Anisotropy in mechanical properties of 3D-printed layered concrete

The article presents the results of studying the mechanical properties of 3D-printed layered concrete (3DPLC), including compressive, flexural, and splitting strength. To assess them, we used a compression test with a load applied perpendicular and parallel to the printed direction; a flexural test with a load applied perpendicular to the printed direction, and a splitting test to evaluate the interlayer bond strength upon the transfer of force along the boundary surface parallel to the printing direction. The mechanical properties of reference cast concrete (CC) were evaluated in accordance with the requirements of Russian standards. We established a significant anisotropy of the mechanical properties of 3DPLC along and perpendicular to the printed layers as well as a significant reduction in all strength values compared to similar values of reference CC. The printing time gap was the determining factor in the reduction of values of the mechanical properties for 3DPLC. When it increased to 20 minutes, a critical decrease in the interlayer bond strength was observed. At the same time, a threefold drop in the strength of 3DPLC compared to similar characteristics of CC could be observed in case of a decrease in humidity and a change in temperature in the range of +(10–30) °C. The impact of the curing condition on the variability of the mechanical properties of 3DPLC depended on the particle size distribution of fillers and aggregates that determined the surface roughness of the printed layer. The range of changes in the strength of sand-based printed concrete in case of varying temperature and humidity of curing (with a similar printing time gap) was 30–70 %, and for limestone-based printed concrete it was 1.5–3 times.