Preparation

Mixing

The efficient mixing of concrete prior to moulding specimens for subsequent testing is essential if quality specimens are to be manufactured.

The object of mixing is to coat the surface of all aggregate particles with cement paste, and bring the mix to a uniform condition. Pan or rotating drum mixers are suitable for the mixing of small quantities of concrete which are generally used in a laboratory.

ELE offer both flat pan and rotating drum mixers to carry out laboratory mixing of concrete.

Moulding Equipment

Test procedures require that specimens are cast in standard sizes convenient for compressive and flexural strength determination.

The engineering tolerances specified for moulds are very stringent and the internal finish of the surface must be of a high order to comply with the recommendations laid down in many International Standards.

Moulds must not deform during manufacture of concrete specimens if the specimen dimensions are to be maintained.

Compaction

The strength, durability and finish of concrete rely in part on the adequate compaction of the mix. An increasing number of contract specifications call for various forms of vibro-compacted concrete as a means to achieve a better and more consistent mixture. It should, however, be remembered that the fluid mixes may segregate when vibrated, in which case it may be more appropriate to compact using a tamping bar or rod during laboratory mix design.

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