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In fresh concrete, early-age shrinkage is affected by many factors, such as thermal deformations moisture loss and the hydration reaction. Novel admixtures for internal curing, like SuperAbsorbent Polymers (SAPs) can be used to mitigate the shrinkage phenomenon. These admixtures strongly modify the microstructure influencing the Acoustic Emission (AE) activity. Acoustic emission has been proven adequate to monitor activities during the curing of fresh cement-based materials. However, so far, it is difficult to distinguish the original mechanisms due to the overlapping nature of the processes that take place. In addition, localization of AE sources is not possible due to the heterogeneous and damping nature of the fresh material. The motivation of this study is to obtain real-time information on the different ongoing processes in fresh concrete, like settlement and shrinkage cracking, using AE and comparing the results to concrete containing SAPs. A preliminary study for 3D source localization in fresh concrete is also performed. The goal is to control concrete curing and confirm suitable final mechanical properties, resulting therefore in more sustainable materials.

Early-age concrete undergoes displacements and volume changes due to ongoing processes such as settlement, hydration, shrinkage, and cracking, which can strongly affect its durability and long-term performance. In this paper, fresh concrete is monitored by the non-destructive techniques of Acoustic Emission (AE) and Digital Image Correlation (DIC). Elastic waves released by the physical processes taking place while concrete is in a fresh state can be well-recorded by AE, while the three-dimensional strain and displacement evolution on the surface can be measured by DIC. Monitoring fresh concrete is of paramount importance to ensure the desired final mechanical properties, especially when novel admixtures for internal curing such as SuperAbsorbent Polymers (SAPs) are added to the mixture. SAPs are particles that can swell by absorbing water when exposed to it, and later release it back to the cementitious matrix when the internal relative humidity linked to the capillary pressure decreases, mitigating autogenous shrinkage. These admixtures strongly interact with the microstructure, resulting in an increased amount of AE activity. The motivation of this study is to obtain real-time information on the different ongoing processes in fresh concrete using AE and compare the results to concrete containing SAPs. Specimens are subjected to different environmental conditions, to monitor the changes in the SAP activity. Results are complemented by DIC to confirm the mitigation of shrinkage by the SAPs. The DIC results showed that SAPs mitigate settlement and shrinkage in early-age concrete, while AE showed SAP concrete exposed to windy conditions demonstrated a delay in the SAP activation, lower amplitude values and higher peak frequency values than the ambient SAP concrete.