Chloride induced corrosion of steel bars in alkali activated slag concretes

The studies on chloride induced corrosion of steel bars in alkali activated slag (AAS) concretes are scarcely reported in the past. In order to make this issue clearer and compare the corrosion performance of AAS with Portland cement (PC) counterpart, an investigation was carried out and the results are reported in this paper. Corrosion properties were assessed with the help of rate of corrosion, electrical resistivity and pore solution chemistry. It was found that: (i) steel corrosion resistance of the AAS concretes was comparable or in some cases even worse than that of Portland cement (PC) concrete under intermittent chloride ponding regime; (ii) the corrosion behaviour of the AAS concretes was significantly influenced by ionic exchange, carbonation and sulphide concentration; (iii) the increase of alkali concentration of the activator generally reduced chloride resulting corrosion, and a value of 1.5 was found to be an optimum modulus for the activator for improving the corrosion resistance.

Corrosion Fatigue Behaviour of Laser-welded Shape Memory NiTi Wires in a Simulated Body Fluid

Corrosion fatigue is a fracture process as a consequence of synergistic interactions between the material structure, corrosive environment and cyclic loads/strains. It is difficult to be detected and can cause unexpected failure of engineering components in use. This study reveals a comparison of corrosion fatigue behaviour of laser-welded and bare NiTi wires using bending rotation fatigue (BRF) test coupled with a specifically-designed corrosion cell. The testing medium was Hanks’ solution (simulated body fluid) at 37.5 oC. Electrochemical impedance spectroscopic (EIS) measurement was carried out to monitor the change of corrosion resistance of sample during the BRF test at different periods of time. Experiments indicate that the laser-welded NiTi wire would be more susceptible to the corrosion fatigue attack than the bare NiTi wire. This study can serve as a benchmark for the product designers and engineers to understand the corrosion fatigue behaviour of the NiTi laser weld joint and determine the fatigue life safety factor for NiTi medical devices/implants involving laser welding in the fabrication process.