Microstructure, Porosity and Mechanical Property Relationships of Calcium-Silicate-Hydrate

摘要

The structure of calcium silicate hydrate (C-S-H) formed as a result ofsolution/sol mixing, and hydration of tricalcium silicate (C3S) under fixed pH conditions was studied. MAS NMR and related analytical techniques (x-ray diffraction, SEM/TEM, and TGA) were used to characterize the hydration products. Two C-S-H phases having distinctly different structures (molecular and micro) and weight loss characteristics exist in the system CaO-SiO2-H2O and along the 10 wt % isoalumina join through the system CaO-Al2O3-SiO2-H2O. Coexisting phases form somewhere between 10 and 20 wt. % alumina. C3S hydrated as a function of pH (11-12) confirmed that at low pHs (<11.5), a C-S-H consisting predominantly of Q2 silicate chains forms. At pH > or = 11.5, a second C-S-H formed which consists of a combination of Q1Q2 silicate units. This C-S-H is more typical of that normally associated with the hydration of C3S or portland cement without pH control. The C3S hydrated at pH 13 contained only silicate dimer (Q1) and large quantities of crystalline Ca(OH)2. In this instance an entirely different gel (perhaps an alkali aluminosilicate hydrate) might be forming. In a parallel study, zeolites have been synthesized from synthetic and waste glasses (fly ash) mixed with alkali hydroxide solutions. Linde B1, chabazite and gobbinsite have been observed under certain conditions (relatively high Ca and alkali content). These data have been used to evaluate the feasibility of producing zeolite-cement composites.