Ultrasonic Pulse Velocity Measurements Research Articles

An appropriate relationship between flexural strength and compressive strength of palm kernel shell concrete

This paper presents the determination of an appropriate compressive–flexural strength model of palm kernel shell concrete (PKSC). The direct and indirect Ultrasonic Pulse Velocity (UPV) measurements, with respective to mechanical properties of compression (cube) and flexural (slab) elements, of concrete at various mixes and water/cement (w/c) ratios were made. A total of 225 cubes and 15 slabs of the PKSC were casted for nominal mixes of 1:1:1, 1:1:2 and 1:11/2:3, and varying (w/c) ratios of 0.3–0.7 at interval of 0.1. The test elements were cured for 3, 7, 14, 28, 56 and 91days in water at laboratory temperature. The elements were then subjected to nondestructive testing using the Pundit apparatus for determination of direct ultrasonic wave velocity and the elastic modulus at the various ages. The cubes were subsequently subjected to destructive compressive test. The 28-day compressive strength–UPV and strength–age statistical relationships at w/c ratio of 0.5 determined from the velocity–strength data set in linear, power, logarithm, exponential and polynomial trend forms. The polynomial trend line in the form y=aln(x) at R2 value of 0.989, found appropriate, among others, was proposed for the formulation of the compressive strength–flexural strength model of PKSC at w/c ratio of 0.5.

Mechanical properties of alkali activated blast furnace slag pastes reinforced with carbon fibers

Alkaline activation has become a useful procedure to obtain high strength cement composites without Portland cement. Different industrial byproducts can be activated using this technique, e.g. blast furnace slag, fly ash or metakaolin. Thus a new generation of more sustainable composites is being developed. However, the main disadvantage of these composites is their high drying shrinkage strain. Among the different approaches to address this problem, shrinkage reducing admixtures are the most used, but the addition of fibers can be useful for this purpose. In this work, alkali activated slag (AAS) pastes have been reinforced with carbon fibers (CF). The effect of the concentration of alkaline activator (Na2O% and silica modulus) and the fiber aspect ratio (using different length fibers with the same diameter) on the mechanical properties has been assessed. Mechanical characterization comprised bending and compressive strength tests, ultrasonic pulse velocity and density measurements, and drying shrinkage tests, in which CF were capable of improving the mechanical strengths of AAS pastes while controlling the specimens strain due to shrinkage. CF additions increased bending strength up to five times, and increases up to 20% in compressive strength were observed. Furthermore, CF can be a convenient addition to control the drying shrinkage of AAS composites. Even in adverse conditions, such us 50% RH, where unreinforced specimens actually broke, CF could guarantee the stability of the specimen.

Ultrasonic Monitoring of Setting and Strength Development of Ultra-High-Performance Concrete.

In this study, the setting and tensile strength development of ultra-high-performance concrete (UHPC) at a very early age was investigated by performing the penetration resistance test (ASTM C403), as well as the direct tensile test using the newly developed test apparatus, and taking ultrasonic pulse velocity (UPV) measurements. In order to determine the optimum surface treatment method for preventing rapid surface drying of UHPC, four different methods were examined: plastic sheet, curing cover, membrane-forming compound, and paraffin oil. Based on the test results, the use of paraffin oil was found to be the best choice for measuring the penetration resistance and the UPV, and attaching the plastic sheet to the exposed surface was considered to be a simple method for preventing the rapid surface drying of UHPC elements. An S-shaped tensile strength development at a very early age (before 24 h) was experimentally obtained, and it was predicted by a power function of UPV. Lastly, the addition of shrinkage-reducing and expansive admixtures resulted in more rapid development of penetration resistance and UPV of UHPC.

Self-healing performance of engineered cementitious composites under natural environmental exposure

The self-healing performance of an engineered cementitious composite (ECC) exposed to the natural environment is presented. Fifteen dog-bone shaped ECC samples were preloaded after 14 d of curing and then placed outside in an open area at Heriot-Watt University (Edinburgh campus). Ultrasonic pulse velocity measurements were used to determine the rate and extent of the self-healing capabilities of the ECC in the natural environment. The results showed that, while the more highly damaged samples displayed the greatest decrease in ultrasonic velocity, they also displayed initial accelerated healing, which implies an increased quantity of individual cracks in the more damaged samples rather than an increase in individual crack widths. It was also found that the self-healing of microcracks in the ECC was robust. Narrow hairline cracks (< 10 μm width) healed in less than 6 d, while 20–30 μm wide cracks either partially or fully healed after 6 d of intermittent rainfall. Wider microcracks (40–75 μm) partially healed after 3 weeks of outdoor exposure.

Study of the Mechanical Properties of a Conglomerate

This paper is devoted to the study of a conglomerate rock formation (Molare Formation) outcropping in southern Piedmont that forms a natural arch of environmental interest. Awareness with respect to the stability of this structure emerged after some intense rains which caused small collapses at the arch foot. The need for a proper characterization of the material in its natural state and its deterioration following increased water saturation is needed. A multidisciplinary approach based on the integration of both in situ and laboratory geophysical tests for the assessment of the rock structure at different scales was performed. Geological surveys together with seismic tomography and GPR have been executed on site. Petrographical and compositional studies of the matrix, ultrasonic pulse velocity measurements, electrical resistivity determinations and standard UCS test on large specimens are under development in laboratory.

Evaluation of correlation between physical properties and ultrasonic pulse velocity of fired clay samples

The aim of this study is to establish a correlation between physical properties and ultrasonic pulse velocity of clay samples fired at elevated temperatures. Brick-making clay and pottery clay were studied for this purpose. The physical properties of clay samples were assessed after firing pressed clay samples separately at temperatures of 850, 900, 950, 1000, 1050 and 1100°C. A commercial ultrasonic testing instrument (Proceq Pundit Lab) was used to evaluate the ultrasonic pulse velocity measurements for each fired clay sample as a function of temperature. It was observed that there became a relationship between physical properties and ultrasonic pulse velocities of the samples. The results showed that in consequence of increasing densification of the samples, the differences between the ultrasonic pulse velocities were higher with increasing temperature. These findings may facilitate the use of ultrasonic pulse velocity for the estimation of physical properties of fired clay samples.

Self-healing of Micro-cracks in Engineered Cementitious Composites

The performance of an Engineered Cementitious Composite (ECC) to self-heal micro-cracks under a controlled laboratory environment is presented. Ten dog-bone shaped samples were prepared; five of them were preloaded to known strains and then left to heal in water in a temperature-controlled laboratory. Ultrasonic pulse velocity (UPV) measurements were undertaken to monitor the crack-healing process. It was found that all samples exhibited recoveries in UPV and were able to recover to between 96.6% and 98% of their pre-test UPV values over a period of four weeks. An accelerated rate of healing was observed in the initial two-day period immediately following the preloading test.

MECHANICAL PROPERTIES AND SELF-HEALING MECHANISM OF EPOXY MORTAR

Crack deformation in concrete start with hairline crack or micro-crack which can lead to major crack if not prevented. Crack can cause a major deterioration to the structure as liquid can penetrate inside and cause damage as a result; the durability of concrete will decrease. Self-healing concrete was introduced to automatically repair hairline crack or micro-crack without external intervention. Previous study had shown that by introducing bacteria into the concrete, the crack will heal itself. This paper presents the study on self-healing mortar by using epoxy resin without hardener as a self-healing agent. The self-healing process was evaluated using Ultrasonic Pulse Velocity measurements up to 180 days. Mortar specimens were prepared with mass ratio of 1:3 (cement: fine aggregate), water-cement ratio of 0.48 and 10% epoxy resin of cement content. All tested specimens were subjected to wet-dry curing; where compressive strength, flexural strength, and tensile splitting strength and self-healing mechanism were measured. The results obtained shows that, all strength properties of the self-healing epoxy mortar were significantly higher than the control sample and became constant at 10 % of epoxy resin content. Based on the pulse velocity measurements, after 60 days the cracks of the mortar healed automatically as a result of the reaction between the unhardened epoxy resin and hydroxyl ion from cement hydrate. This shows the ability of the epoxy to be used as self-healing agent.

Assessing the self-healing capability of cementitious composites under increasing sustained loading

This study investigated the effects of progressively increasing sustained loading on self-healing behaviour of 180-d-old microcracked engineered cementitious composites (ECCs) incorporating different mineral admixtures. After introducing microcracks to the specimens with applied severe pre-loading, some were subjected to progressively increasing sustained loading. All of the specimens were then subjected to continuous moist curing for 150 d to evaluate self-healing performance. Mechanical property (modulus of rupture (MOR) and mid-span beam deflection) characterisations and ultrasonic pulse velocity measurements were used to assess self-healing capability. Experimental results showed that even under progressively increasing sustained mechanical loading, MOR results greater than the original values could be obtained, depending on mineral admixture selection. Although deflection results were more adversely affected by progressive sustained loading compared to MOR results, even the lowest deflection value obtained from different ECCs was still more than 100 times that of conventional concrete after healing. Under continuous moist curing, there were minimal changes in ultrasonic pulse velocity results of all ECCs subjected to progressively increasing sustained loading, so that recovery results similar to those of specimens without sustained loading were obtained, despite the fact that ultrasonic pulse velocity testing was not that sensitive in capturing the effects of self-healing.

Assessing the self-healing capability of cementitious composites under increasing sustained loading

This study investigated the effects of progressively increasing sustained loading on self-healing behaviour of 180-d-old microcracked engineered cementitious composites (ECCs) incorporating different mineral admixtures. After introducing microcracks to the specimens with applied severe pre-loading, some were subjected to progressively increasing sustained loading. All of the specimens were then subjected to continuous moist curing for 150 d to evaluate self-healing performance. Mechanical property (modulus of rupture (MOR) and mid-span beam deflection) characterisations and ultrasonic pulse velocity measurements were used to assess self-healing capability. Experimental results showed that even under progressively increasing sustained mechanical loading, MOR results greater than the original values could be obtained, depending on mineral admixture selection. Although deflection results were more adversely affected by progressive sustained loading compared to MOR results, even the lowest deflection value obtained from different ECCs was still more than 100 times that of conventional concrete after healing. Under continuous moist curing, there were minimal changes in ultrasonic pulse velocity results of all ECCs subjected to progressively increasing sustained loading, so that recovery results similar to those of specimens without sustained loading were obtained, despite the fact that ultrasonic pulse velocity testing was not that sensitive in capturing the effects of self-healing.

Rheological and mechanical properties of cement–fly ash self-consolidating concrete incorporating high volumes of alumina-based material as fine aggregate

Portland cement and natural aggregate are the materials consumed in the greatest quantities in the production of concrete and are thus associated with environmental problems. The 3R keys principles for the production of concrete materials that are relatively environmentally friendly are reduce, reuse, and recycle. This paper presents a laboratory study on the properties of self-consolidating concrete (SCC) incorporating fly ash and recycled alumina waste. Fly ash is used as a cement replacement at a fixed 20%, and recycled alumina waste is used as a fine aggregate replacement at 0%, 25%, 50%, 75%, and 100%. The mixtures were designed to produce a controlled slump flow diameter. The properties examined in the study are workability and mechanical properties by using slump flow, J-ring flow, blocking flow assessment, V-funnel, compressive strength, and ultrasonic pulse velocity measurements. The results show that the use of fly ash and recycled alumina waste significantly improved the workability and increased the compressive strength of SCC mixtures. Further, all the mixtures showed an acceptable performance in regard to slump flow diameter and time tests. Mixes with high cement content and fly ash content into which recycled alumina waste content of up to 75% was incorporated had substantially lower V-funnel flow times and minimal blocking, flow times in the range of 4–6s, V funnel times in the range of 8–12s, and a difference in the slump flow and J-ring flow in the range of 2–3cm. These mixes also exhibited minimal or no apparent blocking compared with conventional SCC. The results further indicate that economical SCC with 28-day compressive strength up to 56MPa can be made using a high volume of recycled alumina waste, which is accompanied by a decrease of only one unit of strength.

Relationship between compressive strength and UPV of GGBFS based geopolymer mortars exposed to elevated temperatures

Geopolymers are innovative materials possessing properties similar to normal OPC, while having less environmental impact. The current research was conducted on GGBFS based geopolymeric mortars. The effects of sodium silicate to sodium hydroxide ratio on the compressive strength of the mortars at 1 and 7days before and after exposure to the elevated temperatures of 200°C, 400°C, 600°C, and 800°C were investigated. Additionally, the relationship between Ultrasonic Pulse Velocity (UPV) and compressive strength was investigated for before and after exposure to elevated temperatures. It was found that the sodium silicate to sodium hydroxide ratio had little or no effect on the compressive strength change between 1 and 7days. However, the compressive strength generally increased with increasing sodium silicate content. Similar trend was observed for elevated temperature exposure, in that the strength increased with increasing sodium silicate to sodium hydroxide ratio, while the overall behavior was such that the compressive strength decreased as the temperature exposure increased. UPV measurements showed similar behavior, which indicated that relationship between UPV and compressive strength was exponential and R2 was between 0.95 and 0.98.

High temperature behaviour of hybrid steel–PVA fibre reinforced reactive powder concrete

Reactive powder concrete (RPC) with dense microstructure are found to perform poorly at elevated temperatures due to a build-up of pore pressure that causes explosive spalling. This paper presents the results of an experimental investigation of the behaviour of six RPC mixes containing hybrid steel and polyvinyl alcohol (PVA) fibres, following exposure to high temperatures up to 700 °C. Residual compressive strength, static elastic modulus and ultrasonic pulse velocity measurements were carried out for all the RPC mixes. A mix containing hybrid steel–PVA fibre is proposed as suitable for high-temperature applications based on these results. Further tests were conducted for the mix at a hot state using a specially designed furnace–loading frame assembly. The hot-state elastic modulus, free thermal strains (FTS) and transitional thermal creep (TTC) were measured at the hot state. Residual compressive strength results for all the mixes indicated an initial increase in strength up to 300 °C, followed by a drastic drop. No apparent changes in elastic modulus and ultrasonic pulse measurements were observed till 300 °C, after which both dropped sharply. RPC containing only either steel fibres or only PVA fibres showed some form of instability, which was explosive in some cases. RPC with no fibres was also susceptible to explosive behaviour; however, the addition of hybrid fibres seemed to have beneficial effects. A mix containing equal volumes of steel and PVA fibres occupying a total fraction of 2 % by volume was found to give the best results. The FTS of that mix was similar to that of siliceous aggregate concretes, and the TTC was significant above 250 °C.

Smart Cement Composites for Durable and Intelligent Infrastructure

The self-healing and self-sensing performances of Engineered Cementitious Composite (ECC) mixtures developed recently at Heriot-Watt University are presented. In the first series of experiments, fifteen dog-bone shaped ECC samples were preloaded to known strains and then left to heal outdoors under a natural environment. Ultrasonic pulse velocity measurements were then undertaken periodically to determine the rate and extent of healing in these samples. It was found that the samples were able to heal micro-cracks and show a recovery in UPV after two loading events over a six month outdoor exposure. In another series of experiments, the effectiveness of incorporating milled carbon (MC) fibers into an ECC mix, with the aim of enhancing the self-sensing functionality of ECC, is demonstrated for the first time. The MC-ECC mix exhibited equivalent tensile response compared to the control ECC mix and displayed a strong relationship between tensile strain and the fractional change in resistivity. The inclusion of MC fibers at 0.75% by volume was found to exhibit high sensitivity to micro-cracks formation, with gauge factor two orders of magnitude larger than that of an ordinary strain gauge, albeit less than that of the control mix. It is envisaged that the use of ECC can create an intelligent infrastructure able to sense and repair damage and monitor the recovery extent.

Effect of superplasticizers on the early age hydration of sulfoaluminate cement

The effects of two types of superplasticizers on the properties of CSA cement pastes during early hydration were studied. The influences of two types of superplasticizers on the properties of cement pastes, including the normal consistency, setting time, fluidity, and compressive strength, were investigated by using various methods. The hydration products of the cement pastes cured for 1 day and 3 days were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the PCE type superplasticizer retards the early age hydration while the FDN type superplasticizer accelerates the early age hydration of the CSA cement. Both types of superplasticizers have no influence on the further hydration of CSA cement, confirmed by the calorimeter tests as well. The ultrasonic pulse velocity measurements were used to probe the influence of two types of superplasticizers on the hydration of CSA cement pastes at a high water-cement ratio (0.45). The results show that the PCE type superplasticizer retards the early age hydration of the CSA cement while the FDN type superplasticizer has little influence on the early age hydration of the CSA cement.

Sugaring marble in the Monumental Cemetery in Bologna (Italy): characterization of naturally and artificially weathered samples and first results of consolidation by hydroxyapatite

The so-called sugaring of marble is a very common degradation phenomenon, affecting both historical monuments and modern buildings, which is originated by environmental temperature fluctuations. Thermal cycles are indeed responsible for micro-cracks formation at the boundaries between calcite grains, so that marble is subjected to granular disintegration and can be reduced to a sugar-like powder of isolated calcite grains by just the pressure of a finger. Since no effective, compatible and durable treatment for sugaring marble consolidation is currently available, in this paper a novel consolidating treatment recently proposed for limestone, based on the formation of hydroxyapatite inside the stone, was investigated for weathered marble. To test the new treatment on suitably decayed marble samples, some naturally sugaring marbles from the Monumental Cemetery in Bologna (Italy, nineteenth century) were firstly characterized by scanning electron microscope (SEM), mercury intrusion porosimetry (MIP) and ultrasonic pulse velocity (UPV) measurement. Then, artificially weathered samples were produced by heating fresh Carrara marble samples at 400 °C for 1 h. The effects of artificial weathering were characterized using the same techniques as above, and a very good agreement was found between microstructure and mechanical features of naturally and artificially weathered samples. Then, the hydroxyapatite-based treatment was tested on the so-obtained artificially weathered samples, and the treatment effects were characterized by UPV, MIP and SEM equipped with energy dispersive spectrometry and Fourier transform infrared spectroscopy. The hydroxyapatite-based treatment exhibited a remarkable ability of restoring marble cohesion and a good compatibility in terms of modifications in pore size distribution, which leads to regard this treatment as a very promising consolidant for weathered marble.

Investigation of the Potential for Evaluation of Concrete Flaws Using Nondestructive Testing Methods

Adoption of periodic or continuous monitoring strategies to assess condition state of infrastructure elements is a vital part of service life management (SLM). NDT methods are increasingly seen as an attractive and viable strategy to support condition monitoring. Over the last 15 years, the LEME research group at UFRGS has investigated several aspects related to the use of the ultrasonic pulse velocity (UPV) method and its potential for real field applications. One of the main advances involved the development of artificial neural network (ANN) models for correlating compressive strength and UPV measurements. Another examined problem was how to deal with the large amount of raw data derived from inspection of large structures. Several studies were carried out to check different mapping techniques, as reported by Lorenzi et al. 2011. This paper relates one investigation where UPV and rebound hammer (RH) measurements were collected from a beam containing several induced defects, simulated using different materials. The results were processed using a mapping strategy, which indicated suspicious points where core extraction was undertaken. All cores taken from points derived from UPV results were found to have flaws providing evidence that this may be a suitable tool to assess concrete structures, when data is properly interpreted.

Experimental Study on Concrete Using Copper Slag as Replacement Material of Fine Aggregate

This paper reports the effect of concrete using copper slag as fine aggregate replacement. In this project work, the concrete grade M40 was selected and IS method was used for mix design. The properties of material for cement, fine aggregate, coarse aggregate and copper slag were studied for mix design. The various strength of concrete like compressive, flexural and split tensile were studied and non-destructive test such as rebound hammer test and ultrasonic pulse velocity measurement were studied for various replacements of fine aggregate using copper slag that are 0%, 20%, 40%, 60%, 80% and 100%. The maximum compressive strength of concrete attained at 40% replacement of fine aggregate at 7 and 28 days. The split tensile strength and the flexural strength were also obtained higher strength at 40% replacement level at 28 days. The rebound hammer test showed higher compressive strength at 40% fine aggregate replacement, this is due to uniformity of concrete. The pulse wave velocity is higher for the 40% fine aggregate replacement, it is understood that the density of the mix is high and free from pores.

Microcracking based rock classification using ultrasonic and porosity parameters and multivariate analysis methods

This work aims at presenting a new methodology, based on NDT ultrasonic techniques and water porosity measurements, to characterize the microcracking state of rocks and classify them in microcracking based equivalent groups. The measurements of ultrasonic pulse velocity, the attenuation coefficient and the porosity by water saturation under vacuum conditions make it possible to compare and validate all these techniques as good practices to classify aggregates and ornamental stones with regard to their rock matrix compactness.Beyond the fact that these developments give new approaches to assess the rock microcracking, it was shown that these parameters have a direct relationship. Indeed, the classification methodology was applied to a database containing 56 cores coming from blocks sampled in an aggregate production quarry. For these cores, ultrasonic parameters (wave velocity, attenuation and anisotropy coefficients) and porosity parameters (total water, crack and pore porosities) were measured. Two multivariate statistical methods (Principal Component Analysis and Cluster Analysis) were applied on this database to assess the relationship between all these parameters and to classify the cores into micro-structurally similar groups.The application of the setup methodology on the core database allows us to study the main correlations between the measured microcracking rock properties. On the other hand, it was shown that the method can be used as an effective way to characterize the differences in terms of microstructure between rock samples.

Using piezoelectric sensors for ultrasonic pulse velocity measurements in concrete

The ultrasonic pulse velocity (UPV) test has been a widely used non-destructive testing method for concrete structures. However, the conventional UPV test has limitations in consistency of results and applicability in hard-to-access regions of structures. The authors explore the feasibility of embedded piezoelectric (PZT) sensors for ultrasonic measurements in concrete structures. Two PZT sensors were embedded in a reinforced concrete specimen. One sensor worked as an actuator driven by an ultrasonic pulse-receiver, and another sensor worked as a receiver. A series of ultrasonic tests were conducted to investigate the performance of the embedded sensors in crack-free concrete and concrete specimens having a surface-breaking crack under various external loadings. Signals measured by the embedded sensors show a broad bandwidth with a centre frequency around 80 kHz, and very good coherence in the frequency range from 30 to 180 kHz. Furthermore, experimental variability in ultrasonic pulse velocity and attenuation is substantially reduced compared to previously reported values from conventional UPV equipment. Findings from this study demonstrate that the embedded sensors have great potential as a low-cost solution for ultrasonic transducers for health monitoring of concrete in structures.