Artigos de Revista

This paper presents an experimental study about the effects of hygrothermal and outdoor ageing on a polyurethane (PUR) adhesive used in civil engineering applications. Small scale adhesive coupons were exposed to different types of ageing environments for up to two years: (i) immersion in demineralised water at 20 and 40 °C, (ii) immersion in salt water at 20 and 40 °C, (iii) continuous condensation environment at 40 °C, and (iv) outdoor ageing in Lisbon, Portugal. At predetermined times, after a desorption period until constant mass, the effects of such exposure on the physical and mechanical responses of the PUR adhesive was investigated using the following techniques: (i) water sorption, (ii) dynamic mechanical analyses (DMA); (iii) flexural; and (iv) in plane shear tests. The diffusion mechanisms observed were not purely Fickian; a long relaxation period was noticed, with water molecules being continuously incorporated in the adhesive until the end of the experiments; two alternative analytical modelling approaches were successfully used to simulate the diffusion processes. After immersion in water and salt water for two years, the viscoelastic behaviour of the adhesive showed signs of post-curing phenomena, and some of the physical degradation was found to be reversible due to drying, although it was not explicitly quantified; accordingly, the Tg showed increasing trends (11 14%). The mechanical properties of the adhesive showed signs of irreversible degradation mechanisms, more relevant on the in-plane shear properties, with reductions up to 26% in strength and 44% in modulus under the harsher conditions. Flexural properties also exhibited irreversible degradation, with maximum reductions up to 30% in strength and 36% in modulus. Increased temperature did not have a significant effect in the flexural and shear strength, but caused higher degradation in the corresponding moduli. The degradation caused by salt water immersion and continuous condensation was comparable to that in demineralized water immersion (at the same temperature).

The multichannel surface-wave method is a current method used in geotechnical and environmental engineering to estimate the near surface shear-wave (S

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This work presents some novel results obtained by using the strain injection techniquesfor modeling crack propagation in challenging 3D benchmark tests. The techniques were already tested and validated by static and dynamic simulations in 2D, so the main goal of this paper is to verify if the most important advantages of the method, low computational cost and independence of the results on the finite element mesh, are kept in 3D.The methodology, implemented in the finite element framework, consists essentially in injecting those elements that are going to capture the cracks with some enhanced strain modes for improving the performance of the elements for modeling propagating material failure.

This paper presents a finite element approach for modelling three-dimensional crack propagation in quasi-brittle materials, based on the strain injection and the crack-path field techniques. These numerical techniques were already tested and validated by static and dynamic simulations in 2D classical benchmarks and, also, for modelling tensile crack propagation in real concrete structures, like concrete gravity dams. The main advantages of the methodology are the low computational cost and the independence of the results on the size and orientation of the finite element mesh. These advantages were highlighted in previous works by the authors and motivate the present extension to 3D cases. The proposed methodology is implemented in the finite element framework using continuum constitutive models equipped with strain softening and consists, essentially, in injecting the elements candidate to capture the cracks with some goal oriented strain modes for improving the performance of the injected elements for simulating propagating displacement discontinuities. The goal-oriented strain modes are introduced by resorting to mixed formulations and to the Continuum Strong Discontinuity Approach (CSDA), while the crack position inside the finite elements is retrieved by resorting to the crack-path field technique. Representative numerical simulations in 3D benchmarks show that the advantages of the methodology already pointed out in 2D are kept in 3D scenarios.

Changes in flagellate protist communities of subterranean termite Reticulitermes gras-sei across different locations were evaluated following four predictions: (i) Rural endemic (Portugal mainland) termite populations will exhibit high diversity of symbionts; (ii) invasive urban populations (Horta city, Faial island, Azores), on the contrary, will exhibit lower diversity of symbionts, showing high similarity of symbiont assemblages through environmental filtering; (iii) recent historical colonization of isolated regions

This article presents the results of a round-robin test performed by 13 international research groups in the framework of the activities of the RILEM Technical Committee 260 RSC ‘‘Recommendations for use of superabsorbent polymers in concrete construction’’. Two commercially available superabsorbent polymers (SAP) with different chemical compositions and gradings were tested in terms of their kinetics of absorption in different media; demineralized water, cement filtrate solution with a particular cement distributed to every participant and a local cement chosen by the participant. Two absorption test methods were considered; the tea-bag method and the filtration method. The absorption capacity was evaluated as a function of time. The results showed correspondence in behaviour of the SAPs among all participants, but also between the two test methods, even though high scatter was observed at early minutes of testing after immersion. The tea-bag method proved to be more practical in terms of time dependent study, whereby the filtration method showed less variation in the absorption capacity after 24 h. However, absorption followed by intrinsic, ionmediated desorption of a specific SAP sample in the course of time was not detected by the filtration method. This SAP-specific characteristic was only displayed by the tea-bag method. This demonstrates the practical applicability of both test methods, each one having their own strengths and weaknesses at distinct testing times.

The rock type plays a key role in the way in which the outermost layer of the cement interacts with the formation, in wells under geothermal environments. The penetration of cement into the rock is controlled by the porosity of the rock which also regulates the amount of CO2 enriched brine that can contact the cement.Samples were prepared by drilling holes into rock blocks, pouring in a cement slurry and hydrothermally treating the whole assembly at 150 °C under typical geothermal environments. The changes in the interfacialtransition zone (ITZ) that forms between geothermal cements and volcanic rocks were examined.Both porosity and the volcanic glass content of the rock have a considerable impact on the way in which thecement and the formation interact and, ultimately, affect the bond between these materials. The porosity has a major influence on the durability of the cement in carbonated brine.

This study investigates the effect of the diethyl carbonate as a carbonation accelerator on the carbonation of lime mortars. Two types of lime mortars were prepared, one using lime putty and standard sand and the other using lime putty, dust and fragments of ceramic and standard sand. After a curing time of two weeks, the accelerator product, diethyl carbonate in a solution of ethanol and water, was sprayed on half of the mortars of each type. The differences in the carbonation performance were analyzed at 28, 90, 120 and 180 days using different analytical methods. Apart from the mineralogical and petrographic characterization, the physical, mechanical and hydric properties of the samples were determined. Mechanical tests were conducted only at 90, 120 and 180 days, because at 28 days the lime mortars were considered still too soft. The mortar samples with the accelerator had steadier carbonation and slight changes in their microstructure.