Durability of marine concrete with nanoparticles under coupled action of fatigue load, dry–wet cycles and Cl− corrosion

The combination of multiple factors in marine environments can accelerate the concrete corrosion. In this work, bending fatigue load, dry–wet cycles and Cl − erosion were experimentally combined to evaluate the endurance of marine concrete incorporating nanoparticles (nano-silica (NS) and nano-titania (NT)). Dry–wet cycles of the nano-concretes were simulated in seawater (5% sodium chloride solution) and bending fatigue loads at stress levels of 0.5, 0.6, 0.7 and 0.8 were applied. The results indicated that the nanoparticles enhanced the resistance to Cl − erosion during dry–wet cycles and bending fatigue load by making the concrete more durable under coupled bending fatigue load, dry–wet cycles and Cl − erosion. The improvements were the most obvious for a NT content of 1% and a NS content of 2%, and the improvement was better with 1% NT than with 2% NS content is 2%. The free Cl − content in the concrete tension zone was larger than in the compressive zone. X-ray diffraction was used to assess the physical phases of the concretes before and after the experiments and to analyse the reasons for the increased concrete durability. The nanoparticles increases the content of hydrated calcium silicate in concrete, changed the orientation of calcium hydroxide and improved the concrete durability.