Investigation On The Production Of Soluble Silicate With Rice Husk Ash And Its Activity To The Potential Hydraulicity Of Fly Ash

Geopolymer, as a kind of green cementing materials which is recycling and helpful to protect environment, has become a hot topic of research in the new century. Based on so many excellent research and seek a new method for the choice of excitation agent, the optimal scheme of sodium silicate prepared using rice husk ash and the activating effect of different kinds of fly ash were studied. First, the structure characteristics of sodium silicate in different modulus were analyzed. Then, the influence of curing conditions and the content or existence of calcium oxide on the activity to fly ash was investigated, comprehensively. The reaction mechanism of geopolymer formed from fly ash activated by sodium silicate was studied by the modern analysis methods including SEM, IR, NMR and XRD.The sodium/potassium silicate was prepared by using the raw material-rice husk ash. The impacts of the concentration of sodium/potassium hydrate, the time of radiation and the proportion of solids and liquids on the modulus of sodium silicate and the deliquescent rate of Si O2 were studied through experiments. The results indicate that the optimal scheme of sodium silicate is that the Na OH concentration is 8mol, the ratio of Na OH solution to rice husk ash is 1:2.5 and the reaction time is 3h; the optimal scheme of potassium silicate is that the KOH concentration is 10 mol, the ratio of KOH solution to rice husk ash is 1:2.5 and the reaction time is 5h; compared to KOH solution, the deliquescent rate of Si O2 from the rice husk ash is higher in Na OH solution.The geopolymer based on fly ash which was activated by sodium/potassium silicate was prepared. The effect of sodium/potassium silicate with different modular and solid content on the compressive strength of geopolymer based on fly ash was conducted. The results show that using sodium silicate with 34% solid content, the modulus 1.1 and dosage of sodium silicate is 33% can gain the maximum compressive strength for the prepared geopolymer; using potassium silicate with 38% solid content, the modulus1.2 and dosage of potassium silicate is 47% can gain the maximum compressive strength.The influence of the curing conditions on the activity of fly ash activated by sodium/potassium silicate. The results show that the higher polymerization degree of vitreous body in fly ash is harder to be depolymerized when in the low-temperature natural curing condition, so the compressive strength of geopolymer is lower. While, the compressive strength of geopolymer is becoming high with the increasing of curing temperature due to the vitreous body depolymerizing to the single body relatively easily.The influence of the calcium oxide content and calcium oxide phase in the fly ash to the fly ash hydraulicity was investigated. The results show that the lower content of calcium oxide, the higher polymerization degree of vitreous body in fly ash, so the fly ash has the lower hydraulicity, and the geopolymer based on fly ash has lower compressive strength; when the free calcium oxide is prior to exist in fly ash, it will produce the delayed calcium hydroxide and lead to the later compressive strength decreasing of fly ash geopolymer.The construction of sodium silicate with different modulus was analyzed by the methods of IR and NMR. The results indicate that the sodium silicate with low modulus(1.0~1.4)has lower polymerization degree of silicon-oxygen tetrahedron and higher activity to fly ash, combined with the microstructure of fly ash in hardened geopolymer, the reaction mechanism of geopolymer based on fly ash activated by sodium silicate can be deduced. Firstly, the hydrolysis of sodium silicate and producing a mass of OH- and Si(OH)4. Secondly, OH- rupturing the bond of Si-O-Al, Si-O-Si and Al-O-Si, and forming to the [Si O4] and [Al O4] monomers. Finally, the [Si O4] and [Al O4] monomers copolymerizing to form three dimensional network structure geopolymer eventually.