Abstract:

To reveal the influence of mineral admixtures on the hydration kinetics of low-heat Portland cement， the isothermal calorimetry was employed to measure the hydration heat evolution rate and cumulative heat of three cementitious systems with fly ash （FA）， ground granulated blast furnace slag （SL）， and their blend at mass replacement levels of 20%， 30%， and 40%， respectively. The Krstulovic-Dabic hydration kinetic model was used to quantitatively analyze the variations of kinetic parameters at different hydration stages， and the results were verified by mechanical property tests. The results show that the incorporation of mineral admixtures reduces the hydration heat and strength of low-heat Portland cement. The fitting results of the Krstulovic-Dabic model indicate that FA and SL exhibit different effects on the hydration kinetics. Specifically， the rate constant K_{\mathrm{3}}^{\mathrm{\text{'}}} in the diffusion-controlled stage decreases with increasing dosage when FA is added alone or when FA and SL are blended， but increases with increasing dosage when SL is added alone. Under a constant total dosage of mineral admixtures， the hydration rate constants and the degree of hydration at the transition points of the FA-SL blended system are intermediate between those of the single FA system and the single SL system， demonstrating a synergistic effect between the two admixtures in low-heat Portland cement. Mechanical property tests macroscopically verify the synergistic optimization effect of FA and SL blending on strength development. Considering both strength development and hydration temperature rise control， the combined use of FA and SL is a balanced strategy to optimize the performance of low-heat Portland cement.

Key words: low-heat Portland cement, fly ash, ground granulated blast furnace slag, hydration kinetic model, hydration reaction rate, mechanical property