scholarly journals INFLUENCE OF MICROSTRUCTURE OF HYDRATE PHASES OF CEMENT STONE ON CONCRETE DURABILITY

2021 ◽  
Vol 6 (3) ◽  
pp. 8-18
Author(s):  
B. Trofimov ◽  
K. Shuldyakov ◽  
A. Mahmudov
Keyword(s):  
Reinforced Concrete ◽  
Cement Paste ◽  
Frost Resistance ◽  
Concrete Structures ◽  
Air Entrainment ◽  
Cement Stone ◽  
Hardened Cement ◽  
Reinforced Concrete Structures ◽  
Hardened Cement Paste ◽  
Structural Element

One of the main problems in modern concrete science is the low durability of reinforced concrete structures and constructions, especially those located in harsh climatic conditions and saturated with marine or mineralized water. Existing standards guide designers and builders to increase the density of concrete with increasing degree of aggressive impact, as well as through cyclical freezing of concrete structures, which taken as the main indicator of durability, air entrainment is mandatory. The problem is not only the provision of high frost resistance of concrete, but also finding a method of controlling it, which, as a rule, takes quite a long time. The destruction of concrete during cyclical freezing occurs not only due to the formation of ice in the pores of concrete, but also as a result of temperature stresses in concrete with ice, as well as the washing out of portlandite and aging of the cement gel – the main structural element of hardened cement paste. This means that the durability of the concrete can be ensured by maintaining the finely dispersed structure of the hardened cement paste, preventing crystallization of the gel from external influences or increasing its basicity. It is shown that only water reduction and pozzolanization, which provides residual portlandite content in Portland cement concrete stone 2–5 % by weight ensure the achievement of increased durability of concrete, reinforced concrete structures and constructions. A method is proposed to assess the stability of hydrate phases as well as the relationship between the durability and frost resistance of concrete.

scholarly journals POROSITY PARAMETERS OF CEMENT STONE CONTAINING CHEMICAL ADMIXTURES OF DIFFERENT PURPOSE / CEMENTINIO AKMENS SU SKIRTINGOS PASKIRTIES CHEMINIAIS PRIEDAIS PORINGUMO RODIKLIAI

2013 ◽  
Vol 5 (5) ◽  
pp. 530-535
Author(s):  
Lukas Venčkauskas ◽  
Mindaugas Daukšys
Keyword(s):  
Cement Paste ◽  
Cement Stone ◽  
Hardened Cement ◽  
Closed Porosity ◽  
Hardened Cement Paste ◽  
Chemical Admixtures ◽  
Average Size ◽  
The Impact ◽  
Plasticizing Admixture

The conducted research has established a complex influenceand the impact of separate chemical admixtures of differentpurpose on the parameters of the porosity of hardened cementpaste such as open and closed porosity, the average size of poresand the rates of pore inequality. According to the parametersof the porosity of hardened cement paste, on the basis of A. E.Sheikin’s methodology, the number of freezing-thawing cycleswas predicted. This research used plasticizing, viscosity modifyingand antifoaming admixtures. It has been found that, when theamount of plasticizing admixture in cement paste (W/C–0.45) isconstant and makes 1.1% of the cement mass, and the amountof viscosity modifying and antifoaming the admixture increasesfrom 0.1 to 0.6% and from 0.05 to 0.3% respectively, the openporosity of hardened cement paste varies between 30.21% and31.06%, while closed porosity varies between 5.39% and 6.22%.When the amount of the plasticizing admixture in cement paste(W/C–0.45) exceeds 1.1% of the cement mass, the open porosityof hardened cement paste increases by 1.4 times and closedporosity decreases by 2.5 times. While adding 0.1% of the viscositymodifying admixture to cement paste, the open porosityof hardened cement paste is increased by 1.5 times and closedporosity decreases by 2.4 times. The amount of 0.05% of thecement mass of the antifoaming admixture results in the increasedopen porosity of hardened cement paste by 1.5 times and reducedclosed porosity by 3.5 times. Santrauka Tyrimo metu nustatyta kompleksinė bei atskirų skirtingos paskirties cheminių priedų įtaka cementinio akmens poringumo rodikliams – atvirajam ir uždarajam poringumui, vidutinio porų dydžio ir porų vienodumo rodikliams. Tyrimuose naudoti cheminiai priedai: plastifikuojantis, klampą modifikuojantis ir mišinyje susiformavusias oro poras suardantis priedas. Nustatyta, kad cemento tešloje (V/C – 0,45) esant pastoviam plastifikuojančio priedo kiekiui – 1,0 % cemento masės, klampą modifikuojančio priedo kiekiui kintant nuo 0,1 iki 0,6 %, o mišinyje susiformavusias oro poras suardančio priedo kiekiui kintant nuo 0,05 iki 0,3 %, cementinio akmens atvirasis poringumas svyruoja nuo 30,21 iki 31,06 %, o uždarasis – nuo 5,39 iki 6,22 %. Cemento tešloje viršijus plastifikuojančio priedo 1,1 % cemento masės, cementinio akmens atvirasis poringumas padidėja apie 1,4 karto, o uždarasis poringumas sumažėja apie 2,5 karto. Pridėjus į tešlą 0,1 % cemento masės klampą modifikuojančio priedo, cementinio akmens atvirasis poringumas padidėja apie 1,5 karto, uždarasis poringumas sumažėja apie 2,4 karto. Oro poras suardančio priedo kiekis 0,05 % cemento masės cementinio akmens atvirąjį poringumą padidina apie 1,5 karto, uždarąjį poringumą sumažina apie 3,5 karto.

scholarly journals Historical reinforced concrete structures – used materials and calculating algorithms

2015 ◽  
Vol 14 (2) ◽  
pp. 105-112 ◽  
Author(s):  
Bartosz Szostak ◽  
Maciej Trochonowicz
Keyword(s):  
Mechanical Properties ◽  
Reinforced Concrete ◽  
Concrete Structures ◽  
Reinforced Concrete Structures ◽  
Structural Element ◽  
Historical Building ◽  
Historical Material ◽  
Low Strength ◽  
Concrete Elements

During designing in historical object we can have a problem with historical reinforced concrete elements. Many designers, classifies this elements as low strength. They are convicted that this type of elements in historical building can be only a monument and cannot be used in this construction as an structural element. It is very important in this type of buildings to keep as many historical material as it is possible. Authors researched the literature which has been a guide in the design and execution of these elements. By comprising used algorithms and physico-mechanical properties of old materials with algorithms and materials, which are using today, we are able to estimate the strength of such elements.

scholarly journals Flexural strength of silica fume, fly ash, and metakaolin of hardened cement paste after exposure to elevated temperatures

2021 ◽  
Author(s):  
Nabil Abdelmelek ◽  
Eva Lubloy
Keyword(s):  
Fly Ash ◽  
Silica Fume ◽  
Cement Paste ◽  
Elevated Temperatures ◽  
The Other ◽  
Hardened Cement ◽  
Hardened Cement Paste ◽  
Structural Element ◽  
Pozzolanic Material ◽  
Pozzolanic Materials

AbstractThe mechanical properties of concrete based mainly on flexural and compressive bearing capacity. Generally, researchers have an interest in the evaluation of compression property through the importance of the flexural performance of the material in the constructions, namely the significance of each mechanical property based upon the position of the structural element. The present experimentally work is directed toward improving the flexural strengths performance of ordinary hardened cement paste (HCP) at ambient and after elevated temperatures exposure. The used parameters were different pozzolanic materials with different replacements ratios to cement mass and different levels of temperature. Results proved the significant contribution of pozzolanic material to enhance the flexural properties of HCP after being exposed to elevated temperatures. The low content of CaO, the high grinding fineness, and the physical morphology of the used pozzolanic materials, made their adoption effective to HCP after exposure to elevated temperatures. Using 3%, 12%, and 15% of silica fume (SF), metakaolin (MK), and fly ash (FA), respectively, showed the highest heat endurance among the other replacements. However, the optimum replacement of MK has shown a better heat endurance than the optimum replacements of SF and FA. On the other hand, the spalling has occurred at high replacements of SF. Finally, the results are supported by means of thermo-gravimetric, SEM, and computed tomography investigations.

scholarly journals CRACK RESISTANCE OF REINFORCED CONCRETED AND REINFORCED RUBBER CONCRETE BEAMS

2020 ◽  
Vol 1 (22) ◽  
Author(s):  
Artem Levchenko ◽  
Aleksei Polikutin ◽  
Dmitry Barabash
Keyword(s):  
Tensile Strength ◽  
Reinforced Concrete ◽  
Crack Resistance ◽  
Voltage Drop ◽  
Concrete Structures ◽  
Polymer Concrete ◽  
Reinforced Concrete Structures ◽  
Longitudinal Reinforcement ◽  
Structural Element ◽  
Concrete Body

The issue of the appearance and development of cracks, as well as an increase the cracking moment is of particular importance for bending elements operating under aggressive environmental conditions. In structures without cracks, steel reinforcement operates in fairly favorable conditions. However, when cracks appear in the sections of the structural element, the reinforcing bar is exposed to aggressive environmental influences, the voltage drop across the reinforcement also increases, etc.In reinforced concrete structures, tensile stresses are perceived by reinforcing bars, an increase in the content of longitudinal reinforcement in the section leads to some increase in crack resistance of structures, however, an increase in the percentage of longitudinal reinforcement causes a number of undesirable phenomena such as increased consumption of reinforcement and increased weight of the structure. Also, the introduction of reinforcement into the concrete body does not eliminate such disadvantages of concrete as susceptibility to corrosion, low elasticity, low tensile strength and tensile strength. The use of polymer concrete improves these properties of reinforced concrete structures, while the density of fiber rubcon and rubcon is slightly lower than that of traditional concrete, and, consequently, the weight of structures made of this polymer concrete.

scholarly journals Forced electric heating use for guaranteed quality of concrete clutching, restoring reinforced concrete structures

2021 ◽  
Vol 2131 (5) ◽  
pp. 052066
Author(s):  
V Molodin ◽  
S Leonovich ◽  
S Shpanko
Keyword(s):  
Reinforced Concrete ◽  
Concrete Structures ◽  
Electric Heating ◽  
Cohesive Strength ◽  
Temperature Gradients ◽  
Cement Stone ◽  
Reinforced Concrete Structures ◽  
Guaranteed Quality ◽  
Long Time

Abstract Concrete adhesion is a decisive factor in restoring performance of reinforced concrete structures. Peeling of the repair concrete is observed, during the structures restoring that have been in operation for a long time in aggressive conditions. The studies of the carbon dioxide effect on cement stone showed crystalline framework destruction of the material and a decrease in its cohesive strength. This has a significant effect on grip. The use of forced heating of the repair mixture when it is placed in contact with the restored structure leads to the temperature gradients that enhance thermal diffusion and thus the impregnation of the damaged cement stone with the liquid phase from the repair concrete mixture. Crystallizing, the cement dissolution products form a new crystalline structure in the damaged cement stone, which enhances its cohesive strength and binds the repair concrete to the intact concrete structure of the restored structure, ensuring adhesion quality.

On the Issue of Standardizing Concrete Frost Resistance to Ensure the Reinforced Concrete Structures Durability

2021 ◽  
Vol 1043 ◽  
pp. 1-7
Author(s):  
Grigorii Nesvetaev ◽  
Yulia Koryanova ◽  
Aleksei Kolleganov ◽  
Nikita Kolleganov
Keyword(s):  
Compressive Strength ◽  
Reinforced Concrete ◽  
Concrete Structure ◽  
Frost Resistance ◽  
Concrete Structures ◽  
Design Stage ◽  
Reinforced Concrete Structures ◽  
Saturated State ◽  
Base Method ◽  
Water Saturated

When erecting monolithic reinforced concrete structures, the structure of concrete can differ significantly from the laboratory standard due to the complexity of providing favorable conditions for hardening, and therefore the compressive strength and especially the frost resistance of concrete may not meet the design requirements, which can negatively affect the reinforced concrete structure durability and require amplification, especially in earthquake-prone areas [1, 2]. Increasing the durability of reinforced concrete structures is possible by creating a rational stress field, for example, by prestressing, incl. variable along the length of the structure [3,4], but this technique is difficult to implement for monolithic reinforced concrete structures. It is possible to use effective materials or methods of manufacturing structures [5, 6]. But this is also mainly problematic for use in the construction of monolithic reinforced concrete structures. Generally accepted methods of calculating the reinforced concrete structures durability subjected to cyclic freezing-thawing during operation, incl. in a water-saturated state, do not exist. At the design stage, ensuring the durability of such reinforced concrete structures is mainly reduced to the reasonable assignment of requirements for concrete quality indicators, depending on the operating conditions, which is the focus of BC 28.13330.2017 (EN 206) and GOST 31384-2017 from the premise of ensuring durability of at least 50 years. In the above-mentioned norms of the Russian Federation, in fact, two approaches are presented to ensure the durability of reinforced concrete structures during cyclic freezing-thawing, incl. in a water-saturated state, namely: designing a concrete structure capable of working under such conditions by standardizing the values of cement consumption, W/C ratio, class of concrete in terms of compressive strength, amount of entrained air, or rationing of concrete grades in terms of frost resistance F1 (first base method GOST 10060-2012 provides for freezing in air, saturation and thawing in water) or F2 (second base method GOST 10060-2012 provides for freezing in air, saturation and thawing in 5% sodium chloride solution). The purpose of this work is to compare various approaches to ensuring the durability of reinforced concrete structures operated during cyclic freezing-thawing and to analyze the provision of durability with standardized indicators when designing the structure of concrete.

scholarly journals Comparison of sizing and modeling of columns

2020 ◽  
pp. 121-146
Author(s):  
Daniely Silva Carvalhaes ◽  
Daniel José Carvalhaes ◽  
Wanessa Mesquita Godoi Godoi
Keyword(s):  
Reinforced Concrete ◽  
Concrete Structures ◽  
Reinforced Concrete Structures ◽  
Project Development ◽  
Structural Element ◽  
Modeling Process ◽  
Entire Structure ◽  
Significant Difference ◽  
Numerical Process ◽  
The Common

The search for the reduction of time in the elaboration of projects becomes a necessity, together with the indigence of understanding recurrent problems in the use of reinforced concrete structures such as pathologies. Thus, uniting the two problems, time and analysis, it becomes imperative to study ways of modeling and analyzing the structures in the common software of project development. The objective is to model a building and compare a structural element, analyzing the loads and dimensions made by the TQS software®. This process is due to the modeling in the TQS software of the example building of José Milton de Araújo (2014). It was observed that the modeling process compared to the numerical process presents significant difference due to the fact of doing the analysis of the complete building, thus being reliable the modeling performed in the software, which allows a previous study of the entire structure.

scholarly journals Cracking in Reinforced Concrete Structures Damaged by Artificial Corrosion: An Overview

2019 ◽  
Vol 13 (1) ◽  
pp. 199-213 ◽  
Author(s):  
Stefania Imperatore ◽  
Zila Rinaldi
Keyword(s):  
Reinforced Concrete ◽  
Current Density ◽  
Crack Width ◽  
Concrete Structures ◽  
Experimental Results ◽  
Reinforced Concrete Structures ◽  
Structural Element ◽  
Concrete Element ◽  
Electrolytic Corrosion ◽  
Current Densities

Background: Corrosion of the reinforcing steel is a significant issue in construction engineering. As the corrosive attack propagates, the oxides accumulated on the steel-concrete interface cause a radial internal pressure in the structural element and induce a tensile stress state in the concrete with the consequent cracking. Except for few cases, the main outcomes on the behavior of reinforced concrete structures damaged by corrosion come from experimental results on artificially corroded specimens. For many years, the scientific community has been discussing the feasibility of artificial techniques to simulate the corrosion process in structural element. Specifically, the most disputed method is the accelerated electrolytic corrosion test, often characterized by high current intensities in order to reduce the duration of the experimental surveys. Objective: In the paper the influence of the current density on the degradation of a reinforced concrete element is investigated with particular reference to the kind of formed oxides and to the crack width. Methods: An experimental survey on steel rebars embedded in concrete cylinders and subjected to an electrolytic corrosion has been performed, with different increasing current densities. Furthermore, an analytical model, based on the classical thick-walled cylinder theory already proposed by the authors, is applied for validating the experimental results. Results: The oxides produced by artificial corrosion with different current densities are analyzed with X-ray diffractometry measurements. The influence of the current density on the crack widths is also pointed out. Conclusion: The analyses of the obtained results show that for the analysed specimens and current density range, no significant differences are found for the oxides composition. On the contrary the influence of the current density on the crack width is pointed out, and an upper limit of this parameter is indicated.

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