The theoretical models for the application of low–field nuclear magnetic resonance (LF NMR) to the cementitious materials are reviewed, in response to the three common questions, namely the data reliability, result stability and model validity problems. The major applications, including the characterization of pores, the quantification of hydration products and the diffusion dynamics, are linked to four theoretical models, namely the two–fraction fast–exchange model, the Korb model, the amplitude model and the cryoporometry related Gibbs–Thomson model. In addition, the limitations in models as well as in instruments are pointed out. In particular, for the mentioned applications, most commonly used pulse sequences together with recommended parameters are provided.Based on the latest progress in the field, challenges and outlooks are discussed.

The addition of chemical admixtures has been an effective approach to improve the performance of cementitious materials. Working mechanisms of the chemical admixtures in molecular scale still need to be clarified. Calcium silicate hydrate (C–S–H), as the main hydration product of cement, determines most macroscopic properties of cement-based materials. Molecular dynamics simulation has been an effective technique to reveal the interaction between chemical admixture molecules and C–S–H and its effect on the properties of C–S–H at the molecular/atomic scale. In this paper, recent progresses in molecular dynamics studies of the interaction between chemical admixtures (organic and inorganic) and C–S–H were reviewed, and their impacts on properties of C–S–H are briefly summarized. In addition, the future research direction of molecular dynamics simulation of chemical admixture–(C–S–H) system is prospected. The summarized chemical admixtures include organic admixtures such as small organic molecules, resins and fibers, water-soluble polymers, and inorganic admixtures such as (modified) graphene, silene, carbon nano-tubes, and various nanoparticles. Most molecular dynamics simulation research focuses on the interaction between the admixtures and C–S–H interface. Understanding of such interfacial interaction is the key to reveal the working mechanisms of the admixtures in improving the mechanical properties of C–S–H. In addition, for admixtures such as small organic molecules, water-soluble polymers and some nanoparticles, a large number of studies have used molecular dynamics method to describe the microscopic processes such as the adsorption of the admixture molecules on C–S–H surface, intercalation into C–S–H layers, aggregation of the admixtures that blocks C–S–H layered structure, so as to clarify the mechanism of these admixtures on the mechanical properties, transport properties and even shrinkage behavior of C–S–H. These understandings provide theoretical inspiration for improving the properties of cement-based materials and for designing the molecular structure of admixtures more effectively.