Influence of Temperature Variations on the Performance of Two-Component 3D Printable Mixtures (2024-09)¶

Extrusion-based 3D concrete printing (3DCP) is a disruptive technology with huge potential to be a sustainable solution for the construction sector. Understanding the performance of the 3D printable mixtures with variations in environmental conditions is quite important to gain confidence in practical applications and thus allow the widespread use of this technology. A two-component mixture with retarded calcium sulfoaluminate cement as one stream and a pHmodifying mixture as the second stream was used in the current study. The two individual streams of concrete have a very long open time (a couple of hours) and high fluidity to facilitate pumping. Once the individual streams get intermixed near the nozzle, just before deposition, rapid hardening occurs due to the chemical reactions between the two streams. To understand the performance of 3D printable mixtures with variations in temperatures, fresh and hardened properties were determined at three different temperatures (5, 20, and 35°C). The rheological tests were carried out to measure the yield stress and plastic viscosity of the mixtures. Also, wall elements were printed at 20°C and the elements were cured at three different temperatures. At the age of 28 days, the mechanical properties of samples cut out from the wall elements were determined by measuring the compressive and flexural strength. Results indicate that the rheological properties of the mixtures are highly sensitive to temperature variations due to changes in the adsorption rate of the superplasticizer and the evaporation of mixing water. An increase in temperature increases the rate of adsorption of the superplasticizer and also increases the evaporation of mixing water. On the other hand, the mixtures without superplasticizer experienced an increase in yield stress due to the enhanced hydration rate with an increase in temperature. With increasing ambient temperature of curing, the compressive and flexural strengths of the mixtures increase; which can be attributed to the higher degree of hydration at elevated curing temperature. This study gives valuable insights into the performance of two-component mixtures in fresh and hardened states with variations in the ambient temperature.