Study On The Effect Of F-CaO On The Setting And Hardening Properties Of The Cyclic Activated Dehydration Phase

Because of that,the waste cement paste after being calcined at suitable temperature,named dehydrated cement phase（DCP）,can be used to prepare regenerated cementitious materials,so many researchers studied the reaction mechanism and the comprehensive utilization of the DCP.Their researches focus mainly on the dehydration phase activation system,hydration mechanism and the microstructure of rehydration products,but the physical properties of the DCP and its cyclic activation performance are not systematically studied.In this paper,we made an exhaustively detailed study about the cyclic activation preparation and the rehydrated propeties of the DCP.By the way,we also studied the influence of f-CaO on the properties of its setting and hardening properties.We have used the waste cement paste to prepare a cyclic activated DCP,and studied the activation system,physical properties,hydration heat release properties and setting and hardening properties of the DCP paste systematically.And the feasibility of the cyclic activation of waste cement paste was discussed.We determined the content of f-CaO in the cyclic activated dehydration phase,and made a comprehensive analysis of the chemical composition of DCP by XRD and FT-IR.When the calcination temperature is increased from 300 to 500℃,due to the decomposition of C-S-H gel,the content of f-CaO in the DCP increase gradually,reaches the maximμm value between 450-500℃.When the calcination temperature is increased from 500 to 600℃,the content of f-CaO due to its crystallization will be reduced.Between 600-750℃,the content of f-CaO in the DCP is almost unchanged;above 750℃,the CaCO₃ begins to decompose,which lead to the increase of the content of f-CaO.And the content of f-CaO will be stable after the temperature is higher than 850℃.At the same time,we studied the rheological properties,pH and heat of hydration of the DCP paste,found that the rheological property is much better,the pH and hydration heat is also the largest when the calcination temperature is between 500℃and 600℃.The heat release of the second DCP is relatively small,but the initial pH value is higher,and the time to reach the highest temperature also has been ahead.At the same time,we also measured the mechanical properties,porosity and hydration degree of the cyclic activated DCP.We studied the composition and microstructure of the hydration products by means of XRD,SEM,TG-DSC and so on,found that the hydration activity and mechanical properties of the second DCP were decreased.In this paper,the effect of free calciμm content on the setting and hardening properties of the DCP with different cycle times was also studied,and found that it had great influence on thermal performance,mechanical properties and mechanical properties of the DCP paste.When the calcination temperature is 600℃,the content of f-CaO in the first DCP is 4.5%,while the second f-CaO is 2.5%,the DCP has the best performance.