碳化-激发作用下MgO-粉煤灰固化淤泥力学性状与微观机理研究

Abandoned sludge was usually solidified by traditional materials such as cement and lime, and how to reuse industrial byproduct – fly ash and activate its potential pozzolanic reactivity becomes the technical difficult and key problem in the green solidification of abandoned sludge, so it’s necessary to study fly ash-based green solidification technology and sludge solidification performance. Various activators (NaOH etc.) that are easily obtained will be considered to study the evolution of compressive strength of solidified sludge and corresponding reaction mechanisms. In combination with novel low carbon reactive MgO and carbonation technique, the mixtures of MgO-fly ash and CO2-MgO-fly ash are applied to sludge solidification, and the influence of many factors such as MgO reactivity and carbonation duration on the mechanical property of sludge will be investigated. The predication mathematical model of strength-deformation-modulus relationship will be proposed taking into account the effect of activation and carbonation. The resistance of activated and carbonated samples to thawing-freezing cycles and wet-dry cycles etc. will be discussed in order to evaluate the effect of simulated extreme weather conditions on strength weakening process and failure mechanism of solidified sludge. The microstructural characteristics of MgO-fly ash solidified sludge with and without CO2 will be investigated through the techniques such as scanning electron microscope and X-ray diffraction to reveal the formation process of new cementitious materials and evolution of microstructure, and the intrinsic reason of improving mechanical performance by the incorporation of MgO-fly ash and CO2-MgO-fly ash will be revealed on solidified sludge. The research results can provide the scientific basis and technological guidance for the disposal and beneficial reuse of abandoned sludge from water environment treatment and engineering construction.

废弃淤泥固化常用水泥或石灰等传统材料，如何利用粉煤灰等副产物并激发其活性是开展淤泥绿色固化技术的难点和关键，因此有必要开展基于粉煤灰绿色经济固化工艺与淤泥固化效果研究。采用不同激发剂，建立考虑激发剂类型的粉煤灰固化淤泥强度变化和微观反应机制。引入新型低碳活性MgO和CO2碳化技术，将MgO-粉煤灰和CO2-MgO-粉煤灰复合固化剂用于淤泥固化，探索MgO活性和碳化时间等因素对淤泥力学性质影响，建立考虑激发和碳化效应固化淤泥强度、变形和模量之间数学预测模型。开展冻融和干湿等耐久性研究，模拟极端天气对激发-碳化淤泥强度弱化过程和破坏机理影响。运用扫描电镜和X射线衍射等，研究CO2、MgO和粉煤灰之间化学反应原理，分析粉煤灰遭破坏后胶结产物形成和微观结构演变，揭示入掺活性MgO和CO2粉煤灰固化淤泥力学性能改良的本质原因，为环境治理和工程建设中大量废弃淤泥处理与资源化利用提供科学依据和技术指导。

疏浚淤泥的处理处置，已成为土木、水利和水环境治理工程中亟待解决的社会难题。研发高效胶凝材料及新型固化技术替代或部分替代水泥与石灰等传统材料，是开展绿色可持续固化淤泥技术研究的难点和关键。提出了碱激发剂-粉煤灰、活性MgO-粉煤灰、CO2-活性MgO基材料三种新型固化淤泥技术，证明了活性MgO/碱-粉煤灰、CO2-活性MgO基材料具有明显改善淤泥力学行为与耐久性的效能，揭示了所研发固化技术诱发淤泥性能改良的微观结构特征和化学作用机制。发现NaOH、Na2SiO3等碱激发剂能有效激发粉煤灰潜在活性，经激发-溶解-再聚合过程形成不同聚合度硅铝酸盐凝胶N-A-S-H是碱激发粉煤灰固化淤泥强度提高的本质原因。活性MgO被证明可有效替代NaOH等碱激发剂，同时发挥碱性激发和化学胶结双重效能，发现Mg(OH)2、M-S-H凝胶生成是活性MgO-粉煤灰固化淤泥的微观作用机制。成功研制一套CO2加速碳化试验装置，可快速提升活性MgO基材料固化淤泥的强度和长期稳定性，0.5-3h内即可达到PC水泥固化淤泥28d强度甚至更优异效果，同时实现CO2永久封存、淤泥快速改良的双赢目的。起骨架支撑作用的棱柱形碳酸镁石、起填充与黏结作用的花骨状和片状的水碳镁石和球碳镁石的生成，是CO2碳化活性MgO基材料改良淤泥力学行为和耐久性的本质机理。发现持续浸水作用促使球碳镁石和水碳镁石向碳酸镁石转化，干湿循环作用促使碳酸镁石向球碳镁石和水碳镁石转化，冻融作用下试样碳化产物之间无明显转化。研究成果可为环境治理和工程建设中废弃淤泥处理与资源化利用提供科学依据和技术指导，具有良好的社会效益和经济效益。