Due to the convenience of visualization in mesoscale, numerical study on permeability and mechanical property of pervious concrete has more advantages than physical experiments in mechanism analysis of performance change. Therefore, the permeability and mechanical property of pervious concrete were studied based on numerical method on the mesostructure level. Initially, the finite element models of pore and pervious concrete were generated according to image reconstruction. Then, the permeability and mechanical property were simulated according to CFD (computation fluid dynamics) analysis and CDP (concrete plastic damage) model. Finally, the permeability was well predicted and the mechanical failure mechanism was revealed intuitively. The results indicate that numerical method is significant for deep understanding the property of pervious concrete on mesostructure level.
This paper proposes a track-tunnel-unsaturated soil model for predicting the vibrations induced by the urban underground rail transit. The track structure subsystem and tunnel-unsaturated soil subsystem were coupled by the force between the slab and tunnel invert. Firstly, the radial displacement frequency response function (FRF) at the tunnel invert was calculated. Then, the coupled equations of rail, slab and tunnel were used to obtain the interaction force between slab and tunnel. Finally, other dynamic response could be calculated by multiply the interaction force by the corresponding FRF. After being validated via comparison with existing saturated soil model, the present model was applied to investigate the effects of water saturation, speed and frequency of train load on the dynamic response of the system. The results show that the radial displacement at tunnel invert is increase with the increase of water saturation. The matric suction amplitudes decrease first and then increases with the increase of water saturation.
Sulfate attack is one of the most frequent environmental attacks affecting concrete structures, which is manifested by
expansive disruption and deterioration of cement paste. However, it is difficult to monitor the deterioration induced by
sulfate attack as these attacks mainly occur in sulfate-bearing soils or ground waters. In this paper, the tentative
experimental investigation on sulfate attack monitoring was carried out by using smart aggregate transducers and an
active sensing method is proposed. A number of plain concrete columns with embedded smart aggregates were
fabricated and then suffered to salt-fog exposure for several months. Active monitoring methods were performed to
detect the deterioration of the specimens using smart aggregates. In addition, testing of the mechanical properties and
water absorption ability of concrete specimens at different deterioration times was performed as well. Then the
transmission mechanism of stress wave in concrete was discussed. The experimental results show that, with the growth
of attacking time, the amplitude of the received signal decreased, and by calculating the damage index, the deterioration
degree of concrete specimens was estimated. It is indicated that the proposed piezoceramic based SA monitoring method
is valid in sulfate attack monitoring.
Damping in structures is commonly provided by viscoelastic nonstructural materials. Due to the large volume of
structural materials in a structure, the contribution of a structural material to damping can be substantial. In this paper,
the experimental investigation on damping ability of concrete materials and its members with Nana SiO2 was carried out
by the method of 3-point bending beam damping measurement and cantilever beam free vibration respectively. The
microstructure of concrete mix with Nano SiO2 was observed by XRD and SEM, then damping mechanism was
discussed. The experimental results show that the damping reinforced effect achieved best with the 4% mixture ratio of
Nana SiO2, but the optimal adulteration quantity of Nano SiO2 was 3% of cement weight by the comprehensive
consideration of cost, workability, strength and dynamic properties. Nano materials as a mixture increase interfaces, and
the non-uniform stress distribution under external force improves frictional damping energy consumption ability of
concrete. The experimental results on the damping ratio and the loss tangent of the concrete materials with Nano
materials are consistent.
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