Effect Of Metakaolin On Cement And Concrete

The resource of kaolin is rich in China, it has a great future. This study is about the effectof calcining system and different amount on the pozzolanic activity of metakaolin, and aboutthe effect of matekaolin on cement and concrete. This study said metakaolin has a highpozzolanic activity. With different calcining system, metakaolin can gain big pozzolanic. Thestrength and durability of concrete can be increased by metakaolin.Kaolin has not pozzolanic activity, it shows noble when added in cement mortar, but aftercalcined, its structure can be changed to gain pozzolanic activity. The calcining temperature,calcining time and cooling methods are important for the pozzolanic activity of metakaolin.The suitable calcining method is that kaolin is calcined at650℃~850℃for2hours,thencooled in air by mixed. The content of metakaolin in cement mortar is important. The bestcontent of metakaolin is8%(it can rise the compression strength by11%), it’s pozzolanicactivity is near that of silica. Metakaolin added in cement can increase the water demand, butthe increasing amount is lower than that of silica, which is lower2%, when the content ofmetakaolin is8%. And it also can be lower by8%, when the content of metakaolin of is12%.The setting time of cement is delay with the increasing of metakaolin. Metakaolin has lesseffect on the spread degree of cement paste, but it can improve the spread degree when thecontent of metakaolin is8%. Metakaolin can increase the strengths of concrete in all the age,and the durability of concrete too. When added metakaolin or silica in concrete, the slumps ofconcrete changed unobviously, but the spreaad degrees of concrete changed obviously. Theeffect of metakaolin on fluidity of concrete is better than that of silica. The early agecompressive strength of concrete with metakaolin is lower than of silica, but it is bigger thanthat with silica in the later ages. The effect of metakaolin on shrinkage of the concrete is lessthan of silica. The compressive strength and durability of concrete are increased when addedfly ash and metakaolin in concrete. The chloride ion permeability of concrete reduced with theincreasing of metakaolin content. When adding fly ash and metakaolin in concrete, thechoride ion permeability of concrete reduced with decreaseing of the water binder ratio. It isbetter for the pozzolanic activity of metakaolin in28d when the content of fly ash andmetakaolin is35%. When the content of metakaolin is same, the choride ion permeability ofconcrete increased when the content of fly ash increased.So metakaolin have a great future used in concrete and cement.