Atomic Simulation And Performance Design Of The Calcium Silicate Hydrates

Calcium-Silicate-Hydrates(C-S-H)is the main hydration product of Portland cement,which has important influence on the strength and durability of cement concrete.Therefore,it has always been the research hot point of cement-based materials The C-S-H gel is amorphous at room temperature,and its molecular structure is still inconclusive.But it has been proposed that a series of natural minerals such as Tobermorite and Jennite has a highly similar structure of C-S-H.Based on this,the physical and chemical properties of calcium silicate hydrates were systematically studied by using the first principle and molecular dynamics method.In this research,calcium silicate hydrates were studied from the theoretical and experimental aspects,the structure,mechanical and dynamics properties were studied from multi-scale.Based on the density functional theory,the first-principles calculation of the non-local van der Waals force is first time carried out.for the structure optimizatio of the calcium silicate hydrates.The results show that the meridional parameters and mechanical properties of Jennite and 9 A,11 A,14 A Tobermorite have well agreement with the theoretical or experimental data from other research,but the Bulk modulus,Shear modulus,Young's modulus and other calculation results are still much higher than the measured value of C-S-H gel.Based on the molecular dynamics method,the nano-structural,mechanical and dynamics properties of 9 A,11 A and 14 A tobermorite was simulated and discussed.The results show that after the dynamic operation,the structures tend to be amorphous in the glass state rather than the regular crystal structure.The interlayer spacing and water content have an important effect on the local structure of the Si and Ca in the simulation system.The amorphous C-S-H gel was successfully prepared by molecular dynamics simulation and Monte Carlo method.The calculated structure was compared with the results of other researchers and the experimental results.The C-S-H gel model with different drying degree was constructed by controlling the water content.The results show that the immersion of water molecules leads to a significant change in the length of the C-S-H gel.Kinematic ability of different atoms in the water-saturated C-S-H gel is proved to be like:Si<Ca ? O<H.With the increase of H2O/Si ratio,C-S-H gradually transformed from the amorphous glass-like structure into a more orderly layered structure.In the experiment,the calcium silicate hydrates were prepared by solution reaction method and C3S hydration method,and were characterized by various methods.The results show that the C-S-H prepared by the solution reaction method is composed of the more loose lamellar particles,and the morphology of the C-S-H prepared by hydration synthesis is needle-shaped.With the increase of the Ca/Si ratio,the degree of C-S-H polymerization decreased.According to the transmission electron microscopy(TEM)image,the C-S-H sample is semi-crystalline,and the interlayer region of C-S-H is resemble to 11A tobermorite.This research provide insight on the nanoscale and microscale characteristics of C-S-H and enrich the application of the first principle calculation and molecular simulation.In the current cement-based materials,atomic simulation research is still relatively lack of circumstances,this area will have a greater development in the future.