In this study, we investigated the effects of paraffin and its types on freeze-thaw resistance, hydration reaction of cement, and combined deterioration resistance of freeze-thaw damage and salt damage in concrete assuming a decrease in entrained air due to the construction process. This investigation found that the mixing of paraffin derived from petroleum improved the freeze-thaw resistance, and the hydration reaction of cement was unaffected. Paraffin-mixed concrete did not exhibit a decrease in the relative dynamic modulus of elasticity even under chloride environment. The mechanism of improvement of the freeze-thaw resistance was presumed to be linked to the existence of paraffin particles in concrete as pore fillers with size of 200 μm or less, which reduce the apparent air void spacing coefficient and block the continuity of capillary pores.

When constructing concrete structures using 3D printing technology, it is important to consider the anisotropy due to the printing process. The print path influences the formation of layer interfaces and inter-filament voids and the fracture propagation behavior of the printed specimen. In this paper, the fracture propagation behavior of mortar printed specimens under compressive, tensile, and flexural stresses are evaluated for different print paths. Under compression loading, the internal structure was observed by X-ray CT, and the displacement distribution was evaluated by 3D scanning. Under tensile and bending stresses, the effects of the print path on fracture propagation behavior were evaluated by digital image correlation. The results show that the fracture propagation behavior changed based on the inter-filament void structure, depending on the print path.