Experimental Study On PHC Pipe Pile Autoclaved New Technology And Concrete Performance

Under the dual-carbon situation,the traditional concrete industry is advancing towards high-end,intelligent and green development.It is imperative to seek new cementitious materials to improve the performance of pipe pile concrete,to seek efficient and intelligent mixing methods,and to seek autoclave-free curing processes to reduce energy consumption.Based on the actual engineering background of the production of prestressed high-strength tubular piles in my country,this paper explores the effects of different steam curing systems and ultrasonic vibration stirring process parameters on the mechanical properties of mortar and tubular pile concrete mixed with new auxiliary cementitious materials,and analyzes the mechanism.The performance indicators such as microscopic morphology and pore characteristic parameters of concrete after autoclave-free curing are evaluated,and the new process effect of autoclave-free curing is evaluated to provide experimental basis for the realization of autoclave-free production process of high-strength prestressed concrete(PHC)pipe piles.The main research contents of this paper are as follows:(1)In order to realize the new autoclaving-free process and improve the early strength of concrete,a new type of auxiliary cementing material was introduced.10% mineral powder,test the flexural and compressive strength of cement mortar specimens at various steam curing ages from 2h to 8h,and explore the change law of mechanical properties of cement mortar specimens mixed with various new auxiliary materials with steam curing time.The results show that the flexural and compressive strengths of the mortar specimens increase gradually with the increase of the steam curing age,and the strength increases the fastest between the curing age of 4h and 8h;when the curing time is 4h,adding partial Compared with the control group,the flexural strength of kaolin increased the most,and the compressive strength of adding semi-encrypted silica fume was the largest compared with the control group.Ash has the highest compressive strength.(2)Determine that the steam curing system is the key technology to realize the new steam curing process.According to the actual mix ratio of concrete pipe piles produced by the factory and the selected new auxiliary cementing materials,design and prepare PHC pipe pile concrete,and set 8 different steams.The curing constant temperature and constant temperature time were used to study the change law of the compressive strength of the pipe pile concrete mixed with the new auxiliary cementitious material with different steam curing constant temperature and constant temperature time.The results show that when the constant temperature of steam curing is 75℃ and the constant temperature time is 8h,the compressive strength of PHC pipe pile concrete with the ratio of mineral powder and 5% metakaolin has the greatest increase.When the constant temperature of steam curing is 90℃,the compressive strength of each proportion of concrete basically increases gradually with the constant temperature time.When the constant temperature time is 8h,the compressive strength of PHC pipe pile concrete with the ratio of mineral powder and 5% metakaolinite increases the most.Finally,it is determined that the steam curing constant temperature for realizing the new steam curing process is 90℃,and the steam curing constant temperature time is 6h～8h.(3)Improving the dispersion effect of cementitious materials is another key technology to improve the effect of autoclave-free curing.Introduce the ultrasonic excitation stirring process into the concrete mixing project,and discuss the influence of the ultrasonic excitation and mixing parameters to coordinate the autoclave-free process on the performance of concrete.The compressive strength of pipe pile concrete under ordinary stirring and ultrasonic vibration stirring was tested by using different air pressure and feeding sequence of exciting stirring,and the variation law of compressive strength of pipe pile concrete with different exciting air pressure was studied to determine the appropriate ultrasonic vibration The results show that ultrasonic vibration stirring can significantly improve the compressive strength of pipe pile concrete.For the same group of specimens,the compressive strength of pipe pile concrete shows a trend of first increasing and then decreasing with the exciting air pressure;the determined feeding sequence In order: sand,glue,water and stones.The influence of the compressive strength of each proportion of concrete under the two mixing methods from small to large is: 5% densified silica fume group < 3% metakaolin + 5% densified silica fume group<5% metakaolin group<8% densified silica fume group<5% undisturbed silica fume group.(4)In order to evaluate the effect of the new process of autoclave-free curing,the microscopic morphology and pore characteristic parameters of PHC pipe pile concrete after autoclave-free curing were studied.X-CT scanning and MIP mercury intrusion method were used to test the PHC pipe pile concrete,and to explore the distribution law of the internal pore characteristics of the PHC pipe pile concrete under the action of different cementing systems.The results show that: the more complex the cementation system is,the smaller the pore size of the PHC pipe pile concrete,and the more uniform the pore distribution;when the degree-time product increases,the porosity of the PHC pipe pile concrete shows a trend of first decreasing and then increasing;The average aspect ratio of the internal pores of kaolin and 5% densified silica fume concrete is the smallest;the change of fractal dimension is related to the change of compressive strength of PHC pipe pile concrete.The number of holes is reduced and smooth.