Study On Microstructure On Hydrated Calcium Silicate And Influence For The Performance Of Fly Ash Baking-free Bricks

The hydrated calcium silicate（C-S-H） is the principal hydration products of cement,which is main source of cement strength, autoclaved brick and aerated concrete strength.The species, structure and morphology play an important role in terms of mechanicalproperties and durability of products and was decided by formation temperature and time inautoclaved products. Other chemical components of raw material besides calcium, silicon andchemicals of activator have a greater impact for the generation rate, capacity, species,structure and morphology of hydrated calcium silicate. Form research on effect of autoclavedsystem on species, microstructure of C-S-H and C-S-H doped aluminum, sodium, magnesium,chlorine, is significant basis to optimize the ratio of autoclaved brick and aerated concrete anddetermine the autoclaved system of autoclaved products. Energy conservation could beachieve in the process of production of autoclaved brick and aerated concrete.The effects of autoclaved system on microstructure of C-S-H, Al³⁺(Na⁺, Mg²⁺, Cl^-) onmicrostructure of C-S-H were investigated by the modern techniques of X-ray diffraction（XRD） and scanning electron microscope （SEM）, A preliminary study on the mechanism ofinfluence of autoclaved system on the performance of fly ash baking-free bricks. The mainresults were as follows.（1）The C-S-H obtained at the temperature100℃and120℃had inferior crystallinity,the tobermorite and xonotlite had high crystallinity were obtained with raising of temperature.contraction of volume could be discovered in the process of transformation gel phase tocrystal. When the temperature was increased to180℃, the size of tobermorite becomes large,the amount of amorphous material was decreased. With the extended of reaction time, thecrystallinity of C-S-H was improved, transformation gel phase to crystal was promoted.（2）The results by XRD as follows: Al³⁺can enter into the structure of C-S-H and canimprove the crystallinity of C-S-H. When the ratios of Al/Si were increased to the values of 0.5and1, the hydrated calcium aluminate and hydrogarnet could be obtained. The results bySEM as follows: Al³⁺can reduce the size of C-S-H crystal and improve the density.After doping Na⁺(Mg²⁺,Cl^-) into C-S-H, its yield was improved, moreover, the bestone-ions for C-S-H was Cl^-. In addition, transformation gel to crystal was hindered by Na⁺.After doping F^-or Ca3（PO4）2into C-S-H, its yield was hindered, but F^-and PO₄^3-had noimpact on the structure of C-S-H. The precipitation of calcium fluoride wrapped inappearance of new hydrated calcium silicate had hindered the growing of C-S-H crystal.（3）With raising of steam curing temperature and extending of steam curing time, thestrength of fly ash baking-free bricks was improved gradually, but when the gel transformedinto crystal, the pore that had badful influence for strength was discovered in structure, so thestrength of baking-free brick did not continue to increase with raising steam curingtemperature and extending steam curing time. Since the produce of more crystal, the ability ofanti-carbonation was improved continuously.