碱渣用作矿物掺合料对砂浆和混凝土性能影响及其机理研究

发布时间：2018-08-31 10:17

【摘要】：碱渣是氨碱法制纯碱排出的废渣,其堆存和排放已造成严重的环境问题,碱渣治理已成为世界性难题。由于碱渣难以处理,发达国家大多已摒弃氨碱法而寻求新的制碱工艺。我国是发展中国家,工业发展水平相对落后,舍弃氨碱法不符合现有国情,故碱渣治理只能走综合利用之路,以期变废为宝,化解其资源和环境问题。目前,碱渣综合利用已在农业、化工、建筑材料等诸多领域进行研究,并取得一定成果,但碱渣利用率低是目前应用的主要问题。2013年,我国碱渣综合利用率不到16%。究其原因,则是农业、化工等领域本来需量较少,而建材领域虽需求量大,但碱渣氯离子含量太高,会严重威胁建筑物耐久性,因此阻碍了其大量应用。针对以上问题,本文首先研究了碱渣的物相组成及微观结构,在此基础上采用浸泡、粉磨、水洗、电渗等方法研究了碱渣的氯离子溶出特性。进而研究了碱渣作为矿物掺合料对砂浆和混凝土性能的影响,得到了碱渣用作矿物掺合料的适宜处理方法及应用方式。本文主要研究内容和研究结论如下：(1)通过X-射线荧光光谱、XRD析、差热分析等方法研究了碱渣化学组成及物相组成,结果表明碱渣主要物相为碳酸钙、二水石膏、氯化钙。通过扫描电镜、激光粒度仪、压汞、氮吸附等方法研究了碱渣的微观结构构成,结果表明碱渣微观结构是：由纳米碳酸钙通过结合和搭接形成2-5umm的团聚体颗粒,团聚体颗粒间结合形成10-74um的聚集体颗粒,聚集体颗粒和二水石膏通过堆积、搭接构成碱渣土的宏观形貌。碱渣土具有发达的孔隙结构,包括：聚集体颗粒间的空隙、聚集体内部的微米级孔隙结构、团聚体颗粒上的纳米级微孔。(2)通过浸泡试验研究了碱渣聚集体颗粒加水分散后空隙中氯离子的溶出特性；通过粉磨试验研究了破坏碱渣聚集体内部微米级孔隙后的氯离子溶出特性；通过高水固比条件下的多次水洗试验研究了聚集体内部微米级孔隙中氯离子的扩散溶出特性；通过电渗试验研究了团聚体内部纳米级孔隙中氯离子在电场作用下的进一步溶出。结果表明,碱渣氯离子主要存在于聚集体颗粒间的空隙中,部分存在于聚集体内部团聚体颗粒间的微米级孔隙中,团聚体上纳米级微孔中氯离子含量极低。碱渣中氯离子的分布约为：空隙水中含73%、微米级孔隙水中含20%、纳米级微孔水中含7%。碱渣氯离子主要为可溶性氯离子,可通过水洗去除。(3)通过正交试验研究了掺加碱渣的优化砂浆胶凝材料组成；采用优化的胶凝材料组成,研究了原状碱渣、水洗碱渣、除氯碱渣对砂浆性能的影响及除氯碱渣用作砂浆保水剂的可行性。结果表明：氯离子含量低于0.30%的除氯碱渣可作为矿物掺合料应用于砂浆。除氯碱渣、粉煤灰、矿粉的较佳掺量组合为：碱渣10%-15%、粉煤灰10%-20%、矿粉10%。除氯碱渣取代15%粉煤灰时,砂浆28d抗压强度可提高74%,胶凝材料可溶氯含量低于钢筋混凝土环境的限值(0.1%),可满足耐久性要求,砂浆可溶性氯离子浸出含量远低于地下水排放限值,不会造成地下水源污染。除氯碱渣用作砂浆保水剂时,掺加减水剂保持水胶比不变时,砂浆保水性能和干缩性能优于传统有机保水剂,可单独作为砂浆保水剂使用。(4)通过碱渣单掺和复掺试验研究了较优的混凝土胶凝材料组成；采用优化的胶凝材料组成,研究了原状碱渣、水洗碱渣、除氯碱渣对混凝土力学性能、耐久性及环境的影响。结果表明,碱渣、粉煤灰、矿粉的适宜掺量分别为10%、10%-20%、10-20%。掺加减水剂保持水胶比不变时,以碱渣取代10%的粉煤灰或水泥后混凝土强度均略有增大。但掺入原状碱渣和水洗一次碱渣均会造成钢筋锈蚀,不能满足耐久性要求。而掺入氯离子含量低于0.30%的除氯碱渣不会造成钢筋锈蚀,其半电池电位测定值远低于钢筋锈蚀电位临界值,且和未掺碱渣的空白组十分接近,可满足耐久性要求。氯离子含量低于0.30%的除氯碱渣可作为混凝土矿物掺合料使用,无需掺阻锈剂即可使用。
[Abstract]:Alkali residue is a kind of waste residue discharged from ammonia-alkali soda process. Its storage and discharge have caused serious environmental problems. The treatment of alkali residue has become a worldwide difficult problem. At present, the comprehensive utilization of alkali residue has been studied in many fields, such as agriculture, chemical industry, building materials and so on. However, the low utilization rate of alkali residue is the main problem of its application. In 2013, the comprehensive utilization of alkali residue in China was carried out. The rate is less than 16%. The reason is that the demand in agriculture, chemical industry and other fields is small, but the demand in building materials is large, but the chloride ion content of alkali residue is too high, which will seriously threaten the durability of buildings, thus hindering its extensive application. The chloride ion dissolution characteristics of alkali slag were studied by soaking, grinding, washing and electroosmosis. The effect of alkali slag as mineral admixture on the properties of mortar and concrete was studied. The suitable treatment methods and application methods of alkali slag as mineral admixture were obtained. The chemical composition and phase composition of alkali residue were studied by means of spectroscopy, XRD and differential thermal analysis. The results showed that the main phase of alkali residue was calcium carbonate, dihydrate gypsum and calcium chloride. The agglomerate particles of 2-5 umm are formed by bonding and lapping, and the agglomerate particles of 10-74 umm are formed by bonding. The agglomerate particles and dihydrate gypsum are stacked together to form the macroscopic morphology of alkali slag soil. (2) The leaching characteristics of chloride ions in the pores of alkali residue aggregates dispersed by adding water were studied by immersion test; the leaching characteristics of chloride ions after destroying the micro-pores of alkali residue aggregates were studied by grinding test; and the leaching characteristics of chloride ions were studied by multiple washing tests under high water-solid ratio. The diffusion and dissolution characteristics of chloride ions in the micron-sized pores in the aggregates were studied by electroosmosis experiment, and the further dissolution of chloride ions in the nano-sized pores in the aggregates under electric field was studied. Chloride ion content in nano-pore of aggregate is very low in meter-scale pore. The distribution of chloride ion in alkali slag is about 73% in pore water, 20% in micro-pore water and 7% in nano-pore water. Chloride ion in alkali slag is mainly soluble chloride ion and can be removed by water washing. (3) The optimized sand with alkali slag was studied by orthogonal test. The effect of original alkali slag, washing alkali slag, removing chlor-alkali slag on the properties of mortar and the feasibility of using chlorine-alkali slag as water-retaining agent for mortar were studied by using optimized cementitious material composition. The optimum content of slag is 10%-15%, fly ash 10%-20% and slag 10%. When the slag is used to replace 15% fly ash, the compressive strength of mortar can be increased by 74%. The soluble chlorine content of cementitious material is lower than the limit value of reinforced concrete environment (0.1%). It can meet the durability requirement. The leaching content of soluble chloride ion of mortar is far lower than that of groundwater discharge. When dechlorinated alkali slag is used as water-retaining agent for mortar, the water-retaining performance and dry shrinkage performance of mortar are better than those of traditional organic water-retaining agent when water-reducing agent is added to keep water-binder ratio unchanged, and can be used as water-retaining agent for mortar alone. (4) Optimum composition of concrete cementing material is studied by mixing alkali slag with single and compound. The effects of original alkali slag, washing alkali slag and removing chlor-alkali slag on the mechanical properties, durability and environment of concrete were studied by using the optimized cementitious material composition. The results show that the suitable dosage of alkali slag, fly ash and mineral powder are 10%, 10% - 20% and 10 - 20% respectively. The strength of the solidified soil increases slightly, but the corrosion of the reinforcing steel bar will be caused by mixing the undisturbed alkali slag with the first washing alkali slag, which can not meet the durability requirements. The slag containing less than 0.30% chloride ion can be used as concrete mineral admixture without any rust inhibitor.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528

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