Effect of replacing gypsum by ferrous sulfate on Cr(Ⅵ) reduction in cement and cement properties
When ferrous sulfate is used to reduce hexavalent chromium Cr(Ⅵ) in cement,its high dosage will increase the content of SO3 in cement and reduce the compressive strength of cement.Because ferrous sulfate and gypsum all belong to sulfate,and they are similar to each other in properties and can prolong the setting time of cement,ferrous sulfate can be used to partially replace gypsum in cement.The effects of replacing gypsum by ferrous sul-fate on the content of Cr(Ⅵ) in cement and the dissolution of Cr(Ⅵ) in cement paste were studied.In addition,the effects of replacing gypsum by ferrous sulfate on the setting time,compressive strength and hydration products of cement were studied as well.The results show that when 0.3%gypsum is replaced by ferrous sulfate,the content of Cr(Ⅵ) decrea-ses from 11.8 mg/kg to less than 2 mg/kg without reducing the compressive strength of ce-ment at 28 d.The replacement of gypsum by ferrous sulfate will promote the formation of ettringite and prolong the setting time of cement paste.When the replacement amount by ferrous sulfate is less than 1.0%,it will promote the hydration of cement.The replacement of gypsum by ferrous sulfate will reduce the dissolution of water-soluble Cr(Ⅵ) in cement paste,and the dissolution of water-soluble Cr(Ⅵ) is 0 at 28 d.
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