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In May of 2015 the International Symposium on Electrochemical Methods in Corrosion Research took place in Tróia, Portugal. The Capdesign team of IST presented their work.

 

 

Monitoring localized pH in cracked concrete during natural carbonation for designing smart self-healing additives

 

 

    1 Y. Morozova, 1 M. Taryba, 1 S.V. Lamaka, 2 A. Behnood, 2 N. De Belie, 1 M. F. Montemor

 

1 CQE, Instituto Superior Técnico, Universidade de Lisboa, Portugal

2 Laboratory of Polymeric and Composite Materials (LPCM), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons, Place du Parc 23, B-7000 Mons, Belgium 

 

Abstract

Many concrete structures suffer from serious deterioration due to crack formation.The cracks serve as the “open gates” for aggressive species such as chlorides and carbon dioxide, driving the reinforcing steel out of the passive state. The accumulation of expansive corrosion products promotes further cracking, accelerating thereby the overall structure degradation. As the consequence, there is a need for regular maintenance and repair in order to minimize these adverse effects. However, many infrastructures such as highways, bridges and tunnels are in continuous service and such operations become hard to implement. Under such conditions, self-healing of cracks could provide an attractive solution.

There are different strategies for self-healing of cementitious materials, i.e. by adding hollow fibers and microcapsules with polymerizable organic agents and expansive minerals, as well as using bacteria and shape memory materials. However, the main disadvantage of all available state-of-the-art solutions is that their premature activity (e.g. rupture of capsules during concrete mixing) can harm rather than help solving the concrete-cracking problem. Therefore, current research strives for the development of smart self-healing materials, which activity is triggered by a predetermined external stimulus.

The pH changes occurring inside a concrete crack are suitable external stimuli to be exploited for the triggering of a self-healing process. During carbonation, the pH of concrete changes due to transformation of calcium hydroxide to its carbonate. Natural carbonation is a slow process, limited by hindered diffusion through the concrete cover. However, at the surface it happens almost instantly. The fresh crack is a newly formed exposed interface, where pH changes should occur at much faster rates.

In the current research work, we monitored the evolution of localized pH inside the artificial crack during natural carbonation of mortar samples. This information is crucial when designing smart pH sensitive additives for self-healing concrete. The study was performed using Ir/IrOx pH sensitive microelectrodes that showed stable potential readings and reliable results. The carbonation rate throughout the crack depth has been measured.

 

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