Decoupling Early-Age Free Shrinkage and Restraint Effects in 3D Printed Concrete Using Digital Image Correlation (2025-11)¶

3D printed concrete (3DPC) undergoes substantial early-age shrinkage and cracking, driven by its formwork-free nature and high surface area-to-volume ratio that accelerates moisture loss. Measuring early-age deformations in 3DPC is complex because of the local heterogeneity caused by layering variations, overburden effects, print geometry, and the restraint effects that result in non-uniform volume changes. This paper utilizes Digital Image Correlation (DIC) to capture early-age (first 24 h) shrinkage deformations in 3D printed elements made using different binders, and with different layer and filament configurations. DIC-based surface strain measurements accurately capture the rapid volume change due to early drying, and the gradual plateauing as the mixture sets and hardens. The differences in restraint effects—both from the substrate as well as the layers and filaments—impose substantial differences in measured shrinkage. Hence, a novel framework is proposed here to quantify the multi-directional restraint effects, and to decouple them from the measured shrinkage. The result is the extraction of free shrinkage strains (geometry- and restraint independent) in 3DPC that is a function of the mixture design and exposure condition. The framework is validated for multiple layers and filaments with different dimensions as well. The approach, in conjunction with measurements of time-dependent elastic modulus, also allows for the determination of tensile stresses and thus the cracking propensity in in-place 3D printed concrete elements.