A STUDY ON BEHAVIOUR OF HIGH PERFORMANCE CONCRETE BEAM WITH

NANO SILICA

**N.VIGNESH*, M.S .RAVI KUMAR**

**P.G Student, N.I University, Kumaracoil.

** Professor, N.I University, Kumaracoil

Abstract - Application of high performance has got

momentum in various fields of construction

globally in the near past. High performance

concrete is being practiced in the fields of

construction of nuclear reactors, runways at

airports, railways, sleepers, cooling towers, silos

chimneys and long span bridges. Considerable

amount of development has been made in the fields

of Ultra high performance concrete using silica

fume as a mineral admixture which is produced

from condensing the gases escaping from furnace of

a ferrosilicon or silicon metal manufacturing

process. The UHPC is essentially a concrete having

a lower water/ binder ratio (w/b). Conventional

concrete and UHPC have noted the quite different

compressive strength but also significantly different

micro structures (quite different shrinkage includes

compressive strength and permeability) and

significantly different overall performance. The

main objective of this project is to evaluate and

demonstrate the Ultra high performance of concrete

by addition of condensed silica fume. By the use of

condensed silica fume certain properties of fresh

concrete is being altered. This alteration in the

properties increases the performance of concrete.

I INTRODUCTION

The use of Ultra high performance concrete

(UHPC) in building construction increased

significantly during the last quarter of the 20th

century. Ultra high performance concrete exhibits

significantly higher compressive strengths than

normal-strength concrete (NSC), which allows for

extensions of structural design by allowing

structural members made from UHPC to carry

higher loads. As a result of its increased application

in many areas of construction, studies are being

conducted to define better the properties of UHPC

and to develop a better understanding of its use.

Application of Ultra high performance has got

momentum in various fields of construction

globally in the near past. Ultra high performance

concrete is being practiced in the fields of

construction of nuclear reactors, runways at

airports, railways, sleepers, cooling towers, silos

chimneys and long span bridges.

Considerable amount of development has been

made in the fields of Ultra high performance

concrete using silica fume as a mineral admixture

which is produced from condensing the gases

escaping from furnace of a ferrosilicon or silicon

metal manufacturing process. The UHPC is

essentially a concrete having a lower water/ binder

ratio (w/b). Conventional concrete and UHPC have

noted the quite different compressive strength but

also significantly different micro structures (quite

different shrinkage includes compressive strength

and permeability) and significantly different overall

performance.

II SCOPE AND OBJECTIVE

The appropriate use of silica fume in

concrete can give a range of benefits in design,

construction and performance of many of concrete

structure – including high-rise buildings, industrial

floors, civil engineering and marine structures. It

can be used for precast and insitu concrete, but this

information paper concentrates on the latter. Silica

fume has specific benefits during construction,

including increased cohesiveness of the fresh

concrete, which can lead to improved handling

characteristics curing can start earlier as there is no

need to wait for bleed water to dissipate. The dense

microstructure of concrete containing silica fume

leads to major improvements in mechanical

performance and resistance to chemicals ( such as,

fuel oil, chlorides sulfates).and characteristics of

hardened SF concrete include :Lower permeability

and improved durability(due to the fine particle size

and reactivity of SF).Greater resistance to abrasion

and impact than conventional concrete of similar

strength grade. Compressive strength in excess of

60N/mm2 are easily achieved. Higher flexural

strength and modulus of elasticity than

conventional concrete of equal compressive

strength SF can be used as an ingredient in ultra-

high performance concrete containing micro-fibers

to combat explosive spalling during exposure to

fire. A properly designed SF Ultra high

performance concrete containing micro-fibers with

a low water/cement ratio will outperform

conventional concretes in terms of resistance to

spalling during fire.

III. EXPERIMENTAL PROGRAM

Experimental investigation have been

carried out on the UHPC specimen to ascertain the

workability and strength related properties such as

compressive strength, split tensile strength, flexural

strength and elastic modulus of the designed trial

mixes strength, flexural strength and elastic

modulus of the designed trial mixes retarder can

control the rate of hardening in the forms eliminate

cold joints and provide more flexibility in

placement schedules.

A.Materials Used

a)Admixtures

Admixtures are widely used in the

production of high strength concrete. These

materials include also entering agent and chemical

and mineral admixtures. Air entering agents are

substances that will develop an air-void system

appropriate for the durability enhancement. Proper

use of high range water reducing admixtures

commonly known super plasticizers becomes

essential for UHPC has low water to binder ratio

and ultra fine particles in the form of micro silica.

This is achieved with the use of super plasticizers.

Super plasticizers typically reduce the water content

from 12 to 35 percent depending upon its type

dosage. Both sulphate Melamine formaldehyde and

nopthalene formaldehyde based admixtures are

commonly used in Uhpc.Super plasticizers are

organic molecules or anionics of colloidal size, with

molecular weight in the region of 20,000.

b. Retarders

A retarder is beneficial in controlling early

hydration. The addition of water to retemper the

mixture will result in marked strength reduction.

Further, structural design frequently require heavy

c. Super plasticizers

Super plasticizers are recently introduced

now class of water reducing admixtures and it is

defined as chemical or mixture of chemical which

when added to normal concrete either import an

extreme workability, without addition of extra

water to produce a “flowing concrete” or permits

large water reduction to be made of constant

workability are synthetic chemical products made

from organics sulphates of the type Rs03 where

Risa complex organic group of high molecular

weight.

d.Nano Silica

Silica fume also referred to as microsilica or

condensed silica fume is another material that is

used as an artificial pozzolanic admixture. It is a

product resulting from high purity quartz with coal

in an electric arc furnace in the manufacture of

silicon or ferrosilicon alloy. It is extremely fine

with particle size less than 1 micron and with an

average diameter of about 0.1 micron, about 100

times smaller than average cement particles. Silica

fume has specific surface area of about 20000m²/Kg

as against 230 to 300 m²/Kg. The use of silica fume

in conjunction with super plasticizer has been the

backbone of modern Ultra high performance

concrete.

Graph-1: Typical particle size distribute

Fig-1 . Dispersion of silica fume particles among

cement grains

Schematic showing the dispersion of silica

fume particles among cement grains. This figure

shows the basic concept of particle packing --

filling the spaces between cement grains with silica

fume particles

Fig-2. Effects of adding silica fume to concrete

Fig-3. Effects of adding silica fume to concrete

Using Silica Fume in Concrete

Enhancing Mechanical Properties

Improving Durability

Enhancing Constructability

Producing High-Performance Concrete

Structures

The above graph shows the effects of adding

increasing amounts of silica fume to a low water-

cementitious ratio, air-entrained concrete Ultra

High-Strength Silica-Fume Concrete B. Mix

Design for UHPC Since there are no specific

methods for mix design found suitable for UHPC, a

simplified mix design procedure, is formulated by

combining the BIS method, ACI methods for

concrete mix design and the available literatures on

UHPC using SF. C. Preparation of test specimen:

The concrete was mix designed asper the

recommended guidelines of ACI. All ingredients

were weigh batched. The grade of concrete

considered were M40. The test specimen were cast

and compaction was done.

D. Curing

The test specimens were steam cured and is

subjected to higher temperature it accelerates the

Hydration process resulting in faster development

of strength. Steam curing will give economical

advantages and also technical advantages.

4. Test and result

1. A simplified mix design procedure for

UHPC using SF and super plasticizer is formulated

by combining BIS and ACI methods of mix design

and available literatures on UHPC.

2. The optimum percentage of cement

replacement by SF is 10% for achieving maximum

compressive, split tensile and flexural strength and

elastic modulus.

3. The BIS 456-2000 code underestimates the

flexural strength and over estimates the modulus of

elasticity for UHPC.

4. The use of SF in concrete reduces the

workability.

5. The concrete mixes containing silica

fume showed less value of pH as compared to

concrete mix without silica fume.

6. From the test results, it is observed that

the percentage of saturated water absorption of the

UHPC mixes containing silica fume was lower

when compared with that of UHPC mixes without

silica fume.

IV. CONCLUSION

Mineral admixtures like fumed silica is an

ideal constituent for Ultra high performance

concrete as it has the inherent ability to contribute

to continued strength development through their

pozzolanic or cementatious reactivity and to

enhance durability and chemical resistance through

their pore reinforcement and reduce sorptivity

characteristics.

Laboratory tests and literature survey of

silica fume concrete show that they have low

chloride permeability and high electric resistivity.

In the presence of silica fume in concrete increases

its strength. This is due to physical and pozzolanic

effects in the bulk matrix and at the interfaces

between the matrix and inclusion. Experience with

silica fume concrete to date has demonstrated that it

can perform well when properly proportioned,

mixed, placed and cured. In this project I have

compared the strengths of Ultra high performance

concrete and concrete using condensed silica fume.

The concrete with the use of condensed silica fume

has achieved more strength compared to the Ultra

high performance concrete on all test parameters.

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