Abstract: The total alkali content of low heat Portland cement, medium heat Portland cement and ordinary Portland cement were adjusted to 1.2% by adding Na₂SO₄ and K₂SO₄ respectively, in which the K₂O/Na₂O (by weight) were in the range of 0.4-13.7. The influence of alkali of different K₂O/Na₂O on shrinkage properties and cracking properties of cement-based materials were explored. Besides, with the help of microcalorimetry, scanning electron microscopy and energy dispersive spectroscopy, the influence mechanism of alkali of different K₂O/Na₂O on shrinkage properties and cracking properties of cement-based materials was revealed. The results show that with the increase of K₂O/Na₂O, the autogenous shrinkage and drying shrinkage of low-heat and ordinary Portland cement intensified, while those of medium-heat cemet first decreased and then increased, and the cracking sensitivity of different cement-based materials always increased. The difference in shrinkage properties caused by K₂O/Na₂O was related to the hydration process of cement-based materials. The difference in cracking sensitivity was not only related to shrinkage properties, but also affected by the morphology of hydrated calcium silicate (C-S-H), calcium hydroxide (CH) and the enrichment of elements in the interfacial transition zone (ITZ).

Key words: K₂O/Na₂O, shrinkage properties, cracking properties, micro-morphology, interfacial transition zone