Active control of properties of concrete: a (p)review.

Concrete properties to a large extent depend on mix design and processing, currently leaving only limited options to actively modify concrete properties during or after casting. This paper gives a (p)review on a more advanced active control of properties of concrete, based on the application of external signals to trigger an intended response in the material, either in fresh or hardened state. Current practices in concrete industry that could be considered as active control are briefly summarized. More advanced active control mechanisms as studied in other fields, e.g. based on hydrogels and other functional polymers, are reviewed and some principles are listed. A specific focus is further given on potential methods for active rheology control. Based on the concepts developed in other fields, substantial progress could be made in order to achieve active control of fresh and hardened concrete properties. However, several challenges remain, like the stability and functioning of the responsive material in a cementitious environment, the applicability of the control signal in a cementitious material, and the economy, logistics and safety of a control system on a construction site or in precast industry. Finding solutions to these challenges will lead to marvelous opportunities in general, and for 3D and even 4D printing more particularly.