K2O/Na2O对不同水泥基材料早期收缩及开裂的影响

通过外掺Na₂SO₄和K₂SO₄将低热硅酸盐水泥、中热硅酸盐水泥和普通硅酸盐水泥总碱含量调节至1.2%,并使K₂O/Na₂O (质量比)控制在0.4~13.7范围内,探讨了K₂O/Na₂O对3种水泥基材料收缩和开裂的影响。并基于微量热技术、电子显微镜技术和能谱技术,揭示了K₂O/Na₂O对不同水泥基材料收缩和开裂的影响机制。研究表明,随K₂O/Na₂O的增加,低热硅酸盐水泥和普通硅酸盐水泥的自收缩和干燥收缩增加,中热硅酸盐水泥的自收缩和干燥收缩先降低后增加,而不同水泥基材料开裂敏感性始终表现为增加。K₂O/Na₂O引起不同收缩特性的主要原因与水泥基材料水化进程有关,而不同的开裂敏感性,除与收缩性能相关外,还受水泥基材料水化产物水化硅酸钙(C-S-H)、氢氧化钙(CH)形貌及界面过渡区(ITZ)元素富集的影响。

Influence of K2O/Na2O on Early-age Shrinkage and Cracking of Different Cement-based Materials

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).