The types of commercial superabsorbent polymer (SAP) mainly include ionic-SAP acrylic acid (AA) and nonionic-SAP acrylamide-acrylic acid copolymer (AM), which have different particle sizes due to the limited preparation methods. This study used H low-field NMR to clarify the influence of type and particle size of SAP on the water distribution of cement paste. Backscattering electrons and nanoindentation were used to quantitatively analyze the area, porosity, and micromechanical properties of internal curing zone. Finally, void system analysis, compressive strength, and autogenous shrinking were systematically studied. The results indicate that the water absorption and retention capacity of AM in cement paste increase with the increase of particle size, and the area of internal curing zone also increased. As the area of internal curing area increases, the autogenous shrinkage of cement paste significantly decreases. The internal curing effect reduces the unhydrated cement content and increases the high-density C–S–H content of internal curing zone, thereby improving the micromechanical properties and to some extent offsetting the decrease in mechanical properties caused by voids. However, larger particle size AM forms larger void and higher air content, leading to a further decrease in strength. Ionic-SAP AA releases a large amount of water before final setting, weakening internal curing effect and reducing the area of internal curing zone. In addition, the early release of water leads to an increase in the local water-cement ratio, which increases the porosity and low-density C–S–H content of internal curing zone, thereby reducing the micromechanical properties.

中文翻译：

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高吸水性聚合物的类型和粒径对水泥浆体早期水分布和内部养护区性能的影响


商业化高吸水性聚合物(SAP)的类型主要包括离子型SAP丙烯酸(AA)和非离子型SAP丙烯酰胺-丙烯酸共聚物(AM)，由于制备方法有限，它们具有不同的粒径。本研究利用 1H 低场核磁共振来阐明 SAP 的类型和粒径对水泥净浆水分布的影响。利用背散射电子和纳米压痕定量分析内部固化区的面积、孔隙率和微观力学性能。最后，系统地研究了空隙系统分析、抗压强度和自收缩。结果表明，AM在水泥净浆中的吸水保水能力随着粒径的增大而增大，内部养护区面积也随之增大。随着内部养护面积的增加，水泥净浆的自收缩明显减小。内部养护作用降低了未水化水泥含量，增加了内部养护区高密度C-S-H含量，从而改善了微观力学性能，在一定程度上抵消了因孔隙引起的力学性能下降。然而，较大粒径的AM形成较大的空隙和较高的空气含量，导致强度进一步下降。离子型SAP AA在终凝前释放出大量的水，削弱了内部固化效果，减少了内部固化区的面积。此外，水的过早释放导致局部水灰比增大，导致内部养护区孔隙率和低密度C-S-H含量增加，从而降低微观力学性能。