Readily processable air-placed concrete

摘要

The present invention deals with air-placed concrete which is still readily processable even at a water/cement ratio of 0.45 to 0.55, is readily sprayable and rapidly sets and solidifies. Apart from the conventional aggregates and additives, it also contains additions of naphthalenesulphonic acid/formaldehyde condensates and highly concentrated aqueous-alkaline solutions of potassium aluminate, potassium carbonate and caustic potash. The concrete according to the invention shows a particularly rapid stiffening behaviour if it additionally also contains up to 3.0% by weight of alkali metal silicates or an adequate quantity of highly disperse silica (SiO2). The additives are preferably added to the concrete directly on site before spraying. In this case, the naphthalenesulphonic acid/formaldehyde condensates are fed in before the dense-stream delivery system and the said potassium salt solution is fed at the end thereof to the air-placed concrete.