PSI - Issue 68

Zili Huang et al. / Procedia Structural Integrity 68 (2025) 266–271

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Z. Huang et al. / Structural Integrity Procedia 00 (2025) 000–000

1. Introduction Three-dimensional concrete printing (3DCP) offers promising opportunities for the construction industry, becoming a transformative asset in construction, providing significant benefits in terms of sustainability, efficiency, and flexibility compared to conventional building techniques. Hou et al. (2021) introduces the principles of 3DCP and highlights the challenges of material consistency and mechanical properties to propose further development with better printing prevision and material durability. However, 3D concrete structures are built by the logic of layering 2D planes, which can lead to weak inter-layer bonds and anisotropic properties (Panda et al. 2017). The strength and anisotropic characteristics of 3D printed cement-based materials can be evaluated by using indirect tensile tests, including Brazilian disc test and three-point bending test. Paritala et al. (2023) investigates the anisotropy with strength variations of 3D printed specimens in three testing orientations and demonstrates preliminary results of the fracture propagation path with respect to the time gap effect. More recently, Nakase et al. (2024) provides more comprehensive verifications of fracture propagations under compression, tension and bending tests with respect to various printing orientations. The intrinsic void shapes within the printed specimens are evaluated from single and cross printing orientations with different fracture propagation shapes. However, snap-back behaviour, with both load drop and displacement reversal, often occurs in indirect tensile testing, affecting the evaluation of both tensile strength and fracture properties of 3D printed cement-based mortars. This paper addresses the challenges of indirect tensile testing by introducing an innovative technique for controlling the loading process to stabilize cracking process. The focus is on applying this method to manage fracture in Brazilian disc testing and highlighting the benefits which offers for advanced instrumentation. The technique, known as AUSBIT (Advanced Universal Snap-Back Indirect Tensile test; Verma et al. 2019, 2021a, 2021b; Verma, 2020), utilizes indirect displacement control, using feedback from the lateral expansion of the disc to stabilize the fracturing process. Since lateral expansion consistently increases, its feedback to the loading machine enables better control throughout the test and makes it possible to capture snap-back behaviour, which is unachievable with direct displacement control. In this way, AUSBIT’s lateral displacement control effectively stabilizes sudden cracking in disc specimens. AUSBIT creates the potential to obtain the intrinsic fracture behaviour with snapback response, the paper also illustrates a successful example of indicating and calculating the fracture energy of 3D printed specimen. 2. Experiment program 2.1. Material Table 1 presents a constant printable mix design for cementitious mortar after serval modification, including five ingredients: ordinary Portland cement (OPC), washed sand, superplasticizer and water. The OPC used is obtained from Adbri, formerly Adelaide Brighton Cement, and washed sand are locally sourced, while superplasticizer is Sika ViscoCrete 10 which is complied with AS1478.1-2000 to enhance the mixture for higher density, strength, and flowability. Conversely, superplasticizer can reduce water content significantly for less shrinkage and creep effect.

Table 1. Printable mix design composition. Component

Weight ( g )

Concentration ( % )

Sand

7044.50 1390.50 2555.60

63.12 13.90 22.90 0.085

Water

Cement

Superplasticizer

9.30

2.2. Specimen preparation In this study, nine layers of 3D printed concrete blocks with 153 mm height and 400 mm length are fabricated by using Delta WASP 3D clay/ mortar printer at UoA as shown in Fig. 1a. All disc specimens are cut by using waterjet cutting equipment, with disc diameter of 100 mm, followed by surface grinding process as shown in Fig. 1b. All disc