Concrete: SCC
Self Compacting Concrete:
Challenge for Designer and Researcher
Joost Walraven
Delft University of Technology, The Netherlands
Self compacting, or “self-consolidating” concrete (SCC) was first developed in Japan in the early nineties. The idea was picked up and
further developed in Europe from about 1997. Substantial research was carried out with regard to the properties of SCC. Because of the
well-controlled conditions, the introduction of SCC in the precast concrete industry was successful. With regard to the application in situ,
the development is slower, because of the sensitivity of the product. In this paper the mechanical properties of SCC in comparison to
conventional concrete are discussed. Examples of applications are shown, both for prefabricated concrete elements and in-situ structures.
The way of measuring the rheological properties is discussed. Examples are given of special self-compacting concrete’s. Needs for further
research are defined.
Self compacting (or self consolidating) concrete (SCC) was
first developed in Japan, in the 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 is robust 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
compacting concrete’s was the option to improve the labor
conditions at the building site and in the factory (noise, dust,
vibrations). During recent years self-compacting concrete
developed to research item nr. 1. A large number of research
projects was carried out, followed by recommendations for
potential users. Especially for the precast concrete industry
self compacting concrete was a revolutionary step forward.
Contrary to that, casting of SCC at the construction site was
regarded with more reservation. The variable conditions at
the construction site, the more complicated control of the
mixture composition and disagreement with regard to the
question how the properties should be measured at the site
were retarding factors. In spite of a number of successful
examples, some problems due to unsuitable use of SCC
generated further scepticism. Hence, the major task now is to
develop SCC mixtures, which are less sensitive to deviations
in properties of the components and external conditions.
the mixture, obtained in this way, is mathematically analyzed,
it is found that this procedure leads to a concrete composition
with a little bit of “excess paste”. That means that slightly more
paste is in the mixture than necessary to fill all the holes between
the particles: this implies that around any particle a very thin
“lubricating” layer exists, by virtue of which the friction between the
particles in the fluid mixture is greatly reduced in comparison
to conventional mixtures, Fig. 1. The optimum thickness of
those layers lies between narrow limits. If the thickness is too
small, there is too much friction to achieve self compactability.
If the thickness is too large, the coarse aggregate sink down
and segregation occurs. The rheologic properties of the
excess paste layers are determined by the choice of the
superplasticizer. Furthermore, in the fresh state around the
cement and powder particles thin layers of water are formed
[1]. In this way a three 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
Properties of Self Compacting Concrete
The Japanese way of composing the optimum mixture
composition of SCC consists of a number of steps. At first, in
a small test, the optimum ratio water to powder is determined.
Then a number of general criteria have to be met, the most
important of which are that the coarse aggregate volume
should be 50% of the solid volume of the concrete without
air, and that the fine aggregate volume should be 40% of the
mortar volume, where particles finer than 0.09mm are not
considered as aggregate, but as powder. If the composition of
72 The Masterbuilder - September 2013 • www.masterbuilder.co.in
Fig. 1. Excess paste layers around aggregate particles
Concrete: SCC
Fig. 4. Formwork pressure for different rising speeds for SCC
Fig. 2. Relation between thickness of excess paste layer and water to powder
ratio for various particle grading curves [2]
thickness of the excess paste layer. Fig. 2 shows the optimum
thickness of the layer for a varying ratio Vw/Vp (volume of water
to volume of powder) for different grading curves. It is seen,
that the thickness of the paste layer, for which the concrete
is still self compacting, increases with decreasing volume of
water. Below Vw/Vp = 0.8 the appropriate thickness increases
overproportionally. For practical application, however, this
area is not relevant. The optimum ratio in this case is in the
range Vw/Vp = 0.8 – 0.9. The mean thickness of the excess
paste layer is then in the order of magnitude of 0.05mm.
Another important aspect for the behavior in the hardened
state is the concrete tensile strength. When the axial tensile
strength of a SCC would substantially differ from that of the
tensile strength of conventional concrete, this should have large
implications for design, since the tensile strength is a governing
aspect in the design for shear, punching, anchorage, crack
width control and the minimum reinforcement. It is obvious
to expect that the tensile strength of SCC is higher than for a
conventional concrete, because of the more homogeneous
interface between the aggregate particles and the cement
past (no direct contact between the aggregate particles). An
evaluation of test results [3] confirms this. However, also here
the results are in the range of scatter of conventional concretes,
so that no complicating exception for SCC has to be made.
Another important aspect is the formwork pressure of self
compacting concrete. Many measurements have been carried
out, but the results were often conflicting. Often the role of the
rising speed of the concrete in the formwork was disregarded.
Fig. 4 shows the results of a number of Swedish [4] and Dutch
[5] tests, collected in one diagram. It is 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 distribution of 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 a reliable 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. The yield value is a measure for the force,
necessary to get the concrete moving. The plastic viscosity
is a measure for the flow rate (toughness) of the mixture. When
the yield value is high and the plastic viscosity is low, it may
happen that the formwork pressure is initially very low, but
suddenly increases due to a shock against the formwork.
It is therefore advisable to work always with the hydrostatic
formwork pressure.
Tailoring SCC to Applications
Fig. 3. Modulus of elasticity of self-compacting concrete [3].
It is often assumed, that SCC is the best solution for every
difficult case. This may result in 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 was decided to change the concrete
composition. As a result, however, air enclosures occurred at
the interface between the two concretes. Fig. 5 right shows
a case, in which the lubricating action of the excess paste
www.masterbuilder.co.in • The Masterbuilder - September 2013 73
Concrete: SCC
layers around the aggregate particles was “too good”, which
resulted in sinking down of the coarse aggregate particles.
Those two examples, however, should not stimulate the
conclusion that SCC is a risky material. But they emphasize,
that it is important to be well informed about the properties of
the SCC that are required for the application considered.
For a reliable application, however, this is insufficient. As
stated before, SCC is a Bingham fluid, characterized by two
parameters. In The Netherlands therefore an extension of the
consistency classes was carried out. For the qualification of the
concrete the Japanese method was used, offering a simple
method on the bases of two tools, the funnel 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, 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.
In this way for the “family of SCC’s” nine sub-classes are
obtained. For any application a most appropriate sub-class
exists, see fig. 8. If, for instance, self compacting concrete is
specified for a lightly reinforced wide floor, for practical reasons
a short funnel time is required. 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
most appropriate. In Fig. 8 also other areas are defined.
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 the concrete
consistency classes according to this code. The flowability
classes F5 and F6 are only characterized by one parameter:
the flow diameter.
Compaction
Class
C0
Slump
Fig. 6. Japanese tools to measure the rheological properties of SCC in the
fresh state: the cone (left) and the funnel (right).
Flow
Class
mm
Class
mm
1.46
C1
1.45-1.26
S1
10-40
F1
C2
1.25-1.11
S2
50-90
F2
350-410
C3
1.10-1.04
S3
100-150
F3
420-480
S4
160-210
F4
490-550
F5
560-620
S5
220
340
F6
Table I: Consistency classes according to EN 206
74 The Masterbuilder - September 2013 • www.masterbuilder.co.in
630
Fig. 7. Extension of conventional consistency classes with SCC, according to
a Dutch proposal.
Of course there are many other ways to define the rheological
properties of a self compacting 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 made with regard to the effectivity and the value of those
Concrete: SCC
Also steel formwork with magnetic couplers is possible.
The time for demoulding and re-installing the formwork has
been reduced by 50%. There is no need for 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. 8. Areas of application of SCC in relation to optimum rheological properties, defined using the criteria funnel time and flow diameter.
measuring methods. Reports on the results of this research
will be given elsewhere at this conference.
Applications in the Precast Concrete Industry
Fig. 9. Architectural element of SCC
Previously, it was pointed out that self compacting concrete
mixtures are sensitive to variations 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 well controlled. The advantages for using
SCC in precast concrete plants are very considerable like,
-
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
For the production of SCC successful production of SCC it is
essential that the basic constituents, like sand, gravel, fillers
and the third generation of superplasticizers, have a constant
quality . This is not always the case. Moreover, not all cement
producers supply a 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 traditional concrete production to the production of SCC
is not a big one. Installations with an age of say 5-10 years are
generally suitable. Further to the traditional equipment a high
intensity mixing 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 only a retaining function. So, the wall
can be made of other materials than timber, like polystyrene.
76 The Masterbuilder - September 2013 • www.masterbuilder.co.in
Fig. 10. Large prestressed SCC girder for metro station in Amsterdam.
Fig. 9 shows an example of an architectural balcony element
of SCC. The element does not only show a beautiful shape
with very sharp profiles, it has also a homogeneous white
color. Fig. 10 shows the assembly of a precast prestressed
concrete girder of SCC for the new 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 cylinder compressive strength of 55 MPa (7850
psi)). The metro station has a length of 350m with 4 tracks.
This means that 60 girders had to be produced with a total
length of 1.4 km. If the girder would have been compacted in
the traditional way, heavy vibrating machines would have been
necessary. Due to that, the formwork would have had to be
replaced after a relatively small number of casts. By virtue of
the use of SCC the life of the formwork was very long. Another
important reason to choose for SCC was the improvement of
the labor conditions in the factory.
Concrete: SCC
Meanwhile many precast concrete firms have changed their
production to SCC, some even for 100%.
Applications of SCC In Situ
The introduction of SCC for in-situ applications was slower
than in the precast concrete industry. There are a number of
reasons for this:
Fig. 11. Foundation piles of SCC
-
in case of failure the consequences for an in-situ application
are much more severe than in the precast concrete
industry. In the latter case the unsuitable elements can be
simply rejected, whereas in the first case demolition might
be the ultimate consequence.
-
There was often no agreement on the way in which the
properties at the building site have to be controlled.
-
Self compacting properties can be more easily reached
with higher strength than with lower concrete strength. In
a number of practical applications the concrete strength
was therefore higher than actually necessary, which has
cost consequences. For many applications a concrete
strength class C25 is sufficient. However, especially for the
lower strengths classes it is more difficult to obtain robust
and reliable self compacting concrete’s.
Meanwhile, however, a lot of barriers have, or are being,
removed. There is now a better insight into the required
properties of SCC for particular applications, like previously
shown in Fig. 8. Furthermore qualifying test methods have
been evaluated. Finally a new generation of superplasticizers
has been introduced.
Fig. 12. Concrete arches made of SCC
Fig. 11 shows a set of foundation piles. The production of
such type of piles in the firm was 70 000 piles a year. For an
average length of 15m a total production length of 1000 km 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 a height of 50mm (2
inches), which created a shock effect. By virtue of the change
to SCC the necessary casting time was reduced from 7.5
minutes to 1.5 minutes. Since mechanical 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 is composed 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 the foam core would move due to vibration. A
production in parts could be an alternative but is by far too
time consuming, and therefore too costly. With SCC perfect
elements could be made.
Nevertheless, a number of convincing examples exist, which
proof that SCC, if applied in an 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 a large façade was made for the National Theatre
in The Hague, which, for architectural reasons, was provided
with fine triangular ribs with a side length of 8mm. In this case
an SCC with relatively high flowability was used (flow diameter
730mm) and a low viscosity (funnel time 8-9 seconds). Fig. 14
Fig. 13. SCC façade in The Hague, Fig. 14. City and County Museum, Lincoln,
The Netherlands
UK.
www.masterbuilder.co.in • The Masterbuilder - September 2013 77
Concrete: SCC
shows the interior of the City and County Museum in Lincoln,
UK, where SCC proved to be the best solution for the sloping
roof slabs. The architect required a formed finish for the top
surface and specified SCC which not only reached those
parts where other concretes could not come, but gave as well
a consistent high quality finish to both sides of the slab, in
spite of the complicated and congested reinforcement [6].
There are many practical problems where SCC gives a suitable
solution. An example is the retrofitting of the Ketelbridge, a
glued segmental bridge in The Netherlands. At the time 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 traffic load had increased, the joints between
the segments opened. Therefore it was decided to increase
the load bearing capacity by external prestressing. A difficulty
was the provision of the deviators inside the box girder.
Because the lower flange of the girder had not been designed
for the transport of heavy materials, casting concrete inside
the girder was no realistic option, even regardless of the
technological difficulties involved. As a solution therefore SCC
was used. The formwork with the reinforcement was built up
in the interior of the girder (Fig. 15), and the SCC was cast
from the outside through a little window in the upper flange.
The concrete strength class was C35. By a suitable use of the
rheological properties an excellent result was obtained.
Fig. 16. Casting the end wall of an element for a submerged tunnel in SCC
it was noted that the addition of fibers to concrete decreased
the workability. However, in his PhD-thesis Grünewald [ 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/m3, if the right combination of
fibers and mixture composition is chosen. Fig. 17 shows the
maximum possible fiber content for which mixtures are still selfcompacting (defined as having a flow circle with a diameter
of at least 600mm, a round shape and a homogeneous fiber
distribution). At the vertical axis the fiber content in kg/m3
is given. At the horizontal axes the fiber type (aspect ratio/
length) and the mixture type (with the sand/gravel vol. ratio)
are given.
Fig. 18 gives an impression of the excellent flowing properties
during casting of a concrete with 125 kg/m3 fibers. Fig. 19
shows the measurement of the flowability of an ultra high
performance fiber reinforced concrete in a U shaped formwork.
The concrete had an average cube strength of about 180 MPa
(25000 psi). It contained 235 kg/m3 steel fibers 20/0.3mm. It
was used in a factory to produce prestressed beams for a
bridge.
Another interesting option is self-compacting lightweight
concrete. High performance lightweight concrete could allow
significant savings in reinforcing- and prestressing steel and
foundations. Self compacting properties would even increase
the attractiveness of such a material. With regard to the
Fig. 15 Remote casting of a wall with openings in the interior of a box girder
bridge for creating deviation points for additional external prestressing tendons, aiming at increasing the bearing capacity (Ketelbridge in The Netherlands, 2002).
Another interesting case for which SCC gave a solution was
the provision of the end walls in elements for a submerged
tunnel. Those end walls had a temporary character and
served only for enabling floating transport and submerging.
After the elements had been coupled 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 walls through small windows in the
formwork SCC appeared to the most appropriate solution.
Special Self Compacting Concretes
A remarkable development occurred with regard to the
workability of fiber reinforced concrete. For a very long period
78 The Masterbuilder - September 2013 • www.masterbuilder.co.in
Fig. 17. Maximum fiber content for SCC in dependence of fiber type and
mixture composition
Concrete: SCC
and if a low or high performance and thus denser lightweight
aggregate is used. The result is that concrete mixtures with
enveloped lightweight aggregate behave with respect to 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
The sensitivity of SCC mixtures for minor variations in the
mixture composition should be decreased. This can be done
by adding appropriate types and amount of fillers. Another,
not yet fully explored possibility is the use of viscosity agents.
Experiments on mixtures with viscosity agents show that the
sensitivity of for instance variations of the water content on the
viscosity can be strongly reduced by applying an appropriate
viscosity agent, see f.i. Grünewald [11]. Especially the potential
of viscosity agents for improving the stability of mixtures with
low and medium strength, suitable for large scale in-situ
applications, deserves further attention.
Also the further development of suitable superplasticizers
for SCC is worthwhile, possibly in combination with viscosity
Fig. 18. Self-compacting concrete, with 125 kg/m3 fibers, in strength class C115.
production technology, there is a major difficulty. The lightweight
aggregate particles are porous and therefore influence the
mixture composition by sucking water from the mixture in
the fresh state. As self compacting concrete is sensitive to
the right composition this causes a major difficulty. A solution
was developed by Müller [9]. He developed a technology
which consists of enveloping the sucking aggregates with
a thin cement bonded surface coating. The composition of
the cement pastes used for the enveloping is optimized in
such a way as to make it economically possible to apply a
thin layer to the agglomerate in the fresh state. After that,
the storage of the freshly enveloped aggregates preventing
them from sticking together is assured and finally after a rapid
setting a high density and strength of the formed 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 in the section is distinctly
recognizable by its lighter color, is equal on the average to
approximately 0.25-0.35 mm.
Compared to non-enveloped aggregates, water absorption
by dry materials is drastically reduced if the dry materials are
stored for 30 minutes in water and under a pressure of 50 bars
80 The Masterbuilder - September 2013 • www.masterbuilder.co.in
Fig. 19. Testing the flowability of a high performance fiber reinforced concrete
C200
Concrete: SCC
4. There is a considerable future for self compacting fiber
reinforced concretes
5. The most important task for research is to develop SCC’s
with decreased sensitivity to variations in constituents and
environmental influences. This holds particularly true for insitu concrete’s, with medium and low strengths.
6. Further research into the potential role of viscosity agents
and their interaction with superplasticizers is worthwhile
Fig. 20. Lightweight aggregate particle with skin of with cement paste [9].
agents. Takada [12] showed in his PhD-thesis that there is
a strong influence of the type of superplasticizer on the
necessary mixing time and mixing intensity. In this area there
is still a need for further research.
A very important aspect to be regarded is the durability of SCC.
There is a tendency that in the near future structures should not
only be designed for safety (ULS) and serviceability (SLS), but
as well – and with the same importance - for service life. This
means that increased demands will be raised on the resistance
of SCC with regard to chloride ingress, carbonation and frostthaw cycles. It was shown by many research projects that
SCC is approximately equivalent to conventional concretes
with regard to the majority of its mechanical properties in the
hardened state. However, with regard to the microstructure
of hardened SCC and its significance to durability there are
still quite a number of open questions. In this respect the
interface between matrix and aggregates plays an important
role. Furthermore the role of (combinations of) additives
(superplasticizers, air entraining agents, viscosity agents) on
the microstructure, including porosity and permeability should
get due attention. In this respect special attention has to be
devoted to the average and low strength concrete’s used in
in-situ structures, if exposed to more severe environmental
conditions.
Conclusions
1. In spite of its short history, self compacting (or – consolidating)
concrete has confirmed itself as a revolutionary step forward
in concrete technology.
2. For the application of SCC in situ, it is necessary that SCC’s
are designed (tailor-made) for any particular case. General
rules are available on the basis of experience.
3. It can be shown by cost analysis, that SCC in precast
concrete plants can be more economically produced than
conventional concretes, in spite of the slightly higher material
price. Cost comparisons should always be made on the basis
of integral costs.
82 The Masterbuilder - September 2013 • www.masterbuilder.co.in
7. Since in the near future service life design (SLD) of concrete
structures will be as important as design for safety and
serviceability, increased attention should be given to the role
of the microstructure of the various types of available SCC’s
and its role for durability.
References
1. Midorikawa, T., Maruyama, K., Shimomura, T. and Momonoi, K.,
“Application of 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 to self compacting concrete with different size
distribution of fine aggregate”, Proceedings of the Second
International Symposium on Self-Compacting Concrete”, 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., “Form pressure generated by self-compacting
concrete”, 3rd 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. Grünewald, S., “Performance based design of self-compacting
reinforced concrete” Dissertation, TU Delft, 4. June 2004.
8. Grünewald, S., Walraven, J.C., “Optimization of the mixture
composition of self-compacting fiber reinforced concrete”,
Conference SCC 2005, Chicago, USA, Oct. 30 – November 2,
2005.
9. Müller, H.S., Guse, U.,“Concrete Technology Development:
important research results and outlook in the new millennium”,
Concrete Plant + Precast Technology, 2000, Nr. 1, pp. 32-45
10. Haist, M., Mechtcherine, V., Beitzel, H., Müller, H.S., „Retrofitting of
building structures using pumpable self-compacting lightweight
concrete”,
Proceedings of the 3rd International RILEM
Symposium on “Self-Compacting Concrete”, pp. 776-795.
11. Grünewald, S., Walraven, J.C., “The effect of viscosity agents
on the characteristics of self-compacting concrete”, Conference
SCC 2005, Chicago, USA, Oct. 30th – Nov. 2nd, 2005.
12. Takada, K., “Influence of admixtures and mixing efficiency on the
properties of self compacting concrete”, PhD-Thesis, TU Delft,
May 11th, 2004.