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Hydration of Cements with Mineral Additions

Many fly ashes cannot be used as supplementary materials or mineral admixtures because they possess low pozzolanic activity. Some activators may be added to make them hydraulic. The addition of Na2Si03 and Ca(OH)2 to fly ash cement mixtures results in the acceleration of the hydration of cement as evidenced by increased intensities of the endother-mal peak (calcium hydroxide decomposition) in thermal analysis techniques. Strengths are also increased.P Fly ash can also be activated by mixing it with phosphog q)sum and wet hydrated lime. The estimation of ettringite and lime may be carried out by DTA, and the results may be used to explain the strength development in such systems. [Pg.299]

Portland cement clinker potential phase composition is presented in Table 4. It could be seen that the C3A content in the clinker was 9.46% which is important for the cement hydration rate and cement sulfate resistance. Common Portland cement is not resistant to the sulfate influence because of the significant C3A content, whose hydrates react with sulfate ions resulting in expansive compounds. Portland cement with the higher resistance to sulfates must have low C3A content. Moderate to high content of mineral alite - C3S (54.72%) is usual for the Serbian cement plants and enables the addition of higher quantities of mineral admixtures without influencing the quality of final cement. [Pg.178]

Mineral additions may be broadly categorized as pozzolanic materials or latent hydraulic cements. Neither type reacts significantly with water at ordinary temperatures in the absence of other substances. Pozzolanic materials are high in Si02 and often also in AI2O3, and low in CaO they are sufficiently reactive that mixtures of them with water and CaO produce C-S-H at ordinary temperatures and thereby act as hydraulic cements. If they contain AI2O3, calcium aluminate or aluminate silicate hydrates are also formed. Because they are low in CaO, this component must be supplied in stoichiometric quantity. In a composite cement, it is provided by the Portland cement through decreased formation of CH and decreased Ca/Si... [Pg.276]

Metakaolinite is the high quality mineral addition to cement or concrete because of the excellent pozzolanic properties. In reaction with caldinn hydroxide C-S-H, C AHjj and gehlenite hydrate ate produced [183], These reactions are rapid and as soon as after 3 days these phases are detectable by XRD [184], The gehlenite hydrate is imstable in the presence of calcium hydroxide, while CjAHg is the stable phase, however, the rate of CH reaction with C2ASH3 is low and the non-equilib-rimn state is existing [185]. [Pg.577]

Pozzolanic additions are siliceous minerals added during mixing of cement matrix to react with hydration products, especially with CaCOH). This reaction is exothermic and occurs between pozzolan and Ca(OH)2 to form hydrated calcium silicate [30,65,66]. [Pg.441]


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Cement hydrate

Hydration additives

Hydration minerals

Mineral additions

Mineral additives

Mineral cements

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