| The cement-based foam concrete contains a large number of pores,and has the advantages of light weight,non-combustible,low resource consumption and good thermal insulation performance.It has been widely used in energy-saving buildings and green buildings.However,the existing foamed concrete has high porosity,large average pore diameter,uneven pore size,and high pore connectivity,resulting in low strength,high water absorption,and poor thermal insulation performance.In this paper,by restraining foaming,regulating the restraint pressure,the pore structure were controlled to improve its performance.This paper prepared and researched the basic properties of restrained foamed concrete;studied the influence of raw materials and curing methods on the performance of restrained foamed insulation board,to obtain the best mix ratio and to determine the relationship between them of restrained foamed concrete;researched the application of nanocatalysts in foamed concrete.The effects of constrained foaming and free foaming on pore structure and properties were studied.CT,computer technology and image analysis technology were applied to determine the advantages of restrained foaming relative to free foaming,while at the same time to determine the relationship between the restrained pressure and pore structure or performance,the relationship between microstructure and macroscopic performance.The main results can be summarized as follows:?1?MnO2 nanocatalysts with different supports prepared by hydrothermal method were a kind of potassium manganese oxide hydrate crystal?JCPDS No.86-0666?.Copper doping may have a beneficial effect on the self-assembly of delta-MnO2 nanosheets.The reaction rate of H2O2 catalyzed by Cu-MnO2@D was the fastest,followed by MnO2@D,and the decomposition rate of MnO2@P was the slowest.The H2O2 bond lengths in MnO2before and after copper intercalation were 1.376?and 1.431?,respectively.In the copper intercalation system,the hydrogen peroxide bond was easier to break to produce hydroxyl radicals,oxygen,etc.Cu-MnO2@D catalyzes the decomposition of hydrogen peroxide to produce more oxygen and more bubbles.?2?The addition of MnO2 nano-catalyst can reduce the amount of foaming agent when the same dry apparent density was reached.The reduction of catalyst Cu-MnO2@D is the greatest,followed by MnO2@D and MnO2@P.When the foaming temperature is low?below 35 oC?,the addition of MnO2 nano catalyst decreased the dry apparent density of foam concrete while the loss of compressive strength was smaller or even improved.?3?Foaming temperature had the greatest influence on compressive strength and water absorption,followed by the amount of foaming agent.The change of moisture content caused by curing conditions had a significant effect on the drying shrinkage of concrete,mass water absorption was positively correlated with the final drying shrinkage of foam concrete specimens.?4?The optimum proportion of restrained foaming cement insulation board was water-binder ratio 0.64,foaming stabilizer 3%,foaming agent 3.2%,40 oC,silica fume B content 9%and mineral powder content 5%.The curing system was 48 hours wet curing at 40 oC,humidity 100%,and 24 hours dry curing under 60 oC.Under these conditions,the surface density,dry apparent density,compressive strength,flexural strength,thermal conductivity,drying shrinkage,mass water absorption and volume water absorption of confined foamed concrete composite insulation board were 14.2 kg/m2,475 kg/m3,1.31MPa,1.62 MPa,0.129 W/?m.K?,0.5 mm/m,9.1%and 4.3%,respectively.?5?The closed-cell ratio of confined foamed concrete was better than that of free-foamed concrete.After restrained foaming,the ratio of closed-cell ratio to open-cell ratio increases from 0.01 to 0.22.The restrained conditions and silicon content of raw materials did not affect the crystal structure of hydration products.The hydration products of foaming concrete mainly included portlandite,ettringite,C-S-H gel and a small amount of six side sheet calcite caused by carbonization.?6?The porosity and average pore size of free foamed concrete were larger than those of restrained foamed concrete.When silica fume added,the restrained foaming pressure was about 80 N.The compressive strength of restrained foamed concrete with SiO2-1 was higher than that with SiO2-2.And the porosity of confined foamed concrete decreaseed with the increase of SiO2-1 content,from 45.8%to 32.3%.When the content of SiO2-1 is 1%,the average pore size was the smallest?0.08 mm?,which was 32.5%lower than that none SiO2-1.The restrained pressure inside the die increaseed with the increase of SiO2-1 content,and it increaseed from 45 N to 80 N. |
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