再生块体混凝土及其部分预制组合柱的力学性能深化研究

Since the applicant put forward the idea of reusing demolished concrete lumps (DCLs) with distinctly larger size than traditional recycled aggregates in structural members, domestic and overseas scholars have made a lot of achievements in related fields. However, the results are mainly for a specific situation (i.e., the size of DCLs employed in the same specimen or the same structural member fluctuates only in a small range, and the shape of DCLs is generally regular). Obviously, the specific situation is very different from the one-time crushing products of waste concrete with various sizes and shapes. Meanwhile, the site construction efficiency of the columns containing DCLs is low. In this project, through compression, tensile-splitting, and direct-shear tests of the compound concrete made of DCLs and fresh concrete, the influence of inhomogeneity of the lump’s size and shape on mechanical properties of the compound concrete will be revealed and quantitatively determined, and the prediction formulas of combined strengths of the compound concrete with inhomogeneous lump size and lump shape will be proposed, meanwhile failure process and key positions of the compound concrete will be observed by DIC and nanoindentation techniques to explain the mechanical mechanisms. On the other hand, the effects of main parameters on shear bearing capacity of the steel tubes filled with precast compound concrete segments and cast-in-situ concrete will be experimentally studied, and the theoretical models and prediction methods of such columns’ axial load bearing capacity and shear bearing capacity will be established. The expected results can significantly improve the utilization of the one-time crushing products of waste concrete, remarkably enhance the site construction efficiency of the columns containing DCLs, and contribute to the development of circular economy.

申请人提出大尺度废旧混凝土块体循环利用思想以来，境内外学者在相关领域取得了丰富研究成果。但既有成果主要是针对特定情况（即同一试件/构件所采用块体的大小只在较小范围内波动且块体形状大多较规整）取得的，这与废旧混凝土一次性破碎产物的形状和大小千差万别的实际情况差异较大，同时采用块体的柱式构件的现场施工效率偏低。本项目通过再生块体混凝土的受压/劈拉/直剪试验，并采用DIC和纳米压痕技术对其破坏过程和关键部位进行观测，科学揭示并定量把握块体大小和形状的不均匀性对再生块体混凝土力学性能的影响并解释其机理，综合构建块体不均匀情况下该类混凝土的组合强度预测公式。提出部分预制钢管再生块体混凝土柱，试验揭示其受剪承载力定量变化规律，结合前期工作推导该类柱的轴压和受剪承载力理论模型，建立相应预测方法。预期成果可显著提升废混凝土一次性破碎产物的利用率，突破柱式构件现场施工效率偏低的局限，为循环经济发展做出贡献。

定义了再生块体的尺寸参数和形状系数，建议了3类块体的形状系数取值范围。揭示了块体形状及大小对再生块体混凝土受压、弯折和直剪性能的影响，发现：块体大小不变时，采用扁平块体试件的抗压强度比采用类球或细长块体试件偏低约10%，含扁平、类球、细长块体试件的抗折强度依次降低且差异随块体大小增加而增大，采用扁平或细长块体试件的直剪强度比采用类球块体试件偏高约10%；块体形状不变时，再生块体混凝土的抗折强度随块体大小增加有所降低，但降幅不超过15%，试件断裂过程所耗能量呈现出与抗折强度类似的变化规律；不同形状和大小块体同时混用对再生块体混凝土的受压、弯折和直剪性能总体上影响有限；所提抗折强度预测公式以及抗折与抗压强度之间的定量关系具有较好精度。采用SEM、DIC和纳米压痕技术，就块体形状及大小对再生块体混凝土不同受力性能的影响机理做了初步分析，发现：不同大小扁平块体与新混凝土的界面过渡区均存在微裂缝，而类球和细长块体与新混凝土的界面过渡区未出现类似情况；无论类球、细长还是扁平块体，块体上方和下方界面过渡区的微观结构无明显差异，呈现出与采用天然石块时明显不同的现象。发明了部分预制钢管再生块体混凝土柱，揭示了主要因素对其轴压、偏压、受剪和抗震性能的影响，发现：偏压作用下钢管对受压区混凝土的约束效应具有明显空间分布特征；偏心方向、剪切路径、水平力方向及后浇混凝土隔离带位置分别对该类柱的偏压、受剪和抗震性能影响有限，这为该类柱设计和施工的大大简化奠定了坚实基础。针对不同受力情况所建立的预测方法，可分别较好地预测等效套箍系数小于 0.6 时该类柱的轴压承载力、剪跨比不大于0.5时该类柱的受剪承载力、等效套箍系数小于0.6且长细比小于50时该类柱的M-N关系曲线，以及该类柱的等效塑性铰区长度。上述成果为提高废混凝土一次性破碎产物的利用率，以及突破再生块体混凝土柱现场施工效率偏低的困境做出了贡献。