Self consolidating concrete properties

16-Jan-2017 23:32 by 5 Comments

Self consolidating concrete properties

In fact, river sand is simply not available in many areas.Although there are studies that have shown that quarry run could be used as a filler instead of limestone for SCC, where X, Y, and Z are dimensions of the aggregate) to indicate the likely degree of potential compaction; values of index between 60 and 10 are cubic, between 30 and 60 indicate flakiness (100 for perfect cube), while values below 30 suggest elongation - Sphericity index to describe the polyhedral shape of the particle, and - Roundness index to describe the degree of angularity; values between 84 and 100 are angular, and between 52 and 68 are rounded Admixtures SCC invariably incorporates chemical admixtures - in particular, a high range water reducing admixture (HRWRA) and sometimes, viscosity-modifying agent (VMA).

Moreover, SCC incorporates high range water reducers (HRWR, superplasticisers) in larger amounts and frequently a viscosity modifying agent (VMA) in small doses.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.Many researchers have been able to produce self-compacting concrete with locally available aggregate.It is observed from these studies that self-compactability is achievable at lower cement (or fines) content when rounded aggregates are used, as compared to angular aggregates.Use of SCC can also help minimize hearing-related damages on the worksite that are induced by vibration of concrete.

Another advantage of SCC is that the time required to place large sections is considerably reduced.

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.

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.

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.

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