This article introduces the concept of self-healing concrete for sustainable infrastructure through reduction of maintenance and repair in the use phase. To realize this goal, self-healing must observe at least six robustness criteria - long shelf life, pervasive, quality, reliable, versatile, and repeatable. Five broad categories of self-healing approaches, namely chemical encapsulation, bacterial encapsulation, mineral admixtures, chemical in glass tubing, and intrinsic healing with self-controlled tight crack width, are evaluated against the robustness criteria. It is suggested that while significant progress has been made over the last decade in laboratory studies, important knowledge gaps must be filled in all categories of self-healing approaches to attain the goal of smart sustainable infrastructures that possess self-repair capability in the field.
Experimental studies are carried out to evaluate the self-healing capability of FRCC using different types of synthetic fibers that have different chemical properties, i.e. poly vinyl alcohol (PVA), ethylene vinyl alcohol (EVOH), polyacetal (POM) and polypropylene (PP). FRCC specimens were subjected to tension tests in order to generate a crack, and the cracked specimens were immersed in water. In order to evaluate the effect of self-healing phenomena, permeability tests and microscopic observation were carried out. Microscopic observation revealed that the high polarity of synthetic composite has high potential of self-healing precipitation around fibers bridging a crack. Moreover, the coefficient of water permeability was generally reduced with this chemical precipitation, especially in the PVA series. However, even when it was confirmed by microscopic observation that precipitation had appeared and filled a crack, we found there is no recovery of water tightness in some cases, i.e. in the EVOH and POM series. It is confirmed that not only the chemical properties of fibers but also the geometrical properties of the crack surface, such as roughness, complexity and continuity, affect the capability of self-healing for water tightness.
The purpose of this study is to develop a new technique for strengthening and repairing existing concrete structures with sprayed fiber-reinforced polymers (FRP) by mixing chopped carbon or glass fibers with epoxy or vinyl ester resins in open air and randomly spraying the mixture onto the concrete surface with compressed air. The use of sprayed FRP for repair and strengthening purposes using epoxy or vinyl ester resins has never been fully investigated. In this study, tensile testing was conducted on material specimens to determine the optimum length of chopped carbon or glass fibers and the mixture ratio of fiber, epoxy, and vinyl ester resin for sprayed FRP. These variables were adjusted to produce a material strength equivalent to that of one FRP sheet. The optimal length of glass and carbon chopped fibers was determined to be 38 mm, and the optimal mixture ratio of chopped fiber to resin was found to be 1:2. The thickness of sprayed FRP required to provide the same strengthening effect as one FRP sheet was also calculated. During this study, experiments were conducted to evaluate the strengthening/repair effects of the sprayed FRP on flexural beams, shear beams, and damaged beams. The results showed that the strengthening effect of sprayed FRP on the flexural and shear specimens was similar to those of one FRP sheet. The maximum strength of the damaged beams reinforced by sprayed FRP was approximately the same as that of the reinforced flexural and shear beams. Moreover, existing design equations for FRP sheets were found to be applicable to flexural beams reinforced with sprayed FRP. The shear beam specimens could be safely designed using the coefficient of shear strength reduction α= 0.18, determined to result in computed values that most closely approximate the experimental values. Overall, the sprayed FRP technique was found to be suitable for strengthening existing reinforced concrete buildings.
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