Study On Preparation And Properties Of Foam Concrete Modified By CO₂

Excessive emission of CO₂ gas leads to global warming,which is one of the serious problems facing mankind all over the world.In order to mitigate the trend of global warming,building energy efficiency and CO₂ capture and reuse have attracted wide attention around the world.As a kind of inorganic thermal insulation material,Foam concrete（FC）is an excellent energy-saving material with good thermal insulation,heat insulation,fire prevention and other properties.Its unique internal pore structure not only reduces the amount of cement,but also can sequester CO₂ and other greenhouse gases.In this study,a new model of CO₂ and FC combination was proposed.CO₂ gas was introduced into FC by physical foaming method,so that CO₂ was evenly distributed in the FC pore structure.The effects of different CO₂ concentrations and basic factors on FC performance were studied,and Image-Pro-Plus software was used to assist the analysis of the internal pore structure.In addition,in order to reveal the action mechanism of CO₂ gas on FC,the diffusion model of CO₂ gas inside the bubble was speculated,and the microstructure and reaction products of CO₂ foam concrete were analyzed by scanning electron microscopy and X-ray diffraction.Finally,the response surface method was used to optimize the ratio,and the excellent performance of CO₂ foam concrete was prepared.The following conclusions can be drawn:（1）The introduction of low concentration CO₂ into the bubble has little influence on the foam quality,and the foam settling distance increases linearly with the increase of CO₂concentration.The higher the CO₂ concentration is,the larger the foam settling distance is,and the foam quality decreases obviously.When 20vol%CO₂ is added,the 28d compressive strength of the test block can reach 3.32 MPa,which is 24.8%higher than2.66 MPa in the reference group,and the drying shrinkage of the test block is 2.56mm/m,which is 23.1%lower than 3.33mm/m in the reference group.The drying shrinkage value of the CO₂ foam concrete is all lower than that in the reference group.The reaction of CO₂with cement optimizes the microscopic pore structure,but high concentration of CO₂ will make the pore size distribution,average pore size and pore shape factor of the test block deteriorate,and has little effect on the porosity.Through microstructure analysis,the diffraction peak of Ca CO₃ increases with the increase of CO₂ concentration.Combined with SEM images,a large number of Ca CO₃ crystals were generated by adding CO₂,and C-S-H gel pores became less and the microstructure of slurry became more dense.（2）The results show that the optimal water-binder ratio is 0.60,the 28d compressive strength of the test block can reach 3.29 MPa,and the mechanical properties are the best.With the increase of water-binder ratio,the thermal conductivity of FC increases first and then decreases.The pore structure directly affects the thermal conductivity.When the water-binder ratio is 0.60,the average pore diameter and shape factor of the samples reach the minimum values of 217μm and 1.17,respectively.Water absorption increased first and then decreased with the increase of water-binder ratio.When the fly ash content is 10%,the compressive strength of FC reaches the maximum,reaching 2.76 MPa.When the fly ash content is 30%,the lowest thermal conductivity is 0.109 W/（m·k）.A small amount of fly ash can improve the fluidity of slurry,water absorption and dry shrinkage value also improve with the addition of fly ash.With the increase of foam volume,the dry density and compressive strength of test blocks decreased at all ages.When the foam content is 80%,the minimum thermal conductivity is 0.107 W/（m·K）,and the thermal conductivity decreases with the increase of the foam volume content.With the increase of foam content,more harmful pore structures were formed,and the dry shrinkage performance and water absorption increased.（3）The response surface method was used to study the influence of different factors on FC performance.The influence degrees of compressive strength and thermal conductivity were water-binder ratio>CO₂ concentration>fly ash content,fly ash content>water-binder ratio>CO₂ concentration.By optimizing the maximum compressive strength and minimum thermal conductivity of 28d,the optimal ratio is as follows:The water-binder ratio is 0.61,the fly ash content is 20%,the CO₂ concentration is19.47%,the 28d compressive strength of CO2 foamed concrete is 3.49 MPa,the thermal conductivity is 0.1143 W/（m·K）,the performance meets the criteria JG/T266-2011"Foamed concrete".By comparing the predicted value with the measured value,the error value of each performance is less than 5%,and the prediction of regression model is reliable.Figure[78]table[25]reference[97]...