SELF COMPACTING CONCRETE(SCC)SELF COMPACTING CONCRETE(SCC)

Dr. AJAY SHARMADr. AJAY SHARMADeptt. of Structural EngineeringDeptt. of Structural Engineering

MBM Engineering College JODHPURMBM Engineering College JODHPUR• PROBLEMS ASSOCIATED WITH

CONVENTIONAL CONCRETE

• DURABILITY CONCERN

• ADVENT OF SCC

• PRESENT STATE- OF- THE -ART

Self Compacting Concrete

Concrete that is able to flow under its own weight and completely fill the form work even in the presence of congestion of reinforcement without the need of any vibration, whilst maintaining homogeneity.

USE OF SCC STARTED IN JAPANUSE OF SCC STARTED IN JAPAN

•BY PROF. OZAWA AND OKAMURA

• FIRST USE WAS REPORTED IN 1988

• FIRST ACI WORKSHOP IN 1994 AT

BANGKOK

Four Anchor Blocks were Four Anchor Blocks were Casted Using SCCCasted Using SCC

GAS TANK USING SCC GAS TANK USING SCC TEHNOLOGYTEHNOLOGY

SELF COMPACTING CONCRETE!SELF COMPACTING CONCRETE!

faster construction

reduction in site manpower

better surface finishes

easier placing

improved durability

greater freedom in design

thinner concrete sections

reduced noise levels, absence of vibration

safer working environment

INTREST IN SCC HAS INCREASED INTREST IN SCC HAS INCREASED DUE TO DIFFICULTY DUE TO DIFFICULTY

EXPERIENCED INEXPERIENCED IN

• HIRING SKILLED LABOUR

• PROPER VIBRATION PRACTICES

• RETEMPERING

• PROPER FORMWORK

• segregation of the aggregates

• greater settlement

• fluctuations in behaviour while setting

• presence of voids, high permeability

and poor distribution of pores if

vibration is insufficient

POOR VIBRATION LEADS TO

• poor surface appearance with regard to

colour, holes and sand streaking• poor impermeability due to bleeding around

the aggregates• poor quality of the “concrete skin”, in other

words of its surface• lack of homogeneity within the concrete,

which leads to variations in strength• honey-combs• cold joints.

RETEMPERING, leading to:

• increase in water cement ratio and

therefore a decrease in strengths

• less cohesivity

• low homogeneity

• poor durability

INAPPROPRIATE USE OF FORMS, leading to:

•greater loss of grout from the formwork due to incorrect sealing of the moulds

•poor outer surface due to non-uniform use of the form release agent.

Why self Compacting Concrete?Why self Compacting Concrete?

The advent of self-compacting concrete represents a considerable step forward in respect of the durability of the structures. Mixing and casting are much easier thanks to its incredible properties of SCC.

WHAT IS DURABILITY?WHAT IS DURABILITY?

"CAPACITY OF A WORK TO WITHSTAND AGGRESSIVE AGENTS OF VARIOUS NATURE, KEEPING THE MECHANICAL AND FUNCTIONAL PROPERTIES UNCHANGED".

The intrinsic causes of deterioration are linked to the fact that the concrete often has weak points .A very important property of concrete is its permeability or porosity, on which its durability mostly depends.

The chemical causes of concrete deterioration are:

sulphate attack

carbon dioxide, inorganic acids (for pH less than 5, the concrete must be protected with a coating)

• organic acids

organic substances

chloride attack (on the reinforcement rods)

others (ammonium salts, magnesium, etc)

The physical causes of concrete deterioration are:

freezing and thawing

shrinkage

high temperatures

The mechanical causes of concrete deterioration are:

abrasion

erosion

cavitation.

The intrinsic causes in the material are:

the composition of the concrete

(water/cement ratio and aggregates/cement

ratio; quality of raw materials; cement,

aggregates , water, admixtures)

workability of the concrete at the time of

casting

curing of the concrete after casting

all our efforts to make a durable and reliable structures which require insignificant maintenance work, then we can say it has been worthwhile.

Self Compacting Concrete offers to some extent the solution to all these problems of concreting at site.

HISTORY OF HISTORY OF DEVELOPMENTDEVELOPMENT

Characteristics of the Characteristics of the mechanism of self-compactionmechanism of self-compaction

CONSTITUENT MATERIALS FOR CONSTITUENT MATERIALS FOR SCCSCC

• Cement• Aggregates• Mixing water• Admixtures (Superplasticizers)• Viscosity modifying Agent(VMA)• Additions including Mineral fillers semi-inert, pozzolanic or latent hydraulic• Fibres• Pigments

Relations between the different properties of Self-Compacting Concrete

RQUIREMENT FOR SELF COMPACTING RQUIREMENT FOR SELF COMPACTING CONCRETECONCRETE

• Filling Ability

• Passing ability

• Segregation Resistance

A Concrete mix can only be classified as self compacting concrete if the requirement for all three characteristics are fulfilled

THREE IMPORTANT PROPERTIESTHREE IMPORTANT PROPERTIES

•The fluidity of the concrete is defined as its capacity to flow into the moulds or forms even if the presence of obstacles which may interfere with its path.

•The deformability of the concrete is its capacity to change shape and to pass through different sections without losing cohesivity and therefore without segregating or blocking.

•Segregation of the concrete is the tendency of the mortar and the coarse aggregates to separate.

The mechanism of self-compaction

• High quantity of fines (500-550 Kg/m3)

• Superplasticizers with high water reduction

• Viscosity modifying agents (VMA)Effect of VMA

Effect of VMAEffect of VMA

                                                                            

 

REQUIREMENT OF REQUIREMENT OF CONCRETE MIX DESIGN CONCRETE MIX DESIGN

• PROPER MIXING OF CONSTITUENT

MATERIAL

• MAINTAINING W/C RATIO FOR STRENGTH

• TESTING WORKABILITY PARAMETERS

• ADJUSTMENTS FOR ADMIXTURES AND

MINERAL FILLERS

• ENSURING STRENGTH

Mix design procedure

List of test methods for workability properties of SCC

S.No. Method Property1 Slump-flow by Abrams cone Filling ability2 T50cm slump flow Filling ability3 J-ring Passing ability4 V-funnel Filling ability5 V-funnel at T5minutes Segregation resistance6 L-box Passing ability7 U-box Passing ability8 Fill box Passing ability9 GTM screen stability test Segregation resistance

10 Orimet Filling ability

ACCEPTANCE CRITRIA FOR SCCACCEPTANCE CRITRIA FOR SCCS.No. Method Unit Min Max

1 Slump-flow by Abrams cone mm 650 8002 T50cm slump flow sec 2 5

3 J-ring mm 0 104 V-funnel sec 6 125 V-funnel at T5minutes

sec 0 +3

6 L-box (h2/h1) 0.8 1.07 U-box (h2 - h1)mm 0 308 Fill box % 90 1009 GTM screen stability test % 0 15

10 Orimet sec 0 5

Depending on the apparent problem, the following courses of action might be appropriate:

the use of additional or different types of filler,

(if available);

modify the proportions of the sand or the

coarse aggregate;

the use of a viscosity modifying agent, if not

already included in the mix;

adjust the dosage of the superplasticizer and/or

the viscosity modifying agent;

• the use of alternative types of Superplasticizers (and/or viscosity modifying agent) which may be more compatible with local materials

different dosage rates of admixture to modify the water content, and hence the water/powder ratio.

A procedure for efficiently designing SCC mixes is shown below. It is based on a method

developed by Okamura.

• Designation of desired air content ( mostly 2 % )• Determination of coarse aggregate volume• Determination of sand content• Design of paste composition• Determination of optimum water:powder ratio and

Superplasticizers dosage in mortar• Finally the concrete properties are assessed by

standard tests.• Definition of desired air content ( mostly 2 % )

Generally coarse aggregate content (D> 4 mm)

should be between 50 per cent and 60 per cent.

The optimal volume content of sand in the mortar varies between 40 – 50 % depending on paste properties.

Design of paste composition

Initially the water:powder ratio for zero flow (p ) is determined in the paste, with the chosen proportion of cement and additions.

Determination of water powder ratio p

Slump flow test flow test

V funnel testV funnel test

ORIMET TESTORIMET TEST

Fill Box testFill Box test

U-Box TestU-Box Test

L-Box TestL-Box Test

Calculate H2/H1, the blocking ratio.

The whole test has to be performed within 5 minutes.

Determination of optimum volumetric water/powder ratio and superplasticizer dosage in

mortar.Target values are slump flow of 24 to 26 cm and V-Funnel time of 7 to 11 seconds.

At target slump flow, where V-funnel time is lower than 7 seconds, then decrease the water/powder ratio.

For target slump flow and V-funnel time in excess of 11 seconds, water/powder ratio should be increased.

If these criteria cannot be fulfilled, then the particular combination of materials is inadequate. A trial with a different superplasticizer is the preferred alternative. Second alternative is a new additive, and as a last resort a different cement.

Summing up, self-compacting concrete clearly has better properties than any other concrete produced today, especially with regard to durability.These properties may be summed up as follows:adequate fluiditysufficient deformabilityhigh resistance to segregationexceptional filling capacityhigh workability;appropriate plastic viscosityexcellent stabilityhigh durability;

Advantages SCC

The advantages for the Building contractor are:decrease in professional diseases of the workers.savings in labour, vibrators and energysolution of site problemsincrease speed of workbetter product quality

THANK YOU VERY MUCH FOR THANK YOU VERY MUCH FOR ENJOYING WITH MEENJOYING WITH ME

HAVE A NICE TIME!