Internal curing for high-performance concrete by a green composite capsule

Improving concrete eco-efficiency is a challenging and ongoing topic in response to the sustainability re-quirements for modern concrete infrastructure. This study proposed a novel, biobased internal curing (IC) agent material for high-performance concrete. A two-step physical method was successfully developed to turn organic alginate and inorganic fly ash into a high-value-added green composite capsule, where the internal alginate bead reserves abundant IC water and the external robust shell supplies the protection to realize steady water release. The composite capsules with a core-shell structure have a particle size of 850 +/- 20 mu m, shell thickness of 65 +/- 10 mu m and water content of 40 wt%. Moreover, the IC effect of composite capsules on cement paste was monitored by the hydration process, the setting time and microstructural observation. Further IC efficiency was quantified by autogenous shrinkage and compressive strength. The results indicate that it is feasible to use the proposed green composite capsules for internally cured high-performance concrete. The composite capsules can not only effectively decrease the autogenous shrinkage but also eliminate the negative degradation of the compressive strength of concrete due to the incorporation of IC agents. The novel IC agent represents superi-orities in terms of IC efficiency and sustainability.