Study On Preparation Of Geopolymer And Hydration Mechanism

Geopolymer was prepared by waterglass alkali-activated fly ash and coal gangues from industrial wastes under the proper technique process in this thesis. Also, the main influences of curing regime, the module of waterglass, the content of alkali activator and the ratio of water/binder on the compressive strength of geopolymer are investigated. The results show the optimal test parameter as follows: the module of waterglass is 1.5, the ratio of water/binder equals to 0.26 and the ratio of alkaline activator/fly ash is 0.20. The compressive strength of the geopolymer approaches 109.84 MPa at the curing time for 28 days under this optimal test parameter.All the microstructures of the hydration products in the different ages were systematically studied by means of X-ray diffraction (XRD), Fourier Transform Infrared spectrometry (FTIR), field emission scanning electron microscope (FESEM) and scanning electron microscopy (SEM) equipping with energy dispersive X-ray analysis (EDS).The XRD and FTIR analysis indicated that the reaction of disaggregation polycondensation carried out on vitreous bodies of fly ash with alkali activator, and formed the new amorphous aluminosilicate gel and a certain content of crystal clinozoisite at curing time for 7 days.The EDS results showed that the content of sodium element increases sharply, especially at the earlier curing time, attributing to that sodium silicate hydrolyzes and forms NaOH to cover on the surface of fly ash particles, and then it reacts with network formed from the silicon-oxygen-aluminum so as to accelerate the cleavage of Si-O-Al, Si-O-Si and Al-O-Al bonds in fly ash. It also showed that a large amount of calcium was extracted from the bulk of fly ash particles and entered into the geoploymer gel. Meanwhile, The ratios of Na/ (Si+Al) and Ca/ (Si+Al) trend to stable value, respectively. The ratio of Si/Al retains within the range of 1.5-2.0 with development of hydration reaction, suggesting that the PSS type of geopolymer has mainly formed. It was found that the fly ash particles hardly reacted with alkaline activator as the ratio of Si/Al is bigger than 3.The morphology and microstructure were observed by SEM. The results exhibited that the fly ash at first formed nanometer size particles and then developed into the compact network gel.The FESEM results showed the geopolymer gel was three dimensional network structures which originate from the network cell consisting of average particle size about 50 nm to intervein and overlap each other. Moreover, the networks become much more compact with increasing the hydration time.