Drying and shrinkage of cement paste for 3D printable concrete

Abstract

The article presents the results of the study of drying and shrinkage of three compositions of cement paste different in the content of microsilica and superplasticiser within the range of variation typical for 3D printable concrete compositions. Plate samples kept in the environment with RH = 20, 30, 50, 70 % were used to simulate different drying conditions of material in thin layers of 3D printing structures. Rates of mass loss and shrinkage of hardened cement paste are compared with criterial parameters of their structure. It is shown that increased dosage of microsilica and superplasticiser ensures the reduction of total volume of pores, increase of the content of nanopores, while simultaneously the area and energy activity of solid phase surface increases. These factors secure the ability of cement paste to better retain the water in the structure under all drying conditions. As a result, reduction of absolute values of mass loss by 3 - 4 times and shrinkage by 2 times in comparison with reference system is ensured for cement paste with maximally dense structure. At the same time, there is a twofold increase of relative deformability on each percent of mass loss, which may lead to significant tension in 3D printing structures due to moisture gradient.