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TECHNICAL PAPER

[8]
Figure 4: Appearance of paste in the Puntke test : (above) Water content lower than saturation; (below) Water content at saturation

cement and fly ash in the combination. The work reported by While the Puntke test is a simple method to assess the binder
[7]
Nanthagopalan et al. provides a clear evidence of the influence combination with the best possible packing, it is also equally
of ideal packing of powders within the cementitious material on important to adopt a systematic approach to determine the
the flow properties of pastes. superplasticizer (SP) and viscosity modifying agent (VMA)
dosage for SCC. Very often, SCC is beset with problems arising
The study conducted by Nanthagopalan and Santhanam from the excess dosage of SP that may cause segregation, or
[8]
undertook to use the ‘Puntke’ test to empirically assess the ideal using a combination of SP and VMA that leads to excessive
packing combination of cement and fly ash for designing SCC. retardation-this implies that the dosages of SP and VMA should
This test employs the determination of liquid content (could be just enough to provide the right workability and segregation
be water or kerosene) that just fills in the voids in a dry mixture resistance, without compromising the rate of setting and
of the cement and fly ash. In the test method, the powders are strength development.
intimately blended in a beaker, and water (or kerosene) is added
to the mixture with continuous mixing up to the point where a The literature on cement-SP compatibility has put forward the
sheen just appears on the surface of the paste-this condition use of Marsh cone and mini slump tests for the purpose of
indicates a complete filling of the voids by the liquid, as the determining the saturation dosage of the SP, and also making
excess liquid just starts appearing on the surface (Figure 4). At an assessment of the retention of the flowability with respect
this stage, the amount (volume) of water added corresponds to to time for SCC [9, 10] . Being simple and quick to perform, these
the voids content in the mixture. The experiment was repeated tests have also been adapted in site laboratories. In the study
with multiple combinations of cement and fly ash. by Nanthagopalan and Santhanam , the optimum dosage
[8]
was determined with the help of the mini slump test to be
Irrespective of the liquid used (in this study, water, water + SP, the dosage at which the mini slump spread was just crossing
and kerosene), the same combination of cement and fly ash was 165 mm, without any water separation at the periphery of the
determined for maximum packing, i.e. the least voids content. spread paste. Further, a rheological assessment performed using
This was at a cement : fly ash (by volume) of 60 : 40, as seen in a Brookefield Viscometer with a coaxial cylinder arrangement
Figure 5.
indicated that the paste had a yield stress close to 0, and plastic
viscosity that decreased with increasing w/b [a linear regression
of the data points was performed to determine the yield stress
as the intercept on the Y axis and plastic viscosity as the slope,
as per the model indicated by Equation 2]. A snapshot of the
results is presented in Table 3.

The issue of selecting the correct dosage of VMA was resolved
by a simple test involving the settlement of an aggregate
inside a paste medium, as described in Nanthagopalan
and Santhanam [11] -see Figure 6. The dosage of VMA in the
paste (with optimized SP) was increased until a point when
the spherical mass (glass marble of specific gravity 2.51 and
diameter 18 mm, tied to a nylon string) just stopped any
penetration into the paste. The experiment was conducted
Figure 5: Packing density achieved in the Puntke test – irrespective of
[8]
the fluid used, the maximum packing density is achieved with the same for all pastes described in Table 3, except for the one with
combination of cement and fly ash w/b of 0.8, which did not require the use of a VMA. The

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