Correlating in-Line Sensor Data to Hardened State Material Properties in Digital Fabrication with Concrete (2026-04)¶

High resolution quality control is essential for many digital concrete fabrication processes, since the systems used are often sensitive to disturbances and the objects that are produced more sensitive to defects when optimized towards material minimization. Furthermore, high-resolution quality control could decrease the uncertainty of the object’s material properties and thereby reduce the cement consumption. In-line measurements are preferred over off-line or on-line measurements to obtain this high-resolution control, since it would require less labor, could be conducted at higher frequency, and would measure the same material that will later be placed in the product. However, the properties of the hardened state govern the quality of the finished concrete objects to a large extent. Since these properties are typically determined after 28 days or later, and tested using destructive, off-line methods, high-resolution quality control would be laborious and material intensive. Furthermore, making informed decisions based upon the results would be significantly delayed. To close this gap, this contribution aims to investigate whether there exists a correlation between in-line measured sensor data and off-line measured hardened state properties obtained at a later age. For the current study, a 3D concrete printing system is used that is equipped with various sensors. The material’s strength is determined at the deposition age by the slugs test, and at an age of 15 min, 1.5 h, 3 h, 1 day, 2 days, 7 days, and 28 days by compression tests. For variations in the water-to-solids ratio, the results show that with increasing age the correlation between in-line quality indicators and the material’s strength is decreasing. At deposition and ages of 15 min, 1.5 h, and 3 h, the R-squared adjusted is above 0.9. For 1 and 2 days, it is around 0.8, and for 7 and 28 days, a negligible correlation with and R-squared of around 0.2 is found, which can be attributed to a low sensitivity of the strength at these ages to variations in the water-to-solids ratio.