Experimental Research On Phosphogypsum As Expansive Agents For Concrete

The crack in the concrete by the dry and cold shrinkages has been a puzzle that can not be well solved in the concrete application. To solve this problem, the common method is to add the expansive agent in the concrete to counteract cracks caused by these shrinkages. At present, the expansive agent that has been adopted commonly is the CSA expansive agent for concrete which is prepared by using the natural gypsum as the raw material. There are many phosphate fertilizer enterprises in our country, which discharge massive waste residue phosphogypsum every year. After being calcined, the phosphogypsum has the similar nature to the natural gypsum. Therefore this research substituted the inexpensive phosphogypsum for natural gypsum to prepare the expansive agent for concrete with the bauxite .Based on the characterization of the chemical analysis DTA XRD to the phosphogypsum and bauxite raw materials, the research carried out the experiment about the best calcination temperature of the two materials and the experiment about the strength of cement and the restrained expansion rate that is under the influence of mixture and ratio . The results show as follows: when the phosphogypsum is calcined at 650℃ bauxite is calcined at 700℃, the ratio is phosphogypsum: bauxite=60:40, the mixture of expansive agent is 8%, the expansive agent under these conditions can reach the best comprehensive effect; when the ratio changes 65:35, the early strength of the cement is low, but the final strength increases quickly, especial the compression strength can achieve the best result; as for the restrained expansion rate, the highest in 3 groups is the mixture 12% ratio 55:45, the mixture 10% ratio 60:40; the mixture 8% ratio 65:35.The results of experiments indicates that the 3d 7d early strength of the cement which is blended with the expansive agent is lower than the unblended's. The expansive agent plays a role of expanding in the cement ,as well as a role to enhance the final strength of the cement. As the mixture of the expansive agent increases, the...