Understanding the tensile strength and failure mechanism of rock–cement interfacial transition zone (ITZ) is of vital significance to the sealing integrity of cement sheath under downhole condition. Taking advantage of multiple techniques, i.e., digital image correlation (DIC), nano-indentation, XRD-Rietveld analysis, 29Si MAS solid NMR, and SEM-EDX, this study is devoted to investigating the impacts of curing temperature, rock type, and the addition of nano-silica (NS), on the tensile strength and failure mechanism of rock–cement sample. The experimental results show that both the curing temperature and the addition of NS leads to the formation of more C-S-H, which densifies the ITZ microstructure and responsible for high tensile strength of rock–cement samples; the tensile strengths of shale-cement samples are consistently higher than those of sandstone-cement sample; the crack velocities for rock–cement samples under three-point bending tests are approximately 1 mm/s, the crack velocities for rock–cement samples are slowed down when the NS is incorporated in cement paste, but they are independent on the rock type and curing temperature.

中文翻译：

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岩石-水泥试样的拉伸强度及破坏机理：固化温度、纳米二氧化硅和岩石类型的作用


了解岩-水泥界面过渡区 （ITZ） 的抗拉强度和破坏机理对于井下水泥护套的密封完整性具有重要意义。本研究利用数字图像相关 （DIC）、纳米压痕、XRD-Rietveld 分析、29Si MAS 固体 NMR 和 SEM-EDX 等多种技术，研究了固化温度、岩石类型和纳米二氧化硅 （NS） 添加量对岩石-水泥样品拉伸强度和破坏机制的影响。实验结果表明，养护温度和 NS 的添加都会导致形成更多的 CS-H，从而致密化 ITZ 微观结构并导致岩石-水泥样品的高抗拉强度;页岩水泥样品的抗拉强度始终高于砂岩水泥样品;在三点弯曲试验下，岩石-水泥样品的裂纹速度约为 1 mm/s，当 NS 掺入水泥浆中时，岩石-水泥样品的裂纹速度会减慢，但它们与岩石类型和固化温度无关。