核壳结构碳化钢渣多孔骨料提升混凝土性能的机制研究

Low hydraulic binding performance and potential unsoundness of steel slag are the key problems hinder its application in cement-based materials. Utilizing the characteristic of aggregates and optimizing the aggregate interface are vital approaches to produce high performance concrete. This study aims to design and prepare carbonated core-shell porous steel slag aggregates with gradient structure, strengthened shell and activated surface through synergetic technologies of multi-components design, particle size adjustment, and accelerated carbonation, by using steel slag as the main raw material and together with other components such as biochar and alumina-silicate materials. The influences of the components of steel slag aggregates and carbonation conditions on their properties will be investigated. The microstructure evolution of the carbonated core-shell porous steel slag aggregates under accelerated carbonation process, and the intrinsic relationship between the microstructure and property of the carbonated steel slag aggregates will be revealed. The key parameters influencing the carbonation efficiency, and the formation mechanism of the microstructure of the carbonated porous steel slag aggregates will be clarified, based on which the principle for microstructure adjustment will be proposed. The influence of carbonated steel slag aggregates with porous core, strengthened shell and activated surface on the performance of concrete as well as its microstructure will be investigated. The key characteristic parameters of the steel slag influencing the performance of concrete will be revealed. Furthermore, the intrinsic relationship between the microstructure and performance of concrete will be uncovered. Eventually the relevant mechanism of the carbonated core-shell porous steel slag aggregates improving the performance of concrete will be clarified. This study will provide theoretical guidance and technical support for producing high quality functional aggregates and preparing high performance concrete by recycling the steel slag environmentally.

钢渣低水化胶凝性及安定性不良是制约其在水泥基材料中应用的关键问题。利用骨料特性和优化界面结构是制备高性能混凝土的重要手段。本项目以钢渣为主要原料，探索利用其与生物炭和铝硅材料多组分复合、颗粒级配优化和加速碳化等技术设计制备结构梯度化、壳层强化和表面活化的核壳结构碳化钢渣多孔骨料。研究钢渣骨料的材料组成、碳化条件等对其特性的影响规律，探究加速碳化下核壳结构碳化钢渣多孔骨料微结构的演变规律，阐明骨料组成、微结构与其特性的内在关系，掌握影响碳化反应效率的关键因素，揭示碳化钢渣多孔骨料微结构的形成机制及调控原理。研究内核多孔、壳层增强、表面活化的核壳结构碳化钢渣骨料对混凝土性能和微结构的影响，阐明骨料影响混凝土微结构的关键特性参数，探究碳化钢渣骨料混凝土性能和微结构的本质关系，揭示碳化钢渣多孔骨料提升混凝土性能的作用机制。研究可为资源化环保利用钢渣制备功能骨料及高性能混凝土提供理论指导和技术支持。

钢渣低水化胶凝性及安定性不良是制约其在水泥基材料中应用的关键问题。本项目以钢渣为主要原料，辅以粉煤灰、生物碳和水泥等材料，设计并通过加速碳化制备出内核多孔、壳层强化和表面活化的核壳结构碳化钢渣多孔骨料。系统研究了钢渣骨料的材料组成、碳化条件等对其强度、表观密度、吸水性等性能的影响规律，探究加速碳化下核壳结构碳化钢渣多孔骨料微结构的演变规律。研究表明，CO2浓度、压力、骨料配比等因素均对钢渣碳化效率及骨料性能有影响，但是，钢渣矿相中钙离子析出和CO2传输供给是影响钢渣骨料碳化效率的本质原因。据此，研究通过掺入EDTA和生物碳两种途径来强化钢渣骨料的碳化，使得钢渣骨料吸碳率增加，密度增大，力学强度提高。EDTA在钢渣碳化中起到催化剂的作用，溶出的Ca2+ 与EDTA络合，从而促进钙析出，增加了钙溶出量，促进钢渣碳化。生物碳则通过在人工骨料内部提供了众多的CO2储罐，从而从钢渣内部提供CO2养护，增强传输，强化钢渣碳化。碳化消纳了钢渣中的大部分游离CaO，使得钢渣骨料体积安定，压蒸安定性合格；碳酸钙、无定型SiO2是钢渣人工骨料的主要碳化产物，碳化形成的碳酸钙相互胶结，使基质致密，产生较高力学强度；同时碳酸钙、无定型SiO2均能参与后续水化，形成单碳铝酸钙和CSH凝胶，不仅增强骨料自身基体，还强化了混凝土中骨料界面，这是掺碳化钢渣骨料混凝土强度提升的根本原因。研究发现经生物碳内养护增强的钢渣人工骨料对混凝土28天抗压强度最高可提高9.1MPa。此外，由于碳化钢渣的多孔结构，使其具有内养护功能，减缓混凝土内部相对湿度的降低，从而显著减少混凝土自收缩，甚至产生微膨胀，这有利于减少混凝土开裂提高耐久性。为避免钢渣大掺量可能带入六价铬超标的问题，研究制备了可吸附六价铬的镁铝水滑石负载材料，用于碳化钢渣人工骨料壳层，使其功能化，有助于拓展碳化人工骨料的应用。综上所述，本项目研究为资源化环保利用钢渣制备功能骨料及提高混凝土性能提供理论指导和技术支持。