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[EN] The microstructural features of heterogeneous and porous materials give rise to unique non-linear dynamic behaviour. The purpose of this work is to investigate the dynamic response of thermally damaged concrete specimens measured by two different techniques: Non-linear Impact Resonance Acoustic Spectroscopy (NIRAS) and new Flipped Accumulative Non-linear Single Impact Acoustic Spectroscopy (FANSIRAS). Specimens were characterised in two different dynamic condition states of the material: relaxed and conditioned. The specimen¿s relaxed state indicates that no previous dynamic excitation event ocurred. The conditioned state denotes that the specimen has been dynamically tested before. The NIRAS results show that the non-linear material parameters, af and aQ , are affected by their previous dynamic history (its conditioning). The recently proposed algorithm, FANSIRAS, extracts from a single resonant signal equivalent results to NIRAS when the specimen is conditioned. In this situation, both parameters af and aQ were equivalent. The results suggest that new NDT parameters based on non-linear hysteretic parameters can quantify the damage level of thermally treated mortar specimens., This work has been supported by the Spanish Administration under grants BIA2014-55311-C2, BIA2017-87573-C2, BES2015-071469, PAID-10-19 and FEDER funds.

New applications of non-destructive techniques (NDT) with ultrasonic tests (attenuation and velocity by means of ultrasonic frequency sweeps) have been developed for the characterization of fibre-reinforced cementitious composites. According to new lines of research on glass-fibre reinforced cement (GRC) matrix modification, two similar GRC composites with high percentages of fly ash and different water/binder ratios will be studied. Conventional techniques have been used to confirm their low Ca(OH)(2) content (thermogravimetry), fibre integrity (Scanning Electron Microscopy), low porosity (Mercury Intrusion Porosimetry) and good mechanical properties (compression and four points bending test). Ultrasound frequency sweeps allowed the estimation of the attenuation and pulse velocity as functions of frequency. This ultrasonic characterization was correlated successfully with conventional techniques. (C) 2015 Elsevier B.V. All rights reserved., This work has been supported by the Government of Spain under Grant TEC2011-23403 01/01/2012

[EN] In this paper, a new approach for characterizing material damage, using ultrasonic waves, is proposed. Two concrete series with two types of cement with different C3A content and similar mechanical properties were subjected to external sulphate attack (ESA) and evaluated using a novel Recurrence Plot Quantification Analysis (RQA) method. This brand new technique was compared with several methods, such as mechanical tests (compressive and flexural strength determination), dynamic test (dynamic modulus) measurements, and traditional ultrasonic measurements (propagation velocity and ultrasonic wave attenuation). In these experiments, RQA showed a high sensitivity to damage in spoiled series, improving the reliability of damage detection with ultrasonics in non-homogeneous materials compared to other non-destructive techniques. Interesting advantages of this new non-destructive technique are: a) the RQA parameter is normalized (range of 0 to 1); b) a calibration process is not required; c) the values of its standard deviation show the dispersion of the damage. It can contribute greatly to the diagnosis of the degree of damage to a material, when combined with other traditional measures such as the attenuation of the material., This work was supported by the Spanish Government under grants TEC2011-23403, BIA2014-55311-C2-1-P and BIA2014-55311-C2-2-P. This work is protected by the Spanish Patent and Trademark Office (SPTO) under reference P201630212.

[EN] An exhaustive monitoring of an internal sulphate attack of Portland cement-based materials is addressed. Four series of Portland cement mortars with different amounts of gypsum (0%¿2% SO3 respect to the cement by mass) were monitored by means of physical, microstructural and non-destructive tests, studying specimens with a low expansion rate to examine the sensitivity of the applied techniques. The expansion analysis has shown the suitability of a fitting model, allowing the examination of two characteristic parameters: the characteristic time of the expansion reaction and the maximum amplitude of the expansion. In the mechanical analysis, higher values of Rc and Rf were attained as the gypsum content decreased. A microstructural analysis (thermogravimetry and FESEM) supported ettringite formation and expansion process. These results have been correlated with non-destructive tests: impact resonance acoustic spectroscopy and ultrasonic measures. The dynamic modulus and ultrasonic pulse velocity have closely predicted the stiffness of the specimens. The total material attenuation (absorbed energy of the chirp signal ultrasonic wave) presented different trends, showing clear differences for the most damaged series (2% SO3). Attenuation supplied interesting information about the hardening process and the microcracking effect due to a mortar expansion higher than 0.04%. The novelties of this study are the exhaustive monitoring of an internal sulphate attack, as well as the examination of the sensitivity of brand new NDT techniques when this damage process overlaps with the curing process., This work has been supported by the Spanish Administration under grants TEC2011-23403, BIA2014-55311-C2-1-P and BIA2014-55311-C2-2-P.

Glass fibre Reinforced Cement (GRC) is a composite material composed of Portland cement mortar with low w/c (water/cement) ratio and high proportion of glass fibres. This material suffers from the ageing process by losing its strength with time because of its exposure to severe weather conditions. Ageing process damages the fibre surface and decreases the mechanical properties of the structural components made of this material. It reduces the elastic modulus and toughness of GRC. Fracture toughness is traditionally measured by four point bending tests. In a previous study by the authors it was observed that ageing related deterioration or damage of GRC could be monitored by Non Destructive Testing (NDT) techniques such as Non-linear Impact Resonance Acoustic Spectroscopy (NIRAS) and other ultrasonic techniques. The scope of this paper is to corroborate previous investigations and offer early damage detection capability by generating more experimental data points by optimizing location of the point of strike and thus generating more resonance vibration modes in NIRAS tests., The authors acknowledge the financial support of the Ministerio de Ciencia e Innovacion MICINN, Spain, and FEDER funding (Ondacem Project: BIA 2010-19933).

Glass fiber reinforced cement (GRC) is a composite material based on Portland cement and alkali resistant glass fibers. This composite has good mechanical properties including toughness and flexural strength. The characterization of this material is carried out by four points bending test. During this test, elastic and plastic behaviour are identified from load vs. deflection curves. The scope of the research is to monitor this bending test by means on ultrasonic pulses in order to detect changes on the material and to correlate them with mechanical behaviour. In this sense, pulse velocity, energy, attenuation and non-linearities of the ultrasonic received signals have been analysed. First changes in energy, attenuation and nonlinearities were detected during the change from elastic to plastic step and the first pulse velocity change were observed during the plastic step.