self c c

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The Formwork Experts.

Doka Knowledge TransferFor internal use only!

Self-Compacting Concrete (SCC)

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Introduction Doka Knowledge Transfer Self-Compacting Concrete (SCC)

Introduc-tion

© by Doka Industrie GmbH, A-3300 Amstetten

Doka Knowledge Transfer Self-Compacting Concrete (SCC) Introduction

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Contents4 General6 Concrete raw materials7 Concrete composition8 Uses of SCC:

10 Production and transport12 Forming SCC structures15 System formwork or design formwork16 Cost efficiency and sustainability of SCC17 Practical examples19 Annex

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Doka Knowledge Transfer Self-Compacting Concrete (SCC)

GeneralThe problems involved in compacting concrete in struc-tures of complex geometry can be considerable, but self-compacting concrete (SCC) often proves a solu-tion. Compacting as such is unnecessary, because SCC is honey-like and flowable in consistency. There is no need for vibrators. This in turn means less worker exposure to noise and vibration and the corresponding improvement in conditions on site or in the prefabricat-ing plant.Self-compacting concrete de-aerates and self-levels under the influence of gravity. Even though the mixture is highly flowable, the aggregate does not settle (the concrete evinces no propensity to segregate). Conse-quently, self-compacting concrete ensures a high degree of homogeneity, minimum voids and uniform compressive strength. The low water/binder ratio, moreover, means that the formwork can be stripped out all the sooner. Range of uses for SCC: ▪ Structural elements with closely spaced reinforcing

bars. ▪ Concrete structures with architecturally modelled

surfaces. ▪ Slim structural elements/elements inclined off-verti-

cal. ▪ Structural elements with many openings.

History of SCC

▪ Self Compacting Concrete (SCC) was developed in the late nineteen-eighties in Japan and has been used in Europe since the mid-nineties. In Austria, SCC was used for the first time in large quantities on the Millennium Tower build in Vienna.

▪ In May 2005 the European standards for SCC were published in English.

▪ The English version was translated into German in 2006.

▪ On the Austrian national level, the use of SCC has been regulated since 2002 by the technical bulletin entitled "Selbstverdichtender Beton" (Self-Compact-ing Concrete). The latest issue is dated March 30, 2009 and can be obtained through www.concrete-austria.com.

Production

The production of SCC requires specialised plant and a well-trained, skilled workforce.The manufacturer has to take the following points into account: ▪ The mixing plant must meter the ingredients as accu-

rately as possible. ▪ The moisture content of the sand has to be meas-

ured continuously. The moisture content of coarse aggregate also has to be known.

▪ Residual water can be used only under certain pre-conditions, because excess solids entrained in the water can have a detrimental effect. Residual water is water from cleaning of the mixing plant, working concrete residue, washing water from aggregate, ...

▪ All traces of rinsing water must be removed from the mixing drum, the transport vehicles and the pumps.

The concreting process

The following points are important with regard to the concreting process as such: ▪ Continuous work without long breaks. ▪ Check that the formwork is leaktight and check the

bracing before and during the concreting process. ▪ Rod the poured mix to prevent the formation of voids

caused by air bubbles getting trapped near the top of the wall.

▪ Avoid lengthy breaks in concreting, because they can cause the crazing effect that mars the top of the concrete.

▪ If the formwork is closed all round, provide a suffi-cient number of windows and de-aerating ports.

▪ The timing for pouring the concrete has to be agreed with the concrete supplier.

▪ Surface quality improves if the concrete is poured slowly.

▪ Use the right release agent and apply it thinly.


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Technical parameters

Properties of the fresh concrete: ▪ Flowability (viscosity) ▪ Stoppage tendency ▪ Self-levelling capability ▪ Self de-aeration ▪ Strength of microstructureProperties of hardened concrete: ▪ Compressive strength ▪ Flexural strength (modulus of elasticity) ▪ Durability ▪ Shrinkage and creep

Principle

The high proportion of meal (meal grain size maximum is 0.125 mm) combines with water and plasticiser to form a highly viscous suspension (grout). All coarser aggregate floats in this suspension and there is no ten-dency to segregate.The meal consists of the following materials: ▪ Cement ▪ Hard-coal fly ash ▪ Silica dust ▪ Slowly reactive stone powderBroadly speaking it makes little difference which mate-rial is used, as long as the interaction with the plasti-ciser produces the necessary flowability properties.In the production process the flowability and flow prop-erties of SCC are adjusted so as to permit adequate flow and optimum flow rate of the concrete.

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Concrete raw materialsCement and additives

In principle, all cements are suitable for use in the pro-duction of SCC. The following are the most commonly used cements: ▪ Portland composite cement ▪ Portland cement ▪ Portland limestone cement ▪ Portland shale cement ▪ Portland slag cementHigh-strength concretes, shorter times to stripping out and pourability at low ambient temperatures are achieved with the following kinds of cement: ▪ Portland composite cement ▪ Portland silica dust cement ▪ Portland cement ▪ Portland shale cementThe following are commonly used as additives (for high cement-grout content): ▪ Hard-coal fly ash: Reduces the water-to-cement

ratio of the concrete (? = 2250 kg/m3). ▪ Slowly reactive quartz or limestone powder (? =

2700 kg/m3).

Water

Water from any public drinking water supply is suitable for the production of self-compacting concrete. Recy-cling water is not used, on account of the possibility of detrimental effects on the properties of the concrete. On account of the effects on flowability, it is very impor-tant for the mix to match the target water content.

Aggregate

Rounded or crushed aggregate is used for SCC. Rounded aggregate means a lower voids content, so less cement grout is needed. The advantage of crushed aggregate derives from the larger surface area for a given weight. This improves float in the concrete mix. Sieve size is generally a maximum of 16 mm in order to facilitate passage between closely spaced reinforcing bars.

Aggregates for SCC

Chemical admixtures

Chemical admixtures

Polycarboxylate-based plasticisers are used to make SCC extremely flowable. Using a plasticiser means that the water content can be reduced. Flowability is influ-enced as well. Adding a stabiliser further reduces the tendency of the SCC to segregate (bleeding, sinking of the coarse aggregate). The right plasticiser for the cement has to be selected by advance tests.

Other slowly reactive additives

Some additives are essential for the production of SCC, but some other substances can be used as additives as well: ▪ Pigments to colourise the concrete structures. ▪ Steel fibres as structural reinforcement. ▪ Polyethylene fibres to increase fire resistance. ▪ Polypropylene fibres (PP fibres) to reduce plastic

shrinkage.

Sie

ve p

ass

[%] b

y m

ass

Sieve mesh [mm]

A Absolute limits B Proven compositions for ordinary concreteC Optimum range for SCC

A

B

C

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60

80

100

0,063

0,125

0,25 0,5 1 2 4

5,6

8 16

22

32


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Concrete compositionIn some cases concrete concepts and concrete recipes vary significantly from country to country.A broad distinction is drawn between the following types of concrete: ▪ Meal type: Less prone to production fluctuations than

the stabiliser type. ▪ Stabiliser type: ▪ Combination type: Closer to the stabiliser type.

Meal content of SCC types:

Comparison between ordinary concrete and SCC

SCC type Meal content [kg/m3] Proportion of additivesMeal type 550 - 650 LowStabiliser type 350 - 500 High

Combination type Depends on quantity of stabiliser Medium

Ordinary concrete SCC

Cement grout: 280 l/m3 Cement grout: 365 l/m3

Aggregate: 720 l/m3 Aggregate: 635 l/m3

Largest grain size: 32 mm Largest grain size: 16 mm

The spaces are filled with cement, additives and water (cement grout).

Cement-grout content is about 65 to 100 l in excess of the quantity necessary to fill the spaces. It is this excess that makes the con-crete flowable.

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Uses of SCC:The window for working SCC is the area in which the special concrete evinces optimum fresh-concrete prop-erties. With many concrete recipes this area is very small. It depends on the relationship between fresh-concrete consistency (measured as slump flow) and viscosity (measured as outflow time from V-funnel).

Workability window for SCC, concrete-meal type

65 to 75 cm slump flow and 10 to 20 seconds outflow time are considered normal as limit values. Both these indices have to be checked in recipe development and also as part of in-process quality monitoring, in order to ensure that the high requirements are satisfied. Work-ing the concrete outside this window leads to the loss of the self-compacting and de-aerating properties and can result in segregation in the SCC mix.

Testing fresh concrete

Slump flow

1) Place a slump cone on a clean plate of adequate size (min. 800 x 800 mm).

Dimensions of slump cone

a ... 100 mm b ... 300 mm c ... 200 mm2) Fill the slump cone with SCC.3) Lift the slump cone off the plate.

The energy in the SCC causes it to slump and spread. When movement ceases the diameter of the puddled concrete should be between 600 and 800 mm. Coarse aggregate should be evenly distributed and there should be no segregated fines around the edge.

a ... Slump flow b ... at least 800 mm

Obstacle ring (J-ring)

The SCC flows through the gaps between the reinforc-ing bars. This is a test to ascertain the tendency of the mix to form stoppages. The diameter of the metal ring is 300 mm. The bars, 16 to 18 mm in diameter, are evenly spaced. Uniform flow and an even grain skele-ton inside and outside the ring are indicative of good-quality SCC.

Obstacle ring (J-ring)

Number of bars of the obstacle ring

Slu

mp

flow

[cm

]

Outflow time, V-funnel [sec.]

A SedimentationB No self-compactionC Formation of airhole voidsD Target area

5

A

B

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D

10 15 20 25

55

60

65

75

70

85

80

a

b

c

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See the "Easily Compacted Concrete" User Information tile, and in particular the section entitled "What is easily compacted concrete?"

Largest grain size Number of bars8 or 11,4 mm 2216 or 22 mm 1632 mm 10

a

b

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V-funnel

1) Fill the funnel brim-full with concrete.2) Open the cap at the bottom.3) Measure how long it takes the funnel to empty.

The outflow time for self-compacting concrete should be between 8 and 14 seconds.

V-funnel

L-box test

Dimensions of L-box

a ... 600 mm b ... 200 mm c ... 100 mm d ... 600 mm e ... 700 mm f ... 150 mm h2/h1 ... greater than 0.80

1) Fill the vertical side of the L-box with SCC.2) Pull the gate right to left to open.

The SCC must envelope 3 reinforcing bars before it reaches the far end of the horizontal leg.Measured flow time must be between 3 and 7 seconds. In addition, the height of the concrete at the near end (h1) and the far end (h2) can also be measured. Quo-tient h2/h1 should be greater than 0.80.

U-box test

This test provides a means of gauging the concrete's self-levelling capability and its tendency to form stop-pages.The U-box consists of two chambers interconnected by an opening in which reinforcing bars are set as obstruc-tions.1) Before pouring in the concrete, close the gate to

seal the outlet from chamber 1.2) Pour the concrete into chamber 1.3) Open the gate.

The concrete envelopes the reinforcing bars, passes through into chamber 2 and rises in this chamber.

Kajima box test

The Kajima box is used to assess the degree of con-crete fill and the de-aeration capability.A Perspex container with reinforcing-bar obstacles is filled with concrete through a filling aperture until the concrete touches the top lay of rebar.

F [%] = (h1 + h2 / 2 · h2) · 100

Criteria for assessment: ▪ Height h1. ▪ Degree of fill F,

target: F min. 90 %. ▪ Visual assessment of the extent to which the fresh

concrete envelopes the reinforcing bars. There should be no cavities between the SCC and the rods.

A GateB Reinforcement

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A

B

c

a

b

f

d

e

h1

h2

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a ... 680 mm b ... 120 mm c ... 340 mm

h2 ... Target: at least 300 mm

A ReinforcementB Gate

A 1. Reinforcing bar

a

bb

c

A

1

2

B

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h2

1

2

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h2

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Production and transportProduction

SCC is produced in all conventional concrete mixing plants.

The moisture content of the aggregate needs strict monitoring, because the permissible range of fluctua-tion is narrow. Moisture sensors in the silo enable the recipe to be adapted automatically to suit. Mixing time is generally 120 seconds.

Transport

Because it is so flowable, SCC is transported only in truck mixers. The mixer's drum remains in constant movement all the way to site. A cap is fitted if the truck has to negotiate steep gradients.

Truck mixer (6 m3)

Truck mixer (15 m3)

The concrete has to be agitated at maximum speed for about 2 minutes immediately prior to discharge. Cor-rections on site are possible if delays occur or the con-sistency of the mix is stiffer. Post-mix addition of plasti-cisers calls for uniform distribution and strict compli-ance with the specified minimum mixing time.

See also the section entitled "Equipment for the production of CIP concrete and precastings" in the "Construction-engineering equipment (for precastings and CIP concrete)" UI.

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Forming SCC structuresAs long as the wall heights remain within the normal range (maximum 3.00 metres high), the requirements for wall formwork are the same for both ordinary con-crete and SCC. When conventional heavy framed form-work is used no special measures are needed for pour-ing SCC up to heights of 3.50 m.Effects on the formwork when SCC is used: ▪ Higher fresh-concrete pressure. ▪ Lift and the danger of bleeding, even at constricted

openings (flowability of the concrete). ▪ The surface structure of the formwork sheeting is

clearly imaged on the finished concrete. ▪ No inherent strength (produced by stiffening of the

concrete) in the the freshly concreted structural ele-ments.

The method of concrete placement and the resultant design features of the formwork system must be detailed in consultation between the construction con-tractor, concrete supply and formwork manufacturer.

Placement of the SCC

SCC is very easy to pour and the process is generally a one-man operation. Conventional techniques such as crane bucket, pump or chute of the truck mixer are all used for placing the concrete.On account of the risk of mix segregation, drop height has to be restricted to 1.00 to 2.00 metres. The rate of concreting influences the time for de-aera-tion of the SCC and ultimately the quality of the finished product.A distinction is made between 2 types: ▪ Filling from above ▪ Pumping in from belowThe SCC should be introduced into the formwork at only one point. This permits unimpeded flow, enabling the concrete to fill the formwork by itself and de-aerate.It is important to note, however, that flow in the horizon-tal direction is subject to restriction. The risk of dynamic segregation increases with distance of flow (empirical rule of thumb: maximum distance of flow is 12.00 to 15.00 metres) and increasing confinement on account of the density of the reinforcement.

Filling from above

When the concrete is poured in this way the fresh-con-crete pressure is controlled by the concreting rate. High concreting rates (with SCC) lead to hydrostatic fresh-concrete pressures. While the wall is still being poured the bottom lays have not yet reached the end of setting (concrete is still soft).The formwork pressure has to be reduced in order to prevent damage to the formwork system. This entails a thorough knowledge of the concrete's properties so that suitable testing can be undertaken and the appropriate conditions for placement of the concrete kept constant. As a basic rule, moreover, the formwork has to be dimensioned for the full permissible formwork pressure (the norm is 24 kN/m³).

Filling from above

Hydrostatic pressure

a ... Height of concrete filling

A Top of concreteB Hydrostatic pressure

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Pumping in from below

When this method of placement is used the fresh con-crete is in constant movement. The hydrostatic con-crete pressure has to be used in all calculations. In order to avoid damage it is common practice to monitor concrete pressure with pressure sensors and adapt the concreting rate accordingly.

Pumping in from below

Pressure of fresh concrete

Time of 5 hours to end of setting tE

Time of 15 hours to end of initial setting tE

max

. fre

sh-c

oncr

ete

pres

sure

[kN

/m2 ]

hydr

osta

tic h

ead

h s [m

]

placing rate v [m/h]

A Consistency class F1B Consistency class F2C Consistency class F3D Consistency class F4E ECC, consistency class F5F ECC, consistency class F6G SCCH Hydrostatic to tE

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A

D

0

1

2

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4

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6

0 1 2 3 4 5 6 7

150

125

100

75

50

25

0

B

CH

G

F

E

max

. wet

-con

cret

e pr

essu

re [k

N/m

2 ]

hydr

osta

tic h

ead

h s [m

]

rate of rise v [m/h]

See the "Doka Knowledge Transfer" Lotus Notes tile and the detailed information on "Eas-ily Compacted Concrete" for more graphs.

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A

D

0

1

2

3

4

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6

0 0,5 1 1,5 2 2,5 3 3,5

150

125

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H

G

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E

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Lift and bleeding

▪ It is important to ensure that the formwork is leak-tight, on account of the flowability of SCC.

▪ Always use the full concrete pressure for calcula-tions involving horizontal and inclined faces.

▪ Use stronger fixings to secure cavity formers in the formwork.

▪ The formwork has to be held down (anchored to the ground) to ensure that it does not lift.

▪ The holes for the ties, all small openings, the upstand and vertical working joints all have to be well sealed to prevent bleeds.

Concrete pressure on formwork surfaces

Imaging of the surface structure

SCC requires formwork sheeting with a high-quality surface. Broadly speaking, all formwork sheets except oriented-strand board (OSB) are suitable for SCC. The interplay of concrete, release agent and formwork sheet should always be tested beforehand, and this is particularly so in the case of fair-faced concrete.

Inherent strength

A freshly concreted SCC wall has no inherent strength, due to the high rate of rise and the composition of the mix. Consequently, adequate bracings and fixings must be provided.

See the "Doka Knowledge Transfer" Lotus Notes tile and the detailed information on "Structural Analysis: Design loads"

A

A

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System formwork or design formworkThe use of formwork systems.

Permissible fresh-concrete pressures Pmax vary for sys-tem formwork; the range is from 40 to 90 kN/m2.

Permissible concreting heights for Doka system formwork

Higher pressures can be dealt with by reducing panel size/width (therefore more formwork ties per m2).

Permissible concreting heights when smaller framed panels are used

The use of design formwork

There is a technical upper limit of about 240 kN/m² or 10 m concreting height for design beam formwork. The formwork is adapted to fresh-concrete pressure by var-ying the number of beams and the beam spacing.

Formwork system (all panel widths)

Per. anchor forces 15.0AUSTRIA, CH: 120 kN

Steel framed formwork 3.30 mAluminium framed formwork 2.70 mSystem beam formwork 3.25 mCircular formwork 3.30 m

Max. panel width

Per. anchor pull120 kN 150 kN

Ste

el fr

amed

form

wor

k

135 cm 3.30 m 3.30 m90 cm 3.80 m 4.05 m60 cm 5.60 m 5.70 m45 cm 7.00 m 7.50 m30 cm 11.00 m 11.40 m

Alu

min

ium

fra

med

fo

rmw

ork

90 cm 2.70 m75 cm 3.00 m60 cm 3.30 m45 cm 4.40 m30 cm 6.30 m

See Technical Circular No. 678 (year 2005), "Selecting formwork for self-compacting or highly flowable concrete".

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Cost efficiency and sustainability of SCCCost efficiency

Better strength development than ordinary con-crete

Economic advantages of SCC

Practical example: Building with 170 residential units

Practical example: School building for 800 pupils

Sustainability

The sustainability of concrete is defined by the follow-ing points: ▪ Ecological aspect ▪ Sociological aspect ▪ Economic aspectSustainability refers to the entire life cycle of a build.

Ecological sustainability

The figures for energy consumption and the resultant emissions are calculated from production through use all the way to final disposal.The following categories are factored into the consider-ations: ▪ Energy ▪ Greenhouse effect ▪ Ozone formation ▪ Eutrophication ▪ Acidification ▪ Human toxicity ▪ Ecotoxicity

Social sustainability

Social sustainability is influenced by the occurrence of accidents and long-term illnesses. The placement of vibratory-compacted concrete, let us say, is associated with certain health and safety risks such as "fall from working platform", for example. Man-hours worked per cubic metre of concrete poured is often used as a com-parative variable for social sustainability.

Economic sustainability

Comparing sums invested over the entire life cycle of the structure yields a unit of measure for economic assessment.The following cost generators are factored into the equations: ▪ Material costs of the concrete ▪ Construction costs ▪ Life cycle costs ▪ Indirect costs

Result in practice

Empirical experience shows that vis-à-vis ordinary con-crete, on a scale of sustainability SCC ranks equivalent to or better than ordinary concrete. The potential for shorter construction times, a reduction in human resource outlay and more degrees of freedom in geo-metrical design all favour the use of SCC. The greater freedom in geometrical design can be translated into optimised construction processes and scheduling. Without vibratory compactors the site generates less noise. The production costs vis-à-vis those for ordinary concrete are countered by the advantages in the place-ment process.

Com

pres

sive

cub

e st

reng

th [N

/mm

2 ]

[days]

A SCC C40/50B SCC C35/45C Ordinary concrete C25/30

Walls (crane) Slabs (pump)Ordinary con-

crete SCC Ordinary con-crete SCC

Manpower 4 2 8 4Performance

[m3/h] 10 20 25 30

Comparison of con-struction time Ordinary concrete SCC

Days per level 9 days 7 daysWalls per day 85 m 110 mConstruction time, carcass 4.5 months 3.5 months

Comparison of con-struction time Ordinary concrete SCC

Planned construction time with ordinary concrete

8 months

Actual build with SCC 6.5 months

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

C

B

A

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Practical examplesLakeside pool, Caldaro, South Tyrol Phaeno Science Center, Wolfsburg

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Wiental collector, Vienna

Innsbruck main station, Tyrol

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AnnexOnline: ▪ www.beton.org ▪ www.wikipedia.org ▪ www.doka.comLiterature: ▪ Experts forum, concrete 2007, "Self-Compacting

Concrete SCC" ▪ "Selbstverdichtender Beton - Änderung der Ober-

flächengüte von Mikrotübbingen durch Betonzusam-mensetzung und textile Schalungsauflagen" (Self-compacting concrete - change of surface quality of microtubbings by concrete composition and textile formwork coverings", degree dissertation submitted by Alexander Schroer, 2001

▪ "Selbstverdichtender Beton" (Self-compacting con-crete), Holcim (Switzerland) AG, 1st edition 2005

▪ "Die Generation SCC" (The SCC generation), Hol-cim (Switzerland) AG

▪ "Rheodynamic für selbstverdichtenden Beton" (Rhe-odynamics for self-compacting concrete), BASF Construction Chemicals Austria GmbH

http://www.beton.org

http://www.wikipedia.org

http://www.doka.com

999452702 - 01/2013Doka GmbH | Josef Umdasch Platz 1 | 3300 Amstetten | Austria | T +43 7472 605-0 | F +43 7472 66430 | [email protected] | www.doka.com

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Doka Knowledge Transfer offers Doka employees the opportunity of acquiring knowledge about various aspects of building construction and civil engineering. The subjects covered by Doka Knowledge Transfer are many and varied. They extend from "Construction

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self c c

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compacting concrete

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