Influence of Hydroxypropyl Methylcellulose Dosage on the Mechanical Properties of 3D Printable Mortars with and without Fiber Reinforcement

Hydroxypropyl Methylcellulose (HPMC) is one of the most frequently used viscosity modifying admixtures in 3D printable cement-based materials. In this study, the effects of HPMC dosage on the mechanical properties of 3D printable cement-based mortars were investigated. For this purpose, mortar mixtures with and without micro steel fibers containing three different HPMC dosages (0%, 0.15%, and 0.30% by weight of cement) were produced. Reliant on the HPMC dosage, heat flow and cumulative heat curves were obtained. At the end of 7 and 28 days of standard curing, flexural, compressive, and shear bond strengths, as well as flexural toughness, were measured. Additionally, porosity values were obtained on molded, single-layer, and three-layer printed specimens. The results showed that the increase in HPMC dosage prolonged the setting times and decreased the heat release. Moreover, the porosity values increased with an increase in the HPMC dosage and the number of printed layers. All mechanical properties were drastically decreased with the use of HPMC. The decrements were more significant at the first 0.15% HPMC dosage and the shear bond strengths. Prolonging the curing period from 7 to 28 days did not lead to meaningful recovery in the mechanical properties. The negative effects of HPMC on flexural and shear bond performances were more pronounced in fiber-reinforced mortars.

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