【作者】 李军；

【导师】 姬永生； 杨建明；

【作者基本信息】 中国矿业大学 ， 结构工程， 2018， 博士

【摘要】 磷酸镁水泥（Magnesium phosphate cement,MPC）是由重烧氧化镁、可溶性酸式磷酸盐和外加剂等按照一定比例,在酸性条件下通过酸碱化学反应及物理作用生成的以磷酸盐为粘结相的无机胶凝材料。磷酸镁水泥具有结构密实、高早强、高体积稳定性、粘结性强、附着性好等特点,可用于混凝土结构的修补和复合材料的基体材料等方面,还具有无机涂料的优势。国内外对磷酸镁水泥基材料的研究主要集中在磷酸镁水泥本身的配制、性能及水化等方面,在磷酸镁水泥缓凝剂的开发以及缓凝剂对水泥水化产物与微观结构的影响等方面的研究也已取得较好的进展。相比之下,对利用磷酸镁水泥配制高性能磷酸镁水泥基涂料的技术和性能以及施工关键技术的研究仍十分匮乏,更谈不上系统性研究。磷酸镁水泥基涂料凝结快,对涂料的施工操作和后期性能均产生不利影响,限制了其使用范围。磷酸镁水泥基涂料长期与水接触,存在水溶蚀现象,水稳定性有待提高,这限制了其在水溶液腐蚀环境下的使用。磷酸镁水泥基涂料长期处于硫酸盐的腐蚀环境中,力学性能也有所下降,这也限制了其在硫酸盐腐蚀环境中的长期使用。因此,实现磷酸镁水泥基涂料的缓凝调控,研究水环境和硫酸盐等腐蚀环境中磷酸铵镁水泥基涂料的耐久性能,提升混凝土的防护和服役性能,具有重要意义,也为建材行业的节能降耗和绿色发展提供了支持和保障。本文围绕磷酸铵镁水泥（Magnesium phosphate ammonium cement,MAPC）涂料的缓凝调控、MAPC涂层的粘结界面和MAPC涂层耐久性等方面展开系统研究。拟实现MAPC涂层的凝结时间可控和施工性能达到要求,提高水环境和硫酸盐环境中的MAPC涂层的耐久性能,从而扩展MAPC涂料的应用范围。（1）MAPC涂料缓凝调控的研究制备MAPC涂料的悬浮液,利用pH计和水化热测试仪测试反应过程中的pH值和水化温度,研究MAPC涂料体系的反应机制。结合物相分析,提出MAPC涂料的反应机理模型。然后,通过测试不同硼砂含量的MAPC涂料体系的水化放热特性、pH值,提出硼砂对MAPC水化体系的缓凝新机理。MAPC涂料体系水化反应过程分为NH₄H₂PO₄的溶解、MgNH₄PO₄·6H₂O初结晶、MgNH₄PO₄·6H₂O继续结晶生成三个阶段。加入硼砂只能稍微延缓MAPC涂料体系的凝结时间,且中间未形成新的水化产物。冰醋酸和硼砂组成的复合缓凝剂可以明显延缓MAPC涂料体系的凝结时间,改善施工性能,但强度影响不大,冰醋酸的最佳浓度为3%。冰醋酸对MAPC涂料体系的缓凝作用可归结为保护膜作用、降温作用和降低pH值作用,加上官能团的作用,也让MAPC涂料体系水化过程不释放氨气。（2）MAPC涂料耐水性能的调控制备磷酸铵镁水泥涂料,测试其基本性能。添加NaCl可以提高MAPC涂层的耐水性能。当含量为3%时,MAPC涂层的厚度、质量吸水率、拉伸强度等性能达到最优。氯离子参与水化反应形成新的络合物,使得涂层在水环境中结构更加致密,同时大幅度提高了涂层与混凝土的粘结强度,从而增强了涂层的耐水能力。（3）硫酸盐腐蚀环境中MAPC涂层粘结界面微观结构演化研究将磷酸铵镁涂层和硅酸盐水泥的粘结试件,在Ca（OH）₂溶液和Na₂SO₄溶液中长期浸泡。测试试件的粘结强度,观察分析试件的断裂位置和断裂面,并对不同浸泡时期涂层粘结界面进行光学显微镜和SEM分析。着重研究不同环境对MAPC粘结强度、界面区显微形貌的影响,得到界面区域的断裂特征、界面裂纹及孔洞形貌及界面微观形貌等界面性能特征,并建立不同环境中的时变模型。MAPC和硅酸盐水泥之间存在明显的界面微区。在界面微区有结晶度较好的晶体生成,呈凝胶状,具有良好的粘附力,使MAPC成为性能良好的修补材料。Na₂SO₄溶液中,水化产物结构疏松,晶体形貌虽有改观,但粘结性能保持稳定。（4）MAPC涂层混凝土的抗硫酸盐侵蚀能力研究通过分析硫酸盐腐蚀环境中MAPC涂层混凝土的抗压强度、超声声速、表观形貌及硫酸根离子含量等变化,借助于XRD、SEM等手段,研究MAPC涂层混凝土的抗硫酸盐侵蚀能力,建立其内在机制。硫酸盐侵蚀环境下混凝土结构表面分为大气区、吸附区、浸泡区三部分,腐蚀主要集中在吸附区和浸泡区。两个区域的腐蚀差异较大,其中浸泡区混凝土受硫酸盐腐蚀破坏程度大于吸附区混凝土的腐蚀破坏。通过混凝土抗压强度变化和超声声速检测分析,MAPC涂层能有效防止硫酸盐溶液的侵入,起到了保护混凝土的作用。MAPC水化产物能与硫酸根离子反应形成新的络合物,使得涂层在硫酸盐溶液中结构更加致密,同时大幅度提高了涂层与混凝土的粘结强度,从而增强了混凝土的抗硫酸盐侵蚀能力。更多还原

【Abstract】 Magnesium phosphate cement（MPC）is a kind of inorganic cementing material produced by dead burning magnesium oxide,soluble acid phosphate and additive at a certain ratio under acid conditions through the acid-base chemical reaction and physical interaction,with phosphate as the binding phase.MPC is characterized by dense structure,high early strength,high volumetric stability,strong cohesiveness and favorable adhesiveness.It can be applied in concrete structural repair,base material of composite,and solidification of harmful and radioactive waste.The research on magnesium phosphate cement-based materials at home and abroad mainly focuses on the preparation,properties and hydration of magnesium phosphate cement.The research on the development of magnesium phosphate cement retarder and the effect of retarder on the hydration products and microstructure of cement have also made good progress.In contrast,the research on the technology and performance of high performance magnesium phosphate cement-based coatings prepared by magnesium phosphate cement and the key construction technology is still very scarce,let alone systematic research.Magnesium phosphate cement-based coatings have a rapid setting,which has a negative impact on the operation and performance of the coatings,and limits its application.Magnesium phosphate cement-based coatings have been in contact with water for a long time.Water-soluble corrosion exists and the water stability needs to be improved,which limits its use in water solution corrosion environment.Magnesium phosphate cement-based coatings have been in sulfate corrosion environment for a long time,and their mechanical properties have also declined,which limits their long-term use in sulfate corrosion environment.Therefore,it is of great significance to realize the retarding control of magnesium phosphate cement-based coatings,to study the durability of magnesium ammonium phosphate cement-based coatings in corrosive environments such as water environment and sulfate,and to improve the protection and service performance of concrete.It also provides support and guarantee for energy saving and green development of building materials industry.In this paper,the retarding control of the coating of Magnesium phosphate ammonium cement（MAPC）,the bonding interface of the coating of MAPC and the durability of the coating of MAPC are systematically studied.It is proposed that the setting time of MAPC coatings can be controlled and the construction performance can meet the requirements,and the durability of MAPC coatings in water and sulfate environments can be improved,so as to expand the application scope of MAPC coatings.（1）Retarding control of MAPC coatingsThe diluted suspension of MAPC coatings is prepared.The pH value and hydration temperature are measured by pH meter and hydration heat tester.The reaction mechanism of MAPC coatings system is studied.Combining with phase analysis,the reaction mechanism model of MAPC coatings is proposed.Then,by testing the hydration exothermic properties and pH value of MAPC coatings with different borax content,a new retarding mechanism of borax on MAPC hydration system is proposed.The hydration process of MAPC coating system can be divided into three stages:dissolution of NH₄H₂PO₄,initial crystallization of MgNH₄PO₄·6H₂O and continuous crystallization of MgNH₄PO₄·6H₂O.The addition of borax can only slightly delay the setting time of the MAPC coating system,and no new hydration products are formed in the middle.Compound retarder composed of glacial acetic acid and borax can obviously delay the setting time of MAPC coating system and improve the construction performance,but the strength has little effect.The optimum concentration of glacial acetic acid is 3%.The retarding effect of glacial acetic acid on the MAPC coating system can be attributed to the protective film,cooling and reducing the pH value,as well as the function of functional groups,so that the hydration process of the MAPC coating system does not release ammonia.（2）Regulation and Control of Water Resistance of MAPC CoatingsMAPC coating is prepared and its basic properties are tested.Adding NaCl can improve the water resistance of MAPC coating.When the content is 3%,the thickness,water absorption and tensile strength of the MAPC coating are optimized.The chloride ion participates in the hydration reaction to form a new complex,which makes the structure of the coating more compact in the water environment,and greatly improves the bond strength between the coating and concrete,thus enhancing the water resistance of the coating.（3）Microstructure evolution of bonding interface of MAPC coatings in sulfate corrosion environmentThe bond specimens of MAPC coating and Portland cement are immersed in Ca（OH）₂ solution and Na₂SO₄ solution for a long time.The bond strength of the specimens is tested,the fracture location and fracture surface are observed and analyzed,and the bond interface of the coatings in different immersion periods is analyzed by optical microscopy and SEM.The effects of different environments on the bond strength and interfacial morphology of MAPC are studied.The interfacial properties such as fracture characteristics,interfacial cracks,void morphology and interfacial micro-morphology are obtained,and time-varying models in different environments are established.There are obvious interfacial micro-zones between MAPC and Portland cement.In the micro interface area,the crystals with good crystallinity are formed in gel form and have good adhesion force,which makes MAPC a good repair material.In Na₂SO₄solution,the structure of hydration products is loose and the crystal morphology is improved,but the bonding property remains stable.（4）Sulfate resistance of concrete coated with MAPCBy analyzing the changes of compressive strength,supersonic velocity,apparent morphology and sulfate ion content of concrete coated with MAPC in sulfate corrosion environment,the sulfate resistance of concrete coated with MAPC is studied by means of XRD and SEM,and its internal mechanism is established.The surface of concrete structure under sulfate attack environment is divided into three parts:atmospheric zone,adsorption zone and immersion zone.Corrosion mainly occurs in adsorption zone and immersion zone.The corrosion of concrete in immersion zone is more destroyed by sulfate than that of concrete in adsorption zone.Through the analysis of concrete compressive strength change and supersonic testing,the MAPC coating can effectively prevent the invasion of sulfate solution and play a role in protecting concrete.The hydration product of MAPC can react with sulfate ion to form a new complex,which makes the structure of the coating more compact in sulfate solution,and greatly improves the bond strength between the coating and concrete,thus enhancing the sulfate resistance of concrete.更多还原