Key Factors Determining the Self-Healing Ability of Cement-Based Composites with Mineral Additives

Abstract

This paper reveals the relationships between key factors that determine the ability of cementitious composites to self-heal autogenously and specific measures for quantifying the effects of this process. The following material factors: water-to-binder ratio (w/b), uniaxial compressive strength and age of the composite at the time of defect formation were considered, as well as the method and degree of damage to the tested material. The subjects of this study were mortars and concretes in which Portland cement was partially replaced, to varying degrees, with mechanically activated fluidized bed combustion fly ash (MAFBC fly ash) and siliceous fly ash. The samples were subjected to three-point bending or cyclic compression tests after 14 or 28 days of aging, in order to induce defects and then cured in water for 122 days. Microscopic (MO) and high-resolution scanning (HRS) observations along with computer image processing techniques were used to visualize and quantify the changes occurring in the macro-crack region near the outer surface of the material during the self-sealing process. Techniques based on the measurement of the ultrasonic pulse velocity (UPV) allowed the quantification of the changes occurring inside the damaged materials. Mechanical testing of the composites allowed quantification of the effects of the activity of the binder-supplementary cementitious materials (SCMs) systems. The analysis of the results indicates a significant influence of the initial crack width on the ability to completely close the cracks; however, there are repeated deviations from this rule and local variability of the self-sealing process. It has been shown that the compressive strength of a material is an important indicator of binder activity concerning crack width reduction due to self-sealing. Regardless of the crack induction method, the internal material changes caused by self-sealing are dependent on the degree of material damage.