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ABSTRACT

High performance concrete (HPC) represents a rather recent development in

concrete materials technology. HPC is not a commodity but a range of products,

each specifically designed to satisfy in the most effective way the performance

requirements for the intended application

The quality or durability of concrete is not only a function of its compressivestrength but as much of its porosity (impermeability)

Durability of concrete identifies the ability of the concrete to resist degradation due

to environmental exposure conditions.

The performance characteristics related to durability include freeze-thaw

resistance, scaling resistance, abrasion resistance, chloride ion penetration, alkali-

silica reactivity, and sulphate resistance.

This project report aims the comparison between the normal concrete and the HPC

undersulphate attackfrom the point of view of durability.

Chemical attack occurs in which sulphates of magnesium, calcium, and sodium, in

solution react with hydrated lime and hydrated calcium aluminate to form a

calcium sulphate and calcium sulfoaluminate, whose formation causes expansion

and disruption of the cement paste

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CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION OF CONCRETE

Concrete, which has the distinction of being the largest man made material onEARTH, is in essence, a proven durable and maintenance free material. A large

number of structures constructed decades back and standing in good shape today,

bear testimony to this. However this image of concrete has been tarnished in recent

years, mainly due to the phenomenon of premature deterioration of concrete

structures being witnessed all over the world. More extensive use of concrete is

limited by its low tensile strength, susceptibility to severe moisture and

temperature changes and its low resistance to chemical attack under adverse

environmental conditions. Expenditure on maintenance, protection and repair /rehabilitation is rising alarmingly, reaching nearly 40 % of the total expenditure on

construction in some of the industrialized countries.

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1.2 HIGH PERFORMANCE CONCRETE

Any concrete which satisfy certain criteria proposed to overcome limitation of

conventional concrete maybe called as High Performance Concrete (HPC). It may

include concrete which provides either substantially improved resistance to

environmental influence (durability in service) or substantially increased structural

capacity while maintaining adequate durability. It may also include concrete,

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which significantly reduce construction time to permit rapid opening or reopening

of roads to traffic, without compromising long term serviceability.

1.2.1 DEFINITION:

a) The American Concrete Institute committee has defined HPC in ACI Special

Publication SP-140 (Goodspeed) as

Concrete that meets special performance and uniformity requirements that can not

always be obtained by using conventional ingredients, normal mixing procedureand typical curing procedures. These requirements may include the following

enhancements.

Ease of placement in consolidation without affecting strength

Long term mechanical properties.

Early high strength

Toughness

Volume stability, and

Longer life in severe environment.

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b) AStrategic Highway research program (SHRP) study reported by

Goodspeed (1996) defined HPC as consisting of :

maximum w/c ratio of 0.35.

minimum durability factor of 80% (as determined by ASTM C 666,

Procedure A and 3).

minimum compressive strength of either a) 21 MPa after 4 hours, b) 34

MPa within 24 hours or 69 Mpa after 28 days.

c) Forster has defined HPC as

a concrete made with appropriate materials combined according to a selected

mix design and properly mixed, transported, placed, consolidated, and cured so

that the resulting concrete will give excellent performance in the structure in which

it will be exposed, and with the loads to which it will be subjected for its design

life, and resistance to some forms of attack.

Aitcin and Neville [1993] stated that

in practical application of this type of concrete, the emphasis has in many cases

gradually shifted from the compressive strength to other properties of the material,

such as high modulus of elasticity, high density, low permeability, and resistance

to some forms of attack

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2. Freezing and thawing Water freezing and thawing in the surface voids, and in

the interior capillary channels and voids, sets up stresses of sufficient magnitude to

cause disruption and progressive disintegration of concrete.

3. Thermal incompatibility When two different aggregates, or an aggregate andmortar mix, are in intimate contact and have sufficient differential in either

coefficient of linear expansion, or thermal diffusivity, or both, stresses set up when

heat transfer occurs cause incipient fractures large enough to cause deterioration of

concrete when exposed to water and freezing action.

4. Erosion Mechanical disintegration of concrete is caused by the abrasive

actions of water or wind-borne particles striking the surface.

5. Cavitation Severe repeated stresses set up by the cycles of negative and

positive pressures on concrete surfaces in areas of turbulency stress the concrete

beyond its elastic limit and cause progressive failure and disintegration.

6. Sulphate attack The formation of ettringite the result of calcium aluminates

reeacting with sulphates which occupies a larger volume, causes distress in

concrete.