The use of links is the most popular and economic method. Great care is needed to retain the position of top steel in thick slabs during concreting operations. These top steels are often disturbed from their true position by placing of concrete, by foot traffic and by vibrating plant and equipment. Compacting The aim is to remove air holes, bubbles etc and achieve maximum density. Compacting is achieved by agitating or vibrating the concrete.
Compaction also ensures good bond with reinforcement and other fixture.
Beware however, of a mix that is too wet as this may cause segregation, bleeding, and lower density due to volume taken up by water. Compacting must not displace reinforcement or formwork, this requires skill and workmanship. Formwork should be adequately braced to prevent movement and grout loss through gaps. Loss of water by evaporation may cause this reaction to stop and so prevent full strength development. In addition evaporation may cause the concrete to shrink and crack.