| 摘要(英) |
The study is aimed
to evaluating the bond strength of reinforcement surrounded by fire
damaged concrete using non-destructive method. The impact-echo method is
applied for the task. The relationships between the local bond strength
obtained by pull-out test and the parameters of non-destructive
evaluation are discussed. The oven temperatures were controlled as
300,400,500,600 and 800℃. The specimens different steel cover thinkness
are 30,40,60 and 80mm. For the impact-echo method, the distribution of
the average steel-amplitude identified by the simulated transfer
function of impact-echo response, the pull-out strength, the coring
compressive strength, as well as the P-wave speed of concrete with
respect to the temperature of the oven were discussed. It was found for
smaller cover thickness, 30 mm and 40 mm, the bond strength is more
closely related to the concrete compressive strength. The affection of
reducing steel-amplitude, which means poor interfacial bonding, is
limited. For larger cover thickness, 60 mm and 80 mm, the bond strengths
are 20% and 10% higher than the one in room temperature when they placed
in oven with constant temperature 300 and 400℃, respectively. It was
found the steel-amplitude is also 30% higher than predicted for 300℃
specimens with both cover thicknesses, which implies a closer bonding at
steel-concrete interfaces. When the bond slip displacement of
reinforcing bar is about 0.5mm, the steel-amplitude becomes large for
the specimens with cover thickness 30 and 40mm. The behavior may be
caused by the reinforcing bar closery contact with the surrounding
concrete at early stage of pull-out test. The variation of
steel-amplitude becomes very large for the cases with bond slip over the
one corresponding to the maximum bonding stress. It may due to large
amount of cracks developed around the rebar. |
