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Effect of marine exposure on fracture properties of epoxy concretes
Polymer Testing 24 (2005) 121–125 www.elsevier.com/locate/polytest
Material Behaviour
Effect of marine exposure on fracture properties of epoxy concretes J.M.L. Reis, A.J.M. Ferreira* Departamento de Engenharia Mecaˆnica e Gesta˜o Industrial, Faculdade de Engenharia da Universidade do Porto, Rua Dr Roberto Frias, Porto 4200-465, Portugal Received 7 May 2004; accepted 16 June 2004
Abstract This paper deals with the evaluation of the fracture properties of epoxy polymer concrete under marine exposure. Plain and fiber reinforced epoxy concretes are considered. The stress intensity factor KIc and the energy of fracture Gf are measured for two different exposure periods, Spring–Summer and Autumn–Winter. We study the influence of the period of the year and the exposure time on the fracture properties of epoxy concrete. The results show that the Spring–Summer exposure period brings strong deterioration in such fracture properties. q 2004 Elsevier Ltd. All rights reserved. Keywords : Polymer concrete; Fracture mechanics; Marine exposure
1. Introduction Durability is still one of the most important factors for service life of Polymer Concrete; both in terms of economy and safety. The most reliable way of assessing the durability of a polymer concrete structure is to study the performance under natural exposure conditions. This of course may not be applicable for most design situations since it requires in principle the same time as the planned service life of the structure in question. For many years, field exposure stations have been used all over the world for the purpose of producing durable concrete structures to last under various severe conditions for at least a century. One of the best-known international exposure stations is probably Treat Island, Maine, USA. The earth surface is degraded due to physical and chemical processes as a result of exposure to the weather. The proportion and rate of degradation depends on the nature of the material:
* Corresponding author. Tel.: C351-225081705; fax: C351229537352. E-mail address: [email protected] (A.J.M. Ferreira). 0142-9418/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2004.06.002
some rocks can withstand millions of years and some organic polymers suffer large property changes within days. Durability of the material depends on the time and type of exposure. Exposure to UV radiation, temperature, wind or rain can bring large variations in properties. There is no climatic classification in terms of material degradation, although the main climatic components which cause degradation are solar radiation, rain, humidity, temperature, wind, dust and contamination [1]. Tropical climates are the most aggressive as they combine high temperature, UV radiation and high humidity. There are several countries, which have their atmosphere data recorded for several years. In our case, the reference used in this paper is the Aveiro University meteorological tower. In this paper, the fracture properties of epoxy polymer concrete and fiber reinforced polymer concrete were investigated by three-point bending tests under the two-parameter model (TPM) suggested in RILEM recommendations [2]. This method evaluates two size-independent fracture parameters; the stress intensity factor, KIc and the critical crack tip opening displacement CTODc. Another fracture parameter calculated from these tests was the fracture energy Gf. The fracture energy is also calculated according to RILEM recommendations [3].
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J.M.L. Reis, A.J.M. Ferreira / Polymer Testing 24 (2005) 121–125
Fig. 1. Aveiro University Meteorological Tower.
Fig. 2. Aveiro temperature during the studied year.
J.M.L. Reis, A.J.M. Ferreira / Polymer Testing 24 (2005) 121–125
Fig. 3. Load vs. CMOD test results for epoxy polymer concrete.
123
Fig. 5. Load vs. CMOD test results for carbon fiber epoxy polymer concrete.
2. Experimental program The meteorological tower in the Aveiro University, Fig. 1, which provides records of temperature and humidity. Fig. 2 shows the temperature profile during the exposition period (1 year). The weather conditions recorded in Aveiro, were as follows: † lowest temperature in January (5.9%, 77% humidity) † highest temperature in September (20.3%, 66% humidity). Epoxy Polymer Concrete and fiber reinforced epoxy were manufactured according to RILEM standards [4] to perform three-point bending tests. After a 7-day cure, specimens were notched with a diamond saw and placed on the roof of a house near Aveiro, a city 60 km south of Porto, nearby the ocean. The samples faced Southwest with the notch free from touching any surface. The material deterioration and structural performance were investigated in a real situation of exposure in two different year periods, Spring/Summer and Autumn/Winter. The relation between different year period, exposure time and load-bearing
Fig. 4. Load vs. CMOD test results for glass fiber epoxy polymer concrete.
capacity of deteriorated Polymer Concrete was studied and fracture mechanics of the specimens are discussed. The formulations of the Polymer Concrete, which consist in essence of an aggregate blend mixed with a polymer resin in convenient proportions as previously studied by the authors [5,6]. The materials used to manufacture the epoxy polymer concrete were a siliceous foundry sand with a uniform granule size, and average diameter of 245 m, at 80% by mass and an epoxy resin system based on a diglycidyl ether bisphenol A and an aliphatic amine hardener. The resin system was processed with a maximum mix ratio to hardener of 2:1, at 20% by mass. The reinforcement used in this research was 1%, by mass, of unsized E-glass fiber, soaked in a 2% Silane A174 solution and 2%, by mass, of carbon fiber with epoxy sizing. All fibers had an average length of 6 mm.
3. Results The results for Spring–Summer and Autumn–Winter exposure cycles, are shown in Figs. 3–5, where Load–CMOD
Fig. 6. Load vs. mid-span displacement test results for epoxy polymer concrete.
124
J.M.L. Reis, A.J.M. Ferreira / Polymer Testing 24 (2005) 121–125 Table 2 Season exposure results for glass fiber reinforced polymer concrete pffiffiffiffi CTODc (mm) Gf (N/m) FVE KIc Mpa m specimens Reference
Autumn/ Winter
Spring/ Summer Fig. 7. Load vs. mid-span displacement test results for glass fiber epoxy polymer concrete.
Fig. 8. Load vs. mid-span displacement test results for carbon fiber epoxy polymer concrete.
curves are displayed. The energy of fracture, Gf, was calculated from the load vs mid-span displacement curves, which are presented in Figs. 6–8. The numerical results for KIc, CTODc and Gf are presented in Tables 1–3. As can be
2.412 2.379 2.576 2.503
0.013 0.025 0.016 0.018
11.575 10.992 11.132 12.838
2.512 2.584 2.404
0.004 0.009 0.015
17.600 15.529 14.126
2.574 2.611
0.022 0.024
12.151 12.467
seen from such results all samples present some form of degradation. As shown in Tables 1–3, the Spring/Summer cycle deteriorates the stress intensity factor, KIc, by 14.8%. For glass fiber epoxy concrete, the KIc deterioration is of the same order as for plain epoxy concrete. The energy of fracture is degraded by 15% when compared to the Autumn–Winter cycle. The increase in the Autumn–Winter cycle is 37% whereas in Spring–Summer it is 15%. For Carbon fiber reinforcement the KIc decreases 7% and the Gf decreases 16% for the Spring–Summer cycle. When compared to reference results, carbon fiber reinforcement produces a decrease of 25% in KIc in the Autumn–Winter cycle and 31% in the Spring–Summer cycle. The energy of fracture increases by 20% in the Autumn– Winter cycle and 1.2% in the Spring–Summer cycle.
Table 1 Season exposure results for epoxy polymer concrete pffiffiffiffi CTODc (mm) Gf (N/m) Epoxy KIc Mpa m specimens
Table 3 Season exposure results for carbon fiber reinforced polymer concrete pffiffiffiffi CTODc (mm) Gf (N/m) FCE KIc Mpa m specimens
Reference
Reference
Autumn/ Winter
Spring/ Summer
2.323 2.344 2.267 2.376
0.008 0.023 0.015 0.005
8.429 7.012 8.183 8.695
2.291 2.254 1.834
0.009 0.007 0.006
9.171 8.904 8.084
1.953 2.108
0.014 0.013
8.373 8.425
Autumn/ Winter
Spring/ Summer
2.711 2.586 2.925 1.954
0.038 0.059 0.032 0.007
28.823 28.857 29.238 37.464
2.045 2.141 1.765
0.066 0.015 0.063
38.846 28.181 33.934
1.916 2.034
0.030 0.017
27.373 26.662
J.M.L. Reis, A.J.M. Ferreira / Polymer Testing 24 (2005) 121–125
4. Conclusions With this experimental plan, we tried to check the reliability of epoxy concretes when exposed to an aggressive environment. The environmental site seems to be adequate for this type of test, with a combination of sun, wind, dust and marine environments. The Spring–Summer exposure period is the most aggressive for epoxy concretes, due mainly to temperature and UV radiation. Glass fiber reinforcement produces a larger improvement in fracture properties than carbon fiber reinforcement. This may be explained by the sensitivity to UV radiation, as in other results [7] carbon fiber has shown to be better than glass fiber reinforcement, even at elevated temperature and humidity [7].
References [1] A. Davis, D. Sims, Weathering of Polymers, Applied Science Publishers, Essex, UK, 1983.
125
[2] RILEM, TC 50-FM, Determination of the fracture parameters (KSIC and CTODC) of plain concrete using three-point bend tests on notched beams, Materials and Structures 23(138) 457– 460. [3] RILEM, TC 50-FMC, Fracture mechanics of concrete, determination of fracture energy of mortar and concrete by means of three-point bend test on notched beams, RILEM recommendation, Materials and Structures 18 (1995) 407–413. [4] RILEM TC/113 PC-2, Technical Committee, 113, Method of making polymer concrete and mortar specimens, Symposium on Properties and Test Methods for Concrete-Polymer Composites, Oostende, Belgium, 1995. [5] J.M.L. Reis, A.J.M. Ferreira, Fracture Properties of Polymer Concrete 8th Portuguese Conference on Fracture, Vila Real, Portugal 2002; 417–421. [6] J.M.L. Reis, A.J.M. Ferreira, Fracture behaviour of glass fibre reinforced polymer concrete, Polymer Testing 22 (2) (2003) 149–153. [7] Y. Shan, K. Liao, Environmental fatigue behavior and life prediction of undirectional glass-carbon/epoxy hybrid composites, International Journal of Fatigue 24 (2002) 847–859.
Material Behaviour
Effect of marine exposure on fracture properties of epoxy concretes J.M.L. Reis, A.J.M. Ferreira* Departamento de Engenharia Mecaˆnica e Gesta˜o Industrial, Faculdade de Engenharia da Universidade do Porto, Rua Dr Roberto Frias, Porto 4200-465, Portugal Received 7 May 2004; accepted 16 June 2004
Abstract This paper deals with the evaluation of the fracture properties of epoxy polymer concrete under marine exposure. Plain and fiber reinforced epoxy concretes are considered. The stress intensity factor KIc and the energy of fracture Gf are measured for two different exposure periods, Spring–Summer and Autumn–Winter. We study the influence of the period of the year and the exposure time on the fracture properties of epoxy concrete. The results show that the Spring–Summer exposure period brings strong deterioration in such fracture properties. q 2004 Elsevier Ltd. All rights reserved. Keywords : Polymer concrete; Fracture mechanics; Marine exposure
1. Introduction Durability is still one of the most important factors for service life of Polymer Concrete; both in terms of economy and safety. The most reliable way of assessing the durability of a polymer concrete structure is to study the performance under natural exposure conditions. This of course may not be applicable for most design situations since it requires in principle the same time as the planned service life of the structure in question. For many years, field exposure stations have been used all over the world for the purpose of producing durable concrete structures to last under various severe conditions for at least a century. One of the best-known international exposure stations is probably Treat Island, Maine, USA. The earth surface is degraded due to physical and chemical processes as a result of exposure to the weather. The proportion and rate of degradation depends on the nature of the material:
* Corresponding author. Tel.: C351-225081705; fax: C351229537352. E-mail address: [email protected] (A.J.M. Ferreira). 0142-9418/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2004.06.002
some rocks can withstand millions of years and some organic polymers suffer large property changes within days. Durability of the material depends on the time and type of exposure. Exposure to UV radiation, temperature, wind or rain can bring large variations in properties. There is no climatic classification in terms of material degradation, although the main climatic components which cause degradation are solar radiation, rain, humidity, temperature, wind, dust and contamination [1]. Tropical climates are the most aggressive as they combine high temperature, UV radiation and high humidity. There are several countries, which have their atmosphere data recorded for several years. In our case, the reference used in this paper is the Aveiro University meteorological tower. In this paper, the fracture properties of epoxy polymer concrete and fiber reinforced polymer concrete were investigated by three-point bending tests under the two-parameter model (TPM) suggested in RILEM recommendations [2]. This method evaluates two size-independent fracture parameters; the stress intensity factor, KIc and the critical crack tip opening displacement CTODc. Another fracture parameter calculated from these tests was the fracture energy Gf. The fracture energy is also calculated according to RILEM recommendations [3].
122
J.M.L. Reis, A.J.M. Ferreira / Polymer Testing 24 (2005) 121–125
Fig. 1. Aveiro University Meteorological Tower.
Fig. 2. Aveiro temperature during the studied year.
J.M.L. Reis, A.J.M. Ferreira / Polymer Testing 24 (2005) 121–125
Fig. 3. Load vs. CMOD test results for epoxy polymer concrete.
123
Fig. 5. Load vs. CMOD test results for carbon fiber epoxy polymer concrete.
2. Experimental program The meteorological tower in the Aveiro University, Fig. 1, which provides records of temperature and humidity. Fig. 2 shows the temperature profile during the exposition period (1 year). The weather conditions recorded in Aveiro, were as follows: † lowest temperature in January (5.9%, 77% humidity) † highest temperature in September (20.3%, 66% humidity). Epoxy Polymer Concrete and fiber reinforced epoxy were manufactured according to RILEM standards [4] to perform three-point bending tests. After a 7-day cure, specimens were notched with a diamond saw and placed on the roof of a house near Aveiro, a city 60 km south of Porto, nearby the ocean. The samples faced Southwest with the notch free from touching any surface. The material deterioration and structural performance were investigated in a real situation of exposure in two different year periods, Spring/Summer and Autumn/Winter. The relation between different year period, exposure time and load-bearing
Fig. 4. Load vs. CMOD test results for glass fiber epoxy polymer concrete.
capacity of deteriorated Polymer Concrete was studied and fracture mechanics of the specimens are discussed. The formulations of the Polymer Concrete, which consist in essence of an aggregate blend mixed with a polymer resin in convenient proportions as previously studied by the authors [5,6]. The materials used to manufacture the epoxy polymer concrete were a siliceous foundry sand with a uniform granule size, and average diameter of 245 m, at 80% by mass and an epoxy resin system based on a diglycidyl ether bisphenol A and an aliphatic amine hardener. The resin system was processed with a maximum mix ratio to hardener of 2:1, at 20% by mass. The reinforcement used in this research was 1%, by mass, of unsized E-glass fiber, soaked in a 2% Silane A174 solution and 2%, by mass, of carbon fiber with epoxy sizing. All fibers had an average length of 6 mm.
3. Results The results for Spring–Summer and Autumn–Winter exposure cycles, are shown in Figs. 3–5, where Load–CMOD
Fig. 6. Load vs. mid-span displacement test results for epoxy polymer concrete.
124
J.M.L. Reis, A.J.M. Ferreira / Polymer Testing 24 (2005) 121–125 Table 2 Season exposure results for glass fiber reinforced polymer concrete pffiffiffiffi CTODc (mm) Gf (N/m) FVE KIc Mpa m specimens Reference
Autumn/ Winter
Spring/ Summer Fig. 7. Load vs. mid-span displacement test results for glass fiber epoxy polymer concrete.
Fig. 8. Load vs. mid-span displacement test results for carbon fiber epoxy polymer concrete.
curves are displayed. The energy of fracture, Gf, was calculated from the load vs mid-span displacement curves, which are presented in Figs. 6–8. The numerical results for KIc, CTODc and Gf are presented in Tables 1–3. As can be
2.412 2.379 2.576 2.503
0.013 0.025 0.016 0.018
11.575 10.992 11.132 12.838
2.512 2.584 2.404
0.004 0.009 0.015
17.600 15.529 14.126
2.574 2.611
0.022 0.024
12.151 12.467
seen from such results all samples present some form of degradation. As shown in Tables 1–3, the Spring/Summer cycle deteriorates the stress intensity factor, KIc, by 14.8%. For glass fiber epoxy concrete, the KIc deterioration is of the same order as for plain epoxy concrete. The energy of fracture is degraded by 15% when compared to the Autumn–Winter cycle. The increase in the Autumn–Winter cycle is 37% whereas in Spring–Summer it is 15%. For Carbon fiber reinforcement the KIc decreases 7% and the Gf decreases 16% for the Spring–Summer cycle. When compared to reference results, carbon fiber reinforcement produces a decrease of 25% in KIc in the Autumn–Winter cycle and 31% in the Spring–Summer cycle. The energy of fracture increases by 20% in the Autumn– Winter cycle and 1.2% in the Spring–Summer cycle.
Table 1 Season exposure results for epoxy polymer concrete pffiffiffiffi CTODc (mm) Gf (N/m) Epoxy KIc Mpa m specimens
Table 3 Season exposure results for carbon fiber reinforced polymer concrete pffiffiffiffi CTODc (mm) Gf (N/m) FCE KIc Mpa m specimens
Reference
Reference
Autumn/ Winter
Spring/ Summer
2.323 2.344 2.267 2.376
0.008 0.023 0.015 0.005
8.429 7.012 8.183 8.695
2.291 2.254 1.834
0.009 0.007 0.006
9.171 8.904 8.084
1.953 2.108
0.014 0.013
8.373 8.425
Autumn/ Winter
Spring/ Summer
2.711 2.586 2.925 1.954
0.038 0.059 0.032 0.007
28.823 28.857 29.238 37.464
2.045 2.141 1.765
0.066 0.015 0.063
38.846 28.181 33.934
1.916 2.034
0.030 0.017
27.373 26.662
J.M.L. Reis, A.J.M. Ferreira / Polymer Testing 24 (2005) 121–125
4. Conclusions With this experimental plan, we tried to check the reliability of epoxy concretes when exposed to an aggressive environment. The environmental site seems to be adequate for this type of test, with a combination of sun, wind, dust and marine environments. The Spring–Summer exposure period is the most aggressive for epoxy concretes, due mainly to temperature and UV radiation. Glass fiber reinforcement produces a larger improvement in fracture properties than carbon fiber reinforcement. This may be explained by the sensitivity to UV radiation, as in other results [7] carbon fiber has shown to be better than glass fiber reinforcement, even at elevated temperature and humidity [7].
References [1] A. Davis, D. Sims, Weathering of Polymers, Applied Science Publishers, Essex, UK, 1983.
125
[2] RILEM, TC 50-FM, Determination of the fracture parameters (KSIC and CTODC) of plain concrete using three-point bend tests on notched beams, Materials and Structures 23(138) 457– 460. [3] RILEM, TC 50-FMC, Fracture mechanics of concrete, determination of fracture energy of mortar and concrete by means of three-point bend test on notched beams, RILEM recommendation, Materials and Structures 18 (1995) 407–413. [4] RILEM TC/113 PC-2, Technical Committee, 113, Method of making polymer concrete and mortar specimens, Symposium on Properties and Test Methods for Concrete-Polymer Composites, Oostende, Belgium, 1995. [5] J.M.L. Reis, A.J.M. Ferreira, Fracture Properties of Polymer Concrete 8th Portuguese Conference on Fracture, Vila Real, Portugal 2002; 417–421. [6] J.M.L. Reis, A.J.M. Ferreira, Fracture behaviour of glass fibre reinforced polymer concrete, Polymer Testing 22 (2) (2003) 149–153. [7] Y. Shan, K. Liao, Environmental fatigue behavior and life prediction of undirectional glass-carbon/epoxy hybrid composites, International Journal of Fatigue 24 (2002) 847–859.