Experimental and molecular dynamics study on the deterioration mechanism of GFRP bars in distilled water and salt solution environments

Abstract

The deterioration speed of glass-fibre-reinforced polymer (GFRP) bars plays an important role in their long-term application in concrete. The deterioration mechanism of GFRP bars in different salt solutions and distilled water (DW) environments was determined by conducting a combination of water uptake, microscopic, Fourier transform infrared spectroscopy, and tensile strength (TS) tests. The interaction between the epoxy resin and water molecules and the effect of salt ions on the interior of the epoxy resin system were revealed by performing molecular dynamics (MD) simulation. The results showed that the water uptake and TS losses of the GFRP bars in DW were higher than those in the salt solution environments. Moreover, the TS losses of the GFRP were mainly due to the water uptake swelling and plasticization of the resin. In addition, the MD simulation, revealed that as the moisture uptake increased, the water molecule diffusion coefficient increased and the water-water hydrogen bonding dominated, leading to the occurrence of the water-clustering phenomenon. However, the presence of salt ions led to a low transport rate of water molecules inside the resin, thereby reducing the water-molecule-clustering phenomenon. Compared with monovalent cations (Na+ and K+), multivalent Ca2+ is more likely to bind to COO− ions inside the network system, reducing the electrostatic repulsion between the COO− ions and hindering the swelling of GFRP.