Variations of Physical Properties and Strength of Magnetite Due to Microorganism

The purpose of this study is to examine the variation of physical properties and strength of magnetite due to microorganism throughout various laboratory tests such as absorption, elastic wave velocity, uniaxial compressive strength. For this purpose, pH and Eh with culture period as well as initial values of magnetite were firstly measured. Secondly, the laboratory test of specimens for the abiotic oxidation and bio-oxidation were performed, then, their differences were compared and analyzed. Finally, variation of physical properties and strength of magnetite were quantitatively analyzed.. The average initial value of the porosity, absorption, and elastic wave velocity for the abiotic oxidation was 0.439 %, 0.109 %, and 1477 m/s, while 0.553 %, 0.138 %, and 1456 m/s for the bio-oxidation, respectively. The average initial uniaxial compressive strength was 168 MPa. The measured pH of the abiotic oxidation test during 45 days ranged from 4.02 to 5.16, while that of the bio-oxidation test ranged from 1.50 to 1.90. The measured Eh of the abiotic oxidation and bio-oxidation tests ranged from 112 to 175 mV and from 285 to 319 mV, respectively. The porosity of the abiotic oxidation test with microorganism and culture period ranged from 0.397 to 0.483 % before culture and 0.333 to 0.433 % after culture, while that of the bio-oxidation test ranged from 0.510 to 0.621 % before culture and 0.519 to 1.499 % after culture. The absorption of the abiotic oxidation test ranged from 0.099 to 0.125 % before culture and 0.084 to 0.126 % after culture, while that of the bio-oxidation test ranged from 0.124 to 0.153 % before culture and 0.125 to 0.383 % after culture. The measured elastic wave velocity of the abiotic oxidation test ranged from 1453 to 1506 m/s before culture and 1344 to 1480 m/s after culture, while that of the bio-oxidation test ranged from 1400 to 1497 m/s before culture and 1210 to 1460 m/s after culture. The uniaxial compressive strength by the abiotic oxidation test was not a significant difference with the initial value, while that by the bio-oxidation test relatively showed a large decrease. As a result, it suggests that the variation of physical properties and strength on magnetite is strongly dependent on the microorganism.