Concrete Additive Manufacturing

Our goal is to devise a binder jetting process that additively prints concrete. Binder jetting is an additive manufacturing process in which a printhead selectively deposits a liquid binding agent onto a thin layer of powder particles, such as metal, sand, ceramics or composites. Layer by layer, the material is filled into a bed and the liquid component is added within the target shape boundary. In comparison to the traditional casting process, it delivers products of complex and customized shapes in low volumes, with small density variability and dimensional tolerance. The heterogeneous in concrete aggregate distribution demands a novel binder jetting process that accommodates concrete, while still leveraging the precision and flexibility binder jetting provides.

Quantitative evaluation of binder permeation

Previous studies have incorporated fluorescent dye to identify W/C ratio of concrete after curing at the nanoscale. We mix fluorescent dye at different concentrations to water and apply it to print of one layer. We seek to see if the intensity in color of the dye can reveal water content during the print process and after the concrete is set.

Water distribution variables

We experiment with different controlled water distribution patterns to minimize bleed while saturating target shape. Through the manual trials, we have asserted that the cement : water ratio for layerwise binding to be 1: 0.06. We predetermine the total water mass for the casting area and per layer. We want to find the adequate frequency of water deposition, and amount of water deposited per dropping that would saturate the target shape of the layer, allowing the material to bind into the intended shape.

We devise a multi-nozzle template with varying number of openings for 1 ml syringes. The total mass of water is divided by the total number of openings resulting in the following variations of water distribution. (a)using the template with more openings, a smaller amount of water would be deposited more frequently, closer together. On the other hand, (b)if the template has fewer openins, a larger amount of water would be placed per opening.