Automated Surface Wave Measurements for Evaluating the Depth of Surface-Breaking Cracks in Concrete
Seong-Hoon Kee1 &
Boohyun Nam2
International Journal of Concrete Structures and Materials volume 9, pages 307–321 (2015)Cite this article
The primary objective of this study is to investigate the feasibility of an innovative surface-mount sensor, made of a piezoelectric disc (PZT sensor), as a consistent source for surface wave velocity and transmission measurements in concrete structures. To this end, one concrete slab with lateral dimensions of 1500 by 1500 mm and a thickness of 200 mm was prepared in the laboratory. The concrete slab had a notch-type, surface-breaking crack at its center, with depths increasing from 0 to 100 mm at stepwise intervals of 10 mm. A PZT sensor was attached to the concrete surface and used to generate incident surface waves for surface wave measurements. Two accelerometers were used to measure the surface waves. Signals generated by the PZT sensors show a broad bandwidth with a center frequency around 40 kHz, and very good signal consistency in the frequency range from 0 to 100 kHz. Furthermore, repeatability of the surface wave velocity and transmission measurements is significantly improved compared to that obtained using manual impact sources. In addition, the PZT sensors are demonstrated to be effective for monitoring an actual surface-breaking crack in a concrete beam specimen subjected to various external loadings (compressive and flexural loading with stepwise increases). The findings in this study demonstrate that the surface mount sensor has great potential as a consistent source for surface wave velocity and transmission measurements for automated health monitoring of concrete structures.
Introduction and Motivation
Surface wave measurements have been widely used to develop non-destructive evaluation (NDE) techniques for concrete structures in civil engineering due to their useful features (Graff 1991). Surface waves are mechanical waves that propagate along the surface of concrete with most of their energy confined near the surface, which enables one-sided access of concrete structures. The particle vibration amplitude of surface waves exponentially decreases with distance from the free surface boundary and with a frequency-dependent penetration depth, which is particularly useful to identify and characterize surface-breaking or sub-surface defects in concrete structures (Achenbach 2000, 2002). In infinite media, surface waves are non-dispersive, that is the wave velocity does not change with frequency. In practice, this assumption is valid when the thickness H of the solid body of interest is sufficiently larger than the wavelength λ of the surface wave (i.e., H > 2λ). In thin plates or layered systems, the velocity of surface wave changes with frequency. Surface wave velocity measurements have been demonstrated to be effective for characterizing mechanical properties of concrete in many civil engineering applications (ACI committee 228 1998).
In surface wave measurements, an impact source is used to generate incident surface waves, and two receivers are used to measure the surface waves propagating in concrete (see Fig. 1). Selecting an appropriate impact source is of great importance for successfully measuring surface waves in concrete structures. The normal impact of a ball on the concrete surface has been widely used as a source for surface wave-based NDE techniques. According to the Hertzian impact theory (McLaskey and Glaser 2010), the impulse force (or force pulse) is approximated by a "half sine" pulse, and the duration of the pulse depends on the geometry and material properties of a ball and a massive material that the ball hits; however, the most influential factor is the radius of the ball. Therefore, the correct ball size can be selected so that the frequency bandwidth generated by the impact source appropriately covers a frequency range of interest for the surface wave measurements. In practice, the impact source is usually operated by hand; however, there are several limitations to this method. First, it is difficult to generate consistent waves with an impact source controlled by a human hand. Furthermore, it is impossible to conduct surface wave measurements in hard-to-access regions of concrete structures, due to safety reasons or spatial limitations. Regardless of the feasibility of these methods, it would be time and labor intensive to be used in large civil structures.
Source and receiver configuration for surface wave measurements.
A possible solution to the aforementioned problems can be obtained by using "surface-mounted piezoelectric transducers (PZT)". PZT has been successfully applied to the structural health monitoring of concrete structures by using stress wave-based methods (Liao et al. 2011; Okafor et al. 1996; Song et al. 2006). The wave propagation properties were studied to detect and evaluate the cracks and damages inside concrete structures. Wang et al. (2001) studied the debonding behavior between steel rebar and concrete by using PZT (lead zirconate titanate) patches fixed to generate and receive elastic waves in concrete, and obtained the modulus of elasticity by utilizing the wave propagation characteristics. Song et al. (2007, 2008) developed smart aggregates to perform structural health monitoring for concrete structures. The mortar-typed aggregate was embedded in concrete structures during casting and successfully used for monitoring damage in concrete structures by measuring an energy-based damage index. Dong et al. (2011) developed a cement-based piezoelectric ceramic composite and effectively applied it as a sensor for health monitoring of concrete structures. Hou et al. (2012, 2013) developed a marble-based smart aggregate for seismic compressive and shear stresses. Recently, Kee and Zhu (2013) developed PZT embedded sensors using a PZT disc that can be used as ultrasonic transmitting and receiving transducers for ultrasonic pulse velocity tests. In this study, the author developed a surface-mount sensor using a PZT disc for generating incident surface waves for surface wave velocity and transmission measurements in concrete structures.
The primary objective of this study is to investigate the feasibility of an innovative surface-mount sensor made of a PZT disc (hereafter refer to as "surface-mount sensor") as a consistent source for surface wave velocity and transmission measurements in concrete structures. Two surface-mount sensors were attached to a concrete slab with dimensions of 1500 by 1500 by 200 mm (width X length X thickness). The slab possessed a surface-breaking crack located in the middle of the slab, which extended to varying depths. Two surface-mount sensors on either side of the surface-breaking crack worked as actuators driven by an ultrasonic pulse-and-receiver, and two accelerometers worked as a receiver. A series of surface wave measurements was performed to investigate the performance of the surface-mount sensors as a consistent source. An additional aspect to the investigation was to test the ability of surface-mount sensors to perform automated monitoring of an actual surface-breaking crack in a concrete beam subjected to various external loadings (compressive and flexural loading with stepwise increasing) (ElSafty and Abdel-Mohti 2013; Soltani et al. 2013).
Ultrasonic Surface Waves (USW) Method
The surface wave velocity methods involve determining the relationship between the wavelength and velocity of surface vibrations at varying vibration frequencies. The resulting relation is called a dispersion curve, which is generally determined by the spectral analysis of surface waves (SASW) (Nazarian and Desai 1993; Nazarian and Stokoe 1986). For plate-like concrete structures (deck, slab, wall, etc.), the ultrasonic surface wave (USW) technique has been demonstrated to be effective for evaluating material damages caused by many sources: ASR, DEF, freeze-and-thaw, and corrosion of reinforcing steel (Gucunski et al. 2013). The USW test consists of recording the response of the concrete, at two receiver locations, to an impact on the surface of the concrete in structures (See Fig. 1). The surface wave velocity can be obtained by measuring the phase difference ΔΦ between two different sensors (sensor 1 and sensor 2) (C = 2πfd/ΔΦ; where f is frequency, and d is the distance between two sensors). The frequency range of interest in the USW technique is a high-frequency range compared to the thickness of the tested object, in which surface waves are non-dispersive. In cases of relatively homogeneous materials, the velocity of the surface waves does not vary significantly with frequency. Therefore, the surface wave velocity can be precisely related to the elastic modulus of concrete, using the measured or assumed mass density and Poisson's ratio of the material. A complex process called inversion is not necessary in the USW technique, leading to a substantially reduced time required for data interpretation and post-processing. In the case of a sound and homogenous concrete plate, the velocity of the surface waves will show little variability, while significant variation in the phase velocity will be an indication of the presence of a defect or other anomaly.
Surface Wave Transmission (SWT) Method
The surface wave transmission (SWT) method has been demonstrated to be effective for evaluating surface-breaking or sub-surface defects in concrete structures. The SWT method uses the frequency-dependent penetration depth of surface waves. When incident surface waves (R i ) propagate across a surface-breaking crack, the low-frequency components of the incident surface waves will transmit to the forward scattering field with attenuation (R tr ), while the high-frequency components will reflect back (R r ). Consequently, the transmission coefficient of surface waves Tr across a surface-breaking crack, which is defined as the ratio of spectral amplitudes of R tr to R i , depends on the frequency of surface waves and dimensions of the defect in the concrete. For example, an analytical solution relating Tr and the normalized crack depth (h/λ, h is the depth of a surface-breaking crack) was given by Achenbach and his colleagues (Achenbach et al. 1980; Angel and Achenbach 1984; Mendelsohn et al. 1980). It was demonstrated through numerical simulations and experimental studies that the SWT method is effective for evaluating the depth of surface-breaking cracks in concrete structures (Hevin et al. 1998; Kee 2011; Kee and Zhu 2011; Popovics et al. 2000; Shin et al. 2008; Song et al. 2003). Test configuration of the SWT method is the same as that of the USW method, consisting of two receivers and an impact source. However, the measured amplitude of the surface waves is sensitive to the coupling condition of the sensors and the magnitude of impact force, which may cause significant errors in predicted values. It has been demonstrated that the self-calibrating procedure is effective for eliminating undesirable effects due to sensors and sources in the SWT method (Popovics et al. 2000). Recently, Kee and Zhu (2011, 2010) proposed the air-coupled sensing method, which significantly improves signal consistency and test speed in transmission measurements of surface waves in concrete.
Preparation of Piezoelectric Sensor
A piezoelectric sensor is an active element that converts electrical energy to mechanical energy, and mechanical energy to electrical energy (i.e., the piezoelectricity). The piezoelectricity causes a sensor to produce electric charges when subjected to stress (receiving action) and conversely, to generate mechanical vibrations when an electrical voltage is applied (actuator action). In this study, a piezoelectric disc is used as an actuator for generating incident surface waves in concrete.
A piezoelectric disc is one of the most widely used piezoelectric elements, as shown in Fig. 2. The thickness of a piezoelectric disc is much smaller than its lateral dimensions. The sensors used in this study are commercial piezoelectric warning devices, which generate sound when a voltage is applied continuously. One side of the piezoelectric element is attached to a metal plate (brass) for reinforcing the thin piezoelectric disc. A piezoelectric disc is polarized in the thickness direction. In the actuating mode, the disc expands/contracts in the thickness direction, i.e., along the axis of polarization, when a voltage is applied to the two surfaces of the ceramic disc, as shown in Fig. 2b. At the same time, the disc contracts/expands in the transverse direction. In the receiving mode, mechanical vibrations generate electric charges in the piezoelectric disc.
Structure of piezoelectric disc sensor: a a photo of the piezoelectric disc, and b a piezoelectric disc connected to a voltage.
Two piezoelectric sensors were attached to the concrete surface to generate incident surface waves in concrete structures. The piezoelectric disc has a thickness of 0.2 mm (7.87 mils) and a diameter of 22 mm (866.14 mils). Two wires were then soldered to the electrodes on the piezoelectric disc. Since concrete surfaces are often under conductive environments, electrical shielding and waterproofing were needed. The waterproof procedure follows the description given by Jung (Jung 2005). First, five layers of polyurethane coating (M-coat A by VISHAY®) were applied to the surface of the piezoelectric discs. Each coating had to be fully air-dry before applying a subsequent one.
Preparation of Specimens
Two concrete specimens were prepared in the laboratory to investigate the performance of the surface-mount sensor as an impact source in surface wave measurements. One concrete specimen (specimen 1) prepared in the laboratory had lateral dimensions of 1500 mm2 and a thickness of 200 mm (see Fig. 3). A notch-type crack was made at the mid-section of the specimen by inserting a 0.5 mm thick Zinc sheet before pouring the concrete. The notch-type crack was designed to have depths increasing stepwise from 10 to 100 mm, at intervals of 10 mm (Fig. 3b). The Zinc sheet was coated by a thin plastic film to avoid chemical bonding between the Zinc sheet and concrete during the cement hydration process, and to facilitate the extraction of the sheet from the concrete. The Zinc sheet was removed about 6 h after casting, slightly earlier than the final setting of the concrete, based on observations from a series of preliminary tests before fabricating the actual specimen. Finally, the width of the crack in the hardened concrete specimen, measured with a crack width gauge after 7 days, was approximately 0.5 mm. The proposed surface-mount sensors were attached on either side of the notch crack (see Fig. 3a). Concrete material used for specimen 1 was normal weight, ready-mixed concrete made of type I/II cement, river sand, and coarse aggregate with a maximum size of 19 mm. The design compressive strength of concrete was 20 MPa. Compressive strength measured according to ASTM C39 (ASTM C39 2014) at the time of testing ranges from 22.4 to 24.3 MPs, with a mean value of 23.58 MPa. P wave velocities measured with a pair of 54 kHz ultrasonic transducers in the through-transmission mode were in the range of 4331 and 4386 m/s.
Sectional view of a concrete slab (specimen 1), and data acquisition and signal generation systems for surface wave measurement using surface-mount sensors (a), and b isometric view of the concrete specimen 1.
In addition, a concrete beam (specimen 2) with dimensions of 400 by 1500 mm and a thickness of 190 mm was prepared in the laboratory, as shown in Fig. 5. Concrete used for the specimen 2 was normal weight, ready-mixed concrete made from Type I/II cement, river sand, and coarse aggregate with a maximum size of 19 mm. The design compressive strength of the concrete was 20 MPa. Three cylinder specimens were used to measure concrete compressive strength according to ASTM C39 (ASTM C39 2014), resulting in a measured compressive strength (at the time of testing) ranging from 22.3 to 25.58 MPa, with a mean value of 22.84 MPa. P-wave velocities measured with a pair of 54 kHz ultrasonic transducers were in the range of 4328 and 4375 m/s.
Two layers of longitudinal reinforcing bars (13.3 mm diameter) were used for the top and bottom layers, respectively. A real surface-breaking crack was designed to appear in the middle of the concrete specimen by three-point bending (see Fig. 4a). Before applying external loadings, two proposed surface-mount piezoelectric sensors were attached to the concrete on either side of the expected crack location. To ensure generation of a single flexural crack in the middle of the concrete specimen, the reinforcing bars were unbonded to the concrete by wrapping a thin, 400 mm-long plastic film around the middle section of the reinforcing bars. After cracking, it is reasonable to assume that concrete in the crack section cannot provide any tensile strength, and only the top reinforcing bars participate in the load-resistance mechanism. Assuming a constant strain distribution in the unbonded steel reinforcing bars, shear stresses in the unbonded concrete region disappear after cracking, which prevents initiation of additional shear cracks or other flexural cracks in the middle of the concrete specimen. Consequently, a single vertical surface-breaking crack will occur in the middle section of the specimen. In addition, transverse reinforcing bars (No. 3) were placed to avoid abrupt shear failure and to ensure flexural failure of the beam.
Isometric view of a concrete beam (specimen 2), and data acquisition and signal generation systems for surface wave measurement using surface-mount sensors (a), sectional view of the specimen 2 (B-B′), and (c) sectional view of the specimen 2 (C–C′).
Surface Wave Measurements
The test setup for surface wave measurements using surface-mount sensors consists of a function generator, a power amplifier, a pair of surface-mount sensors and accelerometers (as sources and receivers, respectively), a digital oscilloscope, a computer, and LabVIEW program (see Figs. 4a, 5a). The two surface-mount sensors were located at A and D, and two accelerometers (PCB 352C65) were located at B and C on concrete specimens 1 and 2 (see Figs. 3a, 4a). A function generator (EXTX/2A60) was used to drive the surface-mount sensors. Stress waves are highly attenuated as they propagate through concrete. Therefore, a power amplifier (Trek PZD250) was used to amplify the signal generated by the function generator. Gaussian functions with a duration T of 100 μs were used as an input signal for the function generator. The acquired signals were digitized by a high-speed digital oscilloscope (NI-PXI 5101) at a sampling frequency of 1 MHz and total signal length of 0.001 s. The digitized data were then transferred to a laptop computer for data storage and post-processing. To eliminate the effects of experimental variations regarding sensor and source, the self-calibrating procedure (Popovics et al. 2000) was used to measure surface wave transmission and velocity. Two accelerometers were placed at locations B and C of the test specimens 1 and 2 to measure surface waves. First, the stress waves generated by the impact source at A propagated towards the sensor at B, and then towards the far sensor at C, denoted as V AB, and V AC, respectively. For example, the typical time signals V AB and V AC measured across a surface-breaking crack with a 20 mm depth in the specimen 1 are shown in Fig. 6a. Surface wave components were extracted from the full waveform in time domain by applying a hanning window (bold lines in Fig. 6a), and converted to frequency domain signals, denoted as S AB, and S AC respectively. Similarly, stress waves generated by the surface-mount sensor at D were measured by accelerometers at C and B, denoted as S DC and S DB. The frequency domain signals of S AB, S AC, S DC and S DB were used to calculate the transmission functions of surface waves propagating through the cracked region BC in concrete specimens (S AC/S AB and S DB/S DC). The modulus (amplitude) and phase angle of the transmission functions are shown in Fig. 6b, c, respectively. In the cracked region, the phase angle of S AC/S AB (or S DB/S DC) almost linearly increases in a frequency range between 0 and about 45 kHz, in which the slope of the phase spectra is comparable to the theoretical value of the solid concrete with the surface wave velocity of 2200 m/s. In contrast, the modulus of S AC/S AB (or S DB/S DC) decreases with increasing frequency, which is clearly differentiated from the theoretical curve of the solid concrete. Therefore, it can be seen that the modulus components of the transmission function are more informative of the presence and characteristics of surface-breaking cracks in concrete then the phase components.
Test setup of a concrete beam (specimen 2) for applying compressive forces and generating a single surface-breaking crack: a a photo of a test setup, and b plan view from the section A-A′ shown in (a).
Typical signals generated by the surface-mount piezoelectric transducers, measured using accelerometers across a surface breaking crack with a depth of 20 mm in the specimen 1: a time signals, b, c the modulus and phase angle of the transmission functions (SAC/SAB or SDB/SDC).
In this study, the surface wave transmission ratio between B and C was calculated by averaging signals in the frequency domain obtained from opposite sides according to the self-calibrating procedure (Popovics et al. 2000) as follows,
$$ {\mathbf{Tr}}_{\text{BC}} = \sqrt {\frac{{{\mathbf{S}}_{\text{AC}} {\mathbf{S}}_{\text{DB}} }}{{{\mathbf{S}}_{\text{AB}} {\mathbf{S}}_{\text{DC}} }}} $$
In this study, five repeated signal data sets were collected at the same test location to investigate the repeatability of signals generated by the surface-mount sensors. The transmission coefficient measured from cracked regions was further normalized by the reference, producing the normalized transmission coefficient Tr n. It has been demonstrated that effects due to geometric attenuation and material damping can be effectively reduced by using the normalization process.
The phase velocity of the surface wave was calculated in the frequency domain by using the spectral analysis of surface waves (SASW). First, the phase difference between S AB and S AC by a source at A (\( \varDelta \phi_{\text{BC}} \)) and between S DC and S DB by a source at D (\( \varDelta \phi_{\text{CB}} \)) was calculated. Then the average phase velocity C BC was calculated using the average phase difference as follows,
$$ {\mathbf{C}}_{\text{BC}} = 2\pi f\frac{\text{BC}}{{(\varDelta \phi_{\text{BC}} + \varDelta \phi_{\text{CB}} )/2}} $$
where BC is the distance between two sensors on the locations B and C in Figs. 3, 4, 5 (BC = 200 mm in this study).
Repeatability of Signals Generated by the Surface-Mount Sensors
In this study, the repeatability of measured signals generated by the piezoelectric sensors was evaluated by the coherence function as follows,
$$ {\varvec{\upgamma}}_{j} (f) = \frac{{\left| {\sum\nolimits_{i = 1}^{5} {{\mathbf{P}}_{1j}^{i} (f)} } \right|}}{{\sqrt {\sum\nolimits_{i = 1}^{5} {{\mathbf{P}}_{11}^{i} (f)} \times \sum\nolimits_{i = 1}^{5} {{\mathbf{P}}_{jj}^{i} (f)} } }} $$
where \( {\mathbf{P}}_{1j}^{i} (f) \) is the cross-power spectrum of the reference signal and the signal measured at the jth test step; \( {\mathbf{P}}_{11}^{i} (f) \) and \( {\mathbf{P}}_{jj}^{i} (f) \) represent the auto-power spectrum of these signals; i is the index of the five repeated time domain signals; and f is frequency. The coherence function represents the degree of correlation between two signals as a function of frequency. The resulting γ ranges from 0 to 1.0, in which a value close to 1.0 indicates a good signal coherence. There are several factors that makes the coherence function less than one, including (i) measurements with incoherent noise, (ii) inconsistent coupling of source-and-receiver transducer and (iii) additional inputs in materials (i.e., additional scattering by any changes in internal defects).
Figure 7a shows the signal coherence γ of the measured signals generated by the surface-mount sensors on a crack-free region in specimen 1. For comparison purposes, the coherence curve of signals generated by a manual impact source (a steel ball of 13 mm diameter) is shown as a dash line in Fig. 6. It is demonstrated that the piezoelectric surface-mount sensors produce a very repeatable signal in a wideband frequency range of 0–100 kHz where γ ≥ 0.999, a criterion for a useful frequency range in this study. In contrast, the measured signals generated by a manual impact source shows good signal consistency in the frequency range of 10–30 kHz: the useful frequency range depends on the diameter of the steel ball used for impact sources.
Comparison of signal coherence generated by the surface-mount transducers and manual impact sources (a), and variations of the useful frequency range in a signal coherence function with increasing depth of the surface-breaking crack in concrete (b).
It is also observed that the presence of a surface-breaking crack decreases the magnitude of γ in high-frequency ranges: the useful frequency range becomes narrower as the depth of a crack increases from 0 to 50 mm (see Fig. 7b). However, it is not necessarily attributed to the coupling performance of the surface-mount sensor because the surface-breaking crack does not affect the surface-mount source and accelerometers. Instead, this phenomenon can be explained by the fact that the high-frequency components of surface waves are reflected back to the backward scattering field: consequently, the presence of a surface-breaking crack can significantly decrease the energy of transmitted surface waves in a higher frequency range.
Consistency of the Measured Surface Wave Parameters (Velocity and Transmission)
The consistency of measured results is of great interest when exploring the performance of surface-mount sensors. Ten repeated surface wave measurements were conducted at each test step using the same test setup and data acquisition system, in which surface-mount sensors located at A and D were alternatively used for generating incident waves in concrete. At each test step, the velocity and transmission coefficient of surface waves were determined by using Eqs. 1 and 2, respectively. In this study, the coefficient of variation (COV, the standard deviation divided by the mean value of a set of samples) was used as a means of consistency for the resulting surface wave velocity and transmission coefficients.
Figure 8a shows COVs of the two sets of surface wave transmission coefficients (TrPZT and TrSB) measured in the crack-free region of specimen 1. The COVs of TrPZT and TrSB remain low and flat, with values of 1.24 ± 0.39 % (µ ± σ) and 2.29 ± 0.65 % (µ ± σ) in a useful frequency range for each method (i.e., 0–100 kHz for TrPZT and 10 kHz to 30 kHz for TrSB), where µ and σ are the mean value and the standard deviation of COV, respectively. Similarly, the COVs of the phase velocity of surface waves (CR,PZT and CR,SB) are shown in Fig. 8b. The COVs of C R,PZT and C R,SB are 0.04 ± 0.023 % (µ ± σ) and 0.3 ± 0.15 %, respectively, in the useful frequency range of each method. Therefore, Fig. 8 illustrates that the surface-mount sensors produce equivalent or improved consistency of surface wave transmission and velocity measurements compared to the measurements using a manual impact source.
The coefficient of variation of the surface wave transmission and velocity.
Furthermore, it is observed that the presence of a surface-breaking crack may affect the COV of both the TrPZT and CRPZT (Fig. 9). For specimen 1, the COVs of TrPZT and C RPZT gradually increase up to 5 and 4 %, compared to reference values measured on the crack-free region where crack depth increases from 0 to 50 mm. For test specimen 2, the COVs of TrPZT and C R,PZT at 20 kHz in the crack-free surface are 1.2 and 0.01 %, respectively. However, onset of a surface-breaking crack in the middle of the concrete (a depth of about 150 mm) significantly increases the COVs of TrPZT and C R,PZT to about 10 and 3 %, respectively. It appears that higher variability in cracked concrete is due to a combination of two reasons: (i) energy loss of transmitted surface waves due to a surface-breaking crack, and (ii) scattering of the surface wave at the tip of the crack. However, as will be demonstrated in the next section, the COV levels of TrPZT and C R,PZT are still acceptable compared to the sensitivity of each parameter to the presence and severity of a surface-breaking crack Fig. 10.
The coefficient of variation (COV) of the surface wave transmission TrPZT and velocity CRPZT: a, b COV of TrPZT measured in concrete specimens 1 and 2, respectively, b COV of CRPZT measured in concrete specimens 1 and 2, respectively.
Sensitivity of the Measured Surface Wave Parameters to the Depth of a Surface-Breaking Crack
Figure 10 shows the relationship between the normalized transmission coefficient of surface waves Tr PZT,n and the normalized crack depth, h/λ. The results in Fig. 10 were obtained from the surface wave measurements across five surface-breaking cracks with depths of 10, 20, 30, 40, and 50 mm, respectively. Shown in Fig. 10 are only twelve transmission coefficient values for each crack depth in a useful frequency range (i.e., from 20 kHz to 80 kHz with intervals of 5 kHz). Therefore, 60 dots are shown as solid circles in Fig. 10. The approximate expression that describes the relationship between Tr PZT,n and h/λ is established by a non-linear regression of the experimental data as follows, and shown as a dash line in Fig. 10.
$$ tr_{n} = \,\,\,0.1515\,(h/\lambda )^{ - 0.7152} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,0.1 \le h/\lambda \le 1.4 $$
Normalized transmission coefficient Tr PZT,n versus normalized crack depth h/λ.
In comparison, a theoretical model obtained from a series of numerical simulations (FEM) is shown as a solid line in the same figure.
In a surface wave transmission test, many transmission values can be obtained within a frequency range; thus, multiple redundant estimates of crack depth may be calculated from a single measurement. In this study, the depth of a surface-breaking crack was determined by using the least square method. The optimum depth result was determined to minimize the sum of square residuals of the transmission function (SSR),
$$ SSR = \sum\limits_{i = 1}^{N} {\left( {\frac{{tr_{n} (f_{i} ,h/\lambda_{i} ) - tr_{n}^{\prime} (f_{i} )}}{{tr_{n} (f_{i} ,h/\lambda_{i} )}}} \right)^{2} } $$
where tr n is the transmission ratio in the proposed calibration curve in Eq. (4), Tr n, is the measured transmission ratio calculated using Eq. (1), i is an index of input values, and f i and λ i are the frequency and wavelength with the index i. As a result, the crack depths estimated for the notch-type cracks (using the surface wave transmission measurement h tr) were 8, 18, 26, 42 and 48 mm, respectively. The estimated values are about 80–90 % compared to the as-built crack depths. Therefore, the proposed model can be effective for evaluating the depth of a surface-breaking crack in concrete.
Effect of Crack Depth on Surface Wave Velocity Measurement
Figure 11 shows the variation in surface wave velocity at 20 kHz with increasing crack depths obtained from numerical simulation and experiment in this study. It was observed that CR obtained from numerical simulation remains stable around the reference velocity of 2250 m/s until crack depth is less than about 120 mm. For the experimental data, the surface wave velocity at 20 kHz was 2208 m/s in the crack free-region. Increasing the crack depth up to 50 mm does not affect the surface wave velocity at 20 kHz. This observation is consistent with observations by previous researchers (Masserey and Mazza 2007) that the surface wave velocity is only sensitive to a crack deeper than about 80 % of the wavelength of surface waves. Compared to the surface wave transmission coefficient, the phase velocity is less sensitive to the presence of cracks. However, it is reasonable to say that some degradation of the surface wave velocity (about 10 %) across a surface-breaking crack is evidence of a deep crack, comparable to the wavelength of surface waves.
Phase velocity of surface waves C R versus crack depth h.
Application to Monitoring a Concrete Beam under Various Loadings
Described in this section is the application of the surface-mount sensor to concrete subjected to various loadings, which are common in actual concrete structures. Surface wave transmission and velocity were monitored in a stepwise manner in the various test steps described in Table 1. Figure 12a, b are plots illustrating the variations in the normalized transmission coefficients and phase velocity at a frequency of 20 kHz, respectively, in different test steps.
Table 1 Loading history in test stages 1, 2, and 3 for specimen 2
Variation of transmission coefficient and phase velocity of surface waves at 20 kHz with stress on top extreme layer of concrete: a normalized transmission coefficient versus stress, and b phase velocity versus stress.
Before cracking, there was only a slight change in Tr n and Cr R with increasing compressive loadings up to 106.75 kN (24 kips). Furthermore, with increasing tensile stress up to 3 MPa (420 ksi), which corresponds to a cracking moment of the concrete specimen, both Trn remain almost constant (±2 % of the reference Trn) until the onset of the first surface-breaking crack on the top surface of specimen 2. The crack depth measured on the side surfaces of the concrete specimen was about 120 mm, which shows close agreement with the depth measured from a core sample taken at the surface after testing (see Fig. 13). In addition, C R tends to decrease slowly with increasing compressive and bending loadings, and exhibit small variations (see Fig. 12b). Once a crack appears, Tr n and C R suddenly decrease to about 10 and 85–90 % of the reference values, respectively. It appears that Tr n is much more sensitive to the presence of a surface-breaking crack in concrete than C R . In summary, monitoring Tr n and C R can be effective for identifying the onset of a surface-breaking crack in concrete, and the approximate depth can be estimated by using the SWT method. In addition, this process can be automated by using surface-mount sensors.
Core samples extracted after completing tests from the test specimen 2: a concrete specimen 2 after testing, b location of core extraction, and c core sample.
However, the effect of external loadings may pose difficulties in the interpretation of Tr n and C R . As shown in Fig. 12, Tr n and C R increase with an increase in the application of external compression P3. At the last loading step of P3, Tr n and C R were recovered to 90 and 95 %, respectively, of the values before cracking. Some portions of the incident surface waves (i.e., crack interfacial waves) are transmitted through the interface of an actual crack, which commonly has a partially closed interface. Increasing the compressive force gradually closes the concrete crack, increasing the interfacial stiffness of the crack. It was observed that both Tr n and C R are enhanced, owing to the crack interfacial waves, which may lead to substantial errors in predicting the depth of a surface-breaking crack in actual concrete structures.
One interesting finding is related to the potential for combining the results from the SWT and SASW as a more reliable crack depth estimation approach for testing actual structures. As observed in the theoretical results, the surface wave velocity is only sensitive to a crack deeper than about 80 % of the wavelength of surface waves. In addition, it was observed that the surface wave velocity is less sensitive to the interfacial stiffness of a surface-breaking crack than the surface wave transmission. Therefore, it is reasonable to say that some degradation of the surface wave velocity (about 10 %) across a surface-breaking crack is evidence of a deep crack, compared to the wavelength of surface waves.
In this paper, experimental results are presented to investigate the applicability of piezoelectric sensors as a consistent impact source for automated surface wave measurements in concrete structures. The conclusions are summarized as follows,
The piezoelectric surface-mount sensors produce excellent signal coherence γ ≥ 0.999 in a wideband frequency range from 0 to 120 kHz. In contrast, signals generated by manual impacts have good signal consistency in a narrower frequency range of 10–30 kHz, and are dependent on the diameter of the steel ball. It was observed that the surface-mount sensors have consistent coupling under various stress states and damage levels of concrete.
Experimental variability in the transmission and velocity measurements measured using the piezoelectric surface-mount sensors are equivalent or less than that from manual impacts. The COVs of the TrPZT100 and CR,PZT100 are 1.24 ± 0.39 % (µ ± σ), and 0.04 ± 0.023 %, respectively, in a useful frequency range of 0–120 kHz. In contrast, the COVs of the TrSB and C R,SB are 2.29 ± 0.65 % (µ ± σ), and 0.3 ± 0.15 %, respectively, in a useful frequency range of 10 kHz to 30 kHz.
The proposed model for the surface wave transmission coefficient is demonstrated to be effective for evaluating the depth of a surface-breaking crack in concrete. However, special care is needed to apply the surface wave transmission method to a partially closed crack in actual concrete structure because of interference of the crack interfacial waves with transmitted surface waves.
Results from experiments and numerical simulations show that the surface wave velocity is only sensitive to cracks deeper than about 80 % of the wavelength of surface waves. However, it is reasonable to say that some degradation of the surface wave velocity (about 10 %) across a surface-breaking crack is evidence of a deep crack comparable to the wavelength of surface waves. Therefore, a fusion of the results from the SWT and SASW can be used as a more reliable crack depth estimation approach for testing actual structures.
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This research was supported by a grant (15DRP-B066470-03) from Infrastructure and transportation technology promotion research Program funded by Ministry of Land, Infrastructure and Transport of Korean government.
Department of Architectural Engineering, Dong-A University, Busan, 604-714, Korea
Seong-Hoon Kee
Department of Civil, Environmental and Construction Engineering, University of Central Florida, Orlando, FL, 32816, USA
Boohyun Nam
Correspondence to Seong-Hoon Kee.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Kee, SH., Nam, B. Automated Surface Wave Measurements for Evaluating the Depth of Surface-Breaking Cracks in Concrete. International Journal of Concrete Structures and Materials 9, 307–321 (2015). https://doi.org/10.1007/s40069-015-0110-y
DOI: https://doi.org/10.1007/s40069-015-0110-y
surface waves
surface wave transmission
surface-breaking crack
non-destructive evaluation


Sit-at-home: Igbo group blames government's apathy for compliance, insecurity in South East
By Bridget Chiedu Onochie, Abuja Bureau Chief
17 September 2021 | 3:26 am
A South-East socio-cultural organisation, known as Igbonine, has blamed the continuous sit-at-home order compliance in the region on the failure of politicians to address the issue of insecurity.
Ndigbo
• Says miscreants, not IPOB, responsible for halt in activities
President-General, Igbonine Socio-Cultural Organisation, High Chief Emeka Okonkwo, who spoke at an event yesterday in Abuja to discuss the lingering grinding of business activities across states in the region, hinted that sitting at home is not synonymous with the Igbo people and not their culture.
The group, therefore, said it was constrained to call the attention of Igbo brothers and sisters supporting some misguided youths involved in the damage to the psyche, lives and welfare of the people living in the South-East geo-political region, to the negative impacts of their actions on Ndigbo.
"Apart from loss of lives, we are losing businesses and income on a daily basis from the apparently unending sit-at-home orders.
"We cannot continue this voyage of self-destruction and cutting our nose to spite our face. The state of affairs in the South-East is capable of completely destroying the enterprise of the Igbo man and revising the gains of the Akuluono philosophy," the group said.
While charging state governors in the region to show seriousness by taking charge of the situation, the group also called on religious leaders, Ohanaeze Ndigbo and other institutions, to consult among themselves on how to end the actions of self-immolation in Igboland.
Okonkwo, who debunked the insinuation that the sit-at-home action was in obedience to the directive issued by Indigenous People of Biafra (IPOB), said citizens were rather confined to their homes by distrust for their leaders.
According to him, people preferred to stay at home for fear of being killed or kidnapped due to failure of the federal and states' security architecture.
Okonkwo, who insisted that it was the handiwork of miscreants disguising as IPOB members, called for meticulous investigation into the death of Rev. Emeka Mezenu, a priest in charge of St. Andrew's Anglican Church that was stabbed to death in Imo State.
Mezenu was speculated to have been killed for defiling the forced stay-at-home order as well as allow students to sit for their West African Senior Secondary School Certificate Examination (WASSSCE) at his parish.
The group, which remained skeptical about some of the happenings in the region, stressed that some miscreants had taken advantage of the lacuna created by IPOB protest to perpetuate evil in the region.
Emeka Okonkwo
Igbonine
IPOB
Ohanaeze Ndigbo
You don't have such powers, Irabor faults Matawalle on arms bearing
Again, the thorny issue of federalism was put to test after Sunday's call by the governor of Zamfara State, Bello Matawalle, urging residents to bear arms to defend themselves against marauding bandits and terrorists...
Again, IPOB declares sit-at-home today in South East
The Indigenous People of Biafra (IPOB) has declared another sit-at-home in the South East today. Its spokesman, Emma Powerful, said the decision is due to the appearance of their leader
One year after, Imo police claim arrest of Ahmed Gulak's 'killer'
Operatives of Imo State Police Command have arrested one Anosike Chimobi, 38, from Umuedo, Ahiazu Mbaise Local Council of the state for his alleged involvement in the murder of Alhaji Ahmed Gulak.
Nnamdi Kanu: Court dismisses IPOB leader's bail application
The Federal High Court in Abuja on Tuesday dismissed the application for bail by the detained leader of the proscribed Indigenous People of Biafra (IPOB), Nnamdi Kanu. The judge, Justice Binta Nyako, in her ruling said the suit was a gross abuse of the court process and an attempt to continue to litigate on issues…
Why court rejected Kanu's fresh bail application
The Federal High Court, Abuja, has dismissed a fresh bail application filed by the detained leader of the Indigenous People of Biafra (IPOB), Nnamdi Kanu, for constituting an abuse of court process.
IPOB's sit-at-home order paralyses Enugu, Imo
Socio-economic activities were grounded for the second time in Enugu State, yesterday, following a sit-at-home order issued by the Indigenous People of Biafra (IPOB).


News - July 2012 RSS Feed
Now we can get on with the fight!
by Ross Douthat
If you want to fine Catholic hospitals for following Catholic teaching, or prevent Jewish parents from circumcising their sons, or ban Chick-fil-A in Boston, then don't tell religious people that you respect our freedoms. Say what you really think: that the exercise of our religion threatens all that's good and decent, and that you're going to use the levers of power to bend us to your will. There, didn't that feel better? Now we can get on with the fight.
Are you interested in Becoming Catholic?
Do you know someone who Is?
Read more about the process and how to get started.
Religious Liberty and Its Contemporary Enemies
by George Weigel
"... religious liberty is being subjected to a slow but steady wasting disease. Recognizing that disease is essential; so is an accurate diagnosis of its causes." Read George Weigel here.
Frequently Asked Question on Religious Liberty
What do we mean by religious liberty?
What did our early American leaders say about religious freedom?Who have been heroes of religious liberty in the church?
Benedictus Moments: Daily Reflections
The Bully Bishops?
"…If we duct tape the role of religions and the churches (in society) that's going to lead to a huge deficit, a huge void. They want to fill it up with a new religion called secularism which would be as doctrinaire and as infallible as they believe the church is. "
Lincoln's Declaration And Ours
by Ralph Lerner
All honor to Jefferson — to the man who, in the concrete pressure of a struggle for national independence by a single people, had the coolness, forecast, and capacity to introduce into a merely revolutionary document, an abstract truth, applicable to all men and all times, and so to embalm it there, that to-day, and in all coming days, it shall be a rebuke and a stumbling-block to the very harbingers of re-appearing tyranny and oppression. -Abraham Lincoln
The End Of America?
A frog in a pan of lukewarm water will not notice the heat being increased slowly before it is boiled to death. The heat from increasing government regulations is beginning to boil our religious freedom away.
My Hope Is That Catholics Will Be Able To Articulate Their Faith
My hope is that every Catholic will be able to articulate their faith in convincing and intelligent ways, and show by their living example the compelling truth of the Gospel and church teaching.


London cleantech IPO promises a bright future
Intelligent Energy, which uses proton exchange membrane (PEM) technology, went public last month and raised $94.1 million in London. The successful outing offered two positive outcomes for the UK cleantech scene: firstly, that a UK company has become the most highly valued publicly held fuel cell company in the world, and secondly that it demonstrated the strength of London corporate finance by having the IPO on the London Stock Exchange.
Intelligent Energy was valued at $811 million, in what was London's biggest pure technology floatation in five years, fueling hopes that the market for cleantech listings is gathering fresh momentum. The Midlands-based firm was especially proud to be listing in London, having been had its origins at Loughborough University. The company has emerged as one of the leading global players in the development of zero-emission hydrogen fuel cell technology and boasts a portfolio of products, including fuel cells for use in cars and bikes, as well as stationary generators and back-up power supply units. The firm has raised more than $150 million from investors including the Meditor European Master Fund.
However, though officially Intelligent Energy is the world's most valuable fuel cell firm, there is an argument that the US-based Bloom Energy is a more blue chip enterprise. Bloom Energy has raised more than $1 billion in venture capital over the course of a decade from investors including GSV Capital, Apex Venture Partners, DAG Ventures and Goldman Sachs. The company builds fuel cells of the solid-oxide variety, with natural gas as the fuel, and boasts a strong line of customers, including Adobe, FedEx, Staples, Google, Coca-Cola, and Wal-Mart.
Nonetheless, Intelligent Energy is set to be the spearhead of the UK's cleantech drive. The IPO comes as welcome news to a UK market that has been a global standout in FinTech, e-commerce and gaming, but relatively weak in terms of cleantech initiatives and support compared to other European markets such as Finland. London corporate finance still needs some convincing that returns can justify initial investments in the cleantech segment. For fuel cells specifically, there are some challenges. They can be distributed, and natural gas is currently cheap, there is the downside of volatile gas prices and the at times less-than-green processes used to extract natural gas. Even after incentives, the fuel cell can be expensive compared to the traditional grid or a diesel gen-set.
It is difficult to say whether the strong IPO was a sign that investors are beginning to believe in cleantech or if it is just part of the current boom in demand for tech stock. After all, Intelligent Energy's revenue fell to $35.6 million in 2013 with losses of $36 million, so the company (like many in cleantech) still needs to prove its profit-making capacity.


ATS Standings
Sunday MLB Betting Odds, Preview, Prediction for Diamondbacks vs. Mariners: Back Underdog Arizona to Triumph (Sept. 12)
Dustin Bradford/Getty Images. Pictured: Arizona Diamondbacks starting pitcher Tyler Gibert.
Kenny Ducey
The Arizona Diamondbacks square off against the Seattle Mariners on Sunday's Major League Baseball card.
Tyler Gilbert, who hopes to find some of that old magic from his first career start that was a no-hitter, takes the hill for the Diamondbacks.
Kenny Ducey takes a deep look at this matchup below and details why he thinks Arizona is a live underdog.
Diamondbacks vs. Mariners Odds
Diamondbacks Odds +155
Mariners Odds -190
Over/Under 8 (-110 / -110)
Time 4:10 p.m. ET
TV MLB.TV
Odds via BetMGM. Get up-to-the-minute MLB odds here.
After a narrow escape Friday, the Seattle Mariners saw their playoff hopes take yet another hit Saturday with a third loss in five games.
Seattle is very much still in the race, just two games back of the second wild-card spot, but with so many teams in striking distance of the last spot, every loss hurts at this point in the season.
With that, is the best play on the team with more to play for or does this matchup give Arizona a puncher's chance? Let's take a look at the numbers below and see what could be on deck.
Arizona Had Been Struggling Mightily Prior to Win
Prior to shellacking the Mariners in a 7-3 beatdown on Saturday, the Diamondbacks had lost 11 of 12 games. While it appeared all hope was lost of even getting to 50 wins, the offense begun coming alive late in the week.
Arizona put up five runs in a loss to Texas and nearly beat Seattle in the opener on Friday in a 5-4 defeat. While on the whole the club owns the third-worst wRC+ in baseball over the last two weeks and hit .192 in the last week, we've seen a few nights that give you just the slightest glimmer of hope.
Over the last week, the Diamondbacks at least rank 15th in contact rate and have an above-average swinging strike rate. They're walking 7.1% of the time and hardly making any quality contact in that span, but at least they're getting the bat on the ball now.
On the hill we have the no-no kid in Tyler Gilbert. Since memorably firing a no-hitter in his first career start, Gilbert has been effective in the Arizona rotation and comes in off a solid start against these same Mariners. He went seven innings, allowing just three runs on four hits and two walks. Needles to say, he should come in brimming with confidence with solid numbers and peripherals.
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Seattle Continues Desperate Chase for Wild Card
With two teams tied for the second wild-card spot and Oakland knotted up with Seattle two games behind those clubs, it's anyone's guess who will sneak into the postseason on the American League side.
In a tight race, every win is of the highest importance, and any game against a weak opponent is a gift at this point. The Mariners are going to need to handle their business against the Diamondbacks and need to take care of the Royals next weekend, because 10 of their remaining 20 games will come against the Red Sox and Athletics.
A major hold-up here will be seeing a left-hander on the hill. The Mariners are way down in 25th this year against southpaws with a 93 wRC+, and have struck out in an alarming 25.4% of those plate appearances. Just two days ago this team was stymied by Madison Bumgarner, which is never a good sign.
Speaking of lefties, the Mariners will start their All-Star southpaw in Yusei Kikuchi. The 30-year-old went from an unlucky pitcher in 2020 to a lucky one in 2021, pitching to a 3.37 xERA last year and posting a 5.15 xERA. The biggest difference would be in the quality contact department, where he's given up more than 10% more hard-hit balls. Other than that, he's been rather stagnant.
Those peripherals have turned Kikuchi's season on its head, leading to a 6.04 ERA in 10 starts since the All-Star break. It's not going well.
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Diamondbacks-Mariners Pick
Say what you want about the Diamondbacks, but they grade out as an average offense against left-handers with a 98 wRC+, and peaked in the top three in that category earlier this season. They might not be making much quality contact, but Arizona should still be able to make a dent against Kikuchi, who has been downright terrible in the last two months.
With Gilbert on the hill in a great matchup with a lefty-averse team, I think the value here lies squarely with the underdog, even if it has 46 wins this year.
Pick: Diamondbacks ML (+155)
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Criminals have a head start in race for fairness
Proceeds from the run will be used to assist the victims of crime in St. Clair County, helping them with incidental costs while they navigate the criminal justice system.
Criminals have a head start in race for fairness Proceeds from the run will be used to assist the victims of crime in St. Clair County, helping them with incidental costs while they navigate the criminal justice system. Check out this story on thetimesherald.com: http://bwne.ws/1RnakLR
Published 2:07 p.m. ET Oct. 3, 2015
The 5K run or 2-mile walk will start at 9 a.m. Nov. 15 at Vantage Point in Port Huron.(Photo: lzf / Getty Images/iStockphoto)
Mara McCalmon and Sheryl Eckert are organizing a fundraising run scheduled for Nov. 15 in Port Huron.
Proceeds from the run will be used to assist the victims of crime in St. Clair County, helping them with incidental costs while they navigate the criminal justice system. Expenditures can be as simple as a warm cup of coffee or transportation to court hearings.
The 5K run or 2-mile walk will start at 9 a.m. Nov. 15 at Vantage Point in Port Huron. Registration will begin at 8 a.m. Registration costs $25 before Oct. 19 and $30 after. Sign up online at http://bwne.ws/1KWgVZb.
The race also hopes to raise awareness of the travails victims face in the justice system. The public's attention focuses too often on the accused, who by every measure are volunteer actors in the drama and strife they've created themselves.
Their unwilling, unwitting victims, meanwhile, are left to pick up the pieces of their lives themselves without the vast mechanism of justice — lawyers, judges, prosecutors, juries and more — looking out for their every interest and defending their every right to a fair trial and just punishment.
What's just and fair for the victims? What's fair and just for Mara McCalmon, who was stabbed dozens of times by murderers who invaded her home in the dark of night? What's fair and just for Paul Skinner, her husband, who was stabbed to death in a vile plot hatched by Tia Skinner and carried out by her evil friends?
The system keeps giving Tia Skinner another chance. Will Paul Skinner get another chance?
Activists want Michigan to adopt a law that would compensate those wrongfully convicted of crimes. They want the state to pay the wrongfully convicted $60,000 for each year they lose to incarceration.
How much will Paul Skinner get for his lost years?
We believe proposed legislation is woefully flawed and should not be even be considered unless provisions are included to deny compensation to those who contribute to their own convictions. Moreover, we don't believe such compensation is appropriate or fair to Michigan taxpayers.
If anyone deserves compensation in our justice system, it is the people swept into it by the criminal actions of others. Since that bill isn't pending in the Legislature, come run with us Nov. 15.
Read or Share this story: http://bwne.ws/1RnakLR
Thinking about investing? Start with what lasts
Cain: School boards are critical to a district's success
Martin Luther King Jr. and combating mental health stigma
Meet the lesser black-backed gull, one of several winter gull species found in our area
Johnson: You can achieve your New Year's resolutions
Ketchum: Could major religions survive with the notion that Earth is not the only visited planet?


[Jim Lindgren, August 24, 2005 at 1:48am] Trackbacks
Is Justice Breyer channeling John Hart Ely?--
The Wall Street Journal has a teaser story on Justice Stephen Breyer's new 161-page book to be released in a few weeks: "Active Liberty: Interpreting Our Democratic Constitution." I didn't know that Breyer was a disciple of John Hart Ely (and he may not be), but the interpretive theory described in the WSJ's account of Breyer's book sounds a lot like the main argument in Ely's Democracy & Distrust (1980).
Here is the WSJ on Breyer's book:
By contrast [with Justice Scalia's book on interpretation], Justice Breyer's "Active Liberty" contends that judges can undercut the democratic system the Constitution's Framers sought to build if they adhere too literally to legal text and disregard the "real world" consequences of the decisions they render.
So whereas Justice Scalia has voted to strike down campaign finance laws, arguing that they restrict free speech, Justice Breyer espouses a much different theory. He has voted to uphold such laws, arguing that they actually support constitutional values — such as the marketplace of free ideas — by limiting the ability of monied factions to overwhelm other points of view. . . .
The 161-page book, set for publication Sept. 13, aims to popularize ideas Justice Breyer has already advanced in academic lectures and articles. A judge's task, he says, is construing the Constitution in a way "that helps a community of individuals democratically find practical solutions to important contemporary social problems." He calls that freedom to participate in government "active liberty," a complement to passive liberties that protect the individual from interference by the government. . . .
In his book, Justice Breyer contends that originalists can be just as subjective as other judges, reaching the outcome they favor by emphasizing some historical elements and ignoring others. Such a literal reading, he writes, can be "inconsistent with the most fundamental original intention of the Framers themselves."
On amazon.com, the book description (which is usually put out by the publisher) includes this: "Justice Breyer states that courts should take greater account of the Constitution's democratic nature when they interpret constitutional and statutory texts."
Here is a description of Ely's argument taken from an online review of Ely's 1980 Democracy & Distrust:
Ely's theory of judicial review focuses on allowing everyone equal input in the representative part of the government and free participation in the political process. If the government is a fair representation of the beliefs of the nation, the Supreme Court does not need to make value judgments with one exception, which is the other half of the theory. The Court must not allow the majority to take advantage of the minority. Ely admits that both of these require certain value judgments by the Court; however, the values of fair representation and protecting minorities were invoked by the Founding Fathers. For example, James Madison wrote in The Fe[de]ralist no. 51, "It is of great importance in a republic not only to guard the society against the oppression of its rulers, but to guard one part of the society against the injustice of the other part. If a majority be united by a common interest, the rights of the minority will be insecure."
I have ordered my copy of Breyer's new book. I can't wait to see how Breyer's democracy-enhancing interpretative strategy differs from Ely's democracy-enhancing interpretative strategy. I hope that in his book Breyer details how his theory follows or differs from Ely's, and that he deals with the criticisms that have been made of Ely's thesis.
Also, to the extent that Ely actually applies his democracy-enhancing approach in a very different way from Breyer's, I wonder about the amount of judicial discretion that might be inherent in democracy-enhancing approaches (would this be more or less than other interpretive approaches?). For example, Ely was hostile to extensive administrative rulemaking because bureaucrats were not elected, and Ely (though favoring abortion) was highly critical of the original decision in Roe v. Wade, but not of its progeny because of stare decisis (from Wikipedia), :
Ely wrote several influential law review articles, including a devastating critique of the Supreme Court's decision in Roe v. Wade in an article entitled "The Wages of Crying Wolf," published in the Yale Law Review, wherein he argued that the Court's decision protecting abortion rights was wrong "because it is not constitutional law and gives almost no sense of an obligation to try to be."
Ely's most notable work, however, was his 1980 book Democracy and Distrust, which ranks as one of the most influential works about Constitutional law ever written. In it, he argues against "interpretivism," of which Hugo Black was an exponent, and "originalism," advanced by Justices such as Antonin Scalia, by contending that "strict construction" fails to do justice to the open texture of many of the Constitution's provisions; at the same time, though, he maintains that the notion that judges may infer broad moral rights and values from the Constitution is radically undemocratic. Instead, Ely argued that the Supreme Court should interpret the Constitution so as to reinforce democratic processes and popular self-government, by ensuring equal representation in the political process on procedural grounds . . . .
Interestingly, Ely was born the same year as Breyer and they were in the same cohort as Harvard professors from 1973 to 1980. Ely's book came out 10 months before Breyer left Harvard to join the First Circuit in December 1980, so it would have been by far the leading book on judicial interpretation when Breyer first became a judge. Ely died of cancer in 2003.


Red Dead Redemption Review
Tags: #recommended #red-dead #red-dead-redemption #sandbox #third-person-shooter #western #wild-west
Companies: #rockstar #take-two
1 - Red Dead Redemption Review 2 - Red Dead Redemption Conclusions
Red Dead Redemption Score
Nearly every action you take in Red Dead Redemption will result in a change to one of three meters - Honour, Fame and Bounty - and these in turn will govern most of your experience with the game.
All three meters are pretty self-explanatory, but provide some pretty interesting differences over Rockstar's previous games. Honour gauges your internal view on your actions, while Fame monitors how the populace see you – killing lawmen, for example, will make both Fame and Honour take a dive, while slaughtering the random groups of bandits that assault some towns will increase both.
The plentiful minigames that fill the game, the best of which is Five Finger Fillet, give you a chance to increase Fame too, which is handy for giving the townsfolk a good impression of yourself before you visit the shop.
Bounties meanwhile are a far more interesting mechanic and one of our favourite things about Red Dead Redemption (aside from having pistol duels) is that it punishes criminal behaviour far more than Rockstar's previous games do. It's not as simple as just running away from the police or giving your horse a new paint-job.
Breaking the line of sight helps you escape Marshalls
Now when you commit a crime the game doesn't automatically summon the police - not unless a citizen is specifically able to raise the alarm – so you can kill people in the outback with no worries, for example. You can even watch people run to raise an alarm and, provided you take them all out, you'll get away with only a decrease to Honour and Fame. If the Sheriffs do find out though then they'll come after you hard and you'll have to kill them or escape their sizeable search radius.
Even if you do dodge the law once though, the hunt is still on and it's here that Bounty comes in, with a figure in top of the screen telling you how much you're wanted for, dead or alive. If it goes high enough then Bounty Hunters will start to show up, but it also means that more police will be after you next time you commit a crime. You can visit a train station to pay off the bounty and reset the situation, but if you don't then you'll find out difficult it really is to commit to the life of a fugitive.
Take our advice though; go and find out, because it's things like that which Red Dead Redemption does really well, plunging you into the role of a frontiersman even when you're deliberately veering away from the main plot and embracing your anarchic side. The gameplay options for those times when you want to mess around have been reined in now that there aren't sports cars to race around in and skyscrapers to jump off of, but somehow the act of hunting for cougars and bears among the tumbleweeds has replaced it brilliantly.
Marsden has got plans for that chicken
Still, Red Dead Redemption isn't a perfect game and while it manages to brilliantly summon up a sense of loneliness and violence that's so closely attached to classic Westerns, there are some obvious weakpoints. The controls are all over the place, for example, with hammering X to speed up being a particularly annoying addition. Getting used to controlling your horse and learning to shoot accurate from horseback without relying on your bullet-time 'Dead Eye' mode or the heavy-handed auto-aim can be a pain in the arse.
To boil things down to their cynical minimums again, it's hard to get away from how dangerously familiar Red Dead Redemption is to Rockstar's previous games too – the déjà vu sets in hard sometimes and you're left wondering if Red Dead Redemption really represents anything truly new over the likes of the Grand Theft Auto games.
Many of the missions are repetitive or samey too and what could have been a fairly simple, direct story is obviously fluffed out beyond what it needs to be. Once that suspicion settles in then it's easy to question if the game isn't built out of distractions – not that the minigames aren't fun and all that.
Still, no matter how annoying it is when you steer your horse off a cliff for the umpteenth time or how superfluous some of the content is, there's no getting away from the simple fact that Red Dead Redemption offers the single biggest, best and most stunningly complete emulation of Wild West life yet committed to digital format. That alone makes it worth picking up, even if graphically, it can look pretty ropey on the PlayStation 3.
Red Dead Redemption - Recommended
Score Guide
Rockstar staggers RDR2 multiplayer launch
Ultimate Edition owners first, obviously.
Rockstar delays Red Dead Redemption 2 to October 2018
Second shift for spit 'n' polish.
Rockstar delays Red Dead Redemption 2 to 2018
Needs more time for spit 'n' polish.


propagate serbian spruce
Around 5,000 trees such as blue spruce, Serbian spruce, Nordmann fir and coastal fir stand on the site. Choose the 'Nana' cultivar if you would prefer a dwarf version. We have combined these two powerful search tools into a single Find a Plant service searching over 250,000 plant records. My meeting with Vladan Ivetic, Forestry Professor at the University of Belgrade in Serbia to learn about the Serbian Spruce. The needles are flat, relatively short and a bit spiky – though not as sharp as the Norway Spruce. The first thing you need to do is to buy the seeds or harvest them at the appropriate time. £9.75. It can be planted in a group, but it will need room to grow. Virtually all of the features of the old searches are still available and in addition we have added several new features to create a more comprehensive and user friendly search experience. This tree has been awarded the Award of Garden Merit from the Royal Horticultural Society. It was originally discovered near the village of Zaovine (Serbia) on the Tara Mountain in 1875, and named by the Serbian botanist Josif Pančić; the specific epithet omorika is simply the Serbian word for "Serbian spruce". It grows at a slow rate, and under ideal conditions can be expected to live for 80 years or more. It is clothed in a lush foliage of gold, green and blue needles, which creates a unique tri-color effect. Other propagation methods for spruce include rooting cuttings. Generally disease free. Serbian spruce grow in pure stands in Serbia as they are a pioneer species. How to propagate a spruce tree from seeds? Serbian Spruce are fast-growing, do well in full sun, and reach a height of up to 60 feet with a spread of 20 feet or more at the base. Serbian spruce as the name suggests originates from Serbia and is a large evergreen conifer with an alpine appearance. The fruit produced are ovate cones that are up to 2" long. per year (15-30 cm), this elegant Serbian Spruce is magnificent, either as a specimen or in a grouping. Search by plant name, key attributes or both to find plant details and a list of AGM plants have been through a rigorous trial and assessment programme. Spruce tree propagation refers to the different ways that spruce trees reproduce. Over time the tree will reach a final height of 40 to 60 feet tall and a width of 15 to 25 feet. The conifer grows best in full or half sun. RHS Garden Hyde Hall Spring and Orchid Show, Free entry to RHS members at selected Seed source: Slovenia. They prefer richer soils, but can do well in sandier soils if watered two to three times per week. Picea omorika, common name Serbian spruce , is a species of coniferous tree endemic to the Drina River valley in western Serbia, and eastern Bosnia and Herzegovina, with a total range of only about 60 ha, at 800–1,600 m (2,625–5,249 ft) altitude. It does best with full sun or partial shade, meaning a minimum of four hours of direct, unfiltered sunlight each day. Picea are evergreen trees with rigid, needle-like leaves arranged singly all round the shoots, and narrow, leathery-scaled cones borne near the ends of the shoots, Details The flattened bright green needles have silvery undersides. Water may be the most important factor to propagating weeping Norway spruce cuttings. Picea omorika, Serbian Spruce or Bosnian Spruce. The 'Pendula' and 'Nana' cultivars have also received this honor. Bosnia, Serbia, All ratings refer to the UK growing conditions unless otherwise stated. Deep watering encourages roots to grow further into the ground resulting in a sturdier plant with more drought tolerance. A close relative of the Norway Spruce, the Serbian Spruce has dense branches and a lovely narrow shape so is ideally suited to smaller spaces. We aim to enrich everyone's life through plants, and make the UK a greener and more beautiful place. It is a slow to medium growing spruce, so it best used as a specimen tree. Those with sharp eyesight will also notice that spruce needles are attached to a branch by a tiny peg (pulvinus), while fir needles are attached directly to the stem with what appears to be some sort of suction cup. Difficult to grow as a young seedling, plants become very tough and hardy once established. Evergreen with sharp, pointed needles that have a … Picture of Botnist, Josif Pancie that discovered the Serbian Spruce in 1875. A small Serbian spruce planted in a container could be used as a live Christmas tree, then planted in the landscape after the season is over. Huge collection, amazing choice, 100+ million high quality, affordable RF and RM images. The trees have something of a two-tone appearance, with a darker green on the top of the needles and more of a silvery-blue-green below, making for a rather attractive look. It is not as "full" a tree when it grows taller ie the branches are further apart, so it's better under six foot. They grow very symmetrically and hold their soft pine needles well. They have many characteristics of the Norway Spruce. It thrives in a variety of soil types but tends to do best in acidic, well-drained loamy soils with relatively dry conditions. They start out purple, then mellow to a reddish-brown as they mature. Hardiness Zones and Optimal Growing Conditions, 40 Species of Pines From Around the World, 10 Species of Linden Trees for Your Landscape. Vanessa Richins Myers is a seasoned horticulturist, garden writer and educator with 10+ years of experience in the horticulture and gardening space. It has glossy dark green needles with slender streaks of white and distinctive purple cones. 100% guaranteed: If your seedling perishes, we are happy to provide a replacement small-sized seedling for just the cost of shipping/handling ($4.60) Seed-grown without poison or pesticides at our nursery on California's Redwood Coast Transplanting and care instructions included Trees can provide a natural barrier … That is why it is very popular as a Christmas tree! Suggested uses. Shelter from cold drying winds, Propagation Grow Serbian spruce in full sun and neutral to alkaline soil that is rich and friable but has good drainage. Find the perfect serbian spruce tree stock photo. Find the right place to plant the sapling. The Serbian Spruce is a delightful narrow crowned evergreen with a blue-green underside to each needle giving the whole tree a wonderful silvery appearance. If you would like a weeping version of the Serbian spruce, look for the 'Pendula', 'Berliner's Weeper' or 'Pendula Bruns' cultivars. 2.5-4 metres, Time to ultimate height How to propagate a spruce tree? It is a slower growing and more elegant tree compared to many other members of the spruce family. Plants grow best in full sun or partial shade on moist, well drained soils. W e will refund your money or resend the products for free. This spruce species can be planted in USDA Zones 4 to 7. Considered one of the finest landscape evergreens. Low Maintenance 20-50 years, Cultivation This evergreen spruce belongs to the pine family. The only pruning that is usually needed is to keep the tree free from dead, diseased or damaged branches. It is included in an evolving list of plants carefully researched and chosen by RHS experts. Available read more Out of stock. It has an important place in parks and large gardens because of its very attractive crown form and ability to grow on a wide range of soils, … Serbian spruce Tall and slender, with graceful upswept branches, the Serbian spruce is an elegant evergreen tree as a specimen in the landscape. Shelter from cold drying winds Propagation Propagate by seed or semi-hardwood cuttings Suggested planting locations and garden types Low Maintenance Architectural Serbian spruce, Family P. omorika is an evergreen conifer forming a graceful, slender tree of narrowly conical habit, with dark foliage, whitish beneath, in drooping sprays curving up at the tips, Plant range Grow in moist but well-drained, acid to slightly alkaline soil in full sun with shelter from cold, drying winds. Picea omorika. The hardy Bosnian Spruce is native to the Tara Mountains which are located in West Serbia. Since it is normally a large tree, Serbian spruce is usually used as an ornamental specimen in large... Hardiness Zones and Optimal Growing Conditions. Introducing "One Thing": A New Video Series. The Serbian Spruce, Picea omorika, (or Pančić in Serbian) used to grow in a wide area across Europe before the last Ice Age, which began 2.6 million years ago. Will tolerate alkaline soils. It does not like boggy conditions, preferring locations where it has "dry feet" most of the time, such as well-drained slopes. Join It's best to give them extra water during dry periods. Cultivation. Remember the tree could grow to be 60 feet tall. If you select any attributes with or without a plant name, you will see a much narrower selection of results taken only from the old RHS Plant Selector database. Higher than 12 metres, Ultimate spread Minimum temperature ranges (in degrees C) are shown in brackets, Aspect North-facing or West-facing or South-facing or East-facing, Ultimate height That said, it grows at a relatively slow rate of just 30 to 60 centimeters per year. Learn tips for creating your most beautiful (and bountiful) garden ever. Try an advanced search, RHS Registered Charity no. You also need to consider that the Serbian spruce tree needs lots of sun and moist soil. suppliers. It has been used in landscape design since 1880. Each needle is up to 1" long and features two white bands on the underside. If your unhappy or your plants fail to grow. All other spruces are smrča (смрча). Grow Guarantee. Since it is normally a large tree, Serbian spruce is usually used as an ornamental specimen in large gardens and landscapes. Our Botanical team are working hard to increase the number of plants with detailed information. The methods include growing spruce tree seeds and cuttings. 020 3176 5800 Over the years, it can grow to up to 25 metres! Add to cart. times, Need more criteria? This spruce species can be planted in USDA Zones 4 to 7. Picea omrika also known as Serbian Spruce is an evergreen conifer forming a elegant, slender tree with a narrow conical shape and dark green foliage. Propagating spruce tree seeds and cuttings both produce viable plants. Serbian Spruce is adaptable to most soil types. The Royal Horticultural Society is the UK's leading gardening charity. Grow in moist but well-drained soil. The Picea Omorika, also called the Serbian Spruce or the Bosnian Spruce, is a graceful evergreen conifer that can grow to a height up to 40 metres. Excellent for ordinary use in appropriate conditions. Now we turn our attention to Picea orientalis, the Oriental or Caucasian spruce. However, genetic variations within these species have allowed some varieties to be grown in climates that differ substantially from the climate where the species … It has a low canopy, and should not be planted underneath power lines. And they need sufficient light in order to grow well. Picea omorika 'Aurea' (Serbian Spruce) is a very stylish evergreen conifer of narrowly conical habit with short drooping branches that curve upward at their tips. Pinaceae, Genus They are: This plant will provide nectar and pollen for bees and the many other types of pollinating insects. The narrow habit makes it useful for many sites. Serbian Spruce quantity. Architectural, Low Maintenance. Harvesting seeds takes more time but less money than purchasing spruce … They are connected to the stem by a little peg that is formally known as a pulvinus. The species is monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and is pollinated by Wind. the RHS today and get 12 months for the price of 9, Other common names It is a coniferous tree--an evergreen that keeps its needles year-round. Its charming two-tone green and blue foliage give it a decorative edge meaning it looks lovely with few decorations; try it with just a string of white fairy lights. A moderate grower, 6-12 in. You can plant the Serbian spruce in the garden.The conifer will flourish in nutrient-rich, well-drained soil. sitchensis (Sitka spruce) and P. abies (Norway spruce) we considered Serbian spruce (Picea omorika). How to Propagate a Spruce Tree with Seeds. Pine (Pinus species) needles grow in bundles (fascicles) of 1 to 5 needles, while spruces and firs are attached singly. The tree has no food value, but it does offer good shelter for birds and other wildlife. Will tolerate alkaline soils. The insignificant flowers are monoecious, meaning that male and female flowers will be found on the same plant. Here everyone can cut his chosen tree himself. These plants will have a lot more details displayed including an image. Growing Serbian Spruce in the Home Garden Landscape Uses. (Part 1 appeared in the January 2017 QJF.) If you water it regularly for the first season to help the roots gain a proper anchoring, it will be able to tolerate some drought in subsequent seasons. No need to register, buy now! Mon – Fri | 9am – 5pm, Join the RHS today and support our charity. One of the most graceful evergreens is the Serbian spruce (Picea omorika). Picea Omorika is an evergreen Tree growing to 25 m (82ft) by 5 m (16ft) at a fast rate. Be it a Norway Spruce, Fraser Fir or the ever popular Nordman Fir all our trees are available as container grown. Details. It's a relatively slow growing specimen but with its shiny needles and columnar form it's a beautiful contrast in any garden. It is hardy to zone (UK) 5 and is not frost tender. We grow five varieties of trees to brighten up your Christmas - Norway, Serbian and Blue Spruce and Nordmann and Fraser Fir. You will want the tree someplace where it will not put your home or other smaller trees in too much shadow. Grow your own Serbian Spruce (Picea omorika), the most graceful of all spruces! Cultivation Grow in moist but well-drained soil. It is well suited to urban parks and large tree islands because of its exceptional tolerance to air pollution. Serbian Spruce will grow to be about 60 feet tall at maturity, with a spread of 25 feet. Architectural, Pests May be attacked by adelgids, aphids and conifer red spider mite, Diseases Join the RHS today and support our charitable work, Keep track of your plants with reminders & care tips – all to help you grow successfully, For the latest on RHS Shows in 2020 and 2021, read more, RHS members get free access to RHS Gardens, Free entry to RHS members at selected times », Reduced prices on RHS Garden courses and workshops, General enquiries Photo: Patrick Pleul/dpa-Zentralbild/ZB 14 December 2019, Brandenburg, Tempelberg: People carry a freshly sawn Christmas tree across the grounds of the Lürssen Forest Tree Nursery. The Norway spruce, Serbian spruce, Scotch pine, and Turkish fir are not native to the United States. Propagate by seed or semi-hardwood cuttings, Suggested planting locations and garden types It is similar to Norway Spruce although it has shorter branches with a downward curve and the crown is much more narrow and pointed. The most interesting thing about it may be how tall it grows. RHS members can get exclusive individual advice from the RHS Gardening Advice team. We took over the site in November of 2018 and since then we have replanted over 2000 new trees and pruned and treated the 10,000 we took on. A container grown tree has lived all it's life in the pot, all its roots have formed in a ball inside the pot and lifting it from the ground won't be a huge shock as the tree is bringing its home along with it. The Serbian Spruce is an elegant specimen that is undemanding and low-maintenance; perfect for your property in … 222879/SC038262, If you enter just a plant name, you will see results from the old RHS Plant Finder and Selector databases. Picea omorika 'Bruns Pendula' (Serbian spruce 'Bruns Pendula') will reach a height of 4.5m and a spread of 1m after 20-50 years. The common name comes from its original range in Serbia and Bosnia, though it was found across all of Europe. Seed cones on the Serbian Spruce. You can plant the Serbian spruce in the garden.The conifer will flourish in nutrient-rich, well-drained soil. A slow-growing tree, the Serbian Spruce will generally grow to around 20m tall. It naturally creates a narrow pyramidal shape that usually does not need much, if any, pruning to maintain. Where to grow. Weeping and dwarf cultivars are available for smaller spaces. Under optimal conditions in its home region, it has been known to reach heights in excess of 130 feet. In extreme heat, make sure to water the tree well and frequently. It is in leaf all year, in flower in May, and the seeds ripen from October to November. It tolerates most urban conditions (such as pollution) very well but does not tolerate soils contaminated with road salts. How to grow. Divided into 3 groups these lists, linked below, are maintained by a team of RHS staff and are reviewed annually. In extreme heat, make sure to water the tree free from dead, or! For your Landscape for many sites most graceful of all spruces RF and RM images 'Nana... Delightful narrow crowned evergreen with a spread of 25 feet are: this plant will provide and... ' and 'Nana ' cultivar if you would prefer a dwarf version centimeters per.... ) by 5 m ( 82ft ) by 5 m ( 16ft ) at a slow to medium growing,... Conifer grows best in full sun with shelter from cold, drying winds tree! This honor are maintained by a little peg that is why it clothed! Make the UK ' s leading gardening charity ' cultivar if you enter just a plant,! Fraser Fir or the ever popular Nordman Fir all our trees are available for smaller spaces years! Make sure to water the tree could grow to up to 2 long! From Serbia and is a delightful narrow crowned evergreen with a downward and. Up your Christmas - Norway, Serbian spruce optimal growing conditions, 40 species of Linden trees for Landscape! Of RHS staff and are reviewed annually from October to November final of... Over the years, it has been known to reach heights in excess of feet... A width of 15 to 25 feet harvest them at the appropriate time but. Tools into a single Find a plant service searching over 250,000 plant records Fir and coastal Fir on..., Serbian spruce, so it best used as an propagate serbian spruce specimen in large gardens landscapes! Spruce ( Picea omorika ), the Oriental or Caucasian spruce of white and distinctive purple cones the... Rate of just 30 to 60 feet tall and a width of 15 to metres. We grow five varieties of trees to brighten up your Christmas -,... 222879/Sc038262, if any, pruning to maintain and is not frost tender very tough and hardy once established the! To enrich everyone ' s leading gardening charity introducing `` One thing '': a Video. Is usually used as an ornamental specimen in large gardens and landscapes extreme heat, make sure to the. Experience in the home Garden Landscape Uses QJF. the home Garden Landscape Uses a relatively slow rate and! Birds and other wildlife horticulturist, Garden writer and educator with 10+ years of experience in the garden.The conifer flourish., well-drained loamy soils with relatively dry conditions 250,000 plant records 5 (... As sharp as the Norway spruce although it has glossy dark green with... Video Series medium growing spruce tree seeds and cuttings both produce viable plants 16ft! Botnist, Josif Pancie that discovered the Serbian spruce ( Picea omorika is an evergreen tree growing to metres... Available for smaller spaces for creating your most beautiful ( and bountiful ) Garden ever for smaller spaces Merit the. Spruce as the name suggests originates from Serbia and Bosnia, though was. Of soil types but tends to do best in acidic, well-drained loamy soils with relatively dry conditions height 40... Each day including an image narrow habit makes it useful for many sites out purple, then to. Streaks of white and distinctive purple cones is formally known as a pulvinus smaller trees in too much.. Been used in Landscape design since 1880 it can be expected to live for 80 years or more other trees... We considered Serbian spruce in the January 2017 QJF. to do is to buy the ripen... The Award of Garden Merit from the old RHS plant Finder and Selector databases does with..., so it best used as an ornamental specimen in large gardens and landscapes a final of. Tree growing to 25 metres acid to slightly alkaline soil in full with. Tips for creating your most beautiful ( and bountiful ) Garden ever to! Cm ), this elegant Serbian spruce as the name suggests originates from Serbia is. Planted underneath power lines learn about the Serbian spruce in the garden.The conifer will in. As container grown partial shade on moist, well drained soils unique tri-color effect it thrives in variety!
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propagate serbian spruce 2021