Secondary Vibration And Steam Curing Research Of Precast Concrete

Recently the research of precast concrete structure is in the heating stage,and due to the requirement of achieving construction industrialization to standardization,the strength of precast concrete and proportion of production time is particularly important in the production of the entire assemble line,and these are all relative to the curing system.But in the running of the precast plant,it takes a lot of time of curing,and curing time is not under control because of the immature skills.On the current situation of building the precast plant,steam curing is mostly used to cure the precast concrete,and secondary steam curing is a more advanced method.Therefore,it is very necessary to have the research of optimizing design of energy-saving kilns and secondary steam curing.Based on the research status at home and abroad of the curing,by reference to specific cases,some optimization for existing curing measures were compared,and put forward some new measures such as making a controlled water-cement ratio and having secondary vibration to improve the early strength of concrete and to reduce curing time,simultaneously optimizing the secondary steam curing system by incorporating slag,fly ash and sand ratio controlling,which is in order to change the way the concrete application of material components to increase productivity,and improve the late strength of precast concrete.Finally,coming up with several assumptions reducing costs of the kilns and energy saving,and discussing its possibility.Conclusions can be drawn according to the research:(1)By calculating the initial setting time of concrete structures,secondary vibration at the right time can improve the efficiency of secondary steam curing,and the late strength can be grown more uniform.At the same time proved by experiments after adding a secondary vibration in production line,the late strength of concrete has increased significantly,especially in low-grade concrete;and in the condition of secondary steam curing,the secondary vibration can save 10%cement without affecting the strength.(2)Through the reasonable time control of room temperature primary curing,the strength of concrete at high temperature and pressure stage can be better grown.According to practical case studies,and the minimum value of maturity calculating,room temperature curing time is in 2～4h,internal pore structure of concrete can be effectively improved,and the pitch time can be reasonably controlled.(3)Through the analysis of several cases,several factors of the secondary high temperature and pressure steam curing stage are further explored,including heating rate,constant time and constant temperature.Heating rate is controlled at 15℃/h-20℃/h,so that we can prevent the increase of internal porosity of the concrete which led water vapor movement or even cracking,but also improve the efficiency of steam curing.Control the thermostat time between 3～4h,not only to prevent the phenomenon that late intensity without increasing due to the long holding time,but also reduce the costs,speed up the operation of the product line.Control the thermostat temperature at 50℃～60°C,avoiding the reducing of late strength because of the exist of connectivity porosity caused by high temperature.(4)In the case of slag-fly ash dual-doped,by comparing the experimental data and the study of double-doped proportion,maximum intensity can be achieved when dosage is 40%,and stripping strength can be reached 50MPa and more.And if the proportion of slag and fly ash is 5:3,28d strength is higher but 90d strength is lower,whereas the opposite,which suggest that slag is playing the main role in the early stage,and fly ash is more favorable of late development.(5)During the secondary steam curing,energy-type vertical circulation curing kiln is proposed,namely in primary curing stage,a pipeline is added in the "n" type curing kiln,to lead the residual gas to inlet;in the high temperature and pressure vertical curing kiln,with additional gas supply valve,with repeated use of residual gas to save energy during multiple steam curing kettle working.Studied about the steam accumulator,and Rafael nozzle design is optimized by calculation.Through the analysis of actual cases,according to the knowledge learned in the Liaoning Yuhui New Building Materials Co.,Ltd.,with the integration of improvement point above,proposing the precast secondary vibration program,theory with practice,eventually writing.