Calcium silicate (aluminate) hydrate (C-(A-)S-H) as a predominant hydration product formed in Portland cementitious materials plays a pivotal role in determining the mechanical strength, durability, and creep resistance of Portland cementitious materials. The complex and intricate micro-/nano-structures of C-(A-)S-H become a challenge in deciphering its characteristics of micro-/nano-structures. Furthermore, the sensitivity of C-(A-)S-H to service environments exacerbates the complexity of micro-/nano-structures analysis. Throughout the operational lifespan of Portland cementitious materials, fluctuations in temperature, mechanical stresses, water flow dynamics, and attack of ions (i.e., Na⁺, Mg²⁺, Cl^- and SO₄^2-) lead to continuous and dynamic changes in the micro-/nano-structures of C-(A-)S-H. Recent work on the methods for characterizing C-(A-)S-H micro-/nano-structures, computational simulations of C-(A-)S-H, and the integration of machine learning techniques are carried out to clarify the micro-/nano-structures of C-(A-)S-H. These advancements facilitate iterative improvements in micro-/nano-structure models, enabling more precise predictions and control of macroscopic properties in micro-/nano-scale in Portland cementitious materials, accurately forecasting the evolution of C-(A-)S-H micro-/nano-structures under ions attack conditions, having a significant promise for further refining micro-/nano-structure models. Such advancements can provide theoretical insights and offer practical avenues and strategies for optimizing the performance and durability of Portland cementitious materials through informed materials design and engineering strategies.It is necessary to explore the advanced characterization of C-(A-)S-H micro-/nano-structures and clarify the intricate development of models depicting micro-/nano-structures of C-(A-)S-H, micro-/nano-structures evolution under ions attack environments and the specific mechanisms by ions (i.e., Na⁺, Mg²⁺, Cl^- and SO₄^2-) interact. A C-(A-)S-H micro-/nano-structure model is developed via utilizing the advanced techniques such as small molecule capping, time-of-flight secondary ion mass spectrometry (TOF-SIMS), molecular simulations and machine learning. The overarching goal remains to provide theoretical foundations for optimizing C-(A-)S-H micro-/nano-structure model.In addition, predicting the evolution of C-(A-)S-H micro-/nano-structures under ions attack conditions accurately is a multifaceted endeavor with a potential to advance theoretical understanding and provide practical solutions. The significance of this undertaking is that it paves a way for Portland cementitious materials optimization through intelligent design, thereby creating cementitious materials that are more durable, efficient, and environmentally sustainable to meet the demands of modern construction and other related fields.Summary and ProspectsThis review represents the micro-/nano-structure models of C-(A-)S-H and discusses recent advancements in understanding its evolution under common marine ions attack (i.e., Na⁺, Mg²⁺, Cl^- and SO₄^2-). This review elucidates the mechanisms by which aluminum-rich supplementary cementitious materials promote the formation of C-A-S-H, highlighting advancements in characterization techniques and the integration of molecular simulation and machine learning. These innovations significantly advance the development of models describing the micro-/nano-structures of C-(A-)S-H.Advancements in characterization techniques supported by cutting-edge technologies such as molecular dynamics simulations and machine learning deepen our understanding of atomic ratios within C-(A-)S-H in relation to its degree of polymerization, average chain length, micro-mechanical properties, and durability. These developments facilitate the establishment of mappings between the micro-/nano-structures of C-(A-)S-H and its properties. Furthermore, this can contribute to advancing sequential studies of silicate (aluminate) tetrahedra on the Dreierketten chains.At present, some aspects merit a further investigation and have a potential to emerge as future research focal points as follows: 1) the micro-/nano-structure model of C-(A-)S-H can be optimized and a framework utilizing first-principles calculations, molecular dynamics simulations, and machine learning techniques needs to be proposed. These aim to predict the mechanical properties and durability of Portland cementitious materials based on the micro-/nano-structure of C-(A-)S-H. It is thus feasible to enhance understanding and predictive capabilities concerning the performance and longevity of Portland cementitious materials at the microstructural level via integrating these advanced computational methodologies. 2) Atomic arrangement analysis of C-(A-)S-H is needed. It is thus feasible to determine the relative abundance of structural units within C-(A-)S-H by nuclear magnetic resonance (NMR). Chemical environment analysis techniques, such as X-ray photoelectron spectroscopy (XPS), enable elemental valence state analysis in C-(A-)S-H. The detailed atomic arrangement analysis of C-(A-)S-H can be obtained, which is crucial for directing the targeted production of Portland cementitious materials. 3) The micro-/nano-structures evolution mechanisms of C-(A-)S-H in marine environments need to be investigated. The micro-/nano-structures evolution mechanisms of C-(A-)S-H under complex ions attack conditions are investigated. The degradation mechanisms of C-(A-)S-H in simulated marine environment need to be further simulated via establishing a database of products under single-factor attack environments and employing thermodynamic simulation techniques, and the simulation results with the micro-/nano-structures of C-(A-)S-H in real marine service environments need to be compared. 4) Low-carbon green building materials are developed. The Ca/Si ratio in C-(A-)S-H can be adjusted based on the optimized models of micro-/nano-structures of C-(A-)S-H, meeting engineering requirements, while optimizing the raw material composition of cement. This approach can reduce CO₂ emissions during cement production, thereby promoting the development of low-carbon green building materials.