石灰-水泥-粉煤灰改性磷石膏对水泥物理性能的影响研究

采用石灰、水泥、粉煤灰对磷石膏进行改性处理，测定了改性磷石膏中硫酸根的溶解性能，对比了原状磷石膏与改性磷石膏对水泥物理性能的影响，并结合X射线衍射（XRD）和扫描电镜（SEM）分析了改性前后磷石膏对水泥不同龄期水化产物的影响。结果表明：随着石灰掺量的增加改性磷石膏的pH逐渐增大，当石灰掺量为4%（质量分数）时磷石膏的pH达到12.22，此时磷石膏中的可溶性磷、氟转化成难溶性的磷酸盐、氟化钙；随着水泥和粉煤灰掺量的增加，改性磷石膏的溶解性能呈现降低趋势。当石灰掺量为4%、水泥掺量为10%（质量分数）、粉煤灰掺量为10%（质量分数）时，改性磷石膏经过7 d养护在水中浸泡8 h所得滤液中硫酸根的质量浓度为0.30 g/L，比未改性磷石膏在水中浸泡8 h所得滤液中硫酸根的质量浓度降低了81.8%。与掺加未改性磷石膏的水泥浆体相比，掺加改性磷石膏的水泥浆体的水灰质量比由0.41降低到0.38、初凝时间和终凝时间分别缩短34.6%和27.2%、28 d抗压强度提高21.1%。石灰、水泥、粉煤灰改性处理磷石膏后，生成的水化硅酸钙和钙矾石等水硬性产物包裹在石膏颗粒表面，使硫酸根在水中的溶出速率降低，减少了对水泥中铝酸三钙的影响，使得硬化体内部结构变得致密、力学性能显著提高。

Effect of phosphogypsum modified by lime-cement-fly ash on physical properties of cement

Lime，cement and fly ash were used to modify phosphogypsum，the solubility of sulfate in modified phosphogypsum was determined，and the effects of undisturbed phosphogypsum and modified phosphogypsum on the physical properties of cement were compared，and the effects of phosphogypsum on the hydration products of cement at different ages before and after modification were analyzed with X-ray diffraction（XRD） and scanning electron microscopy（SEM）.The results showed that the pH value of modified phosphogypsum gradually was increased with the increase of lime admixture，and when the lime admixture was 4%（mass fraction），the pH of phosphogypsum was 12.22，the soluble phosphorus and fluorine in phosphogypsum were transformed into insoluble phosphorous salts and calcium fluoride.With the increase of cement and fly ash content，the solubility of modified phosphogypsum was decreased.When the lime content was 4%，the cement content was 10%，and the fly ash content was 10%，the mass concentration of sulfate radical in the filtrate obtained by soaking the modified phosphogypsum in water for 8 hours after 7 d of curing was 0.30 g/L，which was 81.8% lower than the mass concentration of sulfate radical in the filtrate obtained by soaking the unmodified phosphogypsum in water for 8 hours.Compared with the cement paste with unmodified phosphogypsum，the water cement mass ratio of the cement paste with modified phosphogypsum was reduced from 0.41 to 0.38，the initial setting time and final setting time were shortened by 34.6% and 27.2% respectively，and the 28 d compressive strength was increased by 21.1%.After the modification of phosphogypsum with lime，cement and fly ash，the generated hydraulic products such as hydrated calcium silicate and ettringite were wrapped on the surface of gypsum particles，which reduced the dissolution rate of sulfate in water，reduced the impact on tricalcium aluminate in cement，and made the internal structure of hardened body become dense，and the mechanical properties were significantly improved.