Effect of Superplasticizers on the Workability of Concrete as Evident from Apparent Viscosity, Yield Stress and Zeta-Potential

1992 ◽  
Vol 289 ◽  
Author(s):  
R.I.A. Malek ◽  
D.M. Roy
Keyword(s):  
Yield Stress ◽  
Apparent Viscosity ◽  
Fresh Concrete ◽  
Low Cost ◽  
Aggregate Size ◽  
Unit Weight ◽  
Microstructural Development ◽  
Concrete Durability ◽  
Concrete Technology ◽  
The Individual

AbstractModem concrete technology projections indicate a great expansion in low-cost and time efficient construction. Mixture designers will likely be more concerned with the developments in concrete making materials. Among those is the effective use of chemical admixtures and superplasticizers which will lower the water to cement ratio but will still give a dense workable concrete. An investigation of the workability of fresh concrete and the effect of superplasticizers should, therefore, constitute an essential part of modem concrete durability studies.In this paper we report part of the work on rheological properties of fresh concrete. Various concrete samples covering a range of compositions that are commonly used for highway pavements are prepared. The proportioning parameters are: cement content, aggregate size, gradation and sphericity-roundness, and water and superplasticizer contents. The individual solid ingredients were characterized and the fresh concrete properties were assessed by the slump, two-point workability (Tattersall's) apparatus, air pressure and unit weight methods. The effects of superplasticizer on the apparent viscosity and yield stress of concrete are discussed and the relevance of the findings for field applications (handling of fresh concrete) are discussed. Also discussed are the implications for microstructural development.

scholarly journals ACCURACY ASSESSMENT OF UNDERWATER PHOTOGRAMMETRIC THREE DIMENSIONAL MODELLING FOR CORAL REEFS

2016 ◽  
Vol XLI-B5 ◽  
pp. 821-828 ◽  
Author(s):  
T. Guo ◽  
A. Capra ◽  
M. Troyer ◽  
A. Gruen ◽  
A. J. Brooks ◽  
...  
Keyword(s):  
Coral Cover ◽  
Accuracy Assessment ◽  
Low Cost ◽  
Three Dimensional ◽  
Point Clouds ◽  
3D Modelling ◽  
Relative Accuracy ◽  
3D Point Clouds ◽  
The Individual ◽  
Working Distance

Recent advances in automation of photogrammetric 3D modelling software packages have stimulated interest in reconstructing highly accurate 3D object geometry in unconventional environments such as underwater utilizing simple and low-cost camera systems. The accuracy of underwater 3D modelling is affected by more parameters than in single media cases. This study is part of a larger project on 3D measurements of temporal change of coral cover in tropical waters. It compares the accuracies of 3D point clouds generated by using images acquired from a system camera mounted in an underwater housing and the popular GoPro cameras respectively. A precisely measured calibration frame was placed in the target scene in order to provide accurate control information and also quantify the errors of the modelling procedure. In addition, several objects (cinder blocks) with various shapes were arranged in the air and underwater and 3D point clouds were generated by automated image matching. These were further used to examine the relative accuracy of the point cloud generation by comparing the point clouds of the individual objects with the objects measured by the system camera in air (the best possible values). Given a working distance of about 1.5 m, the GoPro camera can achieve a relative accuracy of 1.3 mm in air and 2.0 mm in water. The system camera achieved an accuracy of 1.8 mm in water, which meets our requirements for coral measurement in this system.

scholarly journals Microstructural Dynamic Study of Grain Growth

1985 ◽  
Vol 63 ◽  
Author(s):  
M. P. Anderson ◽  
G. S. Grest ◽  
D. J. Srolovitz
Keyword(s):  
Monte Carlo ◽  
Grain Growth ◽  
Materials Science ◽  
Primary Recrystallization ◽  
Lattice Points ◽  
Microstructural Development ◽  
Continuous Systems ◽  
Monte Carlo Techniques ◽  
Topological Features ◽  
The Individual

The complete prediction of microstructural development in polycrystalline solids as a function of time and temperature is a major objective in materials science, but has not yet been possible primarily due to the complexity of the grain interactions. The evolution of the polycrystalline structure depends upon the precise specification of the coordinates of the grain boundary network, the crystallographic orientations of the grains, and the postulated microscopic mechanisms by which elements of the boundaries are assumed to move. Therefore, a general analytical solution to this multivariate problem has not yet been developed. Recently, we have been able to successfully incorporate these aspects of the grain interactions, and have developed a computer model which predicts the main features of the microstructure from first principles [1,2]., The polycrystal is mapped onto a discrete lattice by dividing the material into small area (2d) or volume (3d) elements, and placing the centers of these elements on lattice points. Interactions and dynamics are then defined for the individual elements which are analagous to those postulated in continuous systems. This discrete model preserves the topological features of real materials, and can be studied by computer simulation using Monte Carlo techniques. In this paper we report the application of the Monte Carlo method to the metallurgical phenomenon of grain growth with isothermal annealing. Extension of the model to treat primary recrystallization is presented elsewhere [3,4].

The Ethics of Conducting E-Mail Surveys

2004 ◽  
pp. 114-129 ◽  
Author(s):  
Sandeep Krishnamurthy
Keyword(s):  
Low Cost ◽  
Ethical Problem ◽  
Sampling Procedure ◽  
Academic Field ◽  
Mail Surveys ◽  
Effective Form ◽  
The Individual ◽  
Individual Contact ◽  
E Mail

E-mail is a low-cost and highly effective form of individual contact for primary research. However, researchers who contact strangers for their survey research through e-mail are, in essence, sending them Spam. Some academic researchers might argue that due to the low volume and infrequent nature of their surveys and the general positive perception of academia, their e-mail surveys do not add to the Spam problem. However, this is an insufficient resolution of the ethical problem. This chapter examines one solution to avoid this problem—the use of respondent permission prior to contact. Obtaining respondent permission is tricky and can be costly. But, it may be the only long-term solution. Importantly, using this approach could lead to a loss of randomness in the sampling procedure due to self-selection. Ideas for implementation of a permission-based contact system at the individual researcher and academic field level are provided at the end.

scholarly journals Influence of Carbide-Promoting Elements on the Microstructure of High-Silicon Ductile Iron

2020 ◽  
Vol 14 (4) ◽  
pp. 1152-1161 ◽  
Author(s):  
M. Riebisch ◽  
B. Pustal ◽  
A. Bührig-Polaczek
Keyword(s):  
Ductile Iron ◽  
Mutual Influence ◽  
Negative Impact ◽  
Raw Materials ◽  
Low Cost ◽  
Metallographic Analysis ◽  
Steel Scrap ◽  
Experimental Investigations ◽  
High Silicon ◽  
The Individual

Abstract Because of its low cost, steel scrap is one of the most important raw materials for the production of ductile iron (DI). The amount of carbide-promoting elements in steel scrap, such as chromium, manganese, molybdenum, niobium and vanadium, is expected to increase in the future. Most of these elements have a negative impact on the microstructure and mechanical properties of DI. The solubility of carbide-promoting elements in solid solution-strengthened DI materials, standardized in DIN EN 1563:2011, is modified by the high silicon content. For these new materials, the tolerance limits for carbide-promoting elements and their mutual influence must be known to ensure a sustainable production process. To investigate the individual and combined impact of carbide-promoting elements on the carbide content in high-silicon ductile iron EN-GJS-500-14, experimental investigations and thermodynamic–kinetic microstructure simulations were carried out. Microstructure was characterized using metallographic analysis, and quantitative relations between chemical composition and microstructure were developed by means of regression analysis. Besides this quantitative analysis, it was found that the formation of grain boundary carbides can be detected via thermal analysis. Furthermore, experiments and simulations showed that vanadium promotes the formation of chunky graphite in high-silicon DI castings.

scholarly journals Low-Cost IoT Remote Sensor Mesh for Large-Scale Orchard Monitorization

2020 ◽  
Vol 9 (3) ◽  
pp. 44
Author(s):  
Leonor Varandas ◽  
João Faria ◽  
Pedro Gaspar ◽  
Martim Aguiar
Keyword(s):  
Real Time ◽  
Large Scale ◽  
Low Cost ◽  
Experimental Tests ◽  
Remote Measurement ◽  
Land Protection ◽  
Remote Monitoring System ◽  
Solar Powered ◽  
The Individual ◽  
System Nodes

Population growth and climate change lead agricultural cultures to face environmental degradation and rising of resistant diseases and pests. These conditions result in reduced product quality and increasing risk of harmful toxicity to human health. Thus, the prediction of the occurrence of diseases and pests and the consequent avoidance of the erroneous use of phytosanitary products will contribute to improving food quality and safety and environmental land protection. This study presents the design and construction of a low-cost IoT sensor mesh that enables the remote measurement of parameters of large-scale orchards. The developed remote monitoring system transmits all monitored data to a central node via LoRaWAN technology. To make the system nodes fully autonomous, the individual nodes were designed to be solar-powered and to require low energy consumption. To improve the user experience, a web interface and a mobile application were developed, which allow the monitored information to be viewed in real-time. Several experimental tests were performed in an olive orchard under different environmental conditions. The results indicate an adequate precision and reliability of the system and show that the system is fully adequate to be placed in remote orchards located at a considerable distance from networks, being able to provide real-time parameters monitoring of both tree and the surrounding environment.

Red cell and plasma volumes of the rat and of tissues during cold acclimation

1961 ◽  
Vol 16 (3) ◽  
pp. 557-561 ◽  
Author(s):  
Newton B. Everett ◽  
Lorna Matson
Keyword(s):  
Blood Cell ◽  
Blood Volume ◽  
Control Level ◽  
The Body ◽  
Unit Weight ◽  
Red Cell ◽  
Total Blood ◽  
Cell Content ◽  
Blood Cell And Plasma ◽  
The Individual

Red cell and plasma volumes of the total rat and of its individual tissues and organs were determined for animals exposed to 5 C for 4 hr, 24 hr, 2 weeks, and 6 weeks. In addition, the tissue hematocrit ratios were determined. These values were compared with those of rats kept at 24 C. Fe59-labeled erythrocytes and I131-labeled albumin were given intravenously, and after mixing the rats were frozen in liquid nitrogen. The organs and tissues were removed in the frozen state, assayed for radioactivity, and blood cell and plasma volumes were calculated on a unit weight basis. Significant changes in blood cell and plasma volumes were observed for the total rat and for many of the individual organs. There was a significant increase in the red cell content of the total rat within 24 hr of cold exposure. After 6 weeks, total blood volume was increased by approximately 20% over the control level and the increase in erythrocyte volume was slightly more than the increase in plasma volume. The hematocrit ratio of heart blood was 44.8 after 6 weeks exposure compared with 41.5 for controls. In general, it can be said that the somatic parts of the body showed increases in blood volume whereas the visceral parts had decreased volumes. Submitted on August 15, 1960

scholarly journals Making a “Pledge”: Moral Suasion and Health Promotion Practice

Challenges ◽  
2018 ◽  
Vol 9 (2) ◽  
pp. 39
Author(s):  
Glenn Laverack
Keyword(s):  
Health Promotion ◽  
Harm Reduction ◽  
Low Cost ◽  
Health Behaviours ◽  
Individual Behaviour ◽  
Collective Levels ◽  
Moral Suasion ◽  
The Individual ◽  
Health Promotion Practice ◽  
Individual Behaviour Change

Moral suasion offers a versatile and low-cost approach to influence social norms and risky health behaviours, but is often neglected in health promotion in favour of using educational approaches. The purpose of this paper is to discuss the challenges and the benefits of using moral suasion in health promotion. Past and present experiences of using moral suasion to promote health are discussed in conjunction with other approaches, such as harm reduction. The challenge of using moral suasion as an approach is that it focuses on individual behaviour change, rather than addressing the broader structural causes of poor health. However, the paper concludes that the versatility of the moral suasion approach and the success of using “pledges” means that it can be an important intervention, alongside other educational and motivational techniques, to help to change behaviours at the individual and collective levels.

scholarly journals The BErkeley Atmospheric CO<sub>2</sub> Observation Network: field calibration and evaluation of low-cost air quality sensors

2018 ◽  
Vol 11 (4) ◽  
pp. 1937-1946 ◽  
Author(s):  
Jinsol Kim ◽  
Alexis A. Shusterman ◽  
Kaitlyn J. Lieschke ◽  
Catherine Newman ◽  
Ronald C. Cohen
Keyword(s):  
Air Quality ◽  
San Francisco ◽  
Low Cost ◽  
A Priori ◽  
Sensor Nodes ◽  
Bay Area ◽  
Attractive Option ◽  
Global Background ◽  
Zero Offset ◽  
The Individual

Abstract. The newest generation of air quality sensors is small, low cost, and easy to deploy. These sensors are an attractive option for developing dense observation networks in support of regulatory activities and scientific research. They are also of interest for use by individuals to characterize their home environment and for citizen science. However, these sensors are difficult to interpret. Although some have an approximately linear response to the target analyte, that response may vary with time, temperature, and/or humidity, and the cross-sensitivity to non-target analytes can be large enough to be confounding. Standard approaches to calibration that are sufficient to account for these variations require a quantity of equipment and labor that negates the attractiveness of the sensors' low cost. Here we describe a novel calibration strategy for a set of sensors, including CO, NO, NO2, and O3, that makes use of (1) multiple co-located sensors, (2) a priori knowledge about the chemistry of NO, NO2, and O3, (3) an estimate of mean emission factors for CO, and (4) the global background of CO. The strategy requires one or more well calibrated anchor points within the network domain, but it does not require direct calibration of any of the individual low-cost sensors. The procedure nonetheless accounts for temperature and drift, in both the sensitivity and zero offset. We demonstrate this calibration on a subset of the sensors comprising BEACO2N, a distributed network of approximately 50 sensor “nodes”, each measuring CO2, CO, NO, NO2, O3 and particulate matter at 10 s time resolution and approximately 2 km spacing within the San Francisco Bay Area.

Sign in / Sign up

Export Citation Format

Share Document