scholarly journals Influence of Composition and Technological Factors on Variatropic Efficiency and Constructive Quality Coefficients of Lightweight Vibro-Centrifuged Concrete with Alkalized Mixing Water

2021 ◽  
Vol 11 (19) ◽  
pp. 9293
Author(s):  
Sergey A. Stel’makh ◽  
Evgenii M. Shcherban’ ◽  
Alexey N. Beskopylny ◽  
Levon R. Mailyan ◽  
Besarion Meskhi ◽  
...  
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
New Technology ◽  
Building Structures ◽  
Structural Improvement ◽  
Low Energy Consumption ◽  
Integral Characteristics ◽  
Operational Ability ◽  
Positive Effect ◽  
Mixing Water

Alkalization technology and its application to obtain high-performance concrete compositions is an urgent scientific problem that opens opportunities for improving building structures. The article is devoted to the new technology of manufacturing reinforced concrete structures with low energy consumption, resource, and labor intensity based on the improved variatropic configuration of vibro-centrifuged concrete using activated water with high pH. The synergistic effect of the joint use of the proposed novel solutions has been theoretically and experimentally proved. Thus, growth in physical and mechanical characteristics of up to 15–20% was obtained, the structure and its operational ability were improved (the effectiveness of structural improvement, expressed as a percentage, reached values over 70%, concerning control samples). A positive effect on the properties of vibro-centrifuged concrete over the entire thickness of the annular section has been revealed. A method for controlling the integral characteristics of concrete has been obtained. The possibility of regulating the variatropic structure and controlling the differential characteristics of vibro-centrifuged concrete has been established. An assessment of the constructive quality and variatropic efficiency of vibro-centrifuged concrete was carried out, and new calculated dependencies were proposed, expressed in the form of relative coefficients.

scholarly journals Fluorescence Microscopic Investigations of the Retarding Effect of Superplasticizers in Cementitious Systems of UHPC

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1057 ◽  
Author(s):  
Johannes Arend ◽  
Alexander Wetzel ◽  
Bernhard Middendorf
Keyword(s):  
Molecular Structure ◽  
High Performance ◽  
High Performance Concrete ◽  
Ultra High Performance Concrete ◽  
Adsorption Characteristic ◽  
Beneficial Effects ◽  
Retarding Effect ◽  
Cementitious Systems ◽  
Mixing Water

The adsorption of superplasticizer molecules to particle surfaces in cementitious systems is a very important aspect for the desired liquefaction of pastes and concretes. This way, the comb shaped polymers shield attractive forces between the particles and induce a well-dispersed, homogeneous suspension. These admixtures allow the usage of fine fillers even in combination with low amounts of mixing water, and thus, are the basis for modern high performance concretes. However, the adsorption does not cause beneficial effects only: The polymer covered particle surfaces, especially clinker, are hindered to interact with water, thus hydration is retarded. This is the reason for lower early strength and is very disadvantageous for certain applications. Today it is known that the molecular structure of the polymers, for instance the chain length and charge density, affects the retardation strongly. The complexity and diversity of cementitious systems is the main reason why research in this field is quite empiric and time as well as cost intensive. To investigate the adsorption of superplasticizers in various systems in-situ, a fluorescence microscopic approach was applied: By staining the polymers with fluorescent dye they become localizable and the adsorption quantifiable. This work shows the influence of molecular structure to adsorption characteristic of different polymers and the correlation to the retarding effect of superplasticizers, especially concerning the presence of silica fume, which is indispensable for ultra-high performance concrete (UHPC).

scholarly journals Effect of Elevated Temperature on the Bond Strength of Prestressing Reinforcement in UHPC

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4990
Author(s):  
Petr Pokorný ◽  
Jiří Kolísko ◽  
David Čítek ◽  
Michaela Kostelecká
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Elevated Temperatures ◽  
High Performance Concrete ◽  
Future Research ◽  
Ultra High Performance Concrete ◽  
Negative Effect ◽  
Laboratory Investigations ◽  
Increasing Temperature ◽  
Positive Effect

The study explores the effect of elevated temperatures on the bond strength between prestressing reinforcement and ultra-high performance concrete (UHPC). Laboratory investigations reveal that the changes in bond strength correspond well with the changes in compressive strength of UHPC and their correlation can be mathematically described. Exposition of specimens to temperatures up to 200 °C does not reduce bond strength as a negative effect of increasing temperature is outweighed by the positive effect of thermal increase on the reactivity of silica fume in UHPC mixture. Above 200 °C, bond strength significantly reduces; for instance, a decrease by about 70% is observed at 800 °C. The decreases in compressive and bond strengths for temperatures above 400 °C are related to the changes of phase composition of UHPC matrix (as revealed by X-ray powder diffraction) and the changes in microstructure including the increase of porosity (verified by mercury intrusion porosimetry and observation of confocal microscopy) and development cracks detected by scanning electron microscopy. Future research should investigate the effect of relaxation of prestressing reinforcement with increasing temperature on bond strength reduction by numerical modelling.

Study on Energy-Saving Residential Building Structures of Multi-Ribbed Composite Walls with High Performance Concrete

2006 ◽  
Vol 302-303 ◽  
pp. 444-450
Author(s):  
Yin Zhang ◽  
Qian Feng Yao ◽  
Yong Gang Ding
Keyword(s):  
Energy Saving ◽  
High Performance ◽  
High Performance Concrete ◽  
Residential Building ◽  
Economic Benefits ◽  
Building Structures ◽  
New Energy ◽  
Good Energy ◽  
Saving Effect ◽  
Seismic Behaviors

In this paper, the study and application of an entirely new energy-saving residential building structure, whose wall is constructed with multi-ribbed composite wall and latent frame. Based on experimental research and theoretical analysis, it was found that the structure system had good seismic behaviors, strong structure adaptability and good energy-saving effect. At the same time, notable social and economic benefits have been shown in several examples.

Advances in Research on Influence of Raw Materials on Workability of Fresh Concrete: A Review

2009 ◽  
Vol 405-406 ◽  
pp. 83-88 ◽  
Author(s):  
Gai Fei Peng ◽  
Zhan Qi Guo ◽  
Piet Stroeven ◽  
Ri Gao ◽  
Jiu Feng Zhang
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Fresh Concrete ◽  
Raw Materials ◽  
Experimental Tests ◽  
Solid Particles ◽  
Future Research ◽  
Negative Effect ◽  
The Relationship ◽  
Positive Effect

A literature review was carried out to identify advances in research on workability of fresh concrete via both experimental tests and modeling, especially high performance concrete and self-compacting concrete. As to the relationship between fluidity of concrete and that of paste, future research can be conducted in two aspects, i.e. one is the influence of the quantity of paste in concrete, and another is the influence of fluidity of paste affected by a couple of factors. Most literature proved that the flow of concrete depends both on positive effect and negative effect, the former promote fluidity, such as dispersing, filling and lubricating, and the latter restricts fluidity, such as formation of particle coagulation, an increase of wettable surface of solid particles and mechanical interlock.

scholarly journals Influence of Percentage Replacement of Metakaolin on Different Concrete Types Exposed to Internal Sulphate Attack

2018 ◽  
Vol 7 (4.20) ◽  
pp. 514
Author(s):  
Hadeel K. Awad ◽  
Rawaa K. Aboud ◽  
Shatha D. Mohammed
Keyword(s):  
Tensile Strength ◽  
Flexural Strength ◽  
High Performance ◽  
High Performance Concrete ◽  
Splitting Tensile Strength ◽  
Fine Aggregate ◽  
Sulphate Attack ◽  
Concrete Properties ◽  
Reactive Powder ◽  
Positive Effect

This research presents an experimental investigation on the influence of metakaolin replacement percentage upon some properties of       different concrete types. Three types of concrete were adopted (self- compacted concrete, high performance concrete and reactive powder concrete) all of high sulphate (SO3) percentage from the fine aggregate weight, 0.75%.Three percentages of metakaolin replacement were selected to be studied (5, 7 and 10) %. Three types of concrete properties (compressive, flexural and splitting tensile strength) were adopted to achieve better understanding for the influence of adding metakaolin.. The output results indicated that the percentage of metakaolin had a different level of positive effect on the compressive strength for both including and excluding of internal sulphate attack. This effect reached at 28 days of curing to (11.86, 10.22 and 4.75) % in case of excluding sulphate attack and to (13.82, 11.47and 6.53) % in the other case for SCC, HPC and RPC respectively. It can be concluded that the effect of metakaolin in both SCC and HPC are more influence than in RPC. Splitting and flexural strength have showed a similar behavior, flexural strength increased by (15.38, 9.42 and 5,84) % at age of 28 days when the sulphate attack is excluded, while it was (14.02, 10.66 and 4.28)% in case of sulphate attack included for SCC,HPC and RPC respectively. The response of splitting tensile strength for both including and excluding of sulphate attack reached to (13.03, 12.95 and 9.17) % and (16.88, 10.33 and 6.74) % respectively for SCC, HPC and RPC.   

scholarly journals Sustainable Recycling of High-Strength Concrete as an Alternative to Natural Aggregates in Building Structures

2021 ◽  
Vol 13 (8) ◽  
pp. 4286
Author(s):  
Barbara Sadowska-Buraczewska ◽  
Małgorzata Grzegorczyk-Frańczak
Keyword(s):  
Bearing Capacity ◽  
High Performance ◽  
High Performance Concrete ◽  
High Strength ◽  
Recycled Aggregate ◽  
Building Structures ◽  
Load Bearing Capacity ◽  
Load Bearing ◽  
Lower Load ◽  
Natural Aggregates

The application of recycled coarse aggregates (RCA) in high-performance concrete (HPC) was analyzed in the article. In the paper, the behavior of HPC with coarse recycled aggregate and natural coarse aggregate (NCA) was compared. Short-term experiments were conducted, including concrete deformation, deflection, load bearing capacity, and cracking of beams. The analysis involved reinforced concrete T-beams made in 100% of RCA or NCA. The studies indicated that the beams with recycled aggregate are characterized by greater deflection and 7.6% lower load bearing capacity in comparison to the beams with NCA. Substitution of coarse natural aggregate with RCA reduced the compressive and tensile strengths by 20 and 26 (%), whereas and the modulus of elasticity was decreased by 15%.

Seismic performance of a full-scale, reinforced high-performance concrete building. Part II: Analytical study

2008 ◽  
Vol 35 (8) ◽  
pp. 849-862 ◽  
Author(s):  
Sébastien Mousseau ◽  
Patrick Paultre ◽  
Jacky Mazars
Keyword(s):  
High Performance ◽  
Damage Mechanics ◽  
High Performance Concrete ◽  
Full Scale ◽  
Building Structures ◽  
Test Results ◽  
Seismic Behaviour ◽  
Analysis And Design ◽  
Advantages And Disadvantages ◽  
Concrete Building

Full-scale tests provide valuable information on the characteristics of building structures that can be used to evaluate design methods, to calibrate modelling techniques, and to determine damage corresponding to loading levels. These tests are scarce due to the enormous requirements in testing space and specialized testing equipment. The seismic behaviour of a full-scale, two-storey, reinforced high-performance concrete building designed with moderate ductility detailing is evaluated by pseudo-dynamic testing, during which increasing seismic loads are applied, resulting in increasing levels of permanent damage to the structure. This paper presents the analytical predictions of the test results using a global force–displacement parameters approach and a refined approach, half-way between global modelling and finite element modelling, using force–strain parameters and damage mechanics principles. Identification of the parameters required to describe the response parameters are presented together with a description of the numerical procedures used in each approach. It is shown that the predictions are in good agreement with the test results. Advantages and disadvantages of each approach are highlighted in the context of performance-based analysis and design.

Two Options of Self-Curing of High Performance Concrete

2018 ◽  
Vol 272 ◽  
pp. 88-93 ◽  
Author(s):  
David Pytlík ◽  
Vlastimil Bilek
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Internal Curing ◽  
Cement Matrix ◽  
High Dose ◽  
Negative Effects ◽  
Cement Ratio ◽  
Polymer Curing ◽  
The Matrix ◽  
Mixing Water

Some effects of self-curing on the mechanical properties of High Performance Concrete (HPC) are discussed in this paper. The matrix of HPC is very dense and it is very difficult to deliver the curing water into the cement matrix. Two different materials in different dosages were selected to examine self-curing. Polymer curing agent (PCA) was selected as the first, and 0.2% 0.4% 0.6% and 0.8% of PCA were added by weight of cement. This additive should allow the physicochemical binding of a larger portion of the mixing water and then release it slowly for better hydration without negative effects on the products. Pre-soaked slag of 0/4 mm was tested as another source of water for internal curing. The slag was also dosed in 10%, 15%, 20% and 30% volume of sand with the fraction 0/4 mm. Referential HPC was a high-dose cement that consumes a large amount of water for hydration. The water/cement ratio was 0.2. Metakaolin was added to improve the properties of fresh and hardened HPC.

scholarly journals Loosening Wool Machines

2019 ◽  
Vol 8 (4) ◽  
pp. 3650-3655
Keyword(s):  
Energy Efficiency ◽  
Structural Design ◽  
High Performance ◽  
Low Energy ◽  
High Quality ◽  
Primary Processing ◽  
Low Energy Consumption ◽  
Consumption Energy ◽  
Natural Characteristics ◽  
Positive Effect

This article provides information about the technology of primary processing of wool and the feeding part of the baking machine. It analyzes the operating principle and types of baking machines at the enterprise of primary processing of wool. The disadvantages of baking machines affecting the product are considered. The principle of work and the design of new baking machines for the manufacture of quality products are proposed. The article provides information about the technology of primary processing of wool. Studied the mechanisms of machines for the production of wool and identified their design flaws. The designs and sizes of the pegs of the peg drum are analyzed. The designs of the loosening machines used in the loosening process were studied. The types and principles of baking machines working at the enterprises of primary processing of wool are analyzed. The technical characteristics of the machines are given. The negative aspects of the details of the mechanical impact on the product are noted. Defects of baking machines and their effect on the product are explained. The design and operational principle of a new spraying machine for the preparation of high-quality products is proposed. The proposed characteristics of the machine have high performance, structural design, impact on the product, low energy consumption, energy efficiency and effective loosening. In this machine, the optimal version of parts that have a positive effect on the natural characteristics of the product is selected

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