Studying the effect of modifying additives on the hydration and hardening of cement composites for 3D printing

Abstract

The development and application of multicomponent multifunctional additives for cement composites is an important research area since the use of such additives allows controlling both the rheological properties of fresh mixtures and the physical and mechanical properties of the hardened composite. In our study, we used several additives, including metakaolin and xanthan gum together with tetrapotassium pyrophosphate and a SiO2 based complex additive, to modify cementitious sand-based materials. We studied the peculiarities of the influence of these additives on the technological characteristics of mixtures (plasticity and shape retention) and the processes of setting, hydration, and hardening of the composite materials. The optimal values of plasticity, for stability, acceleration of hardening were demonstrated by sand-based systems modified with a complex nanosized additive and metakaolin. The hydration products in the such systems are mainly formed from low basic hydroxides. Metakaolin also results in the formation of ettringite. These systems demonstrate the optimal time of the beginning of setting and the maximum strength gain of the modified cementitious sand-based materials at 28 days. The optimal ratio of indicators of plasticity and shape retention of cement mixtures and the strength of composites based on them obtained by using the studied additives allows us to recommend using these additives in the innovative technologies for 3D-build printing.

Keywords

• cement hardening systems
• modification
• modifying additives
• hydration process
• rheological properties
• compressive strength