PSI - Issue 64

Zohaib Hassan et al. / Procedia Structural Integrity 64 (2024) 1184–1191 Hassan Z. et. al / Structural Integrity Procedia 00 (2024) 000 – 000

1185

2

1. Introduction 3D printing technologies have been successfully implemented in polymers, metals, and ceramics (Ngo et al., 2018). The printing of cementitious materials has recently led the construction industry toward innovation. This is achieved using minerals and chemical admixtures to gain the fresh and hardened properties required to meet target applications (Zhang et al., 2021). Printing of cementitious materials, referred to as 3D concrete printing, has set higher standards for optimum use of materials and geometries, which can be challenging to achieve with conventional construction methodologies (Bi et al., 2022). 3D concrete printing has increased the use of industrial by-products. Several studies have used mixtures containing a large proportion of supplementary cementitious materials, such as metakaolin, silica fumes, fly ash, or blast furnace slag, to replace ordinary Portland cement and made them printable (Hojati et al., 2022). Steel slag, a by-product from the steel-making industry, is a potential raw material for preparing a 3D printable mixture. Steel slag can yield high flow, which imparts appropriate extrusion properties to a 3D printable mixture (Hassan et al., 2024; Yu et al., 2023). This motivated the current study to use steel slag blended with ordinary Portland cement to prepare a set of mortars. 3D concrete printing generally has many challenges mainly associated with the materials. For instance, the mixing material should have sufficient flow with a low water-to-binder ratio during pumping to avoid clogging the pumping system. On the other hand, it should have enough viscosity to prevent bleeding or segregation. The use of superplasticizers helps achieve such properties; however, the compatibility of superplasticizers is crucial when industrial by-products like steel slag are used. Many superplasticizers may yield the same initial flow, but the time dependent flow differs (Hassan et al., 2024). High flow for an extended time is one of the primary parameters influencing the printing quality. Otherwise, several issues can be witnessed, including overdrying of the layer surface, a reason for weak interlayer bond in 3D concrete printed structures (Le et al., 2012). Studies proposed applying grout or mechanical interlocking between the layers to overcome this issue and to ensure a satisfactory interlayer bond (Marchment et al., 2019; Zareiyan & Khoshnevis, 2017). However, all these techniques are passive and practically not feasible with the printing equipment currently available for large-scale printing. Another problem with 3D concrete printing is that using a printer equipment with chemical admixtures added at the extrusion stage (Kuzmenko et al., 2022) makes it challenging to regulate the dosage during printing in progress (Hassan et al., 2024). An overdose of accelerator admixture may cause a complete failure in obtaining the expected quality. Further, 3D printed elements are more prone to shrinkage cracking due to the high early strength requirement and extended exposure due to large surface areas. This study investigates the outlined problems and typical defects that can occur during 3D concrete printing using specified printing equipment. Further, study also proposes the remedies to mitigate the such typical defects or challenges. 2. Experiments 2.1. Materials A blend of CEM I 52.5R (EN 197-1:2011) from Jura cement and steel slag (a mixture of basic oxygen furnace slag and electric arc furnace slag) was used as a binder. Steel slag used has a specific gravity of 2.94 and a specific surface area of 194 m2/kg provided by Carbicrete, Quebec, Canada. Figure 1 shows the particle size distribution of cement and steel slag. The chemical compositions of the CEM I 52.5R and steel slag were determined by X-ray fluorescence and are shown in Tables 1 and 2. Crushed sand after sieving from 750 micron sieve size was used as fine aggregate. The specific density and water absorption of sand used in this study are 2.62 g/cm3 and 0.786%, respectively. Two polycarboxylate superplasticizers, labeled as Type-1 and Type-2, received from Sika AG Switzerland were used as water-reducing agents. An aluminum sulfate-based accelerator, Floquat ASL, received from the SNF group in France, was used to induce the mixture’s early setting at the extrusion end in the bi -component printer (2K).