Performance Design And Optimization Of Foam Gypsum Based On Pore Structure Control

Building gypsum has the performance of thermal insulation,and the foam building materials made by deep processing of gypsum substrate have inherent advantages in the field of inorganic thermal insulation and energy saving.As a kind of porous insulation material,there is an essential relationship between the internal pore structure and the working performance of foam gypsum.In this paper,gypsum,sulphoaluminate cement,Portland cement,calcium stearate,hydrogen peroxide are used as raw materials to prepare composite modified foam gypsum by chemical foaming.The pore structure of the material was studied emphatically,the modification mechanism of the pore structure was explored by X-ray diffraction and SEM(scanning electron microscope),the pore structure was characterized by Image-ProPlus software,and the relationship between the pore structure and the working performance of the material was explored.The change of pore structure caused by the properties of raw materials was explored with reference to the principles of physics.Furthermore,based on the above exploration results,the research on optimizing the working performance of materials with pore structure as a link was carried out,and the optimization mode was summarized.The main results wre obtained as following.(1)It is found that a certain proportion of Portland cement and sulphoaluminate cement can give gypsum-based foam thermal insulation material good foam stability in the early stage through comparative observation and analysis.Through the XRD and SEM analysis of pure foam gypsum and composite modified foam gypsum found that there was an embedded modification mechanism in the composite modified foam gypsum after the pore structure was stable,and the hydration product C-S-H gel of the composite modifier finally covered the surface of CaSO4·2H2O crystal in the form of coating,which strengthened the stability of gypsum crystal structure and improved the ability to resist external interference.The internal microstructure of composite modified foam gypsum in different hydration periods was observed,and the growth process of microbodies in the material and the symbiosis model in different periods were found.The samples were prepared by orthogonal test,the pore structures of different samples were characterized by Image-ProPlus software,the relationship between pore structure and material working performance was explored,and found that the porosity has the greatest influence on material working performance among all factors in pore structure,and the working performance can be optimized by adjusting material porosity,while graded pore size can also affect material performance in similar porosity,especially the thermal insulation performance of the material.(2)Drawing lessons from the physical principle of Plateau region stable bubble forming in the three-phase foam structure,taking the pore structure as the link,the influence of various raw materials on the pore structure were analyzed theoretically.The pore structure of the material was optimized by orthogonal test and single factor test,and the corresponding working performance was improved to a certain extent.Thus,the correctness of the optimization theory of pore structure was verified and the link between raw materials and material performance was consolidated.The influence of the change of raw materials on the pore structure in the actual test was further analyzed.The thermal insulation performance of the material can be improved by improving the expansion power,reducing the expansion resistance and the surface tension.Polycarboxylic acid superplasticizer reduces the optimal water-binder ratio of the material from 0.70 to 0.35,and when the cement content exceeds a certain value,the mechanical performance of the material will decrease.(3)Through the comprehensive study of the test conclusion and optimization analysis cleared that the action mechanism of the composite modifier can be divided into two processes:foam stabilization in the early stage and microstructure reinforcement in the later stage.The appearance of the modifier crystal skeleton in the early stage improves the foam support ability of gypsum-based materials,and the formation of C-S-H coating in the later stage can improve the material's ability to resist external action.At the same time,the microstructure was observed and analyzed in stages,and it was found that the growth process of gypsum-based crystal morphology was gradually regular,the bonding and strengthening mode at the lap joint of gypsum-based crystal skeleton under the action of modifier microbody and the inlay coexistence mode of its surface.With regard to macroscopic performance of pore structure,it is found that giving full play to the link role of pore structure can eliminate the interlacing variation of working performance caused by raw materials to a certain extent.Therefore,the action mechanism theory of composite modifiers is helpful to provide an important theoretical reference for the optimization of material performance of inorganic foam thermal insulation materials based on the regulation of pore structure in the future.