PNIPAm水凝胶对水泥砂浆性能的影响

Effect of Performance of Cement Mortar on PNIPAm Hydrogel

为了解决道路工程中水泥混凝土易出现的早期收缩开裂、抗冻性差等耐久性问题,采用温度敏感性水凝胶(PNIPAm)作为水泥砂浆的内养护剂,分别研究了不同吸水率、不同掺量PNIPAm对水泥砂浆的工作性能、力学特性以及韧性(折压比)的影响;采用平板法测试了水泥砂浆的早期抗裂性,根据冻融循环快冻法测试了水泥砂浆的抗冻性;利用扫描电子显微镜观察了PNIPAm改性水泥砂浆硬化体的微观结构,并采用压汞法定量测试了PNIPAm改性水泥砂浆的内部孔结构,最后分析了PNIPAm对水泥砂浆的改性机理。结果表明:PNIPAm改善了水泥砂浆的工作性能、抗折强度以及韧性,随着PNIPAm含量的升高,水泥砂浆的抗压强度略有下降;随着水泥水化的进行,水泥砂浆体系中的PNIPAm逐渐融合成薄膜网状结构,这种结构可以有效地分散水泥砂浆内部裂纹的尖端应力,降低水泥砂浆的开裂面积,延长水泥砂浆的开裂时间;PNIPAm释放的水分子对水泥砂浆起到了内养护的作用,使其无害孔含量提高,有害孔含量降低,PNIPAm的掺入有效提高了水泥砂浆的抗冻性能;综合PNIPAm对水泥砂浆强度、抗冻以及抗裂性能的影响,PNIPAm的掺量建议为水泥砂浆总质量的0.5%~0.75%。

In order to solve the durability problems of shrinkage cracking in initial period, poor frost resistance of cement concrete, etc. in road engineering, taking PNIPAm as internal curing in cement mortar, the influences of PNIPAm with different content and water absorption rates on the properties of workability, mechanical property and toughness （flexural compression ratio） of cement mortar were analyzed. Flat-type method was used to test the initial anti-cracking performance of cement mortar. Quick freezing method was used to evaluate the frost resistance of cement mortar. SEM was used to detect microstructure of cement mortar specimens with different PNIPAm content. The internal pore structure of modified cement mortar with PNIPAm was tested by mercury intrusion method and modification mechanism of PNIPAm on cement strength of cement mortar slightly decreases with the increase of PNIPAm content. With the hydration of cement, PNIPAm gradually merges into a thin film network structure, which effectively disperses the crack tip stress in the cement mortar, reduces the cracking area and extends the cracking time of cement mortar. Hydrone released from PNIPAm plays an important role in internal curing of the cement mortar. The content of the harmless hole in the cement mortar increases, and the content of harmful holes decreases. The frost resistance of cement mortar was improved by adding PNIPAm. Considering the influence of PNIPAm on the strength, frost resistance and crack resistance of cement mortar, the content of PNIPAm is suggested to be 0.5%-0.75% of the total mass of cement mortar.