Another deficiency in aggregates is poor gradation.
Use of fillers (either reactive or inert) has been suggested as a means of overcoming this problem. In view of on increased awareness of the environmental impact of mining river sand and depleting supplies of the same, use of manufactured sand and other alternative fine aggregate has become essential in some parts of the world.
The overall idea was to overcome local deficiencies in aggregate shape and to arrive at required packing characteristics irrespective of the aggregate.
Incorporation of aggregate shape in mixture design, based on the method developed by O’Flannery and O’Mahony, is explained in Table 1.
Materials for SCC Mixture proportions for SCC differ from those of ordinary concrete, in that the former has more powder content and less coarse aggregate.
Moreover, SCC incorporates high range water reducers (HRWR, superplasticisers) in larger amounts and frequently a viscosity modifying agent (VMA) in small doses.
In fact, river sand is simply not available in many areas.
In the case of SCC, rounded aggregates would provide a better flowability and less blocking potential for a given water-to-powder ratio, compared to angular and semi-rounded aggregates.
The questions that dominate the selection of materials for SCC are: (i) limits on the amount of marginally unsuitable aggregates, that is, those deviating from ideal shapes and sizes, (ii) choice of HRWR, (iii) choice of VMA, and (iv) interaction and compatibility between cement, HRWR, and VMA. Aggregates Aggregates constitute the bulk of a concrete mixture, and give dimensional stability to concrete.
Among the various properties of aggregate, the important ones for SCC are the shape and gradation.
Research studies in Japan are also promoting new types of applications with SCC, such as in lattice type structures, casting without pump, and tunnel linings.
Since the development of SCC in Japan, many organizations across the world have carried out research on properties of SCC.