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Strength properties and durability aspects of high strength concrete using Korean metakaolin
Construction and Building
MATERIALS
Construction and Building Materials 21 (2007) 1229–1237
www.elsevier.com/locate/conbuildmat
Strength properties and durability aspects of high strength concrete using Korean metakaolin Hong-Sam Kim a
a,*
, Sang-Ho Lee b, Han-Young Moon
c
Materials and Environmental Division, Highway and Transportation Technology Institute of Korea Highway Corporation, 50-5 Sancheok-ri, Dongtan-myeon, Hwasung-si, Gyeonggi-do, Republic of Korea b Department of Civil Engineering, Hanyang University and Researcher, Daelim Industrial Co., Ltd., Republic of Korea c Department of Civil Engineering, Hanyang University, 17 Haengdang-Dong, Seongdong-Gu, Seoul, Republic of Korea Received 1 November 2005; received in revised form 16 January 2006; accepted 31 May 2006 Available online 5 December 2006
Abstract Metakaolin is a cementitious material used as admixture to produce high strength concrete. In Korea, the utilization of this material remained mainly limited to fireproof walls but began recently to find applications as a replacement for silica fume in the manufacture of high performance concrete. In order to evaluate and compare the mechanical properties and durability of concrete using metakaolin, the following tests were conducted on concrete specimens using various replacements of silica fume and metakaolin; mechanical tests such as compressive, tensile and flexural strength tests, durability tests like rapid chloride permeability test, immersion test in acid solution, repeated freezing and thawing test and accelerated carbonation test. Strength tests revealed that the most appropriate strength was obtained for a substitution rate of metakaolin to binder ranging between 10% and 15%. It was observed that the resistance to chloride ion penetration reduced significantly as the proportion of silica fume and metakaolin binders increased. The filler effect resulting from the fine powder of both binders was seen to ameliorate substantially the resistance to chemical attacks in comparison with ordinary concrete. Durability tests also verified that concrete using metakaolin bore most of the mechanical and durability characteristics exhibited by concrete using silica fume. The tests implemented in this study confirmed that metakaolin constitutes a promising material as a substitute for the cost prohibitive silica fume. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Metakaolin; Silica fume; Durability; Permeability; Freezing and thawing; Carbonation; Chemical attack
1. Introduction Recently, the diversification of structures emphasized the interest on the workability and durability of concrete resulting from the growing necessity to provide high performance concretes exhibiting high strength and high durability. Representative admixtures that have been developed to date are fly ash, silica fume, blast furnace slag, etc. In most *
Corresponding author. Tel.: +82 31 371 3356; fax: +82 31 371 3359. E-mail addresses: [email protected], hskim68@freeway. co.kr (H.-S. Kim). 0950-0618/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2006.05.007
cases, mortars and concrete containing these materials with pozzolanic or latent hydraulic characteristics have mechanical properties and durability superior to that of OPC concrete [1–4]. In the last years, metakaolin (MK) has been introduced as a highly active and effective pozzolan for the partial replacement of cement in concrete. It is an ultra-fine material produced by the dehydroxylation of a kaoline precursor upon heating in the temperature range of 700–800 °C [5] and has high pozzolanic properties [6,7]. In general, among the supplementary cementitious materials, the remarkable performances exhibited by concrete mixed with silica fume in terms of strength and dura-
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bility favored its active exploitation where high strength or durable concrete were required. In Korea, however, the increase of construction costs due to the increasing price of imported silica fume compared to other admixtures led researchers to turn their interest toward metakaolin, an economical and promising cementitious material presenting similar strengthening effects as silica fume. Recent research trends focused essentially on the basic material and mechanical properties of metakaolin. With the intention to supplement these researches, the approach adopted in this study gives larger consideration on the fabrication and application aspects of high durability and high performance concrete. Therefore, this paper intends to verify the applicability of metakaolin in the fabrication of high-performance concrete exhibiting high strength and high durability through the experimental observation of the strength characteristics, resistance to salt attack and carbonation of concrete using metakaolin.
2.2. Test series 1
2. Experimental details
The purpose of the second test series is to compare the strength properties and thermal characteristics of concrete containing metakaolin or silica fume with fly ash for high strength concrete. Table 2 lists the mix proportions of concrete defined to have design strength of 60 MPa, slump flow of 50 ± 5.0 cm, air content of 3.0 ± 1.0%, and water to binder ratio (W/B) of 0.25. All the mix proportions of concrete were done so as to replace 20% of the weight of binder by fly ash taking account of high heat of hydration of high binder content. Nine mix proportions were manufactured with metakaolin and silica fume mixed at 0%, 5%, 10%, 15% and 20% of the weight of binder.
The purpose of the first test series is to compare the fundamental properties of metakaolin with those of silica fume. To examine the crystallography of the binder materials X-ray diffraction analysis was conducted and to observe the hydrated products instrumental analyses like SEM and EDS and X-ray diffraction method were carried out at 56 days for paste samples with water to binder ratio (W/B) of 0.5 when the replacement levels of the weight of cement were 0%, 5%, 10%, 15% and 20%. On the other hand, the flow value of mortars containing metakaolin or silica fume were evaluated. The mixture proportion of all mortars was binder/sand = 1:2.5 and water to binder ratio (W/B) of 0.5. Mortar mixtures were mixed with metakaolin or silica fume mixed at 0%, 5%, 10%, and 15% of the weight of cement without any chemical admixture. 2.3. Test series 2
2.1. Materials Ordinary Portland cement, silica fume (SF), metakaolin (MK) and fly ash (FA) were used as binder. The chemical and physical properties of these are summarized in Table 1. Washed sand was adopted for fine aggregate, and crushed stone with maximum size of 20 mm was used as coarse aggregate. The high range AE water reduction agent based on the salt of a polymetric naphthalene sulphonate was also introduced as chemical admixture. Table 1 Chemical and physical properties of binder Composition (%)
OPC FA MK SF
SiO2
Al2O3
Fe2O3
TiO2
CaO
MgO
Na2O + K2O
21.95 66.65 56 94.0
6.59 22.98 37 0.3
2.81 1.92 2.4 0.8
– – 0.2 –
60.1 1.61 2.4 0.3
3.32 0.87 0.3 0.4
– – 0.9 1.0
Specific gravity
Surface area (cm2/g)
Appearance
3.15 2.20 2.63 2.20
3112 4258 120,000 200,000
Gray Gray Light pink Gray
Table 2 Mix proportions of concrete in test series 2 W/B (%)
s/a (%)
Unit weight (kg/m3) Cementitious materials
Control MK05 MK10 MK15 MK20 SF05 SF10 SF15 SF20
25 25 25 25 25 25 25 25 25
37 37 37 37 37 37 37 37 37
Cement
FA
MK
SF
563 528 493 458 422 528 493 458 422
141 141 141 141 141 141 141 141 141
35 70 106 141 – – – –
– – – – 35 70 106 141
Water
Fine aggregate
Coarse aggregate
176 176 176 176 176 176 176 176 176
532 529 525 522 518 530 528 526 524
915 909 903 897 891 911 908 904 900
H.-S. Kim et al. / Construction and Building Materials 21 (2007) 1229–1237
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Fig. 1. Setup of the adiabatic temperature rise testing apparatus.
To examine the strength properties of concrete compressive, split tensile and bending tests were carried out at 1, 3, 7, 28, 56 and 91 days according to KS F 2405. To investigate the thermal property of concrete the adiabatic temperature rise test was performed. The test carried out only three mix proportions; these were Control, 10% replacement by metakaolin (MK10) and 10% replacement by silica fume (SF10). This was done to obtain input data that would be needed in the numerical simulation of thermal stress for the examination of the exothermic characteristics developed by the hydration of MK. Generally, the adiabatic temperature increase in concrete is formulated by means of an exponential function such as Eq. (1), which relates the adiabatic temperature rising in terms of the maximum adiabatic temperature gradient (K) and reaction rate (a) (see Fig. 1).
The resistance of concrete to carbonation was assessed by the phenolphthalein indicator method of KS F 2596. The accelerated conditions were 5% CO2, 60% RH and 30 °C. The carbonation depth of concrete was measured at 7, 14, 28 and 56 days. The resistance of concrete to freezing and thawing was assessed by accelerated freezing and thawing cycle test until 300 cycles according to KS F 2456(ASTM C 666). The relative dynamic modulus of elasticity was calculated. The resistance of concrete to acid attack was assessed by immersion test in 2% sulfuric acid solution until 8 weeks after 28 days of water curing. The solution was changed every week. Seven mix proportions of mortar were manufactured with MK or SF mixed at 0%, 5% and 15% of the binder weight with 0.5 water to binder ratio. The reduction rate of compressive strength was evaluated by Eq. (3).
T ¼ Kð1 eat Þ
Reduction ratio of compressive strength ð%Þ
ð1Þ
¼
Cw Cs 100 Cw
ð3Þ
where T is the adiabatic temperature rising gradient at time t (°C), K is the maximum adiabatic temperature rising gradient (°C), a is the reaction rate constant, and t is the age (day).
where Cw and Cs are the compressive strength before and after immersion, respectively.
2.4. Test series 3
3. Results and discussion
The purpose of the third test series is to compare the durability aspects of concrete containing MK or SF with fly ash for high strength concrete. In other to evaluate the resistance of concrete to salt, carbonation, freezing and thawing and acid attack, various accelerated tests were carried out. The mix proportion of concrete was the same in second test series. The resistance of concrete to salt attack was assessed by rapid chloride permeability test (RCPT) at 28, 56 and 91 days of water curing in conformity with ASTM C 1202. The total charge passed was obtained as expressed in Eq. (2).
3.1. Fundamental properties (Test series 1)
Qtotal ¼ 900 ðI 0 þ 2ðI 30 þ I 60 þ þ I 330 Þ þ I 360 Þ
ð2Þ
3.1.1. XRD analysis results of cement, silica fume and metakaolin Fig. 2 plots the XRD patterns of cement, MK and SF. In ordinary Portland cement, typical peaks of alite, belite and ferrite phase were detected. Silica fume was comprised of 94% silica and its XRD pattern indicates the low crystallinity with low intensity peaks corresponding mainly to quartz (Q), silicon carbide (SiC). On the other hand, the metakaolin produced by calcinations of kaolinite in Korea had silicon oxide of 56% and aluminum oxide of 37%. It showed a product of low crystallinity. Crystalline phases consisted of quartz (Q) and mica (M).
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Fig. 2. XRD patterns of ordinary Portland cement, metakaolin and silica fume.
When kaolin is heated to a temperature of 450 °C dehydroxylation occurs and the hydrated aluminosilicates are converted to materials consisting predominantly of chemically combined aluminum, silicon and oxygen. The rate at which water of crystallization is removed increases with increasing temperature and at 600 °C it proceeds to completion [8]. 3.1.2. XRD and SEM analyses results of hydration products Figs. 3 and 4 show the XRD patterns measured at 28 days for the ordinary Portland cement and the pastes mixed with 0%, 5%, 10%, 15% and 20% of MK or SF, respectively. The XRD patterns of the hydrate products are presented in Fig. 3 in the pastes replaced by 5%, 10%, 15% and 20% of MK. It can be seen that the crystalline phase of CH (portlandite) decreases as the replacement ratio of MK and SF increases, while the weak peaks of C–A–H, in pastes replaced by MK, slightly increase. The XRD patterns of the hydrate products are plotted in Fig. 4 in the pastes replaced by 5%, 10%, 15% and 20% of SF. It can be observed that the crystalline peak of CH decreases as the replacement rate increases while the weak peak of C–S–H increases. In Figs. 3 and 4, the decrease of the CH peak is related with the consumption by pozzolanic reaction of MK and SF [9]. Fig. 5 illustrates the results of SEM and EDS analysis obtained for the pastes of ordinary Portland cement, replacement of 10% by MK and SF, respectively. The
Fig. 3. XRD patterns of paste sample with replacement of 0%, 5%, 10%, 15% and 20% by metakaolin.
Results from the EDS analysis revealed the presence of C–S–H and CH as the main hydrated products in the case of ordinary Portland cement, while C–S–H was mainly observed for silica fume paste and C–A–S–H and C–A–H were observed for MK paste. It is known that thermal activation in air (at 600– 900 °C) of many clay mineral leads, by dehydroxylation, to breakdown or partial breakdown of the crystal lattice structure forming a transition phase with high reactivity. A typical example is the production of metakaolinite (Al2O3 Æ 2SiO2) or AS2 by calcining clay or lateritic soils rich in kaolinite [10]. The principal reaction is between the AS2 and the CH, derived from cement hydration, in the water. This reaction forms additional cementitious aluminum containing CSH gel, together with crystalline products, which include calcium aluminate hydrates and alumino-silicate hydrates (i.e., C2ASH8, C4AH13 and C3AH6). The crystalline products formed depend principally on the AS2/CH ratio and the reaction temperature [11–14]. 3.1.3. Flow value of mortars Fig. 6 shows the variations in the flow value of mortars with various replacement levels by MK or SF. In all mortar mixtures, the flow values appeared to decrease as the replacement ratio increased. The results demonstrate the higher water demand of SF as compared to MK. As
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Fig. 4. XRD patterns of paste sample with replacement of 0%, 5%, 10%, 15% and 20% by silica fume.
the replacement level increases, and SF is more demanding in high range water reducing admixture compared to MK. Caldarone et al. [15] observed that although the slump of concrete containing 10% MK was reduced from that of concrete with Portland cement only, the concrete containing MK required 25–35% less high range water reducers (HRWR) than equivalent SF mixtures. This reduction in HRWR demand resulted in the concrete containing MK having less sticky consistency and better finish than the concrete containing SF. 3.2. Strength and thermal properties (Test series 2) 3.2.1. Strength aspects Figs. 7–9 display the results obtained from the compressive, split tensile and flexural strength tests performed on the concrete specimens. The compressive strengths measured is shown in Fig. 7 for tests performed at 1, 3, 7, 28, 56, and 91 days. This demonstrates the level of compressive strength developed according to the replacement ratio of the binder by MK and SF, from 5% to 20%. A replacement ratio of 15% is seen to improve the development of compressive strength, but such effect appears to reduce for 20%. In other words, the most remarkable strengths were developed for replacement rates from 10% to 15%, with poor improvement effect for a replacement rate of 15% compared to 20%.
Fig. 5. SEM micrographs and EDS results of the hydrated pastes: (a) hydrated paste (Ordinary Portland cement), (b) hydrated paste (10% Metakaolin) and (c) hydrated paste (10% Silica fume).
Fig. 7 presents the tensile strengths measured for tests performed at 1, 3, 7, 28, 56, and 91 days. This demonstrates the level of tensile strength developed according to the
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Fig. 6. Flow value of mortar with replacement.
Fig. 7. Compressive strength versus replacement with ages.
Fig. 8. Split tensile strength versus replacement with ages.
Fig. 9. Flexural strength versus replacement with ages.
replacement ratio of the binder by MK and SF, from 5% to 20%. For binder replacement ratios ranging between 10% and 15%, it can be observed that the strength is improved as the replacement ratio increases, while the strength tends to reduce for 20%. It is also seen that the values of tensile strength reach about 6/100 of the compressive strength. The flexural strengths measured at 1, 3, 7, 28, 56 and 91 days is plotted in Fig. 9 to verify the level of flexural strength developed according to binder replacement ratios. Results revealed that the strength increases with the replacement ratio increases for binder replacement ratios ranging between 10% and 15% while, on the contrary, decreases for 20%. It can be verified that the values of the flexural strength reach about 1/100 of the compressive strength. Since the efficiency appears to decrease beyond a replacement rate of 10%, similar to the trend observed for compressive strength, 10% can also be accepted as an optimum replacement ratio for metakaolin considering the economic efficiency. Similar influences of MK on the strength of concrete have been reported by Wild et al. [6]. The authors identify three elementary factors, which influence the contribution that MK makes to concrete strength. These are the filler effect, which is immediate, the acceleration of PC hydration, which occurs within the first 24 h, and the pozzolanic reaction, which has its maximum effect within the first 7–14 days for all MK levels between 5% and 30%. 3.2.2. Thermal property Fig. 10 plots the experimental results of the adiabatic temperature rising tests performed up to 6 days after mixing on three types of concrete mix proportions. The tests revealed that the maximum adiabatic temperature rising gradient at 6 days was the largest for OPC, with a value of 57.1 °C, while MK 10% and SF 10% exhibited relatively lower gradients of 53.1 °C and 53.7 °C, relatively, which verified that concrete mixed with mineral admixtures are
H.-S. Kim et al. / Construction and Building Materials 21 (2007) 1229–1237
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Fig. 10. Results of adiabatic temperature rising tests.
Fig. 12. Accelerated freezing and thawing test results.
advantageous compared to OPC. On the contrary, the reaction rate constant (a) appeared relatively faster for MK 10% and SF 10%, with values of 1.385 and 1.270, than OPC with 0.860. This result shows that the development of strength is faster for mineral admixed concretes.
3.3.2. Resistance to freezing and thawing cycles Fig. 12 illustrates the freezing–thawing characteristics of high-strength concretes mixed with MK and SF. Tests were conducted for W/B of 25% on five mixtures; Control, the specimen without replacement by admixture, and four mixtures replaced by 5% and 10% of MK and SF, respectively. It is seen that the relative dynamic modulus of elasticity remains quasi-constant for the five types of concrete until 300 cycles. This can be explained by the low water to binder ratio of the high performance concretes and the entrained air content. In the scope of the tests achieved in this study, results revealed that concretes mixed with MK also exhibit resistance to freezing and thawing comparable to concretes mixed with SF.
3.3. Durability aspects (Test series 3) 3.3.1. Resistance to chloride ion penetration Fig. 11 illustrates the rapid chloride permeability tests for concretes. The permeability appeared to decrease as the replacement ratio and curing time increased. Also, all of mixtures with MK and SF revealed very low level in permeability. The increase in resistance to chloride permeability is due to the continued hydration and pozzolanic reaction, accompanied by a decrease in porosity and pore sizes [16,17].
Fig. 11. Total charge passed versus replacement level with metakaoin or silica fume.
3.3.3. Resistance to carbonation The accelerated carbonation depths are shown in Fig. 13 by age of concrete for nine mixtures measured at 7, 14, 28 and 56 days according to the phenolphthalein indicator method. It can be observed that the carbonation depth of concrete is larger than the control mix, regardless of the type of admixture and age of concrete. The carbonation depth of concrete replaced by MK in the figure is larger by 20 to 30% than the control mix at 28 days for replacement ratios of 5% and 10%, respectively. The carbonation depth becomes increasingly large at 56 days by 40% and 70% at 56 days for replacement ratios of 5% and 10%, respectively. On the other hand, the carbonation depth increases to about 100–370% for replacement ratios of 15% and 20% regardless of the age of concrete. As can be seen in Fig. 13, significantly large carbonation depths appeared also for concretes replaced by SF regardless of the age and replacement ratio, similarly to the concretes mixed with MK. The carbonation of both concretes mixed with MK and SF is characterized by significant increase of the carbonation depth according to the increase of the replacement ratio. It can be explained from the fact that the replacement of cement by MK or SF decreases the
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H.-S. Kim et al. / Construction and Building Materials 21 (2007) 1229–1237
Fig. 13. Carbonation depth versus replacement level with metakaoin or silica fume.
Fig. 14. Reduction of compressive strength in 2% sulfuric acid solution.
content of portlandite in hydrate products due to pozzolanic reaction. 3.3.4. Resistance to acid attack In Fig. 14, the results of immersion test in 2% sulfuric acid for mortar specimens are shown and compared with the reduction ratio of the compressive strength. Significant reduction of the strength was observed compared to the specimens that were not replaced with MK and SF. The compressive strength at 56 days revealed a reduction ratio difference of about 20% compared to the specimens replaced with 15% of MK and 15% of SF.
(1) Instrumental analysis results revealed that metakaolin is composed of non-crystalloidal SiO2, similar to that of silica-fume, as well as crystalloidal SiO2, mica components, and the presence of C–S–H and C–A–H constituting the main substances generated by the hydration. (2) From the adiabatic temperature rising tests, it was verified that the adiabatic temperature rising gradient of concretes replaced by metakaolin and silica-fume reduced compared to OPC, and that the reaction rate tended to increase according to exothermic characteristics. (3) Concretes replaced by metakaolin and silica-fume, with water to binder ratio of 25%, were seen to develop strength exceeding the design strength of 60 MPa. The replacement by both types of admixtures were verified to enhance the compressive, tensile and flexural strengths until a rate of 15% while, on the contrary, reducing the level of strength developed at a replacement rate of 20%. The improvement effect on strength appeared to be negligible from 10% to 15%, which made it possible to suggest that 10% constituted an appropriate replacement rate considering the expensive cost of metakaolin. (4) Test results related to the resistance of concrete to salt attack, according to ASTM C 1202, revealed that the permeability of chloride reduces as the replacement of admixture increased. This could be explained by the large Blaine values inducing filler effects on the pores of concrete, which subsequently improved the resistance to chloride penetration. (5) The relative dynamic modulus of elasticity was seen to remain quasi-constant, even after the 300 cycles of freezing–thawing tests. Also, hair line cracks could barely be observed in the tested specimens. Results revealed that concretes mixed with metakaolin also exhibited resistance to freezing and thawing comparable to concretes mixed with silica fume. (6) From the carbonation tests, it was verified that the carbonation depth increased with the replacement rate regardless of the type of mineral admixture. (7) Test results related to the resistance of mortar to sulfuric acid verified that the reduction rate of the compressive strength at 56 days was similar for replacement rates of 5% and 15% by metakaolin. Although the resistance presented by metakaolin mixed concretes was slightly below those exhibited by silica-fume replaced concretes, concrete replaced by metakaolin showed nevertheless a promising performance.
4. Conclusions Acknowledgements Mechanical and resistance tests have been conducted on ultra high strength and high durability concrete using metakaolin as admixture. Tests results made it possible to draw the following conclusions.
This study has been a part of a research project supported by Korea Ministry of Construction and Transportation (MOCT) via the Infra-Structures Assessment
H.-S. Kim et al. / Construction and Building Materials 21 (2007) 1229–1237
Research Center. The authors wish to express their gratitude for the financial support.
References [1] Massazza F, Oberti G. Durability of pozzolanic cements and Italian experience in mass concrete. In: Malhotra VM, editor. 2nd Inter conference on durability and concrete, Vol. II. Montreal, Canada: American Concrete Institute; 1991. p. 1259–83. [2] Klimesch DS, Ray A. Autoclaved cement-quartz pastes with metakaolin additions. Adv Cem Based Mater 1998;7:109–18. [3] Silva PS, Glasser FP. Phase relation in the system CaO–Al2O3–SiO2– H2O relevant to MK-lime hydration. Cement Concrete Res 1993;23:627–39. [4] Ambroise J, Maximilien S, Pera P. Properties of MK blended cement. Adv Cem Based Mater 1994;1:161–8. [5] Coleman NJ, Page CL. Aspects of the pore solution chemistry of hydrated cement pastes containing MK. Cement Concrete Res 1997;27(1):147–54. [6] Wild S, Khatib JM, Jones A. Relative strength pozzolanic activity and cement hydration in superplasticised MK concrete. Cement Concrete Res 1996;26(10):1537–44. [7] Bai J, Wild S, Sabir BB, Kinuthin JM. Workability of concrete in incorporating PFA and MK. Mag Concrete Res 1999;51(3):207–26. [8] Highley DE. China clay, Mineral Dossier No. 26. HMSO, London.
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[9] Frias M, Cabrera J. Pore size distribution and degree of hydration of metakaolin–cement pastes. Cement Concrete Res 2000;30:561–9. [10] Pera J, Ambroise J, Messi A. Pozzolanic activity of calcined laterite. Silicates Industry. Ceram Sci Technol 1998;63(7–8):107–11. [11] Wild S, Khatib J, Roose LJ. Chemical and autogenous shrinkage of Portland cement–metakaolin pastes. Adv Cement Res 1998;10(3):109–19. [12] Murat M. Hydration reaction and hardening of calcined clays and related minerals. Cement Concrete Res 1983;13:259–66. [13] Kinuthia JM, Wild S, Sabir BB, Bai J. Self-compensating autogenous shrinkage in Portland cement–metakaolin–fly ash pastes. Adv Cement Res 2000;12(1):35–43. [14] Khatib JM, Sabir BB, Wild S. Some properties of metakaolin paste and mortar. In: Dhir RK, Dyer TD, editors. International congress, concrete in the service of mankind – concrete for environmental enhancement and protection, Theme 6 waste materials and alternative product, University of Dundee, 1996. London: E & F N Spon; 1996. p. 637–44. [15] Caldarone MA, Gruber KA, Burg RG. High reactivity metakaolin: a new generation mineral admixture. Concrete Int November 1994:37–40. [16] Curcio F, DeAngelis BA, Pagliolico S. Metakaolin as a pozzolanic microfiller for high-performance mortars. Cement Concrete Research 1998;28:803–9. [17] Detwiler RJ, Fapohunda CA, Natale J. Use of Supplementary cementing materials to increase the resistance to chloride ion penetration of concretes cured at elevated temperatures. ACI materials journal 1994;91:63–6.
MATERIALS
Construction and Building Materials 21 (2007) 1229–1237
www.elsevier.com/locate/conbuildmat
Strength properties and durability aspects of high strength concrete using Korean metakaolin Hong-Sam Kim a
a,*
, Sang-Ho Lee b, Han-Young Moon
c
Materials and Environmental Division, Highway and Transportation Technology Institute of Korea Highway Corporation, 50-5 Sancheok-ri, Dongtan-myeon, Hwasung-si, Gyeonggi-do, Republic of Korea b Department of Civil Engineering, Hanyang University and Researcher, Daelim Industrial Co., Ltd., Republic of Korea c Department of Civil Engineering, Hanyang University, 17 Haengdang-Dong, Seongdong-Gu, Seoul, Republic of Korea Received 1 November 2005; received in revised form 16 January 2006; accepted 31 May 2006 Available online 5 December 2006
Abstract Metakaolin is a cementitious material used as admixture to produce high strength concrete. In Korea, the utilization of this material remained mainly limited to fireproof walls but began recently to find applications as a replacement for silica fume in the manufacture of high performance concrete. In order to evaluate and compare the mechanical properties and durability of concrete using metakaolin, the following tests were conducted on concrete specimens using various replacements of silica fume and metakaolin; mechanical tests such as compressive, tensile and flexural strength tests, durability tests like rapid chloride permeability test, immersion test in acid solution, repeated freezing and thawing test and accelerated carbonation test. Strength tests revealed that the most appropriate strength was obtained for a substitution rate of metakaolin to binder ranging between 10% and 15%. It was observed that the resistance to chloride ion penetration reduced significantly as the proportion of silica fume and metakaolin binders increased. The filler effect resulting from the fine powder of both binders was seen to ameliorate substantially the resistance to chemical attacks in comparison with ordinary concrete. Durability tests also verified that concrete using metakaolin bore most of the mechanical and durability characteristics exhibited by concrete using silica fume. The tests implemented in this study confirmed that metakaolin constitutes a promising material as a substitute for the cost prohibitive silica fume. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Metakaolin; Silica fume; Durability; Permeability; Freezing and thawing; Carbonation; Chemical attack
1. Introduction Recently, the diversification of structures emphasized the interest on the workability and durability of concrete resulting from the growing necessity to provide high performance concretes exhibiting high strength and high durability. Representative admixtures that have been developed to date are fly ash, silica fume, blast furnace slag, etc. In most *
Corresponding author. Tel.: +82 31 371 3356; fax: +82 31 371 3359. E-mail addresses: [email protected], hskim68@freeway. co.kr (H.-S. Kim). 0950-0618/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2006.05.007
cases, mortars and concrete containing these materials with pozzolanic or latent hydraulic characteristics have mechanical properties and durability superior to that of OPC concrete [1–4]. In the last years, metakaolin (MK) has been introduced as a highly active and effective pozzolan for the partial replacement of cement in concrete. It is an ultra-fine material produced by the dehydroxylation of a kaoline precursor upon heating in the temperature range of 700–800 °C [5] and has high pozzolanic properties [6,7]. In general, among the supplementary cementitious materials, the remarkable performances exhibited by concrete mixed with silica fume in terms of strength and dura-
1230
H.-S. Kim et al. / Construction and Building Materials 21 (2007) 1229–1237
bility favored its active exploitation where high strength or durable concrete were required. In Korea, however, the increase of construction costs due to the increasing price of imported silica fume compared to other admixtures led researchers to turn their interest toward metakaolin, an economical and promising cementitious material presenting similar strengthening effects as silica fume. Recent research trends focused essentially on the basic material and mechanical properties of metakaolin. With the intention to supplement these researches, the approach adopted in this study gives larger consideration on the fabrication and application aspects of high durability and high performance concrete. Therefore, this paper intends to verify the applicability of metakaolin in the fabrication of high-performance concrete exhibiting high strength and high durability through the experimental observation of the strength characteristics, resistance to salt attack and carbonation of concrete using metakaolin.
2.2. Test series 1
2. Experimental details
The purpose of the second test series is to compare the strength properties and thermal characteristics of concrete containing metakaolin or silica fume with fly ash for high strength concrete. Table 2 lists the mix proportions of concrete defined to have design strength of 60 MPa, slump flow of 50 ± 5.0 cm, air content of 3.0 ± 1.0%, and water to binder ratio (W/B) of 0.25. All the mix proportions of concrete were done so as to replace 20% of the weight of binder by fly ash taking account of high heat of hydration of high binder content. Nine mix proportions were manufactured with metakaolin and silica fume mixed at 0%, 5%, 10%, 15% and 20% of the weight of binder.
The purpose of the first test series is to compare the fundamental properties of metakaolin with those of silica fume. To examine the crystallography of the binder materials X-ray diffraction analysis was conducted and to observe the hydrated products instrumental analyses like SEM and EDS and X-ray diffraction method were carried out at 56 days for paste samples with water to binder ratio (W/B) of 0.5 when the replacement levels of the weight of cement were 0%, 5%, 10%, 15% and 20%. On the other hand, the flow value of mortars containing metakaolin or silica fume were evaluated. The mixture proportion of all mortars was binder/sand = 1:2.5 and water to binder ratio (W/B) of 0.5. Mortar mixtures were mixed with metakaolin or silica fume mixed at 0%, 5%, 10%, and 15% of the weight of cement without any chemical admixture. 2.3. Test series 2
2.1. Materials Ordinary Portland cement, silica fume (SF), metakaolin (MK) and fly ash (FA) were used as binder. The chemical and physical properties of these are summarized in Table 1. Washed sand was adopted for fine aggregate, and crushed stone with maximum size of 20 mm was used as coarse aggregate. The high range AE water reduction agent based on the salt of a polymetric naphthalene sulphonate was also introduced as chemical admixture. Table 1 Chemical and physical properties of binder Composition (%)
OPC FA MK SF
SiO2
Al2O3
Fe2O3
TiO2
CaO
MgO
Na2O + K2O
21.95 66.65 56 94.0
6.59 22.98 37 0.3
2.81 1.92 2.4 0.8
– – 0.2 –
60.1 1.61 2.4 0.3
3.32 0.87 0.3 0.4
– – 0.9 1.0
Specific gravity
Surface area (cm2/g)
Appearance
3.15 2.20 2.63 2.20
3112 4258 120,000 200,000
Gray Gray Light pink Gray
Table 2 Mix proportions of concrete in test series 2 W/B (%)
s/a (%)
Unit weight (kg/m3) Cementitious materials
Control MK05 MK10 MK15 MK20 SF05 SF10 SF15 SF20
25 25 25 25 25 25 25 25 25
37 37 37 37 37 37 37 37 37
Cement
FA
MK
SF
563 528 493 458 422 528 493 458 422
141 141 141 141 141 141 141 141 141
35 70 106 141 – – – –
– – – – 35 70 106 141
Water
Fine aggregate
Coarse aggregate
176 176 176 176 176 176 176 176 176
532 529 525 522 518 530 528 526 524
915 909 903 897 891 911 908 904 900
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Fig. 1. Setup of the adiabatic temperature rise testing apparatus.
To examine the strength properties of concrete compressive, split tensile and bending tests were carried out at 1, 3, 7, 28, 56 and 91 days according to KS F 2405. To investigate the thermal property of concrete the adiabatic temperature rise test was performed. The test carried out only three mix proportions; these were Control, 10% replacement by metakaolin (MK10) and 10% replacement by silica fume (SF10). This was done to obtain input data that would be needed in the numerical simulation of thermal stress for the examination of the exothermic characteristics developed by the hydration of MK. Generally, the adiabatic temperature increase in concrete is formulated by means of an exponential function such as Eq. (1), which relates the adiabatic temperature rising in terms of the maximum adiabatic temperature gradient (K) and reaction rate (a) (see Fig. 1).
The resistance of concrete to carbonation was assessed by the phenolphthalein indicator method of KS F 2596. The accelerated conditions were 5% CO2, 60% RH and 30 °C. The carbonation depth of concrete was measured at 7, 14, 28 and 56 days. The resistance of concrete to freezing and thawing was assessed by accelerated freezing and thawing cycle test until 300 cycles according to KS F 2456(ASTM C 666). The relative dynamic modulus of elasticity was calculated. The resistance of concrete to acid attack was assessed by immersion test in 2% sulfuric acid solution until 8 weeks after 28 days of water curing. The solution was changed every week. Seven mix proportions of mortar were manufactured with MK or SF mixed at 0%, 5% and 15% of the binder weight with 0.5 water to binder ratio. The reduction rate of compressive strength was evaluated by Eq. (3).
T ¼ Kð1 eat Þ
Reduction ratio of compressive strength ð%Þ
ð1Þ
¼
Cw Cs 100 Cw
ð3Þ
where T is the adiabatic temperature rising gradient at time t (°C), K is the maximum adiabatic temperature rising gradient (°C), a is the reaction rate constant, and t is the age (day).
where Cw and Cs are the compressive strength before and after immersion, respectively.
2.4. Test series 3
3. Results and discussion
The purpose of the third test series is to compare the durability aspects of concrete containing MK or SF with fly ash for high strength concrete. In other to evaluate the resistance of concrete to salt, carbonation, freezing and thawing and acid attack, various accelerated tests were carried out. The mix proportion of concrete was the same in second test series. The resistance of concrete to salt attack was assessed by rapid chloride permeability test (RCPT) at 28, 56 and 91 days of water curing in conformity with ASTM C 1202. The total charge passed was obtained as expressed in Eq. (2).
3.1. Fundamental properties (Test series 1)
Qtotal ¼ 900 ðI 0 þ 2ðI 30 þ I 60 þ þ I 330 Þ þ I 360 Þ
ð2Þ
3.1.1. XRD analysis results of cement, silica fume and metakaolin Fig. 2 plots the XRD patterns of cement, MK and SF. In ordinary Portland cement, typical peaks of alite, belite and ferrite phase were detected. Silica fume was comprised of 94% silica and its XRD pattern indicates the low crystallinity with low intensity peaks corresponding mainly to quartz (Q), silicon carbide (SiC). On the other hand, the metakaolin produced by calcinations of kaolinite in Korea had silicon oxide of 56% and aluminum oxide of 37%. It showed a product of low crystallinity. Crystalline phases consisted of quartz (Q) and mica (M).
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Fig. 2. XRD patterns of ordinary Portland cement, metakaolin and silica fume.
When kaolin is heated to a temperature of 450 °C dehydroxylation occurs and the hydrated aluminosilicates are converted to materials consisting predominantly of chemically combined aluminum, silicon and oxygen. The rate at which water of crystallization is removed increases with increasing temperature and at 600 °C it proceeds to completion [8]. 3.1.2. XRD and SEM analyses results of hydration products Figs. 3 and 4 show the XRD patterns measured at 28 days for the ordinary Portland cement and the pastes mixed with 0%, 5%, 10%, 15% and 20% of MK or SF, respectively. The XRD patterns of the hydrate products are presented in Fig. 3 in the pastes replaced by 5%, 10%, 15% and 20% of MK. It can be seen that the crystalline phase of CH (portlandite) decreases as the replacement ratio of MK and SF increases, while the weak peaks of C–A–H, in pastes replaced by MK, slightly increase. The XRD patterns of the hydrate products are plotted in Fig. 4 in the pastes replaced by 5%, 10%, 15% and 20% of SF. It can be observed that the crystalline peak of CH decreases as the replacement rate increases while the weak peak of C–S–H increases. In Figs. 3 and 4, the decrease of the CH peak is related with the consumption by pozzolanic reaction of MK and SF [9]. Fig. 5 illustrates the results of SEM and EDS analysis obtained for the pastes of ordinary Portland cement, replacement of 10% by MK and SF, respectively. The
Fig. 3. XRD patterns of paste sample with replacement of 0%, 5%, 10%, 15% and 20% by metakaolin.
Results from the EDS analysis revealed the presence of C–S–H and CH as the main hydrated products in the case of ordinary Portland cement, while C–S–H was mainly observed for silica fume paste and C–A–S–H and C–A–H were observed for MK paste. It is known that thermal activation in air (at 600– 900 °C) of many clay mineral leads, by dehydroxylation, to breakdown or partial breakdown of the crystal lattice structure forming a transition phase with high reactivity. A typical example is the production of metakaolinite (Al2O3 Æ 2SiO2) or AS2 by calcining clay or lateritic soils rich in kaolinite [10]. The principal reaction is between the AS2 and the CH, derived from cement hydration, in the water. This reaction forms additional cementitious aluminum containing CSH gel, together with crystalline products, which include calcium aluminate hydrates and alumino-silicate hydrates (i.e., C2ASH8, C4AH13 and C3AH6). The crystalline products formed depend principally on the AS2/CH ratio and the reaction temperature [11–14]. 3.1.3. Flow value of mortars Fig. 6 shows the variations in the flow value of mortars with various replacement levels by MK or SF. In all mortar mixtures, the flow values appeared to decrease as the replacement ratio increased. The results demonstrate the higher water demand of SF as compared to MK. As
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Fig. 4. XRD patterns of paste sample with replacement of 0%, 5%, 10%, 15% and 20% by silica fume.
the replacement level increases, and SF is more demanding in high range water reducing admixture compared to MK. Caldarone et al. [15] observed that although the slump of concrete containing 10% MK was reduced from that of concrete with Portland cement only, the concrete containing MK required 25–35% less high range water reducers (HRWR) than equivalent SF mixtures. This reduction in HRWR demand resulted in the concrete containing MK having less sticky consistency and better finish than the concrete containing SF. 3.2. Strength and thermal properties (Test series 2) 3.2.1. Strength aspects Figs. 7–9 display the results obtained from the compressive, split tensile and flexural strength tests performed on the concrete specimens. The compressive strengths measured is shown in Fig. 7 for tests performed at 1, 3, 7, 28, 56, and 91 days. This demonstrates the level of compressive strength developed according to the replacement ratio of the binder by MK and SF, from 5% to 20%. A replacement ratio of 15% is seen to improve the development of compressive strength, but such effect appears to reduce for 20%. In other words, the most remarkable strengths were developed for replacement rates from 10% to 15%, with poor improvement effect for a replacement rate of 15% compared to 20%.
Fig. 5. SEM micrographs and EDS results of the hydrated pastes: (a) hydrated paste (Ordinary Portland cement), (b) hydrated paste (10% Metakaolin) and (c) hydrated paste (10% Silica fume).
Fig. 7 presents the tensile strengths measured for tests performed at 1, 3, 7, 28, 56, and 91 days. This demonstrates the level of tensile strength developed according to the
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Fig. 6. Flow value of mortar with replacement.
Fig. 7. Compressive strength versus replacement with ages.
Fig. 8. Split tensile strength versus replacement with ages.
Fig. 9. Flexural strength versus replacement with ages.
replacement ratio of the binder by MK and SF, from 5% to 20%. For binder replacement ratios ranging between 10% and 15%, it can be observed that the strength is improved as the replacement ratio increases, while the strength tends to reduce for 20%. It is also seen that the values of tensile strength reach about 6/100 of the compressive strength. The flexural strengths measured at 1, 3, 7, 28, 56 and 91 days is plotted in Fig. 9 to verify the level of flexural strength developed according to binder replacement ratios. Results revealed that the strength increases with the replacement ratio increases for binder replacement ratios ranging between 10% and 15% while, on the contrary, decreases for 20%. It can be verified that the values of the flexural strength reach about 1/100 of the compressive strength. Since the efficiency appears to decrease beyond a replacement rate of 10%, similar to the trend observed for compressive strength, 10% can also be accepted as an optimum replacement ratio for metakaolin considering the economic efficiency. Similar influences of MK on the strength of concrete have been reported by Wild et al. [6]. The authors identify three elementary factors, which influence the contribution that MK makes to concrete strength. These are the filler effect, which is immediate, the acceleration of PC hydration, which occurs within the first 24 h, and the pozzolanic reaction, which has its maximum effect within the first 7–14 days for all MK levels between 5% and 30%. 3.2.2. Thermal property Fig. 10 plots the experimental results of the adiabatic temperature rising tests performed up to 6 days after mixing on three types of concrete mix proportions. The tests revealed that the maximum adiabatic temperature rising gradient at 6 days was the largest for OPC, with a value of 57.1 °C, while MK 10% and SF 10% exhibited relatively lower gradients of 53.1 °C and 53.7 °C, relatively, which verified that concrete mixed with mineral admixtures are
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Fig. 10. Results of adiabatic temperature rising tests.
Fig. 12. Accelerated freezing and thawing test results.
advantageous compared to OPC. On the contrary, the reaction rate constant (a) appeared relatively faster for MK 10% and SF 10%, with values of 1.385 and 1.270, than OPC with 0.860. This result shows that the development of strength is faster for mineral admixed concretes.
3.3.2. Resistance to freezing and thawing cycles Fig. 12 illustrates the freezing–thawing characteristics of high-strength concretes mixed with MK and SF. Tests were conducted for W/B of 25% on five mixtures; Control, the specimen without replacement by admixture, and four mixtures replaced by 5% and 10% of MK and SF, respectively. It is seen that the relative dynamic modulus of elasticity remains quasi-constant for the five types of concrete until 300 cycles. This can be explained by the low water to binder ratio of the high performance concretes and the entrained air content. In the scope of the tests achieved in this study, results revealed that concretes mixed with MK also exhibit resistance to freezing and thawing comparable to concretes mixed with SF.
3.3. Durability aspects (Test series 3) 3.3.1. Resistance to chloride ion penetration Fig. 11 illustrates the rapid chloride permeability tests for concretes. The permeability appeared to decrease as the replacement ratio and curing time increased. Also, all of mixtures with MK and SF revealed very low level in permeability. The increase in resistance to chloride permeability is due to the continued hydration and pozzolanic reaction, accompanied by a decrease in porosity and pore sizes [16,17].
Fig. 11. Total charge passed versus replacement level with metakaoin or silica fume.
3.3.3. Resistance to carbonation The accelerated carbonation depths are shown in Fig. 13 by age of concrete for nine mixtures measured at 7, 14, 28 and 56 days according to the phenolphthalein indicator method. It can be observed that the carbonation depth of concrete is larger than the control mix, regardless of the type of admixture and age of concrete. The carbonation depth of concrete replaced by MK in the figure is larger by 20 to 30% than the control mix at 28 days for replacement ratios of 5% and 10%, respectively. The carbonation depth becomes increasingly large at 56 days by 40% and 70% at 56 days for replacement ratios of 5% and 10%, respectively. On the other hand, the carbonation depth increases to about 100–370% for replacement ratios of 15% and 20% regardless of the age of concrete. As can be seen in Fig. 13, significantly large carbonation depths appeared also for concretes replaced by SF regardless of the age and replacement ratio, similarly to the concretes mixed with MK. The carbonation of both concretes mixed with MK and SF is characterized by significant increase of the carbonation depth according to the increase of the replacement ratio. It can be explained from the fact that the replacement of cement by MK or SF decreases the
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Fig. 13. Carbonation depth versus replacement level with metakaoin or silica fume.
Fig. 14. Reduction of compressive strength in 2% sulfuric acid solution.
content of portlandite in hydrate products due to pozzolanic reaction. 3.3.4. Resistance to acid attack In Fig. 14, the results of immersion test in 2% sulfuric acid for mortar specimens are shown and compared with the reduction ratio of the compressive strength. Significant reduction of the strength was observed compared to the specimens that were not replaced with MK and SF. The compressive strength at 56 days revealed a reduction ratio difference of about 20% compared to the specimens replaced with 15% of MK and 15% of SF.
(1) Instrumental analysis results revealed that metakaolin is composed of non-crystalloidal SiO2, similar to that of silica-fume, as well as crystalloidal SiO2, mica components, and the presence of C–S–H and C–A–H constituting the main substances generated by the hydration. (2) From the adiabatic temperature rising tests, it was verified that the adiabatic temperature rising gradient of concretes replaced by metakaolin and silica-fume reduced compared to OPC, and that the reaction rate tended to increase according to exothermic characteristics. (3) Concretes replaced by metakaolin and silica-fume, with water to binder ratio of 25%, were seen to develop strength exceeding the design strength of 60 MPa. The replacement by both types of admixtures were verified to enhance the compressive, tensile and flexural strengths until a rate of 15% while, on the contrary, reducing the level of strength developed at a replacement rate of 20%. The improvement effect on strength appeared to be negligible from 10% to 15%, which made it possible to suggest that 10% constituted an appropriate replacement rate considering the expensive cost of metakaolin. (4) Test results related to the resistance of concrete to salt attack, according to ASTM C 1202, revealed that the permeability of chloride reduces as the replacement of admixture increased. This could be explained by the large Blaine values inducing filler effects on the pores of concrete, which subsequently improved the resistance to chloride penetration. (5) The relative dynamic modulus of elasticity was seen to remain quasi-constant, even after the 300 cycles of freezing–thawing tests. Also, hair line cracks could barely be observed in the tested specimens. Results revealed that concretes mixed with metakaolin also exhibited resistance to freezing and thawing comparable to concretes mixed with silica fume. (6) From the carbonation tests, it was verified that the carbonation depth increased with the replacement rate regardless of the type of mineral admixture. (7) Test results related to the resistance of mortar to sulfuric acid verified that the reduction rate of the compressive strength at 56 days was similar for replacement rates of 5% and 15% by metakaolin. Although the resistance presented by metakaolin mixed concretes was slightly below those exhibited by silica-fume replaced concretes, concrete replaced by metakaolin showed nevertheless a promising performance.
4. Conclusions Acknowledgements Mechanical and resistance tests have been conducted on ultra high strength and high durability concrete using metakaolin as admixture. Tests results made it possible to draw the following conclusions.
This study has been a part of a research project supported by Korea Ministry of Construction and Transportation (MOCT) via the Infra-Structures Assessment
H.-S. Kim et al. / Construction and Building Materials 21 (2007) 1229–1237
Research Center. The authors wish to express their gratitude for the financial support.
References [1] Massazza F, Oberti G. Durability of pozzolanic cements and Italian experience in mass concrete. In: Malhotra VM, editor. 2nd Inter conference on durability and concrete, Vol. II. Montreal, Canada: American Concrete Institute; 1991. p. 1259–83. [2] Klimesch DS, Ray A. Autoclaved cement-quartz pastes with metakaolin additions. Adv Cem Based Mater 1998;7:109–18. [3] Silva PS, Glasser FP. Phase relation in the system CaO–Al2O3–SiO2– H2O relevant to MK-lime hydration. Cement Concrete Res 1993;23:627–39. [4] Ambroise J, Maximilien S, Pera P. Properties of MK blended cement. Adv Cem Based Mater 1994;1:161–8. [5] Coleman NJ, Page CL. Aspects of the pore solution chemistry of hydrated cement pastes containing MK. Cement Concrete Res 1997;27(1):147–54. [6] Wild S, Khatib JM, Jones A. Relative strength pozzolanic activity and cement hydration in superplasticised MK concrete. Cement Concrete Res 1996;26(10):1537–44. [7] Bai J, Wild S, Sabir BB, Kinuthin JM. Workability of concrete in incorporating PFA and MK. Mag Concrete Res 1999;51(3):207–26. [8] Highley DE. China clay, Mineral Dossier No. 26. HMSO, London.
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[9] Frias M, Cabrera J. Pore size distribution and degree of hydration of metakaolin–cement pastes. Cement Concrete Res 2000;30:561–9. [10] Pera J, Ambroise J, Messi A. Pozzolanic activity of calcined laterite. Silicates Industry. Ceram Sci Technol 1998;63(7–8):107–11. [11] Wild S, Khatib J, Roose LJ. Chemical and autogenous shrinkage of Portland cement–metakaolin pastes. Adv Cement Res 1998;10(3):109–19. [12] Murat M. Hydration reaction and hardening of calcined clays and related minerals. Cement Concrete Res 1983;13:259–66. [13] Kinuthia JM, Wild S, Sabir BB, Bai J. Self-compensating autogenous shrinkage in Portland cement–metakaolin–fly ash pastes. Adv Cement Res 2000;12(1):35–43. [14] Khatib JM, Sabir BB, Wild S. Some properties of metakaolin paste and mortar. In: Dhir RK, Dyer TD, editors. International congress, concrete in the service of mankind – concrete for environmental enhancement and protection, Theme 6 waste materials and alternative product, University of Dundee, 1996. London: E & F N Spon; 1996. p. 637–44. [15] Caldarone MA, Gruber KA, Burg RG. High reactivity metakaolin: a new generation mineral admixture. Concrete Int November 1994:37–40. [16] Curcio F, DeAngelis BA, Pagliolico S. Metakaolin as a pozzolanic microfiller for high-performance mortars. Cement Concrete Research 1998;28:803–9. [17] Detwiler RJ, Fapohunda CA, Natale J. Use of Supplementary cementing materials to increase the resistance to chloride ion penetration of concretes cured at elevated temperatures. ACI materials journal 1994;91:63–6.