Inverted slump cone test

The correlations obtained by the different test methods have been evaluated in several studies [1,2,6]. Relationships of this kind are presented in Figure 6.2, showing that even at a low slump the fresh FRC responds well to vibration, as estimated by the VeBe test (Figure 6.2(a)). The linear relationship between the results of the inverted slump cone and the VeBe tests (Figure 6.2(b)) suggests that both are sensitive to similar parameters. This indicates that the inverted slump cone test may be a suitable alternative to the VeBe test, in particular for site application. 

In the case of fibre reinforced composites a special measure of workability was proposed by ACI 544.2R-89 called inverted slump cone. A standard Abrams cone is suspended upside down and filled with tested material without any compaction. The internal vibrator is activated and the bottom cover of the cone is removed, then the time of flow out of the material is recorded, which is usually between 10 and 30 seconds. This method is still in use, but is subject to some criticisms. Other methods of the flowability of the fresh mix with dispersed fibres are proposed by Laboratoire des Fonts et Chaussees in France (cf. Section 12.5). 

Inverted slump cone (ASTM C995, Standard Test Method for Time of Flow of Fibre-Reinforced Concrete Through Inverted Stump Cond. This test was developed specifically for FRC. A standard slump cone is inverted over a yield bucket and is then filled with concrete in three approximately equal layers without compaction. A 25 mm diameter internal vibrator is inserted vertically and centrally into the cone and is permitted to descend at a rate such that it touches the bottom of the bucket in 3 s. The time for the cone to become empty of concrete is recorded as the inverted slump-cone time. This test is sensitive to the mobility and fluidity of FRC, and is used for mixes which seem too stiff when evaluated by the slump test (slump < 50 mm). It should not be used if the time of flow is less than 8 s such fluid mixes are better evaluated by the slump test. 

Figure 6.2 Relations between the results obtained by various workability tests of fibre reinforced cements, (a) Slump vs. VeBe (b) VeBe vs. inverted slump cone (after Johnston [I]).

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