Structure And Morphology Of Aluminum Substituted Calcium Silicate Hydrate

Calcium silicate hydrate (C-S-H) gel is the principal hydration products of Portland cement and water, which is responsible for their mechanical cohesion among other consequences, and is main source of cement strength, but its structure is very complicated. Aluminum is one of primary element in cement and plays an important role in hydrated cement. Form research on micro structure and morphology of C-S-H doped aluminum, macroscopic properties can be explained for mineral admixtures containing rich aluminum in cement concrete. And it is significant way to C-S-H guide and control.The series of C-S-H and C-A-S-H samples were prepared by different methods. The effects aluminum on structure and morphology of C-S-H were investigated by the modern techniques of X-ray diffraction (XRD), BET nitrogen adsorption, Infrared spectrum (IR), Raman spectrum, Nuclear magnetic resonance (NMR), Scanning electron microscope (SEM), Transmission Electron Microscope (TEM).Effects of aluminum on interlayer space in C-S-H were research by XED. The results indicated that aluminum element can enter into the structure of C-S-H, and the change of interlayer space is related closely with Ca/Si ratio and content of aluminum. Interlayer space of C-S-H increasing after mixing aluminum is resulted of Al for Si substitution in tetrahedral [SiO4]4-, and the aluminum existence between interlayer. The specific surface area and pore structure characteristic of the samples is researched by BET, which indicate that the specific surface area is decreased significantly and the structure is more compact than C-S-H.Effects of aluminum on Polymerization state of [SiO4]4- in C-S-H were investigated by the techniques of FT-IR,Raman and 29Si MAS NMR. These result consistently indicated that Polymerization state of [SiO4]4- is related to Ca/Si ratio and content of aluminum in C-S-H. With Ca/Si ratio's increasing, the polymerization degree of [SiO4]4- decreases, but With Al/Si ratio's increasing, the polymerization degree of [SiO4]4- increases.Morphology of C-S-H and C-A-S-H were studied by the techniques of SEM and TEM. The results proved that structure of C-A-S-H doped Al is more compact than pure C-S-H. Morphology of C-S-H and C-A-S-H is closely interrelated with Ca/Si ratio and content of aluminum. The main morphology contains fibrous, lamellar, network and block shape. C-S-H samples are damaged easily by TEM electron beam, and their structure and morphology will be changed. There main exist two types of morphology in TEM micrograph for C/S=1.5 pure C-S-H, fibrous shape and irregular spherical particles. But after Al entering into C-S-H, there exist three types of morphology at least, such as fibrous, platy and much regular spherical particles, and for fibrous C-S-H, it is a little longer than before mixing aluminum indicating structural average chain length increases.