Effect of hydroxypropyl methylcellulose and aggregate volume on fresh and hardened properties of 3D printable concrete

Three-dimensional (3D) concrete printing necessitates a balance between various ingredients of the mix composition. This study investigated the effect of hydroxypropyl methylcellulose (HPMC) dosage at various aggregate volumes on fresh, rheological, and mechanical properties of 3D printable concrete (3DPC). Accordingly, 3DPC mixtures having three aggregate volumes, namely 44, 41, and 38 %, were produced at a constant water-to-binder ratio. For each aggregate volume, three HPMC dosages, namely 0, 0.14, and 0.28 % by weight of cement, were studied. A mini-slump flow table and a manual printing gun were used to assess the flow diameter and printability. Rheological properties were determined using a rotational rheometer and extrusion device. The buildability was assessed through green strength testing. Results showed a directly proportional relationship between HPMC dosage and fresh and rheological properties of these mixtures. At a constant w/c ratio, increasing the aggregate volume led to higher green strength and extrusion pressure at all piston-moving velocities. Overall, at an early age, the effect of HPMC dosage was more significant on the static yield stress of mixtures with lower paste volume while being more accentuated on the green strength for mixes with higher paste volume. The positive impact of increasing HPMC dosage on the green strength becomes insignificant at later ages. The effect of increasing HPMC dosage, however, was more pronounced on the extrudability of mixtures with higher paste volume by preserving their extrudability at later ages. Finally, HPMC addition led to strength losses of up to 28.63 and 32.7 % for flexural and compressive strength, respectively.