Pulse Velocity Change Research Articles

Real-time bridge monitoring using ultrasonic techniques combined with six-component (6-C) measurements

This study aims to develop a real time structural health monitoring method by ultrasonic tests combined with advanced six component (6C) translation and rotation measurements. Conventionally, the investigation of the velocity and acceleration response in the translation direction is used to obtain the eigenfrequencies of structures. Recently the measurement of rotation has been considered to fully characterize the dynamic behavior of structures. This research undertakes the evaluation of a novel 6C sensor (IMU50-iXblue) with components originally developed for navigation for the purpose of bridge monitoring. However, as for all vibration recordings, there is a certain influence of environmental conditions (mainly temperature) which may affect evaluation and the results of structural assessment. We propose applying the cross-correlation function to the 6C ambient vibration signals to reconstruct wave propagation and using coda wave interferometry (CWI) to obtain internal velocity variation from waveforms. A field experiment on a large-scale prestressed concrete bridge model is presented. To verify that we are able to identify the pre-stress loss even in presence of temperature effects, we perform measurements in two different scales: the ultrasonic and output-only, vibration measurements. The change in the structural properties due to the pre-stress loss should be detected by the pulse velocity change. The results reveal both the performance and advantages of ultrasonic techniques and the capabilities of 6C sensors. To conclude, the application of CWI to wave signals contributes to a comprehensive assessment for bridge monitoring.

Green options for anti-sulfate of slag cement concrete containing pozzolans

This study mainly adopted densified mixture design algorithm (DMDA) with pozzolans (fly ash and slag), different fineness slag cement (1:1; MF40 and HF40) and Type I cement (E40) to construct the mixtures for w/cm=0.40, and applied ACI 211.1R and Type II cement as control group (CII40, w/c=0.40). Life cycle inventory of LEED suggested by PCA for cementitious materials (kg/m 3 ) contained cement use, CO 2 emission, raw materials, energy consumption, compressive strength, and immersed in different concentration Na 2 SO 4 solution. Results showed cement content, CO 2 emission, raw materials and energy consumption for E40, MF40 and HF40, with respect to CII40, were 14% ∼ 26%, 14% ∼ 26%, 13% ∼ 26% and 17%∼28%. At 28 days, compressive strength(all mixtures) were greater than 41MPa. Repeatedly 25 cycles, specimens immersed in 5000ppm Na 2 SO 4 solution and oven-dried at 105°C, the exterior had no damage, and weight loss ( n ) and pulse velocity change ( nv ) were less than -1% and -5%. But in saturated Na 2 SO 4 solution, the n and nv were ranged from - 0.91% (E40) to -2.62% (MF40) and -6.7% (E40) to -10.9% (MF40). The exterior had been obviously scaling (chalking) or spalling at the second (CII40), the fifth (MF40 and HF40) and the ninth cycle (E40). The comprehensive evaluation of green options for anti-sulfate indicated that the merits of all mixtures were respectively E40 > HF40 > MF40 > CII40.

Assessing the Durability of Engineered Cementitious Composites Under Freezing and Thawing Cycles

Abstract This paper reports the durability performance of non-air-entrained engineered cementitious composites (ECC) when subjected to freezing and thawing cycles. ECC is a newly developed, high-performance, fiber-reinforced, cementitious composite with substantial benefits both in terms of high ductility under uniaxial tensile loading and improved durability due to intrinsically tight crack width of less than 100 μm. To evaluate the frost durability of ECC, freezing and thawing testing in accordance with ASTM C666 Procedure A was conducted. The mass loss, pulse velocity change, and flexural parameters (ultimate deflection and flexural strength) of specimens subjected to freezing and thawing cycles were determined in the test. In addition, air-void parameters, in accordance with ASTM C457, modified point count method, and pore size distribution obtained by mercury intrusion porosimetry technique were studied. To analyze the influence of micro-fibers and high tensile strain capacity on the freezing and thawing durability of ECC, all of the above-mentioned properties were also investigated for a control ECC matrix (ECC without fibers). After 210 cycles of freezing and thawing, the control ECC matrix specimens were severely deteriorated, requiring removal from the test, but still exhibited better performance than the conventional non-air-entrained concrete, which would fail at much earlier cycles. On the other hand, ECC with fibers without air-entrainment had excellent resistance to cycles of freezing and thawing with minimal reduction in ultimate tensile strength and ductility. The observed superior frost durability of ECC over control ECC matrix in terms of lower weight loss, pulse velocity change, and higher flexural load and ductility can be attributed to the following reasons: Increase of pore volume larger than approximately 0.30 μm in diameter, intrinsically high tensile ductility and strength due to the presence of micro-poly-vinyl-alcohol fibers.

Pulse velocity, power, and mode phase in a self-locked He-Ne laser

Changes in pulse velocity and output power when a He-Ne 6328-Å self-locked laser becomes partially unlocked have been measured. The pulse velocity is greater by about 9 parts in 106, and the power is higher by about 0.5% for the locked laser. Measurements on mode phase in the self-locked laser show that the phase angles are not zero, and in a particular case one mode is lagging others by almost 60°. The experimental observations are in general agreement with analytical results for self-pulsing in a unidirectional ring laser.

The effects of age and water/cement ratio upon the relation between ultrasonic pulse velocity and compressive strength of concrete

Summary Experiments have been made on concretes with varying aggregate/cement and water/cement ratios, with the main object of ascertaining the effects of changes in age and water/cement ratio upon the relation between ultrasonic pulse velocity and the compressive strength of concrete. It was found that the ratio of changes in pulse velocity and compressive strength due to a change in water/cement ratio is not generally the same as that due to a change in age. Because of this, the relation between pulse velocity and compressive strength cannot be expected to be independent of age and water/cement ratio. It appears, however, that, for compressive strengths up to about 4,000 lb/in2, the relation may for practical purposes be regarded as being so. For concrete of the same aggregate)cement ratio, it was found that low pulse velocity at an early age predicts low strength at later ages.

Changes in pulse velocity during increased intrathoracic pressure

Changes in pulse velocity during increased intrathoracic pressure