Influence of metakaolin as supplementary cementing material on strength and durability of concretes

Construction and Building Materials 30 (2012) 470–479

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Influence of metakaolin as supplementary cementing material on strength and durability of concretes A.A. Ramezanianpour a, H. Bahrami Jovein b,⇑ a b

Concrete Technology and Durability Research Center, Amirkabir University of Technology, Tehran, Iran Department of Civil Engineering, Amirkabir University of Technology, Tehran, Iran

a r t i c l e

i n f o

Article history: Received 8 May 2011 Received in revised form 8 November 2011 Accepted 2 December 2011 Available online 3 January 2012 Keywords: Metakaolin Compressive strength Water penetration Electrical resistivity RCPT Salt ponding Sorptivity

a b s t r a c t Durability of concrete is an important issue for predicting the service life of concrete structures. Recently, the properties of metakaolin as high-quality pozzolanic materials are investigated by several researchers. It is not widely produced and used due to the lack of adequate experiments on this material in the Middle East. Local kaolin with high kaolinite content was thermally treated by a special furnace at 800 °C and 60 min burning time to produce metakaolin. This study investigates the performance of concrete mixtures containing local metakaolin in terms of compressive strength, water penetration, sorptivity, salt ponding, Rapid Chloride Permeability Test (RCPT) and electrical resistivity at 7, 28, 90 and 180 days. In addition, microstructure of the cement pastes incorporating metakaolin was studied by XRD and SEM tests. The percentages of metakaolin that replace PC in this research are 0%, 10%, 12.5% and 15% by mass. The water/binder (w/b) ratios are 0.35, 0.4 and 0.5 having a constant total binder content of 400 kg/m3. Results show that concrete incorporating metakaolin had higher compressive strength and metakaolin enhanced the durability of concretes and reduced the chloride diffusion. An exponential relationship between chloride permeability and compressive strength of concrete is exhibited. A significant linear relationship was found between Rapid Chloride Permeability Test and salt ponding test results. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Concrete is probably the most extensively used construction material in the world. It is only second to water as the most heavily consumed substance [1]. The majority of the cementitious binders used in concrete are based on Portland cement clinker, the manufacture of which is an energy-intensive process. In addition, it produces a large amount of greenhouse gas emissions, mostly CO2, resulting from release of CO2 from limestone in the pyro-processing of clinker. On the other hand, the concrete industry is one of the major consumers of natural resources. In order to reduce energy consumption, CO2 emission and increase production, cement plants produce blended cements, comprised of supplementary cementitious materials such as metakaolin, silica fume, natural pozzolan, fly ash and limestone. In recent years, metakaolin (MK) has been studied because of its high pozzolanic properties [2–5]. Unlike other pozzolans, it is a primary product, not a secondary product or by-product, which is formed by the dehydroxylation of kaolin precursor upon heating ⇑ Corresponding author. Tel.: +98 21 64543074/915 1110160; fax: +98 21 64543074. E-mail addresses: [email protected], [email protected] (H. Bahrami Jovein). 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.12.050

in the temperature range of 700–800 °C [6,7]. The raw material input in the manufacture of metakaolin (Al2Si2O7) is kaolin. Metakaolin on reaction with Ca(OH)2, produces C–S–H gel at ambient temperature and reacts with CH to produce alumina containing phases, including C4AH13, C2ASH8, and C3AH6 [8,9]. Larbi [10] showed that calcium hydroxide can be virtually eliminated from the cement matrix by using sufficient adapted metakaolin concentrations. Metakaolin is increasingly being used to produce highstrength, high-performance concrete with improved durability. Extensive research is reported in the literature concerning different properties of MK paste and concrete such as porosity, pore size distribution, pozzolanic reaction, compressive and durability of MK concrete [1,11–13]. Brooks and Johari reported that compressive strength increased with the increase in the metakaolin content [14]. Similar results were also reported by Li and Ding where concrete achieved the highest compressive strength with 10% MK content [15]. Metakaolin concrete, compared to PC concrete, exhibits significantly lower sorptivity [16]. The incorporation of metakaolin in concrete led to significant increase of resistance to chloride penetration. Gruber et al. reported that the use of 8% and 12% high-reactivity metakaolin (HRM) significantly lowered the chloride ion diffusion coefficient of concrete [17]. Parande et al. was deduced that up to 15% replacement of

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metakaolin in ordinary Portland cement showed to be good corrosion resistance property, water absorption and resistivity of concrete [18]. Considering the abundant kaolin mines in local area, this study investigates the performance of concrete mixture containing local metakaolin in terms of compressive strength, water penetration, sorptivity, salt ponding, Rapid Chloride Permeability Test (RCPT) and electrical resistivity at 7, 28, 90 and 180 days. Then, relationships between test results of concretes containing metakaolin are discussed. In addition, microstructure of the cement pastes incorporating metakaolin was studied by XRD and SEM tests.

2.2. Specimens preparation The concrete production was carried out in a mixer of 50 l capacity. Two series of concrete mixtures were designed at 0.35, 0.4 and 0.5 water/binder (w/b) ratios and having a constant total binder (cement + metakaolin) content of 400 kg/m3. The percentages of metakaolin that replace PC in this research are 0%, 10%, 12.5% and 15% by mass of cement that were added to clinker in the laboratory. Details of the mixtures are presented in Table 3. Slumps were kept constant at 70 ± 10 mm. Superplasticizer was used at very low percentages according to the results obtained for the slumps. Casting of concrete specimens was conducted in two layers. Each layer was compacted on a vibrating table to ensure good compaction and to reduce the air voids. After casting, the concrete specimens were covered with a wet towel and cured under laboratory conditions. After 24 h they were demolded and cured in lime-saturated water at 23 ± 2 °C to prevent possible leaching of Ca(OH)2 from these specimens.

2. Experimental program 2.3. Test methods 2.1. Material 2.3.1. Compressive strength Concrete cubes of 100  100  100 mm dimension were cast for compressive strength. They were tested for compressive strength after 7, 28, 90 and 180 days of water curing. For each age, three specimens were tested and the mean value of these measurements is reported.

ASTM C 150 type I Portland cement was used for all of the concrete mixtures. Chemical and physical characteristics of cement are shown in Table 1. The C3S, C2S, C3A and C4AF contents of the cement by Bogue calculations were 54.6%, 20%, 5.1% and 9.06%, respectively. Local kaolin with high kaolinite content (K) was thermally treated by the special furnace at 800 °C and 60 min burning time to produce metakaolin. The chemical composition of MK used as supplementary cementitious material and chemical and mineralogical analyses of kaolin are given in Tables 1 and 2, respectively. Local natural sand according to ASTM Standard with maximum aggregate size of 4.75 mm, and crushed calcareous stone according to ASTM Standard with maximum aggregate size of 19 mm were used. The coarse aggregates have a specific gravity and water absorption of 2580 kg/m3 and 1.74%, respectively, and the fine aggregate has water absorption of 2.3% and a specific gravity of 2560 kg/m3. Potable water was used for casting and curing of all concrete specimens. The polycarboxylic acid–based Superplasticizer (GELENIUM-110P) was employed to achieve the desired workability.

2.3.2. Sorptivity The sorptivity was conducted on concrete cubes (100  100  100 mm) which were dried in a 50 °C oven for 14 days. After mass stabilization, the specimens were coated with the epoxy resin on their lateral surfaces only, in order to ensure uniaxial water absorption. The specimen was rested on rods to allow free access of water to the surface and the tap water level was kept no more than 5 mm above the base of the specimen. The masses of the specimens were measured after 0, 3, 6, 24 and 72 h of absorption. Three specimens from each mixture were tested at the ages of 7, 28, 90, and 180 days and the average values were reported.

Table 1 Physical and chemical characteristics of cement and metakaolin. Physical tests

Cement Metakaolin

Chemical analysis (%)

Bogue composition (%)

Specific gravity

Blaine (cm2/g)

SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O

K2O

LOI

C3S

C2S

C3A

C4AF

3.21 2.53

3200 3700

21.32 74.3

3.83 17.8

2.76 0.82

62.02 3.38

3.44 0.22

0.12 0.0

0.73 0.39

2.98 2.56

54.6 –

20 –

5.1 –

9.06 –

Table 2 Chemical and mineralogical analyses of kaolin. Chemical analysis (%)

Kaolin

Mineralogical analysis (%)

SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O

K2O

LOI

Kaolinite

Quartz

Calcite

Other

74.97

17.8

0.81

2.22

0.13

0.05

0.55

7.18

50.73

39.27

6

4

Table 3 Mix proportions of concrete. Series

Mix

W/b

Metakaolin (%)

Metakaolin (kg/m3)

Cement (kg/m3)

Water (kg/m3)

Coarse aggregate (kg/m3)

Fine aggregate (kg/m3)

Slump (mm)

1

OPC MK10 MK12.5 MK15

0.5 0.5 0.5 0.5

0 10 12.5 15

0 40 50 60

400 360 350 340

200 200 200 200

765 765 765 765

935 935 935 935

90 85 90 85

2

OPC MK10 MK12.5 MK15

0.4 0.4 0.4 0.4

0 10 12.5 15

0 40 50 60

400 360 350 340

160 160 160 160

810 810 810 810

990 990 990 990

80 75 80 80

3

OPC MK10 MK12.5 MK15

0.35 0.35 0.35 0.35

0 10 12.5 15

0 40 50 60

400 360 350 340

140 140 140 140

832.5 832.5 832.5 832.5

1017.5 1017.5 1017.5 1017.5

80 80 75 70

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The sorptivity coefficient (S) according to BS EN-480-5:1997 [19] was obtained using the following expression:

pffiffi Q ¼cþS t A

ð1Þ

where Q is the amount of water adsorbed; A is the cross section of specimen that was in contact with water; t is the time (second); c is the constant coefficient; and S is the sorptivity coefficient of the specimen (m/s1/2). 2.3.3. Water penetration The water penetration test, which is most commonly used to evaluate the permeability of concrete, is the one specified by BS EN-12390-8:2000 [20]. In this test, water was applied on one face of the 150 mm concrete cubes specimen under a pressure of 0.5 MPa. This pressure was maintained constant for a period of 72 h. After the completion of the test, the specimens were taken out and split open into two halves. The water penetration profile on the concrete surface was then marked and the maximum depth of water penetration in specimens was recorded and considered as an indicator of the water penetration. 2.3.4. Rapid Chloride Permeability Test (RCPT) The resistance of concrete to salt attack was assessed by Rapid Chloride Permeability Test (RCPT) at 7, 28, 90 and 180 days of water curing in conformity with ASTM C-1202 [24]. Three specimens of 100 mm in diameter and 50 mm in thickness which had been conditioned according to the standard were subjected to a 60-V potential for 6 h. The total charge passed through the concrete specimens was determined and used to evaluate the chloride permeability of each concrete mixture. 2.3.5. Salt ponding The salt ponding test was used similar to the test described in ASTM C 1543 [21]. Before the test, ponding specimens were air-dried, and then the lateral surface of specimens was coated with epoxy that was allowed to harden for up to 24 h. A dike was provided approximately 20 mm high along the perimeter of the top surface of the specimen to retain the ponding solution. The specimens with pond were subjected to continuous ponding with 3.0% NaCl solutions to a depth of 15 ± 5 mm for 90 days. The top of pond was sealed with plastic wrap to retard evaporation, and additional solution was added if necessary to maintain the 15 ± 5 mm depth [21,22]. After 90 days of exposure, the solution was removed and the specimens were allowed to dry. And then the surface of specimens was wire brushed until all salt crystal buildup was completely removed. After brushing, specimens ground in precision miling machine to produce samples at internal depth from the test face. The powder samples obtained were then dried at 105 °C to constant mass and ground to pass a 300-lm sieve. The powder samples were analyzed for total chloride content in accordance with AASHTO T260-97 [23]. After sieving, a 10-g sample of the powder is weighted and digested using concentrated HNO3 solution. Heat the acid solution to boiling on a heater and boil for about 1 min and then left to cool. The cooled samples were filtered through filter paper, the residue being washed with distilled water. Filtrate and washings were made up to 250 ml with distilled water. And the sample of filtrate was analyzed using a potentiometric automatic titratortitration. Two replicate specimens were tested and the mean value of these measurements is reported.

2.3.6. Surface Resistivity (SR) The electrical resistivity meter was used to measure the Surface Resistivity (SR) of the specimens. This non-destructive laboratory test method measures the electrical resistivity of water-saturated concrete and provides an indication of its permeability. The test result is a function of the electrical resistance of the specimen. Saturated cylinders (100  200 mm) were used at each test age. The electrical resistivity test for concretes was carried out by the four-point Wenner array probe technique. The probe array spacing used was 40 mm. The resistivity measurements were taken at four quaternary longitudinal locations of the specimen [25]. To examine the crystallography of the binder materials, X-ray Diffraction (XRD) analysis was carried out and to observe the hydrated products, instrumental SEM analysis was conducted at the ages of 7 and 28 days for cement paste samples.

3. Results and discussion 3.1. Compressive strength The compressive strengths of concrete specimens with varying w/b ratios are shown in Fig. 1. As expected, this demonstrates the level of compressive strength developed with the period of curing and with decreasing the w/b ratio. According to the literature, the main factors that affect the contribution of MK in the strength are (a) the filling effect, (b) the dilution effect, and (c) the pozzolanic reaction of MK with CH [26]. In general, the MK concretes had higher compressive strengths at various ages and up to 180 days when compared with the OPC concrete. As the case in point, the strength of the series2 MK concrete at 180 days age were higher than that of the control by about 13.4%, 24.1%and 14.6% for MK10, MK12.5 and MK15, respectively. The reduction in compressive strength for MK15 compare to MK12.5 is explained as the result of a clinker dilution effect. The dilution effect is a consequence of replacing a part of cement by the same quantity of metakaolin. In MK concrete, the filler effect, pozzolanic reaction of MK with CH and compounding effect (synergetic effect of mineral admixture) react opposite of the dilution effects [18,27]. For this reason, there is an optimum MK replacement for MK concrete. However in series1, replacement rate of 15% gives the best result when compared to other replacement levels. This was in a good agreement with the measurements reported by Parande et al. [18]. 3.2. Sorptivity Sorptivity, which is an index of moisture transport into unsaturated specimens, has been recognized as an important index of

Compressive strength (MPa) w/b=0.4

w/b=0.35

Compressive strength (Mpa)

w/b=0.5

Fig. 1. The effect of metakaolin on the compressive strength at various ages.

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concrete durability, because (a) the test method used for its determination reflects the way that most concretes will be penetrated by water and other injurious agents and (b) it is an especially good measure of the quality of the near surface concrete, which governs durability related to reinforcement corrosion [28]. Fig. 2 shows the variation in sorptivity of the concrete with different replacement levels of MK, w/b ratio, and testing age. It can be seen that sorptivity progressively decreases with the period of curing and increase with increasing the w/b ratio. It was found that the addition of 10% of MK gives the best result when compared to other replacement levels irrespective of w/b ratio and testing age. The increasing MK replacement levels from 10% to 15% adversely affect the inner permeability. The higher replacement levels of 15% MK are not helpful in improving inner durability of concrete and make the inner concrete more permeable [29]. According to the literatures [10,30,31] water absorption of concrete mixtures increased with the increase in MK content at all curing times. After 180 days, the maximum sorptivity coefficient is 7.83 (106) (m/s0.5) for the OPC (series1) mixture and the minimum is 2.07 (106) (m/s0.5) for the MK10 (series3) mixture. 3.3. Water penetration test One of the main factors of concrete durability is permeability. Concrete with lower permeability shows better resistance against chemical attacks. When water penetrates into the concrete, some

soluble salts including chloride ions penetrate into concrete and cause corrosion. Generally, it seems that lower permeability causes higher durability in concretes [32]. Water penetration test was used to evaluate the permeability of concretes and validity of these tests has been approved [20]. Fig. 3 shows the results of the water penetration depths in all concrete mixtures. As expected, the lower depth was obtained at 180 days for all concretes and the metakaolin concretes provided lower water penetration depth than OPC concretes. This issue is related to filler effect, pozzolanic reaction and heterogeneous nucleation. For example in series3, MK10 specimens provided a water penetration depth close to 2 mm, while OPC provided 5 mm water penetration depth. The increase of penetration depths for MK15 compare to MK10 is explained as the result of a clinker dilution effect. However in this study, this phenomenon has insignificant effect on water penetration depth. 3.4. Rapid Chloride Permeability Test (RCPT) The results for chloride penetration, measured in terms of the electric charge passed through the specimens in coulombs, obtained at the age of 7, 28, 90 and 180 days are presented in Fig. 4. With a continuous water-curing of up to 180 days and decreasing the w/b ratio, the charge passed through all concretes; was reduced. Results show that using metakaolin significantly enhances the resistance to chloride penetration compared with the OPC concrete. Kim et al. reported [35] that, all of mixtures with MK revealed very low

sorptivity coefficient (10 -6) (m/s 0.5)

sorptivity coefficient (10 -6) (m/s 0.5) w/b=0.5

w/b=0.4

w/b=0.35

Fig. 2. The effect of metakaolin on the sorptivity coefficient (106) (m/s0.5) at various ages.

water penteration depth (mm)

water penteration depth (mm) w/b=0.5

473

w/b=0.4

w/b=0.35

Fig. 3. The effect of metakaolin on the water penetration depth (mm) at various ages.

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RCPT(Coulomb) w/b=0.35

w/b=0.4

RCPT(Coulomb)

w/b=0.5

Fig. 4. The effect of metakaolin on the rapid chloride ions permeability (Coulomb) at various ages.

level in permeability. Also, Gruber et al. [17] showed that the use of 8% and 12% high reactivity metakaolin significantly decreased penetration of chloride ion in concretes. The enhancement of the resistance to chloride penetration can be related to pozzolanic reaction of MK with Ca(OH)2 and reduced electrical conductivity of MK concrete. In series1, at the age of 28 days, the OPC concretes specimens showed the highest value of 5266 coulombs while the charge passed through the MK15% concrete was 2052 coulombs. According to ASTM C 1202[24], when the charge passed through concrete during a 6 h period is below 1000 coulombs, it is categorized as very low chloride permeability. In series2 (after 180 days), the chloride permeability of the concrete specimens incorporating 12.5% and 15% MK were ‘‘very low’’, while that of the concrete specimens with 0% and 10% MK were ‘‘moderate’’ and ‘‘low’’, respectively. 3.5. Salt ponding test The RCPT test is an indirect measurement of the resistance to chloride ion penetration. The RCPT test has disadvantages such as, heat evolved in the test [33] and alteration in the pore fluid characteristics when pozzolanic materials are used. In addition, the flux in the RCPT may not be in steady-state condition due to the high potential difference of 60 V [34]. Hence, the results obtained may not represent true chloride diffusion in concrete [32]. The true service life models require the measurement of the mass transport coefficients that manage chloride movement in concrete [17]. In this study, the salt ponding test was used to determine the diffusion coefficient of concrete. Diffusion is the process by which matter is transported from one part of a system to another due to concentration gradient [22]. Chloride diffusion into concrete, like any diffusion process, is controlled by Fick’s second law of diffusion. Fick’s second law of diffusion and Crank’s Solution were fitted to the data using the Eqs. (2) and (3) to determine the diffusion coefficient (D) and the surface concentration (C0), respectively. 2

dC d C ¼D 2 dt dx

ð2Þ

where C is the concentration of ions as a function of distance x, at anytime t, and D is the diffusion coefficient.

   x C x;t ¼ C 0 1  erf pffiffiffiffiffiffi 2 Dt

ð3Þ

where Cx,t is the chloride concentration at depth x and time t, C0 is the chloride concentration at surface (x = 0), erf is the error function and D is the diffusion coefficient.

Table 4 The effect of metakaolin on the diffusion coefficient ((1012) (m2/s)) at various ages. Series

w/b

MK (%)

C0 (wt.%/concrete)

D (1012) (m2/s)

1

0.5

0 10 12.5 15

0.5048 0.6117 0.4034 0.3859

24.27 18.89 12.46 6.59

2

0.4

0 10 12.5 15

0.2613 0.2245 0.2166 0.2225

15.77 7.21 5.79 5.16

According to the salt ponding test (see Table 4), it can be concluded that the diffusion coefficient of concrete decreased with the decreasing w/b ratio for two series. The metakaolin concretes result generally in lesser diffusion coefficient and surface concentration. The metakaolin can improve the distribution of pore size of concrete, as the result of pozzolanic reaction and forming more C–S–H gel. Gruber et al. [17] showed that the apparent diffusion coefficients increased with increasing w/b ratio and considerably decreased with increasing HRM content. In series2, the diffusion coefficient in metakaolin concrete varies from 5.16 to 7.21(1012) (m2/s) while diffusion coefficient in OPC concrete is 15.77(1012) (m2/s). 3.6. Surface Resistivity (SR) Concrete Surface Resistivity (SR) test is a suitable indicator for concrete penetration and chloride ion permeability. It is a nondestructive, simple, rapid and economical method that can also be used on site. Electrical resistivity of concrete represents moving ions (such as chloride ions) in pore solution. Concrete resistivity depends both on the microstructure properties of the concrete and the conductivity of the pore solution. The conductivity property of the concrete is predominantly governed by the chemical compositions of the pore solutions, although also affected by the pore structure of the concrete [36]. It can specially be used on concretes when a large portion of their cementitious chemical reactions have been completed such as those concretes made with silica fume or metakaolin [32]. Results of the electrical resistivity tests (see Fig. 5) show that using MK drastically enhances the electrical resistivity compared to OPC concrete at about 2–4 times higher for the 15% MK concrete. In addition the electrical resistivity

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Surface resistivity (kΩcm) w/b=0.4

w/b=0.35

Surface resistivity (kΩcm)

w/b=0.5

Fig. 5. The effect of metakaolin on the Surface resistivity (kX cm) at various ages.

y = 11811e-0.032x R² = 0.8147 RCPT, coulomb

Surface resistivity (kΩcm)

y = 4.4839e0.0331x R² = 0.843

Compressive Strength, MPa

Compressive Strength, MPa

(a) Compressive strength and RCPT

(b) Compressive strength and SR y = 1.8441e-0.033x R² = 0.8683

sorptivity coefficient (10-6) (m/s 0.5)

water penetration depth (mm)

y = 31.864e-0.028x R² = 0.7353

Compressive Strength, MPa

Compressive Strength, MPa

(c) Compressive strength and water penetration

(d) Compressive strength and sorptivity

Fig. 6. Relationship between compressive strength and durability tests for all mixtures.

increases with decreasing the w/b ratio. The highest value of electrical resistivity is 91.75 kX cm for the MK15 (series3) mixture after 180 days and the minimum is 15.75 kX cm for the OPC (series1) mixture. Parande et al. [18] showed that incorporation of MK up to 15% into PC concrete improves the electrical resistivity of concrete.

3.7. Relationship between compressive strength and durability test results Pore structure influenced on both mechanical and durability properties. Hence, the relationship between compressive strength and durability parameters of concrete can be useful and beneficial

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[37]. Exponential regressions were used to correlate the results of compressive strength and durability test results (see Fig. 6). Generally an increase in strength is associated with an increase in electrical resistivity and decrease in sorptivity, water penetration depth and charge passed through the specimens. However, different factors influencing on compressive strength and durability of concrete. As the case, the strength of Interlayer Transition Zone (ITZ) that has no significant effect on concrete resistivity and sorptivity, whereas it is one of the main factors in compressive strength. On the other hand, chemical compound of pore solution has a great influence on concrete resistivity and the results of RCPT test while not affecting the compressive strength of concrete [32]. And also, compressive strength of concrete is governed by the total porosity but, the permeability of concrete is related to the pore connectivity [38,39].

relationship can be used to estimate permeability of concrete from the measured resistivity values. The similar conclusion can be found in the literatures [32,40]. In Fig. 7c, the data of chloride penetration test, expressed as the total charge passed in Coulombs, are plotted against the diffusion coefficients ((1012) (m2/s)). A linear relationship in the form of y = ax ± b seems to be the best fit of the data with a coefficient of correlation R2 = 0.96. It was observed that Rapid Chloride Permeability Test can provide a reasonable indication of ionic diffusivity in metakaolin concrete. Similar results were also reported by Gruber et al. and Thomas et al. [18,41]. On the other hand, there is good relationship between SR and salt ponding test (Fig. 7b), therefore Surface Resistivity (SR) can be used as an electrical indicator of chloride diffusion coefficients of MK concretes.

3.9. Scanning Electron Micrographs 3.8. Correlation between Surface Resistivity (SR), RCPT and salt ponding tests In order to analyze the interdependence between concrete resistivity, rapid chloride penetration and chloride diffusion coefficients measured in the present investigation, the correlation between them was also studied. It can be seen from Fig. 7 that there is significant exponential relationship between SR and RCPT tests and the correlation coefficients are basically larger than 0.92, which indicates that the

SEM micrographs of the cementitious paste with normal consistency of hydraulic cement (ASTM C187), with or without metakaolin at 7 and 28 days after hydration are shown in Fig. 8. The pore structures (tortuosity and constriction or disconnection) are improved with increasing the curing time. This trend deals with the hydration progress. Fig. 8c and d reveal that the microstructure of the MK cement paste is more uniform and compact than that of the ordinary Portland cement paste at 28 days, whereas this difference is not evident at 7 days (Fig. 8a and b). Fig. 9 shows higher

y = 51.239e-0.055x R² = 0.9488

RCPT ,coulomb

diffusion coefficients (10-12 )(m2/s)

y = 6454.4e-0.04x R² = 0.9219

Surface resistivity (kΩcm)

Surface resistivity (kΩcm)

(a) SR and RCPT

(b) SR and Salt ponding at 90 days

diffusion coefficients (10-12 )(m2/s)

y = 0.0067x - 1.4937 R² = 0.9605

RCPT ,coulomb

(c) RCPT and Salt ponding at 90 days Fig. 7. Correlation between Surface Resistivity (SR), RCPT and salt ponding tests.

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(a) 0% MK (OPC) cement paste at 7 days

(b) 15% MK cement paste, at 7 days

(c) 0% MK (OPC) cement paste at 28 days

(d) 15% MK cement paste, at 28 days

Fig. 8. SEM photographs of cement pastes (magnification: 500).

(a) 0% MK (OPC) cement paste at 7 days

(b) 15% MK cement paste, at 7 days

(c) 0% MK (OPC) cement paste at 28 days

(d) 15% MK cement paste, at 28 days

Fig. 9. SEM photograph of cement pastes (magnification: 10,000).

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C OH)2 Ca(O I=2228 Ca(O C OH))2 I= =88

Quaartz I=48

y count Intensity

Intensity count

478

Q Quarrtz =3557 I= Caa(OH H)2 I=1330

Caa(OH H)2 I=37

2θ θ

2

(a)

Ca(O OH)2 II=2448 Ca(O C OH))2 I= =99

Intensity count

Intensity count

(a)

Quaartz Q I=4412

Caa(OH H)2 I= =112

Ca((OH H)2 I=300

Quuartzz =77 I=

2

(b)

2θ

(b)

Fig. 11. XRD patterns of OPC pastes with 15% metakaolin: (a) at 7 days; (b) at 28 days.

Fig. 10. XRD patterns of OPC pastes without metakaolin: (a) at 7 days; (b) at 28 days.

magnification views of electron images than that of micrographs in Fig. 8. Metakaolin reacts with calcium hydroxide due to a pozzolanic reaction, therefore producing calcium silicate hydrates and calcium aluminosilicate hydrates [42]. Incorporation of 15% metakaolin as replacement material, resulted in the reduction of needle-like crystals of ettringite (see Fig. 9a), and Fibrous calcium silicate hydrates and calcium aluminosilicate hydrates are formed (Fig. 9b). In Fig. 9d, calcium hydroxide was no longer discernible. Larbi showed that Ca(OH)2 can be virtually eliminated from the cement matrix by using sufficient adapted metakaolin concentrations [10]. 3.10. X-ray Diffraction (XRD) test results For X-ray diffraction studies, selected cement paste samples cured for 7 and 28 days were used. The XRD patterns for the ordinary Portland cement pastes without metakaolin and with 15% metakaolin are shown in Figs. 10 and 11, respectively. It can be seen that in mixtures containing 15% MK, the peaks of Quartz are significantly larger than that of OPC mixture. On the other hand, The amount of portlandite (Ca(OH)2) in the metakaolin cement paste was lower than in the OPC paste. The results are in a qualitative agreement with the findings in [43] where was reported that the reduction in the calcium hydroxide (CH) diffraction peaks was obvious for metakaolin-concrete mixtures. The comparison between the diffractograms of cement pastes reveals that the addition of 15% metakaolin to cement paste leads to the reduction of intensity count of maximum peak of calcium hydroxide from

248 to 112 at 28 days. This issue is related to transforming calcium hydroxide (CH) into secondary C–S–H gel [15,44]. 4. Conclusion In this study, the effect of local metakaolin as supplementary cementing materials and filling materials on the strength and durability of concretes was investigated. From the results obtained in this study, the following conclusion can be drawn:  Concrete incorporating local metakaolin had higher compressive strength at various ages and up to 180 days when compared with the OPC concrete. The level of compressive strength developed with the period of curing and with decreasing the w/b ratio. For the materials in this study at w/b ratio 0.4 and 0.35, the optimum replacement of metakaolin is 12.5% and 10%, respectively.  The metakaolin concretes provided lower water penetration depth. It was found that in sorptivity test, the addition of 10% of MK gives the best result when compared to other replacement levels irrespective of w/b ratio and testing age.  According to salt ponding and RCPT tests, results show that using metakaolin significantly enhances the resistance to chloride penetration compared with the OPC concrete. This improvement increases with increasing metakaolin content.  Results of the electrical resistivity tests show that using MK drastically enhances the electrical resistivity compared to OPC concrete at about 2–4 times higher for the 15% MK.

A.A. Ramezanianpour, H. Bahrami Jovein / Construction and Building Materials 30 (2012) 470–479

 An exponential relationship between chloride permeability and compressive strength of concrete is exhibited, which indicates that the resistance to chloride penetration of concrete increases with increasing compressive strength. There is a significant linear relationship between Rapid Chloride Permeability Test and salt ponding test.  Scanning Electron Micrographs (SEMs) of cement pastes reveal that the microstructure of the MK cement paste is more uniform and compact than that of the ordinary Portland cement paste.

References [1] Sabir BB, Wild S, Bai J. Metakaolin and cacined clays as Pozzolans for concrete: a review. Cem Concr Compos 2001;23(6):441–54. [2] Wild S, Khabit JM, Jones A. Relative strength pozzolanic activity and cement hydration in uperplasticised metakaolin concrete. Cem Concr Res 1996;26(10):1537–44. [3] Coleman NJ, Page CL. Aspects of the pore solution chemistry of hydrated cement pastes containing MK. Cem Concr Res 1997;27(1):147–54. [4] Frias M, Cabrera J. Pore size distribution and degree of hydration of metakaolin–cement pastes. Cem Concr Res 2000;30(4):561–9. [5] Asbridge AH, Page CL, Page MM. Effects of metakaolin, water/binder ratio and interfacial transition zones on the microhardness of cement mortars. Cem Concr Res 2002;32(9):1365–9. [6] Klimesch DS, Ray A. Use of the second-derivative differential thermal curve in the evaluation of cement–quartz pastes with metakaolin addition autoclaved at 180°C. Thermochim Acta 1997;307(2):167–76. [7] Klimesch DS, Ray A. Autoclaved cement–quartz pastes with metakaolin additions. Adv Cem Based Mater 1998;7(3):109–18. [8] Changling H, Osbaeck B, Makovicky E. Pozzolanic reaction of six principal clay minerals: activation reactivity assessments and technological effects. Cem Concr Res 1995;25(8):1691–702. [9] Zhang MH, Malhotra VM. Characteristics of a thermally activated aluminosilicate pozzolanic material and its use in concrete. Cem Concr Res 1995;25(8):1713–25. [10] Courard L, Darimont A, Schouterden M, Ferauche F, Willem X, Degeimbre R. Durability of mortars modified with metakaolin. Cem Concr Res 2003;33(9):1473–9. [11] Khatib JM, Wild S. Pore size distribution of metakaolin paste. Cem Concr Res 1996;26:1545–53. [12] Coleman NJ, Page CI. Aspects of the pore solution chemistry of hydrated cement pastes containing metakaolin. Cem Concr Res 1997;27(1):147–54. [13] Curcio F, DeAngelis BA. Dilatant behavior of superplasticized cement pastes containing metakaolin. Cem Concr Res 1998;28(5):629–34. [14] Brooks JJ, Johari MMA. Effect of metakaolin on creep and shrinkage of concrete. Cem Concr Compos 2001;23(6):495–502. [15] Li Z, Ding Z. Property improvement of Portland cement by incorporating with metakaolin and slag. Cem Concr Res 2003;33(40):579–84. [16] Badogiannis E, Tsivilis S. Exploitation of poor Greek kaolins: durability of metakaolin concrete. Cem Concr Compos 2009;31(2):128–33. [17] Gruber KA, Ramlochan T, Boddy A, Hooton RD, Thomas MDA. Increasing concrete durability with high-reactivity metakaolin. Cem Concr Compos 2001;23(6):479–84. [18] Parande AK, Ramesh Babu B, Karthik MA, Kumaar KK, Palaniswamy N. Study on strength and corrosion performance for steel embedded in metakaolin blended concrete/mortar. Constr Build Mater 2008;22(3):127–34. [19] BS EN-480-5. Tests methods, determination of capillary absorption. British Standards Institution; 1997. [20] BS EN-12390-8. Depth of penetration of water under pressure. British Standards Institution; 2000.

479

[21] ASTM C 1543-02. Standard method of test for determining the penetration of chloride ion into Concrete by Ponding. ASTM, USA; 2002. [22] Yang CC, Chob SW, Wang LC. The relationship between pore structure and chloride diffusivity from ponding test in cement-based materials. Mater Chem Phys 2006;100(2–3):203–10. [23] AASHTO T 260-97. Standard method of test for sampling and testing for chloride ion in concrete and concrete raw materials. AASHTO, USA; 1997. [24] ASTM C 1202-97. Standard test method for electrical indication of concrete’s ability to resist chloride ion penetration. Philadelphia (PA): American Society for Testing and Materials; 1997. [25] FM 5-578. Florida method of test for concrete resistivity as an electrical indicator of its permeability; 2004. [26] Wild S, Khatib JM, Jones A. Relative strength, pozzolanic activity and cement hydration in superplasticized metakaolin concrete. Cem Concr Res 1996;26:1537–44. [27] Ding Z, Zhang D, Yu R. High strength composite cement. China Build Mater Sci Technol 1999;1:14–7. [28] Dias WPS. Sorptivity testing for assessing concrete quality. In: Proc Int Conf on Concrete under Severe Exposure Conditions (CONSEC ‘95), Spon, London; 1995. p. 433–442. [29] Siddique R, Kaur A. Effect of metakaolin on the near surface characteristics of concrete. Mater Struct 2011;44(1):77–88. [30] Khatib JM, Clay RM. Absorption characteristics of metakaolin concrete. Cem Concr Res 2004;34(1):19–29. [31] Razak HA, Chai HK, Wong HS. Near surface characteristics of concrete containing supplementary cementing materials. Cem Concr Compos 2004;26(7):883–9. [32] Ramezanianpour AA, Pilvar A, Mahdikhani M, Moodi F. Practical evaluation of relationship between concrete resistivity, water penetration, rapid chloride penetration and compressive strength. Constr Build Mater 2011;25(5):2472–9. [33] Gowripalan N, Mohamed HM. Chloride-ion induced corrosion of galvanized and ordinary steel reinforcement in high-performance concrete. Cem Concr Res 1998;28(8):1119–31. [34] Sharfuddin A, Kayali O, Anderson W. Chloride penetration in binary and ternary blended cement concretes as measured by two different rapid methods. Cem Concr Compos 2008;30(7):576–82. [35] Kim HS, Lee SH, Moon HY. Strength properties and durability aspects of high strength concrete using Korean metakaolin. Constr Build Mater 2007;21(6):1229–37. [36] krieg W. Rapid chloride permeability testing, a critical review. Proc Concr Hot Aggressive Environ 2008:147–56. [37] Shekarchi M, Bonakdar A, Bakhshi M, Mirdamadi A, Mobasher B. Transport properties in metakaolin blended concrete. Constr Build Mater 2010;24(11):2217–23. [38] Tanaka K, Kurumisawa K. Development of technique for observing pores in hardened cement paste. Cem Concr Res 2002;32(9):1435–41. [39] Zhao TJ, Zhu JQ, Feng NQ. Correlation between strength and permeability of concrete. Ind Constr 1997;27(5):14–7 [in Chinese]. [40] Julio-Betancourt GA, Hooton RD. Study of the Joule effect on rapid chloride permeability values and evaluation of related electrical properties of concretes. Cem Concr Res 2004;34(6):1007–15. [41] Thomas MDA, Jones MR. A critical review of service life modelling of concretes exposed to chlorides. In: Dhir RK, Hewlett PC, editors. Concrete in the service of mankind radical concrete technology. London: E & FN Spon; 1996. p. 723–36. [42] Kjellsen KO, Lagerblad B. Influence of natural minerals in the filler fraction on hydration and properties of mortars. Swedish Cem Concr Res Inst, CBI Report 1995;3(95):41. [43] Seleem HEH, Rashad AM, El-Sabbagh BA. Durability and strength evaluation of high-performance concrete in marine structures. Constr Build Mater 2010;24(6):878–84. [44] Güneyisi E, Gesog˘lu M, Mermerdas K. Improving strength, drying shrinkage, and pore structure of concrete using metakaolin. Mater Struct 2008;41(5):937–49.