Examining Effect of Printing Directionality on Freezing-and-Thawing Response of Three-Dimensional-Printed Cement Paste

The use of three-dimensional (3-D) printing with cementitious materials is increasing in the construction industry. Limited information exists on the freezing-and-thawing (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-cement ratio (w/c) of 0.275 was used. The critical degree of saturation (DOSCR) as well as the coefficient of 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 the 3-D-printed samples as compared to the cast samples. The use of a low w/c in the 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.