Effects of superabsorbent polymers (SAP) on the rheological behavior of cement mortars: A rheological study on performance requirements for 3D printable cementitious materials

• Published in: Construction & building materials Vol. 392; p. 131856
• Main Authors: Oh, Sangwoo, Choi, Seongcheol
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.08.2023
• Subjects: 3D printing; Cement mortar; Rheological behavior; Superabsorbent polymers (SAP); Superplasticizer (SP); Cement mortar; Superabsorbent polymers (SAP); Superplasticizer (SP); Rheological behavior; 3D printing
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2023.131856

[Display omitted] •SAP particle size and dosage affect the rheological behavior of cement mortar.•The effects of SAP may depend on the presence of SP incorporation or the w/c.•Mortar with & without SP have distinct time-dependency despite having the same flow.•Mortar with & without SP have distinct shear-dependency despite having the same flow.•From a 3D printing material point of view, SAP could be used as a rheology modifier. While the potential of incorporating superabsorbent polymers (SAP) as an additive in 3D printing cementitious materials has been a subject of interest recently, little research has been conducted on the effects of SAP incorporation on the rheological properties of cement mortars and the required performance of 3D printable cementitious materials when no other additives, such as superplasticizer (SP), are present or when SAP is added up to 1.0% by weight of the binder. Accordingly, the effects of SAP on the rheological behavior of cement mortar were analyzed in this study from the perspective of the performance requirements for 3D printable material with the SAP dosage (0%, 0.5%, and 1.0% by weight of cement), SAP particle size (100–180 and 355–425 μm), and superplasticizer (SP) presence (polycarboxylate-ether) as variables. The rheological properties of cement mortars with the same initial slump flow (180 mm ± 5 mm) were measured using a vane rotational rheometer, and their conformance to the performance requirements for 3D printable cementitious materials was studied. Static yield stress, dynamic yield stress, and plastic viscosity were calculated for each specimen using measured torque data obtained from the stress growth and flow curve experiments. The ratios of static to dynamic yield stress, plastic viscosity, and thixotropic areas were analyzed from the perspective of pumpability and extrudability, whereas the yield stress evolution and structural build-up rate were analyzed from the perspective of buildability. The results demonstrated that although the rheological properties of the SAP-incorporated cement mortar with a low water–cement ratio were similar to those of the SAP-incorporated cement mortar with a high water–cement ratio when SP was incorporated, the change in rheological properties with time and shear differed. SAP incorporation promoted the structuration of the mixtures without SP that have a high water–cement ratio due to the physical effects of SAP particles, but the effect was reversed in the mixtures with SP and a low water–cement ratio due to the water migration kinetics associated with SAP. Because a low water–cement ratio with SP is commonly applied for 3D printable materials, the findings of this study indicate that the water migration kinetics of SAP critically determines the printability of cementitious materials mixed with SAP. Given that observed effects are substantial, SAP arguably has potential as a rheology modifier for 3D printable cementitious materials.