Analysis Of Moisture Absorption Behavior And Interfacial Moisture Stress Of AFRP-strengthened Concrete Beam

In recent years, aramid fiber reinforced plastic (AFRP) has become a new kind ofreinforced material due to its many advantages, such as corrosion resistance, lightweight, convenient and quick construction, saved using space and so on. In the future,AFRP will be irreplaceable when it is used for earthquake-resistant, reinforcement,repairment of building, bridge and tunnel structures. However, when RC beamstrengthened with AFRP has been exposed to hygrothermal environment for a longtime, not only the physical and chemical properties of reinforced materials arechanged, but also its operational performance are reduced due to interfacialtemperature stress and moisture stress by hygrothermal environment. The interfacialstress and the decline of interfacial bonding strength generated by moisture absorptionare the main reasons of bearing capacity decline of strengthening members. In orderto research the influence of moisture absorption on interface, this paper does thefurther works for the following aspects:(1) According to the diffusion governing equation of the second Fick’s law, firstlythe moisture governing equations that relative humility of environment is globalvariable are deduced in this paper, and then the general expressions of relativehumility about moisture diffusivity and humidity ratio for AFRP and concretematerial are solved. At same time, we refer to the solution of temperature stressbetween composite material interlayers and take use of sine series and cosine series toexpress shear stress and normal stress for interface of AFRP and concrete,respectively. Castigliano’s theorem is utilized to set up the corresponding equations,the hygroscopic residual shear stress and normal stress of AFRP, concrete and theinterface between AFRP and concrete are obtained.(2) The mass diffusion module in ABAQUS is used to simulate and analyzehygroscopic behavior for AFRP-reinforcd concrete beam. By seting up2D finiteelement model, the concentration field inside material after moisture absorption isobtained. The result shows that the moisture diffusion velocity of concrete material isgreater than AFRP material, and AFRP material is a kind of protective screen to prevent moisture diffusion. At same time, the2D model is extended to3D model, inorder to observe the trend of moisture diffusion and concentration field inside twokinds of material at an actual situation.(3) A finite solid element is used to establish glue line, and the advantage ofcoupled temperature-displacement method of ABAQUS is ultilzed to research themoisture stress and stress distribution of concrete, glue line and AFRP materials atdifferent time. The results show that the level of interfacial moisture stress is greaterthan that of other regions, and the stress concentration at the end of interface appearseasily, which leads to debonding damage at the end of AFRP. Using the concreteplastic damage model, the concrete beams under the uniformly distributed load in themid span and moisture absorption are simulated, and the tensile and compressivedamages inside materials are researched. The results show that the moistureabsorption relieves tensile damage at both end areas on the top of beam, but increasesthe tensile damage at the bottom area of beam, which speeds up material destruction.