实验技术与管理

在我国建筑垃圾年产量激增、资源化利用率较低的背景下，工程渣土的高效利用成为实现“无废城市”及“双碳”目标的关键挑战。该文提出了一种建筑渣土基骨料工程水泥基复合材料，通过“渣土浆预混—分层包裹—后掺PVA纤维”的渣土基ECC材料的全造壳工艺，系统探究了不同渣土掺量（5%～20%）分别替代水泥和细骨料对该复合材料工作性能和力学性能的影响，并借助SEM观测微观结构，揭示了渣土微集料填充孔隙的作用机理。结果表明：(1)新型全造壳工艺下，通过预混渣土浆拌合物可形成“渣土-水泥-水泥渣土”三层包裹层结构的过渡层，纤维后掺的方式可有效缓解基体流动性不足；(2)磨细渣土替代水泥时，其高吸水性导致坍落度线性下降，渣土掺量为20%时坍落度降幅达94%,28 d抗压强度较基准组降低26.69%；(3)磨细渣土替代细骨料时，坍落度呈先降后升趋势，当掺量为10%时，坍落度下降率为84.3%，适量渣土掺入对材料的后期力学性能影响较小；(4)SEM分析表明，随着渣土掺量的增加，磨细渣土颗粒的高比表面积和惰性特性会加剧基体松散化程度。建议调控全造壳工艺中的渣土颗粒级配，构建“主骨架（粗颗粒）-过渡层（中颗粒）-填充相（细颗粒）”的三级分布模式，实现粗颗粒骨架支撑与细颗粒密实填充，从而形成致密的微观结构。

[Objective] Accelerating urbanization in China has considerably increased the annual construction waste production, accounting for over 70% of total municipal solid waste. However, the current resource utilization rate of construction waste is only 10%–20% in China, considerably lower than that in developed countries. Storage and backfilling are currently the main disposal methods for construction waste. At present, landfilling remains a commonly used method for managing construction waste. Large-scale landfilling poses an environmental threat and consumes land resources. Therefore, the efficient utilization of construction waste debris has become a critical challenge for achieving the “zero-waste city” and “dual carbon” goals. Herein, the application potential of a novel construction waste debris–based aggregate engineered cementitious composite(ECC) in building materials was explored. [Methods] Construction waste debris from a Beijing construction site was used. It was pretreated via sun-drying, oven-drying, crushing, and ball milling. Nine specimen groups(Z1–Z9) were created. The benchmark group(Z1) used ECC with a 28-day compressive strength of 50 MPa. During comparative tests, the equivalent masses of either cement(Z2–Z5) or fine aggregate(Z6–Z9) were replaced with different amounts of waste debris(5%, 10%, 15%, and 20%). Each group contained nine specimens, totaling 81 cubic specimens with dimensions of 100 mm × 100 mm × 100 mm. The effects of different waste debris incorporation rates and substitution components on the workability(slump) and mechanical properties(3-, 7-, and 28-day compressive strengths) of ECC were analyzed. A full shell-forming process was employed for specimen casting, which involved pre-mixing waste debris slurry, layered encapsulation, and the addition of PVA fibers to obtain a compact three-layered waste debris–cement–cement and waste debris encapsulation structure with enhanced mechanical performance. The underlying mechanisms of the fabricate a waste debris-based aggregate ECC were observed via Scanning Electron Microscope(SEM), and the filling effect of waste debris particles and their impact on the pore structure of the ECC were analyzed. [Results] Results showed that the full shell-forming process and added fibers effectively mitigated fluidity loss from the mixture. When the cement was replaced with the finely ground construction waste debris, the slump decreased due to its high water absorption rate. At a 20% incorporation rate of debris, the slump decreased by 94%, and the 28-day compressive strength decreased by 26.69% compared with Z1. When the fine aggregate was replaced with finely ground waste soil, the slump first decreased and then increased. When 10% of fine aggregate was added, the slump decreased by 84.3%. In addition, the replacement of 5%–15% fine aggregate with waste debris had a negligible impact on the 28-day compressive strength(≤11.96%). A comparison of using fine aggregate and cement as substitutions revealed that the former increased the compressive strength consistently at the same incorporation rate. SEM revealed that the addition of construction waste debris with a single fine particle size caused matrix loosening and reduced interfacial bonding capability. As the construction waste debris replacement ratio increased, the high specific surface area and low reactivity(chemical inertness) of the debris particles deteriorated the loosening effect and ultimately the interfacial transition zone(ITZ). Consequently, microcracks propagated, and the bonding force of the C-S-H gel weakened. In summary, the incorporation of construction waste debris considerably influenced the microstructure of the material. [Conclusions] These findings indicated that uniform particle size and insufficient gradation of the waste debris particles were critical constraints that hindered the realization of higher incorporation rates and performance improvement. In the future, the incorporation limit of construction waste debris can be overcome via material–process synergy, which involves optimizing particle gradation under the full shell-forming process to establish a three-level distribution: main skeleton(coarse particles)–transition layer(medium particles)–filling phase(fine particles). Thus, a coarse particle skeleton support and fine particle dense filling can be achieved for forming a compact microstructure. The workability and mechanical performance of construction waste debris–based aggregate ECC can be synergistically improved by dynamically adjusting the water–cement ratio and fiber content in the concrete mixture.