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Chp-8

Dr. Aminul Islam Laskar Laxmi Publications PDF

Chapter

8

Rheology of Concrete

In this chapter, a description of fluid rheology and the different measurement techniques of rheological parameters of concrete are presented. Some important definitions related to concrete rheology has also been included so that the reader may easily understand the principles of fluid rheology. Constitutive equations of fluid flow, thixotropy, dilatancy of concrete, wall effect, plug flow, particle migration, particle sedimentation and end effect have made the chapter more comprehensive to the readers. Finally, complete description of the available concrete rheometers including the conceptual design, actual design and derivation of torque-speed relationship is provided.

RHEOLOGY

Rheology is the scientific study of the deformation and flow of materials under load. A material is said to flow, if under the action of constant shear stress, its deformation increases with time.

Both viscous and plastic materials flow and, as they exhibit little or no deformational recovery on unloading, the strain energy of distortion is usually stored as potential energy.

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1    Introduction

David Hickman M-Y Books ePub

CHAPTER 1

Introduction

The importance of PFI to the construction industry

The Private Finance Initiative (PFI) and more recently Public Private Partnerships (PPP) have become an increasingly important area for construction companies, consultants and other players in the construction sector. Annual turnover for the UK construction sector is approximately £60 billion. The PFI element of this is now about £3 billion or 5 per cent and is set to grow further.

Since its launch in 1992 – and after many teething troubles in the mid 1990s – the PFI has become an essential part of the procurement strategy of central and local government in the UK.

Significant PFI projects have been delivered in the following sectors:

The number of projects underway in particular sectors tends to fluctuate according to current government policy. So, for example, the highways and prisons sectors have been quiet since the 1997 election although both now seem likely to take off again.

In most of the other sectors mentioned above there are many new projects coming through the procurement process. Some new sectors such as social housing (local authorities) and flood defence (Environment Agency/local authorities) show good potential.

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2: External Morphology

Vacante, V. CABI PDF

2  External Morphology

Integument

Body Division

In the Acarina, the developing integument appears first as

­undifferentiated tissue, covered by a thin layer of ‘cuticulin’ and separated from the underlying ‘epidermis layer’ by a ‘Schmidt layer’. As development proceeds, the anatomical organization of the integument undergoes further transformation and shows from the outside inwards an ‘epicuticular layer’ (the epicuticle), a ‘procuticular layer’ (the procuticle), which consists of an outer

‘exocuticular layer’ and an inner ‘endocuticular layer’, an underlying Schmidt layer, an epidermal layer and, finally, a basal lamina set below the epidermis. This anatomical organization underlies the external ‘cerotegument’; this consists of an outer

‘cement layer’ and an underlying ‘wax layer’ that are set on the outer epicuticle and the underlying inner epicuticle (Fig. 2.1).

Together, the epicuticular complex – the cerotegument and the outer and inner epicuticle – provides multilayered protection. The cerotegument is a secreted layer that is formed by the epidermis, from which ‘pore canals’ travel towards the inner epicuticle, which includes an underlying cuticulin layer and a covering cuticulin layer. Overall, the cerotegument may have various consistencies, but its cement layer is dense and frequently sculptured. Together, the wax and cement layers of the cerotegument are involved in the regulation of water loss and/or water intake (Alberti et al., 1981; Norton et al., 1997).

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12 : The Bubble Bursts

Raye Ringholz Utah State University Press ePub

The names were appealing. Absaraka. Aladdin. Apache. Arrow. Atomic. Black Jack. Jolly Jack. Lucky Strike. King Midas. Newspaper readers followed daily listings of uranium stocks and figured on all of the money they could have made if they had had the nerve to buy. Many stocks went up thirty—even sixty—times the offering price in days. Soon the temptation to gamble a few bucks was irresistible. Those who had lagged behind took the plunge.

And it seemed they were in good company. The big boys were getting into the picture. How could you go wrong when Atlas, United States Vanadium and Vanadium Corporation of America, Anaconda, Homestake Mining Company, National Lead, Vitro, Kerr-McGee Oil Industries, Climax Molybdenum—to say nothing of the Santa Fe Railroad and New Jersey Zinc Company—had succumbed to the uranium frenzy? Your ordinary working guy couldn’t get out there and dig the stuff himself. But he could have the fun of fantasizing about the millions he might make on a ten-dollar investment.

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Case study

Tony Baxendale Chartridge Books Oxford ePub

CHAPTER 5

Operational Monitoring and Control

Project Progress Control

A project is dynamic and must respond to changing conditions if it is to be completed successfully. There is a continual need for reassessment and reappraisal of the project plan. Factors affecting an existing plan will include:

     Changes in the technical specification.

     Changes in the required dates.

     Changes in relative priorities.

     Revision of activity duration estimates.

     Reassessment of resource requirements for individual activities.

     Changes in resource availabilities.

     Inaccuracies in planned sequences.

     Technical difficulties.

     Failure of deliveries.

     Unexpected weather conditions.

It is therefore necessary to have a monitoring system which generates feedback that enables corrective action to be taken. There are usually some deviations that do not allow the project to proceed in accordance with the plan. It is therefore necessary to review operations periodically and to update or replan when a change is revealed. Close or detailed control of resources is not always considered. Close control is where resources are fully considered during the initial stages of the project and the timing of every activity is fixed, so as to obtain optimum use of resources. Flexible or overall control is often exercised during the initial scheduling of the project. Flexible control only considers resources to avoid peaks in key resources or those resources that are in limited supply. The frequency of review will depend on the overall duration of the project and the timescale on which the activities are measured. In general a weekly programme should be reviewed weekly and a daily programme daily.

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