【作者】 周鑫；

【导师】 刘赞群；

【作者基本信息】 中南大学 ， 材料学， 2024， 硕士

【摘要】 磷酸盐是常用的一类硅酸盐水泥无机缓凝剂,目前研究较广的是碱金属磷酸盐（磷酸钠,Na₃PO₄,NP）,对酸式磷酸盐（磷酸二氢铵,NH₄H₂PO₄,NHP）的研究相对较少。作为磷酸盐,磷酸二氢铵也可用作缓凝剂,碱金属离子能一定程度上促进水泥早期水化,而NH₄⁺易挥发,或可以避免碱金属离子对水泥水化的影响,而且H₂PO₄^–具有比PO₄^3–更大的电离常数,能更快速与碱性的水泥颗粒反应,影响水泥水化。因此,磷酸二氢铵可能是一种优异的硅酸盐水泥用缓凝剂。本文选取相同质量分数掺量（0.5%,0.75%,1%）的磷酸二氢铵与磷酸钠展开对比研究,通过开展水泥凝结时间、流动度、力学性能、干燥收缩、水化热、Zeta电位、热重分析、X射线衍射分析、扫描电镜和早期孔溶液组成等宏观和微观分析试验,研究了磷酸二氢铵与磷酸钠对硅酸盐水泥早期水化的影响;结合对硬化水泥浆体水化产物、C-S-H凝胶的钙硅比以及孔隙结构的微观测试,研究了磷酸二氢铵与磷酸钠对硅酸盐水泥硬化性能的影响。研究结果表明:（1）磷酸二氢铵具有比磷酸钠更为显著的缓凝效果,随着掺量增加,磷酸二氢铵与磷酸钠都能延长硅酸盐水泥的凝结时间,延缓净浆流动度的经时损失,磷酸二氢铵组净浆在30min时的流动度损失率接近20%,磷酸钠组在净浆30min时的流动度损失率约为30%。磷酸二氢铵能提高水泥净浆的抗折和抗压强度,其中0.75%掺量的提升作用最为突出,28d抗折和抗压强度分别提升了12.3%和18.1%;但磷酸钠的掺入导致水泥净浆的抗折和抗压强度降低,其中0.75%掺量的28d抗折和抗压强度分别降低了9.4%和14.1%。磷酸二氢铵与磷酸钠都增大了水泥净浆的干燥收缩,但磷酸二氢铵的影响更小。（2）磷酸钠的缓凝机理是:在硅酸盐水泥颗粒表面沉淀磷酸钙抑制水泥早期水化。磷酸二氢铵的缓凝机理是:一方面磷酸根离子能更容易被硅酸盐水泥颗粒吸附,在水泥颗粒表面迅速沉淀生成羟基磷灰石;另一方面羟基磷灰石具有比磷酸钙更强吸附无机离子的能力,导致磷酸二氢铵能更显著降低水泥水化放热速率,延长水化诱导期。（3）磷酸钠降低水泥净浆抗折抗压强度的机理是:磷酸钠导致硬化水泥浆体的水化程度下降,C-S-H凝胶的钙硅比降低,水泥净浆的大孔增多,浆体累积总孔体积增加,孔隙结构相对松散;磷酸二氢铵提高水泥净浆抗折抗压强度的机理是:磷酸二氢铵能加深硬化水泥浆体的水化作用,提高C-S-H凝胶的钙硅比,水泥净浆的大孔减少,浆体累积总孔体积降低,孔隙结构得到明显细化,水泥浆体的微观结构更加致密。因此,根据本文研究可知,磷酸二氢铵既具有比磷酸钠更持久的缓凝效应,又能够改善硬化水泥浆体的力学性能,磷酸二氢铵是一种比磷酸钠更为优秀的硅酸盐水泥无机缓凝剂。图36幅,表6个,参考文献96篇更多还原

【Abstract】 Phosphates are a commonly used type of inorganic retarder in Portland cement.Among them,alkali metal phosphates（sodium phosphate,Na₃PO₄,NP）are extensively studied,while research on acid phosphates（ammonium dihydrogen phosphate,NH₄H₂PO₄,NHP）is relatively limited.As a phosphate,ammonium dihydrogen phosphate can also serve as a retarder.Alkali metal ions can to some extent promote the early hydration of cement,while NH₄⁺is volatile,potentially mitigating the influence of alkali metal ions on cement hydration.Additionally,H₂PO₄^–has a greater ionization constant than PO₄^3–,enabling faster reaction with alkaline cement particles,thus affecting cement hydration.Therefore,ammonium dihydrogen phosphate may be an excellent retarder for Portland cement.This study conducts a comparative investigation between ammonium dihydrogen phosphate and sodium phosphate,both at identical mass fractions（0.5%,0.75%,1%）.Various macroscopic and microscopic analyses including cement setting time,fluidity,mechanical properties,drying shrinkage,hydration heat,Zeta potential,thermogravimetric analysis,X-ray diffraction analysis,scanning electron microscopy,and early pore solution composition are conducted to explore their impacts on early hydration of Portland cement.Furthermore,microscopic tests on hydration products,Ca/Si ratio of C-S-H gel,and pore structure of hardened cement paste are performed to examine their influences on the hardened properties of Portland cement.The research findings indicate:（1）Ammonium dihydrogen phosphate exhibits a more pronounced retarding effect compared to sodium phosphate.As the dosage increases,both ammonium dihydrogen phosphate and sodium phosphate extend the setting time of Portland cement and delay the time-dependent loss of fluidity of the neat paste.The fluidity loss rate of the neat paste with ammonium dihydrogen phosphate is close to 20%at 30 minutes,while that with sodium phosphate is approximately 30%.Ammonium dihydrogen phosphate enhances the flexural and compressive strength of cement paste,with the most notable improvement observed at a dosage of0.75%,where the 28-day flexural and compressive strengths increased by12.3%and 18.1%,respectively.However,the addition of sodium phosphate results in a decrease in flexural and compressive strength of cement paste,with a reduction of 9.4%and 14.1%,respectively,at a dosage of 0.75%at 28 days.Both ammonium dihydrogen phosphate and sodium phosphate increase the drying shrinkage of cement paste,but the impact of ammonium dihydrogen phosphate is relatively smaller.（2）The retarding mechanism of sodium phosphate involves the precipitation of calcium phosphate on the surface of Portland cement particles,inhibiting the early hydration of cement.The retarding mechanism of ammonium dihydrogen phosphate operates through two main pathways:firstly,phosphate ions can more easily be adsorbed onto the surface of Portland cement particles,rapidly precipitating to form hydroxyapatite on the cement particle surface.Secondly,hydroxyapatite exhibits a stronger adsorption capacity for inorganic ions compared to calcium phosphate,leading to a more significant reduction in the rate of heat evolution during cement hydration and prolonging the induction period of hydration.（3）The mechanism by which sodium phosphate reduces the flexural and compressive strength of cement paste involves decreasing the degree of hydration of hardened cement paste,lowering the Ca/Si ratio of C-S-H gel,increasing the number of large pores in cement paste,and increasing the cumulative total pore volume of the paste.The mechanism by which ammonium dihydrogen phosphate enhances the flexural and compressive strength of cement paste is that it deepens the hydration of hardened cement paste,increases the Ca/Si ratio of C-S-H gel,refines the pore structure of cement paste,reduces the number of large pores,decreases the cumulative total pore volume of the paste,and makes the microstructure of cement paste more compact.Based on the findings of this study,ammonium dihydrogen phosphate not only exhibits a more persistent retarding effect than sodium phosphate but also enhances the mechanical properties of hardened cement paste.It is evident that ammonium dihydrogen phosphate is a superior inorganic retarding agent for Portland cement compared to sodium phosphate.更多还原