Calcium hydroxide calorimetry

An extensive work was carried out by Uchikawa l on the conduction calorimetry of superplasticizers, such as SNF (NS in the figure), lignosulfonate (LS), a co-polymer of acrylic acid with acrylic ester (PC), and a three dimensional polycondensate product of aromatic aminosulfonic acid with trimethyl phenol (AS) (Fig. 11). The first peak in the calorimetry corresponds to the heat of dissolution of alite, the heat of formation of the AFt phase, and the calcium hydroxide formation from free lime. The second peak corresponds to the heat of hydration of alite. The admixtures were found to accelerate the formation ofthe ettringite phase. At w/cratios ofO.3 and 0.5 and a later addition of the admixture, the appearance of the second peak was significantly delayed and the peaks were of lower intensity. Most retardation occurred with polycarboxylic acid and amninosulfonic acid-based admixtures (Fig. 11). DSC was used to determine the amount of lime formed at different times. The DSC results show that the addition of admixtures at different w/c ratios generally decreases the amounts of lime in the presence of superplasticizers (Fig. 12). 

Hydration of fly ash cement differs from pure cement in terms of the hydration rates of the clinker phases, amount of calcium hydroxide formed, composition of the clinker hydration products, and additional hydration products from the reaction of the fly ash.I l Lower amounts of lime are formed in the presence of fly ash because ofthe pozzolanic reaction between the fly ash and lime formed in cement hydration. Fly ash generally retards the reaction of alite in the early stages and accelerates the middle stage reaction. The accelerated reaction is attributed to the existence of nucleation sites on fly ash particles. The aluminate and ferrite phases hydrate more rapidly in the presence of fly ash, and also there is a significant difference in the hydration rate of the belite phase up to 28 days. Table 1 gives the relative hydration rates of cement compounds in the presence of fly ash as derived from conduction calorimetry. [" 1 It can be seen that the earlier rates of hydration are generally retarded, and the later stage hydration rates are accelerated. 

Figure 2.18 shows an example of the use of calorimetry to measure the activity of a biomass fly ash in water without portland cement at 20°C. This approach is sometimes useful to isolate the comparably low fly ash heat of hydration. Figure 2.19 shows a similar example where three different samples of high-calcium fly ash are hydrating in a simulated portland cement environment including 50% calcium hydroxide with 0.5 M NaOH at w/c of 1.0, thus using heat of fly ash hydration as a test method for fly ash activity in a well-defined chemical environment, excluding interference from Portland cement clinker. 

Figure 6.6 A comparison of the effect of aluminium hydroxide and calcium carbonate fillers on the heat release rate from an EVA copolymer using cone calorimetry. Filler loading 60% w/w, irradiance 35 kW m. (After Herbert [34])...

Metakaolin reacts with lime to yield calcium silicate hydrate. Metakaolin may also be activated by other materials such as alkali metal hydroxides, water glass, etc. Activation leads to a polycondensation product with cementing properties. The t5q)e of MK, composition, temperature at which it is produced, surface area, etc., determine the strength development characteristics of the product. In conduction calorimetry, an exothermic peak results by the reaction of MK and the activator. A strong as5mimetric peak in calorimetry is associated with an amorphous inorganic... 

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