Aerated concrete, 1.23

Another difference between the 1950s and the 1980s is that people now live in other types of houses. 70 % of the population lived in wooden houses in 1950 compared with 40 % today. 3 % lived in houses built of aerated concrete based on alum-shale, in 1950. In 1980 the figure was about 10 %. These differences are also an indication on an increased collective radon concentration during the period. 

All these comparisons support the hypothesis of an increase. The arithmetic means and thereby the collective doses seem to have increased by about a factor of four to six. If the aerated concrete based on alum-shale had not been used, the country-wide average has been estimated to be 30 % lower (Swedjemark 1985). 

Other industrial uses of aluminum flake include the building industry (production of aerated concrete) and the chemical industry (e.g., production of titanium dioxide, pyrotechnics, and explosives). Copper powder in flake form is used in the chemical industry (e.g., for phthalocyanine production, for lubricants). 

Ft is doubtful whether XRD can distinguish a mixture of tobermorite and C-S-H from a uniform material of intermediate crystallinity the situation may lie between these extremes (A30). This question is discussed further in Section 11.7.4. Crystallization is probably favoured by low bulk density its extent is apparently minimal in calcium silicate bricks (P49), but considerable in aerated concretes (A30). In cement-silica materials, substantially all the AljOj appears to enter the C-S-H, which as its Ca/Si ratio decreases can accommodate increasing amounts of tetrahedrally coordinated aluminium (S70). NMR results (K34) support an early conclusion (K62) that 1.1-nm tobermorite, too, can accommodate aluminium in tetrahedral sites. Small amounts of hydrogarnet have sometimes been detected, especially in products made from raw materials high in AljOj, such as pfa or slag. Minor amounts of tricalcium silicate hydrate (jaffeite C, S2H,) have sometimes been detected (A29,K61). 

Siliconates impart water repellency to aerated concrete, roofing tiles, facing bricks, floor tiles and damp substrates. Methyl siliconates develop their water repellency only after chemically reacting with atmospheric carbon dioxide. A disadvantage is the relatively slow reaction with carbon dioxide, since the applied material remains water-soluble for some time and can therefore be washed out by rain. 

Silicone resin emulsions. With the aid of suitable emulsifiers and stabilisers, insoluble silicone resins can be converted into water-soluble emulsions and can be diluted with water. Such emulsions are used as water-repellent additives for plaster or silicate emulsion paints as well as for the surface treatment of mineral powders such as perlite, aerated concrete granules, and so on. 

In-plant impregnation of low-fired ceramic products. Low-fired ceramic products such as roof tiles, facing tiles and unglazed floor tiles are made water repellent by immersing them in dilute silicone masonry water repellents thereby preventing efflorescence and imparting water repellency (Wacker-Chemie, 1982). Prefabricated concrete components, plaster of paris and aerated concrete can also be treated in this way. 

Natural stone or artificial stones such as bricks (see Section 5.3.5), sand-lime bricks, aerated concrete bricks (see Section 5.3.2.5) and expanded-clay blocks (see Section 5.3.6.2.3) are used for building walls. 

Building of walls with stones, bricks, sand-lime bricks, aerated concrete bricks... 

Sand-lime bricks and aerated concrete blocks ... 

Large-quantities of quicklime are used in the manufacture of sand-lime bricks and aerated concrete blocks. These are construction materials which are manufactured from lime-containing and silicate-containing raw materials and whose strength is due to the hydrothermal reaction of the raw materials to calcium silicates. 

Aerated concrete bricks are widely used as light building materials. They are obtained by mixing gas-forming additives into a moist mixture of lime, sand and optionally cement. Industrially, the following reaction is generally used ... 

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

For identical calcining conditions, different limestones may produce quicklimes with measurably different reactivities. While the differences in reactivity may not be significant in most operations, they could affect the suitability of the quicklimes for certain applications (e.g. aerated concrete). There may be several causes of such differences, e.g. rate of calcination, effects of impurities and the microstructure of the lime, (e.g. lime produced from oolitic and coarsely crystalline limestones is more prone to sinter and become less reactive [14.2]). 

There are many applications where magnesium is regarded as an undesirable impurity. These include the production of hydrated lime (at atmospheric pressure), aerated concrete, sandlime bricks, and precipitated calcium carbonate, for which MgCOa levels should preferably be less than 2 % and, ideally, less than 1 % in the limestone. 

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. 

Reactivity. Various lime reactivity tests are used in the aerated concrete industry. One of the best, from the viewpoint of the information which it gives is described in Armex 3, Appendix A (see page 432). The reactivity specified by aircrete producers ranges from low to high (see below). 

The corrosion potential of passive reinforcement (Ecorr) is determined by the availability of oxygen at the surface of the rebars. The maximum and minimum values of potential taken on by passive reinforcement under different environmental conditions are, respectively, +100 mV in aerated concrete, and —1 V in the total... 

Asphalt paints, particularly those based on combinations of gilsonite with drying oils, are used to protect exposed steel structures (e.g., bridges, lattice towers, penstocks) and are recommended for these purposes in DIN 55 928. Since they are also heat resistant, paints of this type are used for protection against corrosion in coking plants and blast furnace plants, as well as to protect the reinforcement bars in aerated concrete. Soft-formulated asphalt paints can be obtained by blending with mineral oils, soft bitumens, or drying (fatty) oils. These are used to protect and seal roofs. 

Wm K ) needed to insulate the inside of a brick/cavity aerated-concrete-block wall of U=1.0Wm K to reduce the U value to 0.3 How much energy (in kWh) does this save in 100 days if the average temperature differential is 15° C and the wall area is 100 m . 

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