Healing of cracks

The most striking feature of the stress softening phenomenon of thermoelastoplastics is its complete reversibility under certain conditions, consisting in a reformation process in the stress-free state which involves healing of cracks and reaching the initial integrity of the hard phase 119,120,12 ). The reformation kinetics in stress-softened samples indicates that this process is controlled by diffusion. 

Another major benefit of incorporating lime into mortars is that it confers autogenous healing of cracks. Cracking occurs for a variety of reasons both before, during and after the setting of the mortar. The formation of cracks, both at the mortar-masonry interface and within the mortar reduces the strength of the masonry unit and increases water penetration. 

FIGURE 6.11 Evidence of self-healing of cracks in PE fiber-reinforced HPFRCC (a) and PE-steel fiber-reinforced HPFRCC (b). (From Homma, D. et al., Journal of Advanced Concrete Technology, 7(2) 217-228, 2009. With permission.)... 

FIGURE 6.14 Self-healing of cracks in PE and PVA fiber-reinforced HPFRCC. (From Koda, M. et al.. Self-healing capability of fiber reinforced cementitious composites. Proceedings of the International Workshop on... 

Summary of Studies on Self-Healing of Cracks in HPFRCC... 

Edvardsen, C. (1999). Water permeability and autogenous healing of cracks in concrete, ACIMaterials Journal, 4 448 54. 

A hot rolling treatment has been shown to substantially improve the ductility of PHB. It is proposed that rolling results in the healing of cracks present inside the spherulites leading to more ductile films [172]. A more sophisticated approach seems to be the solid-state processing of PHB powders, which prevents thermal degradation, since... 

Figure 8. Self-healing of cracks in buildings after sand liquefaction. 

The phenomenon of self regeneration of cracks in cement-based matrices, or so-called autogeneous healing, has been known for a long time. D. A. Abrams first published remarks on self-healing of cracks in reinforced concrete bridge elements exposed to external climatic influences over three years. He confirmed that under much higher loads new cracks opened but those previously healed did not re-open, Abrams (1913). 

The healing of cracks is related to prolonged hydration of cement grains when cracked elements are maintained in sufficient humidity. In such conditions new crystallization prodncts partly recover the cracks. It has been observed that the healing is inversely proportional to the crack width that is, rather narrow cracks may exhibit healing. In most cases, these cracks were produced by shrinkage or thermal actions. 

In experimental conditions, healing of cracks 0.6 mm or even 0.8 mm were reported, bnt in the majority of tests, effective healing was observed when the... 

The question of whether crack healing may be considered a phenomenon of appreciable importance for the durability of concrete elements may be answered positively, but all quantitative data published are obtained in laboratory conditions. Moreover, the results found in different laboratories do not supply quite a coherent image as to the scale of healing that may be expected in a given situation. That is certainly the reason that the healing of crack is considered as a process that is favourable for durability of concrete structures, but it is not accounted for in the design of concrete elements. 

Granger, S., Loukili, A., Pijaudier-Cabot, G., Behloul, M. (2006) Self healing of cracks in concrete from model material to usual concretes, in Proc. 2nd Int. Symp. on Advances in Concrete through Science and Engineering, Sept. Quebec City, QC RILEM. 

Mor, A., Monteiro, P.J.M., Hetsre, W.T. (1989) Observations of healing of cracks in high-strength lightweight concrete, Cement, Concrete and Aggregates, CCAGDP, 12(2) 121-5. 

Reinhardt, H.W., Jooss, M. (2003) Permeability and self-healing of cracked concrete as a function of temperature and crack width, Cement and Concrete Research, 33 981-5. 

Fig. 7.6 Self-healing of cracks at an increased temperature (1,200-1,300 °C) in composites containing Si3N4 and/or SiC...

Fig. 7.7 Self-healing of cracks in sealing material of rubbish disposal sites. Note A—pozzolanic material, e.g. fine Si02 of volatile ash B—Ca-containing material C—material filling the crack due to a cycle of reactions 1. CaO + H2O = Ca(OH)2 2. Ca(OH)2 -1- pozzolanic material —> calcium silicate...

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