The Preparation And Property Research Of One-part Alkali-activated Slag

Alkali-activated material is a kind of environment-friendly material made from solid aluminosilicate materials and alkali activator.It has the advantages of early strength,acid resistance,sulfate resistance,thermal stability,and is widely used in building materials.The two-part alkali-activated material requires the aqueous alkali activator,while the one-part alkali activated material can be obtained only by adding water in dry powder,which is easy to store,transport and use,and brings great convenience to the production process.In this experiment,economical and easily available calcium oxide and sodium carbonate were chosen as the combined solid activator of slag,and the effects of activators with different alkali contents on the p H value of paste and the properties of slag-based geopolymer were studied.The direct CO₂ capture technology and one-part alkali activated cement were combined to control the setting time of alkali activated cement.The hydration and carbonization mechanism of Ca O at room temperature and the effect of carbonization rate of Ca O on the setting time and other properties of Ca O as an activator in alkali activated slag were studied.The low-grade bottom ash after ball milling was used as low active admixture in alkali activated slag.The effects of different content of bottom ash on setting time,yield stress,compressive strength,hydration products,microstructure and drying shrinkage of composite paste were investigated.The main conclusion were as follows:（1）The higher the alkali content of the paste,the faster the reaction rate of alkali-activated slag and the shorter the setting time of the paste.The rheological model of the paste fits to the Bingham model,and the yield stress of the one-part alkali activated slag is higher than that activated by sodium hydroxide solution.When the alkali content is 4%,the p H value of one-part alkali activated slag paste is 13.7,which is lower than that activated by sodium hydroxide solution with the same alkalinity.The results of compressive strength measurement and thermogravimetric analysis show that the compressive strength reaches the maximum of 48 MPa when the alkali content of one-part alkali activated slag is4%,and the solid activator can effectively improve the hydration rate and compressive strength of slag.XRD analysis shows that the main hydration products of one-part alkali activated slag include C-A-S-H,hydrotalcite and hydrotalcite-like phase.（2）The results of X-ray diffraction,specific surface area analysis and thermogravimetric analysis show that the specific surface area of calcium oxide particles increases first and then decreases when they are hydrated and carbonized to form calcium hydroxide and calcium carbonate.The capillary condensation effect plays a key role in the hydration and carbonization of calcium oxide.The liquid layer condensed by micropores can act as the transition phase of gas-solid reaction,which promotes the formation of calcium carbonate layer on the surface after CO₂ adsorption.When the carbonation rate of calcium oxide reaches 2-6%,the setting time of paste increases rapidly.The initial and final setting times increased by 131 and 98%,respectively,when the carbonization rate of the activator reached 10.7%.（3）The particle size range of bottom ash obtained after ball milling for 1hour is similar to that of slag.With the increase of bottom ash content,the setting time of paste increases rapidly.With the addition of 30%bottom ash,the yield stress of the composite paste decreases,and the rheological properties of the paste decrease with the increase of bottom ash content.When the bottom ash of 50%is added,the drying shrinkage of paste decreases obviously,and only has 718με_s in28 days.However,the compressive strength of the paste is not significantly affected.With the increase of bottom ash content,the compressive strength of the composite paste decreases and the drying shrinkage increases.Combined with TG and IR analysis,low activity bottom ash can reduce the hydration rate of paste and the polymerization degree of hydration products.