| Foamed concrete is a kind of porous cement-based material prepared by introducing a large amount of foam,and the foam is produced by physical or chemical methods.Foamed concrete possesses the advantages of light weight,high shock absorption and easy to construction.Bridge filler refers to the filler between the bridge deck and the bridge arch in arch bridges.The traditional arch filler is sandstone,but the sandstone possesses the disadvantages of large self-weight and high water absorption.In this study,foamed concrete was used as bridge filler to replace the traditional sandstone filler,which can significantly decrease the self-weight and improve the load carrying capacity of the bridge.This study is based on the repair and reinforcement of the double-curved arch bridge of the south approach bridge of Nanjing Yangtze River Bridge.Based on the performance requirements of the bridge filler,this paper investigated the main factors that can affect the performance of foamed concrete.After the foamed concrete was poured in the Nanjing Yangtze River Bridge,the internal strain change of the foamed concrete was monitored by embedded sensors.In this study,P.II 52.5 cement was used as the main raw material,and the influence of process parameters(stirring time,water-cement ratio and drying system,etc.)on the strength of foamed concrete was studied.The effects of density,foaming agent type,rubber powder content,fiber incorporation on the performance of foamed concrete(such as compressive strength,drying shrinkage,water absorption and frost resistance)was discussed.The microscopic analysis methods such as X-CT and SEM were used to observe and analyze the pore structure inside the foamed concrete.The performance of three commonly used foaming agents(plant protein,animal protein and synthetic foaming agent)was compared.The experimental results showed that the pore wall in the foam prepared by the synthetic foaming agent was thicker,and the foam had higher strength and stability.Therefore,the foamed concrete obtained by mixing this foam into the cement paste possessed higher strength,lower water absorption and stronger frost resistance.The incorporation of the rubber powder can significantly change the pore structure of the foamed concrete,but its effect varies according to the type of foaming agent.The incorporation of PP fiber and lignin fiber can reduce the drying shrinkage of foamed concrete,but PP fiber led to more large pores in the specimens.In order to ensure the safety of foamed concrete as bridge filler,the internal strain of the bridge filler and the bridge deck on the 55 th bridge arch of the Yangtze River Bridge was monitored by embedded strain sensors.The monitoring results revealed that the internal strain of the foamed concrete on the arch was higher than that of the bridge deck.The drying shrinkage of the filler measured in 90 days was 700 microstrain,smaller than the design upper limit of shrinkage(1000 micro strain),which meets the design requirements of the bridge fillers. |
