2018 Volume 16 Issue 11 Pages 549-562
This paper presents the results of research concerning the potential ability of ultra-high performance cementitious composites to self-heal the cracks that appear at various curing stages, and the effect of additional hydrothermal treatment on this ability. Test specimens were fractured in a 3-point bending test. The preload was induced during the initial curing period, i.e. 24 hours after the mix was made, and also in matured materials: concrete that was cured for 28 days in water or subjected to low-pressure steaming or autoclaving. Flexural strength and total fracture energy tests were carried out on reference specimens and also on specimens with a crack healed by immersion in water and by the additional use of steaming at 90℃ and autoclaving at 250℃. The results of studies performed with respect to mechanical properties and microstructure observations show that material that was cracked at early curing stages can be most effectively healed (i.e. its strength restored) by the autoclaving process. The main reason for this is the crystallisation of xonotlite and tobermorite whiskers in the healed crack. The self-healing effect tested in matured composites where binder hydration was determined to be of around 40% turned out to be virtually negligible.