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| 2. |
- Draganovic, Almir, et al.
(författare)
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Dispersion of microfine cement grout with ultrasound and conventional laboratory dissolvers
- 2020
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- Grout based on microfine cement is mainly used for sealing of rock fractures in underground construction with high sealing requirements. This grout is known as hard dispersed, compared to grouts based on ordinary Portland cement. This study investigates the possibility of using ultrasound to improve the dispersion of microfine cement grout. Ultrasound dispersion is compared with dispersion efficiency of an ordinary laboratory mixer equipped with a disk, and using the rotor-stator technique. Dispersion efficiency was measured with a filter pump. The grout dispersed with the laboratory mixer and disk could not pass through a 154 mm filter. The laboratory mixer using the rotor-stator technique showed much better efficiency, with a measured dispersion that varied between 77 and 104 mm. Dispersion with ultrasound yielded more reliable results, with lower variation; the grout passed through a 77 mm filter. These results showed that a laboratory mixer with a disk is not an effective method for dispersion of microfine cement. A laboratory mixer using the rotor-stator method is much more effective. Ultrasound is not only an effective method but is even better than a mixer using the rotor-stator technique.
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| 3. |
- Draganovic, Almir, et al.
(författare)
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Ultrasonic dispersion of hard dispersed ultrafine milled cement-based grout for water sealing of fractured hard rock
- 2022
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 317
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Tidskriftsartikel (refereegranskat)abstract
- Ever higher demands on the sealing of rock around underground structures drive the development of cement based grouts. The results of the previous study demonstrated that it is possible to mill cement to approximately 20 to 25 mu m and use it to seal fracture aperture down to approximately 70 mu m. Further milling deteriorates the penetrability of the grouts due to the flocculation of the fine particles. This study investigates ultrasound as a technique to improve dispersion of grouts based on ultrafine milled cement. The grout tested is based on cement where 95% of the cement mass has particles smaller than 12 mu m and is very hard to disperse. Dispersion with ultrasound is compared with a conventional laboratory mixer equipped with a disk and rotor-stator system. The dispersion efficiency of this mixing equipment was tested by a filter pump. The results confirmed that a conventional laboratory mixer equipped with a disk is not at all suitable for dispersion of this grout. The laboratory mixer equipped with a rotor-stator system is much better than a disc but still cannot disperse this fine milled grout properly. Ultrasound was found to be the most effective method. The dispersion achieved, measured with a filter pump, was around 54 mu m which indicates that it is possible to seal fracture aperture now down to 54 mu m, which is a significant improvement.
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| 4. |
- Elfgren, Lennart, Senior Professor, 1942-, et al.
(författare)
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Infrastrukturprogrammet Väg-Bro-Tunnel : Syntesrapport 1996 - 2007
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Vetenskap – Kunskapspositionerna har flyttats fram beträffande planering, byggande och underhåll av väger, broar, dammar och tunnlar. 21 doktors- och 24 licentiatexamina har avlagts och ytterligare 4 doktors- och 5 licentiatexamina planeras under 2008. Målen för avhandlingarna är i de flesta fall mycket relevanta och ambitiösa. Tankeväckande hypoteser har ställts upp och prövats. Den vetenskapliga metoden har oftast bestått av en omfattande litteraturundersökning följd av laboratorie- och/eller fältförsök, där uppställda hypoteser prövats. Resultaten har sedan analyserats med avancerade teoretiska modeller och värdefulla slutsatser har dragits. De flesta arbetena har mycket god kvalitet, innehåller många originella bidrag och bedöms få stor betydelse för den fortsatta vetenskapliga utvecklingen inom respektive ämnesområde.Genom programmet har Sveriges medverkan stärkts i det europeiska forskningssamarbetet i EU.Näringsliv - Bygg- och infrastruktursektorn inom svenskt näringsliv har genom programmet tillförts 38 forskarutbildade ingenjörer. Detta ger ökad kompetens och konkurrenskraft. Programmets visioner var att reducera byggtid och livscykelkostnader för broar och vägar, att introducera effektiva diagnos-, reparations- och förstärkningssystem för broar och dammar samt att bli världsledande inom tunneldrivning. Dessa visioner håller nu på att uppfyllas. Ett huvudmål var även att utveckla en industrialiseringsprocess inom infrastrukturområdet för att effektivisera byggandet. Här har stora steg framåt tagits.Samhälle - Ett aktivt nätverk har byggts mellan deltagande personer, företag och universitet som stärker Sveriges konkurrenskraft och påskyndar utvecklingen mot ett effektivt, innovativt, marknadsinriktat tjänstesamhälle.
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| 6. |
- Fröjd, Patrik, et al.
(författare)
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Amplitude and phase measurements of continuous diffuse fields for structural health monitoring of concrete structures
- 2016
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Ingår i: NDT & E International. - : Elsevier BV. - 0963-8695. ; 77:January, s. 35-41
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Tidskriftsartikel (refereegranskat)abstract
- Structural health monitoring systems for civil structures based on ultrasonic guided waves face the problem of very high attenuation of mechanical waves in concrete. This means that it is difficult to cover large areas with a reasonable number of transducers. Continuous acoustic transmission, as opposed to pulse transmission, enables narrow-band, coherent measurements, which can be used to detect meaningful signals for very low signal levels. This study investigates the use of amplitude and phase measurements of single-frequency continuous acoustic transmissions, between two piezoelectric transducers, as indicators of damage in a concrete slab. The sensitivity to damage of these measurements are compared to pulsed coda wave analysis. The measurements of the continuous signals are performed with a lock-in amplifier, which is known to be able to detect very low signal levels. The amplitudes of the transmitted signal is decreased in order to simulate increased distance between transmitting and receiving transducer. It is shown that amplitude and phase measurements of the continuous wave field provide indication of damage equal to that of coda wave analysis of transmitted pulses and that these can be detected at much lower signal amplitudes. This indicates the possibility to increase spacing in a network of reciprocal transducers in a structural health-monitoring system.
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| 7. |
- Fröjd, Patrik, et al.
(författare)
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Continuous wave measurements in a network of transducers for structural health monitoring of a large concrete floor slab
- 2016
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Ingår i: Structural Health Monitoring. - : SAGE Publications. - 1475-9217 .- 1741-3168. ; 15:4, s. 403-412
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Tidskriftsartikel (refereegranskat)abstract
- Local, superficial damage was detected and localized on an 8 × 2-m concrete floor slab using a structural health monitoring system. A total of 30 piezoelectric transducers, placed in a grid, transmitted and received continuous ultrasonic waves that were measured using a lock-in amplifier. Tomography was used to create images from the measured amplitude and phase of the continuous waves between all possible transducer pairs. The location of damage induced by impact hits was visible in the resulting images. The signals could easily be detected even between the most distant transducer pairs, indicating the possibility of monitoring even very large concrete structures.
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| 8. |
- Fröjd, Patrik, et al.
(författare)
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Detecting damage events in concrete using diffuse ultrasound structural health monitoring durinbg strong environmental variations
- 2018
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Ingår i: Structural Health Monitoring. - : SAGE Publications. - 1475-9217 .- 1741-3168. ; 17:2, s. 410-419
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Tidskriftsartikel (refereegranskat)abstract
- Diffuse ultrasonic wave measurements used in structural health monitoring applications can detect damage in concrete. However, the accuracy is very susceptible to environmental variations. In this study, a large concrete floor slab was monitored using diffuse wave fields that were generated by continuous-wave transmissions between ultrasonic transducers. The slab was monitored for several weeks while being subjected to changes in environmental conditions. Subsequently, it was damaged using impact hits, resulting in centimeter-scale cracking. The variations caused by the environment masked the effects of the damage in the measurements. To address this issue, the Mahalanobis distance was used to distinguish between the influence of the damage and the influence of the environmental variations. The Mahalanobis model uses amplitude and phase measurements of continuous waves at a set of different frequencies as inputs. A moving window approach was applied to the baseline data set to account for slow trends. This study shows that this technique greatly suppresses most of the variations caused by environmental conditions. All damage events in our data set have been detected.
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| 9. |
- Fröjd, Patrik, et al.
(författare)
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Efficiency of some voice coil transducers in low frequency reciprocal operations.
- 2015
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 1520-8524 .- 0001-4966. ; 137:6, s. 490-495
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Tidskriftsartikel (refereegranskat)abstract
- The feasibility of using different voice coil transducers in applications with reciprocal transducers of mechanical waves is investigated. It was speculated that voice coil transducers could be a more efficient alternative to piezoelectric transducers in low frequency ranges. Five different voice coil transducers, originally constructed for either transmission or reception, were characterized in both modes of operation. A piezoelectric ceramic disk was used for comparison between the transducer types. The results show that voice coils indeed can function as reciprocal transducers and that the most sensitive of the evaluated transducers is more efficient than the piezoelectric disk for low frequencies.
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| 10. |
- Fröjd, Patrik, et al.
(författare)
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Frequency selection for coda wave interferometry in concrete structures
- 2017
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Ingår i: Ultrasonics. - : Elsevier BV. - 0041-624X. ; 80, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- This study contributes to the establishment of frequency recommendations for use in coda wave interferometry structural health monitoring (SHM) systems for concrete structures. To this end, codas with widely different central frequencies were used to detect boreholes with different diameters in a large concrete floor slab, and to track increasing damage in a small concrete beam subjected to bending loads. SHM results were obtained for damage that can be simulated by drilled holes on the scale of a few mm or microcracks due to bending. These results suggest that signals in the range of 50–150 kHz are suitable in large concrete structures where it is necessary to account for the high attenuation of high-frequency signals.
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