Study On The Mechanism Of Gelatinization And Hardening Between Ground Coal Gasification Ash And Cement Under The Synergistic Excitation Of Alkali And Salt

China is rich in coal,but poor in oil and gas.Therefore,the energy structure is still dominated by coal.Nowadays,In order to improve the availability of coal,coal gasification technology has been promoted year by year in China.However,the slag produced by coal gasification not only occupy a large amount of land resources,but also have a lot of adverse effects on environment.Therefore,how to deal with gasification slag reasonably and effectively has become the current mainstream research.Some research shows that coal gasification slag has pozzolanic activity,proving that it is possible to replace cement as cementitious material.The residual carbon in coal gasification slag is the main factor to inhibit the hydration reaction process.Therefore,the coarse coal gasification slag with less residual carbon content and particle size greater than or equal to 2.36 mm is filtered as raw material and ball-milled for 60 min as the research object.The ignition loss,specific surface area and density of milled coal gasification coarse slag were measured,and the microstructure,element composition and phase composition of pulverized coal gasification coarse slag were analyzed by SEM,EDS and XRD.The mill coal gasification coarse slag was used to replace cement in the proportions of 10%,15% and 20%.The mortar strength test was carried out and the optimal proportion of mill coal gasification coarse slag replacing cement was obtained.Seven kinds of commonly used chemical activators were selected to activate the finely divided coal gasification coarse slag,at the same time,the composite cement paste,single activated composite cement mortar and alkali salt were prepared.The optimal combination and dosage of activators were recommended by mechanical properties.The activation and hydration mechanism of each activate system was revealed by hydration heat,electrodeless resistivity meter,SEM and XRD.According to the optimal activation scheme,the finely divided coal gasification coarse slag was activated and used to prepare the semi-rigid base of composite cement.The unconfined compressive strength,dry shrinkage scouring resistance performance and bending tensile strength were evaluated.Through the above tests,it is found that the loss on ignition of coarse slag with a particle size above2.36 mm is extremely low,only 0.13%,and the element composition in the slag was not affected by the ball milling time.When the proportion of cement replaced by fine coarse slag is 10%,the mechanical strength of composite mortar is the highest,and the order of single excitation effect is: sodium sulfate > calcium hydroxide > sodium chloride > calcium sulfate > calcium chloride > sodium silicate > sodium hydroxide.The best combination of alkali-salt synergistic excitation is the combination of calcium hydroxide and sodium sulfate with the corresponding dosage of 3% and 0.6%.Compared with the reference group,its flexural strength at 3d and 28 d is increased by 62.3% and 90.3%,and its compressive strength at 3d and28 d is increased by 42.6% and 52.9%.The alkali-salt synergistic excitation process can improve the alkalinity of the system and promote the generation of ionic monomers.The addition of alkali-salt activator can provide sulfate ion,calcium hydroxide and calcium ion required for the formation of hydration products,so that the hydration products are richer,the corresponding structures are denser,and mechanical properties are better.Compared with the composite cement semi-rigid base without activator,the unconfined compressive strength and flexural tensile strength of the semi-rigid base stimulated by alkali salt grinding fine and coarse slag are increased by 2.2% and 6.2% respectively,and it has better drying shrinkage and scouring resistance than the pure cement semi-rigid base.