Concrete autoclave aerated

RILEM Technical Recommendations for the Testing and Use of Construction Materials Autoclaved Aerated Concrete—Properties, Testing and Design... 

Autoclaved aerated concrete (AAC, or aircrete) was first produced in Sweden in 1924. It is now made in over 200 factories in many countries throughout the world. 

Area covered with algae on autoclaved aerated concretes after accelerated algae growth... 

Enclosures that have been built from elements of autoclaved aerated concrete often are covered with plasters (45). Certain adhesion problems between plasters and surface exist during the mechanized covering of surfaces of the enclosures with the plaster. Some dispersible additives, such as a vinyl acetate polymer or derivatives of acrylic acid esters, are used to improve the adhesion. 

Another problem is the increased water absorption of the autoclaved aerated concrete elements, therefore water retarding additives, e.g., cellulose esters, are used in the mixture of plasters. Due to an insufficient amount of water in the mixture of plasters, the hydration of the cement minerals slows down. The influence of natural zeolite and clinoptilolite on the properties of plaster has been investigated (45). Clinoptilolite is a natural zeolite comprising a microporous arrangement of silica and alumina tetrahedra (46). It commonly occurs as a devitrification product of volcanic glass shards in tuff and as vesicle fillings in basalts, andesites and rhyolites. 

It was found that this additive effectively absorbs water and ensures an adequate hydration of the cement minerals (45). In the mixture of plaster, when the sand is changed by clinoptilolite in an amount of 15% the structure becomes slightly compact and the compressive and flexural strength of the hardened plaster increase by 47% and 12%, respectively. Further, the adhesion to a surface of the autoclaved aerated concrete element increases by 44%. In contrast, the drying shrinkage, the water vapor resistance factor and the coefficient of capillary absorption do not change (45). 

Lightweight agreggate concrete units Autoclaved Aerated Concrete... 

Siporex. Trade-name A lightweight (0.5 kg/1) pre-cast concrete made from Portland cement, fine sand, A1 powder and water. The set aerated blocks are autoclaved. (Costain Concrete Co. Ltd., London.)... 

Kadaschewitsch, I. and Sloyan, D. (2005) Aerated autoclaved concrete stochastic structure model and elastic properties. Proc. Appl Math. Meek (PAMM), 5 (1), 419 20. 

After foaming and pre-ciuring, the aerated concrete is dimensionally stable and stiff. In this state the foamed mass is cut into blocks or elements, after which the final curing is performed with steam in autoclave at approximately 180°C. At this temperature the added lime CaO reacts with quartz Si02 to form calcium silicate hydrates, which increase the strength significantly. 

Figure 1.35. The final strength development in aerated concrete takes plaice during steam curing in approx. 50 m long pressure chambers - so-called autoclaves. The curing period is 10-20 hours at approx. 180°C the vapour pressure in the autoclave is approx. 10 atm.

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