摘要(英) |
In this study, a
systemic test procedures and analysis methods for evaluating degree of
deterioration of mass concrete nuclear facilities caused by weathering,
neutral effect and dry-wet circulation are developed. Surface
longitudinal and Rayleigh waver speed measured by impact-echo method and
compressive strength are used as indexes. Numerical and experimental
studies are used. Models and specimens of concrete plate containing
evenly distributed surface cracks with various depths were constructed
to simulate fine cracks produced on concrete surface while aging. In
addition, P-wave speed and compressive strength were measured for
concrete cylindrical and beam specimens cured in circulated artificial
sea water and oven-dry environments for speeding the aging process. For
the accelerating degraded cylindrical specimens, the P-wave speed
evaluated in frequency domain was closely proportionally related to the
corresponding compressive strength. The P-wave speed measured in time
domain has less correlation with the compressive strength. For beam
specimens, there is no obvious relation between P-wave or R-wave speed
to the compressive strength. For specimens with artificial surface
cracks, P-wave and R-wave speeds were measured by two kinds of
instrumental setup- namely dual receivers, and one recordable impactor
with one receiver. Both numerical and experimental results show the
P-wave and R-wave speed decrease with the depth of cracks up to 0.5 cm.
For the cases larger than 0.5 cm, the speed and crack-depth have no
correlation. It was also found in the numerical simulation that, for
crack depths 1, 1.5 and 2 cm, the impact can generate resonant vibration
in the sliced concrete. Using the resonant theory for column clamped at
base, it can be found that the resonant frequency is inversely
proportional to the square of crack depth. The relation was testified in
both numerical and experimental results with correlation coefficient
close to 1. Thus, it is possible to evaluate the depth of comb-shape
multiple cracks using the distance between cracks and the corresponding
measured resonant frequency. |