Self-healing of moving cracks in concrete by means of encapsulated polymer precursors

Self-healing concrete aims at the autonomous healing of small cracks with widths in the order of a few hundreds of micrometers. Up to now, the existing research on this topic has relied mainly on CaCO3 and rigid polymers to fill the cracks, which are best suited for healing of static cracks due to their high stiffness and brittle behaviour. This study aims at assessing the strain capacity of flexible polymers bridging healed cracks, thus assessing their fitness for healing of moving cracks. The polymers tested result from the release and curing of encapsulated polymer precursors, which cover a wide range of properties in terms of viscosity, foaming and mechanical properties after hardening. The series of tests performed allowed identifying the precursors with good crack-filling potential, leading to successful sealing of cracks. Despite the sealing achieved, regain of mechanical stiffness is limited to a maximum of 30% and only for crack mouth displacements up to 20 μm. The widening of healed cracks that resulted in no significant deterioration of the sealing performance was, at best, between 50% and 100% of their initial width, due to failure in the polymer matrix or at the interface with the crack walls. The strain capacity achieved shows potential for significantly improving the durability of cracked concrete elements under cyclic loading, although the sealing effect may be disrupted for the long term widening of real cracks due to fatigue.