Chemical admixtures in 3D concrete printing: "Sepiolite and Attapulgite as Thixotropic Enhancers"

Digital manufacturing, commonly known as 3D printing, has revolutionized various industries, including automotive, aerospace, and more recently, construction. This article explores the utilization of sepiolite and attapulgite clays as thixotropic enhancers in chemical admixtures for 3D concrete printing.

Role of Chemical Admixtures in 3D Printing:

In 3D printing, chemical admixtures play a crucial role in achieving desired effects such as pumpability of the ink, providing structuration and shape stability of the deposited ink, thixotropy to prevent particle sag, ensuring adhesion between individual layers, enabling rapid strength development, and controlling shrinkage.

Common Inks and Superplasticizers:

In 3D printing of building products, inks exhibit exceptionally high solids volume fractions and contain high cement contents. Achieving pumpability in such suspensions requires the use of superplasticizers, with polycarboxylate (PCE) superplasticizers being the most common. Precast types of PCE are preferred as they develop maximum fluidity that quickly vanishes, ensuring optimal performance.

Thixotropy and Its Importance:

Thixotropy, the property where a fluid becomes viscous once shear subsides, is highly desirable for inks used in 3D concrete printing. The ideal ink should assume a gel-like consistency after extrusion. Thixotropic admixtures, commonly comprised of micronized clays, play a pivotal role in achieving this behavior. Sepiolite and Attapulgite clays, in particular, offer higher thixotropy in ion-loaded cementitious pore solutions.

Importance of Adhesion in 3D Printing:

Sufficient adhesion between individual printed layers is critical to prevent structural collapse. Nano clays, including attapulgite and sepiolite, are known to enhance adhesion.

Impact of Clays on Thixotropy:

The incorporation of clays, specifically sepiolite and attapulgite, significantly enhances the dynamic yield stress and time-dependent evolution of static yield stress in cement-based systems. The addition of these clays improves the thixotropic behavior, particularly in systems containing fly ash.

Conclusion:

In conclusion, the incorporation of sepiolite and attapulgite clays, in combination with viscosity-enhancing admixtures, has proven to enhance yield stress and thixotropic behavior in 3D concrete printing. These advancements open new possibilities for the development of highly thixotropic cementitious systems, addressing the main challenge in additive manufacturing.