2019 CSCE Annual Conference - Laval (Greater Montreal) Conference
Dr. Claudiane Ouellet-Plamondon, École de technologie supérieure
Additive manufacturing for cement-based materials is gaining interest these past years. Printing concrete has the potential to remove the time allowed to casting and molding. Nevertheless, new issues specific to 3D printing emerge. For example, the preservation of the mechanical properties and the stability of the printed layers. The objective of this paper is to identify the characteristics needed for a printed mortar to fulfill its role and propose a mixture that fills the required characteristics. A framework for testing several characteristics of mortar and cement paste are designed, and a small 3D printer prototype is made. The mixtures tested are composed of various combinations of superplasticizer (SP), accelerator (A), nanoclay (C) and viscosity-modifying admixture (VMA). After extracting the pore solution of the fresh cement paste using centrifugation its conductivity is measured. Viscosity is measured following the National Institute of Standards and Technology (NIST) method for Standard Reference Material 2492. The flow of the mortar is determined following the standard ASTMC1437. To propose a value of stability of the mortar the shifting of a fresh cylinder of 35 mm height and 60 mm diameter is recorded under a force of 100 N progressively applied. Finally, the percentage of the height decreasing of a printed mortar layer is computed after its curing period averaging six points on a 60 x 40 mm square in the center of the layer. The collected data are then compiled to train a regression model to predict the height decreasing of a printed mortar layer thanks to the results of the other experiments. Mechanical tests are conducted to study the hardened properties of the mortar. Finally, the aim is to be able to predict the physical measurement only with the composition of the mixture. Doing so, characteristics of printed mortar can be predicted before any test. Next steps are to increase the number of admixture to have a larger database and to validate the mix design to larger printed forms.