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Natural pozzolanas

Main kinds Cement name Main components, % mas Clinker Blast fur- Silica fume K nace slag S D Pozzolana natural P Fly ash industrial Q Siliceous V calcareous W Burnt shale T Lime-stone L LL Secon-dary comp- onents... [Pg.17]

The contents of Ca(OH)2 in the pastes at various times of hydration were determined from the results of the TG studies. Also, the pozzolana nature of the additives has been found out. The ability of combining with Ca(OH)2 was similar in the spent catalyst and the microsilica. In the presence of the spent catalyst, the hydration process was strongly exothermic, which promoted the rapid setting of the cement paste. Calcium carbonate aluminates that are formed in the system, favorably affect the strength of the concrete materials (38). [Pg.205]

Celsius (°C) A scale for measuring temperatures, also known as the centigrade scale, where the freezing point of water is 0°C and the boiling point 100°C. cement A natural or artificial fluid or semifluid substance, or mixture of substances, that hardens to act as an adhesive for binding solid surfaces together, cement, hydraulic A type of waterproof stony cement that sets even under water see pozzolana. [Pg.492]

Many cements used today are composites of Portland cement and industrial waste materials that can enter into the hydration reactions and contribute to the strength of the hardened product. These substances include pulverized fuel ash (PFA) from burning of pulverized coal in thermal power stations, crushed blast-furnace slag (Section 17.7), and natural or artificial pozzolanas—that is, volcanic ash and similar finely particulate siliceous or aluminosilicate materials that can react with the Ca(OH)2 in Portland cement to form hydrated calcium silicates and aluminates. As noted earlier, the solubility of Ca(OH)2 is such that the pH of pore water in Portland cements will be about 12.7, at which the Si-O-Si or Si-O-Al links in the solid pozzolanas will be attacked slowly by OH- to form discrete silicate and aluminate ions and thence hydrated calcium silicate or aluminate gels. [Pg.209]

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). [Pg.299]

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. [Pg.302]

Early studies, reviewed by Malquori (M81), showed that natural pozzolanas take up CH, including that produced by Portland cement, with the formation of products similar to those formed on hydration of the latter material. They also showed that the zeolites present in many of them were at least as reactive in this respect as the glassy constituents. Zeolites are cation exchangers, but the amounts of CaO they take up are much greater than can be thus explained moreover, cation exchange could not explain the develop-... [Pg.302]

Table 9.7 Chemical compositions of some natural pozzolanas... [Pg.303]

Costa and Massazza (C44) concluded from a study of natural pozzolanas of varied types that reactivity in mixtures with CH at w/s = 2 and 40 C depends during the first 28 days on the specific surface area and at later ages on the contents of Si02 and AI2O3 in the active constituents. A comparative study of five natural pozzolanas and three low-CaO pfas in pastes with cement showed that the CH contents of the pozzolanic cements were considerably lower than those of the pfa cements at 3-60 days, but virtually the same at 90 days, the pozzolanas thus appearing to react more rapidly than the pfas at early ages but more slowly later. Determinations of the unreacted mineral admixture in pastes with CH showed that at 90 days 23-30% of the natural pozzolana had reacted, compared with 11-15% for the pfas. The similarity in CH contents suggests, however, that these values may not apply to mixtures with cement. [Pg.304]

X-ray microanalyses of CjS-pozzolana pastes showed a gradual decrease in Ca/Si ratio on passing from regions near the iinreacted CjS to ones near the pozzolana (021). TMS studies of pastes of C3S, (3-C,S and cement with and without natural pozzolanas (U9,M44) showed that, in the presence of the latter, formation of polymeric anions is accelerated and their mean molecular weight is increased. TMS results and determinations of combined water showed that the hydration of P-CjS is almost completely suppressed in the presence of a pozzolana and that, in pastes with CjS, 16-29% of the pozzolana had reacted in 180 days (M44). The eflect on P-CjS hydration is similar to that found using QXDA for pfa (D12). Chemical extraction showed 10-45% of the pozzolanas in pastes with C3S to have reacted in 28 days, compared with under 10% for a pfa (U9). [Pg.305]

Kollek el al. (K68) extended the parallel studies on expansion and pore solution compositions mentioned in Section 12.4.2 to mortars containing pfa, slag or natural pozzolanas. For each mix, several contents of the... [Pg.395]

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],... [Pg.25]

Major Portland cement clinker Granulated blastfurnace slag Natural pozzolanas Thermally activated clays and shales Siliceous fly ash Calcareous fly ash Unslaked calcareous fly ash Burnt shale Limestone Limes... [Pg.269]

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-... [Pg.11]

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. [Pg.12]

Over the millennia, concrete prepared by the Romans using lime, pozzolana and aggregates has survived the elements, giving proof of its durability. Prestigious concrete works have been handed down to us buildings such as the Pantheon in Rome, whose current structure was completed in 125 A. D. and also structures in marine environments have survived for over two thousand years. This provides a clear demonstration that concrete can be as durable as natural stone, provided that specific causes of degradation, such as acids or sulphates, freeze-thaw cycles, or reactive aggregates, are not present. [Pg.397]

In the context of adhesives, cement is a natural rubber- or silicone-based elastomeric. Rubber cements contain a suitable solvent such as naphtha or aromatic hydrocarbons. Pyroxylin cements are adhesives based on solutions of nitrocellulose in alcohol, ether, or another solvent. Hydraulic cements used in construction, such as portland or pozzolana cement, are nonhazardous mixtures composed of some combination of lime, alumina, and silica which sets into a hard product (concrete) when water is added (the term portland... [Pg.1]

The Romans replaced also the natural pozzolana by the ground roofing-tiles, bricks and porcelain. Lea states that the name cement in the Late-Latin or Old-French languages was for the first time used to determine the materials which now are called artificial pozzolanas [1]. Later on this name was used for mortar produced from three components, and only recently the to-day mining was adopted. [Pg.2]

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]. [Pg.2]

Expansion is practically eliminated if 15-40% of pozzolana co-ground with Portland cement chnker is used [98], Some authors recommend 20% of diato-mite addition, the others 30-35%. of volcanic glass. The effectiveness of natural pozzolanas is rather variable [98], The method of verifying their effect is given by Lea [98],... [Pg.407]

However, according to Glasser and Marr [130], slags and natural pozzolanas reduce only the sodium content but they have no influence on potassium content. Natural pozzolanas, because of their high potassium content, will cause the potassium concentration increase in the liquid phase of the paste [60],... [Pg.410]

The concretes produced from cements with natural pozzolana addition are particularly resistant to the chemical corrosion, but the resistance to physical factors is only slightly changed. However, they should be cured for a longer time in humid condition than the concrete produced from Portland cement without mineral additions. They are useful in these conditions where a low heat of hardening and high resistance to chemical corrosion is required [5]. [Pg.536]

The zeolites, which are the components of natural pozzolanas are the subject of great interest too. According to Taylor [7] the activity of zeolites is not lower than the... [Pg.536]

Massazza, R Properties and applications of natural pozzolanas. In Bensted, J., Barnes, P. (eds.) Structure and Performance of Cements, Chap. 13, p. 326,2nd edn. Spon Press, London... [Pg.578]


See other pages where Natural pozzolanas is mentioned: [Pg.531]    [Pg.506]    [Pg.276]    [Pg.276]    [Pg.277]    [Pg.278]    [Pg.299]    [Pg.302]    [Pg.304]    [Pg.304]    [Pg.304]    [Pg.343]    [Pg.396]    [Pg.396]    [Pg.33]    [Pg.537]    [Pg.2]    [Pg.526]    [Pg.529]    [Pg.529]    [Pg.533]    [Pg.535]    [Pg.535]   
See also in sourсe #XX -- [ Pg.2 , Pg.407 , Pg.410 , Pg.533 , Pg.535 , Pg.536 , Pg.563 , Pg.590 , Pg.641 ]




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