3-D printing of concrete: Beyond horizons

3-D printing is a disruptive technology that can have enormous social and economic impacts in years to come. The technology, which took shape in the 1980's and was initially limited to manufacturing small products, is moving to large scale construction applications, utilizing concrete and other cementitious and binder materials. This paper presents a state-of-the-art and state-of-the-practice of 3-D printing of concrete including a historical background and advances in equipment, materials, and computer modeling. Some demonstration projects are presented and opportunities and challenges associated with 3-D printing of concrete are identified. Formulation of ink utilizing local and in-situ materials is a major challenge and will continue to develop. Developments will also continue on large scale construction 3-D printers. The paper should be of value to both the seasoned researchers and beginners in 3-D printing, and also to those working on transitioning 3-D printing in construction from research to practice.