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Materials and components for masonry
Published in Peter Domone, John Illston, Construction Materials, 2018
Hydraulic lime was widely used in the past and is frequently specified for repairing historic buildings to match the original mortar. It is basically a quicklime – calcium oxide – produced by heating impure limestone to a high temperature. The impurities, usually siliceous or clay, lead to the formation of a proportion of hydraulically active compounds such as calcium silicates or aluminates. The binder is made by partial hydrolysis (slaking) of the lime with water. The high temperatures and steam caused by the reaction help to break down the mass to a powder. The mortar is made as normal by gauging (mixing in prescribed proportions) the finely ground binder with sand and water. The classic reference works are Vicat (1837) and Cowper (1927). More recent information is given by Ashurst (1983) and the BRE Good Building Guide 66 (2005).
Materials and components for masonry
Published in Marios Soutsos, Peter Domone, Construction Materials, 2017
Hydraulic lime was widely used in the past and is frequently specified for repairing historic buildings to match the original mortar. It is basically a quicklime – calcium oxide – produced by heating impure limestone to a high temperature. The impurities, usually siliceous or clay, lead to the formation of a proportion of hydraulically active compounds such as calcium silicates or aluminates. The binder is made by partial hydrolysis (slaking) of the lime with water. The high temperatures and steam caused by the reaction helps to break down the mass to a powder. The mortar is made as normal by gauging (mixing in prescribed proportions) the finely ground binder with sand and water. The classic reference works are Vicat (1837) and Cowper (1927). More recent information is given by Ashurst (1983) and the BRE Good Building Guide 66 (2005).
Plastering and plasterboard
Published in Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann, Understanding Housing Defects, 2013
Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann
Lime plaster was common until the 1950s, though its use nowadays is largely confined to conservation work. Lime is produced by heating ground limestone or chalk (calcium carbonate) to a high temperature to remove carbon dioxide. The material thus formed is known as quicklime (calcium oxide). This material was traditionally slaked with water in large pits to produce slaked lime (calcium hydroxide). The lime pits could contain lime putty (slaked lime for later mixing with fine aggregate) or ‘coarse stuff’ (slaked lime and fine aggregate already mixed). The longer the material was left, the better the plaster it produced. In Roman times, it was not uncommon for lime to be left three years before use. Nowadays, there are still some specialist suppliers who slake lime in the traditional way, though most slaking takes place in factories where exactly the right amount of water is added to enable the material to break down into a fine white powder. This bagged material, known as hydrated lime, can be tipped straight into a mixer, though better results are obtained if it is mixed with water and left overnight before use.
Use of calcium oxide as active filler for bituminous stabilised materials
Published in Road Materials and Pavement Design, 2021
Beatriz Chagas Silva Gouveia, Francesco Preti, Elena Romeo, Kim Jenkins, Gabriele Tebaldi
Quicklime is the commercial name of a chemical compound, which consists mainly of calcium oxide (CaO), with some magnesium oxide (MgO) as a secondary constituent (higher is the amount of CaO higher is the pureness of the material). The hydration process of calcium oxide (quicklime) is exothermic and discharges an important amount of heat (Equation (1)) generating calcium hydroxide (Ca(OH)2) commonly named hydrated lime or slaked lime. The heat generated on hydration reaction is 1135 kJ/kg, approximately half of the latent heat to boiling water, 2260 kJ/kg. The weight ratio of calcium hydroxide to calcium oxide is 1.32, based on the molecular weights: it means that for each kilogram of CaO, should be mixed with 320 g of water, to produce 1.32 kg of Ca(OH)2 (Oates, 2008). So, each unit of Ca(OH)2 must be prepared with 76% of its weight of CaO and a minimum of 24% of its weight as a necessary reaction water. This is an important consideration to be taken into account on the BSM mix design phase.
Environmental levels and human health risks of metals and PCDD/Fs near cement plants co-processing alternative fuels in Catalonia, NE Spain: a mini-review
Published in Journal of Environmental Science and Health, Part A, 2021
Joaquim Rovira, Montse Mari, Marta Schuhmacher, Jose L. Domingo
Cement is produced of clinker, gypsum and other additives. Furthermore, clinker is obtained by means of different crushed and homogenized raw materials, including limestone, clay and sands, which are calcinated at 1450 °C in a rotatory kiln. Inside the kiln, calcium carbonates (CaCO3), dissociate into carbon dioxide (CO2) and calcium oxide (CaO), which reacts with silicates (SiO2) to form calcium silicates (Ca2SiO5/Ca3SiO4).[3] Cement production process releases large amounts of CO2 to the atmosphere due the decarboxylation of raw material, as well as the consumption of fossil fuels in the kilns. The emission factors are between 0.9 and 1.2 tonnes of CO2 per tonne of clinker produced, approximately 50% of contribution of each emission (fuel and decarboxylation of raw material).[4]
Mechanism, prevention and remedy of alkali-pumping in new constructed asphalt pavement
Published in International Journal of Pavement Engineering, 2021
Weixiong Li, Duanyi Wang, Chunlong Xiong, Jiangmiao Yu, Bo Chen, Xianshu Yu
One mechanism is referred to as ‘flowing’ alkali-pumping and is illustrated in Figure 4. During the construction of asphalt pavements, if the flow of alkaline materials from the lower synchronous gravel seal and subsidiary structure becomes uncontrolled due to the insufficient stirring of the asphalt mixture, the alkaline substances can easily dissolve in water. Typically, calcium oxide reacts with water to form water-insoluble calcium hydroxide (Equation (2)). During paving, high temperatures develop, and magnesium oxide reacts with water forming magnesium hydroxide, which induces water solubility (Equation (3)). Then, when the water flowing into the pavement structure in the gravel seal and the subsidiary structure is in contact with the high-temperature mixture, part of the magnesium bicarbonate might decompose to form magnesium carbonate (Equation (4)).