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.
Stated in other words, acrylic copolymers (AC) and polycarboxylate ethers (PCE) are effective at lower dosages compared to sulfonated condensates of melamine (SMF) or naphthalene (SNF) formaldehyde.
At present, SNF-based admixture is priced lower (in India) than that based on AC and PCE In the opinion of the authors, SNF-based admixture seems to be preferable that based on PCE.
It is possible that the highly flowable nature of SCC could allow a higher proportion of flaky aggregates compared to normal concrete. O’Flannery and O’Mahony have devised a method for shape characterisation of coarse aggregate, which could assist in designing SCC mixtures having marginally unsuitable aggregates.
The purpose of the study was to determine dimensional parameters for ‘fingerprinting’ any given coarse aggregate sample.
High range water reducers A number of studies have been conducted on the use of different types of HRWRAs with or without viscosity modifying agents in self-compacting concrete.
These studies seem to indicate those that HRWRAs that work on the principle of ‘steric hindrance’ require a lower dosage compared to those based on ‘electrostatic repulsion’.
Moreover, the presence of flaky and elongated particles may give rise to blocking problems in confined areas, and also increase the minimum yield stress (rheology terms are discussed in the next section).
Incorporation of aggregate shape in the mixture design would enable the selection of appropriate paste content required to overcome these difficulties.
Viscosity modifying agents The conventional method of improving the stability of flowing SCC is to increase the fines content by using a large amount of filler, reactive or inert.
Of late, however, attempts are being made to reduce the fines content (and paste content) to the levels of normal concrete (in doing so, reducing the potential for creep and shrinkage) and use viscosity modifying agents (VMAs) to improve the stability.
In fact, river sand is simply not available in many areas.