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Fresh properties of self-compacting concrete (SCC)

Otto-Graf-Journal Vol. 14, 2003179

FRESH PROPERTIES OF SELF-COMPACTING CONCRETE (SCC)

FRISCHBETONEIGENSCHAFTEN VON SELBSTVERDICHTENDEMBETON (SVB)

PROPRIETES DU BETON AUTOPLAANT (BAP) FRAIS

Timo Wstholz

SUMMARY

Several methods existing for testing the flowability of self-compacting

concrete (SCC). In this article a simple method based on the so-called J-Ringtest is presented which allows the quantification of the part of the blockedconcrete volume. Furthermore some empirical relationships between differenttest results are presented which were found for the tested SCC mixtures.

ZUSAMMENFASSUNG

Es gibt eine Reihe von verschiedenen Prfmethoden zur Bewertung derFliefhigkeit von Selbstverdichtendem Beton (SVB). In diesem Artikel wirdeine einfache Methode zur Quantifizierung des blockierten Betonvolumens vor-gestellt, die auf dem sogenannten J-Ring Versuch beruht. Des Weiteren werdenempirische Zusammenhnge zwischen den einzelnen Messwerten angegeben,die fr die untersuchten SVB-Mischungen gefunden wurden.

RESUME

Il existe une srie de diffrentes mthodes de contrle pour valuer la flui-

dit du bton autoplaant (BAP). Dans l'article prsent, une mthode simple pour quantifier le volume de bton bloqu est prsente Cette mthode est basesur le test J-Ring . Des relations empiriques entre les valeurs mesures obte-nus pour les diffrents BAP examins sont galement prsentes.

KEYWORDS: Self-compacting concrete, SCC, blocking, J-Ring, blocking ratio, step of blocking


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2. QUANTIFICATION OF THE PASSING ABILITY

It was already mentioned that SCC has to have the ability to flow throughnarrow openings without hindrance. This means that the so-called blocking of coarse aggregates through bridging has to be avoided. Fig. 2 shows the mecha-

nism of blocking of coarse aggregate by a two-dimensionally illustrative model.

Fig. 2: Mechanism of blocking [3]

One possibility for assessment of the blocking behaviour is to perform thewell-known slump flow test under use of the so-called J-Ring (

Fig. 3).

Fig. 3: Necessary equipment for performing the J-Ring test [5](schematic, just before setting the Abrams cone on the worktop)

After the lifting motion of the Abrams cone the concrete must flow underits dead weight through the steel rods which shall simulate the flow through re-inforcement in a real formwork. Fig. 4 shows a photography of the concreteshape which arose after the J-Ring test was performed. Dependent on the mix-ture composition (and also on the number of steel rods) a clearly increased con-tent of coarse aggregates can be observed within the ring despite reaching a de-

fined spread diameter. Apparently blocking can be determined. A second pa-


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TIMO WSTHOLZ

182

rameter (beside the spread diameter s J and the flow time t 500,J ) can be quoted bymeasuring the height difference of the concrete behind and in front of the rods of the J-Ring. A mean value can then be calculated of four measuring points (twodirections each with two measuring points). This mean value is defined as thestep of blocking st J. The method of measuring the step st J was also stated in [6].

V c

V block V block

st J

D

Fig. 4: Photography of the measurement of the step (J-Ring with 16 rods, st J 30 mm) and idealised spread of concrete for calculation of the blocking index [4].

From the measured step st J the portion of the blocked concrete volume canbe derived (Fig. 4). Thus a blocking index as the ratio of the blocked concretevolume V block related to the total concrete volume V C can be calculated (eq. 1).

The part of the blocked concrete volume is then directly proportional to thestep st J. It has to be annotated that the concrete shape isnt exactly plane. It israther curved due to the concrete yield value and the stresses caused from dead

weight. This is the reason why a step st J can be measured despite apparentlyblocking is not determined. But for a first simplification the concrete shape canconsidered to be plane.

2 2

4 4block J

c c c

D D st

V st

V V V

= = = (eq. 1)

with:

blocking indexVC whole concrete volume (volume of the Abrams cone)

Vblock blocked concrete volumestJ step of blocking, mean value measured in two directions

each with two measuring points at the ends

D diameter of the idealised concrete shape


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3. TEST RESULTS

A set of fresh concrete investigations were accomplished in the context of an European GROWTH project called Testing SCC (GRD2-2000-30024)which served to investigate methods for quantification of the blocking behaviourof SCC. Therefore the filling and passing ability of fresh concrete SCC mixtures(contained crushed granite as coarse aggregates) have been assessed. The spreaddiameters and the flow times of the slump flow test (s, t 500 ) respective the J-Ringtest (s J, t500,J ), the step of blocking st J and the flow time t V of the so-calledV-funnel test were measured.

SCC mixtures are often characterized by their funnel time t V (which is of-ten used as a degree of the apparent viscosity of mix) and their spread diameter swhich stands for the filling ability. Fig. 5 gives an overview over the character-

istic fresh concrete parameters of the tested mixtures; the results are ordered bythe step st J . Apparently no blocking could be observed if the step st J was below10 mm.

0

5

10

15

20

25

30

35

500 550 600 650 700 750 800

Spread s [mm]

F u n n e

l t i m e

t V [ s

]

0 < stJ


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TIMO WSTHOLZ

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Fig. 6 shows the interrelation between the spread s J and s. The differences = s s J between the two diameters decreases with an increasing filling abil-ity. However the there exists a large scatter (Fig. 7).

400

450

500

550

600

650

700

750

800

400 500 600 700 800

Spread s [mm]

S p r e a

d s J

[ m m

]

y = 1.122x - 122.75

R = 0.93

Fig. 6: Spread s J (J-Ring) vs. spread s (slump flow)

0

10

20

30

40

50

60

70

80

90

100

400 450 500 550 600 650 700 750 800

Spread s [mm]

D e v

i a t i o n s = s - s J

[ m m

]

y = -0.172x + 147.5R = 0.36

Fig. 7: Difference s vs. spread s

It was shown in the previous chapter that the part of the blocked concretevolume V block is proportional to the step st J. It might be therefore of interest if there exists a relationship between the difference s and the step st J (Fig. 8).


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0

10

20

30

40

50

60

70

0 20 40 60 80 100

Difference s = s - s J [mm]

S t e p s

t J [ m m

]

Fig. 8: Step st J vs. difference of spread s

Even the difference s is limited to 30 mm, the step st J scatters between8 mm (no blocking) and 65 mm (strong blocking). It can be derived from Fig. 7and Fig. 8 that a s-criterion (alone) is not suitable for quantification andevaluation of the blocking behaviour of a SCC mixture.

In the J-Ring test and also in the V-funnel test the concrete has to overcomea narrow opening obstacle. It can therefore assumed that there also exists a rela-tionship between the measured parameters of these two tests. Fig. 9 contains thestep st J and the flow time t V .

y = 19,376Ln(x) - 21,958R 2 = 0,6946

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30

Funnel time t V [s]

S t e p

s t J

[ m m

]

Fig. 9: Relationship between the blocking behaviour and funnel time


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TIMO WSTHOLZ

186

The funnel time t V is often used to estimate the apparent viscosity of amixture. However, many factors are playing a role and influencing the result of the V-funnel test: the amount, shape and size distribution of aggregates and alsothe viscosity and amount of paste etc. This means that the funnel time does notnecessarily correspond with the viscosity of a mix measured e.g. by a rheometer.

There was also found an empirical relationship between the spread s J andthe step st J (Fig. 10). The relatively good stability index of R = 0,95 can attrib-uted to the fact that a geometric relationship exists among these parameters (thevolume of the Abrams cone is fixed of about 5,5 litres).

0

5

1015

20

25

30

35

40

45

50

55

60

65

70

350 400 450 500 550 600 650 700 750 800 850

Spread s J [mm]

S t e p s

t J [

m m

]

y = -0.169x + 131.9R = 0.95

Fig. 10: Step st J vs. spread s J

It was already shown that the blocked concrete volume is linked with thefunnel flow time t V. But also the segregation resistance is linked with the appar-ent viscosity of a SCC mixture. To achieve a sufficient resistance to segregation,the funnel time may not fall below a minimum value. From practical sight of view it would be convenient to know a reliable relationship between the flowtimes t 500 respective t 500,J and the funnel time t V of a SCC mixture. Then the V-funnel test could be skipped. The relationships which were found between theflow times are plotted in Fig. 11 and Fig. 12. The correlation between the t 500 -

value and the t V-value is for the slump flow test better than for the J-Ring test.


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However, the measurement of the t 500 -value is more operator influenced than themeasurement of the V-funnel flow time t V .

0

12

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30

Funnel time t V [s]

F l o w

t i m e

t 5 0 0

[ s

]

y = 0.261x + 0.523

R = 0.77

Fig. 11: Relationship between the t 500 -value (slump flow test) and the funnel time

0

5

10

15

20

25

0 5 10 15 20 25 30Funnel time t V [s]

F l o w

t i m e

t 5 0 0

, J [

s ]

y = 0.703 x0.884

R = 0.67

Fig. 12: Relationship between the t 500,J -value (J-Ring test) and the funnel time


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4. SUMMARY

Several methods existing for testing the filling and passing ability of SCC.In this article a simple method was presented which allows the quantification of the part of the blocked concrete volume with the so-called J-Ring test. It couldbe shown that the blocked concrete volume is proportional to the step of block-ing which adjusts itself directly in front and behind the steel rods of J-Ring. This method was compared with the conventional method which evalu-ates the blocking behaviour of SCC by the difference of spread between theslump flow test and the J-Ring test. It could be derived that the conventionalmethod is not suitable to quantify the blocking behaviour. Also some empiricalrelationships between different test results were presented which had been foundfor the tested SCC mixtures.

5. REFERENCES

[1] Reinhardt, H.-W. (Hrsg.) et al.: Sachstandbericht SelbstverdichtenderBeton (SVB). Deutscher Ausschuss fr Stahlbeton (DAfStb), Heft516. Berlin, Beuth Verlag, 2001.

[2] Skarendahl, (ed.); Petersson, . (ed.): Self-Compacting Concrete:State-of-the-Art report of RILEM Technical Committee 174-SCC.RILEM Publications, S.A.R.L., Cachan 2000.

[3] Takada, K.; Tangtermsirikul, S.: Testing of Fresh Concrete. In: Self-Compacting Concrete: State-of-the-Art report of RILEM TechnicalCommittee 174-SCC. Ed.: Skarendahl, .; Petersson, ., RILEMPublications, S.A.R.L, Cachan, 2000, pp. 20-34.

[4] Wstholz, T.: Fresh and hardened properties of self-compacting concrete. In: Mitteilung des Instituts fr Werkstoffe im Bauwesen.Jahresbericht 2002/2003 (to be published).

[5] German Guideline for SCC: DAfStb-Richtlinie SelbstverdichtenderBeton (SVB-Richtlinie). Ergnzung zu DIN 1045: 1988-07, Berlin2001.

[6] EFNARC: Specification and Guidelines for Self-Compacting Concrete. Farnham, February 2002.

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