# Development of Cementitious Mortars for Aerial Additive Manufacturing
## 4 Discussion  
The study highlights the trade-off between workability and buildability along with the impact these parameters have upon quantitative material properties. This study suggests that the correct approach to take is to accept the trade-off between workability and buildability and acknowledge that there will be a challenge in one of those parameters for a higher strength material. It is reasoned that the addition of silica fume to mix \(D\), along with the use of sand and fibres, contributed to the requirement for increasing the water:binder ratio from 0.33 to enable an extent of extrusion from the deposition device (Figure 8). It is further reasoned that the higher water:binder ratio contained in mix \(E\) was necessitated by a combination of the addition of silica fume and limeX70 in order to facilitate material extrusion. The addition of polyol resin in Mix \(C\) facilitated an increase in the sand:binder ratio and the addition of Silica fume without compromising workability. With mix \(B\), it is submitted that the lower water:binder made the difference in the mix being challenging to extrude and requiring higher power, whereas Mix \(A\) was too workable in the fresh state and inherently contained a high carbon footprint regarding CEM I content. Table 4 confirms that it is possible for a mix to perform well in workability at the expense of buildability and vice versa. Where the mixes perform well in both parameters and possess a suitable workability-buildability balance, this also may come at a cost. Mix \(C\) was highly workable and held its form well, being able to receive multiple layers. However, as shown in the calorimetry results (Figure 4), the addition of the rheological modifying polyol resin retards the C-S-H reaction during hydration of the mortar mix. C-S-H is  
Figure 8: Radar charts graphically depicting and summarising the mix parameters of the formulated mixes. Values have been scaled up or down from the absolute values for the purposes of visual clarity and portrayal of the relationships between the mix parameters. (**a**) Experimental results and properties of the mixes, (**b**) Summarising the constituent content of the mixes for ease of comparison. an important contributor to the binding properties [40] and reaction inhibition reduces compressive strength. Mix \(E\) also performed well in both workability and buildability - again at a cost, as adding limeX70 to the mix required a significant increase in water:binder ratio to make the mix workable, thus inevitably impacting compressive strength. Highly workable mixes \(C\) and \(E\) additionally displayed the highest deformation during long term loading (Figure 5). While a pure cement paste is certainly workable for the miniature deposition device, it was clear that the addition of fine aggregate promotes the successful printing of multiple layers, as mix \(A\) deformed irreparably during the layer extrusion process. With fine aggregate, mixes \(B\)-\(E\) did not exhibit this deformation. A further purpose of the additional binding materials and fine aggregate is to reduce the level of Portland cement used in the mixes, as an entirely cementitious paste is not favourable when considering sustainability. Portland cement has long been established as a material with an undesirab high carbon footprint, with the raw materials requiring burning at high kiln temperatures of 1400-1500 \({}^{\circ}\)C [37]. The addition of industrial by-products (PFA, silica fume, limeX70) as additives mitigates the higher embodied carbon of the mortar mixes, which is a current characteristic of AM cement slurries, though this can be offset by geometric optimisation of printed elements [17]. It is suggested that workability, defined in this study as the ability of a material to be processed by the deposition device, is the primary qualitative material parameter for the relative miniaturisation of AM required for aerial applications.