Department of Civil Engineering

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Browsing Department of Civil Engineering by Subject "Additive manufacturing"

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    Alkali-resistant glass textile reinforcement of 3D printed concrete
    (Stellenbosch : Stellenbosch University, 2022, 2022-12) Janse van Rensburg, Johannes Jacobus; Combrinck, Riaan; Babafemi, Adewumi John; Civil Engineering; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH 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.
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    Rheo-mechanics, durability and microstructural characterisation of slag-nodified metakaolin-based geopolymer concrete for extrusion-based 3D printing applications
    (Stellenbosch : Stellenbosch University, 2023-11) Jaji, Mustapha Bamidele; Babafemi, Adewumi John; Van Zijl, Gideon P. A. G.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering
    ENGLISH ABSTRACT: Extrusion-based 3D-printed geopolymer concrete (3DPGPC) is a potential alternative to Portland cement concrete (PCC). Research is sparse on the use of metakaolin (MK) for extrusion-based 3D concrete printing applications. The widespread adoption of 3DPGPC is limited due to the unknown durability properties and the long setting time of a two-part geopolymer system. To address the long setting time, this study modified MK-based 3DPGPC with slag up to 30% for 3D printing due to its high Ca2+ ion content. The printable mixture developed comprises M1 (100% MK-3DPGPC) and M2 (95% MK and 5% slag), beyond 5% slag inclusion; the mixtures stiffened with inadequate open time for printing. To address the stiffening, sodium phosphate is incorporated to achieve sufficient open time for constructability of the new mixtures and to improve structural build-up in the mixtures containing slag, M-S10 (90% MK and 10% slag), M-S20 (80% MK and 20% slag) and M-S30 (70% MK and 30% slag), while the mixture without slag, M-S0 (100% MK), is the control. The slump obtained using a mini-slump cone is in the range of 3–5.5 mm and the slump flow using a slump flow table is between 148–157 mm. The setting time using the Vicat apparatus depicts an open time of 6.8 hours for the control (M-S0), and 1.2–1.3 hours for slag-modified mixtures. Rheology tests using an ICAR rheometer reveal that the initial static yield shear stress (𝜏𝑠,𝑖 ) increased from 1898–1900 Pa and initial dynamic yield shear stress (𝜏𝐷,𝑖 ) evolve from 1452–1482 Pa due to 5% slag inclusion. Also, re-floccution (Rthix) and structuration (Athix) rates improved from 5.16 and 0.2 Pa/s to 5.2 and 0.4 Pa/s, respectively. After 28 days of curing age, 70 mm × 140 mm cored cylindrical-3DPGPC specimens exhibited compressive strength of 23.7–33.13 MPa and splitting tensile strength of 1.79–2.43 MPa. Saw-cut 40 mm × 40 mm × 160 mm beam specimens attained flexural strength of 5.48– 7.29 MPa and an interlayer bond strength of 5.40–6.90 MPa. The durability of 3DPGPC is investigated using the water absorption test, capillary and gel porosity test, oxygen permeability index (OPI), and drying shrinkage tests. After 90 days of curing, the drying shrinkages in the vertical direction are 2.98 and 2.86% for the control specimen (M1) and the slag-modified specimen (M2), respectively. In the horizontal direction, the drying shrinkages are 1.14 and 1.1%, respectively. The vertical strain obtained during drying includes plastic shrinkage, drying shrinkage, and vertical creep due to the sustained weight of the upper layers in the fresh state. Drying shrinkage varied along and across the layers of 3DPGPC, depicting anisotropic behaviour. After 90 days of curing, water absorption decreases to 7.33% and 5.2% in M1 and M2 specimens, respectively. The total porosity of 3DPGPC decreases from 20.5–14.5% after 90 days of curing, while mould cast decreasesfrom 15 to 10% in M1 specimens. Slag inclusion further reduce the porosity of 3DPGPC, and mould cast from 17–10.9% and 11.5–8%, respectively. After 90 days of curing, 3DPGPC specimens cored perpendicular to the printing direction (vertical) exhibits (OPI) of 11.07–11.86 kPa, and specimens cored perpendicular to the printing direction (horizontal) exhibits OPI in the range of 10.99–11.74 kPa, while mould cast specimens exhibit OPI of 11.23–11.92 kPa. CT-scan shows that mould-cast specimens have a total porosity of 4.07% and exhibit spherical pores, while 3DPGPC have a total porosity of 1.81% and exhibit elongated pores due to pumping. CT-scan also reveals that porosity is position-dependent in 3DPGPC due to the presence of voids between 0.1–1.7 mm at the interlayer, whereas mould-cast specimens exhibit randomly distributed voids in the range of 0.1–2.5 mm in diameter. Backscattered electron images show increasing C-S-H, N-A-S-H and C-A-S-H gel formation due to the presence of alumina, silica, sodium in MK and high Ca2+ ion as slag content increases. The BrunauerEmmett-Teller (BET) surface area increases with an increase in slag content from 5–23 m2 /g, resulting in the densified 3DPGPC matrix, thereby improving buildability from 27 layers to 42 layers and enhancing mechanical performance. Nitrogen physisorption test shows that the adsorption and desorption isotherms and the hysteresis loops are within the IUPAC Class IV and H3 types, indicating the presence of mesopores (2–50 nm) and macropores (>50 nm). This research demonstrates that MK-based 3DPGPC can be successfully 3D printed and modified with slag to improve the fresh properties, rheology, mechanical properties, microstructural morphology, pore characteristics, and long-term durability performance. It also reveals that 3DPGPC exhibits anisotropy in orthogonal directions. The results obtained from this study are recommended for numerical modelling strategies.