It is well-known that supplementary cementitious materials (SCMs) and low water-to-binder (w/b) ratio increase autogenous shrinkage, but the impact on microcracking and long-term transport properties is less understood. This paper examines the effect of microcracking induced by autogenous shrinkage on transport properties of concretes cured up to ~3.6 years. Variables include SCM type (9% SF, 70% GGBS), w/b ratio (0.20–0.45), maximum-aggregate-size (MSA: 5–20 mm) and shrinkage reducing admixture (SRA). Oxygen diffusivity, permeability and water sorptivity were correlated with microcracks characterised using laser scanning confocal microscopy and 3D X-ray microtomography. Results show greater microcracking in mixes containing SCMs, low w/b ratio and large MSA. At the same w/b ratio and binder type, strong positive correlations are observed between transport and microcracking with increasing MSA, confirming the negative impact of autogenous shrinkage. SRA was effective in reducing these effects. The significance is compared with drying shrinkage and implications for durability are discussed.

众所周知，补充胶凝材料 (SCM) 和低水与粘合剂 (w/b) 比会增加自收缩，但对微裂纹和长期运输性能的影响却知之甚少。本文研究了自收缩引起的微裂纹对固化长达 3.6 年的混凝土运输性能的影响。变量包括 SCM 类型（9% SF、70% GGBS）、w/b 比（0.20–0.45）、最大骨料粒度（MSA：5–20 mm）和减缩外加剂 (SRA)。氧气扩散率、渗透率和吸水性与使用激光扫描共聚焦显微镜和 3D X 射线显微断层扫描表征的微裂纹相关。结果表明，在含有 SCM、低 w/b 比和大 MSA 的混合物中，微裂纹更大。在相同的水包比和粘合剂类型下，随着 MSA 的增加，在运输和微裂纹之间观察到强烈的正相关，证实了自收缩的负面影响。SRA 可有效减少这些影响。将其重要性与干燥收缩进行比较，并讨论了对耐久性的影响。