Alkali-resistant glass textile reinforcement of 3D printed concrete
ABSTRACT Additive manufacturing such as 3D concrete printing (3DCP), has recently gained significant attention due to its numerous benefits. However, 3DCP still has significant challenges to overcome before it can be fully adopted as a feasible alternative to conventional construction methods. The reinforcement of 3D printed concrete elements has proven to be challenging and needs to be addressed. Moreover, there are multiple aspects to this challenge that need to be taken into account, such as the lack of clear space above the filament layer being printed, difficulty in installing the reinforcement in different directions as well as integrating the reinforcement into the printing process. Various strategies have been studied in order to address these challenges, with different materials used as reinforcement before, during or after printing. However, before reinforcement can be applied, the behaviour of the consequent composite materials must first be studied. This study, therefore, investigates the flexural performance and behaviour of two different alkaliresistant (AR) glass textile materials as reinforcement to determine whether it is a feasible solution. During this study, two different methods of printing and applications of the textiles are considered, one where the elements are printed vertically and the textiles are pre-installed, and one where the elements are printed horizontally and the textiles are installed during the printing process. The textiles are applied in two different locations, one at the middle of the depth of the sample and one lower down. Samples are extracted from these printed elements and tested in flexure by conducting fourpoint bending tests 28 days after printing. After conducting these tests, the crack sequence and failure mechanisms of the variations are investigated. Furthermore, an optical microscope is used to gather more information regarding the performance and failure of the various samples. The results show that there is a significant increase in the flexural performance of the samples reinforced with an AR glass Textile A. Textile A is fully impregnated with epoxy resin, with high tensile strength, stiffness, and large cross-section area. Additionally, the application of this textile promotes deflection hardening structural behaviour. However, in contrast, there is a significant increase in ductility with no increase in flexural strength for the samples reinforced with an AR glass Textile B. Textile B is coated with styrene butadiene, with high tensile strength but a small section area. The results further indicate that the samples reinforced lower in the sample experience higher flexural strength with lower ductility and more variability in behaviour. During testing, it is also discovered that voids form underneath Textile A when applied to horizontally printed samples (between the interlayers), and that these voids influence the performance of the samples. The voids further influence the failure mode as well as the cracking sequence. Investigation of the failure of the samples reinforced with Textile A show two failure mechanisms occurring, namely, delamination and shear. Delamination always occurs when the textile is applied in the middle of the depth of the samples, but shear only occasionally occurs for the variation where the textile is applied lower in the sample. Additionally, telescopic failure is detected for Textile B. It is concluded that for both the textiles, the best performance, behaviour and repeatability are observed when the elements are vertically printed, and the textiles are placed in the middle of the depth of the sample. Among others, it is recommended to apply different variations of textiles, use different application techniques (such as retrofitting) and to explore the micro mechanical behaviour of 3DPC elements reinforced with textiles in future studies.