Method of internal care of cement hydration in 3D printing formulations

Introduction. Improvement of 3D printing technology with the use of concrete mixtures based on Portland cement largely depends on the sustainable solution of the problem of ensuring normal hardening of extruded concrete layers. A violation of hardening has known negative consequences and entails significant economic losses. It has been suggested to use polyacrylate solutions, preparation of which before application in concrete mixture allows controlling the process of their polymerization, postponing the sorption function of the additive in time to ensure the required rheology. Materials and methods. Influence of super absorbent polymer (SAP) solution on structural formation processes and properties of cement materials is studied. Assessment of the degree of hydration was carried out by the calorimetric method for total thermal power using the isothermal calorimeter TAM AIR. Identification of main phases of cement stone (CS) by X-ray phase analysis was performed on XRD-6000 diffractometer. Results. It is established that the use of SAP solutions has a positive effect on the mobility of cement mixtures due to the delayed polymerization and the corresponding water absorption by the polymer. The flexural strength range is 6.6–8.7 MPa and the compression strength range is 68.5–71.7 MPa. The porosity is characterized by extreme dependence with minimum at concentration of SAP 1.0 % from weight of Portland cement. Such changes in the properties of the CS are naturally associated with changes in the parameters of its structural formation. It is established that the range of concentrations of SAP less than 1.5 % provides close to the reference composition (without SAP) the total hydration heat power of Portland cement at the age of 86 hours. Conclusions. The dependences of rheological and mechanical properties of cement materials on SAP concentration have been established. It has been proved that the use of SAP solutions is an effective engineering solution to ensure the hardening of concrete in adverse conditions. Further development of the topic may be aimed at studying the effect of SAP solutions on the properties of concrete mixtures of different compositions for 3D printing. Acknowledgements: The paper was supported by a grant of the President of the Russian Federation for state support of young Russian scientists — Candidates of Sciences MK 1394.2020.8.