Experimental Study On Bond Properties Between Cementitious Grout Material And Deformed Steel Bar

As a kind of material with rapid development of early strength(The 3d compressive strength >40 MPa),high strength(>60 MPa),good fluidity(Vibration free),cementitious grout material are widely used in the reconstruction and reinforcement of existing buildings.After the concrete structure is strengthened by cementitious grout material,the bond behavior becomes the preconditions for the monolithic action in cementitious grout material and reinforcing steel bars,and is fundamental importance for the load carrying capacity of strengthened reinforced concrete members.The research on the bond between grouting material and reinforcement can provide theoretical basis for the use of cementitious grout material in the reconstruction and reinforcement of existing buildings and the revision of relevant regulations.A systemic study to investigate the bond behavior of deformed steel bar with inner-embedded strain-gauge in cementitious grout material under monotonic loading was conducted by considering the test variables of the type of cementitious grout material(Ⅰ,Ⅱ,Ⅲ,and Ⅳ),cover thickness(20,30,and 40 mm),bar diameter(12,16,and 20 mm)and testing age(1,2,3,7,and 28 d).The main contents and conclusions of this study are as follows:(1)The pull-out tests under monotonic load were carried out,and the typical failure modes of the bond specimens and the bond stress-slip curves between reinforcement and cementitious grout material were given.Moreover,the effects of type of cementitious grout material,testing age,bar diameter,and cover thickness on the bond behavior between deformed steel bar and cementitious grout material were analyzed.The result indicated that two typical bond failure modes,splitting-shear failure and pull-out failure were observed.Acompanied with the increasing cover thickness and testing age,the bond strength between reinforcement and cementitious grout material increased.With the increasing bar diameter,the bond strength of deformed steel bar in cementitious grout material decreased to some extent.By comparing the bond specimens fabricated by different types of cementitious grout material,it can be found that the bond strength between deformed steel bar and type Ⅳcementitious grout material is largest,which is close to that between deformed steel bar and ordinary concrete with the same strength,moreover,the bond strength between deformed steel bar and type Ⅲ cementitious grout material is the second,and that between deformed steel bar and type Ⅰ cementitious grout material is the smallest.(2)Considering the influence of cover thickness,bar diameter and testing age,the calculation model of bond strength between different types of cementitious grout material and deformed steel bar was established.According to the test results of the reinforcement strain at different anchorage positions,the bond stress and relative slip between the reinforcement and cementitious grout material at different anchorage positions are calculated respectively.The distribution law of the bond stress and relative slip between the reinforcement and cementitious grout material along the effective bond section under various loads was given,the position function reflecting these distribution law was proposed,and the bond stress-slip constitutive model between deformed steel bar and cementitious grout material was established.