Abstract:

The total alkali content of low-heat Portland cement, medium-heat Portland cement, and ordinary Portland cement was adjusted to 0.8% and 1.2% by adding Na₂SO₄ and K₂SO₄ respectively. The impact of alkali on the cracking sensitivity of various cement-based materials was investigated using the elliptical ring method by analyzing drying shrinkage performance, hydration product morphology, micro hardness, and micromechanics of hydration products. Results revealed that an increase in alkali content led to higher cracking sensitivity in various cement-based materials. Low-heat Portland cement exhibited strong crack resistance, and a suitable increase in alkali content could enhance its crack resistance performance. The drying shrinkage performance alone could not fully elucidate how alkali affected the cracking sensitivity of different cement-based materials. The microscopic mechanism behind alkali’s role in enhancing the cracking sensitivity of various cement-based materials included: (1) promoting the transformation of hydration product morphology and elevating micro hardness, thereby reducing the deformation adaptability of cement-based material pastes; (2) decreasing the inter-cluster bonding strength of hydrated calcium silicate (C-S-H), a component with distinct gelling properties, thereby diminishing the crack resistance of cement-based material pastes.

Key words: cement-based material, alkali content, cracking properties, shrinkage properties, micro hardness, micromechanics