Manual Application versus Autonomous Release of Water Repellent Agent to Prevent Reinforcement Corrosion in Cracked Concrete

Kim Van Tittelboom,Nele De Belie,Jeroen Van Stappen,Renaat Callens,Bjorn Van Belleghem,Jolien Van Der Putten,Veerle Cnudde,Maxim Deprez,Philip Van Den Heede

doi:10.3390/pr9122101

Abstract

Cracks in reinforced concrete are preferential ingress paths for aggressive substances such as chlorides. As soon as a critical amount of chlorides has reached the steel reinforcement, corrosion will occur. Therefore, crack healing is of utmost importance. However, manual crack repair is very labour intensive. Therefore, the potential of self-healing through the release of a water repellent agent from embedded capsules was compared with the effectiveness of applying this agent on the concrete surface before or after cracking and the effectiveness of injection of the agent into a crack. From the electrochemical corrosion measurements, it was shown that only uncracked samples were able to withstand 135 weekly cycles of exposure to a 33 g/L chloride solution without corrosion initiation of the reinforcement. While samples with manually injected and autonomously healed cracks resisted the exposure conditions for about 50 cycles or more, samples for which the water repellent agent was applied onto the surface after cracking resisted the exposure conditions for 5–42 cycles, while samples for which the agent was applied onto the surface before cracking showed an immediate corrosion initiation similar as was noted for the untreated cracks. From a visualization of the chloride ingress front and determination of the chloride content in the vicinity of the crack, it was noticed that none of the crack treatment techniques performed as well as the uncracked series. Visual inspection of the corroded rebars and determination of the corroded volume of the rebars through computed tomography and macro-cell corrosion current measurements proved again that the uncracked series outperformed the other series. While the corroded volume of the rebars from the uncracked series was almost zero, this value ranged from 15–95 mm3 for the rebars of the other series. However, the latter investigations also showed that release of the agent into the crack, whether this was done in a manual way or autonomously through release from embedded capsules, resulted in a delayed corrosion initiation and lower corrosion propagation rate compared to the application of a water repellent agent onto the surface. This is a beneficial outcome for the further implementation of self-healing approaches, more specifically though the release of encapsulated water repellent agent, in the market.

Highlights

Reinforced concrete is one of the most widely used construction materials, one of its most important drawbacks is its vulnerability to corrosion
Multiple approaches have been suggested to mitigate corrosion of reinforcement steel, among which reducing the concrete permeability [2], making use of corrosion inhibitors mixed into the concrete or applied onto the steel or concrete surface [3,4,5,6,7], and using corrosion protective coatings or paints applied onto the steel bars or the concrete surface [8]
In the study of Sharma et al [9], a nano-modified epoxy coating with self-healing properties through the use of encapsulated tung oil was applied onto the rebars and resulted in a reduction in steel mass loss when the rebars were exposed to an accelerated impressed current corrosion test with a 3.5% NaCl solution

Summary

Introduction

Reinforced concrete is one of the most widely used construction materials, one of its most important drawbacks is its vulnerability to corrosion. 6–10 times the original steel volume [1] causing concrete cracking and spalling. It leads to a reduction in rebar cross section due to metal dissolution causing an impairment of the structural safety. In the study of Dong et al [10,11], two types of corrosion inhibitors were embedded inside ethyl cellulose microcapsules. In this way, they counteract the negative effect of these inhibitors prematurely binding with unhydrated cement [12]

Methods

Results

Conclusion