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1
Bergmann, Ana Claudia, Gustavo Savaris, Carlos Eduardo Tino Balestra e Lucia Bressiani. "CONCRETOS AUTOADENSÁVEIS E CONVENCIONAIS: ANÁLISE DAS PROPRIEDADES EM ESTADO FRESCO E ENDURECIDO". REEC - Revista Eletrônica de Engenharia Civil 15, n. 2 (12 maggio 2020): 167–78. http://dx.doi.org/10.5216/reec.v15i2.50695.
Testo completoAbstract (sommario):
RESUMO: Os concretos autoadensáveis destacam-se por suas características essenciais: capacidade de preenchimento de fôrmas, habilidade passante e resistência à segregação, permitindo assim o aumento da qualidade de peças estruturais de concreto, assim como a otimização de sua execução. Contudo, para obtenção de suas características essenciais, um fator é imprescindível trata da utilização de materiais finos, com o objetivo de controlar os efeitos negativos de segregação e exsudação à que o concreto fresco é suscetível a apresentar. Neste contexto, o presente trabalho tem por objetivo comparar as propriedades no estado fresco e endurecido de um concreto autoadensável, utilizando cinza volante como material fino, com um concreto convencional, produzidos com materiais disponíveis na região de Toledo-PR. Os resultados demonstraram que o concreto autoadensável apresentou melhor desempenho quanto às propriedades mecânicas em relação ao concreto convencional. As imagens obtidas por meio da microscopia eletrônica de varredura corroboraram para sustentar as afirmativas acerca da melhora nas propriedades mecânicas do concreto autoadensável, uma vez que foi evidenciada uma menor quantidade de vazios graças à atividade pozolânica da cinza volante. Neste sentido, este trabalho contribui para a difusão do concreto autoadensável e seu uso em construções usuais, resultando em estruturas de concreto duráveis e confiáveis, reduzindo a necessidade de manutenções.
ABSTRACT: The self-consolidating concretes stand out for their essential characteristics: flowability, passing ability and segregation resistance, allowing the increase of the structural elements quality, as well as the optimization of their production. However, in order to obtain its essential characteristics, the main factor is the use of fines, in order to control the negative effects of segregation and bleeding to which fresh concrete is susceptible. In this context, the aim of this paper is to compare the properties, in the fresh and hardened states, of self-consolidating concretes, using fly ash as fine material with the properties of a conventional concrete, produced with materials available in the Toledo-PR, Brazil. The results showed that the self-consolidating concrete presented better performance in relation to the mechanical properties compared to conventional concrete. Using scanning electronic microscopy the affirmations about the improvement in the mechanical properties of self-consolidating concrete were proven, since a smaller amount of voids was evidenced due to the pozzolanic activity of fly ash. In this sense, this work contributes to the diffusion of self-consolidating concrete in the literature and its use in usual constructions, resulting in durable and reliable concrete structures, reducing the maintenance works.
2
Žiogas, Vigantas Antanas, Svajūnas Juočiūnas e Giedrius Žiogas. "HYDROTECHNICAL CONCRETE WITH LOCAL AGGREGATES AND THEM USING FOR MONOLITHIC STRUCTURES". Engineering Structures and Technologies 1, n. 2 (30 giugno 2009): 102–10. http://dx.doi.org/10.3846/skt.2009.13.
Testo completoAbstract (sommario):
The article discusses the technological peculiarities of construction monolithic hydrotechnical concrete structures, use of local aggregates for producing special concretes, methods of determining water impermeability of concretes as well as the evaluation of the methods mentioned above. The article presents the requirements for the granulometric composition of aggregate mixes for the production of flowing concrete mixes used for the construction of monolithic hydrotechnical structures. The possibilities and expediency of using local crushed gravel with increased amounts of weak particles for hydrotechnical structures are discussed. The mass loss of weak particles is slight compared with the whole mass of aggregates, and the total mass loss of crushed gravel it occurs due to micro-cracks present in particles. The frost resistance mark of crushed gravel and its suitability for hydrotechnical concretes should be determined by evaluating the amount of weak particles and their frost resistance. The article discusses concrete impermeability data received by means of two methods (according to LSTST 1974:2005 and LSTST EN 12390–8 requirements). Theoretical water penetration depths have been calculated. Determination of water impermeability according to LSTST 1974:2005 is recommended for C25/30 and lower compressive strength class concretes with W≤8. The LSTST EN 12390–8 water impermeability determina-tion method is recommended for C25/30 and higher compressive strength class concretes whose water impermea-bility mark is W≥8. For the construction of certain hydrotechnical structures water impermeable concretes whose water penetration depth should not exceed 20mm are recommended for use instead of the W6 and W8 concretes. Technological peculiarities and potential technological-organizational solutions for high walls of a water treatment plant have been discussed. The analysis of potential concreting methods of the reservoir’s high walls has been made as well as that of the key parameters of the continuous concreting process and their interaction. Dependences for the estimation of continuous concreting volumes and permissible concreted segment lengths have been proposed by evaluating the beginning of the intensive formation structure of concrete, number of layers in the height of the concreted wall and concreting intensity.
3
Meesaraganda, Lakshmi Vara Prasad, Endow Ayar Mazumder e L. Ramaprasad Reddy. "Durability Studies of Conventional Cement Concrete and Geopolymer Concrete". Materials Science Forum 1116 (5 marzo 2024): 97–103. http://dx.doi.org/10.4028/p-o39dkm.
Testo completoAbstract (sommario):
The service life of structural members is significantly impacted by the durability of the concrete and that they are made of. The embedded reinforcing steel in durable concrete is protected from corrosion, and the possibility of concrete spalling in the concrete as a result of chemical attack is reduced. This study investigates the effectiveness of geopolymer concretes prepared using fly ash or a mixture of fly ash and slag (SLG). The performance of OPC concrete is likewise evaluated for comparing the durability of geopolymer concretes. This is done in order to compare the two types of concrete. All of the prepared specimens were submerged in theee types of distinct solutions up to 9 months. Four different types of solutions are (i) sodium chloride with 5% concentration, (ii) sodium sulphate 5% concentration, (iii) combination of magnesium sulphate with sodium sulphate with 5% concentration both, and sulphuric acid 3% concentration. The variation in properties were evaluated throughout the duration of the exposure period. According to the findings, it has been demonstrated that Na2SO4 (sodium sulphate) has the most significant effect on the geopolymer concretes, whereas sulphuric acid has the greatest potential to break down OPC concrete. With the effect of sulfuric acid, the strength reduction was 26.57% for OPC concrete and where as for flyash & SLG concretes it is 10.87% & 7.26% respectively. According to the findings, the durability performance of geopolymer concrete is, in general, better to that of cement concrete.
4
Pani, Luisa, Lorena Francesconi, James Rombi, Fausto Mistretta, Mauro Sassu e Flavio Stochino. "Effect of Parent Concrete on the Performance of Recycled Aggregate Concrete". Sustainability 12, n. 22 (12 novembre 2020): 9399. http://dx.doi.org/10.3390/su12229399.
Testo completoAbstract (sommario):
Recycling concrete construction waste is a promising way towards sustainable construction. Indeed, replacing natural aggregates with recycled aggregates obtained from concrete waste lowers the environmental impact of concrete constructions and improves natural resource conservation. This paper reports on an experimental study on mechanical and durability properties of concretes casted with recycled aggregates obtained from two different parent concretes, belonging to two structural elements of the old Cagliari stadium. The effects of parent concretes on coarse recycled aggregates and on new structural concretes produced with different replacement percentages of these recycled aggregates are investigated. Mechanical properties (compressive strength, modulus of elasticity, and splitting tensile strength) and durability properties (water absorption, freeze thaw, and chloride penetration resistance) are experimentally evaluated and analyzed as fundamental features to assess structural concrete behavior. The results show that the mechanical performance of recycled concrete is not related to the parent concrete characteristics. Furthermore, the resistance to pressured water penetration is not reduced by the presence of recycled aggregates, and instead, it happens for the chloride penetration resistance. The resistance to frost–thawing seems not related to the recycled aggregates replacement percentage, while an influence of the parent concrete has been assessed.
5
Kaitukov, Batraz, Mihail Stepanov e Pavel Kapyrin. "The choice of concrete mixers for the concrete preparation". MATEC Web of Conferences 178 (2018): 06016. http://dx.doi.org/10.1051/matecconf/201817806016.
Testo completoAbstract (sommario):
The production of commodity concretes is a large segment of the construction industry and a testing base for concrete mixers. The choice of high-reliable concrete mixers for high-quality production of various brands of concrete is topical. When choosing concrete mixers, the most important is condition for improving the quality of mixing. Solving this problem, the analysis of various parameters and structural designs of concrete mixers is carried out. Dependencies are established that show the properties of concrete of various brands with their composition and technical characteristics of concrete mixers. Variants of rational selection of concrete mixers that provide high uniformity of concretes and a combination of the components of the mixture are proposed. The capacities of various concrete mixers for the preparation of commodity concrete are determined and the optimum rotational speeds of the working elements of concrete mixers are determined. Reasonable speeds of movement of working elements are revealed and dependences of the Reynolds number on frequency of rotation of a drum between capacity and diameter of a drum of a concrete mixer are established. This method of selecting rational concrete mixers allows reducing operating costs and improving the quality of concrete.
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Stehlík, Michal. "TESTING THE STRENGTH OF CONCRETE MADE FROM RAW AND DISPERSION-TREATED CONCRETE RECYCLATE BY ADDITION OF ADDITIVES AND ADMIXTURES". Journal of Civil Engineering and Management 19, n. 1 (16 gennaio 2013): 107–12. http://dx.doi.org/10.3846/13923730.2012.734853.
Testo completoAbstract (sommario):
Today, concrete comprises more than 65% of the total volume of building constructions. As it undergoes degradation and buildings require refurbishment, the volume of concrete increases at disposal sites. Due to a lack of non-renewable resources and due to high prices of energies, the reuse of concrete seems to be more than desirable. It is common knowledge that in concretes made from recycled concrete, the strengths of the original concretes can hardly be achieved. The addition of dispersion additives and mineral admixtures into the freshly mixed concrete can contribute to improving the mechanical properties of concretes made from recycled concrete. Potential composite action of the recyclate, mineral admixtures and dispersion additives in increasing the compressive strength of concretes made from recycled concrete remains to be a question.
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Santor, M. S., A. L. G. Gastaldini, C. Crauss, G. T. Dos Santos e F. C. Rossini. "Influência de materiais de proteção na resistividade elétrica do concreto". Revista ALCONPAT 2, n. 1 (30 gennaio 2012): 46–56. http://dx.doi.org/10.21041/ra.v2i1.26.
Testo completoAbstract (sommario):
RESUMOA durabilidade das estruturas de concreto armado é resultado da ação protetora do concreto sobre a armadura. Quando a passivação do aço deixa de existir a estrutura torna-se vulnerável ao fenômeno da corrosão, cuja propagação, após iniciada é essencialmente controlada pela resistividade elétrica do concreto. O objetivo deste trabalho foi avaliar a alteração na resistividade elétrica de concretos produzidos com diferentes tipos de cimento, CP II F, CP IV e CP V, submetidos a tratamento superficial com produto obturador dos poros e argamassa polimérica. Para efeito de análise os resultados foram comparados com os mesmos concretos sem aplicação do produto. Esses tratamentos foram realizados em concretos confeccionados com resistências à compressão na idade de 28 dias de 21,6MPa, 26,6 MPa e 31,6 MPa. Para todos os tipos de cimento utilizados e níveis de resistência adotados o tratamento superficial com argamassa polimérica resultou em maiores valores de resistividade elétrica.Palavras chave: Concreto; durabilidade; material de proteção superficial; resistividade elétrica.ABSTRACTThe durability of concrete structures is a result of the protective action of concrete on the reinforcement. When there is no passivation of steel, the structure becomes vulnerable to corrosion, and once corrosion starts its propagation is essentially controlled by the electrical resistivity of concrete. The objective of this study was to evaluate the change in electrical resistivity of concretes produced with different types of cement: CP II F, CP IV and CP V that were surface-treated with pore filler and polymer mortar. For analysis purposes, the results were compared with those of the blanks that were not subjected to surface treatment. These treatments were performed in concretes with the following compressive strengths at the age of 28 days: 21.6 MPa, 26.6 MPa and 31.6 MPa. For all types of cement used and strengths adopted, surface treatment with polymer mortar led to higher electrical resistivity values.Key words: Concrete; durability; surface protection material; electrical resistivity.
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Wang, Chong, Chang Hui Yang, Chao Jun Wan e Yan Feng Tian. "Comparison of Fluidity between Metakaolin and Silica Fume Concretes". Key Engineering Materials 477 (aprile 2011): 95–101. http://dx.doi.org/10.4028/www.scientific.net/kem.477.95.
Testo completoAbstract (sommario):
Aiming at preparing the high performance concrete with metakaolin (MK) replacing silica fume (SF), comparison of fluidity between MK concrete and SF concrete was investigated in this paper. Slump, spread, and slump loss with time of fresh concrete under the condition of superplasticizer adding were tested, which containing with 5 to 15 wt. % replacement of MK, SF, combination of MK and ground granulated blastfurnace slag (GGBS), or combination of SF and GGBS, respectively. The mechanism for exploring fluidity difference of MK concrete and SF concrete were researched by measuring ζ potential and superplasticizer adsorption. The results indicate that concretes containing with 5 to 15 % MK were provided with better workability than concretes with SF. Fluidity of MK concretes incorporating with 5 to 15 % GGBS was better than that of SF concretes. Incorporating with 5 to 15% replacement, MK-cement-superplasticizer system present higher ζ potential, and lower superplasticizer adsorption than SF-cement-superplasticizer, which is an answer to why MK concrete has better fluidity than SF concrete. Physical filling effect of mineral additives is also is helpful to concrete fluidity.
9
Dobshits, Lev M. "Physical and mathematical modeling of frost resistance for cement concretes". Structural Mechanics of Engineering Constructions and Buildings 19, n. 3 (30 settembre 2023): 313–21. http://dx.doi.org/10.22363/1815-5235-2023-19-3-313-321.
Testo completoAbstract (sommario):
The key factor of engineering structures made of concrete and reinforced concrete is insufficient frost resistance of concretes. It is important to identify the causes and prevent concrete damage caused by frost. The research provides the basic points of the developed physical and mathematical theory of cement concretes frost resistance. Under consideration are the processes occurring during cyclic freezing and thawing of concrete in a water-saturated state. The results of the performed theoretical and experimental studies are presented. The criterion of concrete frost resistance, which estimates the pore structure of concrete, was derived on the basis of the obtained results. The suggested criterion has a close correlative relation with the frost resistance of concrete. Using this interrelation, the method was proposed for accelerated determination of actual frost resistance of concrete, as well as the method of selection concretes' compositions for a specified design frost resistance of concretes. The methods of accelerated determination of concrete frost resistance, as well as ways to increase it, are described. The developed physical and mathematical model was used to carry out computational modeling for freezing of an extended concrete structure. This made it possible to determine the changes in humidity, temperature, and pressure in concrete during cyclic freezing and thawing at different distances from the surface of its freezing and also draw graphs of changes in these parameters. The recommendations on assignment of concrete design grades by frost resistance for various elements of concrete and reinforced concrete structures are given.
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Flohr, Alexander, e Andrea Osburg. "Design and Development of Concretes for Special Rehabilitation Tasks". MATEC Web of Conferences 199 (2018): 07001. http://dx.doi.org/10.1051/matecconf/201819907001.
Testo completoAbstract (sommario):
The requirements for concrete restoration are not only aspects of retrofitting or restoration of bearing capacity but also aspects of preservation of historic structures, such as industrial monuments or civil engineering structures and buildings of the 1960s [1]. Thereby the facsimile replication of the concrete surface is a particular challenge. For the manufacture of delicate and complex structures with restricted accessibility self-compacting concrete (SCC) is well suited [2]. A modification with polymers normally ensures the durability of repair mortars or concretes (PCC) [3]. The combination of PCC and SCC to the Polymer-modified Self-Compacting Concrete (PSCC) for the restoration of historic concrete constructions is the logical consequence, to combine the advantages of both materials and is therefore an interesting alternative to well established materials and methods. Historic concrete constructions are often manufactured of concretes with very stiff consistencies, the so called tamped concretes. So there is a need to develop materials and methods for the rehabilitation of structures made of tamped concrete. For this reason, first investigations have been performed to the recipe development and optimization of its composition, but also properties, furthermore to the design possibilities and how polymers influence the concrete properties. In Germany between 1920 and 1970 industrial buildings and hydraulic structures have been built with concretes, where the content of Portland cement clinker was nearly complete substituted by latent hydraulic materials. The binders of those concretes contain large quantities of blast furnace slag and calcium sulphate and are called super-sulphated cement (SSC). Because of the high sulphate content, the compatibility of concrete structure with SSC is not given to concretes or mortars with other cements. If there is an adequate range of moisture, harmful new formations of phases will occur in the contact zone between SSC-concrete and the other concrete. In the field of rehabilitation PCC are well established. These are polymer-modified mortars or concretes with Portland cement, which are not suitable for the rehabilitation of structures of SSC-concrete. An alternative is the polymer-modification of SSC-concretes with polymers.
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Biel, Timothy D., e Hosin Lee. "Magnesium Oxychloride Cement Concrete with Recycled Tire Rubber". Transportation Research Record: Journal of the Transportation Research Board 1561, n. 1 (gennaio 1996): 6–12. http://dx.doi.org/10.1177/0361198196156100102.
Testo completoAbstract (sommario):
Either portland cement or magnesium oxychloride cement was used as binders for concretes that incorporated fine rubber aggregate, ranging from 0 to 25 percent by volume. The concretes were tested for their compressive and split tensile strengths to determine whether the use of a magnesium oxychloride cement along with recycled tire rubbers would improve concrete properties. Failure of the concrete around the rubber particles was attributed to tension failure, leading to weak shear failure of the concrete matrix. Both portland and magnesium oxychloride cement concretes lost 90 percent of their compressive strength with 25 percent rubber by volume. The portland cement concrete retained 20 percent of its tensile strength, and the magnesium oxychloride cement concrete retained 35 percent of its tensile strength. Both compressive and tensile strengths of magnesium oxychloride cement rubber concrete were significantly higher than rubberized portland cement rubber concrete.
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Sanal, Irem. "A Review on Reduced Environmental Impacts of Alternative Green Concrete Productions". International Journal of Public and Private Perspectives on Healthcare, Culture, and the Environment 1, n. 2 (luglio 2017): 55–68. http://dx.doi.org/10.4018/ijppphce.2017070104.
Testo completoAbstract (sommario):
Concrete is being recognized for its environmental benefits in support of sustainable development. In response to growing environmental and economic forces, regulatories, engineers and owners are seeking efficient concrete solutions that conserve non-renewable resources. Global demands for regulating concrete waste arise from the growth of these environmental and economic issues. Thus, the concept of “green concrete” as an eco-friendly alternative to conventional concrete has been emerging. This publication seeks to demonstrate how concrete contributes to future generations' sustainable development, and will be of interest to policy makers, contractors and clients, as well as others involved with the design, construction or operation of buildings and infrastructure. The main objective of this study is to identify key sources contributing to CO2 emissions from concrete and compare 1) traditional concretes with green concretes, 2) concretes produced with blended cements, and 3) fly ash used as replacement of cement, in order to diminish the environmental impact of the concrete production.
13
Marczewska, Julia, e Wojciech Piasta. "The impact of air content on the durability of concrete under combined sulphate and freezethaw attack". MATEC Web of Conferences 163 (2018): 05002. http://dx.doi.org/10.1051/matecconf/201816305002.
Testo completoAbstract (sommario):
The aim of the study was to determine the optimal air content in concretes subjected a combination of exposure conditions. Five series of concretes with different air contents were tested. The article reports the experimental results of the combined sulphate expansion and freeze-thaw attack in ordinary Portland cement concrete. Some of the concrete samples were immersed in a 5% sodium sulphate solution for nine months, and then frozen in air and thawed in water. The resistance of concrete to plain freezing and thawing was also tested. In order to compare the degree of concrete damage in both environments, long-term linear deformations (expansion) and compressive strength of concretes were investigated. To explain the complex damaging process the air-void structure in concretes was investigated. The changes in concrete microstructure after storing in sodium sulphate solution were observed under the scanning electron microscope (SEM). The prior sulphate attack significantly accelerated the deterioration of non-air-entrained concrete and air-entrained concrete with low content of air voids. Optimal air entrainment will protect concrete from the harmful effects of the interaction of sulphate attack and freezethaw damage.
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Noor Azline, M. N., Farah Nora Aznieta Abd Aziz e Arafa Suleiman Juma. "Effect of Ground Granulated Blast Furnace Slag on Compressive Strength of POFA Blended Concrete". Applied Mechanics and Materials 802 (ottobre 2015): 142–48. http://dx.doi.org/10.4028/www.scientific.net/amm.802.142.
Testo completoAbstract (sommario):
The article reports a laboratory experimental programme that investigated effect of ground granulated blast furnace (GGBS) on compressive strength of POFA ternary concrete. Compressive strength tests were performed at a range of cements combinations, including 100%PC, two POFA levels for binary concrete, 35% and 45%, and 15%GGBS inclusion for POFA ternary concrete. The compressive strength results were examined in comparison to PC only and equivalent POFA binary concretes for up to 28 days. Results show that the reduction in compressive strength is greater with the higher cement replacement level for all concretes particularly for POFA binary concretes. However, 15%GGBS in POFA blended concrete has a comparable compressive strength compared to PC concrete at both, 35% and 45%, cement replacement levels except for ternary concrete at 0.65 w/c. In addition, the compressive strength of ternary concrete is slightly higher compared to binary concrete for all concrete combinations. Although there is no significant noticeable influence on strength development, the presence of GGBS did not adverse the strength development of POFA blended concrete. Thus, it can be concluded that GGBS compensates the adverse effect of POFA at early strength development.
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Li, Zhu Guo. "Development and Application of Eco-Friendly Concrete". Advanced Materials Research 250-253 (maggio 2011): 3827–36. http://dx.doi.org/10.4028/www.scientific.net/amr.250-253.3827.
Testo completoAbstract (sommario):
Concrete is the most popular construction material. In its lifetime, natural resources such as limestone and aggregate are consumed. Meanwhile, emission of air pollutants and discharge of waste concrete in large quantities are of great concern. However, in recent years, high performance concrete and new types of concretes have been developed to decrease the environmental burden in its lifespan or in production phase, to utilize a substantial amount of recycled industrial waste, and to improve local environment. These eco-friendly concretes are classified into environmental protection type such as high performance concrete and recycled concrete, and environmental creation type such as porous concrete used for planting and air-purifying concrete with TiO2coating. This paper introduces the concept of eco-friendly concrete and summarizes present technologies and application.
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Grinys, Audrius, Danutė Vaičiukynienė, Algirdas Augonis, Henrikas Sivilevičius e Rėda Bistrickait. "EFFECT OF MILLED ELECTRICAL CABLE WASTE ON MECHANICAL PROPERTIES OF CONCRETE". Journal of Civil Engineering and Management 21, n. 3 (26 febbraio 2015): 300–307. http://dx.doi.org/10.3846/13923730.2015.1005019.
Testo completoAbstract (sommario):
The article focuses on investigation of mechanical and fracture properties of concrete containing electrical cable waste as well as some microstructural features of such concrete. Added to concrete, electrical cable waste reduces the overall concrete bulk density. Compressive, flexural, tensile splitting strengths and elastic modulus decreased when electrical cable waste was admixed to conventional and polymer modified concretes. The best mechanical properties of concrete samples containing electrical cable waste were identified in polymer modified concrete containing 5% of electrical cable waste. Electrical cable waste particles increase the deformability of polymer modified concretes and have almost no influence on normal concrete. Consequently, the optimal amount of electrical cable waste particles can provide concrete with desirable strength that is required for different applications.
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Balabanov, Vadim, Victor Baryshok e Nikita Epishkin. "Concrete based on sulfur binder being modified with inorganic additives". MATEC Web of Conferences 212 (2018): 01013. http://dx.doi.org/10.1051/matecconf/201821201013.
Testo completoAbstract (sommario):
The sharply continental climate of the Irkutsk region is characterized by wide temperature intervals throughout the year. The repeated cyclicity of freezing and thawing of building materials in the water-saturated state influences the change in technical characteristics and the durability of concrete products and structures. The concrete products’ features in such climatic conditions create the need for the production of concretes with improved indicators of physical and mechanical properties. The effect of modifying additives on the technological characteristics of sulfur concrete is established. The effect of all elements of sulfur concrete on its strength and frost resistance. The composition of sulfuric concrete is obtained, which meets all the requirements and also has high strength and increased frost resistance. Formulations with a certain ratio of structural sulfuric concrete mixtures were developed. As a result of the use of technical sulfur in the composition of concrete products, the problem of utilizing annually accumulating reserves of technical sulfur is partially solved. The strength properties of sulfuric concretes easily compete with high-quality brands of concrete, special types of concretes that have in their composition additives.
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Ziane, Sami, Mohammed-Rissel Khelifa e Samy Mezhoud. "A Study of the Durability of Concrete Reinforced with Hemp Fibers Exposed to External Sulfatic Attack". Civil and Environmental Engineering Reports 30, n. 2 (1 giugno 2020): 158–84. http://dx.doi.org/10.2478/ceer-2020-0025.
Testo completoAbstract (sommario):
AbstractThe purpose of this paper is to study the durability of concrete reinforced with hemp fibers in the face of external Sulfatic attack. For this purpose, five types of concrete were formulated; three types of concrete reinforced with hemp fibers (HC-0.25, HC-0.5, and HC-1) at 0.25%, 0.5%, and 1 % of hemp fibers in volume, respectively. And two control concretes, being ordinary concrete (OC) and polypropylene fiber reinforced concrete (PC). To assess the sulfatic attacks, the described concrete types underwent two aging protocols: 1) a complete immersion in 12.5 % Sodium Sulfate (Na2SO4) solution, and 2) an accelerated aging protocol consisting of immersion/drying in the same sulfate solution at a temperature of 60°C. The results show that concrete reinforced with 0.25 % of hemp fibers is the optimal amount compared to control concretes in terms of physico-mechanical performance and durability under sulfate attack. This number of fibers could enable the production of green and durable structural concretes based on untreated hemp fibers.
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Hoffmann Sampaio, Carlos, Bogdan G. Cazacliu, Weslei Monteiro Ambrós, Márcio André Kronbauer, Rejane MC Tubino, Denise CC Dal Molin, Josep Oliva, Gérson L. Miltzarek, Regis P. Waskow e Viviane LG dos Santos. "Demolished concretes recycling by the use of pneumatic jigs". Waste Management & Research: The Journal for a Sustainable Circular Economy 38, n. 4 (12 febbraio 2020): 392–99. http://dx.doi.org/10.1177/0734242x20902835.
Testo completoAbstract (sommario):
Large quantities of construction and demolition waste is generated annually around the world. Part of this material is processed in recycling plants. After removing metals, fines and lights, the construction and demolition waste is crushed and sized and can be used as aggregates for low resistance concrete, for road sub-base, city landfill and other low value-added applications. For their use as coarse aggregate in structural concretes, construction and demolition waste must exhibit high densities and regularity of the material. This material usually is presented in demolished concretes. About 20% of the particles from demolished concretes can be used as coarse aggregates substituting part of natural aggregates in structural concretes. This article presents studies of demolished concretes recycling by the use of a pneumatic jig. All jigging tests were carried out with three different concretes produced in three strength classes: C16/20, ordinary concrete; C50/60, high strength concrete; and C70/85, very high strength concrete. Based on density distribution of the three concretes, there are reasonable masses with densities over 2.7 g cm−3, particle density considered appropriate to the used as coarse aggregate for structural concretes. The concretes present different mass recoveries of the denser particles (different liberation). Coarse aggregates can be recovered with reasonable masses by the use of air jigs: About 65% for high strength concretes and about 75% for the low strength concrete. The jigging concentration efficiency depends on the concrete liberation, density and size distribution.
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Mailyan, Levon R., Sergey A. Stel’makh, Evgenii M. Shcherban’, Alexander K. Khalyushev, Alla S. Smolyanichenko, Alexander K. Sysoev, Ivan A. Parinov e Alexander V. Cherpakov. "Investigation of Integral and Differential Characteristics of Variatropic Structure Heavy Concretes by Ultrasonic Methods". Applied Sciences 11, n. 8 (16 aprile 2021): 3591. http://dx.doi.org/10.3390/app11083591.
Testo completoAbstract (sommario):
The article develops methods and methodology for experimental studies of centrifuged and vibro-centrifuged concrete products of annular cross-section. They assess the real variatropy of the structure and confirm the correctness of the accepted research. An original technique for experimental studies of the variatropy of the cross-sections of vibrated, centrifuged and vibro-centrifuged concretes is proposed to determine their integral (common) and differential (differing in layers) strength and strain characteristics and deformation diagrams. It has been proved that with vibro-centrifugation it becomes possible to obtain concretes with improved structure and higher characteristics compared with centrifugation and vibration techniques. Experimental studies of the differential characteristics of centrifuged and vibro-centrifuged concretes under compression and tension revealed that the outer layer of concrete had the best characteristics after centrifugation and vibro-centrifugation, and the inner layer had the worst ones. The three-layer model of the variatropic structure for centrifuged and vibro-centrifuged concrete has been experimentally confirmed. The concrete of the outer layers had the highest strength and modulus of elasticity and the least deformability; the concrete of the inner layers had the lowest strength and modulus of elasticity and the highest deformability; and the concrete of the middle layers had average characteristics. The deformation diagrams of centrifuged and vibro-centrifuged concretes were also differentiated by layers, confirming the variatropy of the structure of such concretes. The deformation diagrams for the outer concrete layer demonstrated the highest strength; the diagrams for the inner concrete layer showed the lowest strength; and the diagrams for the middle concrete layer corresponded to mean characteristics.
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Ekolu, Stephen O., Zaid Mohamed e Sean Kay. "Experimental Investigation and Yield Line Prediction for Ultimate Capacity of Recycled Aggregate Concrete Slabs". International Journal of Engineering Research in Africa 47 (marzo 2020): 31–44. http://dx.doi.org/10.4028/www.scientific.net/jera.47.31.
Testo completoAbstract (sommario):
The present investigation was conducted to evaluate the influence of recycled aggregates on structural behaviour of reinforced concrete (RC) slabs. Concrete mixtures of 0.6 and 0.4 water/cement ratios were used to produce normal strength concretes and high strength concretes, respectively. Various concrete mixtures were prepared by replacing 19 mm natural coarse aggregates with 0, 25, 50, 100% recycled coarse aggregate (RCA) then used to cast RC slabs of size 500 x 300 x 100 mm thick, and 100 mm cubes. The two-way concrete slabs were reinforced orthotropically with Y12 steel bars. Workability, compressive strength, and split tensile strength properties of concrete were measured, while the RC slabs were subjected to monotonic loading until failure. The experimental results obtained were compared with theoretical failure loads predicted using the yield line theory. It was found that the use of RCA in concrete generally leads to reduction of workability and concrete strength in proportion with the RCA content incorporated into the mixture. The yield line method gave a conservative and accurate theoretical prediction of the actual ultimate loads for control concretes, predicting 10% lower values, but it exhibited loss of prediction accuracy for RCA concretes of normal strengths basically overestimating their failure loads. Accordingly, it would be unsafe to employ the yield line method for design of RCA concrete slabs of normal strengths. Generally, the adverse effects of RCA on concrete properties and structural behaviour can be mitigated significantly by adjusting mixture designs to higher strengths or by employing high strength concretes
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Tolmachov, Sergii, Olena Belichenko e Sergii Pronin. "INCREASING FROST RESISTANCE OF ROAD CONCRETE BY APPLYING SECONDARY PROTECTION". Avtoshliakhovyk Ukrayiny 3, n. 271 (30 dicembre 2022): 32–36. http://dx.doi.org/10.33868/0365-8392-2022-3-271-32-36.
Testo completoAbstract (sommario):
The production of road cement-concrete mixtures, their transportation, laying and compaction usually occurs during periods of high positive temperatures and the presence of wind. When cement concretes harden under such conditions, moisture evaporates from them. This can lead to air shrinkage, which causes to the cracking and collapse of concrete. Therefore, to protect the hardening cement concrete from shrinkage and cracking, film-forming materials are applied to its surface. However, the practice of using road surfaces shows that such protection is not sufficient to ensure the durability of cement concretes. Therefore, to increase the resistance of concrete to aggressive environments, it is proposed to use secondary protection. Secondary protection of concrete consists in applying impregnating compounds to the surface of the pavement. The article presents the results of studies of the effect of impregnating compositions on water absorption and frost resistance of concrete of strength class B30 (C32/40). It is shown that the use of impregnating compositions improves the water resistance of concrete. However, such surface treatment does not lead to an increase the frost resistance of road concretes. It was found that some formulations increase the hardness of the concrete surface and do not reduce the resistance of concrete under the simultaneous action of negative temperatures and chloride salts. The article presents the results of studies of the effect of impregnating compositions on water absorption and frost resistance of concrete of strength class B30 (C32/40). It is shown that the use of impregnating compositions improves the water resistance of concrete. However, such surface treatment does not lead to an increase in frost resistance of road concretes. It has been found that some impregnating compositions increase the surface hardness of concrete. At the same time, they do not reduce the resistance of concrete under the simultaneous action of negative temperatures and chloride salts. At the same time, there are compositions, the use of which leads to peeling of the concrete surface when tested for frost resistance. Such peeling leads to destruction of the protective layer of concrete and can reduce the frost resistance of concrete. The reasons for the low efficiency of secondary protection of road concrete when using impregnating compositions are given. It is shown that such compositions should be used selectively for the protection of road concrete. It is indicated for which strength classes the impregnation is an effective means of protection. The use of impregnation for concretes of other strength classes leads to a decrease the resistance of aggressive environments. Keywords: frost resistance, secondary protection, impregnating compounds, concrete protective layer, water absorption.
23
Liu, Rui Cui, Fu Yi Jiang e Zi Quan Liu. "Research and Development Progress on Concrete Preparation with Seawater". Advanced Materials Research 450-451 (gennaio 2012): 34–37. http://dx.doi.org/10.4028/www.scientific.net/amr.450-451.34.
Testo completoAbstract (sommario):
This document outlined the development of concrete mixing water at first. And then it discussed some properties of concrete prepared with adding sea water and impacts of sea water on effectiveness of concrete. The article also tried to explain some reasons of these impacts. The author emphasized on analyzing the effect to the function of concrete by using seawater as mixing water and the reasons and separately elaborated on the different effects to plain concretes and reinforced concretes. At last, the article predicted the development trend of using seawater as concrete mixing water.
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Ristic, Nenad, Dusan Grdic, Jelena Bijeljic, Zoran Grdic e Gordana Toplicic-Curcic. "Properties of steel-polypropilene hybrid fibers reinforced concrete". Facta universitatis - series: Architecture and Civil Engineering 19, n. 3 (2021): 235–44. http://dx.doi.org/10.2298/fuace211202018r.
Testo completoAbstract (sommario):
This paper present the results of mechanical properties of hybrid reinforced concrete made by adding polypropylene and steel fibers into concrete mixture. For the testing purposes were used steel fibers with hooked ends and monofilament polypropylene fibers. The total of 5 batches of concrete were made: concrete with addition of steel fibers, polypropylene fibers and their combination in amount of 0,5 % of the concrete volume. The test results show that concretes made by adding of 0.4% steel and 0.1% polypropylene fibers have better performance compared to other concretes.
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Yee, Jia Jun, Sheh Ching Khong, JiaLing Che, Kong Fah Tee e Siew Choo Chin. "Sustainable Materials in Concrete Railway Sleepers: A Review of Current Developments and Future Prospects". Journal of Chemical Engineering and Industrial Biotechnology 10, n. 1 (20 giugno 2024): 1–16. http://dx.doi.org/10.15282/jceib.v10i1.10292.
Testo completoAbstract (sommario):
Concretes have been the favoured material to make concrete railway sleepers due to better accessibility and weather compared to their timber counterparts. Railway sleepers are crucial infrastructure and 5% of concrete sleepers fail prematurely. Sleeper failure could result in catastrophic railway accidents. Hence, improvement is needed in the concrete sleeper mixes. Previous literature has identified two methods of improving concrete strength in concrete mixes with wastes, through replacement of concrete constituents or the use of alkali-activated materials. Use of wastes as partial concrete material replacements reduces the volume of concrete materials while alkali-activated material forms a concrete-like compound that eliminates the use of cement. These methods improve the strength performance and sustainability aspects of the concrete. While many studies have been conducted on these two types of sustainable concrete, their application in concrete railway sleepers has not been investigated. Thus, this paper looks to review the two different types of sustainable concretes through some previous literature that has been conducted on its application in concrete railway sleepers as well as those that have yet to be studied. Ultimately, identifying the best sustainable materials for concrete railway sleepers.
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Liu, Guanzhi, Nikola Tošić e Albert de la Fuente. "Recycling of Macro-Synthetic Fiber-Reinforced Concrete and Properties of New Concretes with Recycled Aggregate and Recovered Fibers". Applied Sciences 13, n. 4 (4 febbraio 2023): 2029. http://dx.doi.org/10.3390/app13042029.
Testo completoAbstract (sommario):
The study aims to investigate the feasibility of using recycled aggregate (RA) and recovered fibers (RFs) obtained from recycling polypropylene fiber-reinforced concrete (PPFRC) in new concrete production. The mechanical properties were compared between a parent PPFRC, polypropylene fiber-reinforced recycled aggregate concrete (PPRAC), and recovered polypropylene fiber concrete (Re-PPRFC). All concretes were designed to have the same compressive strength and slump. The parent concrete was produced with 3 and 9 kg/m3 of polypropylene fibers. After recycling, the RA and RF were collected, and new concretes with RA and RF, PPRAC and Re-PPRFC, respectively, were produced with the same fiber content as the parent concretes. Both the compressive and flexural tensile strength (pre- and post-cracking) were characterized and the stress–strain relations derived accordingly. The results obtained for the different concretes were compared, proving that the RA and RF obtained by PPFRC recycling can benefit the design-oriented properties (workability and mechanical performance) of new concretes.
27
Feng, Xiao Xin, Xue Li Xi, Ji Wei Cai, Hong Jun Chai e Yu Zeng Song. "Investigation of Drying Shrinkage of Concrete Prepared with Iron Mine Tailings". Key Engineering Materials 477 (aprile 2011): 37–41. http://dx.doi.org/10.4028/www.scientific.net/kem.477.37.
Testo completoAbstract (sommario):
Concretes of C30 and C60 were prepared with iron mine tailings as fine aggregate and coarse aggregate and with natural sand and common crushed stone separately. The drying shrinkage of concretes cured under the natural condition in the laboratory was tested. The results showed that whether C30 or C60 the drying shrinkage of concrete prepared with iron mine tailings was a little smaller than that of concrete with natural sand and common crushed stone. It was also found that whether the concrete with iron mine tailings or the concrete with natural sand and common crushed stone the drying shrinkage of C60 concrete was larger than that of C30 concrete.
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Shaikh, Faiz. "Mechanical and Durability Properties of Green Star Concretes". Buildings 8, n. 8 (17 agosto 2018): 111. http://dx.doi.org/10.3390/buildings8080111.
Testo completoAbstract (sommario):
This paper presents mechanical and durability properties of green star concretes. Four series of concretes are considered. The first series is control concrete containing 100% ordinary Portland cement, 100% natural aggregates and fresh water. The other three series of concretes are green star concretes according to Green Building Council Australia (GBCA), which contain blast furnace slag, recycled coarse aggregates and concrete wash water. In all above concretes compressive strength, indirect tensile strength, elastic modulus, water absorption, sorptivity and chloride permeability are measured at 7 and 28 days. Results show that mechanical properties of green star concretes are lower than the control concrete at both ages with significant improvement at 28 days. Similar results are also observed in water absorption, sorptivity and chloride permeability where all measured durability properties are lower in green star concretes compared to control concrete except the higher water absorption in some green star concretes.
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Jin, Hu. "Late-Age Properties of Concrete with Different Binders Cured under 45°C at Early Ages". Advances in Materials Science and Engineering 2017 (2017): 1–13. http://dx.doi.org/10.1155/2017/8425718.
Testo completoAbstract (sommario):
It is commonly accepted that high curing temperature (near 60°C or above) results in reduced mechanical properties and durability of concrete compared to normal curing temperature. The internal temperature of concrete structures at early ages is not so high as 60°C in many circumstances. In this paper, concretes were cured at 45°C at early ages and their late-age properties were studied. The concrete cured at 20°C was employed as the reference sample. Four different concretes were used: plain cement concrete, concrete containing fly ash, concrete containing ground granulate blast furnace slag (GGBS), and concrete containing silica fume. The results show that, for each concrete, high-temperature curing after precuring does not have any adverse effect on the nonevaporable water content, compressive strength, permeability to chloride ions, and the connected porosity of concrete at late ages compared with standard curing. Additionally, high-temperature curing improves the late-age properties of concrete containing fly ash and GGBS.
30
Wang, Hai Long, Xiao Yan Sun, Qi Wen Peng e Feng Xue. "Durability and Mechanical Behaviors of Steel Slag Powder Concrete". Applied Mechanics and Materials 438-439 (ottobre 2013): 58–62. http://dx.doi.org/10.4028/www.scientific.net/amm.438-439.58.
Testo completoAbstract (sommario):
The mechanical behaviors and durability of concrete containing steel slag powder (SSP), silica fume (SF) and fly ash (FA) were presented in this study. The fresh concrete properties, compressive strength, split tensile strength, elastic modulus, stress-stain curve, chloride permeability as well as carbonation of concretes mixed with different SSP contents or concretes containing compound mineral admixture were tested. The experimental results reveal that the mechanical behaviors and durability of concrete with 10% SSP replacing cement are both improved than that of the reference concrete. Mechanical behaviors and durability of concrete with 20% SSP replacing cement are similar to the reference concrete. Concrete with compound mineral admixture of SSP and SF obtain the highest enhancement in both strength and chloride resistance.
31
Nguyen, Chanh Van. "RATIONAL PRODUCTION AND TESTING METHOD THROUGH USING SELF COMPACTING CONCRETE". Science and Technology Development Journal 12, n. 18 (15 dicembre 2009): 52–58. http://dx.doi.org/10.32508/stdj.v12i18.2383.
Testo completoAbstract (sommario):
The development of modern concretes to avoid vibration need. These are very fluid concretes called self compacting concrete(SCC). The result from the work show that it is possible to produce a self compacting concrete. Study of the influence of materials on the rheological properties of concrete. Definition of a mix design proceess of SCC. Development of tests for laboratory and constraction site. Promote the development of a more rational concrete production method.
32
Savytskyi, Mykola, Kostyantyn Sukhyy, Oleksandr Savytskyi, Maryna Babenko e Tetyana Shevchenko. "Carbon materials for electrically conductive concrete". E3S Web of Conferences 534 (2024): 01019. http://dx.doi.org/10.1051/e3sconf/202453401019.
Testo completoAbstract (sommario):
In recent decades, the direction of building materials science related to the creation of Smart Concretes has been rapidly developing. Smart Concretes, in addition to the functions of a structural material, also perform other functions that are related to their new properties. Among the large number of Smart Concretes, it is necessary to highlight Electrically Conductive Smart Concrete. This type of concrete is obtained by adding conductive fillers to the concrete mixture. Among them, carbon materials are the most promising in terms of their properties. Despite the large number of conducted studies of conductive fillers and conductive concrete, there is still no generalization and systematization of them. In addition, there are no standards for testing the conductive properties of both fillers and concretes. Therefore, the authors aimed to systematize data on Electrically Conductive Smart Concrete, as well as electrically conductive carbon fillers. A method for testing the electrical conductivity of Carbon Nanomaterials (CNMs) as fillers for Electrically Conductive Concrete is proposed. Approbation of the proposed method was carried out by determining the electrotechnical indicators of carbon fillers, such as coke breeze and carbon black.
33
Feng, Jin Cai, Ping Hua Zhu e Qun Xia. "Mechanical Behaviors of Structural Concrete Using Recycled Aggregates from Repeatedly Recycling Waste Concrete". Advanced Materials Research 450-451 (gennaio 2012): 1379–82. http://dx.doi.org/10.4028/www.scientific.net/amr.450-451.1379.
Testo completoAbstract (sommario):
This paper reports an expermiental study on mechanical behaviors of structural concrete using recycled aggregates from repeatedly recycling waste concrete. Five series of natural aggregate concretes with compressive strengths of 25MPa, 30MPa, 40MPa, 50MPa and 60MPa were used as recycled coarse and fine aggregates to produce recycled concrete with an objective compressive strength of 30MPa after they were cured for 28d. These recycled concretes were used as aggregates to produce concrete with the same objective compressive strength of 30MPa. The cycles were carried on until the indices evaluating the quality of recycled coarse or fine aggregate exceeded the tolerance. The mechanical behaviors of these concrete were tested. The results indicates that that with the increase of the cyclic number, the mechanical properties of recycled concrete, including compressive strength, tensile splitting strength, modulus of elasticity, gradually stabilize after obviously decreaing in the first instance.
34
Węglorz, Marek, Andrzej Ajdukiewicz e Alina Kliszczewicz. "Assessment of recycled concrete aggregate properties required for structural concretes". MATEC Web of Conferences 262 (2019): 06010. http://dx.doi.org/10.1051/matecconf/201926206010.
Testo completoAbstract (sommario):
Assessment of recycled aggregate concrete (RAC) properties by laboratory tests is still required due to lack of precise guidelines and with taking into account slightly different behaviour of such concretes in comparison with natural aggregate concretes (NAC). It is especially important when recycled concrete aggregates are used for the structural elements. In this paper, the following rules for the whole concrete recycling cycle were defined: (1) rules for examination of original concretes selected for recycling and (2) rules for aggregate preparation and their fractionize as well as design rules for recycled aggregate concrete mixtures (including required tests of recycled aggregates and concrete properties). Requirements towards recycled aggregate concrete formulated in this paper are based on the long term experience and research works on the RAC which were held by A. Ajdukiewicz and A. Kliszczewicz in the Department of Structural Engineering of the Silesian University of Technology, practically since 1995.
35
AY, Gorodishenina. "Concrete Pump Transport of Concrete Mixes". Open Access Journal of Waste Management & Xenobiotics 3, n. 4 (2020): 1–4. http://dx.doi.org/10.23880/oajwx-16000150.
Testo completoAbstract (sommario):
The article presents a study of innovative materials in the field of highly mobile and cast concrete mixtures using pipeline transport. The studies were carried out on mixtures with a complex additive based on S-3 superplasticizer. The complex included a plasticizing-air-entraining additive LHD with an air-entraining effect. Studies of the effects of S-3 and LHD additives on the construction and technical properties were carried out on mixtures with different cement flow rates and the same initial mobility. Studies of the rheological parameters of the mixtures were carried out using the mathematical theory of experimental design; measurements of resistivities were performed depending on the flow velocity. The result of the work is a linear dependence of the change in resistivities along the length and height.
36
ALBUQUERQUE, A. C., S. B. dos SANTOS, J. L. CALMON e L. C. P. da SILVA FILHO. "Thermo-mechanical analysis of mass concrete elements made of rubberized concrete". Revista IBRACON de Estruturas e Materiais 12, n. 3 (giugno 2019): 580–89. http://dx.doi.org/10.1590/s1983-41952019000300008.
Testo completoAbstract (sommario):
Abstract In this study, mass concrete samples with tire rubber chips (rubberized concrete) were evaluated in order to determine if the addition of rubber particles would enhance cracking strength due to volumetric variations of thermal origin, compared to a reference concrete, without rubber. Samples of the concretes studied were initially tested to characterize their thermal and mechanical properties. The test results were used as parameters for the analysis of the thermo-mechanic behavior of the rubberized concrete by means of a software that determined the thermal and stress response on a bi-dimensional dominion of a structural element of hypothetical geometry, typical of dam construction, applying FEM (finite element method) analysis. The results obtained indicated that, although the maximum temperatures expected are similar for both concretes (reference and rubberized), those containing tire rubber chips are subjected to lower tensile stresses, about half the stress generated in the control concrete. This behavior indicates that the addition of tire rubber chips in concrete is an efficient strategy to minimize the risk of cracking due to thermal stresses.
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Tanveer Majid, Muhammad. "The effect of twisted polymer fibers on the physical and mechanical properties of C35 concrete". Journal of Research in Science, Engineering and Technology 7, n. 4 (29 settembre 2020): 11–15. http://dx.doi.org/10.24200/jrset.vol7iss4pp11-15.
Testo completoAbstract (sommario):
Concrete as the most used material, is known as an integral part of construction. So far, many studies have been done in the field of improving the quality of concrete that most of them have examined change in concrete mix design; however, the use of additives and also replacing commonly used materials in concrete with new materials always has been considered. Today, different fibers, especially Forta fibers, are used. In this study, experiments on Forta fiber- reinforced concrete are described. The concrete mixing design and Forta fiber properties are also briefly described. The comparison between the results of the tests showed that Forta fiber- reinforced concretes have more bending strength and modulus of elasticity than normal and ordinary concretes.
38
Wan, Chao Jun, Xu Chen, Teng Li, Tai Zhong Huang e Tian Ming Deng. "Effect of Variability of Recycled Aggregate on Properties of Concrete". Applied Mechanics and Materials 174-177 (maggio 2012): 1122–32. http://dx.doi.org/10.4028/www.scientific.net/amm.174-177.1122.
Testo completoAbstract (sommario):
Low, medium and high variability of aggregates of concrete were designed and prepared and the influence of variability of recycled aggregates on the mechanical properties and durability of concretes was investigated. The experimental results indicated that the kinds of strengths, static compressive elastic modulus and durability of recycled concrete were decreased at engineering-acceptable level compared with natural aggregate concrete; the most properties of recycled concrete with high variability of recycled aggregates are not very different from that of recycled concrete with medium variability of recycled aggregates even that of natural aggregate concretes; however, the variability of properties of recycled concrete with high variability of recycled aggregates are much different from that of medium variability of recycled aggregates and more different from that of natural aggregate concretes, which means if only one or limited properties of recycled concrete were tested, the existing high variability of properties of concrete may not be revealed to a full enough extent, and the possible neglect of this high variability may result in potential engineering risk in application of high variability of recycled aggregate; the content of hardened cement paste and mortar attached to the recycled aggregate is found to be the essential factor to influence the properties of recycled concrete.
39
Schindler, Anton, Benjamin Byard e Aravind Tankasala. "Mitigation of early-age cracking in concrete structures". MATEC Web of Conferences 284 (2019): 07005. http://dx.doi.org/10.1051/matecconf/201928407005.
Testo completoAbstract (sommario):
Early-age cracking can adversely affect the behavior and durability of concrete elements. This paper will cover means to mitigate early-age cracking in concrete bridge decks and mass concrete elements. The development of in-place stresses is affected by the shrinkage, coefficient of thermal expansion, setting characteristics, restraint conditions, stress relaxation, and temperature history of the hardening concrete. The tensile strength is impacted by the cementitious materials, the water-cementitious materials ratio, the aggregate type and gradation, the curing (internal/external) provided, and the temperature history of the hardening concrete. In this study, restraint to volume change testing with rigid cracking frames (RCF) was used to directly measure and quantify the combined effects of all variables that affect the development of in-place stresses and strength in a specific application. The laboratory testing performed involved curing the concrete in the RCF under sealed, match-cured temperature conditions to simulate concrete placement in concrete bridge decks and mass concrete. Experimental results reveal that the use of low heat of hydration concretes, concretes that use fly ash and slag cement, and lightweight aggregate concretes (because of reduced modulus of elasticity and coefficient of thermal expansion), are very effective to reduce the risk of early-age cracking in these elements.
40
Yun, Yeon Jun, Kyung Lim Ahn, Won Gyun Lim e Hyun Do Yun. "Effects of Steel Fiber Volume Fraction on Compressive and Flexural Behaviors of Alkali-Activated Slag (AAS) Concrete". Applied Mechanics and Materials 525 (febbraio 2014): 469–72. http://dx.doi.org/10.4028/www.scientific.net/amm.525.469.
Testo completoAbstract (sommario):
This paper describes the experimental results on compressive and flexural behavior of alkali-activated slag (AAS) concrete reinforced with hooked end steel fiber. Two different fiber volume fractions of 0.5 and 1.0% were used for AAS concrete and Ordinary Portland cement (OPC) concretes were also mixed for comparison. Test results indicated that compressive and flexural performance of AAS concretes with water-to-binder (W/B) ratio of 0.55 are equivalent to those of OPC concrete. The addition of steel fiber to AAS concrete improves more compressive and flexural performance than those of steel fiber reinforced concrete.
41
USTABAŞ, İlker. "Use of Weight Maturity Method for Building Concretes Used in Artvin Yusufeli Dam Construction". Journal of Cement Based Composites 1, n. 1 (19 novembre 2019): 1–5. http://dx.doi.org/10.36937/cebacom.2020.001.001.
Testo completoAbstract (sommario):
The aim of this study is to compare the compressive strength determined by weight maturity method in dam concretes with compressive strength obtained from fresh concrete and core samples. Within the scope of the study, normal concretes of C25/30 strength class were produced. Samples were taken from ø15x30 cm cylinder molds from normal concrete mixtures having maximum aggregate grain diameter (Dmax) of 25 mm.In this study, the estimated compressive strengths were measured by using a maturity device and the compressive strengths obtained from samples taken from fresh concrete and core samples taken from hardened concrete were measured at close values. In this context, instead of taking samples from fresh concrete and concrete productions, it was concluded that the pressure resistance measurements made by using a maturity device in fresh concrete are reliable.
42
Koyankin, A. A., e V. M. Mitasov. "JOINTS IN CONCRETES OF DIFFERENT AGE AND TYPE". Vestnik Tomskogo gosudarstvennogo arkhitekturno-stroitel'nogo universiteta. JOURNAL of Construction and Architecture 22, n. 6 (29 dicembre 2020): 94–104. http://dx.doi.org/10.31675/1607-1859-2020-22-6-94-104.
Testo completoAbstract (sommario):
The performance and structural reliability of concrete-to-concrete joints play an important role in precast-cast-in-place constructions, since they are responsible for deformation of concretes of different age, type and strength. The paper studies the effect of the joint type on its bearing capacity under shear loads. A horizontal test bench and a standard vertical press are used in the experiment to provide the shear load along the concrete-to-concrete joint (light cast-situ and heavy precast concretes). The following joint installing is considered: a smooth surface, which provides the concrete joint due to the adhesive and friction forces, and the joint provided by transverse reinforcement. Design features are identified for the joint bearing capacity exhaustion in concretes of different age, type and strength in precast-cast-in-place constructions under shear, depending on the joint type. A comparative analysis is given to the results obtained. It is shown that the transverse reinforcement has a positive effect on the bearing capacity of the concrete-to-concrete joints.
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Khattab, Mohammed, e Samya Hachemi. "Performance of Recycled Aggregate Concrete Made with Waste Refractory Brick". International Journal of Engineering Research in Africa 57 (9 novembre 2021): 99–113. http://dx.doi.org/10.4028/www.scientific.net/jera.57.99.
Testo completoAbstract (sommario):
Concrete containing recycled aggregates have different properties from concrete containing natural aggregates. This work investigates, firstly, the possibility of using recycled refractory bricks (RBA) as coarse aggregate for concrete, and secondly, finds the ideal replacement percentage of natural coarse aggregate (NCA) by RBA. For this, an experimental study was carried out to assess the physical and mechanical properties of concrete produced with the partial and total replacement of NCA by RBA. Two types of RBA from two different sources were used, RBA-1 obtained from the grinding of new refractory bricks and RBA-2 obtained from refractory bricks used in the furnace recovered from the cement plant. For each type of RBA, two concretes with water/cement (w/c) ratios of 0.59 and 0.38 were tested. These concretes were evaluated by density, water porosity, ultrasonic pulse velocity (UPV) and compressive strength, and compared to those obtained on conventional concretes. The results obtained show that concrete can be manufactured using RBA. Concrete containing 20% RBA shows good quality compared with conventional concrete.
44
Batog, Maciej, Michał Tałaj, Katarzyna Synowiec e Zbigniew Giergiczny. "Impact of de‐icing salts on freeze‐thaw resistance of low‐clinker concretes". ce/papers 6, n. 6 (dicembre 2023): 151–57. http://dx.doi.org/10.1002/cepa.2926.
Testo completoAbstract (sommario):
AbstractDe‐icing salts are commonly used in moderate climate zone, where concrete is subjected to freeze‐thaw cycles during winter times. The presence of de‐icing salts requires appropriate frost‐thaw resistance of concrete, which is challengingin case of low‐clinker concretes. Proper air‐entrainment of the concrete mix, which is one of the main factors affecting the frost resistance of concrete is not a simple task. Therefore, it is necessary to constantly improve the process of air‐entrainment of the concrete mix and to constantly control the effectiveness and quality of concrete aeration especially those with low clinker cements. In the paper effect of de‐icing salts on air‐entrained by polymer microspheres and traditional air‐entraining admixtures low clinker concrete was evaluated. The conducted tests indicate that low‐clinker concretes made with the use of polymer microspheres, despite greater repeatability in shaping the correct air‐entrainment structure, are characterized by lower resistance to frost in the presence of de‐icing salts compared to traditionally air‐entrained concretes. This mechanism will be investigated in future work.
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Al-Neshawy, Fahim, Teemu Ojala e Jouni Punkki. "Stability of Air Content in Fresh Concretes with PCE-Based Superplasticizers". Nordic Concrete Research 60, n. 1 (1 giugno 2019): 145–58. http://dx.doi.org/10.2478/ncr-2019-0093.
Testo completoAbstract (sommario):
Abstract Air contents of concrete are necessary for concrete durability in freeze-thaw exposure. According to the Finnish concrete code, the target value for air content varies between 4% and 5.5% for XF - exposure classes. Lately in Finland, some cases showed an elevation of air contents up to 15% in fresh air-entrained concrete at construction site and in drilled concrete samples. The objectives of this study were to investigate the stability of air entrainment by measuring the air content elevation 30 minutes and 60 minutes after concrete mixing and investigating the concrete sensitivity to segregation. Composition of concretes used in this study include 7 different combination of PCE based superplasticizer and air-entraining agent admixtures, cement content of 425 kg/m3, two consistency classes S3 with water to cement ration of 0.33 and F5 with water to cement ration of 0.38. One cement type was used for all concrete mixes. The concretes were mixed for 2 minutes and 5 minutes mixing times. The results show that the elevation of the air content of fresh concrete depends on the consistency of the concrete and on the used combination of superplasticizer and air-entraining agents. The higher consistency classes concretes have more risk of air elevation with some combinations of PCE-based superplasticizers and air-entraining agents. The results also indicate that short mixing time would not be enough to achieve total effectivity of some air-entraining agents, especially for higher consistency classes concrete.
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Pushkar, Svetlana. "The Effect of Different Concrete Designs on the Life-Cycle Assessment of the Environmental Impacts of Concretes Containing Furnace Bottom-Ash Instead of Sand". Sustainability 11, n. 15 (29 luglio 2019): 4083. http://dx.doi.org/10.3390/su11154083.
Testo completoAbstract (sommario):
The results of life-cycle assessments (LCAs) of concrete are highly dependent on the concrete design method. In this study, LCAs were conducted to evaluate the environmental impacts of the replacement of sand with furnace bottom-ash (FBA) in concrete. In the FBA-based concretes, sand was replaced with FBA at proportions of 0, 30, 50, 70, and 100 wt%. Two design methods were studied: (i) concrete with fixed slump ranges of 0–10 mm (CON-fix-SLUMP-0-10) and 30–60 mm (CON-fix-SLUMP-30-60); and (ii) concrete with fixed water/cement (W/C) ratios of 0.45 (CON-fix-W/C-0.45) and 0.55 (CON-fix-W/C-0.55). The ReCiPe2016 midpoint and single-score (six methodological options) methods were used to compare the environmental damage caused by the FBA-based concretes. A two-stage nested (hierarchical) analysis of variance (ANOVA) was used to simultaneously evaluate the results of six ReCiPe2016 methodologies. The ReCiPe2016 results indicate that replacing sand with FBA decreased the environmental impact of the concretes with fixed slump ranges and increased the environmental impact of the concretes with fixed W/C ratios. Therefore, using FBA as a partial sand replacement in concrete production is of debatable utility, as its impact highly depends on the concrete design method used.
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Zhao, Huan Qi, e Guo Zhong Li. "The Influence of Matrix Concrete on the Strength of Recycled Concrete". Advanced Materials Research 532-533 (giugno 2012): 357–60. http://dx.doi.org/10.4028/www.scientific.net/amr.532-533.357.
Testo completoAbstract (sommario):
Recycled coarse aggregates obtained by crushed concrete were used for concrete production in this study. Four different recycled aggregate concretes were produced; made with 50% of recycled coarse aggregates of four intensity levels. The damage of the recycled concrete is the bond failure of the interface of aggregate and mortar, which is basically the same as the damage process and damage mechanism of the natural concrete. The strength of recycled concrete was influenced by matrix concrete. When the strength grade of matrix concrete is less than C35, the recycled strength of concrete will be inferior to that of natural concrete basically. But when the strength grade of matrix concrete is higher than C35, the recycled concrete strength will be higher than that of natural concrete.
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Travush, Vladimir, e Vasily Murashkin. "CONCRETE DEFORMATION MODEL FOR RECONSTRUCTED REINFORCED CONCRETE". International Journal for Computational Civil and Structural Engineering 18, n. 4 (28 dicembre 2022): 132–37. http://dx.doi.org/10.22337/2587-9618-2022-18-4-132-137.
Testo completoAbstract (sommario):
During the reconstruction, or upon expiration of the service life, as well as after external impact, reinforced concrete structures require examination and verification calculations. Existing diagrams of concrete deformation are focused on designing new structures and are not adapted to the concretes of the reconstructed structures. Using the world experience in describing alloy deformation, the concrete deformation model based on using the Arrhenius equation is proposed in this article. A technique for creating an individual deformations model during the reconstruction is demonstrated on a specific example. The physical meaning of the coefficients used in the proposed model is illustrated. Examples confirming the adequacy of the proposed concrete deformations model during the reconstruction are given.
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Ke, Chang Jun, Hao Wang e Tao Ke. "Activation Mechanism of Cement Paste for Waste Concrete Autoclaved Products". Advanced Materials Research 168-170 (dicembre 2010): 949–53. http://dx.doi.org/10.4028/www.scientific.net/amr.168-170.949.
Testo completoAbstract (sommario):
studied types and amount of hydration products in cement paste in waste concretes and effect of the cement paste in waste concrete for compressive strength of autoclaved waste concrete samples simulated by hydrated cement with X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Infrared Spectroscopy (IR). The results showed, compressive strength of autoclaved waste concrete products increased with cement paste in waste concrete increasing, and the effect reduced obviously when amount of cement paste exceed 12.5% in waste concrete. Cement paste calculated amount exceeds 12.5% according to present national specification for mix proportion design of ordinary concrete. And it shows that effect of cement paste in waste concrete is weakly for compressive strength of autoclaved waste concrete sample. And compressive strength of autoclaved waste concrete samples is unrelated to mix and age of waste concretes. Hydrated products such as hydrated calcium silicate (C-S-H), α-C2SH and hydrated calcium aluminate sulfate (AFm or AFt) in cement paste forming during normal temperature curing play a role of crystal seed in autoclaved waste concrete samples.
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Kubissa, Wojciech, Barbara Pacewska e Iwona Wilińska. "Comparative Investigations of some Properties Related to Durability of Cement Concretes Containing Different Fly Ashes". Advanced Materials Research 1054 (ottobre 2014): 154–61. http://dx.doi.org/10.4028/www.scientific.net/amr.1054.154.
Testo completoAbstract (sommario):
The results of research of mechanical properties and selected other characteristics influencing durability of cement concretes containing cement substitutes were presented. Cement concretes performed with conventional fly ash, fluidised fly ash and their mixture were investigated. The obtained results were compared with findings registered for two types of concrete performed without cement replacements and with cement concrete containing silica fume. The results have shown that cement concrete with predetermined 28-day compressive strength of about 50 MPa and good workability may be obtained using different cement replacements. Generally, these cement concretes exhibited also favorable properties related to concrete durability, i.e. low permeability and sorptivity, and significant reduction of chloride migration coefficient. Favourable results were obtained for cement concrete containing mix of conventional and fluidised fly ashes: good workability, compressive strength after 28th day exceeding 50 MPa, low permeability of water, and low sorptivity, as well as low coefficient of chloride migration. These features were similar as for cement concrete containing silica fume.