Utilizing Co2 to Improve Plastic Shrinkage and Mechanical Properties of 3d Printed Mortar

Abstract

Reducing carbon footprint in the construction industry by leveraging construction waste aligns well with the concept of sustainable development in this sector. Utilizing Recycled Fine Aggregates (RFA) as the raw material for 3D Printed Mortar (3DPM) is an eco-friendly and automated construction process. Moreover, treating 3DPM with CO2 can enhance its properties, paving the way for high-performance green materials. This study devised three carbonation techniques: elevated temperature accelerated carbonation of RFA, injecting CO2 as an admixture for the fresh 3DPM mixing (CO2-injecting), and carbonation curing of 3DPM, all aimed at improving 3DPM properties. 3DPM specimens prepared with Natural Fine Aggregates (NFA) and RFA served as the control groups. The study employed the Digital Image Correlation (DIC) method to evaluate plastic shrinkage of 3DPM specimens under three distinct carbonation treatments, and compared their compressive and flexural strength, and interlayer bonding properties. Additionally, SEM-EDS results were integrated to analyze the mechanisms of improvement associated with the carbonation methods. The findings indicated that using RFA resulted in a minor reduction in the plastic shrinkage of 3DPM. After carbonation treatments, the plastic strain concentration was significantly reduced, while alleviating in moisture loss of 3DPM specimens. In the horizontal direction, all specimens displayed a "trapezoidal compression", while a "slope settling" behavior was exhibited in the vertical direction. Compared to 3DP-R, the experimental groups 3DP-R-CM, 3DP-C-CR, and 3DP-R-CC showed that plastic shrinkage rates in the horizontal direction decreased by 14%, 60%, and 77%, respectively. The strength of the casting specimens experienced the most substantial improvement when Carbonated Recycled Fine Aggregates (CRFA) were used. While specimens prepared with CO2-injecting did not show a significant increase in early compressive strength, a notable strength enhancement was observed at 28 days. Carbonation curing not only shortened the curing period for the 3DPM specimens but also bolstered their early strength. Furthermore, the interlayer structure of 3DPM was enhanced by carbonation treatments, which led to the refinement of interlayer microcracks and a strengthening of interlayer bonding.

Keywords: 3D printed mortar；Carbonation；Plastic shrinkage；Carbonation curing, CO2-injecting