1,720,969 research outputs found
Mechanical properties of photocatalytic white concrete subjected to high temperatures
No full textThe paper describes the consequences of progressive damage in architectural high performance concrete
when exposed to different heating treatments. Specimens were tested for uniaxial compressive, direct,
and indirect tensile strengths at ambient conditions approximately one day after the exposure to the high
temperature. Modifications in the microstructure, porosity, and pore size distribution of the fire deteriorated
specimens were identified using scanning electron microscopy and mercury intrusion porosimetry
techniques. Test results revealed no significant variations in the mechanical strengths for specimens
exposed to temperatures up to 250 C. Per contra, significant damage was observed for higher temperature,
500 C and 750 C, treatments, similar to that of ordinary concrete made with similar aggregates.
Based on X-ray diffraction analysis, photocatalytic properties of the concrete were lost at 750 C
Structural Behavior of a Pile-Supported Embankment
No full textThe stress field in a pile-supported 3.9-m-high embankment was interpreted through three-dimensional finite-element modeling, and evaluated by field measurements involving strain gauges on the piles and earth pressure cells at the top and bottom of a 0.9-m-thick geogrid-reinforced platform. Analyses of the numerical results and the experimental data suggest that a vaultlike arch developed within the embankment, such that the vertical stress at the top of the platform was concentrated above the piles and virtually no vertical stress was measured between the piles. A similar situation existed within the platform, where an almost stress-free region between the piles was experimentally detected and numerically verified. From a structural point of view, a supporting skeleton was formed from a pile extension through the platform, a type of stress diffusion problem, and an arching effect appeared mainly in the embankment due to the very large stiffness of the piles in comparison to the surrounding media
Surface Spalling Experiments with Damage Observations
No full textA surface instability apparatus was used to produce spalling in a laboratory setting, and damage in the rock was monitored by acoustic emission (AE) and digital image correlation (DIC) techniques. Lateral displacement served as the feedback signal to control the post-peak response with a closed-loop, servo-hydraulic load frame. A clustering analysis using the concept of a hierarchical dendrogram applied to low signal to noise ratio events provided "super AE" locations that matched the crack trajectories. DIC was used to investigate incremental displacement fields during surface spalling. Real-time images were successfully captured under high stress levels through modification of the device. Displacement fields were computed in the early stage of loading and around peak stress. Young’s modulus was reasonably estimated with the axial strain measured by DIC. Fracture from spalling phenomena was revealed by contours of incremental horizontal displacement around peak stress. A concentration of deformation leading to fracture was identified, as was a region of relaxation behind the damage zone
A problem of scaling in fracture of damaged rock
No full textPre-existing inhomogeneities such as micropores and microcracks dictate the mechanical and physical
properties of rock. Overloading, weathering, changing temperatures, and exceptional events can increase
this damage, usually by microcracking, and as a consequence, modify the effective properties of the rock.
To examine the problem of a structure composed of rock with various stages of damage, three point
bending tests on sandstone specimens exposed to elevated temperatures are presented, with a detailed
evaluation of process-zone size. Both virgin rock, with pre-existing damage and heat-treated rock, with
further damage, were tested by conducting experiments at ambient conditions after exposure to the high temperature. For virgin and heat-treated specimens, high resolution interferometric measurementswere used to characterize the evolution of the process zone as a function of the applied load.
The size and shape of the localized damage zone due to increased microcracking are the significant
factors influencing the strength and post-peak response of quasi-brittle materials. One of the aspects of this phenomenon is that structural scaling evolves with damage, which is explained by the increase of the process-zone size, and a decreasing influence of the scaling problem on nominal strength. As a result, a rigorous interpretation of the experimental data requires an identification of fracture parameters, and a
convenient indirect method is proposed
- …
