scholarly journals Effect of Placing Self-Compacting Concrete Bottom up on the Quality of Bond Conditions

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2346
Author(s):  
Milena Kucharska ◽  
Piotr Dybeł
Keyword(s):  
Alternative Methods ◽  
Bond Properties ◽  
Self Compacting Concrete ◽  
Bottom Up ◽  
Pull Out ◽  
Test Elements ◽  
Concrete Elements ◽  
Steel Rebars ◽  
Bond Tests

A self-compacting concrete (SCC) mixture, due to its special rheological properties, may be placed differently than in traditional variants. The paper presents the results of a study on the effect of a bottom-up placing direction on the quality of bond conditions between steel and self-compacting concrete. Elements with overall dimensions of 160 × 480 × 1600 mm consisting of elementary samples with dimensions of the bond test basic modules were constructed. Ribbed steel rebars with diameters of 16 mm were used and located in formworks perpendicularly to the concrete placing direction. Bond tests were carried out according to the pull-out method. The bottom-up placing contributed to the uniformity of the bond conditions quality in the test elements and an overall improvement of the bond properties, especially in its top part. Given the increasing implementation of alternative methods of mix placing and the promising results, the topic should be further investigated.

scholarly journals Effect of casting direction on bond of reinforcement in High Performance Self-Compacting Concrete (HPSCC)

2019 ◽  
Vol 262 ◽  
pp. 06004 ◽  
Author(s):  
Piotr Dybeł
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Bond Stress ◽  
Concrete Mixture ◽  
Experimental Program ◽  
Bond Properties ◽  
Self Compacting Concrete ◽  
Pull Out ◽  
Significant Change ◽  
Bond Characteristics

This paper presents the results of an investigation into the steel-to-concrete bond in high-performance self-compacting concrete (HPSCC) based on direct pull-out tests. Specifically, the effect of the casting direction on bond properties is examined. Two variants of concrete mixture casting were considered in this work: from the top and from the bottom of a mould with a single casting point at one edge. Horizontal specimens with transverse rebars distributed over their heights (480 mm) and lengths (1600 mm) were cast. The experimental program has shown that the direction of concreting plays an important role in the formation of the bond condition. In the case of casting a mixture from the bottom of a mould, in the lower part of a specimen there is no significant change of the bond stress. However, there is a strong improvement in the upper part. The phenomenon observed eliminates the top-bar effect. What is more, for the rebars situated in the upper part of a specimen, improvements in bond characteristics, such as the bond stiffness, bond strength and the effect of the rebar distance from the casting point are all observed in the case of casting a mixture from the bottom of a mould.

scholarly journals Home Mechanical Ventilation: A Patient’s Perspective Survey Study

2021 ◽  
Vol 18 (8) ◽  
pp. 4048
Author(s):  
Magdalena Kwiatosz-Muc ◽  
Bożena Kopacz
Keyword(s):  
Health Care ◽  
Mechanical Ventilation ◽  
Alternative Methods ◽  
Survey Study ◽  
Home Mechanical Ventilation ◽  
Patient’S Satisfaction ◽  
Satisfaction Index ◽  
Number Of Patients ◽  
The Difference

Background: An increasing number of patients included in home mechanical ventilation (HMV) care has been under observation for many years. The study aimed to assess the patients opinion concerning the expected and perceived quality of care in an HMV system and a patient’s satisfaction with care. Methods: In 2017, patients treated with HMV were surveyed in Poland with the modified SERVQUAL questionnaire. Results: One hundred correctly completed surveys were analyzed. Patient Satisfaction Index was high. In every examined area, the expectations were statistically significant larger than the perception of the services. The biggest gap was in the tangibility dimension and the smallest gap was in the empathy dimension. Perceived respect and understanding for a patient’s needs are close to the expectations. Conclusions: The level of satisfaction with health care among patients treated with HMV in majority of investigated components is high. Moreover, the difference between perceived and expected quality of health care in the HMV system was relatively small in the opinion of the patients themselves. Further investigations with alternative methods are needed.

scholarly journals Evaluation of Self-Compacting Concrete Strength with Non-Destructive Tests for Concrete Structures

2019 ◽  
Vol 9 (23) ◽  
pp. 5109 ◽  
Author(s):  
Miguel C. S. Nepomuceno ◽  
Luís F. A. Bernardo
Keyword(s):  
Compressive Strength ◽  
Concrete Strength ◽  
Surface Hardness ◽  
Pulse Velocity ◽  
Concrete Compressive Strength ◽  
Self Compacting Concrete ◽  
Coarse Aggregates ◽  
Pull Out ◽  
Concrete Maturity ◽  
Non Destructive

Self-compacting concrete (SCC) shows to have some specificities when compared to normal vibrated concrete (NVC), namely higher cement paste dosage and smaller volume of coarse aggregates. In addition, the maximum size of coarse aggregates is also reduced in SCC to prevent blocking effect. Such specificities are likely to affect the results of non-destructive tests when compared to those obtained in NVC with similar compressive strength and materials. This study evaluates the applicability of some non-destructive tests to estimate the compressive strength of SCC. Selected tests included the ultrasonic pulse velocity test (PUNDIT), the surface hardness test (Schmidt rebound hammer type N), the pull-out test (Lok-test), and the concrete maturity test (COMA-meter). Seven sets of SCC specimens were produced in the laboratory from a single mixture and subjected to standard curing. The tests were applied at different ages, namely: 1, 2, 3, 7, 14, 28, and 94 days. The concrete compressive strength ranged from 45 MPa (at 24 h) to 97 MPa (at 94 days). Correlations were established between the non-destructive test results and the concrete compressive strength. A test variability analysis was performed and the 95% confidence limits for the obtained correlations were computed. The obtained results for SCC showed good correlations between the concrete compressive strength and the non-destructive tests results, although some differences exist when compared to the correlations obtained for NVC.

Non-Destructive Identification of Defects in Power Support Structure Foundations by Means of Acoustic Techniques

2014 ◽  
Vol 606 ◽  
pp. 95-98
Author(s):  
Lukasz Sadowski
Keyword(s):  
Construction Industry ◽  
Support Structure ◽  
Air Voids ◽  
Impact Echo ◽  
Acoustic Techniques ◽  
Location Depth ◽  
Concrete Elements ◽  
Non Destructive ◽  
Made In

Prefabricated power support structure foundations are made in prefabrication plants where concrete is laid in layers in moulds. The quality of the prefabricated units depends mainly on proper concrete mixture compaction, which is usually effected by means of immersion vibrators. It happens that when the vibrator is withdrawn too quickly, defects, in the form of, e.g., air voids and zones of insufficiently vibrated concrete, appear. Modern non-destructive acoustic techniques, which in recent years have been increasingly commonly used in the construction industry, are highly suitable for testing concrete elements, particularly prefabricated concrete units. The non-destructive impact-echo technique is particularly useful for determining defect location depth and for locating defective areas.

Fiber Debonding Along a Crack Front in Paper

1998 ◽  
Vol 539 ◽  
Author(s):  
H. Kettunen ◽  
K. J. Niskanen
Keyword(s):  
Fracture Energy ◽  
Crack Front ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Bond Properties ◽  
Crack Line ◽  
Pull Out ◽  
Microscopic Damage ◽  
Debonding Process

AbstractWe follow the accumulation of microscopic damage ahead the crack tip in paper. The fiber debonding process varies even within each specimen because of large variation in fiber and bond properties. In general, stiff and weakly bonded fibers tend to debond as a rigid body while ductile or well bonded fibers pull out gradually in a process that propagates from the crack line to the fiber ends. Particularly in the latter case the network ruptures coherently rather than through debonding of single fibers. Experimental analysis and simulations show that fracture energy correlates closely with the size of the fracture process zone (FPZ) irrespective the nature of the debonding process. Only the cases of low bonding and stiff fibers seem to make an exception in that FPZ can grow in size without a corresponding increase in fracture energy.

scholarly journals Mortality of insects and quality of maize grains in hermetic and non-hermetic storage

2016 ◽  
Vol 20 (5) ◽  
pp. 487-492 ◽  
Author(s):  
Priscila C. Viebrantz ◽  
Lauri L. Radunz ◽  
Rafael G. Dionello
Keyword(s):  
Storage System ◽  
Alternative Methods ◽  
Modified Atmosphere ◽  
Chemical Methods ◽  
Hermetic Storage ◽  
Insect Mortality ◽  
Polyethylene Bags ◽  
Maize Grain ◽  
Storage Units

ABSTRACT Due to the need to improve the quality and safety of foods, chemical methods used to control grain pests have been replaced by alternative methods. For example, modified atmosphere within the storage units has been used. Therefore, the objective was to evaluate maize grain quality and mortality of insects of the species Sitophilus zeamais and Tribolium castaneum in hermetic and non-hermetic environments for 50 days of storage. The hermetic units consisted of polyethylene "bags" with capacity for 60 kg. A cage with 20 adults of each species and 200 g of maize was placed inside each unit. The oxygen level was quantified every five days. Evaluations of insect mortality and survival occurred at 10, 20, 30, 40 and 50 days of storage. At 0, 30 and 50 days, density, moisture and fungal incidence analyses were conducted. The airtight system is efficient in the control of insects, with satisfactory mortality values for both species. Insects favor the development of fungi during the storage, regardless of the storage system.

scholarly journals An 18-Month Analysis of Bond Strength of Hot-Dip Galvanized Reinforcing Steel B500SP and S235JR+AR to Chloride Contaminated Concrete

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 747
Author(s):  
Mariusz Jaśniok ◽  
Jacek Kołodziej ◽  
Krzysztof Gromysz
Keyword(s):  
Comparative Analysis ◽  
Bond Strength ◽  
Complex Geometry ◽  
Zinc Coating ◽  
3D Scanning ◽  
Steel Grade ◽  
Electrochemical Tests ◽  
Test Elements ◽  
Steel Rebars ◽  
Chloride Contaminated

This article describes the comparative analysis of tests on bond strength of hot-dip galvanized and black steel to concrete with and without chlorides. The bond effect was evaluated with six research methods: strength, electrochemical (measurements of potential, EIS and LPR), optical, and 3D scanning. The tests were conducted within a long period of 18 months on 48 test elements reinforced with smooth rebars ϕ8 mm from steel grade S235JR+AR and ribbed rebars ϕ8 mm and ϕ16 mm from steel grade B500SP. The main strength tests on the reinforcement bond to concrete were used to compare forces pulling out galvanized and black steel rebars from concrete. This comparative analysis was performed after 28, 180, and 540 days from the preparation of the elements. The electrochemical tests were performed to evaluate corrosion of steel rebars in concrete, particularly in chloride contaminated concrete. The behaviour of concrete elements while pulling out the rebar was observed using the system of digital cameras during the optical tests. As regards 3D scanning of ribbed rebars ϕ8 mm and ϕ16 mm, this method allowed the detailed identification of their complex geometry in terms of determining the polarization area to evaluate the corrosion rate of reinforcement in concrete. The test results indicated that the presence of zinc coating on rebars had an impact on the parameters of anchorage. In the case of ribbed rebars of 16 mm in diameter, the maximum values of adhesive stress and bond stiffness were reduced over time when compared to black steel rebars. Moreover, it was noticed that the stiffness of rebar anchorage in chloride contaminated concrete was considerably higher than in concrete without chlorides.

A critical review of cardiac rehabilitation in a digital era

2021 ◽  
Vol 16 (8) ◽  
pp. 1-9
Author(s):  
Hazel Nikolov ◽  
Julia Hubbard
Keyword(s):  
Cardiac Rehabilitation ◽  
Cardiac Event ◽  
Social Economic ◽  
Alternative Methods ◽  
Face To Face ◽  
Digital Era ◽  
The Uk ◽  
Economic Constraints ◽  
Traditional Approaches

Cardiac rehabilitation improves the outcomes of individuals following a cardiac event; however, only 50% of those eligible for cardiac rehabilitation in the UK sign up to a traditional face-to-face programme. The principal causes cited for non-attendance include living in a rural area, work or career commitments, lack of choice in location, gender, ethnicity and social economic constraints, and dislike of group participation. Alternative methods of delivery could ensure greater participation in cardiac rehabilitation activities, particularly among women, who are underrepresented. Studies into digital cardiac rehabilitation reveal improved quality of life, dietary intake and increased physical activity all equal to or an improvement compared to traditional approaches. Embracing digital approaches to cardiac rehabilitation is now timely with COVID-19 requirements for social distancing.

Bond behaviour of chemically prestressed textile reinforced concrete

2019 ◽  
Author(s):  
Katarzyna Zdanowicz ◽  
Boso Schmidt ◽  
Hubert Naraniecki ◽  
Steffen Marx
Keyword(s):  
Reinforced Concrete ◽  
Bond Strength ◽  
Crack Width ◽  
Research Programme ◽  
Textile Reinforced Concrete ◽  
Self Compacting Concrete ◽  
Bond Behaviour ◽  
Bond Slip ◽  
Laser Sensors ◽  
Pull Out

<p>The bond behaviour of concrete specimens with carbon textile reinforcement was investigated in the presented research programme. Pull-out specimens were cast from self-compacting concrete with expansive admixtures and in this way chemical prestress was introduced. The aim of the research was to compare bond behaviour between prestressed specimens and non-prestressed control specimens. During pull-out tests, the pull-out force and notch opening were measured with a load cell and laser sensors. Further, bond - slip and pull-out force - crack width relationships were drawn and compared for prestressed and non-prestressed specimens. Chemically prestressed specimens reached 24% higher bond strength than non-prestressed ones. It can be therefore concluded, that chemical prestressing positively influences the bond behaviour of concrete with textile reinforcement and thus better utilisation of its properties can be provided.</p>

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