Influence of Infill Pattern on Reactive MgO Printed Structures

Abstract

The construction industry’s increasing interest in additive manufacturing has generated a parallel interest in alternative and supplementary binders. Reactive magnesia (MgO) binders are an attractive and sustainable alternative to Portland cement; they are produced at lower temperatures and can potentially absorb the equivalent amount of CO2 emitted during production within their service life via carbonation curing. While excessive evaporation in 3D printed Portland cement is usually sought to be prevented, the resulting increase in porosity from the higher surface exposure is a desirable feature for 3D printed MgO that can lead to higher carbon intake. In this work, we utilize nanoclays in combination with methylcellulose as rheological modifiers to produce 25.4 mm MgO paste cylinders with different infill patterns: two open with continuous hollow channels and one solid/closed to mimic a conventionally cast one. Two additional configurations were introduced where the top and bottom layers of the open infills were replaced by a closed layer or a “lid” to conceal the infills’ internal structure. The results show that 3D printing of MgO improves compressive strength over cast ones by up to 380% at 28 days of carbonation curing, reaching 40–48 MPa at 1.1 w/b. The results also suggest that infill patterns play a more critical role in stress transfer than carbon intake as finite element analysis confirmed the introduction of localized stresses at the lid layers.