Research Summary Report A01

Particle-Bed 3D Printing by Selective Cement Activation (SCA) – Particle Surface Functionalisation, Particle-Bed Compaction and Reinforcement Implementation

Herding, Friedrich; Researcher, f.herding@ibmb.tu-bs.de

Mai, Inka; Leading researcher, i.mai@ibmb.tu-bs.de

Lowke, Dirk; Project leader, d.lowke@ibmb.tu bs.de

all: TU Braunschweig, Institute of Building Materials, Concrete Construction and Fire Safety (iBMB)

The main objective of our research in TP A01 is to understand the material-process-interactions in particle bed 3D printing by Selective Cement Activation (SCA) in order to produce concrete elements with high mechanical strength and geometric precision. Besides, we are also investigating different ways of reinforcement integration, which is crucial for the manufacturing of load-bearing building components.

Summary

In Particle Bed 3D Printing (PB3DP) by Selective Cement Activation the water to cement ratio (w/c‑ratio) of the initial printing process is a key influencing factor for both the mechanical performance and the geometrical precision of printed objects. With less water and a lower w/c-ratio there comes a benefit regarding the geometrical precision. The mechanical strength of such printed specimens however, is in need of improvement. On the opposite, specimens printed with an initial high w/c-ratio have good mechanical strength, but the printed geometries are bigger than the designed ones. In order to improve the properties of printed specimens two strategies have been tested recently, (I) an after printing treatment by water curing and (II) the usage of water retaining admixtures in the particle mixture. These allowed for the successful printing of elements such as the figurehead of this year’s concrete canoe from TU Braunschweig, see Fig 1:.

Current state of research

Both, the effect of an after printing treatment by water curing as well as the usage of methyl cellulose ether (MC) on the hardened state properties of printed specimens have in detail been presented at this year’s Digital Concrete Conference. Water curing as well as the addition of MC intend to improve the mechanical properties and geometrical precision of printed specimens, by reducing the amount of water, which uncontrollably flows out of the desired printing area into the surrounding particle bed as seen in Fig 2.

The after printing treatment strategy focusses on printing with an initial low w/c-ratio. This ensures a high geometric precision of the printed object. The mechanical strength is later improved by water curing. The printed object is therefore placed in a water bath. The cement, which might not has been completely activated before, is then enabled for a complete hydration.

The other strategy focusses on the usage of methyl cellulose ether. As an additive it is premixed in the dry particle mixture together with the cement and the aggregates. During the printing process it adsorbs and retains some of the water, keeping it in the desired area of the particle bed. The water is later released over time in the printed object, allowing for a better hydration.