Study On The Formation Of Cementitious Material And Mechanism Of Hydration By Water Glass Activation Of Fine Slag

The geopolymer formed from alkali-activated fine slag powder is a new kind of cementitious material which is helpful to protect environment and able to utilize waste materials as well as the residues from metallurgy industry. The microstructures of the hydration products were studied by means of field emission scanning electron microscope (FESEM), scanning electron microscopy (SEM) equipping with energy dispersive X-ray analysis (EDS), X-ray diffraction (XRD) and Fourier Transform Infrared spectrometry (FTIR).The SEM and FESEM results showed that the vitreous phases in slag began disaggregation and some gels were formed on the edge of small slag particles in the initial setting stages. These gels were continuously reunited with each other in the final setting time. When curing time for 1 day the surface of slag started hydration to form the geopolymers and almost all slag particles were covered with new products. These geopolymers gradually shelled off from the surface of slag, and then network structures started to intervein and joined with each other. After 2 days the surface of sample has formed compact microstructure of geopolymers. When curing time for 28 days, that the FESEM results showed that the compact geopolymers are composed of average particle size of 20 nanometers.The EDS analysis indicated that with a large number of vitreous phase disaggregation, calcium ions, silicon ions, aluminum ions and magnesium ions came out from the particles of slag and silicon and .calcium ions enriched on the local areas, sodium ions moved to the surface of slag particles. After 1 day, much more elements participated in the hydration reaction, the mass ratio of Ca/Si ,Ca/(Si+Al) and Na/ ( Si+Al) approach to stable states with development of hydration reaction, suggesting that final hydration products have formed.The XRD results showed that significant quantities of crystalline hydration products did not form in final setting times. After 1 day, calcium silicate hydrate, tobermorite, gismondine, zoisite, wairakite, natrolite and vuagnatite were formed in gel materials. It was found that there was a little content of calcium silicate hydrate due to mainly formed vitreous hydration products.The results of hydration reaction degree showed that the quantity of chemically coalescent water was increased with the increase of hydration time. From the experimental analysis, it was found that the degree of hydration reaction approaches to 50% after curing time for 1 day, 70% for 7 days and .90% for 28 days.The P^OH results presented that OH^-ions worked as catalyst and promoted hydration reaction.The FTIR results showed that in the early days Si-O group transmited from SiO₃^2- to SiO₂. The degree of polymerization reduced gradually and the slag vitreous phases began disaggregation. In the final of hydration reaction, the degree of polymerization for Si-O and Al-O groups increases. The new absorption peaks occured at 664.0cm^-1 and 714.0cm^-1 indicated that the zeolite-liked material was formed.