The material design of the alkali activated slag (AAS) contributes to the development of the sustainable "Green Building Materials" for the recycle of industrial waste and energy reservation of cement materials production. A computational simulation technique based on reactive molecular dynamics proposed a new view of molecular structure for the main hydrate, C-A-S-H gel, in AAS. In this paper, structure, dynamics and mechanical properties of C-A-S-H gel have been investigated. The proposed C-A-S-H model exhibits heterogeneity layered features with ordered and stable atomistic arrangement in the calcium sheets and disordered chemical connections in the interlayer region. Structurally, Al atoms bridge the neighboring oxygen atoms in the defective silicate chains, contributing to the polymerization of the C-A-S-H gel. The increase of Al or Si can significantly enhance the mean silicate chain length of the structure, and the introduction of Al atoms in the interlayer region can improve the mechanical properties of the C-A-S-H gel. Therefore, the mean chain length can be taken as important parameter to guide the high performance MS materials design. (C) 2017 Elsevier Ltd. All rights reserved.