Tomczak Kamil, Jakubowski Jacek, Kotwica Łukasz
Department of Geomechanics, Civil Engineering and Geotechnics, AGH University of Science and Technology, 30-059 Krakow, Poland.
Department of Building Materials Technology, AGH University of Science and Technology, 30-059 Krakow, Poland.
Materials (Basel). 2020 Jul 27;13(15):3336. doi: 10.3390/ma13153336.
The self-sealing process, associated with chemical and microstructural changes inside damaged cement-based composites, leads to the recovery of the original material integrity. Assessing the magnitude of internal changes in samples using non-destructive techniques to capture only the self-sealing effects is difficult. The challenge is evaluating the differences between subsequent observations in time and between samples with different properties. This paper proposes a new approach to the use of an ultrasonic technique for self-sealing investigation. The method allows the quantification of material changes strictly related to self-sealing processes, excluding changes caused by the naturally progressing hydration of binders. The applied ultrasonic pulse velocity (UPV) data processing procedure allows the investigation of material changes inside and near the cracks, the effects of stimulating the self-sealing of cement composites with mineral additives, and the assessment of changes over time. An important aspect of the method is the sample preparation procedure and testing conditions that reduce the impact of moisture content on the UPV measurements. New parameters allowing the quantitative characterization of the self-sealing process are proposed. The method was evaluated using cement mortars modified with siliceous fly ash with induced cracks 0 to 750 µm wide, which were then cured in water for 152 days. The maximum degree of effective crack filling as a result of autogenous self-sealing in the tested mortars was determined to range from 33% to 57%. Observations of the microstructure of the crack surface confirmed that apart from the volume of the newly formed products, the density of these products may have a key impact on the ultrasonic measurements of the self-sealing performance. The studies were supplemented by the examination of the compression strength of mortars, mortar sample scanning and computer image processing, and observations using an optical microscope and scanning electron microscope with energy dispersive spectroscopy.
自愈合过程与受损水泥基复合材料内部的化学和微观结构变化相关，可使原始材料恢复完整性。使用无损技术评估样品内部变化的程度，仅捕捉自愈合效果具有难度。挑战在于评估不同时间后续观测值之间以及不同性能样品之间的差异。本文提出一种使用超声技术进行自愈合研究的新方法。该方法能够量化与自愈合过程严格相关的材料变化，排除由胶凝材料自然水化进程引起的变化。所应用的超声脉冲速度（UPV）数据处理程序可用于研究裂缝内部及附近的材料变化、用矿物添加剂刺激水泥基复合材料自愈合的效果以及随时间的变化评估。该方法的一个重要方面是样品制备程序和测试条件，可减少含水量对UPV测量的影响。提出了用于定量表征自愈合过程的新参数。使用掺有硅质粉煤灰且诱导裂缝宽度为0至750 µm的水泥砂浆对该方法进行评估，随后将其在水中养护152天。经测定，试验砂浆中自愈合产生的有效裂缝最大填充度在33%至57%之间。对裂缝表面微观结构的观察证实，除新生成产物的体积外，这些产物的密度可能对自愈合性能的超声测量有关键影响。通过对砂浆抗压强度的检测、砂浆样品扫描及计算机图像处理以及使用光学显微镜和带能谱仪的扫描电子显微镜进行观察，对研究进行了补充。
