Abstract

Recycled concrete aggregate (RCA) obtained from construction and demolition waste has been widely studied for its feasible uses to replace natural aggregate in different types of concrete products. For the past few decades, efforts have been made to modify or/and improve conventional mixing approaches for the use of RCA in concrete, such as two-stage mixing approach, paste wrapped recycled aggregate approach, etc. However, there was no direct comparison between these approaches. Therefore, this paper investigates the synergistic effect of pre-carbonated slurry and concrete mixing sequence on the performance of self-compacting modified mortar (SMM) containing RCA and aims to compare with other four mixing approaches. Fresh properties and mechanical strengths of SMM and the characterization of interfacial transition zone were studied and compared. Results proved that a denser matrix and an interfacial transition zone (ITZ) with a better quality reflected a better mechanical performance. Among five mixing approaches, SMM samples produced by pre-carbonation approach had slightly larger drying shrinkage, but exhibited enhanced flowability and reduced permeable voids. The compressive strength and flexural strength increased by about 12.3% and 12.0% compared to those made by normal mixing sequence. Backscattered electrons (BSE) images and Vickers microhardness results also revealed a denser interface between new cement matrix and RCA for the sample prepared with pre-carbonation approach.

Graphic Abstract

中文翻译：

---

预碳酸化淤浆和混合顺序对自密实再生骨料改性砂浆性能的协同作用

摘要

从建筑废料和拆除废料获得的再生混凝土骨料（RCA）已被广泛研究，因为它可用于替代不同类型混凝土产品中的天然骨料。在过去的几十年中，已经做出了努力来修改或/和改进在混凝土中使用RCA的常规混合方法，例如两阶段混合方法，糊状包裹的再生骨料方法等。但是，没有直接比较在这些方法之间。因此，本文研究了预碳化泥浆和混凝土搅拌顺序对含RCA的自密实改性砂浆（SMM）性能的协同作用，旨在与其他四种搅拌方法进行比较。研究并比较了SMM的新鲜性能和机械强度以及界面过渡区的特性。结果证明，密度较高的基体和质量更好的界面过渡区（ITZ）反映了较好的机械性能。在五种混合方法中，通过预碳酸化方法生产的SMM样品的干燥收缩率稍大，但显示出增强的流动性和减少的可渗透空隙。与常规混合顺序相比，抗压强度和抗弯强度分别提高了约12.3％和12.0％。背散射电子（BSE）图像和维氏显微硬度结果还显示，采用预碳酸化方法制备的样品，新水泥基体与RCA之间的界面更密。通过预碳酸化方法生产的SMM样品的干燥收缩率稍大，但显示出增强的流动性和减少的可渗透空隙。与常规混合顺序相比，抗压强度和抗弯强度分别提高了约12.3％和12.0％。背散射电子（BSE）图像和维氏显微硬度结果还显示，采用预碳酸化方法制备的样品，新水泥基体与RCA之间的界面更密。通过预碳酸化方法生产的SMM样品的干燥收缩率稍大，但显示出增强的流动性和减少的可渗透空隙。与常规混合顺序相比，抗压强度和抗弯强度分别提高了约12.3％和12.0％。背散射电子（BSE）图像和维氏显微硬度结果还显示，采用预碳酸化方法制备的样品，新水泥基体与RCA之间的界面更密。

图形摘要