Semi-dry Concrete for Precast Manufacture of Concrete Products

Semi-dry Concrete for Precast Manufacture of Concrete Products

General

Semi-dry concrete is used for the manufacture of small precast concrete products.

·     Concrete paving stones

·     Kerbs

·     Flags and paving slabs

·     Garden products

·     Pipes

The main application is now concrete paving stones.

The special characteristics of semi-dry concrete are

·     Instantly demouldable

·     Stability of unhydrated concrete

·     Dimensional accuracy immediately after compaction (green strength)

The advantages of this process are

·     Only one form per product shape (low capital investment)

·     A compacting installation for all the products

·     Production flexibility due to rapid changing over of the formwork for a new product type

Semi-dry concrete technology

How are these different fresh concrete characteristics obtained technologically?

·     Fine particle size distribution curve (max. particle size 8 mm, high water requirement)

·     Low w/c ratio (0.35 to 0.40)

·     Low binder content

·     High strength cement (42.5 R)

·     Cement substitutes (fly ash, powdered limestone)

This gives a low adhesive matrix content and therefore a granular consistence in the fresh state. The results:

·     Difficult to compact

·     Low air entrainment

·     Susceptible to early water removal drying

The strength develops according to the general laws of concrete technology and is then similar to high strength concretes.