废弃混凝土高效循环利用的基础理论与方法研究

The recycling use of waste concrete can not only reduce the solid wastes but also significantly reduce the consumption of nature resources, which is in line with the national sustainable development strategy. In order to increase the efficiency of waste concrete reusing, this project aims at both the modified recycling use of waste concrete at an aggregate-level and the direct recycling use of waste concrete at a large-scale block-level, focuses on the long-term performances of materials and structural components, and studies the basic theories and methods for the modified recycled aggregate concrete (MRAC) and MRAC beams/columns as well as the concrete mix made of large-scale demolished concrete blocks (DCBs) and fresh concrete (FC) and beams made of DCBs & FC. The main contents include: 1) raising a jointly modifying method for both the recycled coarse aggregate (RCA) and the interface between RCA and fresh cement mortar and revealing the modification mechanism, establishing the constitutive relationships and contraction/creep models of MRAC, and exploring the compression/bending fatigue behaviours and carbonation and chloride ion diffusion properties of MRAC; 2) studying the long-term development of MRAC beams & columns’ deformations, and revealing the fatigue damage evolution of these beams; and 3) proposing a nonlinear mechanical model and a size effect determination method for the concrete mix made of low-strength DCBs & high-strength FC, establishing a creep prediction model for the concrete mix made of DCBs & FC, exploring the compression/bending fatigue behaviours and freeze-thaw properties of the aforementioned concrete mix, and studying the fatigue performances of the beams made of DCBs & FC.

废弃混凝土循环利用可实现固体废弃物减排，还可明显降低天然资源消耗，符合可持续发展国家战略。针对其利用效率亟待提高的现状，本项目从废弃混凝土的骨料层次改性循环利用和大尺度块体层次直接循环利用两方面入手，聚焦材料和构件的长期行为，深入开展改性再生骨料混凝土及其梁/柱构件，以及直接采用大尺度废弃混凝土块体的再生混合混凝土及其梁式构件的基础理论与方法研究，包括：1）提出再生粗骨料及其与新水泥砂浆界面的联合优化改性方法并揭示改性机理，建立改性再生骨料混凝土的不同受力本构关系和收缩/徐变模型，探究其受压/弯折疲劳性能以及碳化和氯离子扩散性能；2）研究改性再生骨料混凝土梁/柱的变形长期发展规律，揭示梁的疲劳损伤演化过程；3）提出低强废弃混凝土块体与高强新混凝土的非线性混合受力模型及其尺寸效应确定方法，建立再生混合混凝土的徐变预测模型，探究其受压/弯折疲劳性能和冻融性能以及再生混合混凝土梁的疲劳特性。

揭示了再生骨料混凝土的CO2改性、纳米SiO2和粉煤灰复掺改性的机理，以及改性效果（抗压性能、抗折性能、劈拉性能）的参数影响规律。考察了不同参数对再生骨料混凝土受压、受剪、冲切的力−变形关系的影响，给出了受压全曲线表达式及冲切承载力公式；揭示了不同参数对钢筋−再生骨料混凝土粘结-滑移性能的影响，建立了粘结滑移本构模型。基于再生骨料混凝土的收缩徐变试验，建立了其徐变系数预测公式。疲劳试验表明，碳化改性和纳米改性后再生骨料混凝土的受压疲劳性能相比改性前有较大提升，疲劳寿命接近常规混凝土。明确了再生骨料取代率对再生骨料混凝土碳化深度及碳化后抗压强度的影响规律，改进了碳化深度预测模型；发现微观裂纹对再生骨料混凝土的离子扩散参数影响显著；揭示了纳米SiO2和粉煤灰复掺改性对提高再生骨料混凝土抗氯离子渗透性能和抗碳化性能的良好效果及其内在机理。通过足尺试验，探究了主要参数对再生骨料混凝土梁徐变行为的影响规律，提出了相应的预测公式以及挠度增大系数确定方法。考察了不同改性方法对再生骨料混凝土梁受弯疲劳性能的影响，发现改性后梁的疲劳寿命普遍增加，纳米SiO2改性后增幅明显。揭示了高强化再生块体混凝土的受压、直剪、劈拉行为及其尺寸效应，建议了其抗压性能、直剪强度和劈裂抗拉强度的预测方法。探究了再生块体取代率等参数对高强化再生块体混凝土和钢管高强化再生块体混凝土的徐变性能的影响规律，建议了相应的徐变预测方法。揭示了再生块体混凝土的受压和弯折疲劳性能及裂缝发展过程，发现在工程常见荷载比和再生块体取代率情况下，再生块体混凝土的疲劳寿命相比常规混凝土未呈现趋势性变化，提出了相应的疲劳寿命预测方法。考察了冻融循环对再生块体混凝土受压和劈拉性能的影响，建议了其冻融后抗压强度和劈裂抗拉强度的预测公式。通过钢筋再生块体混凝土梁的受弯疲劳试验，发现其疲劳变形和疲劳寿命总体上与常规混凝土梁基本相当。