用MgO膨胀剂配制的补偿收缩混凝土的性能调控及预测

At present, MgO expansive agent is mainly applied to compensate temperature shrinkage in hydraulic massive concrete, but it is seldom used in industrial and civil buildings. The poor soundness caused by delayed expansion and the difficulty of quantitative prediction of expansion are the key problems affecting its wide application. Research on the hydration reaction of composite cementitious material with MgO expansive agent will be carried out firstly, and its hydration kinetics will be determined. The influence of the size, morphology and formation position of magnesium hydroxide crystal on the pore expansion will be studied, and the theory of pore expansion due to crystallization will be put forward, and the expansion mechanism of MgO shrinkage-compensating concrete will be revealed. The factors that affect the limit expansion rate will be investigated, and the empirical formula for limiting expansion rate will be established. The behavior of different active MgO expansive agents in shrinkage-compensating concrete cured in different conditions and with different strength will be investigated, and the expansion process model will be established. The evolution rule of mechanical properties and anti-permeability performance of MgO shrinkage-compensating concrete will be studied, and the empirical calculation model of porosity, limit expansion rate and mechanical properties will be established. The quantitative prediction and safety control of expanion process and macroscopic properties of shrinkage-compensating concrete mixed with MgO expansive agent will be realized. And the application of MgO expansive agent in the industrial and civil construction industry will be promoted greatly.

目前MgO膨胀剂主要应用于水工大体积混凝土中补偿温度收缩，很少在工业与民用建筑上使用，其延迟膨胀可能会带来的安定性问题和膨胀难以定量预测是影响其广泛应用的关键问题。本课题将开展掺MgO膨胀剂复合胶凝材料的水化反应研究，确定其水化动力学；研究氢氧化镁结晶大小、形貌、生成位置等对硬化浆体孔隙扩展的影响规律，提出结晶孔隙扩展理论，揭示MgO补偿收缩混凝土的膨胀机理；研究极限膨胀率的影响因素，建立极限膨胀率经验计算公式；研究不同活性MgO膨胀剂在不同强度等级、不同养护条件下补偿收缩混凝土中的表现，建立膨胀过程模型；研究MgO补偿收缩混凝土的力学性能和耐久性的演变规律，建立孔隙率、极限膨胀率与力学性能之间的经验计算模型。本课题研究成果将实现对MgO补偿收缩混凝土膨胀过程和宏观性能的预测和安全调控，对于推广MgO膨胀剂在工民建行业中应用具有重要意义。

使用膨胀剂配制补偿收缩混凝土，是常用的混凝土开裂控制措施。MgO膨胀剂延迟膨胀可能会带来的安定性问题和膨胀难以定量预测是影响其广泛应用的关键问题。本项目系统开展MgO补偿收缩复合胶凝体系的水化硬化过程、膨胀性能、力学性能和耐久性能研究，以期实现补偿收缩混凝土的性能调控及预测。本项目还探索了活性MgO作碱激发剂制备胶凝材料的可行性。研究结果表明，工业化生产的三种活性MgO膨胀剂颗粒粒径分布大体一致，与基准水泥类似，S型粒径略小，但其颗粒表面存在大量微孔，活性越高，越疏松多孔，比表面积越大，堆积密度越小，这会降低混凝土流动性，导致坍损增大，减水剂用量增大；可用堆积密度快速判断其活性类型，方便快捷。MgO膨胀剂水化活性不如水泥，用Krstulovic-Dabic模型较好地模拟了水泥-粉煤灰-MgO补偿收缩复合胶凝体系的水化过程，确定了其水化动力学参数；MgO膨胀剂掺量越大，早期NG和I过程表观活化能增大，但D过程和复合胶凝材料的整体表观活化能减小。MgO膨胀剂活性主要影响膨胀速率和达到膨胀稳定期的时间，活性越大，膨胀速率越快，稳定期越短，极限膨胀率越小；掺量主要影响极限膨胀率大小。MgO膨胀剂的安定掺量按净浆、砂浆、混凝土依次递增，压蒸实验方法可简化。生长在MgO颗粒表面或水化产物表面的Mg(OH)2晶体是主要膨胀源，晶体相互交叠形成支架状的晶体团簇，扩张孔隙，进而产生膨胀，这会导致硬化浆体总孔隙率增大，主要增大10～100nm孔隙；生长在孔隙中的Mg(OH)2对膨胀无益。掺加MgO膨胀剂，可补偿碳化收缩，提高抗氯离子渗透性。约束大小和约束方式对膨胀影响较大，膨胀与强度存在“对立与统一”的矛盾性，外在约束对膨胀的影响大于自身强度；可通过改变各方向的限制程度的相对关系来调整膨胀率，增加补偿收缩能力。研究结果在实际工程试验中得到了证实。本项目最终实现了对MgO补偿收缩混凝土膨胀过程和宏观性能的预测和安全调控，对于推广MgO膨胀剂在工业与民用建筑中应用具有重要意义。