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Combined effect of metakaolin and sea water on performance and microstructures of concrete
Construction and Building Materials 74 (2015) 57–64
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Combined effect of metakaolin and sea water on performance and microstructures of concrete Zhiguang Shi a,b, Zhonghe Shui a,b, Qiu Li a,⇑, Haining Geng a,b a b
State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China
h i g h l i g h t s The compressive strength of concrete was improved by metakaolin and seawater. There is a relationship between average pore diameter and compressive strength. Chloride was immobilized by formation of Friedel’s salt to increase chloride resistance.
a r t i c l e
i n f o
Article history: Received 27 June 2014 Received in revised form 26 September 2014 Accepted 14 October 2014
Keywords: Ordinary Portland cement Metakaolin Compressive strength Pore size distribution Hydration products Friedel’s salt
a b s t r a c t The effect of 0–6 wt% MK and mixing with seawater on the properties, hydration and microstructure of concrete was studied. The compressive strength at 28 days increased by 33% when addition of 5 wt% MK and by 22% when mixed with seawater. The combination of both increased compressive strength by 52%. The pore structure was refined under both conditions. There is a relationship between average pore diameter and compressive strength. MK promoted the formation of Friedel’s salt in concrete mixed with seawater. MK and mixing with seawater improved chloride resistance. This study shows that MK and seawater improved the performance of concrete. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Concrete structures consumed considerable amount of Portland cement, which resulted in substantial amount of carbon dioxide during the heating calcite above 1450 °C to produce one of the main raw materials, calcium oxides [1]. To reduce the carbon footprint and save energy without reducing performance, supplementary cementitious materials (SCMs) are introduced into concrete to substitute part of cement since 1950s. SCMs are mostly pozzolanic materials including industry wastes such as fly ash and slag [2–5]. Pozzolanic materials, especially silicate fume, slag and fly ash, have been widely used in construction. Metakaolin (MK) has the similar effect to improve strength and durability of concrete as silicate fume [6,7]. For the last several decades, the influence of MK on the properties of concrete were studied by a range of researchers, and the results confirmed that MK is a concrete admixture
⇑ Corresponding author. http://dx.doi.org/10.1016/j.conbuildmat.2014.10.023 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.
with high activity and high performance improvement [8–17]. MK is produced by calcining kaolin at 650–800 °C [18,19]. The main components of MK, which are amorphous Al2O3 and SiO2, have high pozzolanic activity. Besides the filling effect, MK reacts with calcium hydroxide (CH), which is one of the hydration products of Portland cement, to form calcium silicate hydrate (C–S–H) gels, the main binding phase of concrete [20,21]. CH was considered to be the main factor leading to the weakness of interfacial transition zone (ITZ) which in turn influences the strength, pore structure and durability of concrete [2]. The addition of pozzolanic materials consumes CH and improves the performance of concrete. As a porous material, the pore size distribution and structure of concrete affect the properties and durability of concrete. The addition of MK refines the pore structure of concrete and so as to improve the strength and durability of concrete [8,22]. Replacing fresh water with seawater during the construction of concrete structure in coastal areas will reduce the cost of transportation and increase the work efficiency. However, according to some previous researches, the use of seawater leads to a shorter
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service life of buildings, where the rapid corrosion of rebar became the main failure factor. In MK modified concrete, chloride ions can be immobilized by formation of Friedel’s salt to improve the corrosion resistance of concrete, which makes the use of MK in marine concrete beneficial. The cost of MK is much higher than that of other SCMs. Currently, most researches focused on the concrete containing 10–30 wt% MK. In this study, the properties and microstructure of concrete with 0– 6 wt% MK addition and artificial seawater substituting fresh water were characterized by a range of analytical techniques to assess the feasibility of low MK addition and seawater mixing in concrete. 2. Materials and experimental 2.1. Materials Type P.I. 52.5 Portland cement was used for all concrete and paste mixes. MK was obtained by calcining kaolin at 750 °C. The chemical composition of cement and MK was characterized by X-ray fluorescence (XRF) (Table 1). Local natural fine aggregate in a maximum size of 4.75 mm, and coarse aggregate in a maximum size of 26.5 mm were used. Artificial seawater was prepared according to the standard ASTM D1141-98 [23] (Table 2). 2.2. Specimen preparation Concrete mixes were designed at water/binder ratio of 0.45. The percentages of MK that replaced cement in this study were 0%, 2%, 3%, 4%, 5% and 6% by mass. Mix design of concretes and pastes are shown in Tables 3 and 4. The density of concrete was 2400 kg m3. After 24 h curing in room temperature and relative humidity of 100%, the concrete and paste specimens were demolded and cured at 20 °C. 2.3. Test methods 2.3.1. Compressive strength Concrete cubes in size of 100 100 100 mm and paste cubes in size of 40 40 40 mm were prepared for compressive strength test after cured for 3, 7 and 28 days at 20 °C. Three specimens were tested for each batch. 2.3.2. Pore size distribution Specimens from the central part of concrete cubes were used for mercury intrusion porosimetry (MIP) test after cured for 3, 7 and 28 days. Specimens were immersed in ethanol to stop hydration after crushed and dried at 105 °C for 24 h before test. 2.3.3. X-ray diffraction (XRD) XRD was performed on freshly ground paste specimens by Bruker D8 Advance under the conditions of Cu Ka = 1.5406 Å, step size of 0.019°, measuring time 141.804 s/step, start position 5° and end position 70°. The acquired data was analyzed by PANalytical X’pert Highscore Plus with PDF2004 database. 2.3.4. Scanning electron microscopy (SEM) SEM was performed on concrete specimens by FEI Quanta 450FEG under the conditions of spotsize 5 and accelerating voltage 20 kV. Hydrated specimens were cut into thick slices and then hydration stopped by immersion in isopropanol before being embedded in resin, then polished and coated with carbon. 2.3.5. Fourier transformation infrared spectroscopy (FTIR) FTIR was employed to analyze the chemical bonding of hydration products by Thermo Nicolet Nexus FTIR under Attenuated Total Reflectance (ATR) mode from 4000 cm1 to 400 cm1. Specimens for FTIR test are the same as those for XRD test. Based on the peak of calcium hydroxide at 3640 cm1, the content of calcium hydroxide of each specimen was calculated by deconvoluting overlapped peaks [24]. A typical FTIR spectrum of specimen is shown in Fig. 1.
2.3.6. Chloride penetration Concrete specimens were prepared in cylinders of 100 mm in diameter and 150 mm in height and cured at 20 °C. After cured for 28, 56 and 70 days, the specimens were cut into pieces of 100 mm in diameter and 50 mm in height. The chloride penetration properties were tested according to the standard ASTM C1202.
3. Results and discussion 3.1. Compressive strength The compressive strength of concretes and pastes are shown in Figs. 2 and 3 respectively. For concrete mixed with fresh water, the compressive strength increased with the time of hydration. For the mixes at the same age, the compressive strength increased with content of MK and reached the maximum at 5 wt% of MK. The highest compressive strength was obtained by C5 at 28 days, which increased by 33% comparing to C1 at the same age. The compressive strength of the concretes mixed with seawater (C7–C12) had a similar trend to that of concretes mixed with fresh water. The compressive strength increased by 24% for C11 comparing to C7. Some research showed that addition of 5 wt% MK did not influence the compressive strength of concrete at 28 days. However, some other research indicated that the compressive strength increased by 25% with the addition of 5 wt% MK [25–28]. The difference may be due to the various composition and microstructures of MK from different sources. The compressive strength of concrete mixed with seawater was higher than that of the concrete mixed with fresh water under the same content of MK and same age. The combination of MK and seawater effectively improved the mechanical performance of concrete. According to the results and discussion later in this study, the reason is that seawater accelerated the hydration of cement to increase the content of CH available for pozzolanic reaction with MK, which resulted in more C–S–H formed in the concrete. The development of relative strength of concretes comparing to the control specimen C1 is shown in Fig. 4, together with those from other researchers [9,29–33]. The trend of change of relative strength from this study is similar to those from other researchers. For specimens mixed with fresh water, the relative strength reached the maximum by 28 days and decreased gradually but was still higher than the control. In this study, addition of 5 wt% MK increased the compressive strength by 33% at 28 days. For the addition of 2–30 wt% MK, the compressive strength increased by 5–35% at 28 days according to Fig. 4. Although the content of MK is relatively low in this study, the compressive strength increase is considerable. For specimens mixed with artificial seawater, the relative strength reached the maximum by 7 days and decreased gradually but still much higher than the control and fresh water specimens at the same age. Addition of 5 wt% MK and mixing with seawater greatly improved the compressive strength of concrete by 56%, 52% and 46% at 7, 28 and 56 days respectively. Fig. 3 shows the compressive strength of paste, which had the similar trend to that of concrete. 3.2. Pore structure The effects of seawater and MK on the pore structure of concrete are studied by MIP, and the results are shown in Figs. 5–7
Table 1 The chemical composition of cement and MK characterized by XRF (%).
a
Oxides
Na2O
MgO
Al2O3
SiO2
P2O5
SO3
K2O
CaO
Fe2O3
LOIa
Cement MK
0.09 0.39
1.60 0.07
4.15 38.63
19.05 57.37
0.09 0.61
3.32 0.15
0.77 0.49
64.43 0.03
3.29 0.77
2.43 1.04
LOI: loss on ignition.
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Z. Shi et al. / Construction and Building Materials 74 (2015) 57–64 Table 2 The chemical composition of artificial seawatera,b (g/L).
a b
Component
NaCl
MgCl2
Na2SO4
CaCl2
KCl
KBr
H3BO3
NaF
Concentration
24.53
5.20
4.09
1.16
0.695
0.101
0.027
0.003
Chlorinity of the artificial seawater is 19.38. pH value is 8.2 after adjustment with 0.1 mol/L NaOH solution.
Table 3 Mix design of the pastes (kg m3). Specimen name
Water/binder ratio
Cement
MK
Fresh water
Seawater
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12
0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45
500 490 485 480 475 470 500 490 485 480 475 470
0 10 15 20 25 30 0 10 15 20 25 30
225 225 225 225 225 225 – – – – – –
– – – – – – 225 225 225 225 225 225
Table 4 Mix design of the concretes (kg m3). Specimen name
Water/binder ratio
Cement
MK
Fresh water
Seawater
Fine aggregate
Coarse aggregate
C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12
0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45
420 411.6 407.4 403.2 399 394.8 420 411.6 407.4 403.2 399 394.8
0 8.40 12.6 16.8 21 25.2 0 8.4 12.6 16.8 21 25.2
190 190 190 190 190 190 – – – – – –
– – – – – – 190 190 190 190 190 190
644 644 644 644 644 644 644 644 644 644 644 644
1146 1146 1146 1146 1146 1146 1146 1146 1146 1146 1146 1146
Fig. 2. Compressive strength of concretes at 3, 7 and 28 days. Fig. 1. FTIR spectrum for P11 at 7 days.
which are the incremental intrusion volume of concrete at 3, 7 and 28 days. The total porosity of specimens is shown in Table 5. According to these results, the addition of MK reduced the amount of pores, and mixing with seawater shifted the peaks to left, indicating the decrease of pore diameter. The volume of pores
decreased with the increase of age for all specimens, due to the hydration of cement and pozzolanic reaction of MK to form more hydration products. Both the addition of MK and mixing with seawater reduced the amount of pores bigger than 10 nm and refined the pore structure, which improved the compressive strength of concrete. C11 specimen, which was mixed with seawater and
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Fig. 3. Compressive strength of pastes at 3, 7 and 28 days.
Fig. 6. Incremental intrusion volume of concrete at 7 days.
Fig. 7. Incremental intrusion volume of concrete at 28 days.
Table 5 Total porosity of concretes (%).
Fig. 4. Relative compressive strength development of concretes.
Fig. 5. Incremental intrusion volume of concrete at 3 days.
Age (day)
C1
C5
C6
C7
C11
C12
3 7 28
13.80 15.81 12.84
9.29 14.05 13.17
10.64 13.45 11.28
14.43 13.45 12.90
15.51 13.60 10.94
16.24 7.18 10.07
Fig. 8. Relationship of the average pore diameter and compressive strength of C1 and C5.
Z. Shi et al. / Construction and Building Materials 74 (2015) 57–64
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added by 5 wt% MK, had the lowest amount of pores at 28 days. Due to the micro aggregate filling and pozzolanic reaction of MK, as well as the acceleration of hydration by ions in seawater, the pore volume of concrete was reduced; the pore size distribution shifted to the small pore diameter portion, and the performance was improved [34,35]. Figs. 8 and 9 show the development of average pore diameter and compressive strength of concrete with a reversed axis for average pore diameter. According to these results, the decrease of average pore diameter had a similar trend to the increase of the compressive strength. There is a relationship between average pore diameter and compressive strength. According to Figs. 8 and 9, introducing MK and seawater together eliminated the disadvantages of seawater, decreased the average pore diameter and improved the compressive strength. 3.3. Hydration products Figs. 10 and 11 show the XRD results of P1, P5, P7 and P11 specimens at 3 and 7 days. Fig. 12 shows the XRD results of P7 and P11
Fig. 11. XRD results of P1, P5, P7 and P11 at 7 days.
Fig. 9. Relationship of the average pore diameter and compressive strength of C7 and C11.
Fig. 12. XRD results of P7 and P11 at 28 days.
at 28 days. Ettringite and CH were identified from these specimens. Friedel’s salt was identified in specimens mixed by seawater, through the reaction of C3A and CaCl2 from seawater (Formula 1) [36]. More Friedel’s salt was identified in P11 than P7 at the same age due to the promotion of Friedel’s salt formation by MK (Formula 2). These results show that MK promoted the formation of Friedel’s salt under the condition of seawater mixing [37]. In all specimens, the content of hydration products increased with the time of hydration.
C3 A þ CaCl2 þ 10H2 O ! C3 A CaCl2 10H2 O
ðFormula1Þ
3CaðOHÞ2 þ CaCl2 þ Al2 O3 þ 7H2 O Fig. 10. XRD results of P1, P5, P7 and P11 at 3 days.
! 3CaO Al2 O3 CaCl2 10H2 O
ðFormula2Þ
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Fig. 13. CH content presented as FTIR peak area for specimens at 3, 7 and 28 days.
To evaluate the activity of MK, CH content of the specimens was calculated from the results of FTIR by deconvoluting the peak at 3640 cm1 which was attributed to CH [38]. The area of peak of each specimen is shown in Fig. 13, which indicated the content of CH. According to these results, for paste without MK, CH content
Fig. 15. Electric flux through the concrete specimens.
increased with the time of hydration. At the same age, CH content of P7 was higher than that of P1 due to the acceleration of hydration by CaCl2 in seawater [39]. For paste containing MK, CH content increased first and then decreased at 28 days due to the pozzolanic reaction of MK with CH. At 3 and 7 days, CH content was lower than that of paste
Fig. 14. SEM secondary electron images for C5 and C11. (a) C5 at 3 days, (b) C11 at 3 days, (c) C5 at 7 days, (d) C11 at 7 days, (e) C5 at 28 days and (f) C11 at 28 days.
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without MK due to the filler effect of MK in the early age. For the same MK content, CH content of paste mixed with seawater was higher than that of paste mixed with fresh water due to the acceleration of hydration by seawater. These results confirmed the pozzolanic reaction of MK with CH, as seen in Formula 3.
Acknowledgement This study was financially supported by ‘‘YangFan Innovative & Entrepreneurial Research Team Project (No. 201312C12)’’. References
Al2 O3 2SiO2 þ nH2 O þ 8CaðOHÞ2 ! C4 AHm þ 2C2 SHy
63
ðFormula3Þ
3.4. Microstructure The microstructures of C5 and C11 were analyzed by SEM and are shown in Fig. 14. For both concretes, the microstructure became denser and the porosity decreased as the hydration progressed. The porosity of C11 was lower than that of C5 at the same age, which confirmed the results from MIP. There was more CH in C11 comparing to C5. CH content of C11 decreased as the time of hydration increased. These results confirmed those from FTIR. 3.5. Chloride resistance Fig. 15 shows the amount of electric flux through the concrete specimens at 28, 56 and 70 days, indicating the chloride resistance of the specimens. According to these results, the electric flux decreased with the increase of amount of MK, showing that addition of MK improved the chloride resistance of concrete. For the specimens with the same amount of MK, specimens mixed with seawater had lower electric flux, indicating that mixing with seawater contributed the chloride resistance. These results show that addition of MK and mixing with seawater increased the chloride resistance of concrete. 4. Conclusions The combined effect of MK and seawater on the properties and microstructures of concrete was studied by a range of analytical techniques. The compressive strength, pore structure, hydration products and microstructure of concrete were affected by the addition of MK and mixing with seawater. According to the results, the following conclusions can be drawn. Addition of 5 wt% MK and mixing with seawater improved the compressive strength of concrete at 28 days by 33% and 22% respectively. The highest compressive strength was obtained by addition of 5 wt% MK and mixing with seawater, which increased the compressive strength by 52% at 28 days. The pore structure of concrete was refined by addition of MK and mixing with seawater. The amount of pores bigger than 10 nm was reduced due to the filling effect and pozzolanic reaction of MK and acceleration of hydration by seawater. There is a relationship between average pore diameter and compressive strength. Ettringite and CH were identified in paste with MK addition and mixing with seawater. Friedel’s salt was formed in paste mixed with seawater and its formation was promoted by MK. In paste containing MK, CH content decreased at 28 days due to the pozzolanic reaction of MK with CH. The chloride resistance of concrete increased with the amount of MK. Mixing with seawater improved the chloride resistance further. This study shows that the addition of MK can eliminate the disadvantage of mixing with seawater in concrete. The compressive strength, pore structure and microstructure were improved in concrete containing MK and mixed with seawater.
[1] Taylor HFW. Cement chemistry. 2nd ed. London: Thomas Telford Services Ltd.; 1997. [2] Duan P, Shui Z, Chen W, Shen C. Effects of metakaolin, silica fume and slag on pore structure, interfacial transition zone and compressive strength of concrete. Constr Build Mater 2013;44:1–6. [3] Duan P, Shui Z, Chen W, Shen C. Efficiency of mineral admixtures in concrete: microstructure, compressive strength and stability of hydrate phases. Appl Clay Sci 2013;83–84:115–21. [4] Shui Z, Sun T, Fu Z, Wang G. Dominant factors on the early hydration of metakaolin–cement paste. J Wuhan Univ Technol-Mater Sci Ed 2010;25(5):849–52. [5] Snellings R, Mertens G, Cizer Ö, Elsen J. Early age hydration and pozzolanic reaction in natural zeolite blended cements: reaction kinetics and products by in situ synchrotron X-ray powder diffraction. Cem Concr Res 2010;40(12):1704–13. [6] Ramlochan T, Thomas M, Gruber KA. The effect of metakaolin on alkali-silica reaction in concrete. Cem Concr Res 2000;30(3):339–44. [7] Guneyisi E, Gesoglu M, Karaoglu S, Mermerdas K. Strength, permeability and shrinkage cracking of silica fume and metakaolin concretes. Constr Build Mater 2012;34:120–30. [8] Basheer L, Basheer PAM, Long AE. Influence of coarse aggregate on the permeation, durability and the microstructure characteristics of ordinary Portland cement concrete. Constr Build Mater 2005;19(9):682–90. [9] Khatib JM. Metakaolin concrete at a low water to binder ratio. Constr Build Mater 2008;22(8):1691–700. [10] Ramezanianpour AA, Bahrami Jovein H. Influence of metakaolin as supplementary cementing material on strength and durability of concretes. Constr Build Mater 2012;30:470–9. [11] Sabir BB, Wild S, Bai J. Metakaolin and calcined clays as pozzolans for concrete: a review. Cem Concr Compos 2001;23:441–54. [12] Sha W, Pereira GB. Differential scanning calorimetry study of ordinary Portland cement paste containing metakaolin and theoretical approach of metakaolin activity. Cem Concr Compos 2001;23:455–61. [13] Siddique R, Klaus J. Influence of metakaolin on the properties of mortar and concrete: a review. Appl Clay Sci 2009;43(3–4):392–400. [14] Li C, Sun H, Li L. A review: the comparison between alkali-activated slag (Si plus Ca) and metakaolin (Si plus Al) cements. Cem Concr Res 2010;40(9):1341–9. [15] Ramlochan T, Thomas MDA, Hooton RD. The effect of pozzolans and slag on the expansion of mortars cured at elevated temperature – Part II: Microstructural and microchemical investigations. Cem Concr Res 2004;34(8):1341–56. [16] Guneyisi E, Gesoglu M, Karaboga F, Mermerdas K. Corrosion behavior of reinforcing steel embedded in chloride contaminated concretes with and without metakaolin. Compos Part B-Eng 2013;45(1):1288–95. [17] Guneyisi E, Mermerdas K. Comparative study on strength, sorptivity, and chloride ingress characteristics of air-cured and water-cured concretes modified with metakaolin. Mater Struct 2007;40:1161–71. [18] Zeng J, Shui Z, Wang G. The early hydration and strength development of highstrength precast concrete with cement/metakaolin systems. J Wuhan Univ Technol-Mater Sci Ed 2010;25(4):712–6. [19] Guneyisi E, Gesoglu M, Ozturan T, Mermerdas K. Microstructural properties and pozzolanic activity of calcined kaolins as supplementary cementing materials. Can J Civ Eng 2012;39(12):1274–84. [20] Frias M, Cabrera J. Influence of MK on the reaction kinetics in MK/lime and MK-blended cement systems at 20 °C. Cem Concr Res 2001;31(4):519–27. [21] Khatib JM, Hibbert JJ. Selected engineering properties of concrete incorporating slag and metakaolin. Constr Build Mater 2005;19(6):460–72. [22] Kumar R, Bhattacharjee B. Porosity, pore size distribution and in situ strength of concrete. Cem Concr Res 2003:10. [23] ASTM Committee. ASTM D 1141-98: Standard practice for the preparation of substitute ocean water. ASTM International; 2003. [24] Poon C-S, Lam L, Kou SC, Wong Y-L, Wong R. Rate of pozzolanic reaction of metakaolin in high-performance cement pastes. Cem Concr Res 2001;31:1301–6. [25] Frias M, Cabrera J. Pore size distribution and degree of hydration of metakaolin–cement pastes. Cem Concr Res 2000;30:561–9. [26] Poon C-S, Azhar S, Anson M, Wong Y-L. Performance of metakaolin concrete at elevated temperatures. Cem Concr Compos 2003;25:83–9. [27] Guneyisi E, Gesoglu M, Ozbay E. Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures. Constr Build Mater 2010;24(10):1878–87. [28] Guneyisi E, Gesoglu M. Properties of self-compacting mortars with binary and ternary cementitious blends of fly ash and metakaolin. Mater Struct 2008;41(9):1519–31. [29] Antoni M, Rossen J, Martirena F, Scrivener K. Cement substitution by a combination of metakaolin and limestone. Cem Concr Res 2012;42(12):1579–89.
64
Z. Shi et al. / Construction and Building Materials 74 (2015) 57–64
[30] Arikan M, Sobolev K, Ertuen T, Yeginobali A, Turker P. Properties of blended cements with thermally activated kaolin. Constr Build Mater 2009;23(1):62–70. [31] Johari MAM, Brooks JJ, Kabir S, Rivard P. Influence of supplementary cementitious materials on engineering properties of high strength concrete. Constr Build Mater 2011;25(5):2639–48. [32] Justice JM, Kurtis KE. Influence of metakaolin surface area on properties of cement-based materials. J Mater Civ Eng 2007;19(9):762–71. [33] Khatib JM. Low temperature curing of metakaolin concrete. J Mater Civ Eng 2009;21(8):362–7. [34] Gueneyisi E, Gesoglu M, Mermerdas K. Improving strength, drying shrinkage, and pore structure of concrete using metakaolin. Mater Struct 2008;41(5):937–49.
[35] Frias M, de Rojas MIS. Influence of the metakaolin on porous structure of matrixes based in mk/cement. Mater Constr 2000;50(259):57–67. [36] Li Z, Ding Z. Property improvement of Portland cement by incorporating with metakaolin and slag. Cem Concr Res 2003;33(4):579–84. [37] Thomas MDA, Hooton RD, Scott A, Zibara H. The effect of supplementary cementitious materials on chloride binding in hardened cement paste. Cem Concr Res 2012;42(1):1–7. [38] Kumar M, Singh SK, Singh NP, Singh NB. Hydration of multicomponent composite cement: OPC-FA-SF-MK. Constr Build Mater 2012;36:681–6. [39] Li Q. The nature of early age hydration products. Leeds (UK): University of Leeds; 2009.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Combined effect of metakaolin and sea water on performance and microstructures of concrete Zhiguang Shi a,b, Zhonghe Shui a,b, Qiu Li a,⇑, Haining Geng a,b a b
State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China
h i g h l i g h t s The compressive strength of concrete was improved by metakaolin and seawater. There is a relationship between average pore diameter and compressive strength. Chloride was immobilized by formation of Friedel’s salt to increase chloride resistance.
a r t i c l e
i n f o
Article history: Received 27 June 2014 Received in revised form 26 September 2014 Accepted 14 October 2014
Keywords: Ordinary Portland cement Metakaolin Compressive strength Pore size distribution Hydration products Friedel’s salt
a b s t r a c t The effect of 0–6 wt% MK and mixing with seawater on the properties, hydration and microstructure of concrete was studied. The compressive strength at 28 days increased by 33% when addition of 5 wt% MK and by 22% when mixed with seawater. The combination of both increased compressive strength by 52%. The pore structure was refined under both conditions. There is a relationship between average pore diameter and compressive strength. MK promoted the formation of Friedel’s salt in concrete mixed with seawater. MK and mixing with seawater improved chloride resistance. This study shows that MK and seawater improved the performance of concrete. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Concrete structures consumed considerable amount of Portland cement, which resulted in substantial amount of carbon dioxide during the heating calcite above 1450 °C to produce one of the main raw materials, calcium oxides [1]. To reduce the carbon footprint and save energy without reducing performance, supplementary cementitious materials (SCMs) are introduced into concrete to substitute part of cement since 1950s. SCMs are mostly pozzolanic materials including industry wastes such as fly ash and slag [2–5]. Pozzolanic materials, especially silicate fume, slag and fly ash, have been widely used in construction. Metakaolin (MK) has the similar effect to improve strength and durability of concrete as silicate fume [6,7]. For the last several decades, the influence of MK on the properties of concrete were studied by a range of researchers, and the results confirmed that MK is a concrete admixture
⇑ Corresponding author. http://dx.doi.org/10.1016/j.conbuildmat.2014.10.023 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.
with high activity and high performance improvement [8–17]. MK is produced by calcining kaolin at 650–800 °C [18,19]. The main components of MK, which are amorphous Al2O3 and SiO2, have high pozzolanic activity. Besides the filling effect, MK reacts with calcium hydroxide (CH), which is one of the hydration products of Portland cement, to form calcium silicate hydrate (C–S–H) gels, the main binding phase of concrete [20,21]. CH was considered to be the main factor leading to the weakness of interfacial transition zone (ITZ) which in turn influences the strength, pore structure and durability of concrete [2]. The addition of pozzolanic materials consumes CH and improves the performance of concrete. As a porous material, the pore size distribution and structure of concrete affect the properties and durability of concrete. The addition of MK refines the pore structure of concrete and so as to improve the strength and durability of concrete [8,22]. Replacing fresh water with seawater during the construction of concrete structure in coastal areas will reduce the cost of transportation and increase the work efficiency. However, according to some previous researches, the use of seawater leads to a shorter
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service life of buildings, where the rapid corrosion of rebar became the main failure factor. In MK modified concrete, chloride ions can be immobilized by formation of Friedel’s salt to improve the corrosion resistance of concrete, which makes the use of MK in marine concrete beneficial. The cost of MK is much higher than that of other SCMs. Currently, most researches focused on the concrete containing 10–30 wt% MK. In this study, the properties and microstructure of concrete with 0– 6 wt% MK addition and artificial seawater substituting fresh water were characterized by a range of analytical techniques to assess the feasibility of low MK addition and seawater mixing in concrete. 2. Materials and experimental 2.1. Materials Type P.I. 52.5 Portland cement was used for all concrete and paste mixes. MK was obtained by calcining kaolin at 750 °C. The chemical composition of cement and MK was characterized by X-ray fluorescence (XRF) (Table 1). Local natural fine aggregate in a maximum size of 4.75 mm, and coarse aggregate in a maximum size of 26.5 mm were used. Artificial seawater was prepared according to the standard ASTM D1141-98 [23] (Table 2). 2.2. Specimen preparation Concrete mixes were designed at water/binder ratio of 0.45. The percentages of MK that replaced cement in this study were 0%, 2%, 3%, 4%, 5% and 6% by mass. Mix design of concretes and pastes are shown in Tables 3 and 4. The density of concrete was 2400 kg m3. After 24 h curing in room temperature and relative humidity of 100%, the concrete and paste specimens were demolded and cured at 20 °C. 2.3. Test methods 2.3.1. Compressive strength Concrete cubes in size of 100 100 100 mm and paste cubes in size of 40 40 40 mm were prepared for compressive strength test after cured for 3, 7 and 28 days at 20 °C. Three specimens were tested for each batch. 2.3.2. Pore size distribution Specimens from the central part of concrete cubes were used for mercury intrusion porosimetry (MIP) test after cured for 3, 7 and 28 days. Specimens were immersed in ethanol to stop hydration after crushed and dried at 105 °C for 24 h before test. 2.3.3. X-ray diffraction (XRD) XRD was performed on freshly ground paste specimens by Bruker D8 Advance under the conditions of Cu Ka = 1.5406 Å, step size of 0.019°, measuring time 141.804 s/step, start position 5° and end position 70°. The acquired data was analyzed by PANalytical X’pert Highscore Plus with PDF2004 database. 2.3.4. Scanning electron microscopy (SEM) SEM was performed on concrete specimens by FEI Quanta 450FEG under the conditions of spotsize 5 and accelerating voltage 20 kV. Hydrated specimens were cut into thick slices and then hydration stopped by immersion in isopropanol before being embedded in resin, then polished and coated with carbon. 2.3.5. Fourier transformation infrared spectroscopy (FTIR) FTIR was employed to analyze the chemical bonding of hydration products by Thermo Nicolet Nexus FTIR under Attenuated Total Reflectance (ATR) mode from 4000 cm1 to 400 cm1. Specimens for FTIR test are the same as those for XRD test. Based on the peak of calcium hydroxide at 3640 cm1, the content of calcium hydroxide of each specimen was calculated by deconvoluting overlapped peaks [24]. A typical FTIR spectrum of specimen is shown in Fig. 1.
2.3.6. Chloride penetration Concrete specimens were prepared in cylinders of 100 mm in diameter and 150 mm in height and cured at 20 °C. After cured for 28, 56 and 70 days, the specimens were cut into pieces of 100 mm in diameter and 50 mm in height. The chloride penetration properties were tested according to the standard ASTM C1202.
3. Results and discussion 3.1. Compressive strength The compressive strength of concretes and pastes are shown in Figs. 2 and 3 respectively. For concrete mixed with fresh water, the compressive strength increased with the time of hydration. For the mixes at the same age, the compressive strength increased with content of MK and reached the maximum at 5 wt% of MK. The highest compressive strength was obtained by C5 at 28 days, which increased by 33% comparing to C1 at the same age. The compressive strength of the concretes mixed with seawater (C7–C12) had a similar trend to that of concretes mixed with fresh water. The compressive strength increased by 24% for C11 comparing to C7. Some research showed that addition of 5 wt% MK did not influence the compressive strength of concrete at 28 days. However, some other research indicated that the compressive strength increased by 25% with the addition of 5 wt% MK [25–28]. The difference may be due to the various composition and microstructures of MK from different sources. The compressive strength of concrete mixed with seawater was higher than that of the concrete mixed with fresh water under the same content of MK and same age. The combination of MK and seawater effectively improved the mechanical performance of concrete. According to the results and discussion later in this study, the reason is that seawater accelerated the hydration of cement to increase the content of CH available for pozzolanic reaction with MK, which resulted in more C–S–H formed in the concrete. The development of relative strength of concretes comparing to the control specimen C1 is shown in Fig. 4, together with those from other researchers [9,29–33]. The trend of change of relative strength from this study is similar to those from other researchers. For specimens mixed with fresh water, the relative strength reached the maximum by 28 days and decreased gradually but was still higher than the control. In this study, addition of 5 wt% MK increased the compressive strength by 33% at 28 days. For the addition of 2–30 wt% MK, the compressive strength increased by 5–35% at 28 days according to Fig. 4. Although the content of MK is relatively low in this study, the compressive strength increase is considerable. For specimens mixed with artificial seawater, the relative strength reached the maximum by 7 days and decreased gradually but still much higher than the control and fresh water specimens at the same age. Addition of 5 wt% MK and mixing with seawater greatly improved the compressive strength of concrete by 56%, 52% and 46% at 7, 28 and 56 days respectively. Fig. 3 shows the compressive strength of paste, which had the similar trend to that of concrete. 3.2. Pore structure The effects of seawater and MK on the pore structure of concrete are studied by MIP, and the results are shown in Figs. 5–7
Table 1 The chemical composition of cement and MK characterized by XRF (%).
a
Oxides
Na2O
MgO
Al2O3
SiO2
P2O5
SO3
K2O
CaO
Fe2O3
LOIa
Cement MK
0.09 0.39
1.60 0.07
4.15 38.63
19.05 57.37
0.09 0.61
3.32 0.15
0.77 0.49
64.43 0.03
3.29 0.77
2.43 1.04
LOI: loss on ignition.
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Z. Shi et al. / Construction and Building Materials 74 (2015) 57–64 Table 2 The chemical composition of artificial seawatera,b (g/L).
a b
Component
NaCl
MgCl2
Na2SO4
CaCl2
KCl
KBr
H3BO3
NaF
Concentration
24.53
5.20
4.09
1.16
0.695
0.101
0.027
0.003
Chlorinity of the artificial seawater is 19.38. pH value is 8.2 after adjustment with 0.1 mol/L NaOH solution.
Table 3 Mix design of the pastes (kg m3). Specimen name
Water/binder ratio
Cement
MK
Fresh water
Seawater
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12
0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45
500 490 485 480 475 470 500 490 485 480 475 470
0 10 15 20 25 30 0 10 15 20 25 30
225 225 225 225 225 225 – – – – – –
– – – – – – 225 225 225 225 225 225
Table 4 Mix design of the concretes (kg m3). Specimen name
Water/binder ratio
Cement
MK
Fresh water
Seawater
Fine aggregate
Coarse aggregate
C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12
0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45
420 411.6 407.4 403.2 399 394.8 420 411.6 407.4 403.2 399 394.8
0 8.40 12.6 16.8 21 25.2 0 8.4 12.6 16.8 21 25.2
190 190 190 190 190 190 – – – – – –
– – – – – – 190 190 190 190 190 190
644 644 644 644 644 644 644 644 644 644 644 644
1146 1146 1146 1146 1146 1146 1146 1146 1146 1146 1146 1146
Fig. 2. Compressive strength of concretes at 3, 7 and 28 days. Fig. 1. FTIR spectrum for P11 at 7 days.
which are the incremental intrusion volume of concrete at 3, 7 and 28 days. The total porosity of specimens is shown in Table 5. According to these results, the addition of MK reduced the amount of pores, and mixing with seawater shifted the peaks to left, indicating the decrease of pore diameter. The volume of pores
decreased with the increase of age for all specimens, due to the hydration of cement and pozzolanic reaction of MK to form more hydration products. Both the addition of MK and mixing with seawater reduced the amount of pores bigger than 10 nm and refined the pore structure, which improved the compressive strength of concrete. C11 specimen, which was mixed with seawater and
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Fig. 3. Compressive strength of pastes at 3, 7 and 28 days.
Fig. 6. Incremental intrusion volume of concrete at 7 days.
Fig. 7. Incremental intrusion volume of concrete at 28 days.
Table 5 Total porosity of concretes (%).
Fig. 4. Relative compressive strength development of concretes.
Fig. 5. Incremental intrusion volume of concrete at 3 days.
Age (day)
C1
C5
C6
C7
C11
C12
3 7 28
13.80 15.81 12.84
9.29 14.05 13.17
10.64 13.45 11.28
14.43 13.45 12.90
15.51 13.60 10.94
16.24 7.18 10.07
Fig. 8. Relationship of the average pore diameter and compressive strength of C1 and C5.
Z. Shi et al. / Construction and Building Materials 74 (2015) 57–64
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added by 5 wt% MK, had the lowest amount of pores at 28 days. Due to the micro aggregate filling and pozzolanic reaction of MK, as well as the acceleration of hydration by ions in seawater, the pore volume of concrete was reduced; the pore size distribution shifted to the small pore diameter portion, and the performance was improved [34,35]. Figs. 8 and 9 show the development of average pore diameter and compressive strength of concrete with a reversed axis for average pore diameter. According to these results, the decrease of average pore diameter had a similar trend to the increase of the compressive strength. There is a relationship between average pore diameter and compressive strength. According to Figs. 8 and 9, introducing MK and seawater together eliminated the disadvantages of seawater, decreased the average pore diameter and improved the compressive strength. 3.3. Hydration products Figs. 10 and 11 show the XRD results of P1, P5, P7 and P11 specimens at 3 and 7 days. Fig. 12 shows the XRD results of P7 and P11
Fig. 11. XRD results of P1, P5, P7 and P11 at 7 days.
Fig. 9. Relationship of the average pore diameter and compressive strength of C7 and C11.
Fig. 12. XRD results of P7 and P11 at 28 days.
at 28 days. Ettringite and CH were identified from these specimens. Friedel’s salt was identified in specimens mixed by seawater, through the reaction of C3A and CaCl2 from seawater (Formula 1) [36]. More Friedel’s salt was identified in P11 than P7 at the same age due to the promotion of Friedel’s salt formation by MK (Formula 2). These results show that MK promoted the formation of Friedel’s salt under the condition of seawater mixing [37]. In all specimens, the content of hydration products increased with the time of hydration.
C3 A þ CaCl2 þ 10H2 O ! C3 A CaCl2 10H2 O
ðFormula1Þ
3CaðOHÞ2 þ CaCl2 þ Al2 O3 þ 7H2 O Fig. 10. XRD results of P1, P5, P7 and P11 at 3 days.
! 3CaO Al2 O3 CaCl2 10H2 O
ðFormula2Þ
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Fig. 13. CH content presented as FTIR peak area for specimens at 3, 7 and 28 days.
To evaluate the activity of MK, CH content of the specimens was calculated from the results of FTIR by deconvoluting the peak at 3640 cm1 which was attributed to CH [38]. The area of peak of each specimen is shown in Fig. 13, which indicated the content of CH. According to these results, for paste without MK, CH content
Fig. 15. Electric flux through the concrete specimens.
increased with the time of hydration. At the same age, CH content of P7 was higher than that of P1 due to the acceleration of hydration by CaCl2 in seawater [39]. For paste containing MK, CH content increased first and then decreased at 28 days due to the pozzolanic reaction of MK with CH. At 3 and 7 days, CH content was lower than that of paste
Fig. 14. SEM secondary electron images for C5 and C11. (a) C5 at 3 days, (b) C11 at 3 days, (c) C5 at 7 days, (d) C11 at 7 days, (e) C5 at 28 days and (f) C11 at 28 days.
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without MK due to the filler effect of MK in the early age. For the same MK content, CH content of paste mixed with seawater was higher than that of paste mixed with fresh water due to the acceleration of hydration by seawater. These results confirmed the pozzolanic reaction of MK with CH, as seen in Formula 3.
Acknowledgement This study was financially supported by ‘‘YangFan Innovative & Entrepreneurial Research Team Project (No. 201312C12)’’. References
Al2 O3 2SiO2 þ nH2 O þ 8CaðOHÞ2 ! C4 AHm þ 2C2 SHy
63
ðFormula3Þ
3.4. Microstructure The microstructures of C5 and C11 were analyzed by SEM and are shown in Fig. 14. For both concretes, the microstructure became denser and the porosity decreased as the hydration progressed. The porosity of C11 was lower than that of C5 at the same age, which confirmed the results from MIP. There was more CH in C11 comparing to C5. CH content of C11 decreased as the time of hydration increased. These results confirmed those from FTIR. 3.5. Chloride resistance Fig. 15 shows the amount of electric flux through the concrete specimens at 28, 56 and 70 days, indicating the chloride resistance of the specimens. According to these results, the electric flux decreased with the increase of amount of MK, showing that addition of MK improved the chloride resistance of concrete. For the specimens with the same amount of MK, specimens mixed with seawater had lower electric flux, indicating that mixing with seawater contributed the chloride resistance. These results show that addition of MK and mixing with seawater increased the chloride resistance of concrete. 4. Conclusions The combined effect of MK and seawater on the properties and microstructures of concrete was studied by a range of analytical techniques. The compressive strength, pore structure, hydration products and microstructure of concrete were affected by the addition of MK and mixing with seawater. According to the results, the following conclusions can be drawn. Addition of 5 wt% MK and mixing with seawater improved the compressive strength of concrete at 28 days by 33% and 22% respectively. The highest compressive strength was obtained by addition of 5 wt% MK and mixing with seawater, which increased the compressive strength by 52% at 28 days. The pore structure of concrete was refined by addition of MK and mixing with seawater. The amount of pores bigger than 10 nm was reduced due to the filling effect and pozzolanic reaction of MK and acceleration of hydration by seawater. There is a relationship between average pore diameter and compressive strength. Ettringite and CH were identified in paste with MK addition and mixing with seawater. Friedel’s salt was formed in paste mixed with seawater and its formation was promoted by MK. In paste containing MK, CH content decreased at 28 days due to the pozzolanic reaction of MK with CH. The chloride resistance of concrete increased with the amount of MK. Mixing with seawater improved the chloride resistance further. This study shows that the addition of MK can eliminate the disadvantage of mixing with seawater in concrete. The compressive strength, pore structure and microstructure were improved in concrete containing MK and mixed with seawater.
[1] Taylor HFW. Cement chemistry. 2nd ed. London: Thomas Telford Services Ltd.; 1997. [2] Duan P, Shui Z, Chen W, Shen C. Effects of metakaolin, silica fume and slag on pore structure, interfacial transition zone and compressive strength of concrete. Constr Build Mater 2013;44:1–6. [3] Duan P, Shui Z, Chen W, Shen C. Efficiency of mineral admixtures in concrete: microstructure, compressive strength and stability of hydrate phases. Appl Clay Sci 2013;83–84:115–21. [4] Shui Z, Sun T, Fu Z, Wang G. Dominant factors on the early hydration of metakaolin–cement paste. J Wuhan Univ Technol-Mater Sci Ed 2010;25(5):849–52. [5] Snellings R, Mertens G, Cizer Ö, Elsen J. Early age hydration and pozzolanic reaction in natural zeolite blended cements: reaction kinetics and products by in situ synchrotron X-ray powder diffraction. Cem Concr Res 2010;40(12):1704–13. [6] Ramlochan T, Thomas M, Gruber KA. The effect of metakaolin on alkali-silica reaction in concrete. Cem Concr Res 2000;30(3):339–44. [7] Guneyisi E, Gesoglu M, Karaoglu S, Mermerdas K. Strength, permeability and shrinkage cracking of silica fume and metakaolin concretes. Constr Build Mater 2012;34:120–30. [8] Basheer L, Basheer PAM, Long AE. Influence of coarse aggregate on the permeation, durability and the microstructure characteristics of ordinary Portland cement concrete. Constr Build Mater 2005;19(9):682–90. [9] Khatib JM. Metakaolin concrete at a low water to binder ratio. Constr Build Mater 2008;22(8):1691–700. [10] Ramezanianpour AA, Bahrami Jovein H. Influence of metakaolin as supplementary cementing material on strength and durability of concretes. Constr Build Mater 2012;30:470–9. [11] Sabir BB, Wild S, Bai J. Metakaolin and calcined clays as pozzolans for concrete: a review. Cem Concr Compos 2001;23:441–54. [12] Sha W, Pereira GB. Differential scanning calorimetry study of ordinary Portland cement paste containing metakaolin and theoretical approach of metakaolin activity. Cem Concr Compos 2001;23:455–61. [13] Siddique R, Klaus J. Influence of metakaolin on the properties of mortar and concrete: a review. Appl Clay Sci 2009;43(3–4):392–400. [14] Li C, Sun H, Li L. A review: the comparison between alkali-activated slag (Si plus Ca) and metakaolin (Si plus Al) cements. Cem Concr Res 2010;40(9):1341–9. [15] Ramlochan T, Thomas MDA, Hooton RD. The effect of pozzolans and slag on the expansion of mortars cured at elevated temperature – Part II: Microstructural and microchemical investigations. Cem Concr Res 2004;34(8):1341–56. [16] Guneyisi E, Gesoglu M, Karaboga F, Mermerdas K. Corrosion behavior of reinforcing steel embedded in chloride contaminated concretes with and without metakaolin. Compos Part B-Eng 2013;45(1):1288–95. [17] Guneyisi E, Mermerdas K. Comparative study on strength, sorptivity, and chloride ingress characteristics of air-cured and water-cured concretes modified with metakaolin. Mater Struct 2007;40:1161–71. [18] Zeng J, Shui Z, Wang G. The early hydration and strength development of highstrength precast concrete with cement/metakaolin systems. J Wuhan Univ Technol-Mater Sci Ed 2010;25(4):712–6. [19] Guneyisi E, Gesoglu M, Ozturan T, Mermerdas K. Microstructural properties and pozzolanic activity of calcined kaolins as supplementary cementing materials. Can J Civ Eng 2012;39(12):1274–84. [20] Frias M, Cabrera J. Influence of MK on the reaction kinetics in MK/lime and MK-blended cement systems at 20 °C. Cem Concr Res 2001;31(4):519–27. [21] Khatib JM, Hibbert JJ. Selected engineering properties of concrete incorporating slag and metakaolin. Constr Build Mater 2005;19(6):460–72. [22] Kumar R, Bhattacharjee B. Porosity, pore size distribution and in situ strength of concrete. Cem Concr Res 2003:10. [23] ASTM Committee. ASTM D 1141-98: Standard practice for the preparation of substitute ocean water. ASTM International; 2003. [24] Poon C-S, Lam L, Kou SC, Wong Y-L, Wong R. Rate of pozzolanic reaction of metakaolin in high-performance cement pastes. Cem Concr Res 2001;31:1301–6. [25] Frias M, Cabrera J. Pore size distribution and degree of hydration of metakaolin–cement pastes. Cem Concr Res 2000;30:561–9. [26] Poon C-S, Azhar S, Anson M, Wong Y-L. Performance of metakaolin concrete at elevated temperatures. Cem Concr Compos 2003;25:83–9. [27] Guneyisi E, Gesoglu M, Ozbay E. Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures. Constr Build Mater 2010;24(10):1878–87. [28] Guneyisi E, Gesoglu M. Properties of self-compacting mortars with binary and ternary cementitious blends of fly ash and metakaolin. Mater Struct 2008;41(9):1519–31. [29] Antoni M, Rossen J, Martirena F, Scrivener K. Cement substitution by a combination of metakaolin and limestone. Cem Concr Res 2012;42(12):1579–89.
64
Z. Shi et al. / Construction and Building Materials 74 (2015) 57–64
[30] Arikan M, Sobolev K, Ertuen T, Yeginobali A, Turker P. Properties of blended cements with thermally activated kaolin. Constr Build Mater 2009;23(1):62–70. [31] Johari MAM, Brooks JJ, Kabir S, Rivard P. Influence of supplementary cementitious materials on engineering properties of high strength concrete. Constr Build Mater 2011;25(5):2639–48. [32] Justice JM, Kurtis KE. Influence of metakaolin surface area on properties of cement-based materials. J Mater Civ Eng 2007;19(9):762–71. [33] Khatib JM. Low temperature curing of metakaolin concrete. J Mater Civ Eng 2009;21(8):362–7. [34] Gueneyisi E, Gesoglu M, Mermerdas K. Improving strength, drying shrinkage, and pore structure of concrete using metakaolin. Mater Struct 2008;41(5):937–49.
[35] Frias M, de Rojas MIS. Influence of the metakaolin on porous structure of matrixes based in mk/cement. Mater Constr 2000;50(259):57–67. [36] Li Z, Ding Z. Property improvement of Portland cement by incorporating with metakaolin and slag. Cem Concr Res 2003;33(4):579–84. [37] Thomas MDA, Hooton RD, Scott A, Zibara H. The effect of supplementary cementitious materials on chloride binding in hardened cement paste. Cem Concr Res 2012;42(1):1–7. [38] Kumar M, Singh SK, Singh NP, Singh NB. Hydration of multicomponent composite cement: OPC-FA-SF-MK. Constr Build Mater 2012;36:681–6. [39] Li Q. The nature of early age hydration products. Leeds (UK): University of Leeds; 2009.