Calcium silicate bricks

Calcium Silicate Brick. Sand—lime brick is used ia masonry ia the same way as common clay brick. The bricks, molded from a wet mixture of sand and high calcium hydrated lime, are heated under pressure ia a steam atmosphere. Complex hydrosiUcates are formed that give the bricks high dimensional stabiUty (6). 

Pel, L., Kopinga, K. and Kaasschieter,E.F. (2000) Saline absorption in calcium silicate brick observed by NMR scanning. J. Phys. D Appl. Phys. 33, 1380... 

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). 

Sandlime bricks, also called calcium silicate bricks, are produced by moulding, under high pressure, a moist mixture of silica sand (or crushed siliceous stone, or flint) and hydrated lime. The green bricks are then autoclaved using steam pressures of at least 11 atmospheres. Under these conditions, the hydrated time reacts with the silica to form hydrated calcium silicate, which bonds the aggregate particles into a strong and durable brick [26.47]. Other shapes, such as blocks and building elements are also produced. 

Although the calcium silicate brick process was patented in the UK in 1866, its commercial exploitation only occurred in Germany towards the end of the 19th Century. In that country, the sandlime brick industry now accounts for some 40 % of the brick production. The process is also used in many other countries, but its penetration has varied considerably, depending on traditional construction methods and on the relative costs of competitive products [26.48]. 

Sandlime (calcium silicate) bricks . Technical Service Note, No. TS/E/19, ICI Mond Division, 1980. 

Sandlime (or calcium silicate) bricks are produced by autoclaving a mixture of sand and lime. 

Capillary absorption/ permeability to water EN 1062-3 Porous clay or calcium silicate bricks, mortar XC3 XC4 G Absorp. coeff. iv<0.1 kg m. h" ... 

Calcium Silicate Bricks. The approved term (replacing sand-lime brick and flint-lime brick) for bricks made by autoclaving a mixture of sand (or crushed siliceous rock) and lime. Requirements and qualities are specified in B.S. 187, and in the USA, in ASTM C73 for calcium silicate facing bricks. Dimensions are specified in BS 4729. Calcium Stannate. CaSn03 sometimes used as an additive to barium titanate bodies, one effect being to lower the Curie temperature. 

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. 

The interaction of zeolite-rich materials with Ca(OH)2 is of special interest, because zeolites, like other reactive aluminosilicate systems, e.g., crushed bricks, give rise to calcium silicates and aluminates, which are able to harden upon hydration in both aerial and aqueous environments. This behaviour, already known in ancient times, is typical of a volcanic, mostly glassy material, called pozzolana, which is the genetic precursor of the mentioned Neapolitan yellow tuff, widely spread in the surroundings of Naples, Italy [61]. That is why every material able to behave as pozzolana is called "pozzolanic material" and the property to react with lime is called "pozzolanic activity". 

The calcium silicates have a number of uses in industry. Among the most important applications are their uses in building materials, such as some types of glass and cement (especially Portland cement), bricks and tiles for roofs, fireproof ceilings, and building boards. The compound is also... 

Mainly aircrete, sandlime bricks, other calcium silicate products and refractories. Mainly mortar, render, plaster, and drying/improvement/stabilisation of soils. Mainly potable water, sewage, liquid effluent and gaseous effluent treatment. 

BS 187 Specification for calcium silicate (sandlime and flintlime) bricks , 1978. 

BS 187 Specification for calcium silicate (sandlime and flintlime) bricks , 1978. BS 594, Part 1 Hot rolled asphalt for roads and other paved areas — Specification for constituent materials and asphalt mixtures , 1992. 

The principal disadvantage of calcined dolomite is its tendency to hydrate, causing bricks made from it to crumble. This hydration tendency is due to the high proportion of lime and persists even after having been calcined to 1600 C. To overcome this, dolomite can be stabilized by being fired with a silicate such as steatite (talc) which combines with the free lime to form calcium silicate partial stabilization can be achieved by water-proofing the bricks with tar. 

Fired cl bricks are generated as a waste product from construction and demolition activities, and their value is an additive in the manufacture of PC-based construction products. It was established that the aluminosilicate phase in the fired clay bricks promoted the development of the tobermorite, the principal binder in most calcium silicate products under hydrothermal conditions. The use of CB waste as a cement replacement for the manufacture of these products was also demonstrated as a viable option. 

Afwillite. A hydrated calcium silicate, 3CaO. 2Si02.3H2O it is formed when Portland cement is hydrated under special conditions and when calcium silicate is autoclaved (as in sand-lime brick manufacture). 

Paver. Dense, well vitrified bricks of normal size or of lesser thickness for use as a material for walkways and paths. B.S. 6677 Pt. 1 specifies materials, sizes, strengths and skid resistance of clay and calcium silicate pavers. (Pts 2 and 3 specify design practice and method of construction of pavements). In the USA a paver may be a dust-pressed, unglazed relatively thick floor tile with a superficial area of at least bin (3871 mm ). ASTM C-902 is the US standard for paving bricks for light traffic areas. 

The bottom heat insulatitHi layer of reduction cells is composed of diatomaceous (moler) bricks, vermiculite slabs, perlite bricks, and calcium silicate boards. To smooth the surface of the bottom of the steel cradles, sometimes people use fireclay grit (grain). 

Fireclay bricks (alumina silica bricks, alumina calcium oxide silica bricks, and other silicate bricks) are not optimal barrier materials for A1 reductirMi cells. As we have mentioned, cryolite-based electrolyte for A1 reduction is a substance that dissolves alumina better than anything else. Certainly, it will dissolve all alumina-based refractory compositions and almost all other oxides similar in chemical structure to alumina. From a chemical point of view, the effective refractory barriers against the penetration of cryolite might be tin oxide, nickel oxide, compounds of nickel oxide, iron oxide, or zinc oxide (such as spinel Fe NiOs). These oxides almost do not react with NaF and aluminium fluoride [175]. Yet the cost of these materials, which is 50-100 times higher than that of firebrick, provides the impetus to find less costly variants of alumina silica materials. 

Although in refractory practice there are hundreds of heat insulation materials, the list of heat insulation materials for the lining of reduction cells is rather limited. For one thing, economic considerations add some limitations, but for another, the heat insulation materials in reduction cells should withstand mechanical compression loads without deformation at temperatures up to 900 °C for a long time, and numerous inexpensive fiber heat insulation materials don t correspond to this requirement. In the Hall-Heroult reduction cell, the heat insulation materials should withstand the pressure of the layer of the electrolyte, the layer of molten aluminium, cathode carbon blocks (taking into account collector bars), and the refractory layer. Currently, only four or five heat insulation materials are used in the lining of reduction cells diatomaceous (moler) and perlite bricks, vermiculite and calcium silicate blocks (slabs), and sometimes lightweight fireclay bricks (but their thermal conductivity is relatively big, while the cost is not small) and fiber fireclay bricks. 

Fig. 2.85 Thermal conductivity of heat insulation materials 7, 2—diatomaceous bricks 3— lightweight fireclay brick 4—diatomaceous brick 5— vermiculite slab 6—calcium silicate slab...

The range of heat insulation materials is rather broad. Heat insulation materials that can withstand relatively high mechanical loads - this list includes lightweight fireclay bricks, vermiculite slabs, perlite bricks, calcium silicate boards, and diatomaceous bricks - are used for the heat insulation of the bottom. The pressure on the walls is lower, so it is possible to use fiber-based boards (in addition to the above-mentioned materials). Sometimes lightweight castables with fillers, such as lightweight fireclay, vermiculite, and fiber, are also used for heat insulation. 

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