摘要(英) |
Abstract Because
of the effect of weathering, neutrality as well as dry wet cycling, very
small cracks on surface of concrete can easily be produced and cause
surface deterioration. This study aims at measuring the amplitude
decaying rate of surface wave (Rayleigh wave) as the index for
quantitatively evaluating depth of the very small cracking on surface of
concrete. The test variables include the effects of changing the size of
impactor and distance between impactor and receiver. The study is
preceded by the ways of theoretical analysis, numerical analysis and
experiments. First, for semi-infinite elastic body the theoretical
relations among amplitude of surface waves, the duration of the impact
and material properties were solved. The theoretical ratio between the
amplitudes of two R-waves recorded from receivers at certain designed
distance is calculated. It was found the ratio is varied with the
impact-duration and P-wave speed. In numerical analysis and experiment,
the ratio of R-wave amplitude is very close to theoretical solution for
the numerical model and for both undamaged concrete and mortar
specimens. Thus, the ratio solved in theory can be used as a standard
for undamaged concrete. When the ratio of experiment is larger than the
theoretical one, it represents the cracks scatters propagation energy of
surface wave and increases the decaying rate of surface wave. The
second stage of the research is studying the effect of multiple
cut-slots on surface of concrete specimens to the impact responses. The
slots are used to preliminarily simulate the cracking condition of aged
concrete. With the range of 40 cm in length, some of the slots are
uniform distributed with 1 cm intervals and the others are cut
irregularly. Cracking depth is varied from 0.25 cm to 2 cm for
establishing the relation between the surface cracking depth and
amplitude decaying rate of surface wave. It was found in the
experimental results, for the depth of cracks less than or equal to
0.75cm, the decaying rate of surface wave is linearly increase with
crack depth. However, for the depth of cracks larger than 1.0cm, the
decaying rate of surface wave is not linearly increase with the crack
depth because a resonant vibration of the concrete slots were triggered
by the impact. Thus, when the depth of cracks is larger than 1.0cm, it
is unable to use the method to estimate the surface condition of aged
concrete. The test method can be applied for measuring the coarse
surface condition. The experimental results show that using the surface
wave amplitude to predict the depth of the dip on the surface, the error
for average depth of the dip is less than 15%. |