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A study on improvement of durability of reinforced concrete structures mixed with Natural Inorganic Minerals
Construction and Building Materials 25 (2011) 4263–4270
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
A study on improvement of durability of reinforced concrete structures mixed with Natural Inorganic Minerals Sung-Ho Tae a,1, Rak-Hyun Kim b,⇑ a b
School of Architecture & Architectural Eng., Hanyang University 1271, Sa 3-dong, Sangrok-gu, Ansan, Gyeonggi-do 426-791, Republic of Korea Department of Sustainable Architectural Eng., Hanyang University 1271, Sa 3-dong, Sangrok-gu, Ansan, Gyeonggi-do 426-791, Republic of Korea
a r t i c l e
i n f o
Article history: Received 2 April 2010 Received in revised form 25 April 2011 Accepted 25 April 2011
Keywords: Natural Inorganic Minerals Carbonation Corrosion resistance Corrosion rate
a b s t r a c t As a fundamental study on the corrosion resistance of reinforced concrete structures using Natural Inorganic Minerals exposed to carbonation environment. The test specimens were concrete(W/C = 60%) with Natural Inorganic Minerals content of 0% and 10%. Accelerated arbonation and autoclave corrosion accelerated curing were then conducted with them. The corrosion resistance of steel in concrete with Natural Inorganic Minerals content of 0% and 10% was examined by corrosion form, half-cell potential, polarization resistance, corrosion area and weight loss after 24 h of autoclave corrosion accelerated curing. The results of the study showed that as for steel in concrete with Natural Inorganic Minerals content of 10%, the corrosion resistance was more excellent than steel in concrete with Natural Inorganic Minerals content of 0%. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Reinforced concrete in general is a construction material with excellent durability and economic feasibility and is being used for a wide variety of structures. The number of year of its use had also been recognized as semi-permanent. However, if design and construction inappropriate for the conditions of use are performed, sound performance is lost before reaching the objective number of years and the structure experiences early deterioration. Such early deterioration of structures has a large influence on the increase in maintenance cost for repairmen and reinforcement, occurrence of construction wastes from remodeling and dismantlement, and effects on global and local environments. Economic loss caused by corrosion of reinforced concrete structures is about 4% of GNP in the United States of 70 billion dollars. In case of our country, a huge economic loss of about 4–5% of GNP is expected to occur from corrosion of reinforced concrete, considering industrial structure of our country with intensive heavy industry. Though there are various factors of such deterioration of reinforced concrete structure, all factors ultimately experience occurrence of cracks in the concrete from corrosion expansion of reinforcement and end up with reduction in load-carrying capacity of the structure [1]. Over 100 years of life span is currently being demanded for reinforced concrete structures, and development of efficient ⇑ Corresponding author. Tel.: +82 31 436 8125; fax: +82 31 406 7118. E-mail addresses: [email protected] (S.-H. Tae), [email protected] (R.-H. Kim). 1 Tel.: +82 31 400 3740; fax: +82 31 406 7118. 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.04.070
and scientific durability improvement technology that can secure long life span with exposure to various corrosion conditions such as sea wind and neutralization is in urgent need [2,3]. In this study, corrosion resistance of reinforcement in the concrete with mixing of Natural Inorganic Compound (called reMEUM hereafter) was evaluated by performing a corrosion acceleration experiment with simulation of a neutralized environment for concretes with mixture of various particle sizes of reMEUM that compose minute organizational structure from air gap mending effect of acicular hydrate products and micro filler effect with excellent Pozzolanic reaction. In addition, electrochemical characteristics of reinforcements deduced from corrosion acceleration experiment under neutralized conditions was used to evaluate durability improvement of reinforced concrete structures with reMEUM mixture under neutralized conditions. 2. reMEUM composite The reMEUM composite used in this study is composed of the main ingredient TVP natural mineral (a natural inorganic mineral that includes tuff, volcanic ash and perlite) extremely effective for improvement in watertightness of concrete and of supplementary ingredients including siliceous powder, pozzolan substances, potential hydroponic substances and sulphate. It is a mixture material for watertight concrete produced using anion surfactant and fatty acid salts. According to existing studies [4], reMEUM concretes compose more compact minute structure in comparison to normal concretes. There are reports that reMEUM concrete is not only superior in terms of watertightness of the concrete but also
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excellent in reduction effect on creation of cracks from suppression of drying shrinkage and improvement in compressive strength. Table 1 shows basic characteristics of reMEUM composite. In addition, Fig. 1 shows the actual photograph of reMEUM composite and enlarged photograph. 3. Experiment outline In order to evaluate corrosion resistance of reMEUM concrete on carbonation, concrete specimens of 60% water-binder ratio (W/B) with 0% and 10% reMEUM were made and carbonated accelerated curing (temperature of 40 °C, relative humidity of 60% and 10% concentration of CO2) was performed. Then, autoclave corrosion acceleration experiment was performed to evaluate corrosion resistance of reinforcement laid in the reMEUM concrete by measuring corrosion form (corrosion patterns in the upper and lower parts of reinforcement), half-cell potential, polarization resistance, ratio of corrosion area, and ratio of corrosion reduction.
(A) Actual photograph
(B) Enlarged photograph
Fig. 1. reMEUM composite.
Table 2 Experimental factors and level.
3.1. Experimental factors and level Table 2 shows experimental factors and level. According to Table 2, W/B ratio is 60% and replacement rate of reMEUM in the concrete is 0% and 10% of cement weight. Measured items include (1) depth of carbonation, (2) corrosion form, (3) half-cell potential, (4) polarization resistance, (5) ratio of corrosion area and (6) ratio of corrosion resistance. Table 3 shows the recipe for the concrete.
Factors
Level
W/B (%) Percentage of reMEUM composite (%) Measurement items
60 0, 10 (% of cement weight)
3.2. Materials used
(1) depth of carbonation, (2) corrosion form, (3) half-cell potential, (4) polarization resistance, (5) ratio of corrosion area and (6) ratio of corrosion resistance
3.2.1. Normal Portland cement Cement used in this experiment is a normal Portland cement manufactured by S company which is appropriate under KS L 5201 regulation. 3.2.2. Compound reMEUM composite was used as the compound material and its basic characteristics are shown in Table 1.
3.5.3. Ratio of corrosion area Upon completion of corrosion accelerated curing, specimens were split to extract reinforcements out to measure the ratio of corrosion area. Corrosion area ratio was computed using software for automatic measurement of area after copying the shape of corrosion on reinforcements using a transparent sheet.
3.3. Carbonation acceleration experiment Fig. 2 shows the shape of specimens used for carbonation. Specimens with the size of 100 100 400 mm were made by applying concrete with 60% W/B ratio on four parallel reinforcements with 20 mm intervals. Also, both ends of the specimens were coated with epoxy resin to inhibit infiltration of corrosive factors. On one hand, carbonation acceleration experiment was performed under conditions of temperature of 40 °C, relative humidity of 60% and 10% CO2 concentration. After acceleration of carbonation, specimen for measurement of carbonation depth was cut and 1% phenolphthalein alcohol solution was sprayed on the inner surface of the specimen. The portion with no color change was considered as carbonated area.
3.5.4. Ratio of corrosion reduction After removing corrosion products by placing reinforcements in an aqueous 10% ammonium citrate, mass of reinforcements was measured to the unit of 0.01 g using an electronic scale. Ratio of corrosion reduction was calculated using following equation [6].
DW ¼
ðWo WÞ Ws 100 Wo
ð1Þ
where DW is weight loss (%), Wo is initial rebar mass (g), W is rebar mass after rust removal (g), Ws is amount of uncorroded part dissolved (g) (separately measured).
4. Experimental results
3.4. Corrosion accelerated curing After completion of prescribed carbonation acceleration experiment, specimens were installed on the autoclave testing device to perform corrosion accelerated curing for 24 h under 200 °C and 10 kgf/cm2 in the container. 3.5. Measurement items 3.5.1. Corrosion form Upon completion of corrosion accelerated curing, corrosion form of reinforcements were observed using unaided eyes after taking them apart from concrete specimens. In observation of corrosion form, reinforcements were divided into upper and lower parts to examine occurrence and degree of microcell corrosion that can result from insufficient filling of the lower part of concrete. 3.5.2. Half-cell potential Half-cell potential of reinforcements was measured at the concrete surface upon completion of corrosion accelerated curing. Copper sulfate electrode (CSE) was used as the standard electrode and variable state of specimens was controlled by digesting them in water for 24 h on the day before the experiment [5].
4.1. Depth of carbonation Fig. 3 represents the result of measurement of carbonation depth according to reMEUM composite status. Primary and secondary corrosion accelerated curing in Fig. 3 each corresponds to carbonation acceleration age of 3 weeks and 8 weeks. Primary carbonation accelerated curing refers to the point in which carbonation reaches the point of reinforcement in the specimen without reMEUM and to the point in which carbonation has not yet reached the reinforcement in the specimen with reMEUM. On one hand, secondary carbonation accelerated curing refers to the point in which depth of carbonation reached inner side surface of reinforcement for the specimen without reMEUM and to the point in which carbonation is progressed to the location of reinforcement for the specimen with 10% mixture of reMEUM. Table 4 shows the basis
Table 1 Chemical composition of reMEUM composite. Unit (wt.%). Weight
Color
Pozzolan
Potential hydroponic
2.4
2.6
Light Gray
Chemical composition unit SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
K2O
Na2O
I/L
61.10
12.18
6.07
6.22
3.35
0.45
1.48
4.28
1.30
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*
W/B (%)
W (kg/m3)
C (kg/m3)
G (kg/m3)
S (kg/m3)
S/A (%)
RE* (kg/m3)
AE water reducing agent (g/m3)
60
185 185
308 308
970 970
810 810
46 46
30.8 (10%) 0 (0%)
500 500
RE: reMEUM composite.
Carbonation deeps (mm)
Fig. 2. Details of test specimen.
50
that results from creation of compact structure. In reality, according to the existing study [7] on reMEUM composite concrete, superior results in air gap filling performance in comparison to artificial pozzolan substance were found in case of reMEUM concrete because of use of different particle sizes of pozzolan substances and microfiller effect. Fig. 4 shows the result of carbonation depth measurement according to the ratio of reMEUM in concretes.
40 30 20 10 0
0%
10%
0%
3 Weeks
10% 8 Weeks
reMEUM Composite mixture Fig. 3. Carbonation depth according to reMEUM composite.
with which primary and secondary carbonation accelerated curing were configured. According to Fig. 3, depth of carbonation has a tendency to increase with progress of carbonation accelerated curing regardless of whether reMEUM concrete was mixed or not. On one hand, depth of carbonation was shallower for specimen with 10% mixture of reMEUM composite in comparison to specimen without reMEUM composite. This is thought to have resulted because pozzolan reactivity of Natural Inorganic Mineral contained in reMEUM is superior to the artificial pozzolan reaction substance and air gap (infiltration path of CO2) filling performance is better because of accelerated formation of ettringite at the initial phase of hydration
4.2. Corrosion form Fig. 5 shows the corrosion form of reinforcement. According to Fig. 5, amount of corrosion in reinforcement showed a tendency to increase with the increase in carbonation accelerated curing. In particular, extensive macrocell corrosion occurred at the lower part of reinforcement of the concrete without reMEUM. However, reinforcement of the concrete with 10% mixture of reMEUM showed a relatively smaller corrosion and there was almost no extensive corrosion in the lower part. Based on such results, concrete reinforcements with 10% reMEUM has relatively low risk against macrocell corrosion in the lower part in comparison to normal concrete reinforcement. This is thought to have results from bleeding control effect of reMEUM concrete, excellent pozzolan reactivity, microfiller effect and air gap filling effect by acicular hydrant products. Fig. 6 shows the SEM photos of reMEUM mixed concrete and non-mixed concrete in 7 days of age. According Fig. 6, in reMEUM mixed concrete, production of ettringite is promoted in comparison with reMEUM non-mixed concrete.
Table 4 Configuration basis for primary and secondary carbonation accelerated curing. Factor
Primary carbonation Secondary carbonation
Carbonation state 0% reMEUM
10% reMEUM
Reached
Not reached Reached
Reached
Basis
Purpose of inspection on corrosion status according to whether or not the specimens reached carbonation Purpose of inspection on corrosion status after carbonation of all specimens
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(a) 0%
(b) 10%
(A) Primary carbonation
(c) 0%
(d) 10%
(B) Secondary carbonation
Fig. 4. Photograph of carbonation depth according to reMEUM composite content.
(a) Primary carbonation
(b) Secondary carbonation
(A) reMEUM composite: 0%
(c) Primary carbonation
(d) Secondary carbonation
(B) reMEUM composite: 10% Fig. 5. Corrosion form in reinforcements.
(A) No addition specimen
(B) Addition specimen
Fig. 6. The SEM photos of reMEUM addition and no addition concretes (age 7 days).
4.3. Half-cell potential
4.4. Polarization resistance
Fig. 7 shows the result of half-cell potential measurement for primary and secondary carbonation accelerated curing. Half-cell potential shown is the average value of half-cell potentials measured from four reinforcements. According to Fig. 7, half-cell potential decreased with increase in carbonation. In addition, half-cell potential showed high results in + direction in reMEUM composite concrete compared to normal concrete. There is no reference point with which occurrence of corrosion in concrete reinforcement can be determined based on the measurement of half-cell potential under carbonation conditions [5]. Therefore, this study used the result of half-cell potential measurement simply for the purpose of comparison between half-cell potentials of reMEUM concrete and normal concrete instead of using it was the basis for determination on the occurrence of corrosion.
Fig. 8 shows the result of polarization resistance measurement for primary and secondary carbonations. Polarization resistance is an electrochemical characteristic value that can be converted to corrosion rate of reinforcement [8,9]. The reciprocal of polarization resistance is corrosion rate. Accordingly, by taking the reciprocal of polarization resistance measured, it is possible to compute corrosion rate. This study also compared relative corrosion rates of reinforcements in 10% reMEUM concrete and normal concrete under identical corrosion conditions by measuring polarization resistance of reinforcements. According to Fig. 8, polarization resistance was reduced with increase in carbonation. This is probably because progress of carbonation to concrete surrounding reinforcements created an environment for easier corrosion. In addition, polarization resistance of reMEUM composite concrete was
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reMEUM Concrete
-0.2
-0.6
Polarization resistance
reMEUM composite 0% reMEUM composite 10%
2.36 10 kX cm2 4.54 10 kX cm2
100 Narmal concrete
Primary
Secondary
Fig. 7. Result of half-cell potential measurement.
Corrosion area (%)
reMEUM Concrete
Carbonation accelerated curing
cm 2 )
Experimental factors
-0.4
-0.8
Polarization resistance (x10 k
Table 5 Polarization resistance of reinforcements under carbonation conditions.
Narmal concrete
75
50
25
15 Narmal concrete
0
reMEUM Concrete
12
Primary
Secondary
Carbonation accelerated curing 9
Fig. 9. Result of corrosion area ratio measurement.
6
1.0 Narmal concrete
3
reMEUM Concrete
0.8 0
Primary
Secondary
Carbonation accelerated curing Fig. 8. Result of polarization resistance measurement.
Weight loss (%)
Half-cell potential (V vs CSE)
0.0
0.6 0.4 0.2
relatively higher than that of normal concrete regardless of carbonation state. This refers to the fact that corrosion speed of reMEUM concrete reinforcement is slower in comparison to the speed of normal concrete reinforcement under identical carbonation state. Reasons for this includes (1) the fact that carbonation reached the position of normal concrete reinforcement in primary carbonation state while failing to reach the position of reMEUM concrete reinforcement because of slower carbonation speed in reMEUM compared to that of normal concrete and (2) the air gap filling effect in reMEUM concrete by bleeding control effect and microfiller effect of hydrant reaction. As a result of actual splitting of specimens and verification of carbonation state, carbonation only reached the position of normal concrete reinforcement as intended by this study for primary carbonation, and both concretes showed progress of carbonation to the position of reinforcements regardless of content of reMEUM for secondary carbonation curing. On one hand, Table 5 shows polarization resistance of reinforcements under carbonation conditions. Polarization resistance shown in Table 5 is the value measured at the point of secondary carbonation. It represents the polarization resistance under carbonation conditions with or without mixing of reMEUM composite. 4.5. Corrosion area ratio and corrosion reduction ratio Figs. 9 and 10 show results of measurement of corrosion area ratio and corrosion reduction ratio for primary and secondary car-
0.0
Primary
Secondary
Carbonation accelerated curing Fig. 10. Result of corrosion reduction ratio measurement.
bonation states. According to Figs. 9 and 10, normal concrete showed a tendency of large increase in corrosion area and reduction ratios with the increase in carbonation accelerated curing, but reMEUM composite concrete did not show an increase as rapid as in normal concrete. On one hand, corrosion area ratio and corrosion reduction ratio of reMEUM composite concrete reinforcement was relatively smaller than those of normal concrete reinforcement regardless of carbonation state.
5. Corrosion resistance of reMEUM concrete structure under carbonation In order to evaluate corrosion resistance of reMEUM concrete structure under carbonation, polarization resistance of reinforcements under carbonation conditions was computed in Section 4.4 and the computed polarization resistance value was applied to Faraday’s Law for computation of corrosion rate of concrete reinforcements according to the content of reMEUM composite with carbonation conditions.
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5.1. Diffusion and infiltration rates of CO2 In general, infiltration rate of CO2 in concretes can be expressed as a square root of time as shown in Eq. (2). In addition, rate constant A in Eq. (2) is defined as shown in Eq. (3). According to Table 6, constant A depends on the (1) type of concrete, (2) type of cement, (3) water to cement ratio, and (4) temperature and humidity. This study computed constant A using the method suggested in Internal Design Construction Guide and Interpretation for Reinforced Concrete Structures by Architectural Institute of Japan [10]. Carbonation depth according to time was computed. Table 6 shows values of variables that decide the value of constant A in carbonation rate equation. In this study, values for each variable in Table 6 were used to calculate the rate of carbonation (Table 7).
A ¼ 1:41 a1 a2 a3 b1 b2 b3
ð3Þ
where C is carbonation depth (m), A is determination coefficient for carbonation rate, t = time (year), a1 is coefficient for concrete type (aggregate type), a2 is coefficient for cement type, a3 is coefficient for proportioning (water–cement ratio), b1 is coefficient for air temperature, b2 is coefficient for moisture, b3 is coefficient for CO2 concentration. 5.2. Corrosion rate of steel This study measured polarization resistance of reinforcements in 10% reMEUM concrete and normal concrete under carbonation conditions in order to compute corrosion rate of steel in concretes. The measured polarization resistance was converted to corrosion rate using Faraday’s Law shown in Eq. (4), and the integral of corrosion rate against time was taken to compute accumulated corrosion amount for each age.
V corr dt ¼
20
10
0
0
25
50
75
100
MK 2F
Z
1 dt Rp
ð4Þ
where G is corrosion loss (g/cm2), Vcorr is rate of corrosion (g/cm2/s), M is atomic weight of Fe (=55.8), K is conversion coefficient (=0.033 V), F is Faraday number (=96,500 C/mol), Rp is polarization resistance (X cm2).
Table 6 Values of variables for constant A. Variable
Content
Value
a1 a2 a3
Normal concrete P1 Normal concrete P1 W/B = 0.6 P 0.22
b1
Coefficient for concrete type Coefficient for cement type Coefficient for proportioning (water–cement ratio) Coefficient for air temperature
b2
Coefficient for moisture
b3
Coefficient for CO2 concentration
Fig. 11. Carbonation rate.
100
Carbonation time (years)
ð2Þ
Z
30
Service life (years)
pffiffi C ¼ A t=100
G¼
Concrete cover thickness (mm)
40
75
63
50
28 25
0
20mm
30mm
Concrete cover thickness (mm) Fig. 12. Time required for carbonation for each cover thickness.
5.3. Calculation conditions for corrosion process (1) Corrosion of steel is in the form of microcell corrosion and is dominated by anode reaction. That is, oxygen that reaches the surface of steel is sufficient for corrosion reaction, and cathode domination by diffusion rate of oxygen does not occur. (2) Corrosion rate of steel differs according to the occurrence of carbonation. Each corrosion speed is computed using polarization resistance in Table 5. 5.4. Infiltration rate of carbonation
Annual average temperature 15.9 °C P 1 Annual average humidity 63% P 1 CO2 concentration 0.05% P 1
Table 7 Conditions used for estimation of life span. Content
Value
W/C (%) CO2 rate constant (A) Diameter of reinforcement (mm) Cover thickness (mm)
60 0.378 19 20, 30
Fig. 11 shows the result of carbonation rate calculation computed based on Section 5.1. According to Fig. 11, carbonation rate was proportional to the square root of time t as in existing study results. According to the result shown in Fig. 11, time required for carbonation with cover thickness of 20 mm and 30 mm was 28 years and 63 years, respectively. According to this result, if carbonation rate is computed based on Section 5.1, time required for cover thickness of 20 mm to reach carbonation is 28 years, which is relatively shorter than the recent demands for over 100 years of life span. However, time for carbonation was largely increased to 63 years with increase in cover thickness to 30 mm (Fig. 12). 5.5. Corrosion Rate Fig. 13 shows corrosion rate of reinforcements in reMEUM concrete under carbonation conditions. Corrosion rate of reinforce-
S.-H. Tae, R.-H. Kim / Construction and Building Materials 25 (2011) 4263–4270
each infiltration rate under the assumption that infiltration rate of CO2 for reMEUM concrete and normal concrete was identical, infiltration rate of CO2 in reMEUM concrete in reality is smaller in comparison to the rate of normal concrete. Therefore, reduction in corrosion rate will not only result from increase in polarization resistance from mixing of reMEUM but also by additional durability improvement from superior infiltration resistance of the material.
Total rust (g/cm2)
2.0
1.5
1.0
reMEUM composite: 0%
0.5
6. Conclusion
10% 0.0 0
25
50
75
100
Service life (years)
(A) Cover thickness = 20mm 2.0
Total rust (g/cm2)
4269
1.5
1.0
0.5
reMEUM composite: 0% 0.0 0
10% 25
50
75
100
Service life (years)
(B) Cover thickness = 30mm Fig. 13. Corrosion rate under carbonation conditions.
ment was expressed as the amount of accumulated corrosion with time. As stated above, corrosion rate of reinforcement can be computed as the amount of corrosion using Faraday’s Law. Relatively comparison for each corrosion condition can be done by comparing the accumulated amount of corrosion. Therefore, this study evaluated corrosion resistance of 10% reMEUM composite concrete by mutually comparing accumulated corrosion amount of reinforcements in 10% mixture of reMEUM concrete and normal concrete without reMEUM. According to Fig. 13, accumulated corrosion amount showed as tendency to increase regardless of changes in corrosion conditions. Also under identical corrosion conditions, reduction in cover thickness showed clear increase in accumulated corrosion. On one hand, accumulated corrosion amount of 10% reMEUM concrete was relatively smaller than the amount of corrosion in normal concrete under identical corrosion conditions regardless of cover thickness. This corresponds to the experimental result of Section 4.4 in which polarization resistance of 10% reMEUM concrete reinforcement was larger than that of normal concrete reinforcement. In conclusion, according to Fig. 13 and 10% reMEUM concrete was verified to show superior performance of protection for reinforcement compared to concrete without any content of reMEUM composite under carbonation state. Accordingly, if a suitable amount of reMEUM composite (about 10%) is mixed in a reinforced concrete structure built according to carbonation conditions, relatively improved corrosion resistance is expected to occur in comparison to normal concrete. In addition, while this study computed accumulated corrosion amount on identical corrosion conditions by computing
This study made concrete specimens with 60% water to cement ratio with mixture of 0% and 10% reMEUM composite material and performed carbonation accelerated curing in order to evaluate corrosion resistance of reMEUM composite reinforced concrete structure. Then, improvement in durability of reinforcement laid in reMEUM composite concrete was evaluated by measuring corrosion form (corrosion patterns in the upper and lower parts of reinforcement), half-cell potential, polarization resistance, corrosion area ratio and corrosion reduction ratio. Results of this study can be summarized as follows. 1. Concrete with 10% mixture of reMEUM composite has carbonation control effect in comparison to concrete without reMEUM. 2. No large corrosion occurred in the 10% reMEUM concrete reinforcement and there was almost no macrocell corrosion in the lower part. 3. Polarization resistance was higher in 10% reMEUM concrete in comparison to normal concrete regardless of carbonation state. This means that corrosion rate of reMEUM concrete reinforcement is smaller than the rate of normal concrete reinforcement. 4. Accumulated corrosion amount of 10% reMEUM concrete reinforcement was relatively smaller in comparison to normal concrete reinforcement under identical carbonation conditions regardless of cover thickness. 5. When 10% of reMEUM composite was mixed, infiltration rate of CO2 was suppressed and electrochemical corrosion reaction under identical corrosion conditions was reduced, producing a result of long term improvement in durability in comparison to normal concrete. Therefore, effects of increase in the number of years of use for reinforced concrete structures can be anticipated from mixture of an appropriate amount of reMEUM composite.
Acknowledgements This work was supported by the research fund of Hanyang University (HY-2010-N).
References [1] Lee HS, Kage T, Noguchi T, Tomosawa F. An experimental study on the retrofitting effects of reinforced concrete columns damaged by rebar corrosion strengthened with carbon fiber sheets. Cem Concr Res 2003;33(4):563–70. [2] Erdogdu S, Bremner TW, Kondratova IL. Accelerated testing of plain and epoxycoated reinforcement in simulated seawater and chloride solutions. Cem Concr Res 2001;31(6):861–7. [3] Callaghan BG. The performance of a 12% chromium steel in concrete in severe marine environments. Corros Sci 1993;35(5–8):1535–41. [4] Kim SB, Song HW, Park SG, Park JY. Waterproof mechanism of natural inorganic minerals for concrete admixtures. In: Proceedings of the Architectural Institute of Korea, Seoul, Korea; 2005. [5] ASTM C 876-80. Standard test method for half cell potentials of reinforcing steel in concrete; 1981. [6] Japan Concrete Institute. Examination method and criterion about corrosion, corrosion resistance of a concrete construction (plan) (JCI-SC1, corrosion evaluation method of steel materials in concrete;1987.
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[7] Kim SB, Park SG, Song HW, Byun KJ, Kim JY. Permeability coefficient properties of mortar using natural inorganic minerals. In: Proceedings of the Korea Concrete Institute conference, Seoul, Korea; 2005. [8] Kyung JW, Yokota M, Leelalerkiet V, Ohtsu M. Practical use of half-cell potential method for NDE of corrosion of reinforced concrete structure. Key Eng Mater 2004;270–273(1–3):1638–44.
[9] Leelalerkiet V, Kyung JW, Ohtsu M, Yokota M. Analysis of half-cell potential measurement for corrosion of reinforced concrete. Constr Build Mater 2004;18(3):155–62. [10] Architectural Institute of Japan. Recommendations for durability design and construction practice of reinforced concrete; 2004.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
A study on improvement of durability of reinforced concrete structures mixed with Natural Inorganic Minerals Sung-Ho Tae a,1, Rak-Hyun Kim b,⇑ a b
School of Architecture & Architectural Eng., Hanyang University 1271, Sa 3-dong, Sangrok-gu, Ansan, Gyeonggi-do 426-791, Republic of Korea Department of Sustainable Architectural Eng., Hanyang University 1271, Sa 3-dong, Sangrok-gu, Ansan, Gyeonggi-do 426-791, Republic of Korea
a r t i c l e
i n f o
Article history: Received 2 April 2010 Received in revised form 25 April 2011 Accepted 25 April 2011
Keywords: Natural Inorganic Minerals Carbonation Corrosion resistance Corrosion rate
a b s t r a c t As a fundamental study on the corrosion resistance of reinforced concrete structures using Natural Inorganic Minerals exposed to carbonation environment. The test specimens were concrete(W/C = 60%) with Natural Inorganic Minerals content of 0% and 10%. Accelerated arbonation and autoclave corrosion accelerated curing were then conducted with them. The corrosion resistance of steel in concrete with Natural Inorganic Minerals content of 0% and 10% was examined by corrosion form, half-cell potential, polarization resistance, corrosion area and weight loss after 24 h of autoclave corrosion accelerated curing. The results of the study showed that as for steel in concrete with Natural Inorganic Minerals content of 10%, the corrosion resistance was more excellent than steel in concrete with Natural Inorganic Minerals content of 0%. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Reinforced concrete in general is a construction material with excellent durability and economic feasibility and is being used for a wide variety of structures. The number of year of its use had also been recognized as semi-permanent. However, if design and construction inappropriate for the conditions of use are performed, sound performance is lost before reaching the objective number of years and the structure experiences early deterioration. Such early deterioration of structures has a large influence on the increase in maintenance cost for repairmen and reinforcement, occurrence of construction wastes from remodeling and dismantlement, and effects on global and local environments. Economic loss caused by corrosion of reinforced concrete structures is about 4% of GNP in the United States of 70 billion dollars. In case of our country, a huge economic loss of about 4–5% of GNP is expected to occur from corrosion of reinforced concrete, considering industrial structure of our country with intensive heavy industry. Though there are various factors of such deterioration of reinforced concrete structure, all factors ultimately experience occurrence of cracks in the concrete from corrosion expansion of reinforcement and end up with reduction in load-carrying capacity of the structure [1]. Over 100 years of life span is currently being demanded for reinforced concrete structures, and development of efficient ⇑ Corresponding author. Tel.: +82 31 436 8125; fax: +82 31 406 7118. E-mail addresses: [email protected] (S.-H. Tae), [email protected] (R.-H. Kim). 1 Tel.: +82 31 400 3740; fax: +82 31 406 7118. 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.04.070
and scientific durability improvement technology that can secure long life span with exposure to various corrosion conditions such as sea wind and neutralization is in urgent need [2,3]. In this study, corrosion resistance of reinforcement in the concrete with mixing of Natural Inorganic Compound (called reMEUM hereafter) was evaluated by performing a corrosion acceleration experiment with simulation of a neutralized environment for concretes with mixture of various particle sizes of reMEUM that compose minute organizational structure from air gap mending effect of acicular hydrate products and micro filler effect with excellent Pozzolanic reaction. In addition, electrochemical characteristics of reinforcements deduced from corrosion acceleration experiment under neutralized conditions was used to evaluate durability improvement of reinforced concrete structures with reMEUM mixture under neutralized conditions. 2. reMEUM composite The reMEUM composite used in this study is composed of the main ingredient TVP natural mineral (a natural inorganic mineral that includes tuff, volcanic ash and perlite) extremely effective for improvement in watertightness of concrete and of supplementary ingredients including siliceous powder, pozzolan substances, potential hydroponic substances and sulphate. It is a mixture material for watertight concrete produced using anion surfactant and fatty acid salts. According to existing studies [4], reMEUM concretes compose more compact minute structure in comparison to normal concretes. There are reports that reMEUM concrete is not only superior in terms of watertightness of the concrete but also
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excellent in reduction effect on creation of cracks from suppression of drying shrinkage and improvement in compressive strength. Table 1 shows basic characteristics of reMEUM composite. In addition, Fig. 1 shows the actual photograph of reMEUM composite and enlarged photograph. 3. Experiment outline In order to evaluate corrosion resistance of reMEUM concrete on carbonation, concrete specimens of 60% water-binder ratio (W/B) with 0% and 10% reMEUM were made and carbonated accelerated curing (temperature of 40 °C, relative humidity of 60% and 10% concentration of CO2) was performed. Then, autoclave corrosion acceleration experiment was performed to evaluate corrosion resistance of reinforcement laid in the reMEUM concrete by measuring corrosion form (corrosion patterns in the upper and lower parts of reinforcement), half-cell potential, polarization resistance, ratio of corrosion area, and ratio of corrosion reduction.
(A) Actual photograph
(B) Enlarged photograph
Fig. 1. reMEUM composite.
Table 2 Experimental factors and level.
3.1. Experimental factors and level Table 2 shows experimental factors and level. According to Table 2, W/B ratio is 60% and replacement rate of reMEUM in the concrete is 0% and 10% of cement weight. Measured items include (1) depth of carbonation, (2) corrosion form, (3) half-cell potential, (4) polarization resistance, (5) ratio of corrosion area and (6) ratio of corrosion resistance. Table 3 shows the recipe for the concrete.
Factors
Level
W/B (%) Percentage of reMEUM composite (%) Measurement items
60 0, 10 (% of cement weight)
3.2. Materials used
(1) depth of carbonation, (2) corrosion form, (3) half-cell potential, (4) polarization resistance, (5) ratio of corrosion area and (6) ratio of corrosion resistance
3.2.1. Normal Portland cement Cement used in this experiment is a normal Portland cement manufactured by S company which is appropriate under KS L 5201 regulation. 3.2.2. Compound reMEUM composite was used as the compound material and its basic characteristics are shown in Table 1.
3.5.3. Ratio of corrosion area Upon completion of corrosion accelerated curing, specimens were split to extract reinforcements out to measure the ratio of corrosion area. Corrosion area ratio was computed using software for automatic measurement of area after copying the shape of corrosion on reinforcements using a transparent sheet.
3.3. Carbonation acceleration experiment Fig. 2 shows the shape of specimens used for carbonation. Specimens with the size of 100 100 400 mm were made by applying concrete with 60% W/B ratio on four parallel reinforcements with 20 mm intervals. Also, both ends of the specimens were coated with epoxy resin to inhibit infiltration of corrosive factors. On one hand, carbonation acceleration experiment was performed under conditions of temperature of 40 °C, relative humidity of 60% and 10% CO2 concentration. After acceleration of carbonation, specimen for measurement of carbonation depth was cut and 1% phenolphthalein alcohol solution was sprayed on the inner surface of the specimen. The portion with no color change was considered as carbonated area.
3.5.4. Ratio of corrosion reduction After removing corrosion products by placing reinforcements in an aqueous 10% ammonium citrate, mass of reinforcements was measured to the unit of 0.01 g using an electronic scale. Ratio of corrosion reduction was calculated using following equation [6].
DW ¼
ðWo WÞ Ws 100 Wo
ð1Þ
where DW is weight loss (%), Wo is initial rebar mass (g), W is rebar mass after rust removal (g), Ws is amount of uncorroded part dissolved (g) (separately measured).
4. Experimental results
3.4. Corrosion accelerated curing After completion of prescribed carbonation acceleration experiment, specimens were installed on the autoclave testing device to perform corrosion accelerated curing for 24 h under 200 °C and 10 kgf/cm2 in the container. 3.5. Measurement items 3.5.1. Corrosion form Upon completion of corrosion accelerated curing, corrosion form of reinforcements were observed using unaided eyes after taking them apart from concrete specimens. In observation of corrosion form, reinforcements were divided into upper and lower parts to examine occurrence and degree of microcell corrosion that can result from insufficient filling of the lower part of concrete. 3.5.2. Half-cell potential Half-cell potential of reinforcements was measured at the concrete surface upon completion of corrosion accelerated curing. Copper sulfate electrode (CSE) was used as the standard electrode and variable state of specimens was controlled by digesting them in water for 24 h on the day before the experiment [5].
4.1. Depth of carbonation Fig. 3 represents the result of measurement of carbonation depth according to reMEUM composite status. Primary and secondary corrosion accelerated curing in Fig. 3 each corresponds to carbonation acceleration age of 3 weeks and 8 weeks. Primary carbonation accelerated curing refers to the point in which carbonation reaches the point of reinforcement in the specimen without reMEUM and to the point in which carbonation has not yet reached the reinforcement in the specimen with reMEUM. On one hand, secondary carbonation accelerated curing refers to the point in which depth of carbonation reached inner side surface of reinforcement for the specimen without reMEUM and to the point in which carbonation is progressed to the location of reinforcement for the specimen with 10% mixture of reMEUM. Table 4 shows the basis
Table 1 Chemical composition of reMEUM composite. Unit (wt.%). Weight
Color
Pozzolan
Potential hydroponic
2.4
2.6
Light Gray
Chemical composition unit SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
K2O
Na2O
I/L
61.10
12.18
6.07
6.22
3.35
0.45
1.48
4.28
1.30
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*
W/B (%)
W (kg/m3)
C (kg/m3)
G (kg/m3)
S (kg/m3)
S/A (%)
RE* (kg/m3)
AE water reducing agent (g/m3)
60
185 185
308 308
970 970
810 810
46 46
30.8 (10%) 0 (0%)
500 500
RE: reMEUM composite.
Carbonation deeps (mm)
Fig. 2. Details of test specimen.
50
that results from creation of compact structure. In reality, according to the existing study [7] on reMEUM composite concrete, superior results in air gap filling performance in comparison to artificial pozzolan substance were found in case of reMEUM concrete because of use of different particle sizes of pozzolan substances and microfiller effect. Fig. 4 shows the result of carbonation depth measurement according to the ratio of reMEUM in concretes.
40 30 20 10 0
0%
10%
0%
3 Weeks
10% 8 Weeks
reMEUM Composite mixture Fig. 3. Carbonation depth according to reMEUM composite.
with which primary and secondary carbonation accelerated curing were configured. According to Fig. 3, depth of carbonation has a tendency to increase with progress of carbonation accelerated curing regardless of whether reMEUM concrete was mixed or not. On one hand, depth of carbonation was shallower for specimen with 10% mixture of reMEUM composite in comparison to specimen without reMEUM composite. This is thought to have resulted because pozzolan reactivity of Natural Inorganic Mineral contained in reMEUM is superior to the artificial pozzolan reaction substance and air gap (infiltration path of CO2) filling performance is better because of accelerated formation of ettringite at the initial phase of hydration
4.2. Corrosion form Fig. 5 shows the corrosion form of reinforcement. According to Fig. 5, amount of corrosion in reinforcement showed a tendency to increase with the increase in carbonation accelerated curing. In particular, extensive macrocell corrosion occurred at the lower part of reinforcement of the concrete without reMEUM. However, reinforcement of the concrete with 10% mixture of reMEUM showed a relatively smaller corrosion and there was almost no extensive corrosion in the lower part. Based on such results, concrete reinforcements with 10% reMEUM has relatively low risk against macrocell corrosion in the lower part in comparison to normal concrete reinforcement. This is thought to have results from bleeding control effect of reMEUM concrete, excellent pozzolan reactivity, microfiller effect and air gap filling effect by acicular hydrant products. Fig. 6 shows the SEM photos of reMEUM mixed concrete and non-mixed concrete in 7 days of age. According Fig. 6, in reMEUM mixed concrete, production of ettringite is promoted in comparison with reMEUM non-mixed concrete.
Table 4 Configuration basis for primary and secondary carbonation accelerated curing. Factor
Primary carbonation Secondary carbonation
Carbonation state 0% reMEUM
10% reMEUM
Reached
Not reached Reached
Reached
Basis
Purpose of inspection on corrosion status according to whether or not the specimens reached carbonation Purpose of inspection on corrosion status after carbonation of all specimens
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(a) 0%
(b) 10%
(A) Primary carbonation
(c) 0%
(d) 10%
(B) Secondary carbonation
Fig. 4. Photograph of carbonation depth according to reMEUM composite content.
(a) Primary carbonation
(b) Secondary carbonation
(A) reMEUM composite: 0%
(c) Primary carbonation
(d) Secondary carbonation
(B) reMEUM composite: 10% Fig. 5. Corrosion form in reinforcements.
(A) No addition specimen
(B) Addition specimen
Fig. 6. The SEM photos of reMEUM addition and no addition concretes (age 7 days).
4.3. Half-cell potential
4.4. Polarization resistance
Fig. 7 shows the result of half-cell potential measurement for primary and secondary carbonation accelerated curing. Half-cell potential shown is the average value of half-cell potentials measured from four reinforcements. According to Fig. 7, half-cell potential decreased with increase in carbonation. In addition, half-cell potential showed high results in + direction in reMEUM composite concrete compared to normal concrete. There is no reference point with which occurrence of corrosion in concrete reinforcement can be determined based on the measurement of half-cell potential under carbonation conditions [5]. Therefore, this study used the result of half-cell potential measurement simply for the purpose of comparison between half-cell potentials of reMEUM concrete and normal concrete instead of using it was the basis for determination on the occurrence of corrosion.
Fig. 8 shows the result of polarization resistance measurement for primary and secondary carbonations. Polarization resistance is an electrochemical characteristic value that can be converted to corrosion rate of reinforcement [8,9]. The reciprocal of polarization resistance is corrosion rate. Accordingly, by taking the reciprocal of polarization resistance measured, it is possible to compute corrosion rate. This study also compared relative corrosion rates of reinforcements in 10% reMEUM concrete and normal concrete under identical corrosion conditions by measuring polarization resistance of reinforcements. According to Fig. 8, polarization resistance was reduced with increase in carbonation. This is probably because progress of carbonation to concrete surrounding reinforcements created an environment for easier corrosion. In addition, polarization resistance of reMEUM composite concrete was
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reMEUM Concrete
-0.2
-0.6
Polarization resistance
reMEUM composite 0% reMEUM composite 10%
2.36 10 kX cm2 4.54 10 kX cm2
100 Narmal concrete
Primary
Secondary
Fig. 7. Result of half-cell potential measurement.
Corrosion area (%)
reMEUM Concrete
Carbonation accelerated curing
cm 2 )
Experimental factors
-0.4
-0.8
Polarization resistance (x10 k
Table 5 Polarization resistance of reinforcements under carbonation conditions.
Narmal concrete
75
50
25
15 Narmal concrete
0
reMEUM Concrete
12
Primary
Secondary
Carbonation accelerated curing 9
Fig. 9. Result of corrosion area ratio measurement.
6
1.0 Narmal concrete
3
reMEUM Concrete
0.8 0
Primary
Secondary
Carbonation accelerated curing Fig. 8. Result of polarization resistance measurement.
Weight loss (%)
Half-cell potential (V vs CSE)
0.0
0.6 0.4 0.2
relatively higher than that of normal concrete regardless of carbonation state. This refers to the fact that corrosion speed of reMEUM concrete reinforcement is slower in comparison to the speed of normal concrete reinforcement under identical carbonation state. Reasons for this includes (1) the fact that carbonation reached the position of normal concrete reinforcement in primary carbonation state while failing to reach the position of reMEUM concrete reinforcement because of slower carbonation speed in reMEUM compared to that of normal concrete and (2) the air gap filling effect in reMEUM concrete by bleeding control effect and microfiller effect of hydrant reaction. As a result of actual splitting of specimens and verification of carbonation state, carbonation only reached the position of normal concrete reinforcement as intended by this study for primary carbonation, and both concretes showed progress of carbonation to the position of reinforcements regardless of content of reMEUM for secondary carbonation curing. On one hand, Table 5 shows polarization resistance of reinforcements under carbonation conditions. Polarization resistance shown in Table 5 is the value measured at the point of secondary carbonation. It represents the polarization resistance under carbonation conditions with or without mixing of reMEUM composite. 4.5. Corrosion area ratio and corrosion reduction ratio Figs. 9 and 10 show results of measurement of corrosion area ratio and corrosion reduction ratio for primary and secondary car-
0.0
Primary
Secondary
Carbonation accelerated curing Fig. 10. Result of corrosion reduction ratio measurement.
bonation states. According to Figs. 9 and 10, normal concrete showed a tendency of large increase in corrosion area and reduction ratios with the increase in carbonation accelerated curing, but reMEUM composite concrete did not show an increase as rapid as in normal concrete. On one hand, corrosion area ratio and corrosion reduction ratio of reMEUM composite concrete reinforcement was relatively smaller than those of normal concrete reinforcement regardless of carbonation state.
5. Corrosion resistance of reMEUM concrete structure under carbonation In order to evaluate corrosion resistance of reMEUM concrete structure under carbonation, polarization resistance of reinforcements under carbonation conditions was computed in Section 4.4 and the computed polarization resistance value was applied to Faraday’s Law for computation of corrosion rate of concrete reinforcements according to the content of reMEUM composite with carbonation conditions.
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5.1. Diffusion and infiltration rates of CO2 In general, infiltration rate of CO2 in concretes can be expressed as a square root of time as shown in Eq. (2). In addition, rate constant A in Eq. (2) is defined as shown in Eq. (3). According to Table 6, constant A depends on the (1) type of concrete, (2) type of cement, (3) water to cement ratio, and (4) temperature and humidity. This study computed constant A using the method suggested in Internal Design Construction Guide and Interpretation for Reinforced Concrete Structures by Architectural Institute of Japan [10]. Carbonation depth according to time was computed. Table 6 shows values of variables that decide the value of constant A in carbonation rate equation. In this study, values for each variable in Table 6 were used to calculate the rate of carbonation (Table 7).
A ¼ 1:41 a1 a2 a3 b1 b2 b3
ð3Þ
where C is carbonation depth (m), A is determination coefficient for carbonation rate, t = time (year), a1 is coefficient for concrete type (aggregate type), a2 is coefficient for cement type, a3 is coefficient for proportioning (water–cement ratio), b1 is coefficient for air temperature, b2 is coefficient for moisture, b3 is coefficient for CO2 concentration. 5.2. Corrosion rate of steel This study measured polarization resistance of reinforcements in 10% reMEUM concrete and normal concrete under carbonation conditions in order to compute corrosion rate of steel in concretes. The measured polarization resistance was converted to corrosion rate using Faraday’s Law shown in Eq. (4), and the integral of corrosion rate against time was taken to compute accumulated corrosion amount for each age.
V corr dt ¼
20
10
0
0
25
50
75
100
MK 2F
Z
1 dt Rp
ð4Þ
where G is corrosion loss (g/cm2), Vcorr is rate of corrosion (g/cm2/s), M is atomic weight of Fe (=55.8), K is conversion coefficient (=0.033 V), F is Faraday number (=96,500 C/mol), Rp is polarization resistance (X cm2).
Table 6 Values of variables for constant A. Variable
Content
Value
a1 a2 a3
Normal concrete P1 Normal concrete P1 W/B = 0.6 P 0.22
b1
Coefficient for concrete type Coefficient for cement type Coefficient for proportioning (water–cement ratio) Coefficient for air temperature
b2
Coefficient for moisture
b3
Coefficient for CO2 concentration
Fig. 11. Carbonation rate.
100
Carbonation time (years)
ð2Þ
Z
30
Service life (years)
pffiffi C ¼ A t=100
G¼
Concrete cover thickness (mm)
40
75
63
50
28 25
0
20mm
30mm
Concrete cover thickness (mm) Fig. 12. Time required for carbonation for each cover thickness.
5.3. Calculation conditions for corrosion process (1) Corrosion of steel is in the form of microcell corrosion and is dominated by anode reaction. That is, oxygen that reaches the surface of steel is sufficient for corrosion reaction, and cathode domination by diffusion rate of oxygen does not occur. (2) Corrosion rate of steel differs according to the occurrence of carbonation. Each corrosion speed is computed using polarization resistance in Table 5. 5.4. Infiltration rate of carbonation
Annual average temperature 15.9 °C P 1 Annual average humidity 63% P 1 CO2 concentration 0.05% P 1
Table 7 Conditions used for estimation of life span. Content
Value
W/C (%) CO2 rate constant (A) Diameter of reinforcement (mm) Cover thickness (mm)
60 0.378 19 20, 30
Fig. 11 shows the result of carbonation rate calculation computed based on Section 5.1. According to Fig. 11, carbonation rate was proportional to the square root of time t as in existing study results. According to the result shown in Fig. 11, time required for carbonation with cover thickness of 20 mm and 30 mm was 28 years and 63 years, respectively. According to this result, if carbonation rate is computed based on Section 5.1, time required for cover thickness of 20 mm to reach carbonation is 28 years, which is relatively shorter than the recent demands for over 100 years of life span. However, time for carbonation was largely increased to 63 years with increase in cover thickness to 30 mm (Fig. 12). 5.5. Corrosion Rate Fig. 13 shows corrosion rate of reinforcements in reMEUM concrete under carbonation conditions. Corrosion rate of reinforce-
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each infiltration rate under the assumption that infiltration rate of CO2 for reMEUM concrete and normal concrete was identical, infiltration rate of CO2 in reMEUM concrete in reality is smaller in comparison to the rate of normal concrete. Therefore, reduction in corrosion rate will not only result from increase in polarization resistance from mixing of reMEUM but also by additional durability improvement from superior infiltration resistance of the material.
Total rust (g/cm2)
2.0
1.5
1.0
reMEUM composite: 0%
0.5
6. Conclusion
10% 0.0 0
25
50
75
100
Service life (years)
(A) Cover thickness = 20mm 2.0
Total rust (g/cm2)
4269
1.5
1.0
0.5
reMEUM composite: 0% 0.0 0
10% 25
50
75
100
Service life (years)
(B) Cover thickness = 30mm Fig. 13. Corrosion rate under carbonation conditions.
ment was expressed as the amount of accumulated corrosion with time. As stated above, corrosion rate of reinforcement can be computed as the amount of corrosion using Faraday’s Law. Relatively comparison for each corrosion condition can be done by comparing the accumulated amount of corrosion. Therefore, this study evaluated corrosion resistance of 10% reMEUM composite concrete by mutually comparing accumulated corrosion amount of reinforcements in 10% mixture of reMEUM concrete and normal concrete without reMEUM. According to Fig. 13, accumulated corrosion amount showed as tendency to increase regardless of changes in corrosion conditions. Also under identical corrosion conditions, reduction in cover thickness showed clear increase in accumulated corrosion. On one hand, accumulated corrosion amount of 10% reMEUM concrete was relatively smaller than the amount of corrosion in normal concrete under identical corrosion conditions regardless of cover thickness. This corresponds to the experimental result of Section 4.4 in which polarization resistance of 10% reMEUM concrete reinforcement was larger than that of normal concrete reinforcement. In conclusion, according to Fig. 13 and 10% reMEUM concrete was verified to show superior performance of protection for reinforcement compared to concrete without any content of reMEUM composite under carbonation state. Accordingly, if a suitable amount of reMEUM composite (about 10%) is mixed in a reinforced concrete structure built according to carbonation conditions, relatively improved corrosion resistance is expected to occur in comparison to normal concrete. In addition, while this study computed accumulated corrosion amount on identical corrosion conditions by computing
This study made concrete specimens with 60% water to cement ratio with mixture of 0% and 10% reMEUM composite material and performed carbonation accelerated curing in order to evaluate corrosion resistance of reMEUM composite reinforced concrete structure. Then, improvement in durability of reinforcement laid in reMEUM composite concrete was evaluated by measuring corrosion form (corrosion patterns in the upper and lower parts of reinforcement), half-cell potential, polarization resistance, corrosion area ratio and corrosion reduction ratio. Results of this study can be summarized as follows. 1. Concrete with 10% mixture of reMEUM composite has carbonation control effect in comparison to concrete without reMEUM. 2. No large corrosion occurred in the 10% reMEUM concrete reinforcement and there was almost no macrocell corrosion in the lower part. 3. Polarization resistance was higher in 10% reMEUM concrete in comparison to normal concrete regardless of carbonation state. This means that corrosion rate of reMEUM concrete reinforcement is smaller than the rate of normal concrete reinforcement. 4. Accumulated corrosion amount of 10% reMEUM concrete reinforcement was relatively smaller in comparison to normal concrete reinforcement under identical carbonation conditions regardless of cover thickness. 5. When 10% of reMEUM composite was mixed, infiltration rate of CO2 was suppressed and electrochemical corrosion reaction under identical corrosion conditions was reduced, producing a result of long term improvement in durability in comparison to normal concrete. Therefore, effects of increase in the number of years of use for reinforced concrete structures can be anticipated from mixture of an appropriate amount of reMEUM composite.
Acknowledgements This work was supported by the research fund of Hanyang University (HY-2010-N).
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