Volume 6, Issue 6 (June 2009)
Changes in Fluid Penetrability and Mechanical Properties of Concrete due to High Temperature Exposure
This paper examines the relationship between changes in mechanical properties and fluid penetrability of a conventional and a high strength concrete mixture resulting from exposure to temperatures of 150°C, 300°C, or both, using a unique experimental technique. Measurements were taken before and after exposure on 100 mm diameter disks, approximately 25 mm thick. The dynamic modulus of elasticity (Ed) was measured using resonant frequency techniques. Fluid penetrability of the disks was characterized by air permeability index (API) and rate of water absorption (sorptivity). The nondestructive nature of these tests allowed multiple testing on the same samples. The changes in API and Ed of high strength concrete disks were greater than those of conventional strength. Damaged high strength concrete was found to have a lower residual rate of water absorption than damaged conventional strength concrete. However, the rate of water absorption of high strength concrete did not show as large an increase as was found with air permeability. The API identified differences between high strength concrete specimens exposed to both 150°C and 300°C compared to similar specimens exposed to 300°C only. This difference was also identified by changes in Ed, but was not identified using the rate of water absorption. The test methods for API and Ed described in this paper are simple and easy to conduct, and appear to provide useful information in studying changes in microstructure of concrete exposed to elevated temperatures.