Potentiometric determination of the chloride ion activity in cement based materials

Abstract

The chloride content at the reinforcement is one of the decisive factors for the initiation and propagation of localised corrosion in concrete structures. A monitoring technique for the chloride concentration which is accurate, non-destructive and continuous would thus be highly desirable. For this reason, the performance of ion selective electrodes (ISEs) was investigated both in alkaline solutions and embedded in mortar. The Ag/AgCl electrodes used in this work showed Nernstian behaviour with a slope of -59 ± 1 mV per decade and a detection limit for chloride ions below 10 -2 mol dm -3 even at pH close to 14; the selectivity coefficient for hydroxide interference was estimated at k pot Cl À ;OH À % 4 Á 10 À3 . The Ag/AgCl membranes show good long-term stability over more than 6 months even in highly alkaline solutions as long as chloride ions are present; in the complete absence of chloride the measured potentials were affected by the pH of the solution. The sensors are, however, able to recover fast as soon as they come into contact with chloride. When using ISEs embedded in concrete, diffusion potentials between the reference electrode and the ISE, as arising e.g. from gradients in pH, significantly affect the potential measurement and present a most important error source for the application of direct potentiometry to concrete. To minimise such errors, the reference electrode has to be positioned as close to the ISE as possible.

Development of an electrochromic device triggered by the macrocell current in chloride‐induced corrosion of steel‐reinforced concrete

“…Mixtures of LiClO 4 and poly(ethylene glycol) with M w = 400 g mol −1 (abbreviated as PEG 400 below, X n = 9) were selected as ion conductive matrices for the electrochrome. The average formula of the polymer is HO (CH 2 CH 2 O) 9 H. At this low molecular weight, the mixtures do not solidify even at high salt contents, which allows for a sufficiently low electrical resistance.…”

“…One possibility is to continuously record the potential of the monitored element with respect to a reference electrode. [4] However, all currently used monitoring systems rely on external power supplies and electronic components with significantly shorter lifetimes than the planned service-life of >100 years for infrastructural buildings. Thus, a sustainable infrastructural development should include long-lasting, robust monitoring systems with little to no maintenance.…”

“…This study thus further describes the development of an electrochromic device (ECD) based on DHV embedded in a polymer electrolyte consisting of poly(ethylene glycol) and LiClO 4 . Similar devices first appeared in the early 1970s as predecessors of the LCD displays, [6] but the main focus of research at that time was optimising the response times, contrast, and cycle numbers.…”

Determinação espectrofotométrica de cloreto em cimento após preparo de amostra por piroidrólise

“…A faixa linear de calibração foi de 0,2 a 10 mg L -1 de cloreto e a sensibilidade do método foi considerada boa, se comparado com outros métodos de determinação. 12,13,15,33 Cabe destacar que, com o aumento da massa de amostra e uso de IC com detector por condutividade, é possível reduzir o LOD para até 0,3 µg g -1 . 16 Entretanto, como a concentração de cloreto em cimento é, na maioria dos casos, superior a 20 µg g -1 , 8,16 o método de preparo da amostra utilizando piroidrólise é adequado para a determinação espectrofotométrica de cloreto em cimento.…”

“…11 Porém, este método não é adequado para determinar baixas concentrações de cloreto, bem como o ponto final é difícil de ser visualizado. 8 Entretanto, outras técnicas empregadas para determinação de cloreto em cimento envolvem o uso de titulação potenciométrica, 10 potenciometria com eletrodo íon seletivo (ISE), 12 espectroscopia de emissão óptica com plasma induzido por laser (LIBS), 13,14 cromatografia de íons (IC) 15,16 e espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES). 7 No entanto, estas técnicas estão sujeitas a interferências diversas e o preparo adequado da amostra é, em muitos casos, a etapa fundamental para que se obtenham resultados confiáveis.…”