Buildability assessment of mortar with fine recycled aggregates for 3D printing

Abstract

In this paper, the buildability of a mortar incorporated with fine recycled concrete aggregates (recycled sand) for the purpose of 3D printing has been assessed according to the bi-linear thixotropy model. The natural sand from a reference, rheology based mortar for 3D printing, is gradually replaced with recycled sand using replacement rates of 25, 50 and 100 vol%. For each mixture, stress growth tests are performed at resting intervals of 0, 10, 20, 30, 40, 50, 60, 90 and 120 s to determine the re-flocculation rate (Rthix) of the 3D printing concrete. In addition, the flowability, rheology and initial setting time of the mixtures are measured with slump flow tests, stress-growth tests using a rheometer and Vicat tests. The results show that mortar with recycled sand is less flowable and has shorter initial setting time compared to the reference mortar for 3D printing. In addition, it is found that recycled sand improves the static yield stress evolution with time of the mixtures which improves the buildability. With recycled sand replacement rates of 25 and 50 vol%, the buildability of the mortar mixture increases respectively 33% and 83%.