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    SELF COMPACTING CONCRETE: CHALLENGE FORDESIGNER AND RESEARCHER

    Joost WalravenDelft University of Technology, The Netherlands

    ABSTRACT

    Self compacting, or self -consolidating concrete (SCC) was first developed in Japan inthe early nineties. The idea was picked up and further developed in Europe from about1997. Substantial research was carried out with regard to the properties of SCC. Becauseof the well-controlled conditions, the introduction of SCC in the precast concrete industrywas successful. With regard to the application in situ, the development is slower, becauseof the sensitivity of the product. In this paper the mechanical properties of SCC incomparison to conventional concrete are discussed. Examples of applications are shown,

    both for prefabricated concrete elements and in-situ structures. The way of measuring therheological properties is discussed. Examples are given of special self-compactingconcretes. Needs for further research are defined.

    INTRODUCTION

    Self compacting (or self consolidating) concrete (SCC) was first developed in Japan, inthe early nineties of the previous century, under the stimulating leadership of Prof.Okamura. The main idea behind self compacting concrete was, that such a concrete isrobust and relatively insensitive to bad workmanship. In Western Europe the idea was

    picked up at the end of the last century. The main drive to develop self compactingconcretes was the option to improve the labor conditions at the building site and in thefactory (noise, dust, vibrations). During recent years self-compacting concrete developedto research item nr. 1. A large number of research projects was carried out, followed byrecommendations for potential users. Especially for the precast concrete industry selfcompacting concrete was a revolutionary step forward. Contrary to that, casting of SCCat the construction site was regarded with more reservation. The variable conditions at theconstruction site, the more complicated control of the mixture composition anddisagreement with regard to the question how the properties should be measured at thesite were retarding factors. In spite of a number of successful examples, some problemsdue to unsuitable use of SCC generated further scepticism. Hence, the major task now isto develop SCC mixtures, which are less sensitive to deviations in properties of thecomponents and external conditions.

    PROPERTIES OF SELF COMPACTING CONCRETE

    The Japanese way of composing the optimum mixture composition of SCC consists of anumber of steps. At first, in a small test, the optimum ratio water to powder is

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    determined. Then a number of general criteria have to be met, the most important ofwhich are that the coarse aggregate volume should be 50% of the solid volume of theconcrete without air, and that the fine aggregate volume should be 40% of the mortarvolume, where particles finer than 0.09mm are not considered as aggregate, but as

    powder. If the composition of the mixture, obtained in this way, is mathematically

    analyzed, it is found that this procedure leads to a concrete composition with a little bit ofexcess paste. That means that slightly more paste is in the mixture than necessary to fillall the holes between the particles: this implies that around any particle a very thinlubricating layer exists, by virtue of which the friction between the particles in the fluidmixture is greatly reduced in comparison to conventional mixtures, Fig. 1. The optimumthickness of those layers lies between narrow limits. If the thickness is too small, there istoo much friction to achieve self compactability. If the thickness is too large, the coarseaggregate sink down and segregation occurs. The rheologic properties of the excess pastelayers are determined by the choice of the superplasticizer. Furthermore, in the fresh statearound the cement and powder particles thin layers of water are formed [1]. In this way athree phase system (coarse particles, fine particles and powder) with intermediate layers

    of paste and water is obtained which minimize the internal friction in the fresh state.Midorikawa [2] carried out tests in order to find the optimum thickness of the excess

    paste layer. Fig. 2 shows the optimum thickness of the layer for a varying ratio V w/V p (volume of water to volume of powder) for different grading curves. It is seen, that thethickness of the paste layer, for which the concrete is still self compacting, increases withdecreasing volume of water. Below V w/V p = 0.8 the appropriate thickness increasesoverproportionally. For practical application, however, this area is not relevant. Theoptimum ratio in this case is in the range V w/V p = 0.8 0.9. The mean thickness of theexcess paste layer is then in the order of magnitude of 0.05mm.

    Vwater /V powder

    Thickness of excess paste [m]

    Vwater /V powder

    Thickness of excess paste [m]

    Fig. 1. Excess paste layers around Fig. 2. Relation between thickness of excessaggregate particles paste layer and water to powder ratio for va-

    rious particle grading curves [2]

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    visible that the rising speed of the concrete in the formwork influences the formwork pressure. For the concretes tested, from a rising speed of about 2m/hour the distributionof the pressure corresponds approximately to the hydrostatic pressure. This, however,does not imply, that for lower rising speeds a reduction of the formwork pressure is areliable assumption. According to the rheologic behavior SCC is a Bingham fluid. Such a

    fluid is characterized by two parameters: the yield value and the plastic viscosity. Theyield value is a measure for the force, necessary to get the concrete moving. The plasticviscosity is a measure for the flow rate (toughness) of the mixture. When the yield valueis high and the plastic viscosity is low, it may happen that the formwork pressure isinitially very low, but suddenly increases due to a shock against the formwork. It istherefore advisable to work always with the hydrostatic formwork pressure.

    Fig. 4. Formwork pressure for different rising speeds for SCC

    TAILORING SCC TO APPLICATIONS

    It is often assumed, that SCC is the best solution for every difficult case. This may resultin disappointments. Fig. 5 left shows a problem which occurred during casting a tunnel

    wall. During casting it was observed that the concrete was too sticky. Therefore it wasdecided to change the concrete composition. As a result, however, air enclosuresoccurred at the interface between the two concretes. Fig. 5 right shows a case, in whichthe lubricating action of the excess paste layers around the aggregate particles was toogood, which resulted in sinking down of the coarse aggregate particles. Those twoexamples, however, should not stimulate the conclusion that SCC is a risky material. Butthey emphasize, that it is important to be well informed about the properties of the SCCthat are required for the application considered.

    0

    1

    2

    3

    0 1

    2

    3

    4

    1,3 1,4

    0,8

    1,0

    Height [m]

    Pressure [ kPa ]

    hydrostatic

    5

    6

    7

    1,6 2 10

    rising speed in m/h

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    Fig. 5. Failures due to unsuitable application of SCC: at the left side air entrapments between two concrete layers, at the right side segregation of the coarse aggregate.

    Even in relatively new codes and recommendations, like the new European code for

    concrete technology EN 206, no special reference is made to SCC. Table I shows theconcrete consistency classes according to this code. The flowability classes F5 and F6 areonly characterized by one parameter: the flow diameter.

    Compaction Slump FlowClass Class mm Class mmC0 1.46C1 1.45-1.26 S1 10-40 F1 340C2 1.25-1.11 S2 50-90 F2 350-410

    C3 1.10-1.04 S3 100-150 F3 420-480S4 160-210 F4 490-550S5 220 F5 560-620

    F6 630

    Table I: Consistency classes according to EN 206

    For a reliable application, however, this is insufficient. As stated before, SCC is aBingham fluid, characterized by two parameters. In The Netherlands therefore an

    extension of the consistency classes was carried out. For the qualification of the concretethe Japanese method was used, offering a simple method on the bases of two tools, thefunnel with defined dimensions and the cone, Fig. 6. The flow diameter and the funnel

    passing time are again two qualifying parameters, alternative to the yield value and the plastic viscosity, with which the behavior of SCC at the construction site can be qualified.The tools are furthermore very suitable to be used at the building site, because they can

    be very easily handled. These tools were used as a basis to extend the consistency classes,

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    Fig. 7. The slump flow is again used as an important characteristic. In addition to that,however, for any range of the slump flow three intervals for the funnel time are defined.

    70

    6 0

    r =1000

    r 1 r 2

    flow

    cone

    paste

    240

    270

    120

    30

    3

    60

    Fig. 6. Japanese tools to measure the rheological properties of SCC in the fresh state: thecone (left) and the funnel (right).

    Fig. 7. Extension of conventional consistency classes with SCC, according to a Dutch proposal.

    In this way for the family of SCCs nine sub-classes are obtained. For any application amost appropriate sub-class exists, see fig. 8. If, for instance, self compacting concrete isspecified for a lightly reinforced wide floor, for practical reasons a short funnel time isrequired. If, on the contrary, a column with congested reinforcement has to be cast, a

    large slump flow in combination with a low funnel time (high viscosity) is mostappropriate. In Fig. 8 also other areas are defined.

    Of course there are many other ways to define the rheological properties of a selfcompacting concrete, like the L-box. the Orimet, the J-ring and others. In a Brite-Euram

    project, with partners from many European countries a thorough evaluation was madewith regard to the effectivity and the value of those measuring methods. Reports on theresults of this research will be given elsewhere at this conference.

    Slump flow

    Consistency classesSelf Compacting Concrete

    Funnel time [sec]

    1 2 3 4 >

    9-25

    5-9

    3-5

    470-570 540-660 630-800 [mm]

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    Funnel time (sec)

    5 6 7 Consistency class

    470-570 540-660 630-800 Slump flow (mm)

    9-25

    5-9

    3-5

    Ramps High &

    Slender

    Walls

    Floors

    Funnel time (sec)

    5 6 7 Consistency class

    470-570 540-660 630-800 Slump flow (mm)

    9-25

    5-9

    3-5

    Ramps High &

    Slender

    Walls

    Floors

    Fig. 8. Areas of application of SCC in relation to optimum rheological properties, definedusing the criteria funnel time and flow diameter.

    APPLICATIONS IN THE PRECAST CONCRETE INDUSTRY

    Previously, it was pointed out that self compacting concrete mixtures are sensitive tovariations in composition and environmental influences. For the precast concrete industry

    this is not a considerable difficulty, since the processes at the plant can be very wellcontrolled. The advantages for using SCC in precast concrete plants are very considerablelike,

    - the substantial reduction of the noise level- the absence of vibration- the reduction of dust (quartzite!) in the air due to vibration- the energy saving- the omission of the expensive mechanical vibrators- the reduction of wear to the formwork- the use of less robust formwork with simpler connections- the reduction of absence for illness

    - the possibility to produce elements with high architectural quality

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    For the production of SCC successful production of SCC it is essential that the basicconstituents, like sand, gravel, fillers and the third generation of superplasticizers, have aconstant quality . This is not always the case. Moreover, not all cement producers supplya constant quality. So, there should be good agreements between the concrete producers

    and the suppliers of the constituents on the quality control. The step from a traditionalconcrete production to the production of SCC is not a big one. Installations with an age ofsay 5-10 years are generally suitable. Further to the traditional equipment a high intensitymixing machine and an installation to dose the fillers are needed.

    As a result of the introduction of SCC the formwork is hardly loaded anymore: it has onlya retaining function. So, the wall can be made of other materials than timber, like

    polystyrene. Also steel formwork with magnetic couplers is possible. The time fordemoulding and re-installing the formwork has been reduced by 50%. There is no needfor the installation of vibration isolators anymore. Rubber joint sealings can be omitted,since by virtue of SCC no leakage through the joints occurs anymore.

    Fig. 9. Architectural element of SCC Fig. 10. Large prestressed SCC girder formetro station in Amsterdam.

    Fig. 9 shows an example of an architectural balcony element of SCC. The element doesnot only show a beautiful shape with very sharp profiles, it has also a homogeneous whitecolor. Fig. 10 shows the assembly of a precast prestressed concrete girder of SCC for thenew metro station at the Amsterdam Arena, the stadium of soccer club Ajax. The girder

    has a length of 22,5m. The concrete strength class is C55 (characteristic cylindercompressive strength of 55 MPa (7850 psi)). The metro station has a length of 350m with4 tracks. This means that 60 girders had to be produced with a total length of 1.4 km. Ifthe girder would have been compacted in the traditional way, heavy vibrating machineswould have been necessary. Due to that, the formwork would have had to be replacedafter a relatively small number of casts. By virtue of the use of SCC the life of theformwork was very long. Another important reason to choose for SCC was theimprovement of the labor conditions in the factory.

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    Fig. 11. Foundation piles of SCC Fig. 12. Concrete arches made of SCC

    Fig. 11 shows a set of foundation piles. The production of such type of piles in the firmwas 70 000 piles a year. For an average length of 15m a total production length of 1000km a year is obtained. Until recently the piles were produced with the so-called shock

    procedure. This means that the formwork was forced to repeatedly fall down from aheight of 50mm (2 inches), which created a shock effect. By virtue of the change to SCCthe necessary casting time was reduced from 7.5 minutes to 1.5 minutes. Sincemechanical compaction was not necessary anymore 12 further minutes were gained.Taking also into account the advantages with regard to the reduction of noise and dust,energy consumption and wear, it is clear that SCC yields considerable advantages. Fig.12 shows a number of concrete arches. Every arch has a length of 65 meter and iscomposed of 5 pieces of 13m. The cross section has a box-shape, with a foam core.Producing such an element with conventional concrete does not make sense, since thefoam core would move due to vibration. A production in parts could be an alternative butis by far too time consuming, and therefore too costly. With SCC perfect elements could

    be made.Meanwhile many precast concrete firms have changed their production to SCC, someeven for 100%.

    APPLICATIONS OF SCC IN SITU

    The introduction of SCC for in-situ applications was slower than in the precast concreteindustry. There are a number of reasons for this:

    - in case of failure the consequences for an in-situ application are much moresevere than in the precast concrete industry. In the latter case the unsuitableelements can be simply rejected, whereas in the first case demolition might be theultimate consequence.

    - There was often no agreement on the way in which the properties at the buildingsite have to be controlled.

    - Self compacting properties can be more easily reached with higher strength thanwith lower concrete strength. In a number of practical applications the concretestrength was therefore higher than actually necessary, which has costconsequences. For many applications a concrete strength class C25 is sufficient.

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    However, especially for the lower strengths classes it is more difficult to obtainrobus t and reliable self compacting concretes.

    Meanwhile, however, a lot of barriers have, or are being, removed. There is now a betterinsight into the required properties of SCC for particular applications, like previously

    shown in Fig. 8. Furthermore qualifying test methods have been evaluated. Finally a newgeneration of superplasticizers has been introduced. Nevertheless, a number of convincing examples exist, which proof that SCC, if applied inan appropriate way, can give excellent results. The first application of SCC in The

    Netherlands according to modern principles was such an example, Fig. 13. In 1998 alarge faade was made for the National Theatre in The Hague, which, for architecturalreasons, was provided with fine triangular ribs with a side length of 8mm. In this case

    Fig. 13. SCC faade in The Fig. 14. City and County Mu-Hague, The Netherlands seum, Lincoln, UK.

    an SCC with relatively high flowability was used (flow diameter 730mm) and a lowviscosity (funnel time 8-9 seconds). Fig. 14 shows the interior of the City and CountyMuseum in Lincoln, UK, where SCC proved to be the best solution for the sloping roofslabs. The architect required a formed finish for the top surface and specified SCC whichnot only reached those parts where other concretes could not come, but gave as well aconsistent high quality finish to both sides of the slab, in spite of the complicated andcongested reinforcement [6].

    There are many practical problems where SCC gives a suitable solution. An example isthe retrofitting of the Ketelbridge, a glued segmental bridge in The Netherlands. At thetime of retrofitting in the year 2002 the bridge was 45 years old. During the years the

    bridge deck was renovated several times, but the old deck was often not totally removed.So, finally the bridge deck was 180mm thick in stead of 50mm. Since as well the trafficload had increased, the joints between the segments opened. Therefore it was decided toincrease the load bearing capacity by external prestressing. A difficulty was the provisionof the deviators inside the box girder. Because the lower flange of the girder had not been

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    designed for the transport of heavy materials, casting concrete inside the girder was norealistic option, even regardless of the technological difficulties involved. As a solutiontherefore SCC was used. The formwork with the reinforcement was built up in theinterior of the girder (Fig. 15), and the SCC was cast from the outside through a littlewindow in the upper flange. The concrete strength class was C35. By a suitable use of

    the rheological properties an excellent result was obtained.

    Fig. 15 Remote casting of a wall with openings in the interior of a box girder bridge forcreating deviation points for additional external prestressing tendons, aiming atincreasing the bearing capacity (Ketelbridge in The Netherlands, 2002).

    Another interesting case for which SCC gave a solution was the provision of the endwalls in elements for a submerged tunnel. Those end walls had a temporary character andserved only for enabling floating transport and submerging. After the elements had beencoupled under water, the walls were demolished. In order to facilitate easy demolishing,SCC in a strength class C20 was used. For casting the concrete between the tunnel wallsthrough small windows in the formwork SCC appeared to the most appropriate solution.

    Fig. 16. Casting the end wall of an element for a submerged tunnel in SCC.

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    SPECIAL SELF COMPACTING CONCRETES

    A remarkable development occurred with regard to the workability of fiber reinforcedconcrete. For a very long period it was noted that the addition of fibers to concretedecreased the workability. However, in his PhD-thesis Grnewald [7] showed that this is

    not necessary at all. He proved that self compacting fiber concretes are very well possible, even up to fiber contents of 140 kg/m 3, if the right combination of fibers andmixture composition is chosen. Fig. 17 shows the maximum possible fiber content forwhich mixtures are still self-compacting (defined as having a flow circle with a diameterof at least 600mm, a round shape and a homogeneous fiber distribution). At the verticalaxis the fiber content in kg/m 3 is given. At the horizontal axes the fiber type (aspectratio/length) and the mixture type (with the sand/gravel vol. ratio) are given.

    Fig. 17. Maximum fiber content for SCC Fig. 18. Self-compacting con-in dependence of fiber type and mixture crete, with 125 kg/m 3 fibers,composition in strength class C115.

    Fig. 19. Testing the flowability of a high performance fiber reinforced concrete C200

    45/3065/40

    80/3080/60

    Mix 1 (57/36.5)Mix 2 (57/39.0)

    Mix 3 (68/36.5)Mix 4 (68/39.0)

    0

    20

    40

    60

    80

    100

    120

    140

    Fibrecontent

    [kg/m3]

    Fibre type

    Referencemixture

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    Fig. 18 gives an impression of the excellent flowing properties during casting of aconcrete with 125 kg/m 3 fibers. Fig. 19 shows the measurement of the flowability of anultra high performance fiber reinforced concrete in a U shaped formwork. The concretehad an average cube strength of about 180 MPa (25000 psi). It contained 235 kg/m 3 steelfibers 20/0.3mm. It was used in a factory to produce prestressed beams for a bridge.

    In another paper at this conference the topic of optimizing the self-compacting propertiesof fiber concrete is treated more in detail [8].

    Another interesting option is self-compacting lightweight concrete. High performancelightweight concrete could allow significant savings in reinforcing- and prestressing steeland foundations. Self compacting properties would even increase the attractiveness ofsuch a material. With regard to the production technology, there is a major difficulty. Thelightweight aggregate particles are porous and therefore influence the mixturecomposition by sucking water from the mixture in the fresh state. As self compactingconcrete is sensitive to the right composition this causes a major difficulty. A solutionwas developed by Mller [9]. He developed a technology which consists of enveloping

    the sucking aggregates with a thin cement bonded surface coating. The composition ofthe cement pastes used for the enveloping is optimized in such a way as to make iteconomically possible to apply a thin layer to the agglomerate in the fresh state. Afterthat, the storage of the freshly enveloped aggregates preventing them from stickingtogether is assured and finally after a rapid setting a high density and strength of theformed envelope is guaranteed. Fig. 20 shows an enveloped lightweight aggregate

    particle of the type Liapor F5, where the thickness of the cement bonded layer, which inthe section is distinctly recognizable by its lighter color, is equal on the average toapproximately 0.25-0.35 mm.

    Fig. 20. Lightweight aggregate particle with skin of with cement paste [9].

    Compared to non-enveloped aggregates, water absorption by dry materials is drasticallyreduced if the dry materials are stored for 30 minutes in water and under a pressure of 50

    bars and if a low or high performance and thus denser lightweight aggregate is used. Theresult is that concrete mixtures with enveloped lightweight aggregate behave with respectto the characteristics and processing of fresh concrete exactly like mixtures with dense,normal weight additive material.Further information on this topic is found in [10].

    NEEDS FOR FURTHER DEVELOPMENT

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    6. Further research into the potential role of viscosity agents and their interaction withsuperplasticizers is worthwhile

    7. Since in the near future service life design (SLD) of concrete structures will be asimportant as design for safety and serviceability, increased attention should be given to

    the role of the microstructure of the various types of available SCCs and its ro le fordurability.

    REFERENCES

    1. Midorikawa, T., Maruyama, K., Shimomura, T. and Momonoi, K., Applicationof the water layer model to mortar and concrete with various powders,Proceedings of the Japan Society of Civil Engineers, No. 578/V-37, pp. 89-98,1997 (in Japanese).

    2. Midorikawa, T., Pelova, G.I., Walraven, J.C., Application of the water layer toself compacting concrete with different size distribution of fine aggregate,

    Proceedings of the Second International Symposium on Self-CompactingConcrete, Tokyo, Japan, 23 -25 October 2001, pp. 237-246.3. Holschemacher, K., Design relevant properties of self compacting concrete,

    Symposium Self Compacting Concrete, Leipzig, Nov. 2001, Proceedings, pp.237-246 (in German).

    4. Billberg, P., F orm pressure generated by self- compacting concrete, 3 rd International Rilem Symposium Self -compacting concrete, 17 -20 August 2003,Reykjavic, Iceland, Proceedings, pp 271-280.

    5. Den Uijl, J.A., Properties of self -compacting concrete, Cement 6, 2002, pp. 88-94 (in Dutch).

    6. www.concretecentre.com .

    7. Grnewald, S., Performance based design of self -compacting reinforcedconcrete Dissertation, TU Delft, 4. June 2004. 8. Grnewald, S., Walraven, J.C., Op timization of the mixture composition of self-

    compacting fiber reinforced concrete, Conference SCC 2005, Chicago, USA,Oct. 30 November 2, 2005.

    9. Mller, H.S., Guse, U.,Concrete Technology Development: important researchresults and outlook in the ne w millennium, Concrete Plant + Precast Technology,2000, Nr. 1, pp. 32-45

    10. Haist, M., Mechtcherine, V., Beitzel, H., Mller, H.S., Retrofitting of buildingstructures using pumpable self-compacting lightweight concrete , Proceedings ofthe 3 rd Inter national RILEM Symposium on Self -Compacting Concrete, pp.

    776-795.11. Grnewald, S., Walraven, J.C., The effect of viscosity agents on thecharacteristics of self- compacting concrete, Conference SCC 2005, Chicago,USA, Oct. 30th Nov. 2 nd, 2005.

    12. Takada, K., Influence of admixtures and mixing efficiency on the properties ofself compacting concrete, PhD -Thesis, TU Delft, May 11 th, 2004.

    http://www.concretecentre.com/http://www.concretecentre.com/http://www.concretecentre.com/
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