Researchers model cement paste flow at the particle scale to explain 3D printability
Concrete 3D printing has a timing problem: the paste has to move through the nozzle easily, then stop almost immediately so the next layer doesn’t crush it. What’s been missing is a particle-level explanation of why fresh cement paste behaves that way at all, rather than just curve-fitting the viscosity with the usual Eyring, Herschel-Bulkley, Bingham, or Vom Berg equations.
A team from Northwestern University and the University of Alabama, publishing in the Journal of Applied Physics, built a multiscale model to close that gap. They started with tricalcium silicate and calculated how water affects the interaction between hydrated cement surfaces at the atomic scale. That atomic-scale interaction was then fed into a larger particle-based model, where cement particles and water are represented as beads, and viscosity was calculated across different shear rates and water-to-cement ratios using dissipative particle dynamics and reverse nonequilibrium molecular dynamics.
Author Subhadeep Pal compared the method to “viewing cement under a microscope at different magnifications” (3D Printing Industry). The approach required a sensitivity analysis first, to find a particle-interaction setting stable enough to run the larger simulations on.
The model reproduced a result already known from lab testing: viscosity goes up at lower water content and lower shear rates. The more interesting part is what the simulation shows underneath that curve. Instead of the particle network breaking down wholesale as shear increases, the researchers found that shear speeds up the rate at which contacts between cement particles are renewed.
That’s a mechanism, and it’s the part of the paper that could eventually feed back into mix design rather than just describing it after the fact.
The model is a deliberate simplification. Real cement particles are irregular, not spherical beads, and the team describes this version as a starting point for isolating how water content, particle interactions, shear, and viscosity relate to each other. Future versions are meant to add more of that real-world irregularity back in.
A separate ASTM effort is working the same problem from the standards side. ASTM International’s additive manufacturing committee (F42) was, as of 2025, developing a proposed standard, WK94968, to define a test method for whether a given cementitious formulation is compatible with a given extrusion printer, including minimum and maximum yield stress and viscosity values. The standard and the simulation are approaching the same printability question from opposite ends, one setting acceptance limits for equipment qualification, the other trying to explain, at the particle level, why those limits exist.
Sources
- Simulations Explain Fresh Cement Flow for 3D Printing, 3D Printing Industry, 12 October 2026