3D printed concrete as stay-in-place formwork: Mechanics during casting and curing

Research in 3D concrete printing has gained an exponential increase in attention over the last decades. The automated production process can be beneficial to reduce material use and increase form freedom of produced elements. Disadvantages are the difficulty to apply reinforcement, the speed of execution if massive elements have to be made and the uncertain durability performance of the printed material. These aspects still lead to reticence in the concrete construction industry to use 3D printing at a large scale. To lower the threshold to move from the conventional toward the new construction technique, a combination of 3D printed and conventional concrete is proposed namely concrete elements with stay-in-place 3D printed formwork. In this paper, experimental research has been performed to investigate the behavior of 3D printed formwork during casting and curing of fresh material. Cylindrical formwork was printed on small scale and filled with self-compacting concrete. During the experiments, strain development and temperature evolution were measured in and around the elements. The obtained data was analyzed taking in attention the material characteristics of both materials in order to separate the different mechanisms. Results showed that the formwork is subjected to the lateral pressure of the cast concrete, moisture warping and thermal curling. The strains in the formwork increase significantly after casting as a result of moisture warping and thermal curling. The peak strain of the concrete element is reached during the hydration phase of the cast concrete. As the cast concrete stiffened in a slightly deformed formwork, residual strains will be present after the element cooled down.