Automated and minimally invasive indentation testing for the characterisation of concrete strength evolution

There is growing interest in the development and application of shaping processes such as milling or trowelling that are applied subsequent to 3D concrete printing. These are used to improve geometric accuracy, create detailed features and improve surface finish. The quality and viability of these processes is heavily dependent on material rheology, however there is a lack of suitable in-situ tests to automatically monitor material strength evolution post 3D concrete printing. To address this need an automated robotic penetration system is described, and a new complementary metric, the Minimally Invasive Strength Indicator (MISI) is defined and evaluated. The automated system combines a manual penetration gauge with an industrial robot arm using a tactile surface detection strategy. The performance of the robot penetration system is evaluated and compared to both manually deployed measurements and laboratory instrumentation. The results provide insight into the limitations of manually deployed testing and guideline parameters for accurate automated measurements. The MISI metric combines indentation force with positional data from the robot to provide a minimally invasive approach for monitoring strength evolution. It reduces insertion force by 60 to 70%, is six times faster, and only requires a shallow 2.5 mm depth indentation, leading to substantially less surface damage than the standard 15 mm deep penetration tests. Experimental trials of the robotic penetration system, conducted across a wide range of material strengths, exceed the performance of manual testing by trained operators and match that of a universal testing machine. MISI also showed a strong linear relationship with early-age compressive strength, demonstrating a viable automation approach and useful new metric for in-situ monitoring of post 3DCP material strength evolution.