【作者】 张同生；

【导师】 余其俊；

【作者基本信息】 华南理工大学 ， 材料学， 2012， 博士

【摘要】 “节能减排、节约资源与保护环境”是我国建设和谐社会、走可持续发展道路的主要途径。然而，水泥工业作为传统产业，是资源、能源消耗大户和碳排放大户，特别是我国正处于基础建设的高峰期，水泥产量和需求量巨大且逐年增长。另一方面，我国各种工业固体废弃物年排放量超过20亿吨，大量工业废渣不仅占用土地、污染环境，同时也是一种巨大的资源浪费。其中，冶金工业废渣及燃煤灰渣可用作辅助性胶凝材料生产复合水泥，是水泥工业发展的重要方向之一。但由于辅助性胶凝材料的活性较低，导致复合水泥的早期强度等性能较差，限制了工业废渣的掺量及复合水泥的应用范围。现有方法大都从“提高辅助性胶凝材料活性”的角度出发来改善复合水泥的性能，虽然在一定程度上改善了复合水泥的性能，但未能优化复合水泥初始浆体结构和水化进程，因而难以从根本上解决复合水泥水化效能不高、辅助性胶凝材料颗粒与水化产物粘接较差等本质问题。本文揭示了水泥熟料、钢渣、粉煤灰的非均相分布规律，并根据各粒度区间胶凝材料的水化、硬化特性及复合水泥理想的水化进程，对复合水泥的组成（胶凝材料种类、用量和粒度）进行设计。通过复合水泥初始浆体结构的优化和水化进程的优化匹配，实现了复合水泥浆体结构合理、有序形成和颗粒间“有效粘接”，在降低水泥熟料用量、提高辅助性胶凝材料（特别是低活性辅助性胶凝材料）掺量的同时，显著改善了复合水泥的强度、体积稳定性等性能。具体工作包括：研究了水泥熟料与辅助性胶凝材料粒度区间与组成、性能的关系。由于非均质材料在粉磨过程中存在分相现象，粗粒度区间胶凝材料中难磨性矿物含量较高，而细粒度区间易磨性矿物含量较高。粒度及组成的差异使各粒度区间胶凝组分的水化、硬化特性差别较大。随胶凝材料粒径的减小，其需水量和早期强度（或活性指数）逐渐增大；但就后期强度而言，并非粒径越小，胶凝材料（特别是熟料和矿渣）强度越高，而是存在一个最佳的粒度区间。其中，8~24μm硅酸盐水泥的需水量较低，中、后期水化较快，早期强度较高、后期强度非常高；细粒度区间高活性辅助性胶凝材料的早期活性指数较高，后期活性指数可超过100%。为优化复合水泥初始浆体结构，分析了水泥基材料常用的颗粒级配理论和模型，发现以S. Tsivilis分布和Fuller分布为代表的经典颗粒级配模型均难以很好地指导复合水泥的制备。本研究根据紧密堆积理论，建立了“区间窄分布，整体宽分布”颗粒级配模型，在按照实际浆体中胶凝材料颗粒间的距离进行修正后，可更好地优化复合水泥初始浆体结构，进一步提高复合水泥浆体的初始堆积密度。本文提出的胶凝材料“胶凝能力”和“强度贡献率”，可用于描述辅助性胶凝材料对复合水泥性能的贡献。细粒度区间钢渣、矿渣水化活性较高，水化中后期生成大量水化产物，对孔隙填充能力较强，表现出良好的胶凝性能，其早期和后期强度贡献均超过了相同粒度区间水泥熟料的强度贡献；中、粗粒度区间辅助性胶凝材料水化活性较低，导致其各龄期强度贡献率均较低。因此，水泥熟料与辅助性胶凝材料的优化匹配原则为：高活性辅助性胶凝材料、水泥熟料和低活性辅助性胶凝材料或惰性填料应分别置于复合水泥的细（<8μm）、中（8~24μm）和粗粒度区间（>24μm）。在“区间窄分布，整体宽分布”颗粒级配模型和优化匹配原则的指导下，实验室内仅采用25%（体积分数）的水泥熟料制备了42.5强度等级的复合水泥。该水泥浆体具有较低的需水量、较高的初始堆积密度和合理的水化进程，硬化浆体结构合理、有序形成并逐渐密实化。与硅酸盐水泥浆体相比，复合水泥浆体中剩余Ca(OH)2量较少，C-S(A)-H凝胶数量、未水化组分含量和总孔隙率相差不大，但有害大孔较少、无害孔较多，从而使复合水泥的早期和后期强度得到了显著提高。采用简化的颗粒级配模型（三区间）及在硅酸盐水泥中掺加粗、细辅助性胶凝材料的方法，均可不同程度地提高复合水泥的早期和后期强度。低熟料用量、高性能复合水泥具有良好的体积稳定性和耐久性，其主要原因是：（1）复合水泥的水化产物多为外部水化产物，引起的化学收缩较小，K~+、Na~+进入C-A-S-H凝胶层间，水化产物层间结合力增强，从而提高了水化产物抵抗体积变形的能力；（2）水化早期少量水泥熟料水化，使浆体逐渐硬化（浆体结构形成），后期水化持续进行且速率较大（矿渣开始水化），大量水化产物填充于浆体孔隙中，使浆体结构较为均匀、密实，浆体内部应力较小且分布均匀，从而改善了复合水泥浆体体积稳定性和耐久性。本研究仅用25%的水泥熟料、36%的矿渣及39%的低活性辅助性胶凝材料或惰性填料（石膏外掺），制备了42.5强度等级的复合水泥（实际生产中水泥熟料用量75%以上），且该水泥具有良好的体积稳定性和耐久性。本研究成果可为大宗量利用工业废渣（特别是低活性或惰性废渣）制备高性能复合水泥奠定了理论基础和技术支持，同时具有极大的节约资源、能源和减少CO2排放量前景，可有效推动“可持续发展”、“节能减排”、“低碳经济”等基本国策的实施，具有极其重大的经济、生态和社会效益。更多还原

【Abstract】 “Energy saving, emission reducing, resources conservation and environment protection”are the main ways for China to achieve sustainable development and harmonious society.However, the production of Portland cement seems unsustainable due to the consumption ofhuge natural resources and energy and significant CO2emissions. China is the largest cementproduction country, and the output of cement is beening continually increased as a largenumber of infrastructures are beening built. Meanwhile, nearly2billion tons of industrialsolid wastes are generated annually in China, leading to numerous environmental problems.Metallurgical slags together with coal combustion ashes can be used as supplementarycementitious materials (SCM) to produce blended cement, which is considered as one of thedevelopment directions of cement industry. Due to the low hydraulic (or pozzolanic) activityof SCM, blended cements usually present low early strength, especially for blended cementswith a high content of low activity SCM. Many attempts, such as chemical activation andultra-fine grinding, have been made to improve the early properties of blended cements.Although these methods, mainly focusing on the enhancement of the activity of SCM,contribute greatly or somewhat to the improvement of the properties of blended cement, theinitial microstructure and hydration process of blended cement paste have not been optimizedcompletely, thus the key factors,“low hydration efficiency” and “poor binding between SCMparticles and hydration products” leading to the low early strength of blended cement, havenot yet been solved perfectly.In this thesis, optimized matching of cement clinker and SCM were investigated.According to the hydration and hardening characteristics of cementitious material fractionswith different particle size, desired hydration process and micro-structural development ofblended cement paste, the type, addition and particle size distribution of cementitiousmaterials consisting of blended cement were redesigned. Through optimization of the initialmicrostructure and hydration process of blended cement paste, the microstructure of blendedcement paste is formed and densified gradually, at the same time hydration products bindSCM particles firmly. Consequently, the strengths and volumetric stability of hardenedblended cement paste are improved significantly, while the addition of cement clinker isreduced and the amount of SCM (especially for SCM with low activity or inert fillers) isincreased. The research significances in this thesis are described in detail as follows:The relationship among the size fraction, composition and properties of cement clinkerand SCM has been clarified. Due to grindability difference of each mineral, coarse cementitious material fractions contain a higher amount of harder grindability minerals, whilehigher proportion of easier grindability minerals is observed in fine cementitious materialfractions. The hydration and hardening characteristics of cementitious materials varysignificantly with their size and mineral composition. The water requirement and earlystrength of cementitious materials are increased dramatically with the decrease of particle size,while cementitious materials (e.g. cement clinker and BFS) only show the highest latestrength when the particle size lie in a certain range. For instance,8-24μm cement clinkerfraction has a low water requirement and high hydration rate at late ages, resulting inrelatively higher early strength and the highest late strength. Further, fine SCM fractions havean acceptable early strength index and late strength index higher than100%, indicating thatthe replacement of cement clinker by these SCM fractions will not lead to late strength loss.The adaptability of the classical particle size distribution (PSD) models generally used incement-based materials has been analyzed. Few of the existed models including S. Tsivilisdistribution and Fuller curve are adapted to blended cements which consist of cement clinkerand SCM with different hydraulic activity (perhaps even inert particles). In order to optimizethe initial microstructure of blended cement paste, a gap-graded PSD was proposed andmodified according to the distance between solid particles in actual pastes. The gap-gradedPSD leads to a reduced water requirement and an increased packing density of blendedcement pastes, and modified gap-graded PSDs have better effects.The term ‘strength contribution ratio’ and ‘cementitious ability’ of SCM fractions wereproposed, by which the contribution of SCM fractions to the properties of blended cement canbe quantitatively described. Fine BFS and steel slag fractions (<8μm) show more desirablehydration processes and higher strength contribution ratios in comparison to thecorresponding cement clinker with the same size, while middle size and coarse SCM fractionshave low early and late strength contribution ratios due to their low hydraulic activity. Theoptimized matching principle of cement clinker and SCM is as follow: SCM with highactivity, cement clinker, and SCM with low activity (or inert fillers) should be preferablyarranged in the fine (<8μm), middle size (8-32μm) and coarse (>32μm) fractions,respectively.42.5grade blended cements with only25%cement clinker by volume can be preparedusing the gap-graded PSD by mixing cementitious materials according to the optimizedmatching principle. The blended cement pastes have a low water requirement and highpacking density, a small amount of hydration products generated from the hydration of clinkerform the initial microstructure of cement paste during the first24h. The hydration products of BFS, accounting for about40%of the total hydration products, densify the microstructure ofblended cement paste gradually after30h. The Ca(OH)2content remained in blended cementpaste is very low, while the total porosity of the matrix and the amounts of C-S(A)-H gels andun-hydrated components almost equal to those in Portland cement paste, and large-size poresare reduced dramatically due to the hydration of SCM at late ages. The above mentionedeffects lead to a significant increase in both early and late strengths of blended cements.Blended cements with simplified gap-graded PSD and prepared by mixing commercialPortland cement, fine BFS fraction and coarse SCM fraction with low activity also havehigher early and late strengths than blended cement prepared by co-grinding.High performance blended cements with low cement clinker content present superiorvolumetric stability and durability. The related improvement mechanisms are summarized asfollows:(a) The main hydration products of gap-graded blended cement are outer hydrationproducts with high Al content, which has a low chemical shrinkage compared with innerhydration products. To maintain the charge balance of hydration products, a large amount ofK~+and Na~+are absorbed into the layer of C-A-S-H gel, leading to an enhanced interactionforce among gel layers (van der Waals force), thus the hydration products show a superiorresistance to volumetric deformation.(b) Stress and strain remained in gap-graded blendedcement pastes are low and uniformly distributed due to low hydration heat and morehomogenous, densified microstructure.The cement clinker content in42.5grade blended cement is usually higher than75%inindustrial practice, however42.5grade blended cement can be prepared using only25%cement clinker,36%BFS and39%low activity SCM (or inert fillers) in present study, and theblended cements also have superior volumetric stability and durability. The results providetheoretical foundation and technical support for the preparation of high performance blendedcements with larger amount of industrial wastes (especially for low activity and inertindustrial wastes). By this method, huge natural resources and energy can be saved, andsignificant CO2emissions can also be reduced, resulting in numerous economic, social andenvironmental benefits.更多还原