Determinación del contenido de OH^- en la fase acuosa de los poros de matrices cementantes por un método empírico de lixiviación

Abstract

RESUMENEl método más fiable de determinación de iones hidroxilo en una fase acuosa de materiales cementantes es la extracción de la misma mediante aplicación de presión (pore-pressing). Sin embargo, este método necesita un equipo especial además de una cantidad de muestra relativamente alta. En la presente investigación, se propone la determinación de la concentración de OH' en la fase acuosa del hormigón mediante un método de lixiviación en muestra granulada. El programa experimental se ha realizado a partir de morteros con 5 diferentes materiales cementantes y tres disoluciones de lixiviado distintas. En el tratamiento de los resultados, se han considerado diferentes fenómenos (dilución + disolución de las fases sólidas) que tienen lugar durante la lixiviación, hasta llegar a obtener los resultados obtenidos por la técnica de extracción por presión. La concordancia encontrada es suficientemente buena para todos los materiales ensayados, a pesar de que el mecanismo de la extracción no se ha clarificado en su totalidad y de que son las concentraciones y no las actividades de los iones las que se han tenido en cuenta para los cálculos. Por tanto, en esta etapa de la investigación, el método que se propone se puede considerar como empírico. SUMMARYThe most reliable method to determine the concentration of hydroxyl ions in the aqueous phase of hardened cementitious materials is the squeezing of concrete at high pressures. However, this method needs special equipment as well as a relatively high amount of sample to be carried out. In present research, the determination of the OH concentration in the concrete pore solution is undertaken by a leaching method in granulated samples. The experimental program has been made using mortars with 5 different binders and three different leaching solutions. In the treatment of the results, different phenomena (dilution + dissolution of solid phases) occurring during leaching have been taken into account until reaching the target values validated by comparison with those obtained by means of the high pressure technique. The agreement found is good enough, for every binder tested, in spite of the fact that fully understanding of the leaching mechanism is not achieved and that concentrations and not activities of the ions are taken into account in the calculations. Therefore, the method suggested is empirical at present stage.PALABRAS CLAVE: fase acuosa de los poros, iones hidroxilo, análisis, lixiviación, método empírico.

Estimating Na+ and K+ concentrations of the pore solution based on ex-situ leaching tests and thermodynamic modeling

“…The second step of ESL methods generally involves stirring the powdered sample in a solvent, which is most commonly deionized water, and then filtering to obtain a diluted solution for chemical analysis. Several studies on ESL test methods have investigated in numerous factors, including the temperature of the leaching solution [10,16] (Natkunarajah et al recently showed a negligible effect of solution temperature on the results of ESL for concrete [24]), liquid-to-solid ratio [16][17][18][19][20], the duration of the leaching period [19,21,22], and the particle size of the pulverized sample [16,19,21,22]. The list of ex-situ leaching methods resulting from multiple studies includes cold water extraction (CWE) [9,18,19,[21][22][23][24], hot water extraction (HWE) [13,25], and the "espresso" method [11,26].…”

“…Several studies on ESL test methods have investigated in numerous factors, including the temperature of the leaching solution [10,16] (Natkunarajah et al recently showed a negligible effect of solution temperature on the results of ESL for concrete [24]), liquid-to-solid ratio [16][17][18][19][20], the duration of the leaching period [19,21,22], and the particle size of the pulverized sample [16,19,21,22]. The list of ex-situ leaching methods resulting from multiple studies includes cold water extraction (CWE) [9,18,19,[21][22][23][24], hot water extraction (HWE) [13,25], and the "espresso" method [11,26]. These methods have been used to obtain the alkali metal content in g/g of dry sample -a useful metric for AAR studies [9].…”

“…We hypothesize that correcting alkali concentrations from ESL using the approach proposed herein for calculating V PSE can reconcile ESL concentrations with those from PSE. The CWE procedure described by Plusquellec et al [23] was selected based on its suitability for cementitious materials at earlier ages of hydration and extensive literature that informed its development [16][17][18][19]21,22,28]. In this paper, both PSE and CWE methods of pore solution extraction were used for three cementitious systems with a range of alkali contents.…”