Study On Microstucture Charateristics & Structure Simualtion Of Calcium Silicate Hydrates

Calcium Silicate Hydrates (abbr. C-S-H) is the major hydration products of Portland cement and the resource of the strength of cement-based materials. The high performance superplasticizers, whose main ingredient is organic macromolecule, have been became the essential raw material for making high performance concrete. So the influence of high performance superplasticizers, such as polycarboxylic superplasticizer and polycarboxylate-type superplasticizer, on the pore structure and surface of C-S-H has been studied in this paper. Meanwhile the simulation of C-S-H's structure at atomic level by molecular dynamics simulation has been made, too.C-S-H and two samples containing above organic macromolecule were synthesized by the solution of Na2SiO3·9H2O and Ca(NO3)2·4H2O, their pore structure characteristics were determined by N2 adsorption, the surface fractal characteristics of the three samples were analyzed as well based on Frenkel-Halsey-Hill (FHH) model and Neimark model respectively in this dissertation. The results indicate organic macromolecule have great influence on the pore structure and fractal surface of C-S-H:○1 Both polycarboxylic macromolecule and polycarboxylate-type macromolecule increase the specific surface area of C-S-H markedly,○2 Polycarboxylic macromolecule is in favor of forming small mesopore in C-S-H, while polycarboxylate-type macromolecule contributes to generating large mesopore and○3 Both the surface of C-S-H containing polycarboxylic macromolecule and that containing polycarboxylate-type macromolecule have fractal characteristics, but the surface fractal dimension D of the latter is smaller than that of the former, it means that the surface of the latter is smoother than that of the former.The structure of crystal and amorphous C-S-H (Ca/Si=0.66)was simulated by molecular dynamics simulation (the software is DL_POLY), which is a new method to research materials. The simulation was achieved via using Hamid's model as initial structural input and selecting suitable potential functions and corresponding parameters. The results show that○1 the structural parameters obtained by simulation, such as interatomic distance and coordination numbers and so on, are nearly consistent with that obtained by experiment,②the order character of amorphous C-S-H structure only exists in short range, although the structural unit of it is still tetrahedral, which is the same as that of crystal C-S-H, the chains are only linked in Q2 instead of Q3 and Q4,③the structure of amorphous C-S-H becomes very disordered in long range relative to that of crystal C-S-H, although the chains are still made up of dreierkettens, yet they already twist, rotate, even rupture, and the dreierkettens chains don't stretch along b , too.