Influence of the pore morphology of high strength concrete on its fatigue life

The use of porous concrete in structural elements subjected to compression cyclic loads is inevitable in those situations in which it is necessary to withstand, simultaneously, important amount of freeze-thaw cycles and cyclic loads. However, the presence of pores, which is essential to withstand freeze-thaw cycles, can drastically reduce the fatigue life of concrete in some cases. This paper analyses a total of 60 40-mm edge cubic specimens, belonging to 5 series, each of them with a different content of air entraining agent. The specimens were first scanned using computerized tomography scan in order to visualize the internal porosity of the specimens. Through the use of specific software, the morphological parameters of the porosity of each test was defined. Nine specimens of each series were tested at cyclic compression load until fatigue failure. The fatigue life of each specimen was obtained. Using these data, the characteristic fatigue life of each series were obtained. The comparison between the morphology of the porosity and its fatigue life provides interesting relationships, which allow to understand better how the porosity influences the response to compression fatigue of the concrete. Finally, empirical relationships between porosity morphological parameters and fatigue life were obtained. The correlations show that a greater porosity leads to a lower fatigue life. And also, concretes with a higher percentage of small pores show a better behaviour against fatigue.