## 3 Test Results and Discussion
### Mortar Properties
#### 3.2.2 Microstructure and Porosity
Figure 9: (**a**) SEM image showing the different particles in the EXW mortar matrix, (**b**) SEM image showing a large pore with hydration products forming in the pore and the area analysed by EDS for spectrum 112 and 114, (**c**) SEM image of metakaolin particle in the inter transitional zone (ITZ) of the mortar paste between the aggregates. A visual overview of the void microstructure of the mortar samples investigated by XCT is shown in Figure 12a-d. It shows the micro-CT porosity images of specimens in 3D XYZ-plane and the pore sizes are colour coded according to size. The pores with sphericity larger than 0.6 and size larger than 80 \(\upmu\)m were identified. The percentage of the void in each mortar is shown in Figure 13. The distribution of the pore sizes and the summary of the statistical analyses of the pore diameters are given in the Appendix A (Figure A6 and Table A1). Generally, the higher the percentage of voids in the mortar specimen, the greater the durability issues. Porosity affects the mass transport properties of the mortar [24; 32]. Therefore, the void of the mortar can help to evaluate the durability of the LC\({}^{3}\) system compared to that of the PC as a control (Figure 12a). Figure 11: (**a**) SEM image showing the different particles in the MFN mortar, (**b**) Electron image showing analysed EDS spectrums 154, 155, and 159. OPC, the control specimen, has a porosity percentage of 1.78 % as seen in Figure 13, and has the largest range and mean values of pore diameters as seen in the Appendix A.1. MFN LC\({}^{3}\) mortar has the lowest porosity, 31% less than the control (PC), followed by BFN (8%), while EXW has a porosity 25% higher than the PC. This implies that the SEM 2D microstructure evaluation may not be adequate to indicate the mortars' overall porous nature, as it visually suggests that EXW seems to have less porosity than the PC. From the void size distribution and statistical analysis in the Appendix A (Figure A6 and Table A1), a larger percentage of the void sizes is around 0.21 mm for PC and LC\({}^{3}\) systems. However, the PC generally has a higher pore diameter (average and maximum) than the LC\({}^{3}\) systems. This indicates the better pore refinement generally associated with LC\({}^{3}\) systems [4; 7; 10]. Earlier studies suggest that higher kaolinite content leads to better pore refinement [4; 6]. This is not the case in the current study, where EXW LC\({}^{3}\) mortar with the highest kaolinite content has the highest percentage of porosity and vice versa. It should be noted that the former studies refer to binder paste gel pores (<10 nm) and capillary pores less than 1000 nm (that is, nanoscale), while the current study examines mortar air voids at macroscale \(\geq\)60,000 nm (60 \(\upmu\)m). This is a size range similar to the maximum grain size of the binders (Figure 3). This suggests that the inclusion of sand complicates the influence of kaolinite content on the mortar microstructure and accentuates the importance of using fine limestone. From Section 3.1.5, clay mortars with the least calcite (CaCO\({}_{3}\)) content signify the highest limestone consumption, which is found to translate into lower porosity. This suggests that the degree of consumption (hydration) of limestone becomes more important than the kaolinite content for the microscale void refinement of LC\({}^{3}\) mortar.