Resistencia química del hormigón. XXIV. Influencia de la adición de escoria a un cemento portland resistente al yeso. Estudio de la concentración iónica del sistema cemento 2/escoria-agua de mar artificial

Abstract

This work, which follows on from previous ones, studies the development of the solid-stage quantity formed in ASTM D 1141-75 artificial sea-water, in which the series of samples of mortar (1:3), made up of a portland cement resistant to sulfate (cement 2 < > P 450-Y) and the mixtures: cement 2/slag = 85/15, 65/35, 40/60 and 30/70, in weight, were submerged for periods of 56, 90, 180 and 360 days (conservation-attack periods) at this stage. This took place after the curing period (1 day in a humid chamber and 21 days submerged in filtered drinking water). The change in the pH value and the concentration of Ca (II), Mg (II), SO₄ (II) and Cl (I) ions in this ASTM artificial seawater are likewise studied, as are the content of Ca (II), Mg (II) and SO₄ (II) ions from the aforementioned solid stages. The structural composition of these solid stages and of the enriched fraction from the samples of mortar was determined by XRD; an account of this was given in (3). In the cases under study it has been shown that an increase occurs in the concentration of Ca (II) during dissolution and in the pH value, the Mg (II), SO₄ (II) and Cl (I) content is reduced and a new solid stage is formed, these being the function of the mixture used for making the series of samples mentioned and of the conservation-attack period. Furthermore, it has been proved that the evolution in the Ca (II) and Mg (II) content is closely linked; when evolution in the first increases, that of the second decreases and vice-versa, there being a point which corresponds to the Ca (II) ↔ Mg (II) ionic balance. Quantities of Ca (II) in to the dissolution and in the new solid stage, from compounds of dissolved, hydrated cement, show an increase in keeping in accordance with the conservation-attack period of each serie of samples made up of a cement 2/slag mixture, and decrease sharply in accordance with the reduction of cement 2 content in the aforementioned mixture. If, moreover, the Ca (II) content in the ASTM artificial sea-water is taken into account, the dissolving process of the Ca (II) compounds in the cement (average values) may be added. The Mg (II) ion has virtually disappeared from the ASTM artificial sea-water, in which were submerged the series of mortar samples made up of cement 2 and of the mixture containing 15% slag, in weight; in these environments, it has precipitated in the form of brucite. In the other environments, it is found in various quantities, according to the mixture used in making up the samples. The greatest quantities of SO₄ (II) and Cl (I) ions that have disappeared from the artificial sea-water correspond to the environments containing the mortar samples made up of cement 2 and the mixtures with 15% and 35% slag for the first, and 35%, 60% and 70% slag in the case of the second. In the new solid stages, SO₄ (II) ions have been detected in quantities of less than 0.07 X 10^-2 moles.