Experimental Study On The Performance Of Foamed Concrete Mixed With Fly Ash And Slag

As a new type of building material,foamed concrete is valued by people for its good working performance,simple construction technology and excellent thermal insulation performance.It is suitable for external wall thermal insulation and other important engineering construction.Adding fly ash,slag and other industrial waste residues into foamed concrete can not only save raw materials and reduce costs,but also meet the requirements of national green environmental protection,energy conservation and emission reduction.But the foamed concrete inherent shortcoming is the durability is poor,the strength is low,the water absorption rate is big and so on the question.In this paper,the physical and mechanical properties,thermal properties and frost resistance and durability of foamed concrete with double fly ash slag are studied through systematic tests,and the influence of fly ash and slag on the composite cementing system of foamed concrete is analyzed.The research on the micro-pore structure and hydration products of double-fly ash slag foamed concrete was carried out in depth,and the interaction rules between the macro-performance,material composition and micro-pore structure were discussed.The main work and conclusions of this paper are as follows:With the increase of foam content,the dry density and compressive strength of foamed concrete decrease gradually,but its water absorption rate increases gradually.Different mixing time will also affect the performance of foamed concrete.Too short mixing time?less than 200s?will lead to uneven mixing of foam and slurry,and too long mixing time?more than 280s?will lead to foam bursting in the slurry.With the increase of mixing time,the strength and dry density of foamed concrete will decrease first and then increase.The dry density of foamed concrete is positively correlated with its thermal conductivity,that is,the thermal conductivity of foamed concrete increases with its dry density.The compressive strength and flexural strength of foamed concrete increase with the increase of slag content in the range of 10%³0%.The hydration mechanism of fly ash and slag in foamed concrete was analyzed by studying hydration products.With the increase of the content of slag and fly ash in foamed concrete,the content of Ca?OH?₂,the hydration product,is significantly reduced,and the amount of unhydrated C₂S and C₃S minerals in the Portland cement foamed concrete specimen is also significantly reduced,and the strength of foamed concrete becomes lower.The thermal conductivity of foamed concrete increases with the increase of slag content and the water absorption decreases.In addition,a calculation model for the dry density of foamed concrete with double fly ash slag was established through research.After verification,it was found that the model met the requirements for the grade of dry density in‘Foamed concrete block'JC/T1062-2007.As the number of freeze-thaw cycles increases,the compressive strength of foamed concrete gradually decreases,and its compressive strength decreases slowly in the early stage.With the repeated freeze-thaw cycle tests,the compressive strength of foamed concrete declines rapidly.The 0.50-15%-30%group and the 0.50-35%-20%group have the worst frost resistance and durability.After 75 cycles the damage occurred.The samples in the groups of0.40-25%-20%and 0.45-15%-20%were destroyed after 175 freeze-thaw cycles.Moreover,the specimens in the 0.50-15%-30%group and the 0.50-35%-20%group showed obvious cracks on the surface of the specimens after 25 freeze-thaw cycles.The surface cracks were scanned with crack width gauge,and the cracks were counted.It was found that the existence of cracks greatly reduced the frost resistance durability of foamed concrete.The pore size analysis of double-fly ash slag foamed concrete shows that the porosity of the 0.40-25%-20%group and the 0.45-15%-20%group are relatively small,the internal structure of the foamed concrete is relatively dense,and the overall pore volume is relatively small,so the inner pore wall is relatively thick,and the resistance to freeze-thaw cycle is strong.However,the0.50-15%-30%group and 0.50-35%-20%group have relatively large porosity,and their internal stomatal walls are relatively thin,which are easy to be damaged in the freeze-thaw cycle.As a result,the internal macropores and connected pores increase,and the water absorbed increases correspondingly.The damage time is relatively short and the damage degree is relatively serious.After the freeze-thaw cycle was completed,the specimen sections were processed and the observation hole structure was observed with 50 times of polarizing microscope,and the destruction mechanism of freeze-thaw cycle was verified.