Working mechanism of sugar retarders: Insights obtained by oil well cement hydration kinetics study at elevated temperatures

To study the working mechanism of Portland cement retarders, the influences of various types of sugars (sucrose, glucose, and maltodextrin) on the hydration kinetics of oil well cement was evaluated primarily using isothermal calorimetry (IC) test method in the temperature range from 60 °C to 89 °C. By thorough analysis of the experimental data of this study and other relevant studies in the literature, a new retardation mechanism is proposed. Sugars inhibit the hydration of oil well cement by primarily retarding the hydration of silicate phases (mainly C 3 S). The hydration of aluminate phases, which is normally inhibited by the silicate hydration, can be accelerated when the silicate phases are strongly inhibited under high dosage of retarders. Indeed, strong aluminate hydration peaks are observed during the pre-induction period with sugar dosages of 0.2% and higher, and the effect intensifies at high temperatures. The initiation of the silicate hydration peak (main peak) is simultaneously controlled by the overall hydration extent of the cement (which can disrupt the retarder action) and the adsorption stability of the retarder (which is influenced by both retarder type and dosage). Therefore, high sugar dosages (≥0.3%) often causes strong inhibition of C 3 S hydration initially, but the resulted strong acceleration of aluminate hydration can cause earlier initiation of the main peak, resulting in decreased induction period with increasing sugar dosage, especially at elevated temperatures (≥80 °C). The proposed mechanism is further verified using thermogravimetric analysis (TGA) and quantitative XRD (QXRD) analysis of partially hydrated cement.