The recycling of concrete, bricks and masonry rubble as concrete aggregates is an important way to contribute to a sustainable material flow. However, there are still various uncertainties limiting the widespread use of recycled concrete (RC). The fluctuations in the composition of commercial grade recycled aggregates (RAs) and their influence on the properties of fresh and hardened concrete are of particular concern regarding the use of RC. In this project, variations in the composition of RA were studied over a period of several weeks. Concrete mixtures were then produced with these aggregates in order to evaluate the resulting variations in concrete properties. Using two of them, consisting a high content of RA, the principal applicability of RC-mixtures for structural use in comparison to conventional concrete (CC) was shown in web shear and flexural reinforced beams, which were tested to their ultimate shear force resistance. Evaluating experimental and analytical results based on the modified truss methodology, no significant drop for beams made of RA in their shear force resistance was observed. Although the high variability in aggregate composition causes corresponding variations in concrete properties, the results obtained demonstrate that RA is suited for a wide variety of applications in the building industry.

The recycling of demolition rubble and its reuse in building materials is desired, but the question rises how reinforced concrete members made with recycled aggregate concrete has to be designed. Since a similar flexural behavior of recycled aggregate concrete and natural aggregate concrete was shown in several studies, this paper focuses on the shear resistance of slabs without shear reinforcement. The slabs were made of concrete using different types of aggregates: (a) 100% wt recycled concrete aggregate, (b) 50% wt mixed rubble aggregates and 50% wt natural aggregates, (c) 100% wt mixed rubble aggregates as well as (d) natural aggregates. The latter was used as a reference concrete. In order to determine the shear resistance, slabs were loaded until shear failure occurred in a four-point-bending test. The slabs made of recycled aggregate concrete showed similar crack distributions as the slabs made of natural aggregate concrete. Predictions for the shear resistance were obtained using the critical shear crack theory of Muttoni as well as the Swiss and the European standards (SN 505 262 and Eurocode 2). The predictions by the critical shear crack theory and the European standard showed good correlation with the experimental results (mean ratio between experimental and predicted value: 1.00 +/- 0.05 and 0.99 +/- 0.04, respectively). But the predictions by the critical shear crack theory and the European standard overestimated the shear resistance of the slabs made of concrete with 100% wt mixed rubble aggregate. Especially for these slabs the Swiss standard predicted 8-11% tower shear resistances than the critical shear crack theory and the European standard. (C) 2012 Elsevier Ltd. All rights reserved.

Since timber bridges are light-weight structures with a high life-load to death-load ratio, they are susceptible to vibration and thus satisfying vibration serviceability is a governing design criterion. A good knowledge of the damping properties of timber bridges is therefore a key aspect for guaranteeing a sufficient serviceability. Since observations suggest that timber bridges with an asphalt pavement increase the damping, this work investigates the influence of asphalt pavement on the damping and the resonance frequencies of two laboratory bridges: (1) a cable-stayed bridge with a main span of 15.6 m, a secondary span of 3.6 m and a width of 1.6 m and (2) a smaller simply supported bridge with a total length of 9.6 m and a width of 1.6 m. The deck plates were made from two different kinds of panels: cross-laminated timber (CLT) and a stress-laminated plate (SLP). Due to the asphalt pavement the first resonance frequency decreases 23%-26% for the cable-stayed bridge and 16%-18% for the simply supported bridge. This result suggests that the additional mass overtops the effect of an additional stiffness. The damping of the first vibration mode is about zeta = 0.5% ... 0.66% for both bridges without pavement, and increases to zeta = 2.2% ... 2.6% and zeta = 6.2% ... 7.4% for the cable-stayed and the simply supported bridge, respectively, after deployment of an asphalt pavement. The comparison of the experimental results for the first resonance frequency and the damping with Finite-Element computations indicate that a noticeable amount of shear forces are transferred during the dynamic measurement and thus the pavement contributes to the stiffness of the bridges. The beneficial effect of the asphalt pavement at ambient temperatures on the damping has to be validated by measurements at different temperatures, since the asphalt is very temperature dependent. (C) 2010 Elsevier Ltd. All rights reserved.

The assessment of tree stability requires information about the location and the geometry of fungal decay or of a cavity in the interior of the trunk. This work aims at specifying which size of decay or cavity can be detected non-destructively by acoustic wood tomography. In the present work, the elastic waves that propagate in a trunk during a tomographic measurement were visualized by numerical simulations. The numerical model enabled to systematically investigate the influence of fungal decay on tomographic measurements neglecting the heterogeneity of wood. The influence of wood heterogeneity was studied in laboratory experiments on trunks. The experiments indicated that the waveforms of the measured signals are by far more sensitive to the natural heterogeneity of trunk wood than the travel times, thereby making waveforms unsuitable for decay detection. Thus, it is recommended to further develop the travel time inversion algorithms for trunks and to neglect the information in waveforms or amplitudes. Fungal decay is detectable if the influence of the decay is distinguishable from the influence of the heterogeneity. It was found from the numerical analysis that the cross-section of a cavity, which is larger than 5% of the total cross-section of the trunk, can be detected by acoustic wood tomography.

Modal analysis was used to determine the rolling shear modulus of Norway spruce samples that were either untreated and inoculated by fungi. The resonance frequencies of centimeter ranged cuboids were measured using contact-less laser interferometry. A three-dimensional theoretical model describing the orthotropic behavior of the material was used to calculate the resonance frequencies. Using an iterative scheme based on the least squares method, the value of the rolling shear modulus was then extracted. In this first investigation, the decrease in the rolling shear modulus and the weight loss of Norway spruce inoculated with white-rot fungi Heterobasidion annosum and Ganoderma lipsiense were studied for three different exposure times ranging from 4 to 12 weeks. Comparison of measured and theoretical resonance frequencies confirmed that operation was in the applicable range of the theoretical model for the inoculated specimens. A decrease in rolling shear modulus of up to 10% (H. annosum) and 50% (G. lipsiense) was found.

Anisotropy of acoustic propagation velocities is a ubiquitous feature of wood. This needs to be considered for successful application of travel time tomography, an increasingly popular technique for non-destructive testing of living trees. We have developed a simple correction scheme that removes first-order anisotropy effects. The corrected travel-time data can be inverted with isotropic inversion codes that are commercially available. Using a numerical experiment, we demonstrate the consequences of ignoring anisotropy effects and outline the performance of our correction scheme. The new technique has been applied to two spruce samples. Subsequent inspection of the samples revealed a good match with the tomograms.

Visual tree assessment (VTA) is carried out to evaluate the stability of urban trunks. For identification of fungal decay non-destructive methods, based on elastic wave propagation, are used to supplement VTA. This study aims at a profound understanding of the wave propagation phenomena in the radial-tangential plane of a trunk with the intention of enhancing those methods for identification of decay. The simulation model is described in detail. Since no closed form analytical solution of this propagation problem exits, numerical simulation based on the finite-difference-time domain method (FDTD) is used. Thus, a two-dimensional cylindrical FDTD code is developed, which represents the cylindrical cross-section and considers the anisotropy of wood. The characteristics of wave propagation in the anisotropic material are studied by a "healthy" reference model using snapshots of the displacement amplitudes at different propagation times. The influence of fungal decay is investigated for two different sizes of decayed regions (5% and 11% of the total area) and two different degrees of decay: total degradation of the wood (cavity) and reduced wave velocities (75%). Subsequently these results are compared with the influence of a heterogeneous distribution of density and different moisture content. The anisotropy of the material results in a characteristic wavefront of the P-wave. The influence of size and degree of decay is significant in the synthetic data. However, the uncertainties according to the natural grown material wood and to the measurement system require a robust and overdetermined data processing algorithm to interpret the travel-times.

Cross-laminated solid wood panels are used in timber structures as load bearing plates and shear panels. Since timber is a relatively soft construction material, the design of such structures is driven by serviceability criteria. Therefore, accurate elastic properties are required. In this paper a fully automated procedure to determine global elastic properties of full-scale cross-laminated wood panels is developed. Experimental modal analysis is used to determine resonance frequencies and mode shapes of rectangular wooden specimens. An analytical model based on Reddy's higher order plate theory is applied to calculate natural frequencies and mode shapes numerically. Corresponding frequencies are allocated using the modal assurance criterion. All three shear moduli and the two in-plane stiffness moduli are identified successfully by minimizing the difference between measured and estimated resonance frequencies in a total least squares sense. By comparing resonance frequencies and additionally by a static bending experiment, it is shown that the global mechanical behavior of the specimen is accurately described using an orthotropic, homogenized, linear elastic material behavior.

Internal decay of trees due to degradation by rot fungi may lead to failure of trees and therefore hazards to life or property. Hence, non-destructive methods for identification of decay are required. Today, investigations of the state of decay are carried out by traveltime measurements of elastic waves owing to the assumption that wood degradation leads to a change in the propagation velocity. This study aims at a profound understanding of the wave propagation phenomena in the radial-tangential plane of a trunk with the intention of enhancing those methods for identification of decay based on structural waves. Since no closed analytical solution of this propagation problem exits, numerical sim- ulation based on the finite-dierence- time domain method (FDTD) is used. Thus a two-dimensional cylindrical FDTD code is developed, which represents the cylindrical cross-section and implements the anisotropy of wood. Since the code has a singularity in the center, a special treatment of the center is proposed. The characteristics of wave propagation in the anisotropic material are studied by a "healthy" reference model using snapshots of the displacement amplitudes. The influence of fungal decay is investigated for two dierent sizes of decayed regions (5% and 11% of the total area) and two dier- ent degrees of decay: total degradation of the wood (cavity) and reduced wave velocities (75%). The anisotropy of the material results in a characteristic wavefront of the P-wave. This is validated by comparison with numerical and analytical results from literature. The influence of size and degree of decay is significant in the synthetic data. However, the uncertainties according to the natural grown material wood and to the measurement system require a robust and over-determined data processing algorithm to interpret the traveltimes.

Wooden cuboids (Picea abies) in the size-range of centimeters were investigated by resonant ultrasound spectroscopy (RUS) to determine the shear modulus of the radial-tangential plane and the damping characteristic. This approach accounts the homogenized, orthotropic behavior of wood and the three dimensional geometry of the specimen. The method is non-destructive and the specimens have a suitable geometry for the exposure to fungal pathogens, thus the decay of the shear modulus of a single specimen, due to white-rot fungi, was determined. The relation between decrease of shear modulus and specimen mass is the basis for simulation and evaluation of non-destructive testing methods using resonances or elastic waves for detection of fungal decay. RT G