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Wet and dry cured compressive strength of concrete containing ground granulated blast-furnace slag
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Building and Environment 42 (2007) 3060–3065 www.elsevier.com/locate/buildenv
Wet and dry cured compressive strength of concrete containing ground granulated blast-furnace slag Cengiz Duran Atis- , Cahit Bilim Engineering and Architecture Faculty, Civil Engineering Department, Cukurova University, 01330 Balcali-Adana, Turkey Received 23 August 2005; received in revised form 13 July 2006; accepted 24 July 2006
Abstract This paper reports a part of an ongoing laboratory investigation in which the compressive strength of ground granulated blast-furnace slag (GGBFS) concrete studied under dry and wet curing conditions. In the study, a total of 45 concretes, including control normal Portland cement (NPC) concrete and GGBFS concrete, were produced with three different water-cement ratios (0.3, 0.4, 0.5), three different cement dosages (350, 400, 450 kg/m3) and four partial GGBFS replacement ratios (20%, 40%, 60%, 80%). A hyperplasticizer was used in concrete at various quantities to provide and keep a constant workability. Twelve cubic samples produced from fresh concrete were de-moulded after a day, then, six cubic samples were cured at 2272 1C with 65% relative humidity (RH), and the remaining six cubic samples were cured at 2272 1C with 100%RH until the samples were used for compressive strength measurement at 28 days and three months. Three cubic samples were used for each age and curing conditions. The comparison was made on the basis of compressive strength between GGBFS concrete and NPC concrete. GGBFS concretes were also compared within themselves. The comparisons showed that compressive strength of GGBFS concrete cured at 65%RH was influenced more than that of NPC concrete. It was found that the compressive strength of GGBFS concrete cured at 65%RH was, at average, 15% lower than that of GGBFS concrete cured at 100%RH. The increase in the water-cementitious materials ratios makes the concrete more sensitive to dry curing condition. The influence of dry curing conditions on GGBFS concrete was marked as the replacement ratio of GGBFS increased. r 2006 Elsevier Ltd. All rights reserved. Keywords: Concrete; Ground granulated blast-furnace slag; Curing; Compressive strength
1. Introduction Granulated blast-furnace slag is defined as the glassy granular material formed when molten blast-furnace slag is rapidly chilled as by immersion in water [1–3]. Fast cooling results with minimum crystallization and converts the molten slag into fine aggregate sized particles (smaller than 4 mm), composed of predominantly noncrystalline material [1]. Due to its high content of silica and alumina in an amorphous state, GGBFS shows pozzolanic behavior similar to that of natural pozzolans, fly ash and silica fume [1]. Blast-furnace slags have been widely utilized as ingredients in cement or concrete with potential hydrauli-
Corresponding author. Fax: +90 322 338 6126.
E-mail address: [email protected] (C. Duran Atis-). 0360-1323/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2006.07.027
city from the point of view of effective use industrial byproducts [4]. Erdogan [1] reported that the use of granulated blastfurnace slag as finely divided mineral admixture in NPC concrete mixes was initiated in South Africa in 1953. The use of GGBFS in concrete increases the workability, reduces bleeding of fresh concrete or mortar. It improves strength, reduces heat of hydration, reduces permeability and porosity, reduces the alkali–silica expansion [1,4–7]. Regarding influence of curing conditions, Ramezanianpour and Malhotra [8] stated that ‘‘if the potential of concrete with regards to strength and durability is to be fully realized, it is most essential that it be cured adequately. The curing becomes even more important if the concrete contains supplementary cementing materials such as fly ash, or ground, granulated blast-furnace slag or silica fume, and is subjected to hot and dry environments immediately after casting’’.
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Since curing conditions influence the hydration and pozzolanic reaction, it is expected that curing conditions influence the GGBFS concrete as influence the plain NPC concrete. Ramezanianpour and Malhotra [8] reported that dry curing at room temperature after demoulding resulted in 38% drop for concrete containing 25% GGBFS, and 50% drop for concretes made with 25% fly ash, 50% GGBFS or high volume fly ash. They concluded that the concretes incorporating supplementary cementing materials are more sensitive to the lack of supply of moisture, and show significant loss of strength compared with the strength obtained after moist curing. Influence of curing conditions on plain concrete have been extensively studied and results have been established [9,10]. The aim of this research is to investigate and evaluate the influence of curing conditions for different relative humidity (RH) on compressive strength of GGBFS concrete. 2. Properties of materials 2.1. Cement The cement used was ASTM Type I normal Portland cement (PC 42.5 N/mm2) with a specific gravity of 3.16 g/cm3. Initial and final setting times of the cement were 230 h and 330 h, respectively. Its Blaine specific surface area was 3250 cm2/g and its chemical composition is given in Table 1. 2.2. Ground granulated blast-furnace slag (GGBFS) GGBFS was supplied from Iskenderun Iron–Steel Factory in Turkey. Its chemical oxide composition is given in Table 1. The specific gravity of GGBFS was 2.81 g/cm3. The GGBFS was ground granulated in Iskenderun Cement Factory to have a Blaine specific surface area about 4250 cm2/g. According to ASTM C 989 [11] hydraulic activity index, the GGBFS used was classified as a category 80 slag. 2.3. Aggregate and its grading Dry and clean natural, river aggregate was used in concrete mixture. The gravel was 16 mm maximum nominal size with 1.3% absorption value and its relative density at saturated surface dry (SSD) condition was 2.70 g/cm3. The absorption value of the sand used was 1.8% and its relative density at SSD condition was 2.67 g/cm3. The grading of the mixed aggregate was presented in Table 2 with the standard limit [12]. Table 2 shows the aggregate grading is suitable for concrete production. 2.4. Concrete mixture proportions For each concrete of a cubic meter, approximate concrete composition is given in Table 3. Mixture design
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Table 1 Chemical composition of cement and GGBFS (%) Oxide
SiO2
Al2O3 Fe2O3 CaO
Cement 19.71 5.20 GGBFS 36.70 14.21
3.73 0.98
MgO SO3 K2O Na2O LOI
62.91 2.54 2.72 0.90 32.61 10.12 0.99 0.76
0.25 0.42
0.96 NA
Table 2 Mixed aggregate grading with standard limit [12] Sieve size (mm)
16 8 4 2 1 0.5 0.25
% Passed TS 706 lower limit
TS 706 medium limit
TS706 upper limit
Mixed aggregate
100 60 36 21 12 7 3
100 76 56 42 32 20 8
100 88 74 62 49 35 18
100.0 74.7 41.0 23.7 17.4 12.9 3.0
is made with according to absolute volume method given by Turkish Standard TS802 [13]. At the beginning of the mixture design, binder content (350, 400, 450 kg/m3) and water–cement ratio (0.3, 0.4, 0.5) were chosen as constant, then, the volume of aggregate was determined for each control NPC concrete by assuming 2% air is trapped in fresh concrete suggested by TS802. The volume of aggregate was used to determine the aggregate weight. GGBFS concrete was produced by modifying NPC concrete. The modification is made by replacing the cement with GGBFS for a given ratio on mass basis. The increase in the paste volume due to inclusion of GGBFS was considered. Then, the volume of aggregate for each GGBFS concrete was compensated accordingly using absolute volume method. A carboxilic-type hyperplasticizing (HP) admixture was used at various amounts to maintain the workability of fresh concrete. The amount of hyperplasticizer was given in Table 3. Measured unit weight of fresh concrete was in the range of between 2350 and 2550 kg/m3, however, theoretical fresh unit weight determined from mixture proportions was in the range of between 2270 and 2500 kg/m3. Workability value of fresh concrete obtained from flow table was in the order of 40–50 cm. Twelve cubic samples (with 150 mm a side) produced from fresh concrete were de-moulded after a day, then, six cubic samples were cured at 2272 1C with 65%RH, and the remaining six cubic samples were cured at 2272 1C with 100%RH until the samples were used for compressive strength measurement at 28 days and three months. Three cubic samples were used for each age and curing conditions. Compressive strength measurements were carried out using ELE International ADR 3000 hydraulic press with a capacity of 3000 kN, the loading rate was 0.3 MPa/s.
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Table 3 Approximate concrete composition for a cubic meter Mixture
PC (kg/m3)
GGBFS (kg/m3)
W (lt/m3)
HP (kg/m3)
Aggregate (kg/m3)
CP 350-0.3-00 GS 350-0.3-20 GS 350-0.3-40 GS 350-0.3-60 GS 350-0.3-80 CP 350-0.4-00 GS 350-0.4-20 GS 350-0.4-40 GS 350-0.4-60 GS 350-0.4-80 CP 350-0.5-00 GS 350-0.5-20 GS 350-0.5-40 GS 350-0.5-60 GS 350-0.5-80
350 280 210 140 70 350 280 210 140 70 350 280 210 140 70
0 70 140 210 280 0 70 140 210 280 0 70 140 210 280
105 105 105 105 105 140 140 140 140 140 175 175 175 175 175
12.25 11.55 8.75 7.00 5.60 5.25 4.20 3.50 1.75 2.80 0.70 0 0 0 0
2030 2025 2015 2010 2000 1940 1930 1925 1915 1910 1845 1840 1830 1825 1815
CP 400-0.3-00 GS 400-0.3-20 GS 400-0.3-40 GS 400-0.3-60 GS 400-0.3-80 CP 400-0.4-00 GS 400-0.4-20 GS 400-0.4-40 GS 400-0.4-60 GS 400-0.4-80 CP 400-0.5-00 GS 400-0.5-20 GS 400-0.5-40 GS 400-0.5-60 GS 400-0.5-80
400 320 240 160 80 400 320 240 160 80 400 320 240 160 80
0 80 160 240 320 0 80 160 240 320 0 80 160 240 320
120 120 120 120 120 160 160 160 160 160 200 200 200 200 200
16.00 14.00 9.60 6.00 4.80 6.00 4.00 4.00 2.40 3.60 0.40 0 0 0 0
1950 1940 1935 1925 1915 1845 1835 1825 1820 1810 1735 1730 1720 1710 1705
CP 450-0.3-00 GS 450-0.3-20 GS 450-0.3-40 GS 450-0.3-60 GS 450-0.3-80 CP 450-0.4-00 GS 450-0.4-20 GS 450-0.4-40 GS 450-0.4-60 GS 450-0.4-80 CP 450-0.5-00 GS 450-0.5-20 GS 450-0.5-40 GS 450-0.5-60 GS 450-0.5-80
450 360 270 180 90 450 360 270 180 90 450 360 270 180 90
0 90 180 270 360 0 90 180 270 360 0 90 180 270 360
135 135 135 135 135 180 180 180 180 180 225 225 225 225 225
18.00 14.40 11.70 9.00 8.10 4.50 3.60 2.25 2.25 1.35 0 0 0 0 0
1865 1860 1850 1840 1830 1750 1740 1730 1720 1710 1630 1620 1610 1600 1590
3. Results and discussion Average compressive strength of control and GGBFS concrete at 28 days and 3 months were illustrated in Table 4 for dry and wet curing conditions separately. The compressive strength values at three months are given in the parenthesis. The ratios of compressive strength obtained from dry curing to wet curing were presented in Table 5. The relative differences between compressive strength of dry curing and wet curing were determined and given in Table 5.
In general, Table 4 shows that, wet cured compressive strength of GGBFS is higher than that of control NPC concrete for 20% and 40% replacement ratios at 28 days and three months. Compressive strength of GGBFS is found to be equivalent to that of control NPC concrete for 60% replacement ratio. However, compressive strength of GGBFS is found to be satisfactory when compared to control NPC concrete for 80% replacement ratio. Table 4 also shows that, for dry curing conditions, compressive strength of GGBFS concrete is found to be equivalent to that of control NPC concrete for 20% and 40% replacement
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Table 4 Compressive strength of concrete at 28 days and three months (MPa) Mixture
Wet cured
Dry cured
Name W/C
0.3
CP-350-00 GS-350-20 GS-350-40 GS-350-60 GS-350-80
75.8 81.4 81.0 73.3 62.7
(83.9) (86.8) (87.8) (81.2) (70.6)
63.9 65.8 67.2 61.8 50.4
(71.3) (73.7) (76.3) (74.0) (58.9)
53.6 57.0 55.9 45.1 29.9
(61.5) (65.4) (65.9) (58.3) (38.1)
72.4 73.3 72.0 57.2 50.2
(80.2) (83.8) (82.0) (62.2) (57.1)
63.9 60.4 57.6 52.6 42.7
(65.6) (68.6) (67.2) (61.0) (49.2)
52.3 50.6 46.5 40.4 26.9
(57.6) (54.1) (53.0) (42.9) (27.6)
CP-400-00 GS-400-20 GS-400-40 GS-400-60 GS-400-80
80.7 81.4 82.0 77.8 67.7
(85.2) (90.1) (88.3) (79.0) (76.2)
63.9 66.0 66.9 61.1 53.1
(67.9) (72.4) (77.9) (75.1) (56.8)
51.4 52.6 51.6 40.1 25.3
(56.8) (61.4) (57.9) (49.6) (31.6)
73.1 69.6 66.5 68.2 54.4
(78.1) (82.3) (79.4) (74.9) (57.5)
65.6 63.1 61.6 59.0 47.2
(67.1) (69.2) (69.9) (66.3) (51.9)
36.9 37.5 35.4 30.5 19.7
(41.4) (39.4) (37.2) (37.7) (22.1)
CP-450-00 GS-450-20 GS-450-40 GS-450-60 GS-450-80
80.3 81.8 83.8 80.6 66.3
(85.7) (90.1) (91.4) (92.5) (77.4)
64.3 73.5 66.4 61.8 46.8
(71.0) (82.3) (81.0) (73.4) (54.6)
48.7 50.4 49.3 39.5 27.7
(50.5) (56.2) (53.4) (49.1) (35.0)
75.0 73.2 76.4 58.2 56.0
(84.2) (85.4) (87.2) (70.0) (62.1)
68.2 69.1 61.7 54.2 42.6
(70.2) (73.6) (71.9) (61.6) (44.6)
41.7 36.3 35.1 28.3 17.6
(45.3) (38.9) (36.6) (30.2) (18.3)
0.4
0.5
0.3
0.4
0.5
Table 5 Compressive strength ratio (dry/wet) and relative difference between dry and wet curing ((wet–dry)/wet) for 28 days and three months Mixture
Dry/wet
Name W/C
0.3
CP-350-00 GS-350-20 GS-350-40 GS-350-60 GS-350-80
0.96 0.90 0.89 0.78 0.80
(0.96) (0.97) (0.93) (0.77) (0.81)
1.00 0.92 0.86 0.85 0.85
(0.92) (0.93) (0.88) (0.82) (0.84)
0.98 0.89 0.83 0.90 0.90
(0.94) (0.83) (0.80) (0.74) (0.72)
0.04 0.10 0.11 0.22 0.20
(0.04) (0.03) (0.07) (0.23) (0.19)
0.00 0.08 0.14 0.15 0.15
(0.08) (0.07) (0.12) (0.18) (0.16)
0.02 0.11 0.17 0.10 0.10
(0.06) (0.17) (0.20) (0.26) (0.28)
CP-400-00 GS-400-20 GS-400-40 GS-400-60 GS-400-80
0.91 0.86 0.81 0.88 0.80
(0.92) (0.91) (0.90) (0.95) (0.75)
1.03 0.96 0.92 0.97 0.89
(0.99) (0.96) (0.90) (0.88) (0.91)
0.72 0.71 0.69 0.76 0.78
(0.73) (0.64) (0.64) (0.76) (0.70)
0.09 0.14 0.19 0.12 0.20
(0.08) (0.09) (0.10) (0.05) (0.25)
0.03 0.04 0.08 0.03 0.11
(0.01) (0.04) (0.10) (0.12) (0.09)
0.28 0.29 0.31 0.24 0.22
(0.27) (0.36) (0.36) (0.24) (0.30)
CP-450-00 GS-450-20 GS-450-40 GS-450-60 GS-450-80
0.93 0.89 0.91 0.72 0.84
(0.98) (0.95) (0.95) (0.76) (0.80)
1.06 0.94 0.93 0.88 0.91
(0.99) (0.89) (0.89) (0.84) (0.82)
0.86 0.72 0.71 0.72 0.64
(0.90) (0.69) (0.69) (0.62) (0.52)
0.07 0.11 0.09 0.28 0.16
(0.02) (0.05) (0.05) (0.24) (0.20)
0.06 0.06 0.07 0.12 0.09
(0.01) (0.11) (0.11) (0.16) (0.18)
0.14 0.28 0.29 0.28 0.36
(0.10) (0.31) (0.31) (0.38) (0.48)
0.4
0.5
ratio at 28 days and three months. Compressive strength of GGBFS is found to be satisfactory when compared to control NPC concrete for 60% replacement ratio. However, concrete containing 80% GGBFS developed lower strength than that of control NPC concrete. Furthermore, it can be seen from the table that compressive strength of each concrete decreases as a result of increase in water–cementitious material ratio. It can also be seen from the table that compressive strength obtained at three months were higher than that of compressive strength obtained at 28 days for all concrete mixture. When a closer examination made at the relative difference column of Table 5, it can be seen that most of
Relative
Difference
((Wet–dry)/wet)
0.3
0.4
0.5
the compressive strength of concrete made with 0.3 and 0.5 water-binder ratios were influenced by dry curing conditions more than that of concrete made with 0.4 waterbinder ratio. Therefore, it may be concluded that an optimum water-binder ratio, for which the influence of curing conditions becomes minimum, exist for a concrete mixture. This is explained in the following. A water-binder ratio, which is higher than the optimum value, results higher porosity and larger capillary porous, thus, permitting freewater evaporate rapidly, resulting higher loss in strength for a concrete when compared to concrete made with optimum water-binder ratio.
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Water content of a concrete made with water-binder ratio lower than the optimum value may become critical, because, a concrete needs certain amount of mixing water for hydration of its cementitious material content. Therefore, loss of water from a concrete made with low waterbinder ratio results in a larger reduction in the compressive strength of concrete when compared to concrete made with optimum water-binder ratio. When the difference between dry and wet curing conditions in terms of compressive strength was compared between control and GGBFS concrete, in general, it can be concluded that dry curing conditions influenced GGBFS concrete more than that of control NPC concrete. Most of the concrete compressive strength indicated that the more the GGBFS content in concrete is the more the reduction in compressive strength due to dry curing condition (see Table 5). Furthermore, it can be observed from Table 5 that there is a weak evidence indicating that the increase in the binder content make the concrete more sensitive to dry curing conditions for both NPC and GGBFS concrete. A statistical analysis was carried out to establish a linear relationship between compressive strengths obtained from dry curing and wet curing. A linear best-fit relationship was established for control NPC and GGBFS concrete separately. The relationships established were presented in Fig. 1, which shows that there is a strong linear relation between compressive strengths of dry and wet cured samples regardless whether the concrete made with or without GGBFS. The comparison made between the relationship established for control and GGBFS concrete shows that, dry curing resulted in a 6% average reduction in compressive strength for control NPC concrete, and 15% average reduction in compressive strength for GGBFS concrete compared to wet curing compressive strength. It also shows that GGBFS concrete was influenced more than that of NPC concrete.
It was stated in another study [14], in which the influence of dry and wet curing on compressive strength of concrete containing silica fume was presented, that in order to understand why concrete containing pozzolan was influenced more than that of NPC, it should be looked at the definition of a pozzolan. A pozzolan is defined as ‘‘a silicous or silicous and aluminous material which in itself possesses little or no cementitious value but which will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties’’ [2,3]. From this definition, it is understood that a pozzolan needs a moist environment with calciumhydroxide to show its binding property. Calcium hydroxide (portlandit) is available in the system due to chemical reaction of C2S and C3S which are main compound of NPC. When the available water in the medium begins to evaporate, it will prevent pozzolan to show its binding property, thus, dry curing conditions would influence the concrete made with pozzolan more than that of concrete made without pozzolan. 4. Conclusions From the laboratory investigation, following conclusions were made. 1. Dry curing conditions influenced GGBFS concrete more than that of control NPC concrete. 2. The increase in the water-binder materials ratios makes the concrete more sensitive to dry curing condition. 3. The influence of dry curing conditions on GGBFS concrete was marked as the replacement ratio of GGBFS increased 4. A linear relationship exists between dry and wet curing conditions for concrete made with and without GGBFS.
Dry Cured-Compressive Strength (MPa)
Acknowledgment The authors would like to thank C - ukurova University Scientific Research Projects Directorate (Project number: MMF 2004 D16).
90 y = 0.94 x, R2 = 0.87, Control Concrete (circles)
80 70
References
60 50 40 30 20
y = 0.85 x, R2 = 0.89, GGBFS Concrete (dots)
10 20
30
40 50 60 70 80 90 Wet Cured-Compressive Strength (MPa)
100
Fig. 1. The relation between dry and wet cured concrete compressive strength.
[1] Erdogan TY. Concrete. Ankara: Metu Press; 2003 (in Turkish). [2] ASTM C-125. Standard terminology relating to concrete and concrete aggregates, Annual book of ASTM Standards. 1994. [3] ACI Committee 116, 116R-90, Cement and concrete terminology, ACI manual of concrete practice, 1994. [4] Sakai K, Watanabe H, Suzuki M, Hamazaki K. Properties of granulated blast-furnace slag cement concrete, Proceedings of fourth international conference on fly ash, silica fume, slag, and natural pozzolans in concrete. Istanbul, Turkey: American Concrete Institute Publication, ACI-SP132; 1992. p. 1367–383. [5] Bijen J. Benefits of slag and fly ash. Construction and Building Materials 1996;10(5):309–14.
ARTICLE IN PRESS C. Duran Atis- , C. Bilim / Building and Environment 42 (2007) 3060–3065 [6] Park CK, Noh MH, Park TH. Rheological properties of cementitious materials containing mineral admixtures. Cement and Concrete Research 2005;35(5):842–9. [7] Aldea CM, Young F, Wang K, Shah SP. Effects of curing on properties of concrete using slag replacement. Cement and Concrete Research 2000;30(3):465–72. [8] Ramezanianpour AA, Malhotra VM. Effect of curing on the compressive strength, resistance to chloride-ion penetration and porosity of concretes incorporating slag, fly ash or silica fume. Cement and Concrete Composites 1995;17(2):125–33. [9] Neville AM. Properties of concrete, 4th ed. London: Longman Group UK Limited Press; 1995.
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[10] Mehta PK. Concrete: structure, properties, and materials. Englewood Cliffs, NJ: Prentice-Hall; 1986. [11] ASTM C-989. Standard specification for ground granulated blast furnace slag for use in concrete and mortars, Annual book of ASTM Standards. 1994. [12] TSI. TS 706-Aggregate for concretes. Ankara, 1980 (in Turkish). [13] TSI. TS802-Design of concrete mixture. Ankara, 1985, (in Turkish). [14] Atis CD, O¨zcan F, Kilic A, Karahan O, Bilim C, Severcan MH. Influence of dry and wet curing conditions on compressive strength of silica fume concrete. Building and Environment 2005;40(12):1678–83.
Building and Environment 42 (2007) 3060–3065 www.elsevier.com/locate/buildenv
Wet and dry cured compressive strength of concrete containing ground granulated blast-furnace slag Cengiz Duran Atis- , Cahit Bilim Engineering and Architecture Faculty, Civil Engineering Department, Cukurova University, 01330 Balcali-Adana, Turkey Received 23 August 2005; received in revised form 13 July 2006; accepted 24 July 2006
Abstract This paper reports a part of an ongoing laboratory investigation in which the compressive strength of ground granulated blast-furnace slag (GGBFS) concrete studied under dry and wet curing conditions. In the study, a total of 45 concretes, including control normal Portland cement (NPC) concrete and GGBFS concrete, were produced with three different water-cement ratios (0.3, 0.4, 0.5), three different cement dosages (350, 400, 450 kg/m3) and four partial GGBFS replacement ratios (20%, 40%, 60%, 80%). A hyperplasticizer was used in concrete at various quantities to provide and keep a constant workability. Twelve cubic samples produced from fresh concrete were de-moulded after a day, then, six cubic samples were cured at 2272 1C with 65% relative humidity (RH), and the remaining six cubic samples were cured at 2272 1C with 100%RH until the samples were used for compressive strength measurement at 28 days and three months. Three cubic samples were used for each age and curing conditions. The comparison was made on the basis of compressive strength between GGBFS concrete and NPC concrete. GGBFS concretes were also compared within themselves. The comparisons showed that compressive strength of GGBFS concrete cured at 65%RH was influenced more than that of NPC concrete. It was found that the compressive strength of GGBFS concrete cured at 65%RH was, at average, 15% lower than that of GGBFS concrete cured at 100%RH. The increase in the water-cementitious materials ratios makes the concrete more sensitive to dry curing condition. The influence of dry curing conditions on GGBFS concrete was marked as the replacement ratio of GGBFS increased. r 2006 Elsevier Ltd. All rights reserved. Keywords: Concrete; Ground granulated blast-furnace slag; Curing; Compressive strength
1. Introduction Granulated blast-furnace slag is defined as the glassy granular material formed when molten blast-furnace slag is rapidly chilled as by immersion in water [1–3]. Fast cooling results with minimum crystallization and converts the molten slag into fine aggregate sized particles (smaller than 4 mm), composed of predominantly noncrystalline material [1]. Due to its high content of silica and alumina in an amorphous state, GGBFS shows pozzolanic behavior similar to that of natural pozzolans, fly ash and silica fume [1]. Blast-furnace slags have been widely utilized as ingredients in cement or concrete with potential hydrauli-
Corresponding author. Fax: +90 322 338 6126.
E-mail address: [email protected] (C. Duran Atis-). 0360-1323/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2006.07.027
city from the point of view of effective use industrial byproducts [4]. Erdogan [1] reported that the use of granulated blastfurnace slag as finely divided mineral admixture in NPC concrete mixes was initiated in South Africa in 1953. The use of GGBFS in concrete increases the workability, reduces bleeding of fresh concrete or mortar. It improves strength, reduces heat of hydration, reduces permeability and porosity, reduces the alkali–silica expansion [1,4–7]. Regarding influence of curing conditions, Ramezanianpour and Malhotra [8] stated that ‘‘if the potential of concrete with regards to strength and durability is to be fully realized, it is most essential that it be cured adequately. The curing becomes even more important if the concrete contains supplementary cementing materials such as fly ash, or ground, granulated blast-furnace slag or silica fume, and is subjected to hot and dry environments immediately after casting’’.
ARTICLE IN PRESS C. Duran Atis- , C. Bilim / Building and Environment 42 (2007) 3060–3065
Since curing conditions influence the hydration and pozzolanic reaction, it is expected that curing conditions influence the GGBFS concrete as influence the plain NPC concrete. Ramezanianpour and Malhotra [8] reported that dry curing at room temperature after demoulding resulted in 38% drop for concrete containing 25% GGBFS, and 50% drop for concretes made with 25% fly ash, 50% GGBFS or high volume fly ash. They concluded that the concretes incorporating supplementary cementing materials are more sensitive to the lack of supply of moisture, and show significant loss of strength compared with the strength obtained after moist curing. Influence of curing conditions on plain concrete have been extensively studied and results have been established [9,10]. The aim of this research is to investigate and evaluate the influence of curing conditions for different relative humidity (RH) on compressive strength of GGBFS concrete. 2. Properties of materials 2.1. Cement The cement used was ASTM Type I normal Portland cement (PC 42.5 N/mm2) with a specific gravity of 3.16 g/cm3. Initial and final setting times of the cement were 230 h and 330 h, respectively. Its Blaine specific surface area was 3250 cm2/g and its chemical composition is given in Table 1. 2.2. Ground granulated blast-furnace slag (GGBFS) GGBFS was supplied from Iskenderun Iron–Steel Factory in Turkey. Its chemical oxide composition is given in Table 1. The specific gravity of GGBFS was 2.81 g/cm3. The GGBFS was ground granulated in Iskenderun Cement Factory to have a Blaine specific surface area about 4250 cm2/g. According to ASTM C 989 [11] hydraulic activity index, the GGBFS used was classified as a category 80 slag. 2.3. Aggregate and its grading Dry and clean natural, river aggregate was used in concrete mixture. The gravel was 16 mm maximum nominal size with 1.3% absorption value and its relative density at saturated surface dry (SSD) condition was 2.70 g/cm3. The absorption value of the sand used was 1.8% and its relative density at SSD condition was 2.67 g/cm3. The grading of the mixed aggregate was presented in Table 2 with the standard limit [12]. Table 2 shows the aggregate grading is suitable for concrete production. 2.4. Concrete mixture proportions For each concrete of a cubic meter, approximate concrete composition is given in Table 3. Mixture design
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Table 1 Chemical composition of cement and GGBFS (%) Oxide
SiO2
Al2O3 Fe2O3 CaO
Cement 19.71 5.20 GGBFS 36.70 14.21
3.73 0.98
MgO SO3 K2O Na2O LOI
62.91 2.54 2.72 0.90 32.61 10.12 0.99 0.76
0.25 0.42
0.96 NA
Table 2 Mixed aggregate grading with standard limit [12] Sieve size (mm)
16 8 4 2 1 0.5 0.25
% Passed TS 706 lower limit
TS 706 medium limit
TS706 upper limit
Mixed aggregate
100 60 36 21 12 7 3
100 76 56 42 32 20 8
100 88 74 62 49 35 18
100.0 74.7 41.0 23.7 17.4 12.9 3.0
is made with according to absolute volume method given by Turkish Standard TS802 [13]. At the beginning of the mixture design, binder content (350, 400, 450 kg/m3) and water–cement ratio (0.3, 0.4, 0.5) were chosen as constant, then, the volume of aggregate was determined for each control NPC concrete by assuming 2% air is trapped in fresh concrete suggested by TS802. The volume of aggregate was used to determine the aggregate weight. GGBFS concrete was produced by modifying NPC concrete. The modification is made by replacing the cement with GGBFS for a given ratio on mass basis. The increase in the paste volume due to inclusion of GGBFS was considered. Then, the volume of aggregate for each GGBFS concrete was compensated accordingly using absolute volume method. A carboxilic-type hyperplasticizing (HP) admixture was used at various amounts to maintain the workability of fresh concrete. The amount of hyperplasticizer was given in Table 3. Measured unit weight of fresh concrete was in the range of between 2350 and 2550 kg/m3, however, theoretical fresh unit weight determined from mixture proportions was in the range of between 2270 and 2500 kg/m3. Workability value of fresh concrete obtained from flow table was in the order of 40–50 cm. Twelve cubic samples (with 150 mm a side) produced from fresh concrete were de-moulded after a day, then, six cubic samples were cured at 2272 1C with 65%RH, and the remaining six cubic samples were cured at 2272 1C with 100%RH until the samples were used for compressive strength measurement at 28 days and three months. Three cubic samples were used for each age and curing conditions. Compressive strength measurements were carried out using ELE International ADR 3000 hydraulic press with a capacity of 3000 kN, the loading rate was 0.3 MPa/s.
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Table 3 Approximate concrete composition for a cubic meter Mixture
PC (kg/m3)
GGBFS (kg/m3)
W (lt/m3)
HP (kg/m3)
Aggregate (kg/m3)
CP 350-0.3-00 GS 350-0.3-20 GS 350-0.3-40 GS 350-0.3-60 GS 350-0.3-80 CP 350-0.4-00 GS 350-0.4-20 GS 350-0.4-40 GS 350-0.4-60 GS 350-0.4-80 CP 350-0.5-00 GS 350-0.5-20 GS 350-0.5-40 GS 350-0.5-60 GS 350-0.5-80
350 280 210 140 70 350 280 210 140 70 350 280 210 140 70
0 70 140 210 280 0 70 140 210 280 0 70 140 210 280
105 105 105 105 105 140 140 140 140 140 175 175 175 175 175
12.25 11.55 8.75 7.00 5.60 5.25 4.20 3.50 1.75 2.80 0.70 0 0 0 0
2030 2025 2015 2010 2000 1940 1930 1925 1915 1910 1845 1840 1830 1825 1815
CP 400-0.3-00 GS 400-0.3-20 GS 400-0.3-40 GS 400-0.3-60 GS 400-0.3-80 CP 400-0.4-00 GS 400-0.4-20 GS 400-0.4-40 GS 400-0.4-60 GS 400-0.4-80 CP 400-0.5-00 GS 400-0.5-20 GS 400-0.5-40 GS 400-0.5-60 GS 400-0.5-80
400 320 240 160 80 400 320 240 160 80 400 320 240 160 80
0 80 160 240 320 0 80 160 240 320 0 80 160 240 320
120 120 120 120 120 160 160 160 160 160 200 200 200 200 200
16.00 14.00 9.60 6.00 4.80 6.00 4.00 4.00 2.40 3.60 0.40 0 0 0 0
1950 1940 1935 1925 1915 1845 1835 1825 1820 1810 1735 1730 1720 1710 1705
CP 450-0.3-00 GS 450-0.3-20 GS 450-0.3-40 GS 450-0.3-60 GS 450-0.3-80 CP 450-0.4-00 GS 450-0.4-20 GS 450-0.4-40 GS 450-0.4-60 GS 450-0.4-80 CP 450-0.5-00 GS 450-0.5-20 GS 450-0.5-40 GS 450-0.5-60 GS 450-0.5-80
450 360 270 180 90 450 360 270 180 90 450 360 270 180 90
0 90 180 270 360 0 90 180 270 360 0 90 180 270 360
135 135 135 135 135 180 180 180 180 180 225 225 225 225 225
18.00 14.40 11.70 9.00 8.10 4.50 3.60 2.25 2.25 1.35 0 0 0 0 0
1865 1860 1850 1840 1830 1750 1740 1730 1720 1710 1630 1620 1610 1600 1590
3. Results and discussion Average compressive strength of control and GGBFS concrete at 28 days and 3 months were illustrated in Table 4 for dry and wet curing conditions separately. The compressive strength values at three months are given in the parenthesis. The ratios of compressive strength obtained from dry curing to wet curing were presented in Table 5. The relative differences between compressive strength of dry curing and wet curing were determined and given in Table 5.
In general, Table 4 shows that, wet cured compressive strength of GGBFS is higher than that of control NPC concrete for 20% and 40% replacement ratios at 28 days and three months. Compressive strength of GGBFS is found to be equivalent to that of control NPC concrete for 60% replacement ratio. However, compressive strength of GGBFS is found to be satisfactory when compared to control NPC concrete for 80% replacement ratio. Table 4 also shows that, for dry curing conditions, compressive strength of GGBFS concrete is found to be equivalent to that of control NPC concrete for 20% and 40% replacement
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Table 4 Compressive strength of concrete at 28 days and three months (MPa) Mixture
Wet cured
Dry cured
Name W/C
0.3
CP-350-00 GS-350-20 GS-350-40 GS-350-60 GS-350-80
75.8 81.4 81.0 73.3 62.7
(83.9) (86.8) (87.8) (81.2) (70.6)
63.9 65.8 67.2 61.8 50.4
(71.3) (73.7) (76.3) (74.0) (58.9)
53.6 57.0 55.9 45.1 29.9
(61.5) (65.4) (65.9) (58.3) (38.1)
72.4 73.3 72.0 57.2 50.2
(80.2) (83.8) (82.0) (62.2) (57.1)
63.9 60.4 57.6 52.6 42.7
(65.6) (68.6) (67.2) (61.0) (49.2)
52.3 50.6 46.5 40.4 26.9
(57.6) (54.1) (53.0) (42.9) (27.6)
CP-400-00 GS-400-20 GS-400-40 GS-400-60 GS-400-80
80.7 81.4 82.0 77.8 67.7
(85.2) (90.1) (88.3) (79.0) (76.2)
63.9 66.0 66.9 61.1 53.1
(67.9) (72.4) (77.9) (75.1) (56.8)
51.4 52.6 51.6 40.1 25.3
(56.8) (61.4) (57.9) (49.6) (31.6)
73.1 69.6 66.5 68.2 54.4
(78.1) (82.3) (79.4) (74.9) (57.5)
65.6 63.1 61.6 59.0 47.2
(67.1) (69.2) (69.9) (66.3) (51.9)
36.9 37.5 35.4 30.5 19.7
(41.4) (39.4) (37.2) (37.7) (22.1)
CP-450-00 GS-450-20 GS-450-40 GS-450-60 GS-450-80
80.3 81.8 83.8 80.6 66.3
(85.7) (90.1) (91.4) (92.5) (77.4)
64.3 73.5 66.4 61.8 46.8
(71.0) (82.3) (81.0) (73.4) (54.6)
48.7 50.4 49.3 39.5 27.7
(50.5) (56.2) (53.4) (49.1) (35.0)
75.0 73.2 76.4 58.2 56.0
(84.2) (85.4) (87.2) (70.0) (62.1)
68.2 69.1 61.7 54.2 42.6
(70.2) (73.6) (71.9) (61.6) (44.6)
41.7 36.3 35.1 28.3 17.6
(45.3) (38.9) (36.6) (30.2) (18.3)
0.4
0.5
0.3
0.4
0.5
Table 5 Compressive strength ratio (dry/wet) and relative difference between dry and wet curing ((wet–dry)/wet) for 28 days and three months Mixture
Dry/wet
Name W/C
0.3
CP-350-00 GS-350-20 GS-350-40 GS-350-60 GS-350-80
0.96 0.90 0.89 0.78 0.80
(0.96) (0.97) (0.93) (0.77) (0.81)
1.00 0.92 0.86 0.85 0.85
(0.92) (0.93) (0.88) (0.82) (0.84)
0.98 0.89 0.83 0.90 0.90
(0.94) (0.83) (0.80) (0.74) (0.72)
0.04 0.10 0.11 0.22 0.20
(0.04) (0.03) (0.07) (0.23) (0.19)
0.00 0.08 0.14 0.15 0.15
(0.08) (0.07) (0.12) (0.18) (0.16)
0.02 0.11 0.17 0.10 0.10
(0.06) (0.17) (0.20) (0.26) (0.28)
CP-400-00 GS-400-20 GS-400-40 GS-400-60 GS-400-80
0.91 0.86 0.81 0.88 0.80
(0.92) (0.91) (0.90) (0.95) (0.75)
1.03 0.96 0.92 0.97 0.89
(0.99) (0.96) (0.90) (0.88) (0.91)
0.72 0.71 0.69 0.76 0.78
(0.73) (0.64) (0.64) (0.76) (0.70)
0.09 0.14 0.19 0.12 0.20
(0.08) (0.09) (0.10) (0.05) (0.25)
0.03 0.04 0.08 0.03 0.11
(0.01) (0.04) (0.10) (0.12) (0.09)
0.28 0.29 0.31 0.24 0.22
(0.27) (0.36) (0.36) (0.24) (0.30)
CP-450-00 GS-450-20 GS-450-40 GS-450-60 GS-450-80
0.93 0.89 0.91 0.72 0.84
(0.98) (0.95) (0.95) (0.76) (0.80)
1.06 0.94 0.93 0.88 0.91
(0.99) (0.89) (0.89) (0.84) (0.82)
0.86 0.72 0.71 0.72 0.64
(0.90) (0.69) (0.69) (0.62) (0.52)
0.07 0.11 0.09 0.28 0.16
(0.02) (0.05) (0.05) (0.24) (0.20)
0.06 0.06 0.07 0.12 0.09
(0.01) (0.11) (0.11) (0.16) (0.18)
0.14 0.28 0.29 0.28 0.36
(0.10) (0.31) (0.31) (0.38) (0.48)
0.4
0.5
ratio at 28 days and three months. Compressive strength of GGBFS is found to be satisfactory when compared to control NPC concrete for 60% replacement ratio. However, concrete containing 80% GGBFS developed lower strength than that of control NPC concrete. Furthermore, it can be seen from the table that compressive strength of each concrete decreases as a result of increase in water–cementitious material ratio. It can also be seen from the table that compressive strength obtained at three months were higher than that of compressive strength obtained at 28 days for all concrete mixture. When a closer examination made at the relative difference column of Table 5, it can be seen that most of
Relative
Difference
((Wet–dry)/wet)
0.3
0.4
0.5
the compressive strength of concrete made with 0.3 and 0.5 water-binder ratios were influenced by dry curing conditions more than that of concrete made with 0.4 waterbinder ratio. Therefore, it may be concluded that an optimum water-binder ratio, for which the influence of curing conditions becomes minimum, exist for a concrete mixture. This is explained in the following. A water-binder ratio, which is higher than the optimum value, results higher porosity and larger capillary porous, thus, permitting freewater evaporate rapidly, resulting higher loss in strength for a concrete when compared to concrete made with optimum water-binder ratio.
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Water content of a concrete made with water-binder ratio lower than the optimum value may become critical, because, a concrete needs certain amount of mixing water for hydration of its cementitious material content. Therefore, loss of water from a concrete made with low waterbinder ratio results in a larger reduction in the compressive strength of concrete when compared to concrete made with optimum water-binder ratio. When the difference between dry and wet curing conditions in terms of compressive strength was compared between control and GGBFS concrete, in general, it can be concluded that dry curing conditions influenced GGBFS concrete more than that of control NPC concrete. Most of the concrete compressive strength indicated that the more the GGBFS content in concrete is the more the reduction in compressive strength due to dry curing condition (see Table 5). Furthermore, it can be observed from Table 5 that there is a weak evidence indicating that the increase in the binder content make the concrete more sensitive to dry curing conditions for both NPC and GGBFS concrete. A statistical analysis was carried out to establish a linear relationship between compressive strengths obtained from dry curing and wet curing. A linear best-fit relationship was established for control NPC and GGBFS concrete separately. The relationships established were presented in Fig. 1, which shows that there is a strong linear relation between compressive strengths of dry and wet cured samples regardless whether the concrete made with or without GGBFS. The comparison made between the relationship established for control and GGBFS concrete shows that, dry curing resulted in a 6% average reduction in compressive strength for control NPC concrete, and 15% average reduction in compressive strength for GGBFS concrete compared to wet curing compressive strength. It also shows that GGBFS concrete was influenced more than that of NPC concrete.
It was stated in another study [14], in which the influence of dry and wet curing on compressive strength of concrete containing silica fume was presented, that in order to understand why concrete containing pozzolan was influenced more than that of NPC, it should be looked at the definition of a pozzolan. A pozzolan is defined as ‘‘a silicous or silicous and aluminous material which in itself possesses little or no cementitious value but which will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties’’ [2,3]. From this definition, it is understood that a pozzolan needs a moist environment with calciumhydroxide to show its binding property. Calcium hydroxide (portlandit) is available in the system due to chemical reaction of C2S and C3S which are main compound of NPC. When the available water in the medium begins to evaporate, it will prevent pozzolan to show its binding property, thus, dry curing conditions would influence the concrete made with pozzolan more than that of concrete made without pozzolan. 4. Conclusions From the laboratory investigation, following conclusions were made. 1. Dry curing conditions influenced GGBFS concrete more than that of control NPC concrete. 2. The increase in the water-binder materials ratios makes the concrete more sensitive to dry curing condition. 3. The influence of dry curing conditions on GGBFS concrete was marked as the replacement ratio of GGBFS increased 4. A linear relationship exists between dry and wet curing conditions for concrete made with and without GGBFS.
Dry Cured-Compressive Strength (MPa)
Acknowledgment The authors would like to thank C - ukurova University Scientific Research Projects Directorate (Project number: MMF 2004 D16).
90 y = 0.94 x, R2 = 0.87, Control Concrete (circles)
80 70
References
60 50 40 30 20
y = 0.85 x, R2 = 0.89, GGBFS Concrete (dots)
10 20
30
40 50 60 70 80 90 Wet Cured-Compressive Strength (MPa)
100
Fig. 1. The relation between dry and wet cured concrete compressive strength.
[1] Erdogan TY. Concrete. Ankara: Metu Press; 2003 (in Turkish). [2] ASTM C-125. Standard terminology relating to concrete and concrete aggregates, Annual book of ASTM Standards. 1994. [3] ACI Committee 116, 116R-90, Cement and concrete terminology, ACI manual of concrete practice, 1994. [4] Sakai K, Watanabe H, Suzuki M, Hamazaki K. Properties of granulated blast-furnace slag cement concrete, Proceedings of fourth international conference on fly ash, silica fume, slag, and natural pozzolans in concrete. Istanbul, Turkey: American Concrete Institute Publication, ACI-SP132; 1992. p. 1367–383. [5] Bijen J. Benefits of slag and fly ash. Construction and Building Materials 1996;10(5):309–14.
ARTICLE IN PRESS C. Duran Atis- , C. Bilim / Building and Environment 42 (2007) 3060–3065 [6] Park CK, Noh MH, Park TH. Rheological properties of cementitious materials containing mineral admixtures. Cement and Concrete Research 2005;35(5):842–9. [7] Aldea CM, Young F, Wang K, Shah SP. Effects of curing on properties of concrete using slag replacement. Cement and Concrete Research 2000;30(3):465–72. [8] Ramezanianpour AA, Malhotra VM. Effect of curing on the compressive strength, resistance to chloride-ion penetration and porosity of concretes incorporating slag, fly ash or silica fume. Cement and Concrete Composites 1995;17(2):125–33. [9] Neville AM. Properties of concrete, 4th ed. London: Longman Group UK Limited Press; 1995.
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[10] Mehta PK. Concrete: structure, properties, and materials. Englewood Cliffs, NJ: Prentice-Hall; 1986. [11] ASTM C-989. Standard specification for ground granulated blast furnace slag for use in concrete and mortars, Annual book of ASTM Standards. 1994. [12] TSI. TS 706-Aggregate for concretes. Ankara, 1980 (in Turkish). [13] TSI. TS802-Design of concrete mixture. Ankara, 1985, (in Turkish). [14] Atis CD, O¨zcan F, Kilic A, Karahan O, Bilim C, Severcan MH. Influence of dry and wet curing conditions on compressive strength of silica fume concrete. Building and Environment 2005;40(12):1678–83.