# Additive Manufacturing as an Alternative to Core Sampling in Concrete Strength Assessment
## 2 Materials and Methods
### Physical and Mechanical Testing of Core Samples Extracted from Printed Structures  
The compressive strength of concrete cores extracted from the printed structures was determined using a standard methodology [41]. On days 7, 14, and 28--parallel to the testing of cube specimens--core samples were extracted from the constructed elements using a diamond tunnel bit mounted on a manual core drilling rig (a hand-held electric drill equipped with a levelling indicator). Drilling was performed without water cooling, at low rotational speed. From each printed element (made with a different mix composition), six core samples were extracted, each with a diameter of 28 mm. The samples were then trimmed (faced) using a dry-cut diamond saw. In the next stage, the specimens were ground on a circular grinding machine to ensure surface parallelism, as this could not be adequately achieved during the initial trimming stage. Before compressive strength testing, the core specimens extracted from the printed structures were visually inspected for defects. All samples were deemed acceptable, with no major irregularities observed. Minor burrs along the edges were removed using an abrasive stone. Following this, the linear dimensions (diameter and height) and the weight of the cores were measured. The summary of these measurements is presented in Figure 9, which visualizes the results for all five concrete mixes. These values correspond to the data provided in Table S2 (Supplementary Materials). Additional related variability results are shown in Figure 10.  
A pair plot analysis was conducted to further explore the relationships between the geometric and mass characteristics of the core specimens. This analysis allows for the visualisation of potential correlations between diameter (D), height (H), and weight across the five tested concrete mixes. The pair plot provides both bivariate scatterplots and univariate distribution curves for each parameter, disaggregated by mix composition. The dataset used corresponds to the results presented earlier in Table S2 (Supplementary Materials). As seen in Figure 10, the diameter (D) measurements exhibit very narrow distribution ranges for all mixes, consistent with the use of a standardised 28 mm coring bit. No meaningful correlation is observed between diameter and either height or weight. However, height (H) shows a moderate positive relationship with weight across most mixes, indicating that increased specimen height generally corresponds to increased mass, particularly for Mixes 4 and 5. Figure 9: Boxplots showing dimensional and weight characteristics of core specimens extracted from printed structures by mix: (**a**) diameter (mm); (**b**) height (mm); (**c**) weight (g). Data correspond to Table S2 in the Supplementary Materials. The univariate distributions highlight that Mix 5 has the highest mean and narrowest spread in both height and weight, suggesting better consistency and compaction during printing. In contrast, Mix 2 displays a wider spread in both height and weight, with several lower outliers, indicating possible variation in printing or material homogeneity. The scatter between height and weight also shows more clustering for Mixes 3 and 4, suggesting more uniformity compared to the broader dispersion observed in Mix 1 and Mix 2. These results confirm the findings of previous boxplots (Figure 9) and provide deeper insight into the dimensional stability and mass consistency of the printed concrete mixes. Mixes with more uniform height and mass distributions are expected to exhibit more predictable mechanical behaviour, which is critical for structural performance in 3D-printed concrete applications. Figure 10: Pair plot visualisation showing distributions and pairwise relationships between diameter (D), height (H), and weight for core specimens across all five concrete mixes. The data correspond to Table S2 in the Supplementary Materials.