Modèle mathématique pour la corrosion sulfatique des mortiers: Fid-Bau Portal

Modèle mathématique pour la corrosion sulfatique des mortiers

Solacolu, C. / Facaoaru, I. / Solacolu, I.

Résumé On établit des polynômes du type: $$y = \alpha _1 (x - t)^{\beta _1 } + \alpha _2 (x - t)^2 + ...$$ qui représentent la variation par rapport au temps de certaines caractéristiques des mortiers de ciment soumis à l'action agressive des solutions sulfatiques, notamment: la longuer, la fréquence de résonance propre en flexion et la vitesse de propagaton longitudinale des ultra-sons. Les valeurs des constantes des modèles mathématiques ont été établies par l'interprétation des données de recherche en laboratoire sur des mortiers de compacités différentes. La validité de chaque modèle mathématique a été vérifiée par le test Fischer-Snedecor. Les modèles mathématiques proposés ont résussi à mettre clairement en évidence les phases du processus de corrosion par les sulfates des mortiers de ciment et la contribution de chaque phase au processus global.

Summary On the basis of experimental data, the polynomial equations of type $$y = \alpha _1 (x - t)^{\beta _1 } + \alpha _2 (x - t)^{\beta _2 } + ...$$ are derived. These equations express the variation in time of certain characteristics of cement mortars, under sulphatic aggressivity such as: natural frequency in flexion, lingitudinal pulse velocity and length. The constant factors values of the equations, were established by the interpretation of the experimental results when testing mortars with various initial compacities. The difference of compacity was obtained by changing the water/cement ratio and the granularity of the aggregate. The behaviour of test specimens 2×2×12 cm, prepared from mortar with cement/aggregate=1/3, was followed during 18 months in high concentrated natrium sulphate solution (about 10%) and in ordinary water, as dummy specimens. Measurements of natural frequency in flexion, pulse velocity and length changes were performed. The checks on the validity of mathematical models was done by the Fischer-Snedecor test. The mathematical models chosen were to put in evidence the three phases of sulphatic corrosion process, namaly: (i) filling and supplementary hydration of the structure due to immersion in liquid; (ii) compaction due to accumulaton of solid state products of reaction in the pores and capillary tubes of the mortar; (iii) destruction of the structure by surpassing the limit of internal stresses corresponding to the tensile strength of the material. A good agreement was found between the measured experimental values and the computed results by using the proposed regression formulae. The ability of acoustical methods to highlight clearly all the phases which characterise the process of sulphatic corrosion was evident. It is to be mentioned also the dependence of the three stages from the initial compacity of mortar, which especially influence the rate of deterioration phenomena in time.