Portland cement paste calorimetry

Abdelrazig, B. E. L, Boimer, D. G., and Nowell, D. V., Estimation of the Degree of Hydration in Modified Ordinary Portland Cement Pastes by Differential Scaiming Calorimetry, Thermochimica Acta, 168 291-295 (1990)... 

In an investigation of various pol5miers, it was found that sodium carboxy methyl cellulose and versicol acted as strong retarders. For example, with the reference portland cement pastes, the peak in the conduction calorimetry occurred at 11 hours, and with versicol, the peak shifted to 20, 29, and 34 hours at dosages of 0.25, 0.50, and 0.75% respectively,... 

Dry mix mortars often exhibit a quite complex mix composition, especially if they are rapid setting and/or rapid hardening. In the latter case, they generally contain binary or ternary binders based on calcium aluminate or calcium sulfoaluminate cements in blends with calcium sulfate without and with portland cement. Isothermal calorimetry is an efficient method to use for optimising mix designs of such mortars with respect to the hydration kinetics. As only small cement mortar or paste samples are used, the influence of the binder composition as well as of different combinations of accelerators, retarders, water reducers, plasticisers, etc. can quickly be tested. Two examples of how the amount of calcium sulfate addition is able to influence hydration kinetics are shown for blends of calcium aluminate cement with hemihydrate (Figure 2.22) and ternary binders based on port-land cement, calcium sulfoaluminate cement and anhydrite (Figure 2.23). 

Problem. In their paper Studies of the Physical Properties of Hardened Portland Cement (J.of ACI, Vol 18, No.3), T.C.Powers T.L.Brownyard mention an investigation of the heat development properties of cement using solution calorimetry. The paper specifies, among other things, the solution heat of a cement paste that is fuUy dissolved in an acid. 

Another similar application of isothermal calorimetry is the assessment of the thermal power at different curing regimes see Figure 2.11. Sealed conditions, which are the usual case in isothermal calorimetry, are compared to pastes with extra water added on top of the sample. This extra water causes an increase in cumulative heat and thus an increased hydration degree. The effect becomes more pronounced at lower w/c, where the samples tend to undergo self-desiccation. The same effect can be seen also with other types of cement, such as calcium sulfoaluminate cements. As this type of cement needs a higher w/c for complete hydration compared to Portland cement (around 0.5-0.6 instead of 0.4 see Winnefeld and Lothenbach 2010), the effect of the extra water is already very evident at a w/c of 0.7 see Figure 2.12. 

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