Investigating PCM encapsulated NaOH additive for set-on-demand in 3D concrete printing

Abstract

This study investigates the print head activation of an encapsulated additive to attain on-demand setting in 3D concrete printing for buildability enhancement. Sodium hydroxide (NaOH) is considered as a set accelerating additive, and it is encapsulated using a phase change material (PCM). The encapsulated NaOH is added during the initial mixing stage and the mix is heated at the print head to release the NaOH, which subsequently reacts with cementitious materials to attain the on-demand setting of the printed layer. The dosage of NaOH was varied from 0 to 5 wt% of the cement to determine the optimum dosage for buildability enhancement. The results showed that the static yield strength of the printable concrete after the print head activation increased with the NaOH dosage, however, this has resulted in reducing the compressive strength of the mixes. The fresh and hardened properties of the mixes with encapsulated NaOH were compared with the mix with nano-clay to assess two buildability enhancement approaches (set-on-demand vs traditional). It was found that the buildability enhancement using nano-clay was limited by pumpability constraints, whereas the activation of encapsulated NaOH was limited by compressive strength reductions.