Special hydrated lime

Special hydrated lime see Type S hydrated lime. 

T pe S hydrated lime (also called special hydrated lime) is defined in ASTM specification C-207. It is produced by heating lime (generally dolomitic) in an autoclave at ca. 180 °C. It may contain up to 8% of unhydrated oxide. It is required to meet specified plasticity, water retention and particle size requirements. 

Puilding lime may be quick or hydrated lime, but usually coimotes the latter, where the physical characteristics make it suitable for ordinary or special stmctural purposes (see Building materials, survey). 

The protective measures for quicklime, hydrated lime, lime putty and milk of lime are more comprehensive than for limestone [34.2]. The eyes are particularly vulnerable to damage and adequate eye protection should be worn at all times when handling lime products. Hot lime putties and milks of lime require special precautions as splashes can burn both physically and chemically. 

Quicklime slaker S3rstems (Figure 5-2) require special handling. Hydrated lime is first formed by slaking quicklime with a small amount of water. When water is added to quicklime, it produces heat, which helps dissolve (convert) the unreacted quicklime more efficiently to hydrated lime. The hydrated lime formed is mixed with more water to form a slurry that is delivered to the point of application. Huge lime softening plants in the midwestern United States use quicklime and this particular chemical feed system. 

Lurgi CFB Process. In this SO2 removal process, hydrated lime is injected into a circulating fluid bed (CFB) reactor located ahead of the particulate removal system. Water is also injected into the reactor to cool and humidify the gas and increase the SO2 removal efficiency. A mixture of fly ash and reacted and unieacted sorbent particulate in the gas from the CFB reactor is collected in a special downstream mechanical dust collector curtain followed by an ESP. Most of the collected particulate is recycled to the CFB reactor (Keetii et al., 1991B). In 1993, eight systems of this type were operating or were under construction in Europe, and two were under construction in the U.S. (Moore, 1993B). 

Mutoclaved lime is a special form of highly hydrated dolomitic lime, used largely for stmctural purposes, that has been hydrated under pressure in an autoclave. 

Other Phases in Portland and Special Cements. In cements free lime, CaO, and periclase, MgO, hydrate to the hydroxides. The in situ reactions of larger particles of these phases can be rather slow and may not occur until the cement has hardened. These reactions then can cause deleterious expansions and even dismption of the concrete and the quantities of free CaO and MgO have to be limited. The soundness of the cement can be tested by the autoclave expansion test of Portiand cement ASTM C151 (24). 

The apparatus shown in Fig. 2 is assembled in a good hood. One liter of liquid ammonia and 0.5 g. of hydrated ferric nitrate are placed in the 2-1. three-necked flask A, which is equipped with a stirrer and a special reflux condenser cooled with Dry Ice. This condenser is attached to a soda-lime tower which is connected to a source of compressed air through the T-tube C. Over a period of about forty-five minutes, 92 g. (4 gram atoms) of clean sodium shavings is added to the liquid ammonia, and the mixture is stirred until the blue color disappears (one to two hours). 

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". 

In this framework, in the specially designed mortars consisting of binders of either lime and metakaolin or natural hydraulic lime and fine aggregates of carbonate nature, nano-titania of anatase (90 per cent) and rutile (10 per cent) form has been added (4.5-6% w/w of binder). The aim was to study the effect of nano-titania in the hydration and carbonation of the above binders and to compare the physico-chemical properties of the nano-titania mortars with those mortars without nano-titania, used as reference. Thermal analysis (DTA-TG), infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed to investigate the evolution of carbonation, hydration and hydraulic compound formation during a six-month curing period. Furthermore, the stone-mortar interfaces, the adhesion resistance to external mechanical stress, relative to the physicochemical characteristics of the stone-mortar system and the role of the nano-titania as additive, were reported and are discussed in this chapter. 

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). 

Supersulphated cement is obtained from blast-furnace slag (80-85%), calcium sulphate (10-15%) and lime or Portland cement klinker (approximately 5%). After hardening, the strength comparable to that of ordinary Portland cement may be obtained with a considerably lower heat of hydration. Supersulphated cement may be used in various special concrete structures, particularly in situations where the action of acid fluids, sea water and oils should be expected e.g. for foundations and harbour structures. Mixing supersulphated cement with Portland cements and special treatment, such as accelerated hardening, is not possible. 

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