Research On Preparation Of Geopolymer Material And Its Hydrate

Slag-based geopolymer cement is a new green cement which is synthesized mainly from natural aluminum silicate mineral materials or industrial solid waste, actived by alkaline solution ,has a property like ceramic, whose molecular structure is made up of [SiO₄] and [A1O₄] tetrahedron, showing three-dimension network structure.Through the calcine kaolin and slag in diffrient temperature to change the oxide activity and Through the change of n(SiO₂)/n(Al₂O₃), n(Na₂O)/ n(Al₂O₃)and water cement ratio molar ratio of raw materials, tested the compressive strength of slag-based geopolymer paste, concrete, and the best oxide molar ratios were got through the orthogonal test. XRD and SEM analysis were also made to discover the hydration process of geopolymer.The results show that, the compressive strength of slag-based geopolymer paste, mortar and concrete increase and then decrease with n(SiO₂)/n(Al₂O₃), n(Na₂O)/n(Al₂O₃)and water cement ratio molar ratio increase. As oxide molar ratios were n(SiO₂)/n(Al₂O₃)=3.9, n(Na₂O)/n(Al₂O₃)=0.4, n(H₂O)/n(SiO₂)=2.3, oxide activity was 0.42, the 28d compressive strength of slag-based geopolymer past can be up to 79.94MPa. As oxide molar ratios were n(SiO₂)/n(Al₂O₃)=3.9, n(Na₂O)/n(Al₂O₃)=0.3, water cement ratio=4.2, oxide activity was 0.42, the 28d compressive strength of slag-based geopolymer concrete can be up to 65.88MPa. 28d compressive strenght mathematical model was set up through multiple linear regression, the relationship of 28d compressive strength with n(SiO₂)/n(Al₂O₃)(x₁),n(Na₂O)/n(Al₂O₃) (x₂) and water cement ratio (x₃)is:y=85. 9+2.94x₁ +3.41x₂-22.28x₃.Through the single linear regression analysis, it shows that 28d compressive strength of the paste and 28d compressive strength of concrete with the corresponding molar ratio of oxides have a remarkable linear relationship.On the base of mathematical analysis, the mathematical model was set up.The relationship between paste compressive strength and concrete compressive strength is:y=22.99 +0.62x₁ -21.88x₂The results show that the greater the slag activity leads to more complete hydration, the greater degree of hydration. At the same time, a large number of slags in the hydration potential of hard water glass was excited. pH value in the hydration of 3 days was the largest. That means most singles produced in the third days. Silicon content increased with age decreased and continuously involved in chain formation. Na⁺ was constantly being released and its content increased with age. Ca²⁺ continuously involved in the formation of complex phase and increased with age decreased. Moreover, the ratio of silicon to aluminum is not the larger the better. The degree of hydration and strength are the best when Si/Al=3.9. At the same time, by incorporating of different alkaline activator (sodium hydroxide), the hydration process will be greatly affected. When NaOH was 1g under the low dosage condition, the potential activity of the water can not be activated. As a result, the development of hydration is slow. The reason for this phenomenon is that most of the slag particles were highly hydrated in a short time. This phenomenon can prevent further hydration of the particles inside to a certain extent. When the NaOH dosage was 3g, the samples showed the highest degree of hydration during different age periods. Additionally, the hydration process will be greatly affected under different ratios of water to silicon which controlled by the amount of water we used. However, research results show that the hydration degree of the samples were not increased with more water consumption. On contrary, when water is greater than 22g, the retraction phenomenon appears.XRD analysis showed that the crystal raw material disappeared, but amorphous materials were generated. XRD spectrum varied with the activity of inorganic mineral polymer. The peak is gradually increased which indicates the samples of low activity within the hydration were incomplete. SEM analysis showed high activity when inorganic minerals polymer structure is more compact. With the growth of age, the surface structure gradually completed. Crystal structure appears during 3d to 7d period. But this structure disappeared, during 14d to 28d period when the surface gradually compacted.