Study On Properties Of Plant Ash Cotton Stalk Fiber Cement-based Materials And Analysis Of Environmental Benefits

Under the"double carbon"circumstances,the efficient utilization of solid waste is a important way to reduce carbon emission and promote green development.In recent years,southern Xinjiang industry has grown rapidly and the cotton industry has gone strength to strength,the proportion of solid waste with industrial and agricultural has gradually increased.The application of solid waste in building materials has become a road on resource utilization.In this study,cotton stalk fiber was used as reinforcing material of cement-based materials,and plant ash from biomass power plant was used as admixture to replace cement to prepare plant ash cotton stalk fiber cement-based materials.Firstly,the fineness of plant ash is taken as the control index,and the appropriate fineness of plant ash is obtained by analyzing the changes of water consumption of cement standard consistency,fluidity and strength of cement mortar with different fineness of plant ash,and The feasibility of replacing cement with plant ash is analyzed by comparing the mechanical properties of cement mortar with plant ash and fly ash in the case of single and compound mixing;By studying the effect of cotton stalk fiber content on the physical and mechanical properties of cement-based materials,the appropriate cotton stalk fiber content was determined;The effects of plant ash replacing cement on the physical and mechanical properties and microstructure of cotton stalk fiber cement-based composites were studied by combining macro and micro methods,and the appropriate content of plant ash was determined;Finally,the life cycle assessment（LCA）method is used to qualitatively and quantitatively evaluate the two treatment methods of plant ash（direct landfill and replacement of cement）.The main research contents and results are as follows:（1）The fixed value of plant ash to replace the amount of cement is at 10%,and explore the influence of plant ash with different fineness on the water consumption of standard consistency of cement and the fluidity and strength of cement mortar.The results show that with the decrease of the fineness of plant ash,the water consumption for standard consistency of cement first decreases and then increases,the fluidity of cement mortar is firstly increased and then decreased,and the strength of cement mortar has similar trend.By general comparison,the best fineness of plant ash is 6.9%.Through the study on the mechanical properties of cement mortar,it is found that the compressive strength of the plant ash cement mortar is higher than that of the fine coal ash cement mortar in the first 28 days when the plant ash and fine coal ash are mixed alone.When the amount of admixture replacing the cement is 10%,the compressive strength of the plant ash cement mortar at 3,7 and 28 days is 21%,17%and 18%higher than that of the fine coal ash cement mortar respectively;When the curing age reaches 90 days,the compressive strength of fine coal ash cement mortar is higher than that of plant ash cement mortar.When the amount of admixture replacing cement is 5%,10%and 15%,the 90 day compressive strength of fly ash cement mortar is 2%,5%and 31%higher than that of plant ash cement mortar respectively.The compressive strength of cement mortar mixed with plant ash and fine coal ash is higher than that of cement mortar mixed with fine coal ash,The compressive strength of cement mortar mixed with 5%fly ash and 10%plant ash for 3,7,28 and 90 days is 5%,5%,4%and 32%higher than that of cement mortar mixed with 15%plant ash.Analyzed separately from the aspect of compressive strength,plant ash can be used as an admixture with the same effect as fine coal ash.（2）With the increase of cotton stalk fiber content,the dry apparent density and thermal conductivity of cement-based materials decreased,and the pressure to deflection ratio of cement-based materials firstly decreased and then increased.The study on the mechanical properties of cotton stalk fiber cement-based composites shows that the flexural strength of cement-based materials decreases with the increase of cotton stalk fiber content,and the compressive strength increases slowly in the early curing period（<7 days）and later curing period（>56 days）;The flexural strength of cement-based materials firstly increased and then decreased with the increase of cotton stalk fiber content.The flexural strength of cement-based materials increased first and then decreased with the increase of curing age.When the content of cotton stalk fiber is fixed at 2%,the flexural strength of cement-based materials is the highest and the value of compression folding ratio is the lowest.（3）With the increase of plant ash replacement rate,the water absorption of cotton stalk fiber cement-based composites increased,the dry apparent density decreased,and the thermal conductivity firstly decreased and then increased;The compressive strength of cotton stalk fiber cement-based materials decreased with the increase of plant ash replacement rate.The effect of plant ash on the later compressive strength of cotton stalk fiber cement-based materials was stronger than that on the earlier compressive strength.When the amount of plant ash replacing cement was fixed at 20%,the compressive strength at 3days,28 days and 56 days decreased by 42%,38%and 32%respectively compared with the reference group;The flexural strength of cotton stalk fiber cement-based materials generally decreased with the increase of plant ash replacement rate.When the amount of plant ash replacement cement was less than10%,the flexural strength of cotton stalk fiber cement-based materials did not decrease significantly.From the aspect of strength,the best replacement of cement with plant ash is at 5%.Through the analysis of SEM and XRD,it was found that the plant ash improved the internal structure of cotton stalk fiber cement-based material,reduced the content of Ca（OH）₂and AFT,and promoted the hydration degree of cement.（4）Through the full life cycle environmental impact assessment of the two schemes of plant ash,（direct landfill of plant ash and replacement of cement with plant ash）,it is found that direct landfill of plant ash will bring various environmental impacts.Replacement of cement with plant ash can bring various environmental benefits,and the environmental benefits of it far exceed the environmental impacts of direct landfill.According to the explanation of life cycle results,it is found that in the process of resource utilization,long-distance transportation of plant ash should be avoided,because during transportation the energy consumption and emission may offset the advantages of resource utilization of plant ash.