Experiment Research On Fly Ash As Expansive Agents For Concrete

Based on expansive agents for concrete, expanded cement develop for making up compensate shrinkage concrete and expanded concrete , improving anti-crack and impervious properties of concrete, and increasing dense structure of concrete. Expansive agents for concrete are widely used in modern projects. At the present time, CSA expansive agents for concrete are the main products in market. The source of expansion is ettringite. This kind of expansive agent not only has superiority performance and wide application but also convenience exploitation and long guarantee period. Combined with the research of formation mechanics of ettringite, this paper produce CSA expansive agents for concrete can be made by using industrial residue- fly ash and phosphogypsum. Under the excitation action of Ca(OH)₂ solution in the hydration of cement, active-Al₂O₃ in fly ash and CaSO₄ in phosphogypsum would occur physical action and generate ettringite for supplying volume expansion and displaying the action of expansive agents for concrete.Through analytical method of chemical compositions , XRD, DTA and SEM for raw materials, composition and the preprocessing method can be assured. When making up expansive agent, phosphogypsum need calcinations for 1.5h under 650 ℃ to make it have identical performance of natural gypsum; bauxite need calcinations for 1.5h under 700 ℃ to form the calcined bauxite as active- Al₂O₃ content conditioning agent in fly ash which won't be calcined. Through the orthogonal experiment of different mixture ratio of expansive agent and direct-vision analysis of its property, the best mixture ratio condition is A₁B₂C₁,: the ratio of phosphogypsum and fly ash is 55 : 45, the adding amount of bauxite is 10% in fly ash and the expansive agent is 8%. The most prominent property of this kind expansive agent have a high the restrained expansion rate when the adding amount is 8%,which agree with the develop tendency of low adding amount of expansive agent.The factor of making up raw materials which influence concrete expansive property is analyzed in this paper. The most influence factor is adding amount of expansive agent, then is the phosphogypsum: fly ash and the adding amount of bauxite in it. With the increment of adding amount of expansive agent and the limiting expansion rate of the accumulation of cement and sand, the early strength has a reduction, but the final strength can be sure have an increase. In addition, fineness and...