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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...

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ABSTRACT:Hydration processes in cement pastes and mortars both with the addition of silicoaluminous pozzolans (metakaolin MK and catalyst used in catalytic cracking FCC) have been studied in this paper. Additionally, the amount of hydrates and portlandite in cured pastes from 5 to 20° C and for 3 to 28 days curing time has been determined. The microstructural study by using thermogravimetric analysis in pastes has shown that, at low temperatures (5-10°C) the FCC acts mainly as a pozzolan, whereas MK also produces acceleration in the hydration of cement. The influence from the mechanical point of view is a relative increase in the compressive mechanical strength of mortars cured at 5° C for both pozzolanic materials, through replacement of cement and through replacement of aggregate. These two pozzolans are effective materials to compensate for setting and curing conditions at low temperatures, especially in aggregate replacement mortars.

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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The Valencia coastline has been a leading tourist region in Spain since the nineteen-sixties and its 35 popularity has given rise to the massive construction of residential buildings in the area. Many of 36 these have been raised close to beaches, where this was possible, at between 10 to 20 metres from 37 the waterline. Being so close to the sea, the buildings are exposed to the marine environment and in 38 many cases also to the direct effect of the marine aerosol. 39 40The main cause of the loss of durability in coastal buildings is the corrosion of the reinforcement 41 rebars due to the chloride ion effect [1], which is often found in combination with carbonation 42 processes [2]. Both phenomena contribute to the destruction of the passive film on the surface of the 43 reinforcementexisting in the steel surface protected to the corrosion. 44 45Salt particles suspended in the marine atmosphere are deposited on the surface of the concrete and 46 the chloride ions then penetrate to the interior, where there is a strong likelihood of them corroding 47 the reinforcement. The rate of the deposit depends on the saline content of the sea breeze and is 48 rapidly reduced with distance from the sealine. Some studies have shown that there are different 49 concentration levels in the salt spray zone in relation to distance from the shore line, especially in 50 the first 200 m [3]. The chloride ions build up faster than atmospheric carbon dioxide (which is 51 responsible for carbonation of the concrete), so that the action of chlorides is usually the chief factor 52 in the corrosion of reinforcement in this type of atmosphere, when the structure is exposed to a sea 53 breeze. 54 55The depassivating effect of chloride ions becomes apparent when a threshold value of chloride 56 concentration is reached in the concrete. Factors that influence this threshold value include 57 atmospheric conditions such as moisture content, the presence of oxygen, and period of exposure to 58 the marine environment, as well as aspects related to the composition of the concrete, including: 59 different conditions of the reinforcement passivation, water/cement ratio, type of cementitious 60 matrix, and hydroxide content of the porous network [4,5]. 61 62 Distance from the sea is an important factor in the quantity of salt particles deposited on a surface 63 and therefore also in their reaching the reinforcement. In addition, the wetting-drying cycles of the 64 concrete affect the content of chloride ions, which can be from 3 to 8 times higher when these 65 cycles are absent [6]. when the same type of steel is exposed to different ambient conditions, the characteristics of the 87 corrosion products vary in relation to different ambient conditions. However, they also found that 88 certain corrosion products are always present, regardless of the environmental conditions and type 89 of steel studied. 90 91The location of different crystalline phases in the oxide layer has also been thoroughly studied; in 92 particular for highly corroded steel, dif...

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