Applying interface binder is a common method to enhance the bonding performance between new and old concrete. Traditional cement mortar interface binders face issues such as inadequate bonding strength and poor crack resistance, which may limit their effectiveness in practical applications. Hence, in this study, the effects of the water-binder ratio, sand-binder ratio, and NMK dosage of the interface binder on the bonding performance between new and substrate concrete were investigated using orthogonal experimental methods. The bonding strength of the new-old concrete after the application of these binders were evaluated through splitting tensile tests. The optimal mix proportion of NMK binder were determined through range analysis. Furthermore, the failure process and damage behavior of the new and substrate concrete were analyzed using acoustic emission(AE) and digital image correlation(DIC) methods. The effects of the NMK binder on the hydration products and microstructure at the new-old concrete interface were examined through microstructural testing methods. The results indicate that the application of the NMK binder improves the bond strength between substrate and new concrete by 19 %–98.2 %, compared to new-old concrete without an binder(A1). The incorporation of 5 % NMK in mortar binder enhances the cracking load and splitting tensile strength of composite specimens by 25.6 % and 14.0 %, respectively, compared to ordinary mortar binder. When the w/b ratio is 0.25, the s/b ratio is 1.5, and the NMK content is 5 %, the composite specimen (W1A3N3) exhibits the highest initial crack and splitting tensile strengths at the interface, reaching 93.39 kN and 3.38 MPa, respectively. Additionally, the NMK binder enhances the overall integrity of the bond specimens. At the Pmax, the maximum principal strain of W1A3N3 increased by 38.5 % compared to A1, and the b-value change increasing by 7.2 %. The NMK interface binder also shifts the failure mode from interface debonding to a composite failure mode. The AE peak frequency results indicate that the proportion of interface debonding signals in W1A3N3 is 58.2 % lower than in A1. Microstructural tests show that the W1A3N3 specimens exhibit a higher amount of hydration products and a denser microstructure, which enhance the bond performance between the old and new concrete.This research provide novel insights into the application of nanomaterials in strengthening and repair projects. Additionally, applying NMK interface binder to improve the bond strength between new and old concrete contributes to improving the efficiency and quality of repair and strengthening of existing concrete structures.

中文翻译：

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纳米偏高岭土改性水泥砂浆粘结剂对新旧混凝土粘结性能及破坏行为的影响


应用界面粘结剂是提高新旧混凝土之间粘结性能的常用方法。传统的水泥砂浆界面粘结剂存在粘结强度不足、抗裂性差等问题，这可能会限制其在实际应用中的有效性。因此，本研究采用正交试验方法研究了界面粘结剂的水与粘结剂比、砂与粘结剂比和 NMK 掺量对新混凝土与基材混凝土之间粘结性能的影响。通过劈裂拉伸试验评估了使用这些粘合剂后新旧混凝土的粘合强度。通过范围分析确定 NMK 粘合剂的最佳混合比例。此外，采用声发射 （AE） 和数字图像相关 （DIC） 方法分析了新型混凝土和基体混凝土的破坏过程和损伤行为。通过微观结构测试方法研究了 NMK 粘合剂对新旧混凝土界面处水化产物和微观结构的影响。结果表明，与无粘结剂的新旧混凝土 （A1） 相比，使用 NMK 粘结剂可将基材与新混凝土之间的粘结强度提高 19 %–98.2 %。与普通砂浆粘合剂相比，在砂浆粘合剂中加入 5% NMK 可将复合试样的开裂载荷和劈裂拉伸强度分别提高 25.6 % 和 14.0 %。当 w/b 比为 0.25、s/b 比为 1.5、NMK 含量为 5 % 时，复合试件 （W1A3N3） 在界面处表现出最高的初始裂纹和劈裂拉伸强度，分别达到 93.39 kN 和 3.38 MPa。此外，NMK 粘合剂增强了粘合试样的整体完整性。 在 Pmax 处，W1A3N3 的最大主应变比 A1 增加了 38.5 %，b 值变化增加了 7.2 %。NMK 界面粘合剂还将失效模式从界面剥离转变为复合失效模式。AE 峰值频率结果表明，W1A3N3 中界面解粘信号的比例比 A1 低 58.2 %。微观结构测试表明，W1A3N3 试样表现出更多的水化产物和更致密的微观结构，这增强了新旧混凝土之间的粘合性能。这项研究为纳米材料在强化和修复项目中的应用提供了新的见解。此外，使用 NMK 界面粘合剂来提高新旧混凝土之间的粘合强度有助于提高现有混凝土结构的修复和加固的效率和质量。