# Additive Manufacturing as an Alternative to Core Sampling in Concrete Strength Assessment
## 1 Introduction
In other words, no comprehensive set of performance requirements or test methods for printed mixtures exists. Some authors have proposed a laboratorytesting framework for freshly printed concrete mixtures [8], but corresponding data for hardened printed concrete remain very limited. In tests using gypsum-cement-based powder, discrepancies in compressive strength were observed between cube specimens of 70.7 mm and 50.5 mm and half-beam samples of 160 mm \(\times\) 40 mm \(\times\) 40 mm. Smaller cubes (50.5 mm) exhibited higher strength, possibly due to differences in curing time, while larger specimens required longer print durations, affecting stability and quality. The half-beam samples showed the lowest compressive strength, possibly due to variations in testing methods or issues like nozzle clogging during the extended print time required for 160 mm samples [9]. A previous study also compared the properties of 3D-printed concrete samples with those of identically formulated mixtures cast on a vibrating table [10], using a custom-designed laboratory printer. The mixtures, based on Portland cement, included various mineral additives: ground granulated blast-furnace slag, fly ash, limestone powder, and granite dust. The results showed lower density and compressive strength in printed samples due to the absence of vibration-induced compaction and less efficient particle packing. Notably, the most minor strength reduction occurred in mixtures with fly ash. The introduction of hardening accelerators (up to 4% of the binder mass) was suggested to improve the strength of 3D-printed elements in both compression and bending. In another study, a geopolymer paste based on potassium silicate and metakadin with added sand and local soil was tested for printability using a manual extrusion tool [11]. Beam samples of 160 mm \(\times\) 40 mm \(\times\) 40 mm were cast from the developed mixture for strength testing. However, the study did not assess concrete that had been printed directly. Additional investigations used X-ray computed tomography to evaluate aggregate distribution uniformity in 3D-printed concrete. Cylindrical samples were produced by casting, and additional cores were cut from the printed layer and nozzle output using a cartridge-type 3D-printing extruder [12]. The results confirmed inhomogeneous aggregate distribution within both the printed layer and the nozzle, emphasising the need for further studies to distinguish the mechanical behaviour of lab-prepared printable mixtures versus actual 3D-printed concrete components. Thus, further research is required to validate the use of these developed mixtures in large-scale 3D concrete printing (3 DCP) systems [13]. Table 1 summarises previous findings on 3D-printed concrete elements. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Reference** & **Materials** & **Printing Method** & **Testing Method** & **Printer Model** & **Key Findings/Limitations** \\ \hline \multirow{4}{*}{[4]} & Ordinary Portland cement, & \multirow{4}{*}{\ \begin{tabular}{} \end{tabular}  } & Jet printing. & \multirow{4}{*}{Not-specified} & Custom-built laboratory \\  & Ordinary Portland cement, & & & & \\  & fast-setting cement, quartz & & & & \\  & sand & & & & \\  & & & & & \\  & and flexural strength testing. & & & & \\ \hline \multirow{4}{*}{[8]} & Portland cement, sand, & \multirow{4}{*}{ \begin{tabular}{} \end{tabular}  } & Custom-built laboratory \\  & polyacrylamide-based & & & & \\  & water-reducing agent, & & & & \\  & viscosity-modifying & & & & \\  & admixture, polypropylene & & & & \\  & fibre, dimeified silica, humic, & & & & \\  & high-purity atapuligte clay & & & & \\  & & & & & \\  & & & & \\ \hline \multirow{4}{*}{[9]} & Gyspum-based & Powder-based printing.