Study On Preparation And Properties Of High-Strength Slag-Based Geopolymer

As a new kind of environmental-friendly cementitious material,alkali-activated slag-based geopolymer material is characterized by low energy consume,low CO2 emission and low cost.The effects of the activators and specific surface area of the slag on the hydration properties of the slag were investigated in this study.In addition,high-strength geopolymer material was prepared from slag and fly ash,and its durability was also studied.Sodium hydroxide(NaOH)and water glass(Na2O·nSiO2)are commonly used as activators for slag,which can effectively activate the hydration reactivity of slag.The compressive strength test showed that the optimum dosage of NaOH was 6%by mass ratio of the slag.The compressive strength of the mortars with 6%NaOH reached 16.5 MPa and 42.5 MPa at 1 day and 28 days,respectively.Compared with the NaOH-activated mortars,the water glass-activated mortars could obtain higher compressive strength.The optimum dosage of water glass was 15%,and the 1-day and 28-days strength reached 27.8 MPa and 83.0 MPa,respectively.XRD and TGA test results suggested that the main hydration products of pastes were calcium silicate hydrate(C-S-H)gels,whether in NaOH-activated pastes or water glass-activated pastes.The increase of the activators dosage prompted the formation of C-S-H gels in the pastes.The results of 29Si NMR and SEM further indicated that the hydration degree of slag would be improved with the increase of the activator dosage.However,the polymerization degree of C-S-H gels would be reduced if the activator dosage was higher than certain level(the MCL of NaOH-activated slag pastes and water glass-activated slag pastes decreased from 7.61 to 6.08 and 11.55 to 9.78,respectively),causing a decrease in the compact degree of microstructure,which adversely affected the strength of the binders.The modulus(SiO2/Na2O)of water glass has a significant influence on the hydration properties of the slag.The optimum modulus was about 1.5,and the compressive strength of the mortars reached 30.5 MPa and 81.0 MPa at 1 day and 28 days,respectively.The change of the modulus of water glass had no obvious influence on the type of hydration products,and the main hydration products of pastes were C-S-H gels.The results of 29Si NMR and SEM showed that the decrease of the modulus of water glass would increase the hydration degree of slag,but the too low modulus would reduce the polymerization degree of C-S-H gels(the MCL decreased from 12.06 to 8.93),which was adverse to the development of the microstructure of the pastes,resulting in a reduction in the strength.The specific surface area of slag also plays an important role in modifying hydration properties of the slag.The volume of particles less than 5?m and 20?m increased with the specific surface area of slag,which accelerated the hydration rate of slag.The compressive strength test results suggested that,within a certain range,the increase of specific surface area of slag could significantly improve the compressive strength.The Compressive strength of mortars with specific surface area of 451m2/kg reached 40.9MPa and 83.9MPa at 1 day and 28 days,respectively.The geopolymer material with high-strength and excellent durability were prepared by mixing slag,fly ash and water glass.The compressive strength test results suggested that with the increase of fly ash dosage,the compressive strength of mortars continuously reduced,owning to the low hydration activity of fly ash.But,the compressive strength of the mortars with fly ash dosage of 40%could still reach 27.1 MPa and 68.0 MPa at 1 day and 28 days,respectively.In addition,the frost resistance,sulfate attack resistance,acid corrosion resistance and alkali corrosion resistance of geopolymer material were better than 52.5 ordinary Portland cement,which could be used in the field of road repair materials.