Abstract
The sensitivity of temperature on the decomposition/polymerisation of ground granulated blast-furnace slag (GGBS) was investigated through the dissolution experiments at high water to solid ratio under controlled temperatures (5, 20, and 40 °C). The aqueous compositions during the dissolution in neutral and alkali media were determined by ICP-OES (Inductively coupled plasma-optical emission spectrometry) and the saturation conditions with respect to the possible precipitations were estimated by thermodynamic modelling. The depolymerisation of silicate groups and the chemically combined water in the residual GGBS was examined by FTIR/SEM (Fourier Transform Infrared spectroscopy/Scanning Electron Microscopy) and TG (Thermogravimetric) analysis respectively. The results demonstrated that the effect of temperature on the dissolution of GGBS is more pronounced from 5 °C to 20 °C than that from 20 °C to 40 °C. The extremely low temperature (∼ 5 °C) restricts the hydration of GGBS even in a high pH environment. The temperature does not affect the depolymerising sequences of silicate groups in GGBS in a neutral environment but changes the overall dissolution rate. The major silicate spices (Q0 to Q3) in GGBS tend to dissolve evenly in DI water, whereas the Q2 tends to depolymerise faster than others in the NaOH solution. The decreasing Ca concentration in the NaOH solution corresponds to the formation of ∼ 50 nm needle-like precipitates regardless of temperature. Based on the results collected, the dissolving potential and the temperature sensitivity of the major components in GGBS can be divided into three batches: the easiest/most sensitive group: Na-Ox; intermediate group: K-Ox, Si-Ox, Ca-Ox, Al-Ox; the hardest/least sensitive group: Mg-Ox. The intermediate batch required an initial activation energy of ∼ 15 kJ/mol in DI water. The relevant data could be considered as experimental evidence in the thermodynamic modelling of the hydration of GGBSs.
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