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- 2016 (11) (entfernen)
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- Beitrag zu einem Tagungsband (4)
- Vortrag (4)
- Zeitschriftenartikel (2)
- Posterpräsentation (1)
Schlagworte
- Moisture (3)
- Microwave (2)
- Pore radius (2)
- Relaxation time (2)
- Screed (2)
- Spectral induced polarization (2)
- Clustering (1)
- Concrete evaluation (1)
- Consolidated materials (1)
- Corresponding relative humidity (1)
Eingeladener Vortrag
- nein (4)
Zur Bestimmung des Feuchtezustands und insbesondere der Belegereife von Estrichfußböden kommen in Deutschland zerstörende Prüfverfahren zum Einsatz, die eine punktuelle Probenahme erfordern. Hierbei ergeben sich immer wieder Fehlinterpretationen, da zum einen die Probenahme selbst zu einer Veränderung des Feuchtezustands führt und zum anderen, weil die Verfahren an sich mitunter ungenau sind (z.B. abhängig von der Estrichzusammensetzung). Zusammen mit vier Forschungsinstituten und dem Industriepartner Bosch wurden an der BAM zerstörungsfreie Prüfverfahren auf deren Tauglichkeit zur Estrichfeuchtemessung untersucht und mit den herkömmlichen zerstörenden Verfahren verglichen.
Für diesen Versuch kamen verschiedene geophysikalische Verfahren zum Einsatz, darunter Nuklear Magnetische Resonanz (NMR), elektrische Widerstandsmessungen und Impulsradar (GPR). Es wurden neun verschiedene Estrichsorten hergestellt und während der Trocknungsphase bei Konstant-Normklima gelagert. Diese wurden sowohl zerstörend als auch zerstörungsfrei mit den o. g. Verfahren untersucht. Gleichzeitig wurden die Masseänderungen der Proben zur Bestimmung des integralen Feuchtehalts aufgezeichnet.
Die Ergebnisse zeigen zum einen, dass das Abtrocknungsverhalten von zementgebundenen Estrichen grundsätzlich unterschiedlich von dem anhydritgebundener Estriche ist. Während sich bei ersteren zügig ein deutlicher Feuchtegradient über die Höhe der Proben einstellt, verläuft dieser bei der zweiten Probengruppe sehr flach. Dies lässt sich vor allem in den NMR Daten räumlich hochaufgelöst nachvollziehen - die Datenakquise erfolgte mit einer NMR MOUSE PM 25. Ein ähnliches Bild ergibt sich auch aus den elektrischen Widerstandsmessungen, die mittels sog. Multi-Ring-Elektroden (MRE) durchgeführt wurden. MRE bezeichnen als Vertikalprofil angeordnete Ringelektroden mit einem Abstand von ca. 1-2 mm, zwischen denen jeweils Zwei-Punkt Widerstandsmessungen durchgeführt werden. Bei sehr geringen Feuchtegehalten (z.T. auch um die Belegereife) waren mit dieser Methode jedoch wegen der zu hohen Übergangswiderstände nur bedingt Messungen möglich. Im Gegensatz zu NMR und MRE sind mit dem Radarverfahren (2 GHz Antenne) keine tiefenbezogenen Aussagen möglich. Jedoch lässt sich über eine Amplitudenauswertung von direkter und an der Rückwand reflektierter Welle teilweise eine Aussage über Restfeuchtigkeit im Volumen treffen. Ebenso zeigt die Laufzeitdifferenz der beiden Wellen eine starke Abhängigkeit vom Feuchtegehalt.
In Germany there is an existing built infrastructure worth about 50 trillion Euros. The expected lifetimes of individual structures are up to 100 years. Considerable costs (annually about 35 billion Euros, the trend continues upwards) are involved in order to maintain and rehabilitate both residential as well as transportation infrastructure buildings. Most damages we observe on our built infrastructure are moisture-induced processes. Consequently reliable moisture measurement tools a highly needed for meaningful building diagnosis investigations. The optimal moisture measuring technique would be non-destructive, fast, repeatable, reliable, independent of steel in the vicinity, the surface condition or possible salt loads of the material under test. Since this is unfortunately not the case for any non-destructive method, it is often very difficult to decide for users which method to use for the particular testing problem. The only standardized methods in Germany are the “direct” and destructive Darr- and the CM tests. Although they can be highly accurate (when handled with care during the sampling), they deliver only punctual information and cannot be used for monitoring. The other, non-destructive methods are based on the change in humidity-dependent physical material properties. The underlying physics, their particular advantages and disadvantages are discussed in this paper.
Permeability estimation from spectral induced
polarization (SIP) measurements is based on a
fundamental premise that the characteristic relaxation
time (t) is related to the effective hydraulic radius (reff)
controlling fluid flow. The approach requires a reliable
estimate of the diffusion coefficient of the ions in the
electrical double layer. Others have assumed a value for
the diffusion coefficient, or postulated different values for
clay versus clay-free rocks. We examine the link between
t and reff for an extensive database of sandstone samples
where mercury porosimetry data confirm that reff is
reliably determined from a modification of the Hagen-
Poiseuille equation assuming that the electrical tortuosity
is equal to the hydraulic tortuosity. Our database does not
support the existence of 1 or 2 distinct representative
diffusion coefficients but instead demonstrates strong
evidence for 6 orders of magnitude of variation in an
apparent diffusion coefficient that is well correlated with
both reff and the specific surface area per unit pore
volume (Spor). Two scenarios can explain our findings:
(1) the length-scale defined by t is not equal to reff and is
likely much longer due to the control of pore surface
roughness; (2) the range of diffusion coefficients is large
and likely determined by the relative proportions of the
different minerals (e.g. silica, clays) making up the rock.
In either case, the estimation of reff (and hence
permeability) is inherently uncertain from SIP relaxation
time.
Moisture measurement methods
(2016)
Moisture can cause imperfect sealings, faulty roof constructions, cracks and other kind of damages. For measuring the moisture in construction materials like concrete and screed, there are destructive(direct) and non-destructive(indirect) methods, that can be used. This presentation gives an overview and a comparison of these methods.
We have compared the performance of the typical Darr and CM moisture testing techniques, which are destructive with several non-destructive testing techniques on two types of floor screeds. In case of cement based screeds these destructive tests failed to deliver reliable results. Moreover, our measurements indicate significantly different drying and moisture transport behavior for the investigated cement based and calcium-sulphate based screeds. Whereas we have strong with depth decreasing moisture gradients in the CT material, we observe in the penetrated volumes of our ndt methods basically no clear moisture gradient in the CA samples. The findings with ndt methods could be supported by moisture gradient studies with nuclear magnetic resonance measurements.
Eight different screed types are tested including two different sample heights of 35 and 70 mm. The moisture of the four cement based and four sulphate based screeds are monitored during hydration and evaporation. All samples are stored in a climatic chamber at 23◦ C and 50 % relative humidity. Embedded sensors like temperature arrays, humidity sensor arrays, and multi-ring electrodes are embedded in the samples to yield a detailed moisture evolution with high depth resolution. Furthermore, nuclear magnetic resonance is used to quantify the water content at different depths. This multi-sensor approach allows a comprehensive monitoring of the moisture and its gradient in the different screed samples. This yields a deeper insight into the hydration, moisture convection, and diffusion processes.
Um den Feuchtegehalt von Fußbodenestrich vor der Verlegung von Holz- oder anderen
Bodenbelägen zu bestimmen, werden zerstörende Prüfverfahren wie die Calcium-Carbid
Methode (CM) oder das thermogravimetrische Darr-Verfahren eingesetzt. Diese liefern
jedoch einmalig nur punktuelle Informationen und sind je nach Estrichtyp auch störanfällig.
Zusammen mit Partnern aus Forschung und Industrie wurde an der BAM ein Ringversuch
durchgeführt, dessen Ziel es war, verschiedene nach Möglichkeit zerstörungsfreie oder –
arme Prüfverfahren hinsichtlich ihrer Genauigkeit und Sensitivität vor allem im Bereich der
Belegereife zu testen. Hier dargestellt sind die Ergebnisse aufgenommen an einer
Calciumsulphat-Estrich Probe vom Typ Knauf FE80 Largo mit drei Verfahren, die auch
Aussagen über die Feuchtegradienten in die Tiefe zulassen. Die Proben wurden bei
Konstant-Normklima mit T=23 °C und rH=50 % zur Trocknung gelagert.
Measuring the moisture state of screeds is critical for floorers in order to prevent structural damages of bottom coverings. Typically destructive tests are carried out on small samples delivering only punctual information. We tested several non-destructive testing methods in terms of sensitivity in the critical low moisture range and observed substantially different drying behavior for the two tested cement based and calcium-sulphate based screed samples. Our findings are supported by moisture gradient measurements using the nuclear magnetic resonance technique.
We present the results of a machine learning (ML)- inspired data fusion approach, applied to multi-sensory nondestructive testing (NDT) data. Our dataset consists of Impact-Echo (IE), Ultrasonic Pulse Echo (US) and Ground Penetrating Radar (GPR) measurements collected on large-scale concrete specimens with built–in simulated honeycombing defects. In a previous study we were able to improve the detectability of honeycombs by fusing the information from the three different sensors with the density based clustering algorithm DBSCAN. We demonstrated the advantage of data fusion in reducing the false positives up to 10% compared to the best single sensor, thus, improving the detectability of the defects. The main objective of this contribution is to investigate the generality, i.e. whether the conclusions from one specimen can be adapted to the other. The effectiveness of the proposed approach on a separate full-scale concrete specimen was evaluated.
Permeability estimation from induced polarization (IP) measurements is based on a fundamental premise that the characteristic relaxation time τ is related to the effective hydraulic radius reff controlling fluid flow. The approach requires a reliable estimate of the diffusion coefficient of the ions in the electrical double layer. Others have assumed a value for the diffusion coefficient, or postulated different values for clay versus clay-free rocks. We have examined the link between a widely used single estimate of τ and reff for an extensive database of sandstone samples, in which mercury porosimetry data confirm that reff is reliably determined from a modification of the Hagen-Poiseuille equation assuming that the electrical tortuosity is equal to the hydraulic tortuosity. Our database does not support the existence of one or two distinct representative diffusion coefficients but instead demonstrates strong evidence for six orders of magnitude of variation in an apparent Diffusion coefficient that is well-correlated with reff and the specific surface area per unit pore volume Spor. Two scenarios can explain our findings:
(1) the length scale defined by τ is not equal to reff and is likely much longer due to the control of pore-surface roughness or
(2) the range of diffusion coefficients is large and likely determined by the relative proportions of the different minerals (e.g., silica and clays) making up the rock. In either case, the estimation of reff (and hence permeability) is inherently uncertain from a single characteristic IP relaxation time as considered in this study.