Reclaimed Gypsum Properties Change Law And Mechanism

Building gypsum can be got by heating dihydrate gypsum, and after hydration thenbecome dihydrate gypsum. Each year the world’s emissions of waste gypsum is large，most of them placed as waste. Theoretically, the main components of waste gypsum isdihydrate calcium sulphate, after crushing, grinding, screening, and after calcination thewaste gypsum can serve as raw materials for the production of gypsum buildingmaterials, and realize recycling, and does not produce construction waste, thereforewaste gypsum had the requirement to reuse completely.To carry out the research on the performance of degradation law and mechanism ofrenewable gypsum not only provide theoretical basis for the reuse of waste gypsum, atthe same time as renewable gypsum and its dehydration phase as a variant of thegypsum, the study of it also enriched and expanded the basis of gypsum theory, and thecomprehensive utilization of renewable gypsum resources is of great significance forthe protection of natural environment, conserve natural gypsum resource, improve theenterprise economic benefit and sustainable development, and in the national policy ofenergy conservation、environmental protection and sustainable development, recyclingof waste gypsum will be get more and more attention from society.This project made research on the properties comparison of building gypsum andregenerative gypsum under the same calcination process, analyzed the influence ofdifferent tastes of natural gypsum plaster on reclaimed gypsum, using a variety ofanalysis methods, water of crystallization analysis, differential thermal analysis, X-raydiffraction analysis, scanning electron microscopy (SEM) analysis, mercury intrusionmethod analysis deeply the reasons of the decrease of the reclaimed gypsum.Compared to building gypsum the performance of reclaimed gypsum is declining,and the decline of reclaimed gypsum performance is more obvious, mainly showed onthe setting time extented,2h strength and dry strength reduced, the condensed waterdemand increased greatly, sclerotium bibulous rate increased. Reclaimed gypsumgenerated by YingCheng gypsum （super grade），its performance degradation rateis close to50%compared to the original performance; represented by liangping gypsum（first grade）its performance degradation has the highest level,2h compressivestrength degradation rate can reach62%. Mainly performance: compared to buildinggypsum, the2h flexural strength of reclaimed gypsum fell. And different taste of natural gypsum have greater effects on the performance of reclaimed gypsum, because highgrade gypsum content more dihydrate gypsum, few impurities, generated by the phasedistribution after calcination is better and more hemihydrate gypsum, lower specificsurface area; to the contrary the low grade of gypsum containing dihydrate gypsum less,content more impurity, the gypsum phase distribution is poorer after calcination, andlower hemihydrate gypsum phase, higher specific surface area.Compared with building gypsum plaster, the particles of reclaimed gypsum tend tofine particles, and the dispersion is larger, and with the same particle size, its specificsurface area is much larger than building gypsum, so the reclaimed gypsum contentmore internal defects; and its crystals mainly exists in the form of granular, and thesurface is rough, specific surface area is big; its hardened structure within more pores,and porosity enlarged, crystal arranged loosely. because the effective lap between thecrystals is reduced, the strength of the contact point in crystallization is reduced, so thestrength of hardened body drops greatly, the products performance decreases.For the reason of the thermal performance and mechanical properties of reclaimedgypsum is different from natural gypsum, so adopting natural gypsum calcining processapplied to reclaimed gypsum is not suitable, in order to get better performance ofreclaimed gypsum to promote waste gypsum resource, we need research a reasonablecalcine system for reclaimed gypsum.