Mix design of self consolidatingconcretes

Exercise 8

Exercise 8: Learning outcomes

• Understanding the basics of SCC

• Being familiar with the requirements andlimits of designing a SCC concrete mix

• Implementing the SCC concrete mix designtool “Excel work sheet”

• Being able to adjust the SCC mix ingredients

Comparison of mix proportioning between selfconsolidating concrete and conventional concrete.

The materials used in SCC are the same as inconventional concrete except that an excess offine material and chemical admixtures are used.

Also a viscosity-modifying agent (VMA) may beused .

The powdered materials used are for example:• fly ash,• silica fume,• limestone powder and• quartz powder.

According to Okamura and Ozawa (1995) self-compactability can be achieved using thefollowing methods:• Limited aggregate content• Low water-powder ratio• Use of superplasticizer

SCC can be manufactured in all strength classesas ´normal´ concretes.

However because of the high compactability,strengths of 40 MPa and over are morecommon.

Test methods for self compatibilityConventional workability tests, devised for normalranges of concrete mixtures are not suitable forself-compacting concrete because they are notsensitive enough to detect the tendency tosegregation.

Therefore test equipment has been made forjudging the following characteristics of SCCs:• Self-compatibility• Deformability• Viscosity• Filling ability

Many different methods have been developedto characterise the properties of SCC.In Finland the consistency of SCCs is describedusually with• Slump flow (650…800 mm)• T50 slump flow (2…10 s)Also used for testing for example the passingability are• L-box• J-ring

Slump flow test

Slump flow test

L-box

J-ring

The method for achieving self-compactabilityinvolves:• high deformability of paste or mortar• resistance to segregation between coarse

aggregate and mortar when the concreteflows through the confined zone ofreinforcing bars.

Rheology is the science of the deformationand flow of materials.

It is used to understand the workabilitycharacteristics of SCC.

The two most important properties ofSCC’s rheology are:

1) Yield stress2) Plastic viscosity

Rheology of SCCs

1) Yield stress (myötöjännitys): the measure of theamount of energy required to make SCC flow. To beconsidered self compacting, concrete must flow easilyunder its own weight, so its yield stress must be verylow.

2) Plastic viscosity: the measure of the resistance ofSCC to flow due to internal friction.SCC must have a high viscosity in order to suspendaggregate particles in a homogenous manner withinthe concrete matrix without segregation, excessivebleeding, excessive air migration, or pasteseparation.

In summary, SCC must have low yield stress andhigh viscosity!

SCC mix design: Penttala design method

• non-air entrained SCC• rapid and extra rapid cements were used

v CEM IIA 42,5 R,v CEM IIA 52,5 R

• presented in Equations 1 and 2.

Coefficients: slide 27

SCC mix design: Penttala design method

• non-air entrained SCC• sulphate resistant cement

v CEM I 42,5 SR• presented in Equations 3 and 4.

Coefficients: slide 27

SCC mix design: Penttala design method

• air entrained SCC• all three cements types

• CEM IIA 42,5 R,v CEM IIA 52,5 Rv CEM I 42,5 SR

• presented in Equations 5 and 6.

Coefficients: slide 27

SCC mix design: Penttala design method

Mix design guide for SCC developed atTKK/HUT

Input the particle-size distribution # [mm]

Remember quantity of absorbed water in aggregatesand the water content of the concrete

Variable Minimum MaximumSlump flow [mm] 600 850

T50 time [s] 2 15

Amount of cement [kg/m3] 200 420

Amount of fly ash [kg/m3] 0 200

Amount of limestone filler [kg/m3] 0 200

Amount of superplasticizer [kg/m3] 2 10

Amount of water [kg/m3] 155 170

• Select the target slump D and T50

• Select the SCC concrete ingredients:– Binder: cement, Fly ash, limestone filler– Normal filler– Water– Super Plasticizer

XL - columnsXL

-Row

s

Laboratory exercises

• Fly ash is added to the SCC concrete• Limestone filler is NOT used• Consider the amount of water (absorbed and

free water) in aggregates• Consider the compressive strength of SCC

concrete at 28 days• Concrete batch is 30 dm³

Solver – Excel

Solver – Excel

• Start the iteration using solver• Press “SOLVE”

• Select: “Keep solver solution”• Press “OK”

0102030405060708090100

0,00

1

0,00

2

0,00

4

0,00

8

0,01

6

0,03

1

0,06

3

0,12

5

0,25

0

0,50

0

1,00

0

2,00

0

4,00

0

8,00

0

16,0

00

Läpä

isyp

rose

ntti

Particle-size distribution # [mm]

In weight fraction

Mix design curve

Target curve

Mix Design Curve

Selected values vs Calculated values

SCC - Mix adjustmentSlump [mm] T50 [s]

General rule­ ¯

¯ ­

non-air entrained SCC

CEM IIA 42,5 RCEM IIA 52,5 R

Waterà increase ­ ­ slightly

Super plasticizerà increase ­ ­

Cementà increase ¯ ¯

Lp125à increase ¯ ­

non-air entrained SCC

CEM IIA 42,5 SR

Waterà increase Little ¯ ¯

Super plasticizerà increase ¯ slightlyFine aggregates volume V125 ­ ­

Fine aggregates weight F125 ­ ­

Air entrained SCC

Waterà increase ¯ ¯

Cementà increase ­ ­

Fine aggregates volume V125 ­ ­

Air contentà increase ­ slightly ­

¯: Decrease ­: increase

based on the 1st

iteration result and thetype of concrete andcement, change:- the amount of water- amount super

plasticizer- amount of cement- air content

Use solver again forthe 2nd iteration

30 dm³ for the laboratory exercise

Concrete batch