Chloride Induced Corrosion and Carbonation in 3D Printed Concrete

The durability of reinforced concrete structures is dependent on the ability of the concrete cover to combat the ingress of chlorides and carbon dioxide in marine and urban environments. In recent years, interest in additive manufacturing), specifically referring to extrusion based three-dimensional concrete printing (3DCP), has been growing in the construction industry. Despite this being a promising technology that can save construction time, costs and resources, certain issues regarding the lack of fusion between subsequent printed layers have been brought to light. Research has shown that the lack of fusion at the interlayer regions can act as ingress pathways for corrosion contaminants, such as carbon dioxide and chloride aqueous solution, that can cause deterioration. This study investigates the interlayer bond strength (flexural strength) and durability performance of 3D printed concrete subjected to pass times between 0 and 30 min and compares the results to reference cast concrete of the same concrete mixture. The durability study includes Durability Index testing (oxygen permeability, water sorptivity and chloride conductivity index), accelerated concrete carbonation and chloride-induced corrosion. The results show that the cast samples outperform printed samples, yielding greater flexural strength and durability properties, and emphasize the importance of improving the 3DCP interfacial bond. Cast samples are shown to have randomly distributed, compact voids compared to the interconnected and elongated pores located at the interlayer regions of printed samples. In addition, printed samples yield lower interlayer bond strength and durability properties with an increase in pass time, which is attributed to surface moisture evaporation as well as the thixotropic behaviour of the concrete mixture. Good relationships between the mechanical strength and durability performance are also presented.

Mitigation of chloride induced corrosion in reinforced concrete structures and its modeling

The paper is primarily focused on the description of transport of harmful species in concrete such as chlorides on one side and transport of corrosion inhibitors and nanoparticles used to diminish corrosion of steel reinforcement or seal the microstructure of concrete on the other side. The studied processes are helpful in reverting the chloride induced corrosion of the reinforcement in reinforced concrete structures. The transport mechanisms are summarized with the emphasis on their mathematical description and numerical solution. The paper shows modeling results of the processes including a comparison with experimental data on several typical examples. The efficiency of the methods is shown supported by experimental and numerical results. A good correlation of the models with experiments is achieved.