Abstract:

The setting and hardening properties of gypsum materials are critical to its application. The effects of steel slag-phosphoric acid system on setting time, absolute dry compressive strength and flexural strength of phosphogypsum based building gypsum were investigated. A method of controlling the setting performance of gypsum by using the initial pH of gypsum slurry was proposed. It was found that when the initial pH of slurry was 1.5 with phosphoric acid and the content of steel slag was 3%, the initial setting time of phosphogypsum was increased from 9min to 119min, the loss of absolute dry flexural strength and the loss of absolute dry compressive strength was 12.68% and 22.97%, respectively. Compared with the system with citric acid or sodium polyphosphate, the loss of mechanical strength was smaller. The hydration characteristics of the modified gypsum system were obtained by investigating its hydration rate and hydration temperature rise. The hydration products of the modified gypsum system were analyzed by using XPS and XRD. The mechanism was obtained that calcium oxide in steel slag reacted with phosphoric acid to release Ca²⁺, which combined with HPO{}_{\mathrm{4}}^{\mathrm{2}-} to form dicalcium phosphate. The insoluble salts deposited on the surface of the crystal of calcium sulfate dihydrate, which blocked the formation and growth of the crystal nucleus of gypsum dihydrate and reduced the hydration rate of gypsum dihydrate. SEM analysis showed that the pores in the microstructure of hardened body of steel slag-phosphoric acid modified gypsum increased compared with the blank, and the crystal morphology was still needle bar shape, but the size was slightly smaller.

Key words: phosphogypsum based building gypsum, steel slag, setting time, hydration rate, crystallization

摘要：

石膏材料的凝结硬化性能对其应用至关重要。本文研究了钢渣-磷酸体系对磷建筑石膏的凝结时间、绝干抗压及抗折强度的影响，提出一种利用石膏浆料初始pH调控石膏凝结性能的方法。结果表明：当磷酸调节石膏浆体初始pH为1.5、钢渣掺量为3%时，磷建筑石膏的初凝时间由空白组的9min延长到119min，绝干抗折强度及抗压强度损失分别为12.68%、23.17%，与添加柠檬酸和多聚磷酸钠的石膏体系相比，力学性能损失显著降低。通过水化温升及水化率变化研究了石膏体系的水化过程，借助XPS及XRD分析水化产物，得出钢渣-磷酸体系对于磷建筑石膏凝结性能的调控作用机制：钢渣中的氧化钙与磷酸反应释放出Ca²⁺，Ca²⁺与HPO{}_{\mathrm{4}}^{\mathrm{2}-}结合生成磷酸氢钙难溶盐覆盖在二水硫酸钙晶体表面，阻滞了二水石膏晶核的生成及长大，降低了半水石膏的水化速率。SEM分析发现，钢渣-磷酸体系改性石膏水化硬化体的微观结构中空隙较空白组有所增加，晶体形貌仍然呈针棒状，但 尺寸略小。

关键词: 磷建筑石膏, 钢渣, 凝结性能, 水化率, 结晶