Fresh and hardened properties of self consolidating concrete
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.
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.
Current Developments in Self-Compacting Concrete Introduction Self-compacting concrete (SCC) is a flowing concrete mixture that is able to consolidate under its own weight.
The highly fluid nature of SCC makes it suitable for placing in difficult conditions and in sections with congested reinforcement.
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.
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’.Although there have been several studies on the effect of coarse aggregate content on the flow behaviour of SCC, enough attention has not been paid to quantify the effect of the shape of the aggregate.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.When the construction industry in Japan experienced a decline in the availability of skilled labour in the 1980s, a need was felt for a concrete that could overcome the problems of defective workmanship.
This led to the development of self-compacting concrete, primarily through the work by Okamura. The first usable version of self-compacting concrete was completed in 1988 and was named “High Performance Concrete”, and later proposed as “Self Compacting High Performance Concrete”.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).