Buzzi Unicem USA and Lehigh University have established a strategic partnership spanning research, recruitment, outreach, and cultural activities. Lehigh is a research university located in Bethlehem, Pennsylvania, close to Buzzi Unicem’s USA headquarters. Lehigh’s Civil and Environmental Engineering Department is considered one of the leaders in the world for structural mechanics and design, and it is currently ranked best in the USA (third in the world) for research in Civil Engineering by the prestigious Academic Ranking of World Universities, which according to Wikipedia is “one of the three most influential and widely observed university measures”.

The flagship project of this industry-academia collaboration focuses on the development of a new methodology for 3D printing concrete components and structures. The most common techniques for concrete 3D printing consist in extruding premixed low-slump concrete through a large nozzle attached to a robotic arm. While this approach was instrumental in popularizing concrete 3D printing and allowed to build the first simple structures, it has several drawbacks. The main issue is that it progresses by depositing subsequent layers, one over the other, with the previous layers supporting the new ones, and this prevents the creation of openings and overhangs. In addition, the resulting surfaces show the layers, and they are aesthetically unappealing.

In contrast, the methodology developed by Lehigh and Buzzi Unicem USA consists in precisely jetting micro-droplets of a water-based liquid on extremely thin layers of concrete and fine aggregates. The printer automatically spreads layer after layer of the dry mix, and the automated print-head selectively activates the cement hydration only in the locations that are needed for that layer, by jetting droplets only in those regions. The inert cement and aggregates serve as support for the following layers, allowing the creation of openings, cavities, and overhangs. At the end of the printing process, the dry mix that did not react can be easily collected and reused. This manufacturing process is completely automated and free from the constraints of traditional formwork, which also enables the manufacturing of geometries that could not be formed with traditional casting. The geometric precision is millimetric, and the surface finish confers an appealing look to the manufactured objects.

The collaboration first focused on the development of an effective manufacturing protocol and the selection of appropriate materials. After a broad range of tests, Buzzi Unicem USA CSA cement emerged as the best option for the binder, especially due to its fast set time (which confers strength during the printing process) and its ability to rapidly absorb water, which is important to prevent “bleeding” of water to locations where hydration should not occur and preserve geometric accuracy. These results obtained with Buzzi Unicem USA CSA were featured in an article recently published in the prestigious international journal Construction and Building Materials.

The collaboration between Buzzi Unicem USA and Lehigh was also brought to the attention of the State of Pennsylvania, which decided to co-fund the effort. In the future, the project will aim at increasing the size of the produced objects, through the use of larger printers and modular printing of components assembled with post-tensioning cables. Along this line, the team is also investigating a novel way of applying reinforcement, with the same geometric freedom that 3D printing confers to concrete. Another goal is to develop a new design paradigm, which embraces this unprecedented geometric freedom not only for architectural decoration, but also for structural optimization. To this end, the team has started investigating the use of techniques for topology optimization.

While the methodology is not yet ready to be deployed in practice, it has the potential to revolutionize the precast industry, and the entire construction sector. New shapes that do not need formwork will enable visionary designs and cost savings. Lehigh University and Buzzi Unicem USA have formed a team that combines world-class expertise in cementitious materials, structural design, additive manufacturing, and numerical optimization. For this reason, the team is well positioned to be a leader in the field, commercialize a “cement mix for 3D printing”, and accelerate the adoption in practice of this new approach.