[show abstract][hide abstract] ABSTRACT: En este trabajo se presentan resultados preliminares de una amplia investigación que busca analizar la resistencia a impacto de mortero de cemento reforzado con fibra de vidrio (glass fibre reinforced cement, GRC), así como la influencia de diversos aditivos sobre la pérdida de resistencia con el tiempo. Se utilizan los ensayos no destructivos por ultrasonidos para valorar el daño a impacto en placas de GRC. La valoración de los daños se ha realizado mediante imágenes ultrasónicas (BSCAN, CSCAN y DSCAN), obtenidas a partir de inspecciones pulso/eco realizadas a las frecuencias de 2 y 5 MHz. Este trabajo ha sido realizado mediante la financiación del MEC dentro del proyecto BIA 2006-15188-C03-01, del P. N. I+D+i, y del M. Fomento C14/2006. La Dra. M.G. Hernández esta soportada por un contrato postdoctoral CSIC-I3P financiado por los Fondos Sociales Europeos. Peer reviewed
[show abstract][hide abstract] ABSTRACT: Currently, the use of precast concrete elements has gained importance
because it offers many advantages over site-cast concrete. A
disadvantage of site-cast concrete is that its properties vary according
to the manufacturing method, the environment and even the operator who
carried out the mixing, pouring and implementation of the concrete.
Precast concrete elements are manufactured in a controlled environment
(typically referred to as a precast plant) and this reduces the
shrinkage and creep. One of the key properties of precast concrete is
the capability to gain compressive strength rapidly under the
appropriate conditions. The compressive strength determines if the
precast can be stripped from the form or manipulated. This parameter is
measured using destructive testing over cylindrical or cubic samples.
The quality control of precast is derived from the fracture suffered by
these elements, resulting in a "pass or fail" evaluation. In most cases,
the solution to this problem is to allow the material to cure for a few
hours until it acquires sufficient strength to handle the precast
element. The focus of this paper is the description of the research
project "CUREND". This project aims to design a non-destructive
methodology to monitor the curing process in precast concrete. The
monitoring will be performed using wireless sensor networks.
IOP Conference Series Materials Science and Engineering 12/2012; 42(1):2050-.
[show abstract][hide abstract] ABSTRACT: In this paper, the influence of steel fibers on the ultrasonic velocity of steel–fiber-reinforced cementitious materials was studied using a micromechanical model. To this end, a three-phase micromechanical model was extended and generalized to multiphase materials. Firstly, such a model was used to predict the influence of the geometry and volume fraction of steel inclusions on the ultrasonic velocity of steel–fiber-reinforced cementitious materials. Experimental validation was carried out on steel-reinforced and non-reinforced mortar specimens through destructive and non-destructive testing by ultrasound. Comparisons between predicted and measured ultrasonic velocity were in good agreement, with errors less than 1.5%. Moreover, the model was also validated on experimental data obtained from steel–fiber-reinforced concrete specimens [Yazıcı et al. Constr Build Mater 2007;21:1250–3].
Construction and Building Materials 01/2011; 25:3066-3072. · 2.29 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper examines ultrasonic wave propagation through strongly heterogeneous materials such as cementitious materials, and deals meanly with the formulation of a multiphase approach of a self-consistent multiple scattering model, the so-called dynamic generalized self-consistent model (DGSCM) proposed by Yang [J. Appl. Mech. 70(2003) 575-582]. This extended model can describe the influence of the size and volume fraction of aggregates on cementitious materials, as well as the interaction, contribution, and influence of entrapped air voids together with the aggregates on frequency-dependent parameters such as the phase velocity and the attenuation coefficient. To show the performance of this approach, theoretical predictions were compared with experimental ultrasonic measurements over a wide frequency range from several mortar specimens with different features in their microstructure properties and concentrations of aggregates up to 60%. The multiphase approaches of both the DGSCM and the Waterman-Truell model (WT) were also compared. The obtained results of the multiphase DGSCM were found to be significantly better than those obtained from the N-phase WT model for ultrasonic measurements from cementitious materials at high aggregate concentrations. The feasibility of material characterization using the multiphase approach of DGSCM was also discussed.
[show abstract][hide abstract] ABSTRACT: This paper deals with the measurement of frequency-dependent ultrasonic attenuation in strongly heterogeneous materials, such as cementitious materials. To improve the measurement of this parameter on this kind of materials, a linear swept-frequency signal is used to drive an emitter transducer to conduct a through-transmission inspection in immersion. To filter out undesirable frequency content, time-frequency filtering and detection process are performed. The use of this method has been compared with two excitation techniques, the broadband and the narrowband pulses. The results obtained using the swept-frequency excitation together with the time-frequency filtering, allows the determination of the attenuation curves with high accuracy over a wide frequency range without the need for complicated equipment, and improves the effective bandwidth by using a unique pair of transducers.
[show abstract][hide abstract] ABSTRACT: This work presents the results obtained in a long-term experiment focused on the study of the evolution of cementitious materials immersed in pig slurry at real conditions. Cement mortars were made with four different cement types and immersed in pig slurry for 48 months. Furthermore, to separate pure hydration process from pig slurry effect, mortar samples were immersed in water for 12 months at laboratory conditions. Compressive strength, X-ray diffraction and ultrasonic measurements were made in all samples. Ultrasonic measurements were made from ultrasonic images obtained from automatic ultrasonic inspections. Use of ultrasonic images has allowed the extraction of information about the state of the studied materials. An empirical relationship between ultrasonic velocity and compressive strength has been obtained and the long-term effect of pig slurry on cementitious materials has been determined.
[show abstract][hide abstract] ABSTRACT: A method for non-destructive detection of microcracks in ceramic composites is described. The method involves the combination of ultrasound characterisation with the application of a three-phase micromechanical model, which considers cracks and pores as void constituents. Four alumina-aluminium titanate materials with different levels of microcracking, from no cracks (monophase alumina) to severely cracked (alumina + 40 vol.% of aluminium titanate) including an alumina + 10 vol.% aluminium titanate material with incipient microcracking have been developed to test the validity of the method. Specimens have been fabricated by colloidal processing and the longitudinal and transverse ultrasound velocities have been determined by the ultrasonic pulse-echo and transmission ultrasound-immersion techniques, employing a digital signal processing. It has been demonstrated that it is possible to differentiate between pores and microcracks, both modelled as void constituents, in terms of the aspect ratio.
[show abstract][hide abstract] ABSTRACT: Predominant physical phenomenon in highly scattering materials is the attenuation due to dispersion. Therefore, received echo has high frequencies more severely attenuated than low frequencies and the structural noise can be modeled as a non-stationary random process. Most of the proposed techniques for enhancing the flaw visibility do not exploit the frequency dependency of the incoming flaw signal, assuming homogeneous behaviour of the insonified material. In this work, a new technique based on exploiting the non-stationary nature of the incoming UT signal is presented. Proposed technique is based on the prediction error obtained with a linear and time-varying parametric model of the noise. By this method, when the analyzed UT echo has only structural noise, the prediction error is low, however, if it contains a flaw, high prediction error occurs because a flaw is a non-predictable alteration of the material structure. Experiments with stainless steel show that this method has an excellent performance on SNR enhancement.
[show abstract][hide abstract] ABSTRACT: Degradation of concrete structures located in high humidity atmospheres or under flowing water is a very important problem. In this study, a method for ultrasonic non-destructive characterization in aged mortar is presented. The proposed method makes a prediction of the behaviour of aged mortar accomplished with a three phase micromechanical model using ultrasonic measurements. Aging mortar was accelerated by immersing the probes in ammonium nitrate solution. Both destructive and non-destructive characterization of mortar was performed. Destructive tests of porosity were performed using a vacuum saturation method and non-destructive characterization was carried out using ultrasonic velocities. Aging experiments show that mortar degradation not only involves a porosity increase, but also microstructural changes in the cement matrix. Experimental results show that the estimated porosity using the proposed non-destructive methodology had a comparable performance to classical destructive techniques.
[show abstract][hide abstract] ABSTRACT: In ultrasonic non-destructive evaluation of highly scattering materials, detection of flaw echoes is difficult due to the masking effects of the structural noise. This paper presents a method for the reduction of the structural noise on highly scattering materials. The method consists of a multi-resolution analysis using wavelets and a time-frequency thresholding applied to the approximation coefficients. This threshold is estimated by considering the mean and the standard deviation of the time-frequency energy representation. This method exploits spectral properties of the structural noise and the incoming flaw signal, resulting in a processed signal that maintains the defect pulse shape. In order to validate this strategy, synthetic and experimental signals have been evaluated. The performance of this method is compared with known selection rules as Minimax and Universal threshold.
19$^th$ International Congress on Acoustics; 01/2007
[show abstract][hide abstract] ABSTRACT: The objective of multiphasic models applied to cement-based materials is to estimate the global elastic constants as a function of properties of their constituents. However, these models have limited success for porosity characterization.In this investigation, a new approach that determines the elastic properties of three-phase materials is presented. The proposed model takes into account the microstructural characteristics of the constituent phases, as well as their elastic properties. The micromechanical model of three phases is applied to mortar, considering the material composed by cement paste matrix and two types of inclusions, aggregate and pores. The influence of geometry and elastic properties of both inclusions on the ultrasonic velocity has been evaluated theoretically. The effect of the volume fraction of pores on the ultrasonic velocity is also presented.
Cement and Concrete Research - CEM CONCR RES. 01/2006; 36(4):609-616.
[show abstract][hide abstract] ABSTRACT: Among the factors that affect the durability of cement-based materials, porosity is important due to its role in transporting substances inside the material. Porosity can be determined using destructive testing methods, but the civil construction industry needs a nondestructive method for the estimation of the volume of pores in cement-based materials to evaluate the deterioration process.In this investigation, a micromechanical model of three phases developed in a previous paper is used to estimate the porosity of a series of mortar samples. The proposed model takes into account the microstructural characteristics and elastic properties of the constituent phases. In a first stage, the model is used to predict the influence of both the volume fraction of sand and pores and the elastic constants of the matrix and the sand on the ultrasonic velocity. Next, experimental measurements are made on a series of mortar samples of varying water/cement ratio, cement type and sand concentration, with the results used to demonstrate that porosity can be estimated using the proposed nondestructive method.
[show abstract][hide abstract] ABSTRACT: Structural noise is a very important limitation to the visibility of flaw echoes in ultrasonic testing and evaluation of highly scattering materials. In order to enhance the signal-to-noise ratio, different algorithms have been developed. One of these techniques is based on filtering the spectrum low band of the received echo to obtain a significant improvement of the defect visibility. Based on this idea, in this work a new time-frequency technique is presented. In this method, block-processing autoregressive techniques are used to estimate the instantaneous center frequency of the traveling wave. From this information, a time-frequency filter is designed tuned at half the estimated instantaneous center frequency. Experimental results and the comparison with the non-time-frequency filtering technique are also included, showing that the proposed method has an excellent performance on SNR enhancement.
[show abstract][hide abstract] ABSTRACT: The durability of cement composites significantly depends on the movement of the fluids into the material through the porous system. The aqueous phase contained in the pores can cause irreversible damage from the dimensional stability viewpoint. In this sense, methods for non-destructive characterization of both, the porous structure and water content should be investigated. In this work, the effect of the fluid in the inclusions of the cement paste on the ultrasonic velocity is studied. Firstly, a theoretical analysis based on the micromechanical model, considering the microstructural information of the matrix and the fluid filling the pores, is presented. Some experimental work is made later using cement paste samples, whose porous structure is maintained dry or saturate with water. In both cases, the ultrasonic velocity is measured and compared to the one predicted by the micromechanical model. Using this technique, the ultrasonic velocity can be predicted with errors below 2% in the cases of dry or water saturated cement paste.
[show abstract][hide abstract] ABSTRACT: In order to enhance the defect in relation to background noise of large grained materials different algorithms have been developed. Wiener filtering techniques have proved to be efficient for the SNR enhancement of ultrasonic signals coming from highly scattering materials. These processing algorithms are based on designing a filter that has large gain at frequencies where the SNR is high and low gain at frequencies where SNR is small. However, this technique does not consider two important ultrasonic effects: the finite-time duration of the flaw UT signal coming from a defect and the distortion of the frequency components of the traveling wave-front due to the dispersion. In this work, a time-frequency Wiener filter is proposed that takes into account these two characteristics. Experimental results are presented, showing that the proposed time-frequency algorithm has an excellent performance on SNR enhancement.
[show abstract][hide abstract] ABSTRACT: Mechanical properties of concrete and mortar structures can be estimated by ultrasonic non-destructive testing. When the ultrasonic velocity is known, there are standardized methods based on considering the concrete a homogeneous material. Cement composites, however, are heterogeneous and porous, and have a negative effect on the mechanical properties of structures. This work studies the impact of porosity on mechanical properties by considering concrete a multiphase material. A micromechanical model is applied in which the material is considered to consist of two phases: a solid matrix and pores. From this method, a set of expressions is obtained that relates the acoustic velocity and Young's modulus of mortar. Experimental work is based on non-destructive and destructive procedures over mortar samples whose porosity is varied. A comparison is drawn between micromechanical and standard methods, showing positive results for the method here proposed.