engleski

Application of thermal methods in the chemistry of cement: Kinetic analysis of Portlandite from non-isothermal thermogravimetric data

Kinetic investigations are, today, one of the most important application of thermal analysis. Under the methods summarized by thermal analysis, differential scanning calorimetry (DSC) and thermogravimetry (TGA) have outstanding significance. In present work, a procedure for evaluating the thermal decomposition kinetics of the calcium hydroxide, Ca(OH)2-Portlandite formed into hydrated ordinary Portland cement (OPC) paste with use of non-isothermal thermogravimetric data is proposed. The investigation was made at the temperature of the thermal decomposition of Ca(OH)2 ranging from 330-460 oC in the nitrogen atmosphere at four heating rates, β = 5, 10, 15 and 20 oC/min. The activation energy was determined by using the Flynn-Wall and Ozawa (FWO) isoconversional method. The results showed that activation energy (E) is decreasing function of conversion (α ), which is in good agreement with literature data. The E values obtained for Portlandite were compared with those for pure, analytic grade calcium hydroxide and, are discussed taking into account the complexity of the cement hydration reaction. The proposed approach is also substantiated using thermo-kinetic results on effect of pozzolanic additions (such as silica fume) on the cement hydration and is shown to be of practical importance.

Cement Hydration; Calcium Hydroxide (Portlandite); Kinetic analysis; Flynn-Wall-Ozawa method; Activation energy; TGA.

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