Aluminum-induced structure evolution and mechanical strengthening of calcium silicate hydrates: an atomistic insight

How Al³⁺ dissolved from supplementary cementitious materials influences the performance of cement paste is far from being fully understood, especially from an atomistic insight. Herein, Al³⁺ is introduced into calcium silicate hydrate (CSH, the main phase of cement paste) to evaluate its effect using atomistic simulation. Structurally, Al³⁺ heals defects in the silicate chains, forms cross-links between calcium aluminosilicate layers, and reduces interlayer space and H₂O content. The chemical stability of interlayer H-bonds and Ca-O bonds is also improved. The diffusion of the interlayer H₂O and Ca²⁺ is decelerated, attributed to Al-induced channel blocking and stronger interfacial adhesion with the calcium silicate layers. Mechanically, the Al-induced chain bridging enhances the load-bearing capacity of aluminosilicate chains along y direction, resulting in ∼ 57.1% and ∼ 100.4% enhancement of Young's modulus and tensile strength. In z direction, the cross-links provide ultra-strong connections between the layers by raising Young's modulus and strength by ∼ 4 and ∼ 6 times. This study provides profound guidance for future design of environmental-friendly cement with promising mechanical properties and durability.