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Reference

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References

V M Malhotra, N J Carino (Ed). Nondestructive Testing of Concrete, CRC Press, ASTM

International, USA, 2000.

V S Ramachandran, J J Beaudoin (Ed). Handbook of Analytical Techniques in Concrete

Science and Technology (Indian Edition), Standard Publishers Distributors, New Delhi,

2006.

E G Nawy. Fundamentals of High Performance Concrete, John Willey and Sons, Inc., New

York, 2001.

P C Aïtcin. High Performance Concrete, E & FN Spon, London, 1998.

P K Mehta, P J M Monteiro. Concrete: Microstructure, Properties and Materials, Mc Graw

Hill Inc., New York, 2006.

A M Neville, J J Brooks. Concrete Technology, Pearson Education (Singapore) Pte Ltd, Delhi,

2002.

A M Neville. Properties of Concrete, ELBS Singapore Edition, 2003.

M S Shetty. Concrete Technology, S Chand & Company Ltd, New Delhi, 2008.

M L Gambhir. Concrete Technology, Tata Mc Graw Hill Compamy, New Delhi, 2004.

H F W Taylor. Cement Chemistry, Thomas Telford Publishing, London, 1998.

S Tangstermsirikul. Durability and Mix Design of Concrete, Thammasat University, Thailand,

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Chp-5

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Chapter

5

Concre te in Plastic and Early Stage

The contents of this chapter, cover the problems of concrete that may take place in plastic stage and early stage of concrete. The occurrences such as settlement, plastic shrinkage and thermal cracks may lead to future durability problems if these are not properly appreciated and treated.

SETTLEMENT CRACKS

Settlement cracks arise due to the differential settlement of the concrete. Settlement of concrete happens during the plastic state when the concrete had been already placed but still does not reach its time of setting. Settlement is usually accompanied by bleeding of the concrete. Settlement cracks may occur by various mechanisms as stated below.

(i)

There are obstructing subjects to the setting concrete such as reinforcing steels

(Figs. 5.1 and 5.2). In slabs or beams, cracks can happen on the top surface of the concrete in the direction along the reinforcing bars. Cracks may be happen along the main reinforcements (Fig. 5.2(a)) or along the stirrups (Fig. 5.2(b)). Voids under the reinforcing bars are frequently formed due

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Prelims

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Foreword

I feel privileged to write the foreword of the book, entitled Concrete Technology by Dr Aminul

Islam Laskar, Associate Professor of Civil Engineering, National Institute of Technology Silchar.

From a pile of books on the subject, what makes this book interesting is the effort taken by the author to make the subject very interesting to the first timers as well as to the professionals. The author presented the concepts in a very lucid and simple manner to be attractive for the target audience. The book covers most of the recent developments in concrete material science. Also, extensive references are made to IS codes and practical design considerations throughout the book for easy clarity and understanding. Thus the book should serve as a textbook for undergraduates and a reference compendium for practicing civil engineers. I hope the prospective readers will greatly benefit from the book.

Dr Bishwajit Bhattacharjee

Professor of Civil Engineering

Indian Institute of Technology,

New Delhi

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Chp-12

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Chapter

12

High-Performance Concrete

High strength concrete seems to have become the key word in today’s concrete technology. In the early 1940s, 30 N/mm2 (at 28 day) was considered to be the representative of high strength concrete. This level jumped to 50 N/mm2 in the late 1950s and early 1960s. Concrete strengths of 100–130 N/mm2 is now being viewed as the criteria for high strength. Just how far we can go to reach an ultimate in strength in the future is nobody’s guess. High strength concrete is among the most significant ideal materials available in the market to rehabilitate and enhance the performance of the nation’s crumbling infrastructure such as assisting the widespread problems of deteriorated bridge structures and tall buildings. In the precast and prestressed concrete industries, the use of high strength concrete has resulted in a rapid turnover of moulds, higher productivity and less loss of products during handling and transportation. The well-known ‘Laws’ and ‘rules of thumb’ that apply to normal strength concrete may well not apply to high strength concrete. ACI 363R and other ACI guidelines address some recommendations on placing, compacting and curing of high strength concrete. However design of high strength concrete entails detailed knowledge of properties of local materials, i.e., aggregates, cement and pozzolanic admixtures.

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Chp-15

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Chapter

15

Non-destruc tive

Testing of Concrete

The need for non-destructive testing (NDT) of concrete may arise due to variety of reasons.

These are: assessment of structural integrity or safety following material deterioration, structural damage caused by fire, fatigue or overload, adequacy of members suspected to contain unspecified material, fault in design, and monitoring long term changes in material properties and structural performance. NDT is generally defined as not impairing the intended performance of element or member under test, and when applied to concrete is taken to include methods which cause localized surface zone damage. All NDT methods can be performed directly on the in-situ concrete without removal of a sample.

Broadly speaking, there are two classes of NDT methods. The first class consists of those methods that are used to estimate strength. The surface hardness, penetration resistance, pullout, pull-off, break-off, and maturity techniques belong to this category. Some of these are not truly

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