Self-healing capacity of hardened cement suspensions with high levels of cement substitution

Abstract

Aqueous cement suspensions without aggregates have been commonly applied as a remedial technique in structural and geotechnical applications, often comprising part of the permanent infrastructure. These suspensions derive their mechanical characteristics and properties through the same hydration processes and binding chemistry as concrete; thus they are susceptible to the same deleterious environmental factors and inherent properties. This can endanger the long-term functionality of the installation. Therefore there is a strong incentive of compositional alteration of the basic binder by incorporating supplementary cementitious materials that have been acknowledged to improve the physical properties and enhance the durability characteristics of the hardened matrix. However the latter does not offer a robust long term solution. Therefore a compositional enhancement through biomimetic approach of damage response for the design of high performance cement suspensions is put forward. This study involves two stages, i.e. determination of the autogenous crack sealing behaviour of various optimised blended compositions and the subsequent enhancement of the intrinsic autogenous healing processes through the inclusion of microencapsulated healing agents. Herein the results of this preliminary investigation on the effect of compositional variation on the intrinsic properties of physical response to cracking are presented. Ternary and quaternary blends of minerals -including Portland cement, slag, MgO and silica fume- are being developed and investigated. Upon cracking and water ingress, the unreacted particles are activated and yield hydration products that crystallize in the crack, sealing it off and recovering mechanical characteristics. The self-healing capacity of the samples is quantified through microscope observation, gas permeability test and three-point flexural bending. The findings on the crack healing efficiency and mechanical recovery of initially cracked specimens confirm the existence of self-healing mechanisms in supplementary cementitious materials.