【作者】 李宁；

【导师】 张祖华； 史才军；

【作者基本信息】 湖南大学 ， 土木工程， 2020， 博士

【摘要】 碱激发混凝土是以化学激发硅铝酸盐废弃物而成的胶凝材料制备的混凝土,具有耐腐蚀性好、强度发展快等优点。碱激发混凝土可利用硅铝酸盐固体废弃物作为主要原料,无需普通硅酸盐水泥熟料的高温煅烧过程,其生产和应用具有显著的节能减排特点,有利于水泥混凝土工业的可持续发展。但目前关于碱激发混凝土的原材料活性评价方法、凝结硬化控制技术、混凝土组成设计和制备等基础理论研究仍然不足,成为制约碱激发混凝土工程应用的瓶颈。针对上述问题,本文围绕“不同组成矿渣粉的碱活性指数、碱激发混凝土凝结硬化与微结构形成及性能调控、碱激发混凝土的配合比设计理论和方法”等三个科学问题展开研究。首先研究了不同组成特点的矿渣其碱激发水泥的反应动力学特点。结果显示,矿渣组成中CaO和MgO的含量对碱激发矿渣水泥反应动力的影响较大。在早期的碱激发反应过程中,CaO控制了C-（N）-A-S-H凝胶的生成速率,MgO控制了镁铝水滑石（Mg-Al-OH-LDH）的生成速率,而过多的Al含量则会和矿渣中的CaO和SiO₂生成水化钙铝黄长石C₂ASH₈。碱激发反应的孔溶液相组成演变和C-（N）-A-S-H凝胶Ca/Si和Al/Si的变化与碱激发矿渣水泥的反应放热过程有很好的关联。研究发现碱激发矿渣水泥的反应动力与矿渣中（CaO+MgO）/SiO₂的值存在一定关系,因为矿渣组成中的CaO和MgO含量在高碱浓度下的溶解速率控制了早期凝胶产物的物相组成发展。紧接着研究了矿渣组成对碱激发水泥的抗压强度和微观结构的影响,并通过热力学模拟建立了矿渣组成与碱激发水泥反应产物的相含量和本征孔隙率之间的关系。结果显示,受矿渣组成的影响,碱激发不同组成矿渣水泥的抗压强度不同。在所有的碱激发矿渣水泥中均观察到C-（N）-A-S-H凝胶和镁铝水滑石相。Al₂O₃的含量对碱激发矿渣水泥的物相种类和组成有重要影响,Al₂O₃的组成越低,C-（N）-A-S-H凝胶的含量越高,水化钙铝黄长石的含量越低。当矿渣中Al₂O₃组成的质量分数在13%以下时,体系不会生成水化钙铝黄长石。镁铝水滑石的含量和体系中的MgO的含量有关,通常体系中的MgO的含量越高,生成的类水滑石的含量越高。此外,硅酸钠激发水泥的孔隙率要低于Na OH激发体系的。热力学模拟结果表明,在反应程度一定的情况下,矿渣中CaO的含量越高,其碱激发体系的产物填充孔隙越小,体系的化学收缩越大,孔隙越高,不利于水泥浆体的最终强度。最终,在本文提出的矿渣“活性指数”公式中,首次考虑了CaO这种负作用,新的活性指数和碱激发矿渣水泥的抗压强度之间具有良好的相关性。此外,测试了碱激发矿渣水泥在Na₂CO₃-Na OH-Na₂O·2Si O₂混合碱组分体系下的凝结时间和强度发展。通过水化量热仪、孔溶液化学分析了混合碱组分激发矿渣水泥的反应进程。结果表明,在Na₂CO₃-NaOH-Na₂O·2SiO₂混合碱组分体系中,碱矿渣水泥水化反应受激发剂阴离子复杂的物理化学作用影响。OH^-能够破坏矿渣,加速矿渣水化,同时促进Ca²⁺、Mg²⁺和Al³⁺等与容易使CO₃^2-反应形成碳酸盐,加快凝结;而（Si O₄）^4-不仅加速矿渣的水化,还因与CO₃^2-在结构上相似,改变溶液的物理性质;CO₃^2-可以和矿渣溶解出的Ca²⁺发生反应,延缓C-A-S-H凝胶的生成,抑制Na₂O·2Si O₂的水解。三元混合激发剂中,Na₂CO₃的用量达到50%以上,碱激发矿渣水泥的凝结时间将大大延长。通过合理的控制三种碱组分的相对含量,不仅可保证浆体的凝结时间,还可以使硬化体抗压强度高且孔隙率低。最后在以上研究成果的基础上,本文提出了矿渣基碱激发混凝土的组成设计理论。第一步通过测试混合骨料的堆积密度确定其最大值,保证骨料最紧密堆积和计算骨料间最小空隙率;然后根据抗压强度确定水胶比和碱胶比;再根据骨料间的最小空隙率和工作性对骨料表面富余浆体厚度的要求,确定混凝土中浆体的使用量;最后可通过二元或三元单一质心设计法进一步优化胶凝材料的组成,得到满足不同性能要求的碱激发混凝土组成。在具体研究中,由于碱激发混凝土组成设计方法的研究工作较少,组成设计参数无从参考,且原材料组成特性变化大,所以首先采用正交设计法系统探究了碱胶比、水胶比、粉煤灰在矿渣-粉煤灰复合原料中的用量、水玻璃模数和富余浆体厚度对碱激发矿渣基混凝土坍落度、凝结时间和抗压强度的影响。通过直观分析和极差值计算,建立主要因素与目标性能之间的关系,并根据性能需要提出了碱激发混凝土的组成设计方法。依照此方法可以设计出初凝时间1-3 h,坍落度200 mm以上,强度等级为C40-C80的碱激发矿渣基混凝土。更多还原

【Abstract】 Alkali-activated cement concrete is a composite material made by chemically activated alumino-silicate cementitious binders.It has excellent corrosion and high temperature resistance and performs even better than conventional Portland cement concrete in terms of the mechanical properties.Alkali-activated cement concrete can be produced solely upon the use of alumino-silicate materials that do not need any calcination of the raw materials.The production and usage of alkali-activated cement concrete can lead to a significant reduction in environmental pollution,carbon emission and energy consumption,and therefore,meets the needs of sustainable development of the national economy and construction industry.Nevertheless,there is a lack of systematic research on the theories for evaluation method of raw material reactivity,setting and hardening control technology,and composition design and production of alkali-activated cement concrete.This has heavily impeded the wide use of alkali-activated cement concrete in the construction industry.To fill in the above knowledge gap,this paper aims to conduct a systematic research program focusing on three key scientific issues:（1）development of alkali reactivity index of different slag composition;（2）the mechanisms for the setting and hardening,microstructure development and optimization of alkali-activated slag cement;and（3）composition design theory and method of alkali-activated cement concrete.As the first section of this study,the effect of different slag composition on the reaction kinetics of alkali-activated slag cement was investigated.The results showed that the reaction kinetics of alkali-activated slag cement mainly depended on the total contents of Ca O and Mg O in the slag,among which Ca O was beneficial to the generation of C-（N）-A-S-H gel,Mg O was beneficial to the generation of hydrotalcite（Mg Al-OH-LDH）,while excessive Al and Ca O and Si O₂ in the slag would generate hydrated mililite（C₂ASH₈）.The phase evolution of pore solution and the changes of Ca/Si and Al/Si in C-（N）-A-S-H gel are well correlated with the reaction exothermic process of alkali-activated slag cement.The chemical composition of slag has a significant effect on the reaction kinetics of alkali-activated slag cement,and the reaction kinetics of alkali-activated slag cement has a certain relationship with the ratio of（Ca O+Mg O）/Si O₂ in slag,because the dissolution rate of Ca O and Mg O contents in slag at high alkali concentration controls the development of the phase composition of early reaction products.Then the effects of different slag compositions on the compressive strength and microstructure of alkali-activated slag cement were studied.The results showed that the compressive strength of alkali-activated slag cement with different slag compositions is different due to the different reaction products.C-（N）-A-S-H gel and Mg Al-OH-LDH phase were observed in all alkali-activated slag cement,and hydrated C₂ASH₈ was usually observed in the slag composed of high aluminum content,while katoite was more easily generated in the Na OH acitation system.The content of Al₂O₃has an important effect on the phase types and composition of alkali-activated slag cement.The lower the Al₂O₃ content is,the higher the content of C-（N）-A-S-H gel is,and the lower the content of hydrated C₂ASH₈ is.When the Al₂O₃ content in the slag is less than 13%,the system will not produce hydrated C₂ASH₈.The content of Mg Al-OH-LDH phase is related to the Mg O content in the system.Generally,the higher Mg O content in the system,the higher Mg Al-OH-LDH.In addition,the intrinsic porosity of sodium silicate activated cement is lower than that of Na OH activated slag system.The thermodynamic results showed that,with a certain reaction degree,the higher Ca O content in the slag,the smaller pore filled capacity by the reaction products,and the greater the chemical shrinkage of the system.Eventually,the higher porosity was formed in the matrix,which is negative for the final compressive strength of alkali-activated slag cement.Thus,for the formula of"alkali"reactivity index of slag proposed in this paper,Ca O is considered as a negative factor for the first time,and the new reactivity index has a good correlation with the compressive strength of alkali-activated slag cements.Moreover,sodium silicate-activated slag often gives high early strength but sets too rapidly.Commercial retarders for Portland cement and partial replacement with other cementitious components in alkali-activated slag（AAS）system have been proven ineffective.This study investigated the approach of controlling setting by altering activator ion composition and silica polymer status.The roles of activators during the alkali-activation process were studied via pore solution chemistry analysis and microstructural analysis of hydration products.The addition of Na₂CO₃ does not,but Na OH does alter the polymerization of silicate ion groups in sodium silicate solution due to the increases in p H and Na₂O concentration.The specific effects of Na₂CO₃ on the setting and hardening of AAS depend on the relative contents of Na OH and Na₂O·2Si O₂ in alkaline solution.The reaction degree of AAS is dependent on activator compositions,which govern the kinetics of formation and intrinsic characteristics of the reaction products calcium aluminosilicate hydrates.The setting and strength development of sodium silicate-activated slag can be controlled by manipulating the compositions of Na₂CO₃-Na OH-Na₂O·2Si O₂.Finally,this paper reports a general mixture design procedure for alkali-activated slag concrete,which is an essential step towards industrial application.The procedure involves three steps:1)the determination of coarse and fine aggregate ratio according to close packing model;2)the determination of liquid phase（water content and activator）based on compressive strength;and 3)the determination of excess paste content by workability requirement and measurement.Effects of mixture proportional factors,including activator composition,water content,fly ash content,and binder/aggregate ratio are examined on consistency,setting time and compressive strength.The relationship between performance and precursor composition is established using simplex centroid design method.Using the mixture proportioning method,alkali-activated concretes with compressive strength grades of C40,C60,and C80 are successfully prepared with initial setting time of 1 to 3 h and slump of more than 200 mm.更多还原