The improvement of microstructure and mechanical properties of concrete via addition of polycarboxylate ether modified C/M-S-H

Phosphorus tailings, as industrial waste, present challenges in disposal and environmental management. This study proposes a novel approach to enhance the hydration performance of dehydrated calcium magnesium silicate hydrate (C/M-S-H) derived from phosphorus tailings by modifying it with polycarboxylate ether (PCE), thereby converting it into a high-value cementitious additive. Key findings show that PCE significantly alters the crystallinity and microstructure of C/M-S-H (abbreviated as CM). Specifically, low molecular weight PCE 20,000 transforms CM into granular flocs, while high molecular weight PCE 40,000 induces the formation of foil-like structures with surface-attached particles. The optimal dehydration temperature inversely correlates with PCE molecular weight: it is 600°C for CM modified by PCE 20,000 (PCE2-CM) and decreases to 400°C for that modified by PCE 40,000 (PCE4-CM), and exceeding these temperatures leads to structural damage and loss of rehydration capacity. The modified dehydrated materials exhibit excellent early-strength performance. When replacing 5 % cement, they reduce the initial and final setting times of the slurry by 43.9 % and 38 % respectively (due to accelerated hydration), with a slight 18.6 % decrease in flowability. Notably, the foil-like structure of PCE4-CM promotes surface-distributed hydration products, enhancing contact with concrete aggregates and providing sheet-like nucleation sites. This results in a more uniform distribution of calcium silicate hydrate (C-S-H) and a 161.5 % increase in early strength through microstructural densification. This work provides experimental evidence and mechanistic insights to make high-performance cementitious materials from phosphorus tailings.