Role of admixtures in the production of architectural concrete

The most important function of architectural concrete is the aesthetical function – such a composite should in the first place assure a good appearance. This reasoning leads to the necessity of formulating a mix of sufficiently high quality to assure that ready panels are as resistant as possible to external factors or the passage of time. Thanks to high execution quality the concrete casing maintains it appearance over quite a long time, is not likely to crush or become cracked. This is of particular importance for example in the context of elevation panels, which are generally exposed to the impact of adverse weather conditions or UV radiation.
Desired features of a concrete mix may be achieved in a few ways. As regards architectural concrete, in most cases special admixtures are applied, which help the composite acquire properties that are of interest. Interestingly, generally admixtures are generally associated with dyes that assure colour to the composite, yet the role of admixtures goes far beyond clearly aesthetical features of concrete. What is more, specialists consider dyes, dispersed reinforcing or various types of fibres (of steel, carbon, plastic, or even optical fibres) to be additives, and not admixtures.
For this reason the most popularly used admixtures in the production of architectural concrete are plasticisers. Those are substances that allow the production of composite with the use of a smaller amount of water which assures new properties to the concrete mix. In the first place thanks to plasticisers and superplasticisers the risk of formation of shrinkage cracks in setting concrete decreases, and consequently, its surface is not marred by cracks. In addition such a composite tends to dry quicker, becomes more durable, and it is also more workable, e.g. by modelling its surface to obtain the required textures and patterns.
Also aeration admixtures are added to concrete, which enhance its resistance to weather conditions, especially to frost. In some cases admixtures that hasten or retard setting are also applied. Their presence depends, however, on external circumstances, such as for example long transport time of a concrete mix or the necessity of quick placing of architectural concrete.

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