Saponification and scaling in ordinary concrete exposed to hydrocarbon fluids and high temperature at military airbases

The conventional Portland cement concrete (PCC) aprons that house Air Force and Navy aircrafts are reported to experience significant scaling on the surface, which is a serious concern for the safe operation of military aircrafts. The purpose of this study is to investigate the underlying scientific facts for the scaling of PCC aprons at military airbases. An experimental program was developed to replicate the physical and environmental circumstances that prevail in aprons at military airbases. Standard sized PCC cylinders were repeatedly exposed to aviation oils and high temperature, both simultaneously and separately, until surface scaling became obvious. Chemical analyses were conducted on the aviation oils, scaled concrete as well as on the original PCC; analysis results revealed that aviation oils contain ample hydrocarbon compounds to trigger surface scaling at high temperature. When PCC cylinders were repeatedly exposed to aviation oils and high temperature simultaneously, they underwent a saponification process after a couple of cycles of exposure, and rapidly developed scaling on the surface after subsequent exposures. Saponification increased with the increase in numbers of cyclic exposures and consequently resulted in the development of a significant volume of loose fines on the surface of the PCC cylinders. The repeated saponification and deposition of calcium phosphate (salts) at the top layer caused rapid scaling, by acting together. On the other hand, PCC cylinders that were exposed to aviation oils at ambient temperature neither experienced a saponification process nor developed scaling. The influence of w/c ratio on the saponification, scaling and thermal cracking was examined as a part of the current study. The present study reveals a relationship between the depth of scaling and aviation oils’ penetration depth, and the effect of high temperature, microcracks and voids, and their influences on the scaling process of PCC are also reported herein.