Summary and Conclusions

A modification of the standard slump test intended to evaluate the two Bingham characteristics of fresh concrete is presented. This test allows a better quality control of the fresh concrete in the field. The procedure has been described in detail and the results of tests obtained on 78 mixtures have been reported. The conclusions are as follows:

1. The final slump combined with the unit mass of the concrete allows an estimation of the yield stress of the concretes in the field for concretes with slumps greater than 100 mm;

2. The slump time combined with the preceding measurements can provide an estimate of the plastic viscosity for concretes with a slump comprised between 120 and 260 mm. The range of application is therefore limited, fortunately, this is the slump range of most useful high-performance concretes, currently being used.

Additional areas of research to support the development of a standard test method include the following:

1. The reproducibility of the measurements made with this modified slump test should be further evaluated;
2. The suitability of a model linking the slump time to the plastic viscosity should be verified with other concretes made with different components;
3. The range of values of the viscosity and the yield stress that are required for placement and finishing under different conditions should be determined.

ACKNOWLEDGMENTS

The authors wish to specially thank John Winpigler of the National Institute of Standards and Technology for his participation in the preparation of materials and for the conduct of the rheological tests and Frank Davis, also from NIST, for repair of the concrete mixer. Finally, they wish to mention the contributions of W.R. Grace Co. which provided the mixer and the HWRA and the Elkem Company which provided the silica fume. We also would like to thank Drs. James Clifton, Edward Garboczi, Nicholas Carino and Geoffrey Frohnsdorff for the review of this paper.