, 14 and 28. The results showed that the volume change of rocks with higher water absorption percentage was less and there is a direct relationship between the compressive strength of self-compacting concretes treated in water and sodium sulfate solution with the strength of the parent rock. We also see an increase in compressive strength of self-compacting concrete placed in sodium sulfate solution at a young age compared to samples placed in water. There is also a linear relationship with a high correlation coefficient between the results of the friction transfer test and the core correction test. Compressive strength of crystalline green tuff, green tuff, andesite, rhyolite, travertine, lime, marble, granite and basalt are 31.76, 33.12, 39.92, 43.43, 48.41, 51/97, 59.66, 62.17 and 75.41 Mpa, respectively. With increasing compressive strength, the results of friction transfer test also increased so that for the mentioned rocks are equal to 132.4, 146.9, 155.9, 168, 176.3, 185.3, 189.8, 5 / 198 and 9/207 Nm.

The durability of concrete is one of the main criteria in the implementation and operation of concrete structures exposed to environmental risks. One of the most important causes of rebar corrosion is the presence of chloride ions. Therefore this paper investigated the effect of using xanthan gum, which is a type of polysaccharide, on the durability characteristics of self-compacting concrete. By selecting step xanthan additives in the amount of 0.2% by weight of cement, Silica fume in the amount of 5, 7, and 10% by weight of cement, and Nano silica in the amount of 2, 3, and 4% by weight of cement, mechanical and durability characteristics have been evaluated experimentally. In this paper, by controlling the rheological properties of self-compacting concrete, the parameters of migration coefficient; Chloride penetration refers to the depth to which chloride ions from the environment penetrate into the concrete; electrical specific strength and compressive strength of concrete were evaluated. Self-Compacting Concrete Benefits and the expansion of its application, multi-parameter evaluation is needed to be considered. The results indicate that xanthan gum additive improves viscosity, reduces slump flow, and reduces the separation of self-compacting concrete, and its effect on improving durability characteristics such as specific strength, migration coefficient, and penetration depth of chlorine ion, combined with each other is better than used separately. Microstructural images indicated the formation of a stable composition in the three-additive design and xanthan gum, Silica fume, and Nano-silica were evaluated to provide the desired viscosity, strength, and durability of self-compacting concrete, respectively.

Reinforced concrete structures on the shores of the Persian Gulf experience a severe corrosion environment, and in the case of the structures that are in tidal conditions or some of their members are submerged in the sea, such as piers and ports, this problem is more acute due to the penetration of chloride ions. To increase the efficient life of concrete structures in the Persian Gulf, the use of self-compacting concrete along with cement substitutes has been suggested by researchers. In this paper, two powdered materials, slag and micro-silica, have been selected to replace part of the cement content in concrete. The durability test in submerged and tidal conditions has been performed on the specimens. Based on the results of experiments on 216 concrete specimens, the use of the proposed concrete on average increases the compressive strength by 22%, electrical resistance by 50% and decreases the permeability of volumetric water absorption by 12% and capillary water absorption by 30% in tidal conditions.

Concrete is widely used as a building material all over the world, but it is not considered an environmentally friendly material due to environmental degradation and the use of large amounts of natural resources. Therefore, it is necessary to provide a solution to reduce the effects of recycled aggregate pollution. In the present study, the effect of the strength of recycled aggregates on the rheological and mechanical properties of self-compacting concrete is investigated experimentally and numerically. Hence, two types of recycled aggregates with known and unknown strength origins are utilized for the studied samples. The experimental design in this research is accomplished by the Box Behnken method, which is one of the response surface methods. Input variables in mixtures, including micro silica in the range of 5-15% as a percentage substitute for the weight of cement and recycled coarse and fine grains in the range of 0-50% for both series of recycled materials, are replaced by natural materials. The studied responses are slump flow, funnel V, compressive and tensile strengths. The results indicate that the increase in recycled aggregates reduces the rheological and mechanical properties of the mixtures, while micro silica effectively improves the mechanical properties. In addition, the sensitivity of most of the studied responses is related to recycled fine particles. It should be noted that recycled materials of known strengths are shown better results than recycled materials of unknown strengths. Some mathematical relationships are also provided using analysis of variance for all responses to predict the rheological and mechanical properties of mixtures.

Accuracy in pouring concrete, concrete density and also the appearance of concrete as an exposed material is always a concern of designers and executors of construction projects. Self-compacting concrete with weight compression properties can always be one of the options available to designers. The variety of materials used in self-compacting concrete, including recycled materials, with pozzolanic properties and fillers to achieve rheological and mechanical goals, is one of the challenges that designers face. Also, accurate determination of mixing ratios and their results is very time consuming and costly. Using soft computing and neural networks inspired by the biological structure of the human brain, computer science seeks to increase speed, accuracy, and cost reduction to prevent malicious experiments. In this study, with the help of ANN and LSTM networks, using 320 samples of self-compacting concrete with dispersion and comprehensiveness of common materials used in it by various researchers, tried to predict 28-day compressive strength of self-compacting concrete, evaluate performance and increase accuracy by 6 different training algorithms. In total, about 200 repetitions of training were performed on 320 samples of self-compacting concrete with 14 characteristics, which by comparing the best results obtained from training algorithms, best performance with root mean square error of 4.97 and correlation coefficient of 0.9484 in the test, for the network. ANN was reported with the Beyesian Regularization training algorithm, which indicates the high accuracy of that network.