Durability of GFRP Pultruded Profiles made of Unsaturated Polyester Resin and E-glass fibers used in Rehabilitation Bruno Miguel Abreu da Silva

Transcription

1 Durability of GFRP Pultruded Profiles made of Unsaturated Polyester Resin and E-glass fibers used in Rehabilitation Bruno Miguel Abreu da Silva M.Sc. Dissertation Extended Abstract November 212

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3 B. Silva Instituto Superior Técnico (212) DURABILITY OF GFRP PULTRUDED PROFILES MADE OF UNSATURATED POLYESTER RESIN AND E-GLASS FIBRES USED IN REHABILITATION Bruno Miguel Abreu da Silva Department of Civil Engineering, Arquitecture and Georesources, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, Lisbon Portugal November 212 ABSTRACT: Since service life of civil infrastructures is generally expected to exceed at least 5 years, materials durability performs an influent role on design criteria and standards [1]. Regarding glass fiber reinforced polymers (GFRP), several authors have identified durability as one of the most critical gaps between perceived need of information and available information [2,3]. This paper presents new findings of an ongoing experimental research, developed in collaboration between Instituto Superior Técnico (IST) and the National Laboratory of Civil Engineering (LNEC), on the mechanical and physical changes suffered by GFRP pultruded profiles made of unsatured polyester resin and E-glass fibers, following accelerated exposure to moisture, water and salt-water, and natural aging to Lisbon climate conditions. Keywords: GFRP, Pultruded profiles, Polyester, Durability, Aging environments, Experimental test 1. INTRODUCTION Regulation and current design criteria have been influenced by traditional materials durability [4]. Nevertheless, the durability limitations experienced by steel and reinforced concrete, associated with higher construction speed demands in civil engineering have been fostering the development of new materials [1]. Within these new solutions, civil engineering structural application of GFRP pultruded profiles has been growing considerably during the last decades, especially due to their several advantages, namely high mechanical performance, lightness, corrosion resistance, low electromagnetic interference and good insulation properties [1,5]. However, actual data on GFRP durability is generally sparse and not well documented noreasily accessible. Moreover, there is a wealth of contradictory data published in a variety of sources. The lack of a comprehensive, validated and easily accessible database on GFRP pultruded profiles durability, mostly regarding the long-term behavior in critical conditions of service when submitted to severe and variable environmental conditions, is a crucial issue which hampers the material usage on a routinely basis [2,6]. This paper presents results of an ongoing experimental research on the physical and mechanical performances suffered by GFRP pultruded profiles made of unsaturated polyester resin and E-glass fibers, following accelerated exposure to demineralized water, salt water, moisture, and to Lisbon climatic conditions. This study also aims to understand the influence of a subsequent drying process after the aging period in order to access reversibility effects, as well as the effect of coating unprotected specimen parts, thereby protecting them from direct exposure. 1

4 2. MATERIALS B. Silva Instituto Superior Técnico (212) The material under study was obtained from pultruded E-glass fiber reinforced unsaturated polyester square tubular profiles (5 mm x 5 mm, thickness of 5 mm), produced by ALTO Perfis Pultrudidos Lda. Structurally, the fibres were disposed in alternate layers of unidirectional fiber rovings and strand mats embedded in the resin matrix. This type of profile is commonly applied as ladders, parts and handrails. 3. METHODS 3.1 Exposure environments In order to study the potential degradation of the GFRP profiles in representative civil engineering application environments, test specimens were cut and subjected to the exposure conditions described in Table 1, which also indicates the batches of aged samples already tested within the IST-LNEC research project. Table 1 Exposure aging conditions Type of exposure Duration Conditions Phase 1 (represents the ongoing study related to prior studies) Immersion in demineralized water (W-2), (W-4), (W-6) 3, 6, 9, 12, 18, 24 months (a) - Temperatures: 2 (±2) ºC, 4 (±1) ºC, 6 (±1) ºC Immersion in salt-water (S-2), (S-4), (S-6) Natural aging 3, 6, 9, 12, 18, 24 months (a) 1, 2, 5, 1 years (b) - Temperatures: 2 (±2) ºC, 4 (±1) ºC, 6 (±1) ºC - Solution composition: 35g/l NaCl - In the roof of LNEC building - Temperature, relative humidity and UV radiation are continuously monitored Phase 2 (represents the ongoing study related to isolated (I) and dried (D) specimens) Immersion in demineralized water (WD-2), (WD-4), (WI-2), (WI-4) 6, 12, 18 months (c) - Temperatures: 2 (±2) ºC, 4 (±1) ºC Continuous condensation (CCD-4), (CCI-4) 6, 12, 18 months (c) - Temperature: 4 (±2) ºC - Humidity: 1% Batches of aged material previously tested: (a) 3, 6 and 9 months [7] Batches of aged material tested during this study: (a) 12 and 18 months; (b) 1 year; (c) 6 months 3.2 Experimental procedures Before exposure, Phase 2 batches were prepared according to the following techniques: 2

5 B. Silva Instituto Superior Técnico (212) (i) Isolated specimens: refers to specimens whose unprotected parts (due to cutting and preparation, namely their sides), were protected by an epoxy resin. Following the coating of the unprotect parts, the resin was cured for 8 days at 21 ºC, in a room with forced ventilation (five times per hour air renewal), supplementing the curing process at 5 ºC in a dried environment for 24 hours. The protection resin was Icosit K 11 N provided by Sika. (ii) Dried specimens: specimens that, finished the exposure period, were submitted to moderate temperature until no significant mass changes were verified, according to ASTM D 5229 standard [8]. After exposure to the different aging conditions outlined in Table 1, the aged batches were subjected to the following characterization techniques: (i) Sorption behavior: mass changes of control specimens, with similar geometry as the specimens used in dynamic mechanical analysis, were recorded using an electronic scale AE24 model of Mettler, with,1 g of precision. To evaluate their mass variation, the control specimens were removed periodically from immersion and continuous condensation exposures. Besides the mass change control specimens defined for each type of exposure and system analyzed, extra specimens totally coated with the chosen protection resin were submitted to the aging environments defined for Phase 2, in order to evaluate the coating influence on the sorption behavior of the material. (ii) Dynamic mechanical analysis (DMA): DMA technique has been used to analyze the viscoelastic performance of GFRP and to assess the glass transition temperature (T g ), in accordance with parts 1 and 5 of ISO 6721 standard [9,1]. Three-point bending type clamp specimens with 5 x 15 x 6 mm were tested at a constant frequency of 1 Hz and strain amplitude of 15 μm, through the use of a Q8 model of TA Instruments. For each batch, three replicates were tested. The analysis was carried out from room temperature up to 2 ºC at a rate of 2 ºC/min. (iii) Mechanical behavior: Five specimens for each aging condition and duration were submitted to different mechanical tests in the longitudinal direction: Shear properties: interlaminar shear tests were conducted in accordance with ASTM D2344 standard [11]. Specimens with 3 x 15 x 5 mm were tested in a 2 mm span at a loading rate of 1 mm/min, using a system from Seidner Form Test, constituted by a hydraulic press with a 1 kn load capacity. Flexural properties: according to ISO standard [12], three-point bending tests were carried out in specimens with 15 x 15 x 5 mm in a 1 mm span and at a loading rate of 2 mm/min. As for the interlaminar shear tests, a Seidner Form Test system was used. Tensile properties: tensile tests were performed in accordance to parts 1 and 5 of ISO 527 standard [13,14] in specimens with 3 x 25 x 5 mm, without end tabs. Tests were conducted in an Instron universal testing machine with a load capacity of 1 kn at a 2 mm/min loading rate. Immediately after being removed from the different exposure environments, the specimens were placed inside polyethylene bags until further testing. The bags were hermetically closed, in order to maintain the moisture content of the material, and placed inside a room with controlled temperature at 2 (±2) ºC. The specimens were stored inside the bags until the testing moment, not experiencing any further conditioning. 3

6 Mass variation (%) B. Silva Instituto Superior Técnico (212) There were exceptions to the procedure described, namely for specimens used to study mass changes and for specimens used to study the reversibility of the degradation the latter were tested after being dried to constant mass. 4. RESULTS AND DISCUSSION 4.1 characterization In order to fully understand the changes during the specimens aging period, physical and mechanical characterization was performed on un-aged batches - results are listed in Table 2. Table 2 Physical and mechanical properties of GFRP unaged profiles Property Method Results Glass fiber content (%) Calcination 68,4 ± 1,81 Mass density (g/cm 3 ) Immersion 1,87 ±,11 T g (ºC) DMA (Flexural vibration non-resonance method) E initial 11,4 ± 11,4 tan δ 146,1 ± 2,3 Mechanical properties Interlaminar shear σ u,sbs (MPa) 38,5 ± 2,7 Flexure σ fu (MPa) 417 ± 65 E f (GPa) 2, ± 6,9 Tension σ tu (MPa) 46 ± 31 E t (GPa) 37,6 ± 2,6 The mechanical performance exhibited in all characterization tests (interlaminar shear, flexural and tensile) revealed a well-defined linear elastic behavior up to failure, which is one of the main features of this material. 4.2 Sorption behavior The mass variations of Phase 1 control specimens that occurred during the aging exposure to immersion, including both demineralized and salt water solutions, for each temperature (2 ºC, 4 º and 6 ºC) are illustrated in Figure 1. Regarding Phase 2 control specimens, Figure 2 shows the evolution of the sorption behavior related to totally (TI) and partially coated (I) specimens, and the mass changes of dried specimens (D), in demineralized water at 2 ºC and 4 ºC and in continuous condensation at 4 ºC. 2, 1,5 1,,5, W-2 W-4 W-6 S-2 S-4 S-6 -, Time (h) Figure 1 Mass variation for different hygrothermal aging conditions for Phase 1 specimens 4

7 Mass variation (%) B. Silva Instituto Superior Técnico (212) 2,5 2, 1,5 1,,5, WI-2 WTI-2 WD-2 WI-4 WTI-4 WD-4 CCI-4 CCTI-4 CCD Time (h) Figure 2 Mass variation for different hygrothermal aging conditions for Phase 2 specimens Regarding Phase 1 control specimens, during an initial short period until 84 hours, the rates of mass uptake increased with temperature showing, roughly, a Fickian response. However, the highest uptakes during the aging time were observed at the lowest temperatures. Analyzing the mass evolution in W-2 and W-4 environments, at 4 ºC the saturation point seemed to be achieved after 7. hours, while at 2 ºC that only happened afterwards, at around 11. hours of exposure. This suggests post-curing effects on the matrix due to temperature, increasing the crosslink density and subsequently decreasing the available volume for water diffusion. Although this phenomenon could substantiate why mass uptakes are higher at lower temperatures, it does not justify the inversion on mass variations verified in all environments. The lack of correlation between temperature and mass uptake levels associated with the cutback mass after a certain time of exposure, especially in aging environments at 6 ºC, implies the disassociation of matrix molecules, possible via hydrolyses reactions. This phenomenon also clarifies why the mass is decreasing to values below the initial ones at W-6 and S-6 environments. The same effects were observed by Robert et al. [6], who in addition have noted for immersions at 6 ºC the beginning of certain effects like thermal expansion, which generally occurs around T g. Also Gu [15] has confirmed through SEM analysis the dissociation of unsaturated polyester resin after immersion in salt water. The values of maximum percentage of weight gain as well as the sorption curve gradients over time were always lower for salt water immersions in comparison with demineralized immersions at similar temperatures, which is in agreement with results reported by Liao et al. [16] and Chin et al. [17]. The presence of NaCl molecules hampers the diffusion of water molecules through the matrix, fostering the sorption delay. Concerning Phase 2, the diffusion rate results for immersion environments indicate decreasing values as the protection degree increases, therefore showing sorption retention by the applied epoxy resin. Thereby, totally isolated specimens presented a lower mass uptake compared to partially isolated specimens and these ones over dried specimens. In continuous condensation, despite the agreement of results for isolated and dried specimens relative to immersion environments, it was the totally isolated specimens which presented the higher mass uptake. This could be due to changes of the epoxy resin from a glassy state to a viscoelastic state, subsequently reducing the diffusion protection properties. 5

8 Tg (E' initial ) [ºC] Tg (E' initial ) [ºC] B. Silva Instituto Superior Técnico (212) Dried specimens, which were tested in the same conditions as Phase 1 control specimens, reveled a superior mass uptake capacity when compared to these last ones, whose sorption evolution was even lower than that of isolated specimens at similar temperatures. This could have happened due to some prior saturation of Phase 1 control specimens, presenting also in their initial mass water molecules weight that occupied part of the free volume. Even though, the resemblance of the mass variation evolution between dried and Phase 1 specimens was notorious. 4.3 Dynamic mechanical analysis Figures 3 and 4 plot, in summary, the T g variation (mean value and standard deviation) against time for all aged batches exposed to the different aging environments of Phases 1 and 2, respectively. The T g results were given by the E initial values of the glass transition region obtained from the dynamic storage modulus (E ) curves W-2 W-4 W-6 S-2 S-4 S-6 3 months 6 months 9 months 12 months 18 months Figure 3 T g variation after Phase 1 aging conditions W-2 W-4 CC-4 Figure 4 T g variation after Phase 2 aging conditions Phase 1 Isolated Dried Regarding Figure 3, immersions at 4 ºC in demineralized water have shown the lowest T g values during the first 9 months of exposure, although an accentuated decrease was noticed just after 3 months at 2 ºC. On the other hand, results attained following 9 months of aging revealed a recovery of the T g values, notably at 6 ºC exposures. In this case, the T g values became even higher than the T g corresponding to the un-aged material. These T g values variation through the exposure time could be associated to post-cure phenomena, 6

9 Tg (E' initial ) [ºC] B. Silva Instituto Superior Técnico (212) induced by the increased temperature, which may also substantiate the initial T g decrease observed at 2 ºC in comparison with higher temperature exposures. Moreover, is important to highlight that after 18 months results for W-6 present a considerable standard deviation. Disregarding the most scattered result, the T g value decreases to 118,4 ºC (with a standard deviation of 1,7 ºC), which is still above the un-aged T g but is now lower than the T g for S-6. Since moisture is one of the main responsible agents for T g decreasing in GFRP profiles, for environments with higher sorption rates one should expect major T g reductions, which is corroborated by the overall results of Phases 1 and 2. Furthermore, results have shown similar T g evolutions between demineralized and salt water. Drying specimens proved to have a positive factor, as it attenuated the degradation process and even showed a considerable T g increase in W-4 and CC-4 environments, due to the partially recovery of initial properties and post-cure phenomena acceleration through the drying period. On the other hand, isolated batches have not presented an improved behavior compared to Phase 1 batches, excluding the immersion at 2 ºC. During DMA analysis, specimens with protective coating E curves showed generally two distinct slopes due to the different T g of the epoxy resin and the GFRP material. Figure 5 shows the T g variation after 12 months of natural aging to Lisbon climatic conditions Natural aging Figure 5 T g variation after 12 months of natural aging Following 12 months of natural aging, the material suffered a 9% T g reduction relative to the un-aged batch, a similar value to those observed after 3 months of exposure in all salt water environments and in demineralized water at 6 ºC. 4.4 Mechanical behavior Interlaminar shear strength Figures 6 and 7 illustrate the variation of the interlaminar shear strength as a function of time, for different aging conditions of Phases 1 and 2, respectively. Results obtained for natural aging are presented in Figure 8. 7

10 Interlaminar shear strengh (MPa) Interlaminar shear strengh (MPa) Interlaminar shear strengh (MPa) B. Silva Instituto Superior Técnico (212) months 6 months 9 months 12 months 18 months W-2 W-4 W-6 S-2 S-4 S-6 Figure 6 Interlaminar shear strength of Phase 1 aging conditions W-2 W-4 CC-4 Figure 7 Interlaminar shear strength of Phase 2 aging conditions Phase 1 Isolated Dried Natural aging Figure 8 Interlaminar shear strength after 12 months of natural aging Interlaminar shear strength showed a higher decrease in material aged in immersion in demineralized water than in salt water. Furthermore, the temperature demonstrated to directly influence the interlaminar shear resistance of the material, which decreases for higher temperature of exposure. Phase 1 results suggest post-cure effects due to a general strength regain after 9 months of exposure to aging conditions. Despite some slight recover, the strength decreased around 43% in W-6 and S-6 environments after 18 months, possibly associated to the matrix dissolution due to hydrolysis reactions, which leads to fiber-matrix adhesion reduction and delamination. Dried specimens presented similar results than Phase 1 batches following 6 months of exposure to equivalent environments, except for 4 ºC demineralized water immersion. However, the sorption rates were notoriously higher for dried specimens in comparison to Phase 1 specimens, which could have accelerated 8

11 Flexural modulus (GPa) Flexural strengh (MPa) B. Silva Instituto Superior Técnico (212) the degradation effects due to faster moisture diffusion through the matrix. In this case, major regain of properties could have occurred if there was a direct correlation of the degradation process with the sorption behavior, during the aging period. Isolated specimens, even considering the same reason mentioned for dried specimens, did not show an increase of resistance through aging relative to Phase 1 batches, suggesting a lower impact of lateral coating in interlaminar shear strength. The strength of natural aged batches had a slight decrease, considerably lower than those observed following 3 months of exposure to Phase 1 aging conditions Flexural properties Results obtained from flexural tests, namely the flexural strength and modulus as a function of time for the different aging conditions are presented in Figures 9 to W-2 W-4 W-6 S-2 S-4 S-6 Figure 9 Flexural strength of Phase 1 aging conditions : 2nd batch 3 months 6 months 9 months 12 months 18 months W-2 W-4 W-6 S-2 S-4 S-6 : 2nd batch 3 months 6 months 9 months 12 months 18 months Figure 1 Flexural modulus of Phase 1 aging conditions Results show an overall tendency of flexural strength and modulus degradation over time, with signs of post-cure effects after 12 months of aging. Moreover, salt water environments tend to be less deteriorative through time than demineralized water environments, which was also corroborated by Chen et al. [18]. Regarding the flexural modulus values at 9 months of exposure, a general accentuated increase is noticeable. However, following 12 months overall results continue to exhibit the decreasing tendency observed until 6 months of exposure, suggesting that 9 months values may result from an external factor, like some variation occurred during the mechanical tests, rather than any degradation phenomena due to environmental agents. Regardless, it is important to note the considerable standard deviation values of the flexural modulus results. 9

12 Flexural strengh (MPa) Flexural modulus (GPa) Flexural modulus (GPa) Flexural strengh (MPa) B. Silva Instituto Superior Técnico (212) A second batch of un-aged specimens were tested in order to validate if there was a real overall flexural strength increase after 3 months of aging, nevertheless, it is unclear which un-aged batch presents the more realistic value as the standard deviations are significant on both. However, if the most scattered value from the flexural strength average in both batches is discarded, the two achieve an approximate result of 445 MPa, which is probably a more realistic value and still, higher than the 3 months results : 2nd batch Phase 1 Isolated Dried W-2 W-4 CC-4 Figure 11 Flexural strength of Phase 2 aging conditions W-2 W-4 CC-4 : 2nd batch Phase 1 Isolated Dried Figure 12 Flexural modulus of Phase 2 aging conditions / 2nd batch Natural aging / 2nd batch Natural aging Figure 13 Flexural strength (left) and flexural modulus (right) after 12 months of natural aging Phase 2 environments revealed that coated batches experience an overall flexural strength loss similar to Phase 1 batches. However, the overall flexural modulus behavior was more similar to dried batches performance instead, with the exception of CC-4 environment. Dried batches also showed a partial strength and modulus regain capability. Regarding natural aging, Lisbon climatic conditions caused negligible flexural strength loss and a flexural modulus reduction similar to 3 months aged batches at W-2, W-4, W-6 and S-2 environments. 1

13 Tensile strength (MPa) Tensile modulus (GPa) Tensile strength (MPa) B. Silva Instituto Superior Técnico (212) Tensile properties Figures 14 to 18 illustrate the variation of the tensile strength and the tensile modulus as a function of time, for the different aging conditions defined in Table months 6 months 9 months 1 W-2 W-4 W-6 S-2 S-4 S-6 Figure 14 Tensile strength of Phase 1 aging conditions 12 months 18 months months 6 months 9 months 1 W-2 W-4 W-6 S-2 S-4 S-6 Figure 15 Tensile modulus of Phase 1 aging conditions 12 months 18 months As for flexural properties, results show an overall tendency of tensile strength and tensile modulus degradation over time. The same post-cure effects are noticeable, in this case, after 9 months of exposure. Salt water tends to be less aggressive than demineralized water, which is also correlated with the sorption rates presented in Figure 1. Moreover, temperature demonstrates to directly influence degradation through time. The higher tensile strength decrease occurred in demineralized water at 6 ºC with a 25% reduction after 18 months of aging. The tensile modulus variation suggested to be more related with the exposure time than with the type of solution. Immersions in salt water at 2 ºC and 4 ºC present a modulus increase after 3 and 6 months of aging, and the same is observed at 6 ºC after 6 months of exposure. However, the standard deviations associated to these results are considerable Phase 1 Isolated W-2 W-4 CC-4 Figure 16 Tensile strength of Phase 2 aging conditions 11

14 Tensile strength (MPa) Tensile modulus (GPa) Tensile modulus (GPa) B. Silva Instituto Superior Técnico (212) Phase 1 Isolated W-2 W-4 CC-4 Figure 17 Tensile modulus of Phase 2 aging conditions Natural aging Natural aging Figure 18 Tensile strength (left) and tensile modulus (right) after 12 months of natural aging The isolated specimens demonstrate a lower decrease of tensile strength in all Phase 2 environments compared to Phase 1 batches. Nevertheless, isolated specimens have not showed any resistant benefit during interlaminar shear and flexural strength tests and further, have presented a superior sorption rate than Phase 1 specimens. Therefore, it is plausible to reconsider if the coated resin has not provided an additional tensile resistance to the tested specimens. Regarding the natural aged batch, after 12 months of exposure the tensile strength reduced 1% while the tensile modulus decrease was around 19%. 5. CONCLUSIONS This paper presents new achievements of an ongoing experimental research. The main objective of this study was successfully achieved, leading to the determination of the mechanical and physical variations suffered by the GFRP pultruded profiles under different aging conditions through time. Based on the results obtained, the following conclusions can be addressed: (i) The sorption behavior confirmed to be dependent of the immersion solution content and of temperature, mainly during the initial states. However, immersions at 6 ºC highlighted mass losses after 1.2 hours of exposure, leading to lower mass values compared to the un-aged material after 13. hours in demineralized water immersion and after 16. hours in salt water immersion. The same phenomenon is notable at 4 ºC immersions, although afterwards a decreasing rate is initiated after 9. hours in demineralized water and past 15. hours in salt water. The matrix dissolution is strongly related to hydrolysis; still post-cure effects are also notorious at higher temperatures due to the lower saturation rates. 12

15 B. Silva Instituto Superior Técnico (212) (ii) The coating protection appears to reduce the moisture diffusion, with greater expression on totally isolated specimens, when compared with the sorption behavior of dried specimens. Moreover, the mass uptake observed on totally isolated specimens reveals that the elected protective resin hindered the moisture diffusion but did not isolate the material, according to the proposed purpose. However, Phase 1 control specimens showed lower mass uptake rates than isolated specimens which does not clarify if the unprotected specimens provide indeed conservative results. (iii) DMA analysis revealed that temperature and moisture uptake play both an important role on the material viscoelastic behavior. Phase 1 batches presented a generally decreasing T g during the first 9 months, which indicates plasticization effects. However, after this period, a regain in glass transition properties was observed, possible due to post-cure phenomenon. The isolated specimens showed negligible differences compared to Phase 1 batches, with the exception of immersion at 2 ºC in demineralized water, for which the isolated batch presented a higher T g value. Nevertheless, isolated specimens revealed also superior mass uptake rates possibly with large influence in the degradation process. Dried specimens presented T g gain over time, reaching higher values than the initial one in W-4 and CC-4 environments. These results from partial recovery of properties associated to post-cure phenomenon during the drying process. (iv) All mechanical tests showed the linear elastic behavior of the material until rupture. Mechanical behavior showed a decreasing performance related to the solution content and temperature. Salt water immersions caused lower performance variations compared to demineralized water immersions, corroborated by the mass uptake variations. In addition, increasing temperature generally resulted on higher strength variations. At some time, in all tests, the material properties variation showed gains implying post-cure effects in the matrix. Isolated specimens in general did not present enhanced results related to Phase 1 specimens, although one could expect such improvement owing to the lowest sorption rates observed on the former. Dried batches showed overall notorious properties recovery, associated in some cases, to post-cure phenomenon during the drying process. The natural aged batch mechanical behavior was better than the results obtained for Phase 1 batches after 3 months of immersion in demineralized water. Comparing with Phase 2 batches only dried specimens at 2 ºC immersion showed higher strength and merely on the tensile test. Hereupon, natural aging results correlation with accelerated aging results suggests that the values observed for the different accelerated aging environments could be equivalent to years of natural aging to Lisbon climatic conditions. 6. REFERENCES [1] S. Cabral-Fonseca, J.R. Correia, R. Costa, A. Carneiro, M. Paula Rodrigues, M. Isabel Eusébio, F.A. Branco, Environmental degradation of GFRP pultruded profiles made of polyester and vinylester resins, 15 th International Conference on Composite Structures (Editor: A.J.M. Ferreira), 1-17, Porto, 29. [2] V.M. Karbhari, J.W. Chin, D. Hunston, B. Benmokrane, T. Juska, R. Morgan, J.J. Lesko, U. Sorathia, D. Reynaud, Durability gap analysis for fibre-reinforced polymer composites in civil infrastructure, Journal of Composites for Construction, vol. 7, issue 3, ,

16 B. Silva Instituto Superior Técnico (212) [3] V.M. Karbhari, Durability of composites for civil structural applications, Woodhead Publishing Limited, Cambridge, England, July 27. [4] J.R. Correia, GFRP pultruded profiles. GFRP-Concrete composite beams applied in construction, MSc Dissertation in Construction, Instituto Superior Técnico, Technical University of Lisbon, March 24. [5] H. Kim, Y. Park, Y. You, C. Moon, Short term durability test for GFRP rods under various environmental conditions, Composite Structures, vol. 83, issue 1, 37-47, March 28. [6] M. Robert, P. Wang, P. Cousin, B. Benmokrane, Temperature as an accelerating factor for long-term durability testing FRPs: should there be any limitations?, Journal of Composites for Construction, vol.14, issue 4, , July/August 21. [7] R. Costa, Durability of GFRP pultruded profiles made of polyester resin, MSc Dissertation in Civil Engineering, Instituto Superior Técnico, Technical University of Lisbon, November 29. [8] ASTM D 5229 Standard test method for moisture absorption properties and equilibrium conditioning of polymer matrix composite materials, American Society for Testing and Materials, West Conshohocken, PA, 24. [9] ISO , Plastics Determination of dynamic mechanical properties Part 1: General principles, International Organization for Standardization, Genève, [1] ISO , Plastics Determination of dynamic mechanical properties Part 5: Flexural vibration Non-resonance method, International Organization for Standardization, Genève, [11] ASTM D 2344, Standard test method for short-beam strength of polymer matrix composite materials and their laminates, American Society for Testing and Materials, West Conshohocken, PA, 2. [12] ISO 14125, Fibre-reinforced plastic composites Determination of flexural properties, International Organization for Standardization, Genève, [13] ISO 527 1, Plastics Determination of tensile properties Part 1: General principles, International Organization for Standardization, Genève, [14] ISO 527 5, Plastics Determination of tensile properties Part 5: Test conditions for unidirectional fibre-reinforced composites, International Organization for Standardization, Genève, [15] H. Gu, Behaviours of glass fibre/unsaturated polyester composites under seawater environment Materials & Design, vol. 3, issue 4, , April

17 B. Silva Instituto Superior Técnico (212) [16] K. Liao, C.R. Schultheisz, D.L. Hunston, Effects of environmental aging on the properties of pultruded GFRP, Composites Part B, vol. 3, issue 5, , July [17] J.W. Chin, K. Aouadi, M.R. Haight, W.L. Hughes, T. Nguyen, Effects of water, salt solutions and simulated concrete pore solution on the properties of composite matrix resins used in civil engineering applications, Polymer Composites, vol. 22, issue 2, , April 21. [18] Y. Chen, J.F. Davalos, I. Ray, H.Y. Kim, Accelerated aging tests of evaluations of durability performance of FRP reinforcing bars for concrete structures, Composite Structures, vol. 78, issue 1, , March