Rheology and printability of cement paste modified with filler from manufactured sand

Manufactured sand is increasingly used in concrete production. We study the effects of substituting parts of the binder with manufactured filler (par-ticle size 0.04 - 0.250 mm) on the printability of cement paste experimentally and numerically.

An experimental program explored water-to-binder ratios of 0.4 and filler-to-binder mass ratios fi/b = 0.15 - 0.85. The study investigated suspension properties and rheology like maximum packing, mini-slump, plastic viscosity, and yield stress. Printability, on a lab scale, was observed by printer flow measurements (“extrudability”) and buildability (shape retention, deformation layer adhesion, deformation, macro voids). Additionally, a computational fluid dynamics model (CFD) is developed to simulate the 3D printing of the filler-modified cement paste and assess its printability.

Results show that as maximum packing increases, slump flow (yield stress) decreases as expected. The best shape retention and layer adhesion were found in mixes with maximum packing = 0.94, 0.96, and 0.98. The mix with the highest yield stress showed the best shape retention but had more macro voids in the cross-section and rougher surfaces. To confirm the accuracy of the CFD model, the cross-sectional shapes of the deposited part from simulations are compared with the printed ones. It seems more work is needed to get a good correlation with the same process parameters.