Effect of some additives on the reactions in fly ASH-Ca(OH)2 system

Differential thermal analysis and thermogravimetry were used to evaluate the effect of some additives, such as CaSO₄, CaCl₂ and silica fume amorphous silica from ferrosilicon synthesis on the mechanism and kinetics of reactions occurring in fly ash-Ca(OH)₂ system. The accelerating role of these additives was demonstrated from the data relating to Ca(OH)₂ consumption in hydrated pastes, determined by TG measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Use of DTA in the investigations of fly ashes from fluidized bed boilers

DTA method was used to follow the hydration process of cement admixtures containing fluidized bed combustion by-product, formed on joined combustion and desulphurisation in some installations with fluidized bed. Based on endothermic peaks attributed to the dehydration of phases formed on hydration, the conditions leading to the formation of so-called ‘delayed’ ettringite were found. This calcium alumino-sulphate hydrate is responsible for lower durability of fluidized bed ash containing material. DTA method is also beneficial in the studies of fluidized bed combustion by-product itself, giving information about the un-burnt carbon content and pozzolanic properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydration studies on the system pulverized fly ash—Ca(OH)2-CaCl2 using DTA and TG

Differential thermal analysis and thermogravimetry were used to monitor the course of hydration in the system fly ash - Ca(OH)₂ - CaCl₂. It was shown that the CaCl₂ admixture is an activating agent in this system. The results should be used for the correction of the mixture ratio of binders and builiding materials based on fly ash.

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Zusammenfassung Mittels DTA und Thermogravimetrie wurde die Hydratation im System Flugasche-Ca(OH)₂-CaCl₂ verfolgt. Dabei wurde gefunden, dass CaCl₂ in diesem System als Aktivator wirkt. Die Ergebnisse sollen zur Korrektur des Mischungsverhältnisses von Bindemitteln und Baumaterialien auf Basis Flugasche verwendet werden.

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-()₂-l₂, , . .

     

The hydraulic activity of high calcium fly ASH

Cementitious mixtures with so-called high calcium fly ash show better strength parameters as compared to the ones with conventional siliceous fly ash. This practical feature is the consequence of improved hydraulic activity. Differential thermal analysis and thermogravimetry were used, together with the other methods, to evaluate the reactivity of high calcium fly ash in mixtures with cements. This type of fly ash exhibits hydraulic properties (setting and hardening on hydration) and durability, after hardening, in the presence of water. The so-called pozzolanic activity is the feature of high active silica containing fly ash while the hydraulic activity is related to the high calcium ones. However, the chemical and phase composition is variable and related to the particle size. The hydraulic/ pozzolanic properties are strongly improved by additional grinding (specific surface increase).