Use of anthocyanin solutions in portland cement concrete to identify carbonation depth
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ORIGINAL ARTICLE
Use of anthocyanin solutions in portland cement concrete to identify carbonation depth Servando Chincho´n-Paya´
. Carmen Andrade . Servando Chincho´n
Received: 11 December 2019 / Accepted: 21 June 2020 RILEM 2020
Abstract A method is proposed which comprises placing a portland cement concrete or mortar sample with a harmless solution, based on a variety of anthocyanins, which acts as an indicator yielding a color which is visibly different in zones where an alkaline reserve exists (pH * 12) (green) from that observed in carbonated areas (pH B 9) (blue). We firstly experimented with various solutions containing anthocyanins extracted from flowers and fruits, after which food colors commercialized in the European Union were utilized seeking to prepare a reproducible method. The tested products are three food colors coming from grape, black carrot and red cabbage obtained by means of extraction and later dehydrated by spray dying. The solutions which seem most appropriate to us contain 2.5% of color dissolved in a liquid where alcohol and water are mixed at a 70/30 ratio.
S. Chincho´n-Paya´ (&) Instituto Eduardo Torroja de Ciencias de la Construccio´n (IETcc-CSIC), Madrid, Spain e-mail: [email protected] C. Andrade International Centre for Numerical Methods in Engineering CIMNE-UPC, Madrid, Spain S. Chincho´n Instituto del Agua y las Ciencias Ambientales, University of Alicante, Alicante, Spain
Keywords Concrete Carbonation Anthocyanins PH indicators
1 Introduction Concrete is made up of different-sized aggregates joined to one another thanks to the agglomerating capacity of hydrated cement. In order to improve the physical qualities of this material and to endow it with greater resistance, steel bars are usually embedded composing the so-called reinforced concrete. Cement hydration forms a number of new compounds amongst which stand out alkaline hydroxides (sodium and potassium) and alkaline earth hydroxides (mainly of calcium), calcium hydroxide—also known as portlandite—being the most important of all for its quantity. All these hydroxides confer upon the pore solution a pH of about 12.5 [1]. This effect is referred to as ‘alkaline reserve’ and turns out to be beneficial in the case of reinforced concretes because, at such a high pH, the steel of reinforcements becomes coated with a thin layer of oxy-hydroxides which prevents oxidation inside the metal. However, portlandite is not a perennial compound and gradually disappears over time. It does so in processes of reaction with environmental agents, with compounds that are present in the atmosphere such as SOx and CO2 [2, 3]. The main reaction taking place is
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carbonation through reaction with CO2 where calcium hydroxide progressively becomes carbonated to form calcium carbonate according to the following reaction: Ca(OH)2 ? CO2 ? CaCO3. Carbonation is a process controlled by the diffusion of atmospheric CO2 from the outside, and it needs a certain degree of humidi
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