| With the development of urbanization,a large amount of construction and demolition waste is produced,and a large amount of recycled fine powder is produced in the process of using it to produce recycled aggregate.The regenerated powder contains inert quartz and calcium carbonate,resulting in low activity of the regenerated powder,and it is difficult to find a suitable way to use it.In this paper,according to the composition characteristics of recycled fine powder,ball milling treatment is selected as the modification method of recycled fine powder.The activation effect of ball milling treatment on different mineral components in recycled fine powder is the key to its application in cement-based materials.In this paper,based on the different activation effects of recycled fine powder with different ball milling time,the feasibility of preparing autoclaved aerated concrete with different fineness of recycled fine powder is analyzed,and the effect of dosage of high fineness recycled fine powder on the performance of autoclaved aerated concrete when replacing cement is further studied.Then,according to the composition of recycled fine powder,the cement and fly ash in autoclaved aerated concrete are replaced,and the influence of the content of high fineness recycled fine powder on the foaming performance,physical and mechanical properties and hydration products of autoclaved aerated concrete is studied.Finally,the effects of ball milling treatment on the activity of recycled fine powder and the effect of high fineness recycled fine powder on the temperature and consistency of autoclaved aerated concrete slurry were investigated.The effect mechanism was further explored by the activity of recycled fine powder,hydration products and the microstructure of autoclaved aerated concrete(AAC).The results show that:(1)AAC products with dry density of 525.57 kg/m~2 and compressive strength of2.25 MPa were prepared by using refined recycled fine powder.Many properties of recycled fine powder based autoclaved aerated concrete meet the requirements of A2.0B05 grade in GB/T11968-2020.More unhydrated cement particles are released in the recycled fine powder after ball milling treatment,and more amorphous C-S-H gel can be produced in the pre-curing stage,and more tobermorite is generated by reacting with calcium source,thereby increasing the compressive strength of autoclaved aerated concrete.The high-fine quartz sand in the recycled fine powder has higher solubility and can react with the calcium source to form more tobermorite.(2)AAC products with dry density of 544.26 kg/m~2 and compressive strength of2.10 MPa can be prepared by replacing cement with fine recycled powder.Many key properties of recycled fine powder-based AAC meet the requirements of A2.0B05 in GB/T11968-2020.With the incorporation of RFP-30,due to the small fineness of RFP-30,the consistency of autoclaved aerated concrete slurry increases,resulting in a decrease in the foaming rate of the slurry,and the bulk density of the product increases.The high consistency leads to a decrease in the porosity of AAC products.At the same time,due to the small amount of C-S-H gel generated in the pre-curing stage,the content of tobermorite in AAC products decrease after autoclaved,which eventually lead to the decrease of compressive strength of AAC products.(3)AAC products with dry density of 523.99 kg/m~2 and compressive strength of2.38 MPa can be prepared by replacing cement and fly ash with finer recycled fine powder.Compared with replacing cement,the physical and mechanical properties of AAC products prepared by RFP-30 replacing both cement and fly ash are improved.The replacement of fly ash by quartz sand in recycled fine powder can promote the formation of tobermorite.This is because the solubility of quartz sand is low.In the process of replacing fly ash with quartz sand in recycled fine powder,the effective calcium-silicon ratio in the system will gradually increase,and a high calcium C-S-H gel that is easy to transform into tobermorite will be generated,thereby increasing the total amount of tobermorite in the system.At the same time,the silica content of quartz sand is high,which provides dissolved silicon in the later stage of autoclaving,thus promoting the further development of tobermorite crystals.Figure[51]table[20]reference[145]... |
