Abstract
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.
Highlights
Alexander and Beushausen [1] define the durability of a reinforced concrete (RC)structure as ‘The ability of a structure or component to withstand the design environment over the design life, without undue loss of serviceability or need for major repair’
RC structures exposed to the tidal, splash and spray zone in coastal environments, in combination with abrasion, is much more prone to Chloride-induced corrosion (CIC) compared to structures exposed to airborne salts with no direct contact with water [3]
PT from 0 to 20 min, which could be attributed to the lack of fusion (LOF) induced by the PT allowin more water to an absorbed through the critical layer (CL), similar to the results reported by Bran A
Summary
Alexander and Beushausen [1] define the durability of a reinforced concrete (RC)structure as ‘The ability of a structure or component to withstand the design environment over the design life, without undue loss of serviceability or need for major repair’. The reinforcement of concrete structures is protected against corrosion by the concrete cover and the protective passive layer that forms owing to the alkaline nature of the concrete. RC structures are exposed to chlorides, which penetrate the concrete cover, lower the pH of the concrete by forming hydrogen chloride (HCl) and destroy the protective passive layer [2]. Scott and Alexander [4] and Otieno et al [5] reported that the binder type and cover depth influenced CIC. Both studies reported that an increased in cover depth from 20
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