磷酸二氢铵对硅酸盐水泥早期水化的影响  

Effect of Ammonium Dihydrogen Phosphate on Early Hydration of Portland Cement

作　　者：周鑫 刘赞群[1] 赵倚琳 黄佳雯 ZHOU Xin;LIU Zanqun;ZHAO Yilin;HUANG Jiawen(School of Civil Engineering,Central South University,Changsha 410075,China)

机构地区：[1]中南大学土木工程学院,长沙410075

出　　处：《硅酸盐学报》2024年第2期614-623,共10页Journal of The Chinese Ceramic Society

基　　金：国家重点研发计划(2022YFB2602602)资助项目。

摘　　要：磷酸盐是常用的一类硅酸盐水泥无机缓凝剂,目前对碱金属磷酸盐(磷酸钠)研究较广,缺乏对酸式磷酸盐(磷酸二氢铵)的研究。以相同质量的磷酸钠作为参照,通过水泥凝结时间、水化热、Zeta电位、早期孔溶液组成、热重分析、X射线衍射分析和扫描电镜等试验,研究了磷酸二氢铵对硅酸盐水泥早期水化的影响。结果表明:磷酸钠掺入后在水泥颗粒表面沉淀磷酸钙抑制水泥早期水化。磷酸二氢铵一方面能更快速被硅酸盐水泥颗粒吸附,在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,导致磷酸二氢铵比磷酸钠能更显著地降低水泥水化放热速率,延长水化诱导期,水泥的水化3 d总放热量更低,磷酸二氢铵具有比磷酸钠更持久的缓凝效应。Introduction Phosphates are one of commonly used inorganic retarding agents in Portland cement,including monophosphates(i.e.,sodium phosphate)and polyphosphate compounds(i.e.,sodium pyrophosphate,sodium tripolyphosphate,and sodium hexametaphosphate).Different phosphate salts exhibit distinct retarding mechanisms.Among these,sodium phosphate is extensively investigated as an alkaline metal monophosphate-type retarder.However,there exist varying interpretations of the retarding action of sodium phosphate in different studies,potentially impacting its practical application,and necessitating a clear elucidation of its retarding mechanism.Ammonium dihydrogen phosphate as an acid phosphate can also serve as a retarder and exhibits a more enduring retarding effect rather than the commonly used sodium phosphate.Compared to PO_(4)^(3-),the volatility of NH_(4)^(+)or its potential to mitigate the influence of alkaline metal ions on the cement hydration and the larger ionization constant of H_(2)PO_(4)^(-)can have a quicker reaction with alkaline cement particles,affecting the hydration process.Some work indicate that ammonium dihydrogen phosphate has a favorable retarding effect on cementitious slurries,but its specific retarding mechanism remains less explored.It is thus necessary for the analysis of their impact on the kinetics of Portland cement hydration to conduct a comparative study between ammonium dihydrogen phosphate and sodium phosphate.Methods Cement used was conformed to the GB 8076—2008 standard with a strength grade of 42.5.Ammonium dihydrogen phosphate and sodium phosphate were of analytical reagent grade(AR).The dosage of ammonium dihydrogen phosphate and sodium phosphate was 0.5%(in mass fraction),with a fixed water-to-cement ratio of 0.4.Cement samples for microstructural tests were prepared in 60 m L plastic bottles.The cement paste was prepared via dissolving ammonium dihydrogen phosphate and sodium phosphate,and mixed with cement.The well-mixed cement paste was placed in the plastic bottles and cured

关 键 词：磷酸二氢铵 硅酸盐水泥 缓凝 水化 

分 类 号：TU528.04[建筑科学—建筑技术科学]