在国家重大战略决策“双碳”的背景下，水泥基材料的绿色低碳化和建筑垃圾的资源化已成为行业发展的必然趋势。本研究采用热活化方法以恢复废弃水泥基材料的再水化能力，从而制备低碳再生水泥。本文系统地研究了不同热活化温度下常见矿物掺和料复合水泥硬化浆体中水化产物的数量、微观结构及物相变化规律，探究了再生水泥再水化的动力学过程、微观结构的演变以及力学性能发展规律，探明了不同前驱体的最优热活化温度及再水化机理。针对再生水泥需水量大、凝结时间短以及抗压强度较差等缺点，利用碳化养护增强了不同热活化温度下常见复合再生水泥浆体的强度，并研究了增强规律和机理。利用磷石膏矿渣改性了再生水泥复合胶凝材料体系性能，研究了磷石膏矿渣组分构成对复合胶凝材料新拌性能、水化历程、产物特征、硬化浆体微观结构和力学性能的影响规律及作用机理。论文的主要结论如下：（1）前驱体为基准水泥、硅灰或石灰石复合水泥的最佳热活化温度约为750°C，前驱体为粉煤灰或矿渣复合水泥的最佳热活化温度约为650°C，再生水泥的高需水量、速凝以及早期高放热速率与脱水无定形C(-A)-S-H的高比表面积以及热活化烧结时晶体结晶缺陷有关。（2）再生水泥再水化形成了以致密的，纤维状，蜂窝状或扫帚状C(-A)-S-H凝胶在内，钙矾石、单碳铝酸钙、半碳铝酸钙、Ca(OH)2等晶体在外的双层结构。水化晶体产物在双层结构中起搭接作用，其中AFm相较于AFt可以发挥更好的搭接效果，在内部水化产物之间提供更强的连接，提供优异的力学性能。（3）相较于基准水泥浆体，再生复合水泥浆体中含有更多的贝利特和更高的初始孔隙率，为CO2养护增强提供了更多的反应物和更好的反应条件。CO2养护对凝胶孔和小毛细孔的填充是碳化养护再生复合水泥浆体强度增长的最关键原因。（4）磷石膏矿渣协同作用可以改性增强再生水泥。再生水泥中的CaO快速反应，体系迅速达到高碱性，促进矿渣的分散和溶解，从而形成C(-A)-S-H凝胶和莱粒硅钙石Ca5(SiO4)2(OH)2，磷石膏中的CaSO4·2H2O对矿渣中的活性Al2O3起到激发作用，生成钙钒石，其形态由细针状变为短柱状，起到搭接凝胶的作用，从而有效提高改性再生水泥的强度。
Under the background of achieving dual carbon goals, the green and low-carbon development of cementitious materials and the utilization of construction and demolition waste have become an inevitable trend. This study adopted the thermal activation technique to revive the hydration ability of waste cementitious materials for the purpose of preparing low-carbon recycled cement. In this study, the amount, microstructure, and phase changes of hydration products in hardened SCMs blended cement pastes at different thermal activation temperatures were systematically studied. The kinetic process, microstructure evolution, and mechanical property development during the rehydration process of recycled cement, as well as the optimal thermal activation temperature and the corresponding rehydration mechanism of different precursors were also investigated. To deal with the drawbacks including high water demand, rapid setting, and poor compressive strength of recycled cement, the CO2 curing method was used to enhance the strength of recycled SCMs blended cement pastes at different thermal activation temperatures, and the strengthen mechanism was studied. The performance of recycled cement was modified using phosphogypsum (PG) and granulated blast furnace slag (GGBS), and the influence of the composition of PG and GGBS on the fresh performance, hydration process, product characteristics, microstructure and mechanical properties of the modified blended cementitious material with its mechanism were studied.The conclusions drawn from the study include:(1) The optimal thermal activation temperature for recycling reference cement and blended cement with silica fume or limestone as the precursor is about 750 °C, while the optimal thermal activation temperature for blended cement with fly ash or GGBS as the precursor is about 650 °C. The high water demand, rapid setting, and early high rehydration heat of recycled cement are related to the large specific surface area of dehydrated amorphous C(-A)-S-H and crystal crystallization defects during thermal activation sintering.(2) During the rehydration of the recycled cement, the double-layer structure, composing of a dense, fibrous, honeycomb or broom shaped C(-A)-S-H gel phases inside, with ettringite, monocarboaluminate, hemicarboaluminate, Ca(OH)2 and other crystals outside is formed. Hydrated crystal products play an overlapping role in the double-layer structure, and AFm can achieve better overlapping effect compared to AFt, providing stronger connections between internal hydration products and excellent mechanical properties.(3) Compared to the reference cement paste, the recycled blended cement paste contains more belite and more initial pores, providing more reactants and better reaction conditions for CO2 curing. The filling of gel pores and small capillary pores by CO2 curing is the key reason for the strength growth of CO2 curing recycled blended cement paste.(4) The synergistic effect of PG and GGBS can improve the modified recycled cement. The CaO in the recycled cement reacts quickly, leading to the system quickly reaching high alkalinity, promoting the dispersion and dissolution of GGBS, thus forming C(-A)-S-H gel and Ca5(SiO4)2(OH)2. Gypsum (CaSO4·2H2O) in PG plays an excitation role on the active Al2O3 in the GGBS, resulting in the formation of AFt. The shape of AFt changes from fine needle to short column, playing the role of overlapping gel, thus effectively improving the strength of modified recycled cement.
