减缩剂对混凝土抗冻性能的影响及其冻害劣化机理研究

Shrinkage reducing admixture (SRA) has a significant effect on reducing concrete shrinkage and shrinkage. It is listed as one of the main measures to prevent and reduce concrete shrinkage cracking. However, the frost resistance performance of concrete with shrinkage reducing admixture is low, which seriously affects the service life of construction projects. This becomes the bottleneck of the application and development of SRA.To clarify the cause and mechanism of the reduction of concrete frost resistance performance caused by shrinkage reducing admixture, the core problem is to investigate the internal influencing factors of frost resistance performance of shrinkage reducing concrete and explore the transmission behavior of pore solution during freezing and thawing process. In this project the multi-component shrinkage reducing admixture concrete was taken as the research object, the pore solution characteristics and microscopic characteristics of cement slurry was taken as the core. Based on the key scientific problems such as the influence of surface tension and viscosity change of the shrinkage reducing admixture on the freezing point of the solution, the freezing damage of hydration products. and hydrostatic pressure was analyzed. The effects of freezing water, supercooling water and hydration product degradation on concrete performance under freeze-thaw conditions are systematically studied. Combined with theoretical calculation and multi-scale micro-deterioration analysis, the micro-mechanism of freeze-thaw damage of shrinkage reducing admixture concrete is finally revealed. The research results provide important theoretical basis and technical support for improving the frost resistance of shrinkage-reducing concrete and prolonging the service period.

减缩剂(SRA)抑制混凝土干燥收缩的效果显著，被列为预防和减少混凝土收缩开裂的主要措施之一，但是掺减缩剂混凝土的抗冻性能低下，严重影响建筑工程的使用寿命，是限制减缩剂应用和发展的瓶颈。要阐明减缩剂引起混凝土抗冻性能降低的起因和机理，其核心问题是研究减缩剂混凝土抗冻性能的内部影响因素，探索孔隙溶液在冻融过程中的传输行为。本项目以多组分减缩剂混凝土为研究对象，以水泥石的孔隙溶液性质和微观特性为核心，基于减缩剂的表面张力和粘度变化对溶液结冰点影响等关键科学问题，建立孔隙溶液结冰点的计算模型。对水化产物的冻害劣化和静水压变化进行理论分析，系统研究冻融条件下可结冰水量、过冷却水和水化产物劣化对混凝土性能的影响，结合宏观性能和多尺度微观劣化分析，最终阐明减缩剂混凝土冻融破坏的微观机理。研究成果对提高减缩剂混凝土的抗冻性能，延长服役期提供重要的理论依据和技术支撑。

减缩剂抑制混凝土干燥收缩的效果显著，被列为预防和减少混凝土收缩开裂的主要措施之一，但其抗冻性能低下是限制减缩剂应用和发展的瓶颈。要阐明减缩剂在水泥基材料中的作用机理及其引起混凝土抗冻性能降低的起因，其核心问题是研究减缩剂混凝土抗冻性能的内部影响因素，探索孔隙溶液在冻融过程中的传输行为。1）采用不同单体合成不同的减缩剂并进行性能表征，研究了减缩剂对水泥基材料性能的影响规律。聚乙二醇单甲醚-1200合成的减缩剂预期效果较好。减缩剂不仅可以通过降低孔隙溶液表面张力来降低收缩，还降低了离子在孔溶液中的溶解扩散速度，增大了溶液粘度。2）减缩剂对碱激发材料也呈现了较好的收缩抑制效果，这主要是减缩剂阻碍了干燥过程C-A-S-H的硅酸盐链的聚合，以及与凝胶结合后缓解了部分毛细张力。3）减缩剂的掺入也减少了孔隙液中的Na+和K+的含量。通过统计分析，20-30nm孔径对掺入减缩剂的水泥基材料性能影响最大，具有保水特性的“墨水瓶”孔型会影响干燥收缩和抗冻害性。4）水泥基材料的结构因微观孔隙中冰晶的膨胀而被破坏，具有保水特性的墨水瓶孔洞的增大会增加可冻水量。SRA在毛细管孔隙中的浓度可引起渗透压的升高， SRA的掺量越大，渗透压越大，这也从微观层面解释了减缩剂导致混凝土冻融破坏的原因和作用机理。该项目的研究成果对提高减缩剂混凝土的抗冻性能，延长服役期提供重要的理论依据和技术支撑。