Self-ignition coal gangue (SCG) used as one of precursors to fabricate aerated autoclaved concrete (AAC). Aiming at studying water absorptivity and frost resistance performance of self-ignition coal gangue aerated aut...
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Domain pattern variations with temperature were studied by polarizing light microscopy for the morphotropic phase boundary composition 0.67Pb(Mg1/3Nb2/3)O3−0.33PbTiO3 (PMN-0.33PT) single crystal. At room temperature, ...
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Domain pattern variations with temperature were studied by polarizing light microscopy for the morphotropic phase boundary composition 0.67Pb(Mg1/3Nb2/3)O3−0.33PbTiO3 (PMN-0.33PT) single crystal. At room temperature, the monoclinic MA phase is the dominant phase in the unpoled crystal, which coexists with a small fraction of the tetragonal (T) phase. The orientation of spontaneous polarization was calculated to be ∼4.8∘ away from the pseudocubic 〈111〉C in the {001}C plane family. Under an electric field of 6 kV/cm along [011]C, a single domain orthorhombic (O) phase was induced but partially switched back to MA a few hours after the removal of the E field. It was found that the temperature induced phase transition sequence of the [011]C poled PMN-0.33PT single crystal is strongly hysteretic. On heating, the phase transition sequence is as follows: coexistence of O phase and MA→rhombohedral→monoclinicMC→cubic(C). On cooling, the phase transition sequence is given by C→T→MA. The complete set of dielectric, piezoelectric, and elastic constants for the [011]C poled PMN-0.33PT single crystal was measured, which showed the strong feature of the single domain O phase with high shear (d15=2321pC/N,d24=1941pC/N) and low longitudinal piezoelectric coefficients (d33=165pC/N).
Although concrete is the world's most widely used manufactured material, basic questions persist regarding the nature of its binding phase, namely, the calcium-silicate-hydrate (C-S-H) gel. Here, based on reactive...
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Although concrete is the world's most widely used manufactured material, basic questions persist regarding the nature of its binding phase, namely, the calcium-silicate-hydrate (C-S-H) gel. Here, based on reactive molecular dynamics simulations, we address the following fundamental question: Is the chemical composition of C-S-H controlled by the kinetics or thermodynamics of its precipitation? As a major outcome of this study, we demonstrate that the average stoichiometry of the C-S-H gel forming upon the hydration of ordinary portland cement (i.e., Ca/Si = 1.75) is determined by the composition of the C-S-H phase presenting the fastest precipitation kinetics, rather than the highest thermodynamic stability.
In this paper, the mechanical property of damaged concrete after impact was investigated. Firstly, the specimen was crushed by using drop hammer impact test machine in order to cause initial damage. Then compression-a...
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In this paper, the mechanical property of damaged concrete after impact was investigated. Firstly, the specimen was crushed by using drop hammer impact test machine in order to cause initial damage. Then compression-after-impact tests were carried out to examine and compare the damage responses of the specimens, and some stress-strain curves of the specimens under different damage degrees were obtained. Test parameters, such as the strength grade, height of the fall and drop weight were studied. The damage behaviors of the 24 tested specimens with the acquired UT (ultrasonic test) data were analyzed. The experiment results indicate that using UT to test the damage of concrete is highly sensitive;Concrete elastic modulus and compressive strength after impact are reduced. Brittle fracture of the concrete specimen after impact is remarkable.
Carbonation may potentially lead to corrosion of steel bars in reinforced concrete. This concern presents a major barrier against the implementation of sustainable low-clinker cementitious materials in the design of r...
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Carbonation may potentially lead to corrosion of steel bars in reinforced concrete. This concern presents a major barrier against the implementation of sustainable low-clinker cementitious materials in the design of reinforced concrete structures. Various studies have documented the relationship between different equilibrium moisture states in carbonated concrete and the corrosion rate of the embedded steel. However, limited attempts were focused on visually observing the dynamic (time-dependent) behavior of moisture penetration into concrete and the related corrosion state and rate. Moreover, there is a lack of data on the local moisture state in the cementitious matrix in the steel-concrete interfacial zone. In this study, liquid water uptake in carbonated mortar was in-situ and over time monitored by neutron imaging. The corrosion state of embedded steel was monitored by means of electrochemical measurements. This combined experiment revealed that the arrival of the waterfront at the steel surface led to a sharp decrease of the steel potential. The corrosion rate increased from negligibly low values (<1 µm/year) to about 31 µm/year within a couple of minutes. Based on the neutron images, it is concluded that the moisture ingress through the concrete cover is locally affected by the heterogeneity of projected (depth-averaged) porosity distribution, and that large obstacles such as entrapped air have an effect. These observations were further confirmed by numerical simulation results of water transport, which also showed that liquid water permeability of the studied carbonated mortar determined by the inverse analysis is much higher than reported values in the literature. Overall, this study highlights the importance of considering the dynamic and coupled corrosion and moisture transport behavior during the periods which active corrosion can occur in carbonated concrete exposed to cyclic wetting/drying conditions.
作者：
TAGGART, ROBERTThe author graduated from Webb Institute of Naval Architecture in 1942
with a degree of Bachelor of Science in Naval Architecture and Marine Engineering. He has been employed by the Maritime Commission the Naval Research Laboratory the Army Transportation Corps the Bureau of Ships Reed Research Inc. and served as a Naval Officer during World War II. In 1958 he formed Robert Taggart Incorporated. He has been engaged in research and development work for the past twenty years all of which has been related to naval engineering and oceanography. Extensive experience was gained in ship stability and seaworthiness noise shock and vibration of ships model and full scale tests of ship resistance propulsion and maneuverability ship structural behavior at sea and the design and control of unusual ship propulsion systems. Among his publications are reports papers and articles on side launching calculations ship standardization and fuel economy trials maneuvering trials hull form studies development of underwater acoustic facilities noise control of submarines and mine sweepers ambient noise surveys underwater missiles barge and tug design utilization of ships for research the development of ship propulsion systems and the development of propulsion and control systems for the dynamic positioning of ships on the ocean surface. Mr. Taggart is a licensed professional engineer in the District of Columbia and in Virginia. He is a member of the Society of Naval Architects and Marine Engineers the American Society of Naval Engineers the Northeast Coast Institution of Engineers and Shipbuilders the American Institute of Physics the Acoustical Society of America the American Institute of Aeronautics and Astronautics the American Geophysical Union and the Interntional Oceano-graphic Foundation.
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