scholarly journals Features of using cement suspension in concrete mixture recycling technology

Vestnik MGSU ◽  
2021 ◽  
pp. 1573-1581
Author(s):  
Svetlana V. Samchenko ◽  
Egor S. Egorov ◽  
Mihail A. Abramov
Keyword(s):  
Mechanical Characteristics ◽  
Setting Time ◽  
Hydraulic Press ◽  
Normal Density ◽  
Hydrated Cement ◽  
Technological Properties ◽  
Standard Methods ◽  
Concrete Mixtures ◽  
Cement Additive ◽  
The Difference

Introduction. Recycling technologies may solve the problem of landfill waste. The problem of hydraulic active cement waste using not fully resolved in concrete mixtures recycling technologies. Using hydraulic active cement waste as an addition directly influences the technological and mechanical characteristics of new concrete mixtures. That requires additional research. Materials and methods. The cement waste obtained after recycling was simulated by pre-hydrated cement suspension produce at V/C equal to 0.7 for 6 hours of hydration. Different compositions of cement mixtures were investigated. The difference of which was amount of introduced pre-hydrated cement additive, both in the presence and without plasticizer. Technological properties, namely the normal consistency and setting time of cement compositions were investigated by standard methods of GOST 30744-2001. Mechanical properties, namely the compressive strength at the age of 28 days, were determined by destructive method on a hydraulic press PSU-10. Results. The introduction of a pre-hydrated suspension causes an increase in normal consistency, a reduction in the setting time and a decrease in strength with an increase in its quantity. The use of such a suspension in conjunction with a superplasticizer can level out the increase in normal density, as well as increase the strength of the samples. Timing of setting remained similar to the results of the test without the plasticizer. Conclusions. The results of the study show influences of cement waste obtained after recycling on the technological and mechanical characteristics of new mixtures. These influences are important and must be taken into account in the design of new concretes and mortars.

Viability of turbine blade material with a long service life

2019 ◽  
pp. 28-35
Author(s):  
O. B. Berdnik ◽  
I. N. Tsareva ◽  
M. K. Chegurov
Keyword(s):  
Heat Treatment ◽  
Service Life ◽  
Yield Strength ◽  
Mechanical Characteristics ◽  
Operating Time ◽  
Structural Features ◽  
Operating Conditions ◽  
Standard Methods ◽  
Experimental Values ◽  
Plasticity Coefficient

This article deals with structural features and characteristic changes that affect the mechanical characteristics after different service life in real conditions using the example of the blades of the 4th stage of turbine GTE-45-3 with an operating time of 13,000 to 100,000 hours. To study the change in the state of the material under different operating conditions, determine the degree of influence of heat treatment on the regeneration of the microstructure, and restore the mechanical characteristics of the alloy after different periods of operation, non-standard methods were used: relaxation tests on miniature samples to determine the physical yield strength and microplasticity limit and quantitative evaluation of the plasticity coefficient of the material from experimental values of hardness, which allow us to identify the changes occurring in the microvolumes of the material and predict the performance of the product as a whole.

Multiscale Model of Influence of Heat Curing on Fly-Ash Concrete Mixtures

2014 ◽  
Vol 1054 ◽  
pp. 162-167
Author(s):  
Tomáš Váchal ◽  
Rostislav Šulc ◽  
Pavel Svoboda
Keyword(s):  
Fly Ash ◽  
Mechanical Characteristics ◽  
Multiscale Model ◽  
Heat Energy ◽  
Correct Treatment ◽  
Fly Ash Concrete ◽  
Concrete Mixtures ◽  
Heat Curing ◽  
Time Period ◽  
Quantity Of Heat

This paper describes influence of time and temperature of heat curing on progress of mechanical characteristics of concrete mixtures based on alkali activated fly-ash (POPbeton). One of the major impacts for the correct treatment of alkaline activation is the quantity of heat energy in a given time period which is supplied during activation. The paper describes the dependence of progress of compressive strength of POPbeton on the time and temperature of heat curing. It was assembled a predictive model which describes the dependence of the supplied heat energy over time on the resulting properties of POPbeton. The result is a tool that can predict the resulting values of mechanical characteristics of test samples of POPbeton.

scholarly journals COMPOSITE BINDERS BASED ON CONCRETE SCRAP

2020 ◽  
pp. 8-18
Author(s):  
A. Ahmed ◽  
R. Lesovik ◽  
S. Al Mamouri ◽  
T. Gunchenko
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Setting Time ◽  
Normal Density ◽  
Composite Binder ◽  
Construction Products ◽  
Normative Documentation ◽  
Optimal Strength ◽  
Vibration Mill

The object of research is composite binders obtained from concrete scrap of destroyed buildings and structures for the production of various construction products and structures. Fractions of concrete scrap of 0,0–0,16 mm and 0,16–0,315 mm are used, since x-rayphase analysis of various fractions of concrete scrap shows that these fractions have the highest content of non-hydrated particles of alite and belite. The influence of the specific surface area on the normal density of cement dough and the setting time of binders is established. Comparative physical and mechanical indicators of hardening of binders with different specific surfaces indicate that the most stable results with a uniform increase in strength is the composition of a binder with a specific surface of 964 m2 / kg, with an increase in strength from 2 to 7 days – 27 % and from 7 to 28 days – 21 %. This binder is characterized by optimal strength at the age of 28 days – 25,5 MPa. With a specific surface of 964 m2/kg, the best conditions are created for the formation of the primary frame and its further fouling with various calcium crystalline hydrates, which ensure optimal density and strength. This composite binder has a specific surface area of 964 m2/kg and is more energyefficient. Composite binders obtained in a vibration mill from concrete scrap fractions (0,0–0,16 and 0,16–0,315 mm) meet the requirements of normative documentation on setting time and physico-mechanical parameters, which allows to recommend them for use as binders in the production of construction products and structures for various purposes.

Sonographic Association Of Placenta Accreta Spectrum In Patients Of Placenta Previa-A Systematic Review

2021 ◽  
Vol 15 (11) ◽  
pp. 3050-3053
Author(s):  
Maida Saadat ◽  
Muhammad Mawaz Anjum ◽  
Faiza Farooq ◽  
Rehan Aslam Gill ◽  
Abeer Yasin ◽  
...  
Keyword(s):  
Diagnostic Accuracy ◽  
Placenta Accreta ◽  
Placenta Previa ◽  
Meta Analysis ◽  
Retrospective Case ◽  
Standard Methods ◽  
Placenta Accreta Spectrum ◽  
The Difference ◽  
Obstetric Population ◽  
High Level

Aim: To determine the diagnostic accuracy and epidemiology of placenta accreta spectrum (PAS) in patients of placenta previa. Methods: PubMed, Google Scholar, ClinicalTrials.gov and MEDLINE were searched between January1992 and December 2020. Studies on placenta previa complicated by PAS diagnosed in a defined obstetric population. This research was carried out using standard methods and protocols and keeping in view Newcastle-Ottawa scale for observation and assessment of case study along with the difference approved by consensus. The overall diagnostic accuracy of ultrasonographic findings is the main outcome of this study, whereas the prevalence of placenta accreta in patients of placenta previa and its incidence among different countries all over the world is also described. Results: In this review study, about 300 articles were evaluated. More over about 15 prospective and 14 retrospective case studies incorporated for assessment having complication with placenta previa and PAS. According to the meta-analysis, a significant (p<0.001) heterogeneity was found between case research that evaluate PAS prevalence and incidence in the placenta previa cohort. The median prevalence in case of placenta previa along with PAS came out to be 0.113% (IQR 0.048–0.17).Whereas incidence in females having placenta previa along with complication of PAS came out to be 11.3%. Conclusions: The high level of diversity observed in results obtained by diagnostic and qualitative data showed strong emphasis should be made on implementation of standard methods and protocols for assessment and diagnosis of pregnancy complication like placenta previa, its type and PAS. Keywords: Sonography placenta previa, placenta accreta spectrum

scholarly journals A Comprehensive Model for Estimating Heat Vulnerability of Young Athletes

2020 ◽  
Vol 17 (17) ◽  
pp. 6156
Author(s):  
Wenwen Cheng ◽  
J. O. Spengler ◽  
Robert D. Brown
Keyword(s):  
Heat Budget ◽  
Preventive Measure ◽  
Heat Index ◽  
Heat Illness ◽  
Young Athletes ◽  
Standard Methods ◽  
Comfa Model ◽  
The Difference ◽  
Heat Vulnerability ◽  
Football Field

Current methods for estimating heat vulnerability of young athletes use a heat index (HI) or a wet bulb globe thermometer (WBGT), neither of which fully include the environmental or physiological characteristics that can affect a person’s heat budget, particularly where activity occurs on a synthetic surface. This study analyzed and compared the standard methods, HI and WBGT, with a novel and more comprehensive method termed COMFA-Kid (CK) which is based on an energy budget model explicitly designed for youth. The COMFA model was presented at the same time to demonstrate the difference between a child and an adult during activity. Micrometeorological measurements were taken at a synthetic-surfaced football field during mid-day in hot environmental conditions. Standard methods (HI and WBGT) indicated that conditions on the field were relatively safe for youth to engage in activities related to football practice or games, whereas the CK method indicated that conditions were dangerously hot and could lead to exertional heat illness. Estimates using the CK method also indicated that coaches and staff standing on the sidelines, and parents sitting in the stands, would not only be safe from heat but would be thermally comfortable. The difference in thermal comfort experienced by coaches and staff off the field, versus that experienced by young players on the field, could affect decision making regarding the duration and intensity of practices and time in the game. The CK method, which is easy to use and available for modification for specific conditions, would lead to more accurate estimates of heat safety on outdoor synthetic surfaces in particular, and in sports with a high prevalence of heat illness such as football, and should be considered as a complementary or alternative preventive measure against heat.

scholarly journals Effective binder based on the artificial anhydrite for manufacturing of filling mixtures

2018 ◽  
Vol 193 ◽  
pp. 03048
Author(s):  
Nadezda Galtseva ◽  
Anfisa Bogdanova
Keyword(s):  
Compressive Strength ◽  
Setting Time ◽  
Potassium Sulfate ◽  
Technological Properties ◽  
Start Time ◽  
Filling Materials ◽  
Binder Ratio ◽  
Sufficient Set ◽  
Concentrated Sulfuric Acid ◽  
Derivation Method

The article exposes the results of research on the development of filling mixtures based on artificial anhydrite obtained after the interaction of concentrated sulfuric acid and limestone flour. The anhydrite derivation method has a significant impact on its properties and brings more options for the application. The key features of artificial anhydrite are high compressive strength which is more than 50 MPa and extended setting time which is more than 10 hours. In order to use it as a binder in the filling mixtures, it is necessary to modify properties of the anhydrite by integrating the hardening activators. In the relation to the study it was found that the optimal activator providing desirable setting start time (at least 2 hours) and a sufficient set of strength in the first 7 days of hardening is a mixture of 5% portland cement CEM I 42,5 and 1% of potassium sulfate, where 100% is the mass of binder. The additional inclusion of Melment F10 plasticizer in the amount of 0.4 to 1% of the binder ensures the achievement of the such parameters as the 0.3 water-binder ratio, setting start from 120 to 225 min, final setting time from 180 to 355 min, compressive strength after 24 hours from 6.9 to 13.3 MPa, after 7 days from 24.0 to 33.5 MPa. The microstructure of the binder has been analyzed and the modification options of the artificial anhydrite have been revealed in order to regulate its technical and technological properties., Two compounds of the filling mixture have been developed on the basis of the obtained binder, technical properties of compounds satisfy the maximum requirements for filling materials for depleted underground spaces. Research results have shown an opportunity and a prospectively of integrating the modified artificial anhydrite in structures of filling mixtures.

Production Waste as a Component of Raw Materials for Construction Ceramics

2020 ◽  
Vol 839 ◽  
pp. 184-188
Author(s):  
Victoria A. Gurieva ◽  
Anastasia A. Ilyina
Keyword(s):  
Mechanical Characteristics ◽  
Raw Materials ◽  
Raw Material ◽  
Material Base ◽  
Technological Properties ◽  
Orenburg Region ◽  
Existing Problems ◽  
Ceramic Mixture ◽  
The Russian Federation

The paper considers the existing problems of the production of ceramic products in the territory of the Russian Federation, presents the priority directions of development of this industry. The study includes the determination of the properties of samples based on the raw material base of the Orenburg region, namely, waste generated during the development of brown coal from the Tyulgansk deposit - white and red clays and nickel slag of OJSC Yuzhuralnickel Combine of the Orenburg region. The study presents data from the study of the technological properties of the raw materials, the development of the composition of the ceramic mixture. The influence of the material composition of the clay / slag mixture on the physic mechanical characteristics of the products of the experimental compositions was determined: compressive strength, fire shrinkage, water absorption and density.

In Situ Hardening Biodegradable and Malleable Polymer-Nanoapatite Composites

2010 ◽  
Vol 638-642 ◽  
pp. 693-699
Author(s):  
Stefan Berger ◽  
Jürgen Weisser ◽  
Eberhard Müller ◽  
Matthias Schnabelrauch
Keyword(s):  
Mechanical Characteristics ◽  
Setting Time ◽  
Polymer Networks ◽  
Bone Material ◽  
Foaming Agents ◽  
Composite Systems ◽  
Young’S Moduli ◽  
Porous Composites

Composite systems composed of nanocrystalline apatites and oligolactide-based polymer networks were prepared resulting in malleable and even injectable formulations which can be cured to compact materials at body temperature. Porous devices with inter-connective porosity were obtained after addition of suitable foaming agents to the composite mixtures. Setting time, porosity and mechanical properties of the composites can be properly adjusted by varying the educt composition. The determined compressive strengths and Young’s moduli of the porous composites perfectly match the mechanical characteristics of cancellous bone material. Preliminary in vitro cell culture experiments with compact composite materials demonstrated their good cytocompatibility. Based on these findings, the synthesized nano-structured composites represent promising candidates for the development of new biomaterials usable in hard tissue regeneration.

Effect of Slag Content and Hardening Accelerator Dosage on the Physico-Mechanical Properties of Cement and Concrete

2011 ◽  
Vol 324 ◽  
pp. 392-395
Author(s):  
Riad Derabla ◽  
Imen Mokrani ◽  
Mohamed Larbi Benmalek
Keyword(s):  
Blast Furnace ◽  
Blast Furnace Slag ◽  
Mechanical Characteristics ◽  
Setting Time ◽  
Absorption Capacity ◽  
Early Age ◽  
Granulated Blast Furnace Slag ◽  
Furnace Slag ◽  
Physical And Mechanical Characteristics

Our contribution consists at the study of the effect of (0 %, 0.2 % and 0.34 %) dosage of an hardening accelerating plasticizer (Plastocrete 160, produced by Sika Aldjazair) on the properties of normal mortar and concretes prepared with portland cement artificial of Hadjar Soud cement factory (Skikda – Algeria) with addition of (10 % and 20 %) of granulated blast furnace slag finely crushed of the El Hadjar blast furnace (Annaba - Algeria). The tests are focused to the physical and mechanical characteristics of elaborated materials to knowing: setting time, porosity, water absorption capacity and the test of compressive strength at 2, 7 and 28 days. The results obtained show clearly the reliability of the additive used to accelerate the hardening and to obtain high strengths at early age, which increase by increasing of the additive dosage. For the slag, its low hydraulic capacity does not make it profitable than at the long term (beyond 28 days).

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