THE SVANHOLM GROUP OF COMPANIES

TOBERMORITE The compressive strength of an AAC product is a function of a number of parameters. The most important are: Density, grain size of sand and amount of binder. The influence from density is obvious. Of course a more compact material can stand a higher compressive load but it will also have less insulation capability. Grain size of sand and amount of binder is of great interest to us whereas there is an optimal relationship between these two components. By using this relationship and autoclaving the product in the optimal way we will form TOBERMORITE. This is what gives our product its outstanding performance. Tobermorite occurs in nature but is very rare. It belongs to a group of minerals known as calcium silicate hydrates or CSH in short. The amounts of calcium, silica and water is approximately 1 to 1 to 1. Tobermorite is a crystal and a crystal is a piece of matter where the molecules or atoms are arranged in a rigid pattern with a constant distance between the particles. These distances are very small and it would be very impractical to measure in metres or feet. Usually a unit called “Ångström”, after a Swedish scientist, is used. One Ångström is 1/10 000 000 000 m. The Tobermorite that we are interested in is often technically referred to as 11Å-Tobermorite, since the crystal lattice distance is approximately 11 Ångström. This is to avoid misunderstandings, since the word Tobermorite sometimes has been used somewhat loosely. During the autoclaving process this important mineral is formed from lime, silica and water. An important consideration is that half of the Tobermorite is made from the expensive binder - lime. The other half comes from the cheap sand. The efficiency of the binder is thus doubled. The Tobermorite crystals are plate-shaped and combine to form a rigid lattice. Since the silica grains have been supplying the silica part of the crystals they are also well glued into the structure. The result is thus a structure of silica grains rigidly held together by Tobermorite plates. Although the Tobermorite lattice distance is 11 Å, the crystals are relatively big even if they are only clearly visible in an electron microscope. This is important for the chemical and physical stability of the product. The finer a structure is, the larger surface it has. The larger surface it has , the more likely it is that a chance chemical reaction, on the atomic level, takes place on the surface. Cement reacts with water and binds into CSH and other similar minerals. These minerals are nearly crystalline. However, the particles are much smaller than our Tobermorite platelets. The surface is thus much larger and the possibilities for chemical attack from i.a. carbon dioxide of the air much greater. A perhaps more serious problem with cement is that the particles are so small that if it dries out to equilibrium with normal air it will shrink so much that it will crack severely. The only reason why it is possible to use cement for structural purposes is that concrete is aggregate, such as stone, gravel or sand, held together by a limited amount of cement paste. The aggregates do not shrink since they are solid. Since the Tobermorite crystals are relatively large, the influence from water content is much less, which prevents Tobermorite products from shrinking appreciably.