Molecular dynamics simulation of C-S-H corrosion in chloride environment

Calcium silicate hydrates (C-S-H) is the main hydration product of cement, and C-S-H gel is a porous structure. The physicochemical reactions of harmful ions in the external solution, such as chloride ions and sulfate ions, will cause the hydrolysis of C-S-H gel and therefore resulting in the decrease of the strength of the concrete. In this work, the corrosion characteristics of C-S-H gel in Cl- environment were studied by means of reactive force field molecular dynamics simulation. The interaction characteristics between solution and C-S-H pore interface was explored. The uniaxial tensile simulation of C-S-H gel in x, y and z directions was carried out. Results show that: (1) The addition of water will increase the interaction degree between free calcium atom (Ca) in C-S-H and oxygen atom (Ow) in water, but has no effect on the interaction degree between Ca and oxygen atom (Os) in silicon chain; (2) The presence of gel pores and water in the gel pore both promote the movement of water molecules in C-S-H, while the mobility of calcium silicate skeleton is only affected by gel pores; (3) When C-S-H is in the defect free state, the strength in y is the largest, followed by x and the smallest in z. When there are defects, the weakening range of strength in y direction is largest; (4) Gel pore, aqueous solutions, Cl- and so on will reduce the peak strain in the direction of x and z stretching, and z direction will have obvious stress stability stage.