Glass fiber reinforced cement (GRC) is a composite material made of portland cement mortar and alkali resistant (AR) fibers. AR fibers are added to portland cement to give the material additional flexural strength and toughness.However ageing deteriorates the fibers and as a result the improvement in the mechanical properties resulted from the fiber addition disappears as the structure becomes old. The aim of this paper is monitoring GRC ageing by nondestructive evaluation (NDE) techniques. Two different NDE techniques -1) nonlinear impact resonant acoustic spectroscopy analysis and 2) propagating ultrasonic guided waves -are used for this purpose. Both techniques revealed a reduction of the nonlinear behavior in the GRC material with ageing. Specimens are then loaded to failure to obtain their strength and stiffness. Compared to the un-aged specimens the aged specimens are found to exhibit more linear behavior, have more stiffness but less toughness. Finally, undisturbed fragments on the fracture surface form mechanical tests are inspected under the electron microscope, to understand the fundamental mechanisms that cause the change in the GRC behavior with ageing.Keywords: Glass Fiber Reinforced Cement, Material Ageing, Ultrasonic Guided Waves, Nonlinear Impact Resonant Acoustic Spectroscopy, Nondestructive Evaluation. IntroductionAlkali resistant glass fiber reinforced portland cement is a cement-based composite material that has higher flexural strength and toughness than plain cement [1]. However, GRC undergoes a rapid ageing process especially in humid and alkaline environment (pH>12). This ageing can nullify the positive effects of glass fibers undergoing from a ductile to a brittle material. Different strategies for improving the durability of GRC have been attempted by modifying the fibers and/or by altering the alkalinity of the matrix [7][8][9]. All these improvements have been evaluated by mechanical tests after accelerated ageing. Accelerated ageing tests have been broadly accepted for testing the durability of GRC. They can be classified as i) Deemed to satisfy tests, (EN 1170-8 [10]) where the GRC specimens are exposed to severe conditions, and ii) predictive accelerated ageing tests [11] that are commonly used to predict the service life of the material, in real weather conditions. For example, Purnell et al. [2] established that GRC soaked for 1 day in water at 55ºC, corresponds to 100 days of exposure to the real weather conditions in the United Kingdom. However, it should be noted that the correspondence between the accelerated ageing tests and the real aging conditions is still being investigated, especially when different matrix compositions are to be compared [11][12]. Typically the ageing process has been assessed by mechanical testing or by strand in cement (SIC) tests [13][14]. The aim of this work is to assess the ageing process in GRC by two nondestructive testing techniques -1) resonance frequency tests at different impact energy levels called Nonlinear Impact Resonance Acousti...

The management of worn tires is a concern in industrialized countries. The application of crumb rubber as lightweight aggregate in cement based materials is a green alternative for reusing this material, and it is more interesting than energy recovery from an ecological point, regarding the waste hierarchy. High replacements of natural sand by crumb rubber were studied, and an air-entraining agent was employed in order to achieve a cellular structure in the composite. The obtained results from tests in fresh state reveal an improvement in workability. The tests conducted on hardened composite reveals promising properties that postulate the resulting materials as candidate for applications where thermal and acoustic properties are required. The minimum requirement of mechanical strength for masonry units was also achieved since the obtained compressive strength varies between 1.04 to 10.04 MPa. Finally, potential applications as a construction material have been highlighted for civil and building applications.

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9In this paper, we investigate the utility of vibration-based NDT tests to detect the 10 subtle microstructural modifications and cracking damage in portland cement mortars 11 subjected to oven drying treatment. Both linear (resonant mode frequency and damping) 12 and nonlinear (nonlinear hysteretic behavior) vibration test data are reported, collected 13 from samples having a range of water to cement ratios and at two different aggregate 14 contents. All test data are affected by the drying treatments, but it appears that the 15 resonant mode frequency response is dominated by the reduction in internal moisture 16 content with drying and changing aggregate cement ratio of the mixture. On the other 17 hand, the linear mode damping, and more so the nonlinear hysteretic parameter, are 18 more influenced by the microstructural modification and cracking damage caused by 19 drying. In particular it appears that the nonlinear hysteretic parameter is very sensitive 20 to internal damage and microstructural modifications caused by oven drying, but not 21 notably sensitive to pore moisture content, and water to cement and aggregate to cement 22 ratios. 23

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The scope of this paper is to study the sulphate attack on concrete with new testing methods based on vibrational spectroscopy with mechanical waves. These are based on Non-linear Impact Resonance Acoustic Spectroscopy (NIRAS) that allows detecting the frequency shift of its resonant modes. Both, signal quality factor and alpha, are measured to monitor the increase of the non-linearity of the material due to the stiffness change on the matrix after being attacked. Different Portland cement matrices were assessed and results between vibrational tests and the traditional expansion ASTM method were compared. Two types of cement with different C 3 A content were tested for external sulphate attack and one cement with high C 3 A content with different amount of addition of SO 3 on the original mix was tested for internal attack. NIRAS was suitable for monitoring external sulphate attack process. A microstructual analysis was carried out with thermogravimetry (TG), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques in order to detect harmful products on damaged series.