The influence of MgO-type expansive agent incorporated in self-healing system of Engineered cementitious Composites

Engineered Cementitious Composites (ECCs) are found to be better replacements for traditional concretes due to their higher damage tolerance under loading, as well as the ability to induce multiple-cracking with a smaller width and potential crack healing capability. This paper presents the development and performance of an effective self-healing concrete system made of ECC and MgO-type expansive agent (MEA) (made of lightly burnt MgO powder). New measures were implemented in examining the performance of ECC-MgO self-healing system based on accelerated autoclave test to simulate the experimental results relevant to the field conditions. Test results suggested the best calcination system to be 900 °C with 2 h of holding time using 45 µm particle size based on higher hydration activity of MEA in a powder state. Low calcium Class-F fly ash was found to be the best supplementary cementing materials (SCMs) to produce ECC-MgO system based on lower expansion effect of MgO. The high volume of fly ash (HVFA) was used to achieve very low expansion within the crack walls just to heal hairline micro-cracks in ECC-MgO self-healing system without jeopardizing the durability. Similar behavior was shown by the MgO in powder state in terms of loss of CO2 content and remaining hydration activity as well as after utilizing it in the ECC-MgO system in water and autoclave linear expansion tests coupled with scanning electron microscope (SEM) and thermogravimetric analyses (TGA). The higher flexural strength recovery of pre-cracked ECC-MgO prismatic specimens cured under accelerated autoclaved conditions compared to their pre-cracked ECC (without MgO) counterparts confirmed the self-healing capability and potential of the proposed ECC-MgO system.