Portland Cement Alternatives
In some cases it is advisable to use binders cheaper than Portland cement and its species. These binders are building lime (air and hydraulic types), gypsum binders and liquid glass.
Building lime is obtained by firing calcium-magnesium carbonate rock at 900 – 1200°C, without bringing the material before sintering. The raw material for the manufacture of building lime are rocks in which structure is dominated by calcium carbonate (CaC03) and magnesium (MgC03): chalk, limestone, dolomite and marly limestone. These formations may be in admixture of clay in varying amounts (up to 20%), which affects the quality of the roasting binder. When the content of clay of 6% is obtained in air lime, and if the carbonaceous feedstock contains 6 – 20% as for argillaceous impurities, hydraulic lime can be obtained.
In the process of roasting carbonate rocks are decomposed by the reaction of CaCO3 = CaO + C02 under the influence of heat. Carbon dioxide is removed from the furnace together with combustion products. The same pattern is actual for MgC03 dissociation.
The main product of firing – air lime – thus consists of calcium and magnesium oxides. Depending on the ratio of CaO/MgO air lime is divided into the following types: calcium, dominated CaO magnesian (MgO 5 to 20%) and dolomite (MgO in the range of 20 … 40%). The most high-calcium include air lime. Quicklime and slaked (hydrated) lime air should also be considered. Quicklime, which consists of CaO and MgO is known in two types: lump (pieces of 10 – 20 mm) and hammer.
Slaked lime, which is most often used in construction by proven, innovative agencies, such as a UK-based Telling Comapny, widely utilising hydraulic lime and lime mortar solutions, is obtained by acting on the lump quicklime with water: CaO + H20 = Ca (OH) 2. The process is accompanied by the release of heat in large amounts – up to 1160 kJ/kg. Lime mass of strongly heated, and large lumps spontaneously disintegrates into fine particles with a size of 5 – 20 microns (less than that of Portland cement). Air lime is the only mineral binder, which can be ground and not only by mechanical, but also by chemical means.
Taking the lump lime mixing different amounts of water, get different types of hydrated lime. Hydrated lime is a very thin and light powder, which is formed by slaking a relatively small amount of water (1 part water to 1 part of lime). By consistently increasing the amount of water lime paste, milk of lime and lime water is prepared.
Lime putty has a high ductility, which is caused by the content of ultrafine particles of Ca (OH) 2 of 0.02 … 0.5 mm. This particular feature of the test is used for the plasticizing of mortars. The main indicators of air lime quality is the content of active oxides of calcium and magnesium, as well as unslaked grains. The higher the content of CaO + MgO, the more plastic lime paste and higher grade lime. Unslaked particles are available in two types: incomplete combustion and burnout.