Ordinary Portland cement (OPC) conforming to the Australian Standard, AS 3972 [21] general purpose cement (Type GP) was used in this study. Table 12.1 presents the chemical composition and loss on ignition (LOI) of the OPC determined by X-ray Fluorescence. The total does not add up to 100% because of rounding-off of the percentages. The percentages of C3S, C2S, C3A, and C4AF as the main constituents of OPC were 57.59%, 14.87%, 4.10%, and 13.94%, respectively, calculated from the chemical composition shown in Table 12.1 using the Bogue formula [22]. In Part I of the study, sieve-graded high silica purity sands with two different particle sizes were used. The finer silica sand denoted as “FS” with a maximum particle size of 300 mm was supplied by TGS Industrial Sand Ltd., Australia. The coarser silica sand denoted as “CS” with a maximum particle size of 500 mm was supplied by Building Products Supplies Pty Ltd., Australia. Fig. 12.1 presents the particle size distribution of the OPC and silica sands used in this study determined by using a CILAS particle size analyzer model 1190. In Part II, a mixture of two types of premium graded sand (supplied by Sibelco Pty Ltd., namely the 16/30 and the 30/60) was used. Sand Type-1 (16/30) is a course sand with a particle size of 700 µm and sand Type-2 (30/60) is a finer sand with a particle size of 300 µm.

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Figure 12.1. Particle size distribution of ordinary Portland cement, silica sands, and 3D printable concrete mix used in Part I.

Table 12.2 presents the mix proportions of the 3D printable concrete used in Part I of this study. According to Le et al. [13], the most critical fresh properties of a 3D printable concrete mixture are extrudability and buildability, which have mutual relationships with workability and open time. In other words, the fresh concrete needs to be able to be extruded through a nozzle to form small filaments (i.e., extrudability requirement). In addition, the fresh concrete needs to be stiff enough to retain its shape after being extruded and support further layers without substantial deformation and collapsing due to self-weight and yet provide a suitable bond between layers (i.e., buildability requirement) [13]. The methods used to measure the fresh properties are described in detail in Le et al. [13]. Several trials were performed before arriving at the final mix proportions (presented in Table 12.2) which satisfied the extrudability and buildability requirements. Initially, a mix with water to cement ratio (w/c) of 0.5 and CS sand to cement ratio (s/c) of 3.0 was trialed. It was observed that the mix was too flowable and did not hold its shape when extruded. Therefore, the w/c of the mix was reduced to 0.38. It was found that some of the extruded filaments were fractured during extrusion. Therefore, the s/c was reduced to 1.5. However, some cracks were still observed on the surface of the extruded filaments. To tackle this issue, 25% of CS sand was replaced by FS sand. The particle size distribution of the 3D printable concrete mix is given in Fig. 12.1.