Pulse Velocity Measurements Research Articles

In-situ strength testing of high strength concrete

High strength concrete is being used increasingly in major civil engineering and building projects. Measurement of the in-situ strength is often required as a means of determining early age strength development and form work stripping times, or, for verifying structural performance. A number of techniques for the estimation of the in-situ strength of high strength concrete have been examined. The use of temperature matched cured test cubes was found to give the closest correlation with in-situ strength although ultrasonic pulse velocity measurements and pull-out tests were useful techniques. One aspect of testing high strength concrete that emerged as significant, was the need to base calibration or correlation curves on specimens sealed against moisture ingress or moisture loss. rather than on water-cured specimens. Two high strength concrete mixes incorporating different aggregate types (with mean 28 day cube strengths of 90 MPa and 100 MPa) were investigated in large-scale test items. A comparison of maturi measurements, UPV and pull-out tests is given together with discussion of the nature of in-situ strength development in high strength concrete.

Water in the stems of sessile oak (Quercus petraea) assessed by computer tomography with concurrent measurements of sap velocity and ultrasound emission

ABSTRACTConcurrent measurements of heat pulse velocity and ultrasound acoustic emission were performed on the trunks of adult Quercus petraea plants under different water stress conditions. On the trunk section of the plants the wood density was measured non‐destructively using a mobile computer tomograph which measures the attenuation of a collimated beam of radiation which traverses the trunk. By scanning the trunk in different directions, it is possible to map wood density in the section. As wood density is strictly correlated with water content, this method allows evaluation of the water content in the trunk section and the water conditions in the different parts of the section. The computer‐tomograph technique is non‐invasive and is not influenced by climatic fluctuations. A close agreement was found between wood density and heat pulse velocity; the relationship between these two parameters and ultrasound acoustic emission is discussed. Trunks of sessile oak appear well suited as water storage reservoirs playing an important role in tree survival during extended periods of low soil water availability, especially in the context of global climatic change. Here the computer‐tomograph methodology is described and suggestions arc made for further research development.

Evaluation of the heat pulse velocity technique for measurement of sap flow in rainforest and eucalypt forest species of south‐eastern Australia

ABSTRACTSap flow in the stems of two cut saplings each of Eucalyptus maculata (a canopy eucalypt forest tree), Doryphora sassafras and Ceratopetalum apetalum (both canopy rainforest trees of south‐eastern coastal Australia) was measured by the heat pulse velocity technique and compared with water uptake from a potometer. Scanning electron micrographs of wounding caused by implantation of temperature sensor and heater probes into the sapwood showed that wounding was similar in rainforest and eucalypt species and was elliptical in shape. A circular wound has been implicitly assumed in previous studies. Accurate measurements of sapling water use were obtained using the smaller transverse wound dimension rather than the larger longitudinal dimension because maximum disruption of sap flow through the xylem vessels occurred in the transverse plane. Accurate measurements of sap flux were obtained above a minimum threshold sap velocity. These velocities were 15·7,10·9 and 9·4 cm h−1 for E. maculata, C. apetalum and D. sassafras, respectively. Below the threshold sap velocity, however, sap flow could not be accurately calculated from measurements of heat pulse velocity. The minimum threshold sap velocity appeared to be determined by probe construction and xylem anatomy. Despite the elliptical wounding and inaccurate measurement of sap flow below the threshold sap velocity, total sap flow over the experimental period for two saplings of each species was within 7% of water use measured by the potometer.

Ultrasonic signal-processing techniques for the measurement of damage growth in structural materials

In recent years, the ultrasonic signal-processing technique, which has been enormously successful in material testing, has found few applications in the analysis of concrete damage because of the heterogeneous nature of this material. In the present study, frequency-domain analysis of the ultrasonic signals, based on the Segmented Chirp Z-Transform, has been used to both detect and monitor the crack growth in structural materials. In comparison with the usual methods of pulse velocity or attenuation measurement, a very sensitive and accurate testing method was obtained. The experimental setup is described and the preliminary results, relating to uniaxial compression tests carried out on cubic concrete specimens and bricks, discussed. >

若材齢で凍結融解を受けた普通および軽量骨材コンクリートの塩化物イオン透過性

The chloride permeability of normal weight and lightweight concretes subjected to freeze-thaw damage at the age of 3 days was evaluated by using the AASHTO T277 chloride permeability test method and the freeze-thaw test method similar to that recommended by JSCE-1986. The relative dynamic modulus of elasticity was obtained from the results of ultrasonic pulse velocity measurements for each specimen before and after the freezing and thawing test. The results showed that the chloride permeablity of the normal weight concretes having an air content of at least 7.6% changed little with the repeated cycles of freezing and thawing ranging from 18 to 44 cycles, irrespective of the presence and the type of mineral admixtures. It was found that the application of freeze-thaw cycles obviously decreased the values of the relative dynamic modulus of elasticity in the normal weight concretes, but that the reduction in the relative dynamic modulus of elasticity did not always result in an increase in the chloride permeablity of the concretes. The test results also indicated that most of lightweight concretes made with fully-saturated expanded shale aggregates exhibited an extremely high chloride permeability, when they were subjected to a single freeze-thaw cycle. Furthermore, the type of microcracks developing in the normal weight concretes under the repeated freeze-thaw cycles was discussed.

Frame moduli of unconsolidated sands and sandstones

In this study, we investigate the elastic moduli of the empty grain framework (the “frame” moduli) in unconsolidated sands and consolidated sandstones. The work was done to improve the interpretation of seismic amplitude anomalies and amplitude variations with offset (AVO) associated with hydrocarbon reservoirs. We developed a laboratory apparatus to measure the frame Poisson’s ratio and Young’s modulus of unconsolidated sands at seismic frequencies (0.2 to 155 Hz) in samples approximately 11 cm long. We used ultrasonic pulse velocity measurements to measure the frame moduli of consolidated sandstones. We found that the correlation coefficient between the frame Poisson’s ratio [Formula: see text] and the mineral Poisson’s ratio [Formula: see text] is 0.84 in consolidated sandstones and only 0.28 in unconsolidated sands. The range of [Formula: see text] values in unconsolidated sands is 0.115 to 0.237 (mean = 0.187, standard deviation = 0.030), and [Formula: see text] cannot be estimated without core or log analyses. Frame moduli analyses of core samples can be used to calibrate the interpretation of seismic amplitude anomalies and AVO effects. For use in areas without core or log analyses, we developed an empirical relation that can be used to estimate [Formula: see text] in unconsolidated sands and sandstones from [Formula: see text] and the frame P‐wave modulus.

Developments in Assessing the Structural Integrity of Applied Surfaces to Concrete Buildings

Debonding, leading to the subsequent detachment of applied finishes to concrete buildings, is becoming a serious problem in many parts of the world. Checking building elevations by employing the technique of Infra‐red Thermography using a process developed by the writer can give advance warning of potential defects. This can enable early remedial action to be undertaken to repair a building surface before it becomes detached from the concrete substrate, possibly resulting in a hazard to passers‐by. The thermographic test method has been compared with other more traditionally used NDT methods including sounding, rebound hammer, and ultrasonic pulse velocity measurements. Although the thermographic equipment is initially more expensive, the surveying method can be shown to be faster and more accurate than any other technique currently available for this type of building evaluation.

Use of Dynamic Nondestructive Test Methods to Monitor Concrete Deterioration Due to Alkali-Silica Reaction

Abstract The use of dynamic nondestructive test methods such as pulse velocity and dynamic modulus to monitor the initiation and progress of concrete deterioration due to alkali-silica reactions (ASR) is described. The tests reported cover a range of parameters: two different types of reactive aggregates; varying environments; concretes without and with mineral admixtures such as fly ash, ground-granulated blast-furnace slag, and silica fume; and concrete beams with and without reinforcement. The results show that both pulse velocity and dynamic modulus are sensitive to material and structural changes arising from ASR and that they can respond reliably to changes prior to first crack, at first crack, and the progress of deterioration with time in concrete both with and without cementitious materials other than portland cement. With engineering judgment, pulse-velocity measurements can be used confidently to assess structural deterioration due to ASR.

Effect of early overloading of concrete on strength at later ages

An experimental investigation to study the effect of early over-loading of concrete on its strength development is reported. Concrete and mortar samples were subjected to different loading levels at ages of 8, 16, 24 and 72 hours. The samples were then retested, along with control specimens, at ages of 7, 28, and 90 days. More than 900 specimens were used in this investigation. Ultrasonic pulse velocity measurements were taken to evaluate the healing capacity of damaged specimens. The results indicate that loading concrete, beyond 8 hours after casting, up to 90% of its compressive strenght has no effect on later strength development. However, loading concrete up to failure resulted in strength loss between 10% to 50%, depending on age at time of loading, age at time of retesting and curing conditions.

A comparison of the properties of OPC, PFA and ggbs concretes in reinforced concrete tank walls of slender section

This Paper compares the properties of cores taken from the walls (250 mm thick) of a 2·5 year old reinforced concrete tank constructed using ordinary Portland cement (OPC), pulverized fuel ash (PFA) and ground granulated blastfurnace slag (gghs) concretes of equal strength grade. Measurements taken during and shortly after construction showed the PFA and ggbs to be beneficial in terms of reducing hydration temperatures and the amount of secondary steel required to control thermal and shrinkage cracking. Ultrasonic pulse velocity measurements carried out on the tank walls before coring showed no significant difference between the three concretes, and laboratory tests on cores showed them to have comparable compressive and tensile strengths. The PFA and ggbs concretes showed greater carbonation depths than the OPC concrete, although the PFA concrete was significantly less permeable to both gas and liquid. These results are discussed with reference to pore structure measurements, which show the PFA concrete to have a coarser pore structure than the OPC concrete close to the surface—at depth the situation is reversed. Generally, the results show the three concretes to have very similar properties, suggesting that the early-age benefits observed for concretes containing PFA and ggbs can be achieved in slender concrete elements without compromising strength and durability requirements.

The behaviour of ultrasonic pulses in concrete

First the difficulties, as well as fallacies, of the estimation of concrete strength from pulse velocity measurement are discussed. Then an attempt is made to transfer some of the new findings of the research on materials testing by ultrasonic methods to concrete. The role of compositeness, dispersion, and a feature-based computer system are discussed among others. Supporting test results are presented showing that 1. the pulse velocity in the longitudinal direction of a concrete cylinder differs from the velocity in the lateral direction; 2. more specifically, at low velocities the longitudinal velocities are greater, whereas at high velocities the lateral ones; 3. this difference is more pronounced with lower frequencies; 4. the pulse velocity in concrete increases with higher frequencies, that is, concrete is a dispersive material; 5. the dispersive nature of concrete decreases with age; 6. the pulse velocity is independent of the stresses in concrete to a large extent; 7. feature-based computer system is applicable to concrete. The practical consequences of these findings are pointed out.

Studies With Narrow Cement Thickness Lead to Improved CBL in Concentric Casings

Etude experimentale de l'influence de l'interface formation/ciment et partie externe du tubage/ciment sur le signal de la diagraphie d'adhesivite du ciment

Correlation between cube strength, ultrasonic pulse velocity and volume change for oil well cement slurries

Four types of cement slurries used in cementing oil well casings have been examined to determine whether strength build-up during the first 24 hours after mixing can be predicted from measurements of ultrasonic pulse velocity and volume change. The pulse velocity method was found to be a useful predictive technique but there was no general correlation between bulk volume change and cube strength.

Comparison of shear modulus and pulse velocity techniques to measure the build-up of structure in fresh cement pastes used in oil well cementing

Fresh cement slurries typical of those used in the oil industry during drilling operations are assessed for the growth of structure in the first few hours after mixing by the use of shear modulus and ultrasonic pulse velocity measurements. It is shown that during the first two hours, the shear modulus technique is a much more sensitive measure of the developing physical structures but after initial set the ultrasonic pulse velocity is an effective method of differentiating between different mix formulations.

Effect of exposure time and rates of heating and cooling on residual strength of heated concrete

Synopsis The paper describes tests on 100 mm concrete cubes heated to temperatures in the range of 200–800°C to determine the effect of varying time of exposure and rates of heating and cooling on the residual compressive strength of concrete. These variables were found to have a significant effect on concrete heated to the lower range of temperatures but their effect became less pronounced at high temperatures. Almost all the loss of compressive strength occurred within two hours of exposure to the maximum temperature. Pulse velocity measurements did not predict the residual strengths accurately and appeared to be more indicative of the levels of temperature to which the concrete had been exposed.

Transpiration from a kiwifruit vine as estimated by the heat pulse technique and the Penman-Monteith equation

Abstract Heat pulse velocities were measured at 4 depths in the stem of a kiwifruit plant (Actinidia chinensis Planchon) throughout one lateautumn day, and sap velocities and total stem sap flux were calculated from physical principles without resorting to empirical calibration. Concurrent measurements of net radiation, air temperature, vapour pressure deficit, wind speed, and stomatal conductance were utilised in a second, independent calculation of transpiration based on the Penman-Monteith combination equation. Results indicated that most flow occurred in the outer ring or rings of the stem xylem tissue, and there was a close relationship between fluxes estimated by the 2 methods. We conclude that heat pulse velocity measurement is potentially a practicable method for measuring transpiration rates in kiwifruit.

Radial Variation in the Axial Conductivity ofPopulusand its Significance in Heat Pulse Velocity Measurement

Conductivity (defined as permeability divided by viscosity) was estimated as a function of radial position in the sapwood at three height levels, for two species of Populus. Stem sections 210-260 mm long and comprising the entire cross section were de-aerated and then infused axially with toluidine blue dye solution until emergence just occurred from the opposite end. Measurements were made of: (i) maximum penetration within each ring, and (ii) axial penetration at 10 mm radial increments starting at the cambium. The corresponding conductivity values were calculated for each measurement, and the values were fitted to a quadratic equation for each stem section. The equations were found to be suitable for calculating stem flux from sap velocities derived from heat pulse velocities measured at different depths in the xylem.

Acoustic emission and ultrasonic pulse velocity of concrete

Both acoustic emission and ultrasonic pulse velocity measurements were used to try to monitor the structural integrity of concrete. Specimens in the form of 150 mm cubes were loaded monotonically to failure, and acoustic emission and ultrasonic pulse velocity were measured simultaneously. Four different concrete mixes were each tested at ages up to two years to provide a wide range of concrete strengths. The results indicated that ultrasonic pulse velocity measurements began to show internal cracking at stresses of about 33 to 66% of the ultimate stress; this method therefore appeared to be more sensitive to damage than acoustic emissions, which indicated severe cracking only at about 80 to 90% of the ultimate stress. However, both ultrasonic pulse velocity and acoustic emission seemed to be affected by the age of the concrete. It was concluded that, for acoustic emission to be used as a reliable indicator of concrete damage, extensive work would have to be done to establish a standard test procedure.

Discussion: The practical use of ultrasonic pulse velocity measurements in the assessment of concerte quality

Discussion: The practical use of ultrasonic pulse velocity measurements in the assessment of concerte quality

The practical use of ultrasonic pulse velocity measurements in the assessment of concrete quality

Synopsis The wider use of limit-state methods for the design of structures has increased the desirability of being able to assess the quality of a structure as built rather than isolated test pieces of the material supplied. Ultrasonic pulse velocity measurements are a particularly suitable way to measure the quality of a concrete structure, although the importance of competent engineering judgement in their analysis must be properly stressed. This paper indicates some ways in which the pattern of pulse velocity measurements may be used to assess the quality of concrete construction. The suggested patterns have been derived by applying the fundamental relationships, obtained by research, to site surveys and assessing the deviations permissible before the variations from the normal indicate a defect of engineering significance. The comparative evaluation of structural strength is also discussed.