Effects of additives on the mechanical properties, rheology, and printing properties of Pcc-based 3DPMs

Abstract

A study was performed on printing concrete made with Portland cement clinker (Pcc) (the base material), quartz sand (the aggregate), a water reducer, and the additives hydroxypropyl methyl cellulose ether (HMC), redispersible latex powder (RLP), lithium carbonate (LC) and triethanolamine (TEA) were used to adjust the material properties. A clinker-based 3D printing material exhibiting excellent rheology, extrudability, buildability, and mechanical properties was developed. Admixture incorporation decreased the spread and slump of the Pcc while improving the rheological properties (G', G'', |η*|, and the torque). The addition of HMC and appropriate quantities of RLP and LC increased the slump and expansion of the cement paste, but the addition of TEA had adverse effects on the slump and expansion of the slurry paste. The admixture decreased the setting time of the Pcc slurry, and the effect decreased in the order TEA, LC, RLP, and HMC. The admixture also degraded the mechanical properties of the slurry. The use of a D-2 mix design consisting of 0.25% HMC, 0.20% RLP, 0.08% LC, and 0.010% TEA resulted in the maximum extrusion length of the printed sample, 90 mm, and the maximum number of printing layers, 32. SEM images showed that the main hydration products were calcium silicate hydrate (C–S–H) and calcium hydroxide (CH). The admixture mainly affected the early performance of the samples and had little influence on the late performance. This result was consistent with those obtained from hydration tests on Pcc. A reaction model for the addition of an admixture to a Pcc slurry was proposed.