Fluage du béton en fonction de la température Compléments expérimentaux

Résumé

On présente quelques compléments expérimentaux sur le fluage du béton en fonction de la température. Les résultats du fluage du béton séché, confiné (sealed) et à différentes hygrométries sont donnés séparément. On constate que les énergies d'activation apparentes sont différentes suivant la quantité d'eau que le béton retient.

Summary

In a previous article (Rilem Symposium 1968, Materials and Structures, n⁰ 8, March–April 1969) we had presented tests of creep at high temperature showing that concrete freed of its evaporable water obeyed the Arrhenius law, by evidencing an appreciably constant activation energy, and that on the other hand the curve of the rate of deformation of an undried and yet aged concrete as a function of temperature seems to show a maximum at around 50–60°C.

The tests have been continued. It seemed necessary, however, to separate the parameters involved in these phenomena and to attempt to assess separately the action of the temperature and that of the hygrometry. We accordingly found ourselves having to consider on the one hand the concrete freed of its evaporable water, and at the other extreme the concrete constantly saturated, and the intermediate state—that of desorption—with two possible choices: the case of the hygrometry parameter alone and the combined case of the hygrometry and the temperature.

We shall come back to the tests carried out on concrete previously freed of its evaporable water. The measurements were made on several concretes and bring out a rather interesting result which seems to confirm, on the one hand, that for a identical cement batching, whatever the mineralogical origin, with the exception however of the granulous mixture containing mineralogical fragments of different dilation coefficients, the macroscopic activation energies are of the same order of magnitude, and that afterwards these activation energies are appreciably constant, which would tend to demonstrate that after the desorption of the evaporable water the interstitial hydric bonds do not obey the habitual law of variation of the viscosity of water as a function of temperature, since the water's activation energy diminishes to an important degree when the temperature increases. In the case of saturated concrete, the rate of creep of the sealed concrete presents an inverse variation of that of dried concrete. In an intermediate stage the concrete undergoing desorption and kept in equilibrium at different hygrometries presents a growing variation of rate of creep up to 60 per cent and then decreasing to 10 per cent, and after this minimum a new growth up to the total desorption of the evaporable water. On the contrary, if one adds the effect of temperature, the decrease in the rate observed to 10 per cent HR continues until the total desorption of the evaporable water to rejoin the previously mentioned curve of the dried concrete. What now remains to be done, through the tests in progress, is to justify the odd point of the increase in the rate of creep from 10 per cent, of which the probable explanation found so far does not appear fully satisfying.