含白云石碳酸盐岩在水泥混凝土中高效和安全应用基础研究

To meet the urgent needs for cement with low embodied carbon and concrete with optimized durability, based on the "duplex effects" of dedolimitization reaction in cement and concrete, i.e. both positive and negative effects may occur depending on the sizes of dolomite-bearing particles which is related to the limitation spaces of the reaction, a new approach trying to turn harmful effect into beneficial effect is put forward for developing dolomite powders as supplimentary cementitious materials (SCMs) and safe application of harmful alkali carbonate reactive rocks. In reference for the experiences in the application of limestone powders and the studies on alkali-carbonate reaction (ACR), as well as the distinct difference of calcite and dolimite in their alkali reactivities, the key scientific problem for the project, the effects, mechanisms and their affecting factors of dedomitization of dolomite with different rock particle sizes, is proposed. The key problem will be elucidated by combining the macro performance study with microstructural examinations. Comparative study on the effect of dolomite powders and aggregates with various fineness and reactivity levels on the strength, dimensional stability and corrosion resistence of dolomite-bearing cement and concrete will be carried out, following with the compositional and microstructural evolution examination by advanced characterization techniques, such as electron microscopy, x ray diffraction, thermal analysis, etc. The following results are expected. The differences between dolomite powders and aggregates in their dedolomitizations in cement and concrete, including the process, mechanism, effect and their controlling factors, etc. will be clearified. The combination effects and coupling mechanism between dolomite powders and SCMs with reactive aluminates constituents will be elucidated. New technique approaches for suppressing harmful ACR and for developing high performance dolomite-bearing SCMs with reactive carbonate rocks will be proposed.

针对水泥低碳和混凝土高耐久性需求，以及去白云石化反应在水泥混凝土中的"双关"效应，提出"化弊为利"开发白云石微粉辅助性胶凝材料（SCMs）和安全使用碱碳酸盐活性集料的新思路。基于白云石与方解石化学活性的显著差异、石灰石粉及碱碳酸盐反应（ACR）的研究和应用经验，围绕"不同细度含白云石碳酸岩的去白云石化反应效应、机理及其影响因素"这一核心问题，采用力学、变形、耐蚀等宏观性能研究与电子显微分析、X射线衍射、热分析等组成和微结构表征技术相结合，分别对比研究从微粉到集料不同细度和不同活性的白云石在水泥与混凝土中的物理、化学行为，以及反应程度、产物组成和结构演变规律。以期阐明：白云石微粉和集料在水泥基材料中去白云石化反应过程、效应、机制及其影响因素的差异；白云石微粉与其它含活性铝质SCMs的复合效应及耦合机制；提出有害ACR的抑制措施及利用活性ACR岩石制备高性能复合SCMs的技术途径。

项目围绕开发低碳波特兰白云石水泥的关键科学问题，采用宏观性能研究与组成和微结构表征相结合，以石灰石微粉为参照，研究了不同细度白云石微粉在水泥基材料中的物理、化学行为，以及反应程度、产物组成和结构演变规律。主要研究内容包括：（1）波特兰-白云石水泥早期物化学性能；（2）不同养护条件下的强度、产物组成和微结构演化规律；（3）体积稳定性及其机理；（4）白云石与偏高岭土的复合效应及耦合机制（5）抗硫酸盐侵蚀性能。.主要进展如下：（1）白云石微粉与石灰石微粉类似，可以改善水泥浆体的流动度，减少泌水。不同之处在于白云石微粉具有明显的缓凝和降低早强效应，其根源在于白云石表面荷更多负电荷且减小体系堆积密度。（2）白云石和石灰石微粉对水泥砂浆强度的影响与掺量、养护条件和龄期密切相关，决定于两者的物理和化学效应差异。高掺量、长龄期以及提高细度和养护温度，均利于白云石化学效应发挥，从而呈现优于石灰石对强度的效应。（3）与传统块体岩石中去白云石化反应可能引起水泥基材料有害膨胀不同，白云石微粉优先与浆体中的铝质组分反应生成碳铝酸钙或水滑石，在体系铝相不足时才生成膨胀性水镁石。白云石微粉在浆体中的化学反应对水泥强度和体积稳定不仅无害，反而促进砂浆强度发展和浆体微膨胀效应。（4）白云石微粉与偏高岭土优化复合可显著强化碳铝酸盐形成效应，提高砂浆后期强度。（5）碳酸盐微粉掺量大于10%时，水泥的抗硫酸盐侵蚀性能劣化，但同比条件下含白云石微粉砂浆的抗硫酸盐侵蚀性能明显优于石灰石微粉体系。.项目完成原计划研究内容。成果的科学意义在于证实了白云石微粉反应不会引起水泥基材料体积稳定性问题，不仅为白云石微粉在水泥混凝土中的安全应用提供了实验和理论依据；同时，对阐明传统碱碳酸盐反应具有启示意义。应用价值在于提出了基于白云石的活性效应开发低碳水泥体系的新途径。