Study of mechanical properties of concrete with low concentration of magnetic nanoparticles

Concrete samples containing small amounts (0.6 wt%) of agglomerated magnetic nanoparticles of cobalt (Co/C) or iron carbide (Fe3C/C) coated with carbon have been synthesized. The time dependence of the compression, bending and contraction strength of samples with and without magnetic nanoparticles have been investigated. Twelve different samples have been prepared and tested during 28 days to detect variation in compression, bending and contraction properties. The temporal change of the bending strength for concrete with and without nanoparticles has showed measurable differences. During the initial stage (first 3 days) of hardening all samples with nanoparticles were less resistant to bending than samples without nanoparticles. After 1 week samples with iron carbide agglomerates and cobalt nanoparticles showed an increase in resistance to bending in comparison with undoped concrete, 3% and 6%, respectively. After 28 days in both cases the bending strength slowly decreased for samples containing magnetic nanoparticles. The compression strength after 28 days decreased by about 9% for samples containing cobalt and 12% with iron carbide. The contraction increased by about 38% for sample with cobalt ions, however no change was observed for samples containing iron carbide. The FMR investigation has shown that the resonance line has shifted more for samples with cobalt and it has been suggested that this process could be connected with contraction caused by decreasing temperature after freezing [P.C. Aitcin, Cement Concrete Res. 30 (2000) 1349]. This study can be very important for magnetic shielding effects and the selection of optimal conditions for building materials with magnetic nanoparticles. It can also be useful for new technological solutions aimed at increasing the functionality of these materials.