3D-printable concrete with specific decorative and technological properties

The object of research is a 3D-printable decorative concrete. The effect of the cement type and the iron oxide pigment dosage on the setting kinetics and heat release as the significant characteristic of 3D-built printable mixtures has been investigated. Materials and Methods. Two types of 3D-built printable mixtures have been used. Their mix design was regulated by the kind of cement (gray CEM I 42.5 and white CEM I 52.5 R) with the different content of the  phase and dosage of the pigment. The inorganic synthetic pigment based on Fe₂O₃ oxide was used. The setting kinetic was studied by the penetrometric method. The heat release was controlled using a contact alcohol thermometer. The X-ray and SEM-microscopy methods were used to evaluate the microstructure and hydrate phase composition. The plasticity and shape stability were carried out based on the results of squeeze rheometry methods. The compressive strength was measured according to Russian State Standard GOST 10180-2012 "Concretes. Methods for strength determination using reference specimens". Results. The setting kinetic of 3D-built printable mixtures depends on a combination of cement type and iron oxide pigment dosage. The heat release depends on the iron oxide pigment dosage because the combination aluminate phase of metakaolin and iron oxide pigment in the mix determines the acceleration of hydration phase formation. The temperature increases 1.2 - 1.3 times and 2.5 – 2.7 times for gray cement-based and white cement-based systems, respectively. The combination of a high-strength white cement (CEM I 52.5 R) with a highly active aluminosilicate modifier and iron oxide pigment causes a technologically unacceptable setting reduction. As a result, the open time of white cement-based mixtures is 15 min. Conclusion. The high heat release and fast setting kinetic lead to a technologically unacceptable acceleration of the setting process and open time reduction. The mix design of 3D-build printable mixtures must be based on setting process control.