Abstract
Self-healing of cracked concrete beams after 25 years of marine exposure was investigated. The extent of self-healing and the chemical and mineralogical composition of the self-healing products were characterized, and mechanisms proposed. There was no effect of varying silica fume (4%, 12%) and fly ash content (0%, 20%) on the mineralogy and chemistry of the self-healing products and the extent of self-healing. Crack widths smaller than 0.2 mm appeared closed. With increasing crack depth, a sequence of changing mineralogy of self-healing products was found. In the outer part of the crack (0–5 mm depth from the exterior surface) only calcite was precipitated followed by brucite layers from 5–30 mm depth. The brucite was occasionally intermixed with calcite. At crack depths >30 mm only ettringite was observed. It is hypothesized that the mineralogical sequence observed with increasing crack depth occurs due to an increasing pH of the solution inside the crack with increased crack depth. Self-healing of cracks in marine exposed concrete is proposed to happen through precipitation of ions from seawater partly in reaction with ions from the cement paste in the outer part of the crack and through dissolution and reprecipitation of ettringite at larger crack depths.
Highlights
The formation of cracks due to mechanical stresses and volume deformation is inevitable in concrete structures
The results showed that the precipitation of calcium carbonate was the main cause of autogenous self-healing in all samples and that the type of cement used had no influence on the extent of self-healing [13]
This paper aims to increase the understanding of the long-term impact of marine exposure and binder type on the mechanisms of autogenous self-healing of cracks in concrete
Summary
The formation of cracks due to mechanical stresses and volume deformation is inevitable in concrete structures. Cracks facilitate the ingress of aggressive substances like chlorides, and laboratory experiments showed that the time to initiate steel corrosion in reinforced concrete may be reduced [1,2]. The impact of cracks on the long-term corrosion of steel in reinforced concrete (propagation) is still an issue of debate [3,4,5]. During long-term exposure, self-healing of cracks in concrete might limit the ingress of aggressive substances. In field exposed concrete structures, autogenic self-healing is typically the only relevant mechanism. One possible chemical self-healing mechanism in concrete is the further hydration of unreacted cement and supplementary cementitious materials (SCMs).
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