碱含量对水泥基材料开裂敏感性的影响

Influence of Alkali Content on the Cracking Sensitivity of Cement-based Materials

选择低热硅酸盐水泥、中热硅酸盐水泥和普通硅酸盐水泥作为研究对象,利用外掺Na2SO4和K_(2)SO_(4)将其总碱含量调节至0.8%和1.2%,利用椭圆环法,并从干燥收缩性能、水化产物形貌、显微硬度及水化产物微观力学的角度,探究了碱对不同水泥基材料开裂敏感性的影响。结果表明:随着碱含量的提高,不同水泥基材料的开裂敏感性增加;低热硅酸盐水泥具有较高的抗裂能力,且适当地提高碱含量,有助于提高其抗裂性能;干燥收缩性并不能完全揭示碱对不同水泥基材料开裂敏感性的影响机制。碱对不同水泥基材料开裂敏感性的提高还与其微观特性有关,通过促使水化产物形貌发生转变,提高其显微硬度,降低水泥基材料浆体适应变形的能力;通过降低唯一具有胶凝特性的水化硅酸钙(C-S-H)簇间粘结力,降低水泥基材料浆体抵抗开裂的能力。

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 Na_(2)SO_(4)and K_(2)SO_(4)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.