Optimization of synthesis parameters for C-S-H/PCE nanocomposites: A comprehensive study using orthogonal experiments and multi-analysis approaches

Calcium silicate hydrate (C-S-H) is considered a novel early strength agent, showing immense potential in enhancing the early strength of cement-based materials. Polycarboxylate (PCE) is widely used as a dispersant in the synthesis of nano-C-S-H to prevent agglomeration during synthesis. However, a comprehensive investigation is still required to establish a stable method for preparing stable C-S-H/PCE nanocomposites using chemical co-precipitation. This study employed orthogonal experiments, range analysis, variance analysis, and multi-index matrix analysis to explore the effect of the chemical co-precipitation synthesis process on the stability of C-S-H/PCE nanocomposites. It conclusively identified the calcium-to-silicon (C/S) ratio as the sole significant influencing factor, establishing optimal synthesis parameters: a C/S ratio of 1.6, stirring at 8000 r/min, a 2-hour reaction time, and a reaction temperature of 30 °C. Additionally, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were utilized to investigate the impact of the C/S ratio on the structure and morphology of C-S-H/PCE nanocomposites. Results indicated that under the optimal synthesis parameters, the average particle size and precipitation rate of the synthesized C-S-H/PCE nanocomposites were 0.122 µm and 0.44%, respectively, exhibiting a 4.7% and 47.6% improvement over the best samples in the orthogonal test. Increasing the C/S ratio decreased the crystallinity of the C-S-H/PCE nanocomposites, resulting in the emergence of multiple crystal structures, compact and ordered morphology, and reduced sedimentation. These findings collectively underscore that C-S-H/PCE nanocomposites with higher C/S ratios exhibit enhanced dispersion and stability, validating the rationality of the optimal synthesis parameters identified in this study.