Examining Effect of Printing-Directionality on Freezing-and-Thawing Response of Three-Dimensional-Printed Cement-Paste (2023-07)¶

The use of 3-D printing with cementitious materials is increasing in the construction industry. Limited information exists on the freeze and thaw (FT) performance of the 3-D printed elements. A few studies have used standard FT testing procedures (ASTM C666) to assess the FT response, however, ASTM C666 is insensitive to anisotropy caused by printing directionality. This paper investigates the FT response of 3-D printed cement paste elements using thermomechanical analysis (TMA) to examine the influence of directionality in comparison to cast counterparts. Cement paste with a water-to-cement ratio (w/c) of 0.275 was used. The critical degree of saturation (DOSCR) as well as the coefficient of the thermal expansion (COTE) were determined for specimens with varying degrees of saturation (DOS). Micro-computed tomography (micro-CT) was conducted to quantitatively understand the heterogeneities in the pore microstructure of 3-D printed materials. For the specimens fabricated in this study, the COTE and DOSCR are independent of the 3-D printing directionality and were comparable to conventionally cast specimens. For samples at 100% saturation, the FT damage was higher in 3-D printed samples as compared to cast samples. The use of a low w/c in 3-D printed materials, desired from a buildability perspective, led to low capillary porosity, which thus decreased the amount of freezable pore solution, and increased the FT resistance of the 3-D printed materials. Micro-CT analysis demonstrated a significant 4.6 times higher average porosity in the interfacial regions compared to the filament cores.