Tough double-bouligand architected concrete enabled by robotic additive manufacturing.

Nature has developed numerous design motifs by arranging modest materials into complex architectures. The damage-tolerant, double-bouligand architecture found in the coelacanth fish scale is comprised of collagen fibrils helically arranged in a bilayer manner. Here, we exploit the toughening mechanisms of double-bouligand designs by engineering architected concrete using a large-scale two-component robotic additive manufacturing process. The process enables intricate fabrication of the architected concrete components at large-scale. The double-bouligand designs are benchmarked against bouligand and conventional rectilinear counterparts and monolithic casts. In contrast to cast concrete, double-bouligand design demonstrates a non-brittle response and a rising R-curve, due to a hypothesized bilayer crack shielding mechanism. In addition, interlocking behind and crack deflection ahead of the crack tip in bilayer double-bouligand architected concrete elicits a 63% increase in fracture toughness compared to cast counterparts.

Numerical Simulation of the Freeze-Thaw Behavior of Mortar Containing Deicing Salt Solution.

This paper presents a one-dimensional finite difference model that is developed to describe the freeze-thaw behavior of an air-entrained mortar containing deicing salt solution. A phenomenological model is used to predict the temperature and the heat flow for mortar specimens during cooling and heating. Phase transformations associated with the freezing/melting of water/ice or transition of the eutectic solution from liquid to solid are included in this phenomenological model. The lever rule is used to calculate the quantity of solution that undergoes the phase transformation, thereby simulating the energy released/absorbed during phase transformation. Undercooling and pore size effects are considered in the numerical model. To investigate the effect of pore size distribution, this distribution is considered using the Gibbs-Thomson equation in a saturated mortar specimen. For an air-entrained mortar, the impact of considering pore size (and curvature) on freezing was relatively insignificant; however the impact of pore size is much more significant during melting. The fluid inside pores smaller than 5 nm (i.e., gel pores) has a relatively small contribution in the macroscopic freeze-thaw behavior of mortar specimens within the temperature range used in this study (i.e., +24 °C to -35 °C), and can therefore be neglected for the macroscopic freeze-thaw simulations. A heat sink term is utilized to simulate the heat dissipation during phase transformations. Data from experiments performed using a low-temperature longitudinal guarded comparative calorimeter (LGCC) on mortar specimens fully saturated with various concentration NaCl solutions or partially saturated with water is compared to the numerical results and a promising agreement is generally obtained.