Self-Compacting Concrete: Methods of Testing and Design: P Kumar, Non-Member
Self-Compacting Concrete: Methods of Testing and Design: P Kumar, Non-Member
Self-Compacting Concrete: Methods of Testing and Design: P Kumar, Non-Member
P Kumar, Non-member
Nowadays, the performance required for concrete structures is more complicated and diversified. The concrete is required to have properties like
high fluidity, self-compactability, high strength, high durability, better serviceability and long service life of concrete structures. Self-compactability
is desirable to attain rationalized and labour saving effects in manufacturing and placing of concrete. Self-compacting concrete (SCC) is a highly
engineered concrete that addresses these requirements. It was developed around 1988 in Japan, to improve the durability of concrete structures.
The early stage deteriorations of concrete structures are a result of the manual placing and the inadequate consolidation. Therefore, the need for
the development of concrete with high fluidity and no segregation was felt. This paper deals with the history of SCC development and its basic
principle, different testing methods to test high-flowability, resistance against segregation, and passibility. Different mix design methods using a
variety of materials has been discussed in this paper, as the characteristics of materials and the mix proportion influences self-compactability to
a great extent, also its applications and its practical acceptance at jobsite and its future prospects have also been discussed.
Keywords: Self-compacting concrete; Self-compactability testing method; Mix-design method
INTRODUCTION DEVELOPMENT
For several years, the problem of the durability of concrete In Japan, in early eighties, premature deterioration of concrete
structures has been a major problem posed to engineers. To structures were detected almost everywhere in the country. The
make durable concrete structures, sufficient compaction is main cause of the deterioration was recognized as inadequate
required. Compaction for conventional concrete is done by compaction. In addition, the gradual reduction in the number
vibrating. Over vibration can easily cause segregation. In of skilled workers in Japan’s construction industry led to a
conventional concrete, it is difficult to ensure uniform material reduction in the quality of construction work. As a solution for
quality and good density in heavily reinforced locations. If steel these social and technical requirements, the concept of SCC
is not properly surrounded by concrete it leads to durability was proposed by Prof Okamura1 at Tokyo University in 1988.
problems. The answer to the problem may be a type of concrete He gave the first prototype of SCC using materials already in
which can get compacted into every corner of form work and the market. Later studies to develop SCC, including a
gap between steel, purely by means of its own weight and fundamental study on the workability of concrete, were carried
without the need for compaction. The SCC concept was out by Ozawa and Maekawa2. SCC has now been taken up with
introduced to overcome these difficulties. This concept can be enthusiasm across Europe and other parts of the world, in both
stated as the concrete that meets special performance and site and precast concrete work. Practical application has been
uniformity requirements that cannot always be obtained by using backed up by research on its physical and mechanical
conventional ingredients, normal mixing procedure and curing characteristics of SCC.
practices.
Early SCC relied on very high contents of cementitious paste,
The SCC is an engineered material consisting of cement, the mixes required specialized and well-controlled placing
aggregates, water and admixtures with several new constituents methods to avoid segregation, but the high contents of cement
like colloidal silica, pozzolanic materials, portland flyash (PFA), paste made them prone to shrinkage and high heat generation.
ground granulated blast furnace slag (GGBS), microsilica, The overall costs were very high and applications therefore
metakaolin, chemical admixtures to take care of specific remained very limited. After series of advancements it is no
requirements, such as, high-flowability, compressive strength, longer a material consisting of cement, aggregates, water and
high workability, enhanced resistances to chemical or mechanical admixtures. As already mentioned it is now an engineered
stresses, lower permeability, durability, resistance against material with several constituents.
seg regation, and passibility under dense reinforcement
conditions. BASIC PRINCIPLE
The properties, such as, fluidity and high resistance to The SCC is that which gets compacted due to its self-weight
seg regation enables the placement of concrete without and is deaerated (no entrapped air) almost completely while
vibrations and with reduced labour, noise and much less wear flowing in the form work. In densely reinforced structural
and tear of equipment. Use of SCC overcomes the problem of members, it fills completely all the voids and gaps and maintains
concrete placement in heavily reinforced sections and it helps nearly horizontal concrete level after it is placed. With regard
to shorten construction period. to its composition, SCC consists of the same components as
conventionally vibrated normal concrete, ie, cement, aggregates,
P Kumar resides at 2B/26/10, Bhilai, Chattisgarh 490 006.
water, additives or admixtures. However, the high dosage of
This paper (revised) was received on October 17, 2005. Written discussion on this super-plasticizer used for reduction of the liquid limit and for
paper will be entertained till April 30, 2006. better workability, the high powder content as ‘lubricant’ for
Superplasticizer enhances deformability and with the reduction conventional one in the way that the concrete sample placed
of water/powder segregation resistance is increased. High into the mould has no reinforcement rod and when the slump
deformability and high segregation resistance is obtained by cone is removed the sample collapses. The diameter of the
limiting the amount of coarse aggregate. These two properties spread of the sample is measured, ie, a horizontal distance is
of mortar and concrete in turn leads to self-compactability measured as against the vertical slump measured in the
limitation of coarse aggregate content. Figure 1 shows the basic conventional test. While measuring the diameter of the spread,
principles for the production of SCC. the time that the sample takes to reach a diameter of 500 mm
(T50) is also sometimes measured. The Slump Flow test can give
INVESTIGATIONS ON SELF-COMPACTING
an indication about the filling ability of SCC and an experienced
CONCRETE
operator can also detect an extreme susceptibility of the mix to
Several investigations have been carried out to make SCC a segregation. However, this information cannot be obtained from
standard construction material. The most important research numerical results alone, a substantial previous experience in
investigations on SCC include: using the test and carrying out construction in SCC is essential.
(b) mix-design method including evaluation methods for The V-funnel test was developed in Japan and used by Ozawa,
materials. et al 5. The equipment consists of a V-shaped funnel, shown in
Figure 3. The funnel is filled with concrete and the time taken
(c) construction method including acceptance test at jobsite. by it to flow through the apparatus measured. This test gives
account of the filling capacity (flowability). The inverted cone
Testing of SCC
shape shows any possibility of the concrete to block is reflected
At the stage before solidification, self-compacting concrete is in the result.
required to have three qualities: high-flowability, resistance
U-type Test
against segregation and passibility, ie, ability that is necessary to
pass the space between reinforcing bars. Other additional The U-type test6 proposed by the Taisei group is shown in Figure 4.
properties, such as, washout resistance and finishability, may be In this test, the degree of compactability can be indicated by
significant and specified for individual projects/applications.
Therefore, it is important to test whether the concrete is self- 490 mm
compactable or not and also to evaluate deformability or
75 mm
viscosity for estimating proper mix proportioning if the concrete
does not have sufficient self-compactability. The existing
procedures for self-compacting characteristics are those, which
425 mm
100 mm
450
590
100 mm
500 mm
Rebars 3 × φ13
Distance 4 × 50 mm
140
h= 300
50 mm
140 140
280
50 mm
Unit : mm 300 mm
the height that the concrete reaches after flowing through an 150 mm 350 mm
obstacle. Concrete with the filling height ‘h’ of over 300 mm
can be judged as self-compacting.
Figure 6 Fill box test
L-box Test
between two sides of the container is taken as the measure for
The L-box test method uses a test apparatus comprising a the filling ability (flowability).
vertical section and a horizontal trough into which the concrete
is allowed to flow on the release of a trap door from the vertical Orimet Test
section passing through reinforcing bars placed at the
The Orimet test is based on the principle of an orifice rheometer
intersection of the two areas of the apparatus (Figure 5)7. The
applied to fresh concrete. The test involves recording the time
time it takes to flow a distance of 200mm (T-20) and 400 mm
taken for a concrete sample to flow out from a vertical casting
(T-40) into the horizontal section is measured. The concrete
pipe through an interchangeable orifice attached at its lower
ends of the apparatus H 1 and H2 measure the height of the
end (Figure 7) 8. The shorter the flow-time, the higher is the
concrete at both ends. The L-box test can give an indication as
filling ability of the fresh mix. The Orimet test also shows a
to the filling ability and passing ability.
potential to assess resistance to segregation at a site.
Fill Box Test
Slump Flow/J-Ring Combination Test
The fill box test uses a test apparatus comprising transparent
This involves the slump cone being placed inside a 300 mm
container with a flat and smooth surface (Figure 6)4. Thirty-
diameter steel ring attached to vertical reinforcing bars at
five obstacles each of 20 mm diameter made of PVC with a
appropriate spacing (the J-ring itself) (Figure 8)9. Like in the
centre-to-centre distance of 50 mm are present in the container.
Slump Flow test, the diameter of the spread and the T-50 time
At the topside is put a filling pipe (diameter 100 mm height 500
are recorded, but the height of the concrete after the test within
mm) with a funnel (height 100 mm). The container is filled with
concrete through this filling pipe and the difference in height
100
200
980
Rebars 3× φ12
600
Gap 0.35 mm
1090
600
60
200
150
H1
H2
0-200 0-400
800
Unit : mm Unit : mm
Figure 5 L-box test Figure 7 Orimet test
60 mm
This recently developed test involves the J-Ring being placed
centrally below the orifice of the Orimet apparatus, allowing
the discharged mix to fall into it and flow outwards. The Orimet
time is recorded as in the conventional Orimet test, along with
d= 100 mm
the diameter of the concrete spread and the height of the
concrete within the J-ring 9. The more dynamic flow of concrete
dz dz
in this test simulates better the behaviour of a SCC mix when
placed in practice compared with the Slump-flow variation. The
Orimet/J-ring combination test shows great promise as a
method of assessing filling ability, passing ability and resistance
to segregation. Definition of Γp/m=(d/d0)2 - 1, where d = 1/2 (d1+d2)
Figure 9 Flow cone and flow table to determine the relative slump-flow Γp
GTM Segregation Test
270
The GTM segregation test has been developed by the French
30
contractor, GTM, to assess segregation resistance (stability). It
consists of taking a sample of 10 litres of concrete, allowing it
to stand for 15 ± 0.5 min to allow any internal segregation to
occur, then pouring half of it on to a 5 mm sieve of 350 mm
240
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in actual structures has gradually increased worldwide. SCC Performance Concrete Based on Durability Design of Concrete Structures’.
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reduction in noise level in the factory as well as on site, reduction
in personal injuries from noise and manual handling, reduction 3. F Dehn, K Holschemacher, K and D Weibe. ‘Self-Compacting Concrete (SCC)
7. Ö Petersson, P Billberg and B K Van. ‘A Model for Self-compacting Concrete’. 13. S Surlekar. ‘Self Compacting Concrete’. ICI Journal, vol 2, no 4, January-March
Proceedings of International RILEM Conference on ‘Production Methods and Workability 2002, pp 5-9.
of Concrete’, edited by P J M Bartos, et al, Chapman & Hall/E & FN Spon, Paisley,
1996, pp 483-490. 14. K Ozawa (editor), et al. Proceedings of the International Workshop on Self-Compacting
Concrete (CD-ROM), including State-of-the Art Report on Self-compactability
8. P J M Bartos. ‘An Appraisal of the Orimet Test as a Method for On-site Evaluation, Materials and Design, Construction, Manufacturing and Concrete
Assessment of Fresh SCC Concrete’. Proceedings of International Workshop on Self- Products and Summary of Recommendations and Manuals for Self-compacting
Compacting Concrete, Japan, August 1998, pp 121-135. Concrete in Japan. Also available from Concrete Engineering Series, no 30, Japan
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Concrete’. CEN/STAR PNR Workshop on Measurement, Testing and Standardisation: 15. R Gaimster R. ‘Self-compacting Concrete’. Concrete , April 2000, pp 23-27.