Resistencia química del hormigón XXVI. Influencia de la adición de escoria a un cemento Portland. Estudio de la concentración iónica (del sistema cemento 3/escoria-agua) de mar artificial

Abstract

This work, which is a follow-up of others, studies the development of the solid-stage quantity formed in ASTM D 1141-75 artificial seawater, in which the series of samples of mortar (1:3), made up of a portland cement (cement 3 P-450) and the mixtures cement 3/slag = 85/15 - 65/35 - 40/60 and 30/70, in weight, were submerged during 56 - 90 - 180 and 360 days (periods of conservation-attack) in this stage, after the curing period (1 day in a curing chamber and 21 days under drinking filtered water). The changes in the pH value and the concentration of Ca (II), Mg (II), SO 4 (II) and Cl (I) ions in this ASTM artificial sea-water are likewise studied, so as the content of Ca (II), Mg (II) and SO 4 (II) ions of the new solid phase formed. In the studied cases it has been shown that an increase of Ca (II) in the solution and of the pH value is produced, the Mg (II), SO 4 (II) and Cl (I) content is reduced and a solid phase is formed, these being a 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 it increases in the first one, that of the second decreases and vice versa, being there a point which corresponds to the Ca (II) ↔ Mg (II) ionic equilibrium. Quantities of Ca (II) into the solution and in the new solid phase, from the compounds of hydrated cement, show an increase, in accordance with the conservation-attack period of each serie of samples made up with a cement 3/slag mixture, and decrease sharply in accordance with the reduction of cement 3 content in the 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 of the cement (average values) may be added. The Mg (II) ion has practically disappeared from the artificial sea-water where the series of mortar samples made up of cement 3 and the mixture which has 15% slag in weight, have been submerged; in these means it has precipitated, in a part, as brucite. In the other means this ion is found in diverse quantities, according to the mixture and to the conservation-attack time. The content of SO 4 (II) and Cl (I) in the artificial sea-water has, in likewise experience, a decrease which depends on the mixture used in the manufacture of the mortar samples and the time of conservation-attack. The greatest quantities that have disappeared correspond to the means containing the mortar samples made with cement 3 and the mixtures with 15% and 35% slag, in weight, for the SO 4 (II) ions and the mixtures with 35%, 60% and 70% slag for the Cl (I) ions.