Pozzolanas/pozzolanic materials

Pozzolana—(=pozzolanic material) a material with a high eontent of Si02 or Si02+Al203 in amorphous form, which—if sufficiently dispersed—reacts at an ambient or moderately elevated temperature with water and calcium hydroxide to yield a hydrate (or hydrates), causing setting and hardening. 

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 ability to act as a pozzolanic material is typical of any zeolilic luff, but the activity is function of different chemical parameters, especially nature, chemistry and content of tuff constituents. Fig. 4 summarizes the results of the reactivity test of four tuff samples with Ca(OH)2, i.e., the ability of these materials to fix lime more or less readily [63J. It is evident that (a) all the luffs denote a remarkable reactivity for Ca(OH)2 (b) the fastest kinetics is presented by the erionite-rich tuff, which is able to fix in 15 hours the same amount of lime fixed by the other three tuffs in 3 days. The reactivity of the four tuffs is comparable to or ever higher than that of the same pozzolana. Although this statement can not be generalised, it is interesting to note that a typical pozzolana, subjected to the same test, was able to fix the same maximum amount of Ca(OH)2, reported in Fig. 4, in times of the order of 90 days [64],... 

Pozzolanic materials can be either natural, like pozzolana, or artificial, like fly ash and silica fame [2]. They are mainly glassy siliceous materials that may contain aluminous compounds but have a low lime (calcium hydroxide) content. In them-... 

Natural pozzolana. This is a sedimentary material, usually of piroclastic origin, that is derived from the sediment of volcanic eruptions that have produced incoherent deposits or compact deposits that have been chemically transformed with time (such as Italian pozzolana, which was used by the Romans). Pozzolanic materials may also have other origins, such as diatomaceous earth composed of the siliceous skeleton of micro-organisms. The pozzolanic activity of these materials is related to their siliceous component in the vitreous state and to their fineness. There are also pozzolanas that are obtained by calcination of natural substances. 

There ate proofs that already in buildings in Create the cmshed ceramic potsherds (minoyen culture) were added to lime to give it the hydrauhc properties [1]. On this basis the assumption was developed that Romans used firstiy artificial pozzolanic materials, before they check the natural pozzolanas. Jaworski stats that in twelveth century before Christ Phoenician used hydraulic lime to mortar building the temple in Cypms [2]. Already about tenth century before Christ they used the bricks flour as the admixture giving to hme mortar hydraulic properties [2]. 

Pozzolanic materials or pozzolanas are defined as siliceous or siliceous and aluminous materials that on their own have little or no cementitious value, but will—if present in finely divided form and in the presence of moisture—react chemically with calcium hydroxide at ordinary temperature to yield phases that possess cementing properties. The pozzolanicity — that is, the readiness to react with calcium hydroxide— may vary greatly in different pozzolanic materials. 

Pozzolanic materials or pozzolanas do not exhibit cementing properties if mixed with plain water. However, they possess the capacity to react at ambient temperatures with calcium hydroxide, in the presence of water, to yield strength-developing calcium silicate/aluminate hydrates. They include a variety of materials of natural and artificial origin, such as fly ash, microsilica, burnt clays, and diatomaceous earths. 

Pozzolanas, or pozzolanic materials, are defined as siliceous and aluminous materials that ou their own possess little or no cementitious value, but which will—if preseut iu fiuely divided form aud in the presence of moisture— react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties (ASTM C 619-89). The required calcium hydroxide may also be introduced in the form of materials that liberate this compound in the course of their hydration, such as Portland cement. 

Most natural pozzolanas are of volcanic origin, though some are sedimentary. Some clays and other materials that are unsuitable for use in concrete in their natural state become usable as pozzolanas if heat treated. Both natural pozzolanas and heat-treated materials have been used with lime since ancient times, but today they are mainly used as constituents of pozzolanic cements. Several reviews are available (M81,M82,M83). 

Diatomaceous earth is composed of the siliceous skeletons of microorganisms. It is pozzolanic, but its use in concrete is much restricted by its very high specific surface area, which greatly increases the water demand. Some clays react significantly with lime at ordinary temperatures, but while this property can be of value for soil stabilization, their physical properties preclude their use in concrete. Many clay minerals yield poorly crystalline or anrorphous decomposition products at 600-900 C (Section. 3.3.2), and if the conditions of heat treatment are properly chosen, these have enhanced pozzolanic properties. Heat-treated clays, including crushed bricks or tiles, can thus be used as pozzolanas in India, they are called surkhi. Other examples of natural rocks that have been used as pozzolanas, usually after heat treatment, include gaize (a siliceous rock containing clay minerals found in France) and moler (an impure diatomaceous earth from Denmark). The heat-treated materials are called artificial pozzolanas, and this term is sometimes used more widely, to include pfa. 

Also Pozzolana. Finely divided siliceous or siliceous and aluminous material that reacts chemically with slaked lime at ordinary temperature and in the presence of moisture to form a strong, slow hardening cement. Having the properties of pozzolan. 

Pozzolanic is used to describe materials, which, like pozzolana, contain reactive silica, and which, when mixed with quicklime and water, set to a hard mass. They include pulverised fuel ash, trass and burnt shale. 

The commonly used term metakaolin is not correct this pozzolana should be determined as bumed kaolin . The term metakaolinite is brief and relates to the component controlling the pozzolanic properties of material. 

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