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Download fileSelf-healing cementitious composites incorporating innovative materials
thesis
posted on 08.06.2021, 12:48 by Mohamed A. A. SherirDiscovering new cement based materials characterized by higher durability and longer service life is crucial for sustainable infrastructure. Engineered Cementitious Composite (ECC) with high potential of micro-crack healing can enhance ductility/durability of concrete structures. However, low water-to-cement ratio in ECC matrix in addition to the lack of cementitious properties of newly formed healing-products in micro-cracks could be an obstacle to implementing continuous hydration to stimulate self-healing and stop re-opening of old healed micro-cracks during re-loading. MgO-type expansive agent (MEA), widely used to compensate effectively autogenous shrinkage in mass concrete, can be used to eliminate such obstacles and to induce self-healing. This research studied self-healing capability of MEA in ECC through an extensive experimental investigation and developed/proposed an ECC-MgO system. Test results indicated “900°C-2 hours of holding time-45 μm particle size” as the best calcination system based on higher MEA hydration in powder state. Additionally, 5% lightly burnt MgO combined with low-calcium Class-F-fly ash (as 55% cement replacement) was found to be a better choice in designing self-healing-ECC-MgO system in terms of lower expansion effect of MEA.
Further, self-healing property of ECC-MgO system under different environmental exposures (laboratory/water/natural(field)/autoclave curing) was investigated based on mechanical/durability properties of control/pre-cracked specimens compared with their ECC counterparts. The ECC-MgO system exhibited remarkable self-healing property in multiple-cracked/damaged specimens when test results were analyzed based on development/recovery of compressive/flexural strength/load resistance, ultrasonic pulse velocity, heat of hydration, expansion/drying shrinkage, rapid chloride permeability, sorptivity/water absorption and freeze/thaw resistance in addition to crack healing/cracking characteristics and microstructural characterizations through Thermogravimetric Analysis (TGA)/Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM). Finally, the self-healing ability of ECC-MgO system was evaluated through structural performance (regarding strength/stiffness/energy absorbing/crack-healing capacity recovery) of damaged and subsequently healed water/field cured link slabs used for joint-free bridge deck construction. Superior self-healing ability of ECC-MgO system was attributed to low MEA water demand coupled with its delayed hydration characteristics which lead to the formation of more cohesive/strong cementitious MgO crystals within crack walls (at later ages) supplementing CaCO3 precipitations (formed earlier) leading to more effective crack-healing and developing post-healed cracks at new locations upon reloading