A study of the hydration and setting behaviour of OPC-HAC pastes

Abstract An impedance measurement technique was applied to an investigation of the hydration process and setting behaviour of ordinary portland cement-high alumina cement (OPC-HAC) paste systems. Evidence indicates that the impedance and capacitive response are sensitive to ionic concentration changes in the liquid phase and microstructural development of the hydrating pastes. Rapid increases in impedance value occurred at about 30 minutes and 450 minutes hydration. The first impedance increase corresponded to the nucleation of ettringite contributing to fast setting behaviour; the other was attributed to HAC hydration processes. The decrease of matrix impedance at hydration times greater than 450 minutes may be due to the dissolution of calcium hydroxide (CH) generated from C 3 S and C 2 S hydration.

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