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Properties of concrete prepared with crushed fine stone, furnace bottom ash and fine recycled aggregate as fine aggregates
Construction and Building Materials 23 (2009) 2877–2886
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Properties of concrete prepared with crushed fine stone, furnace bottom ash and fine recycled aggregate as fine aggregates Kou Shi-Cong, Poon Chi-Sun * Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China
a r t i c l e
i n f o
Article history: Received 4 August 2008 Received in revised form 29 December 2008 Accepted 8 February 2009 Available online 12 March 2009 Keywords: Fine aggregates Furnace bottom ash Fine recycled aggregate Crushed fine stone Concrete
a b s t r a c t This paper presents the results of a study to compare the properties of concretes prepared with the use river sand, crushed fine stone (CFS), furnace bottom ash (FBA), and fine recycled aggregate (FRA) as fine aggregates. Two methods were used to design the concrete mixes: (i) fixed water–cement ratio (W/C) and (ii) fixed slump ranges. The investigation included testing of compressive strength, drying shrinkage and resistance to chloride-ion penetration of the concretes. The test results showed that, at fixed water– cement ratios, the compressive strength and the drying shrinkage decreased with the increase in the FBA content. FRA decreased the compressive strength and increased the drying shrinkage of the concrete. However, when designing the concrete mixes with a fixed slump value, at all the test ages, when FBA was used as the fine aggregates to replace natural aggregates, the concrete had higher compressive strength, lower drying shrinkage and higher resistance to the chloride-ion penetration. But the use of FRA led to a reduction in compressive strength but increase in shrinkage values. The results suggest that both FBA and FRA can be used as fine aggregates for concrete production. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Natural materials such as river sand and crushed fine stone are generally used in concrete as fine aggregates. However, with the booming in urban infrastructure development and the increasing demand on protecting the natural environment, especially in build-up areas such as Hong Kong and some southern Chinese cities in the Pearl River Delta, the availability of the natural resources is diminishing rapidly. Other sources of fine aggregates are urgently needed. Furnace bottom ash (FBA) is a waste material generated from coal-fired thermal power plants. Unlike its companion – pulverised fuel ash (PFA), it usually has much lower pozzolanic property which makes it unsuitable to be used as a cement replacement material in concrete. However, as its particle distribution is similar to that of sand which makes it attractive to be used as a sand replacement material especially in concrete masonry block production. But few studies have been done on exploring the feasibility of using FBA for making concrete. Previous studies carried out by Bai et al. on using FBA as a natural sand replacement material in concrete indicated that, although FBA has no adverse effect on the strength of concrete, beyond 30% replacement level, the permeation properties of the concrete would be detrimentally affected [1,2]. The porous structure of the FBA particles has been considered to have caused the increase * Corresponding author. Tel.: +852 2766 6024; fax: +852 2334 6389. E-mail address: [email protected] (C.-S. Poon). 0950-0618/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2009.02.009
in the permeation properties. However, the porous nature of the aggregate is believed to be a benefit for reducing the shrinkage of concrete [3,4], which is considered to be due to its ‘‘internal curing effect’’ through slow release of moisture from the saturated porous particles [5,6]. Recycled aggregates are produced from the re-processing of mineral waste materials, with the largest source being construction and demolition (C&D) waste. The coarse portion of the recycled aggregates has been used as a replacement of the natural aggregates for concrete production. The potential benefits and drawbacks of using recycled aggregates in concrete are well understood and extensively documented [7–13]. In general, the quality of recycled aggregates is inferior to those of natural aggregates. The density of the recycled aggregates is lower than the natural aggregates and the recycled aggregates have a greater water absorption value compared to the natural aggregates. As a result, a proper mix design is required for obtaining the desired qualities for concrete made with recycled aggregates [14,15]. In addition to the coarse recycled aggregates, fine recycled aggregates (FRA, <5 mm) can also be used to replace natural fine aggregates in the production of concrete. Khatib [16] reported that when natural fine aggregates in concrete were replaced by 0%, 25%, 50%, 75% and 100% fine recycled aggregates and the free water/cement ratio was kept constant for all the mixes, the 28-day strength of the concrete developed at a slower rate. Furthermore, the concrete mixtures containing fine recycled aggregates had higher shrinkage than the natural aggregates concrete. Evangelista et al. [11] indicated that the use of fine recycled concrete aggregates
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up to 30% replacement ratios would not jeopardize the mechanical properties of concrete. This paper compares the properties of concretes that are prepared with the use river sand, crushed rock fine, furnace bottom ash, and recycled fine aggregates as fine aggregates. The mechanical properties, deformational behaviour and durability of the concrete were investigated by testing of compressive strength, drying shrinkage and resistance to chloride-ion penetration of the concretes, respectively.
2.2. Mixture proportions
2. Experimental details
2.3. Details of specimen
2.1. Materials
For each concrete mix, twelve 100 mm size cubes were cast to determine the compressive strength. Three 75 75 285 mm prisms with an indentation at the centre of the two ends were cast to determine the drying shrinkage. Two 100 200 cylindrical specimens were cast to determine the resistance to chloride-ion penetration. All concrete specimens were prepared in accordance with BS 1881: Part 125:1986 [19]. All specimens were cast in two layers and compacted on a vibrating table until no more air bubbles appeared. They were covered with a plastic sheet and left in the mould in the laboratory at 22(±1) °C for 24 h. After that, different curing regimes were used as described below: (1) The 100 mm cubes were cured in water 27(±1) °C until they were tested at 3, 7, 28 and 90 days to determine the compressive strength; (2) the concrete prisms were covered with a damp Hessian cloth and a plastic sheet. After 1 day, the covers were removed and the specimens were wiped clean, and then the initial length was measured. The prisms were then stored
The cement used was the ASTM Type I Portland cement complying with BS EN 197 – 1:2000 [17]. The coarse aggregate used was 10 and 20 mm crushed natural granite. The natural fine aggregates used were river sand sourced from the Pearl River and crushed fine stone (CFS, granite) obtained from a local quarry. Both materials comply with BS EN 12620:2002 [18]. The FBA used was obtained from a local coal-fired power plant. Before the FBA was used, it underwent a process of sieving so that all materials used in the experiment were <5 mm. The fine recycled aggregate (FRA) was obtained from a local C&D waste recycling plant. The physical and chemical properties of the materials used are shown in Tables 1 and 2. Fig. 1 shows the particle size distributions of the FBA, the CFS, the FRA and the river sand used in this study.
Two series of concrete mixes were prepared. In the concrete mixes, natural river sand was replaced by the FBA, CFS and FRA at replacement levels of 0%, 25%, 50%, 75% and 100% by mass, respectively, and the cement content was fixed at 386 kg/ m. In Series I, the concrete mixes were designed at fixed water–cement ratio of 0.53. In Series II, the concrete mixes were designed to have a near constant slump in the range of 60–80 mm; and as such, the free water content (and hence the water–cement ratio) varied. Table 3 shows the detailed mix proportions. The concrete mixes were designed based on the saturated surface dried condition as reflected in Table 3. Water compensation was made during concrete batching.
Table 1 Chemical composition (% by mass) of cement and FBA.
Cement FBA
SiO2
Al2O3
Fe2O3
MgO
CaO
Na2O
K2O
TiO2
SO3
Others
LOI
19.6 60.7
7.33 18.3
3.32 6.56
2.54 1.28
63.15 3.25
– 0.89
– 2.12
– 0.95
2.13 0.82
– 1.00
2.97 4.13
LOI: loss on ignition.
Table 2 Properties of aggregates. Property
Granite
Density (SSD) (kg/m3) Fineness modulus 1-h Water absorption (%)
10 mm
20 mm
2620 – 0.48
2620 – 0.47
CFS
River sand
FBA
FRA
2610 3.56 0.89
2620 2.18 0.38
2190 1.83 28.9
2310 3.18 2.38
Cumulative percentage passing (%)
120
100
80
60 FBA 40
River sand CFS
20
FRA
0 10
5
2.36
1.18
0.6
0.3
0.15
Size of test sieve (mm) Fig. 1. Comparison of particle size distributions of FBA, river sand, CFS and FRA.
0.075
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II
a
Mix notation
SRLa (%)
Cement
Free water
W/C
Sand
FBA
FRA
CFS
Coarse agg.
FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
0 25 50 75 100 25 50 75 100 25 50 75 100
386 386 386 386 386 386 386 386 386 386 386 386 386
205 205 205 205 205 205 205 205 205 205 205 205 205
0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53
652 457 262 67 – 473 293 114 – 489 325 162 –
– 163 326 489 545 – – – – – – – –
– – – – – 163 326 489 592 – – – –
– – – – – – – – – 163 326 489 650
1110 1110 1110 1110 1110 1110 1110 1110 1110 1110 1110 1110 1110
FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
25 50 75 100 25 50 75 100 25 50 75 100
386 386 386 386 386 386 386 386 386 386 386 386
190 170 150 130 200 195 190 185 208 211 214 217
0.49 0.44 0.39 0.34 0.52 0.51 0.49 0.48 0.54 0.55 0.56 0.57
494 318 138 – 490 307 130 – 487 322 161 –
167 343 529 725 – – – – – – – –
– – – – 164 331 500 671 – – – –
– – – – – – – – 162 323 482 640
1127 1126 1135 1184 1114 1086 1073 1086 1105 1099 1093 1087
SRL: sand replacement level.
in an environmental chamber at 23(±1) °C and 50(±1)% RH until the drying shrinkage was tested at the ages of 1, 4, 7, 14, 28, 90 and 112 days; (3) The concrete cylinders were cured in water at 27(±1) °C until the curing ages of 28 days and 90 days. The cylinders were then cut by a diamond saw to obtain 100 mm diameter 50 mm thick concrete discs for the chloride-ion penetration test. 2.4. Test procedures 2.4.1. Workability The workability of fresh concrete was measured by the slump test, in accordance with BS 1881: Part 102: 1983 [20]. 2.4.2. Compressive strength The compressive strength was measured by crushing 300 mm cubes in accordance with BS 1881: Part 116: 1983 [21] using a Denison compression machine with a capacity of 3000 kN. The loading rates were 200 kN/min for the compressive tests. The compressive strengths of the hardened concrete were determined at the ages of 3, 7, 28 and 90 days. 2.4.3. Drying shrinkage The drying shrinkage values were determined following ASTM C490-07 [22]. The prism specimen size was 75 75 285 mm. The specimens were demolded after curing for 24 h and the initial lengths of the specimens were measured. After the initial reading, the specimens were conveyed to a drying-chamber with a temperature of 23 °C and a relative humidity of 55% until the time when the next measurement at 1, 4, 7, 28, 56, 90 and 112 days was reached. The accuracy in the length change measurement was ±0.0025 mm. 2.4.4. Chloride-ion penetration The resistance to chloride penetrability of concrete was determined in accordance with ASTM C1202-94 [23]. The resistance of concrete against chloride-ion penetration is represented by the total charge passed in coulombs during a test period of 6 h.
3. Results and discussion 3.1. Property of fresh concrete The slump values of the fresh concretes in Series I and II are shown in Figs. 2 and 3, respectively. From Fig. 2, it can be seen that, at the fixed W/C ratio, the slump of the FBA and FRA concrete mixes was increased with an increase in FBA or FRA content. This
was due to FBA and FRA had higher water absorption values than that of river sand making more free water was made available to increase the fluidity of the fresh concrete. However, the slump of CFS concrete mixes was decreased with an increase in CFS content probably due to the angular shape of the CFS when compared to river sand. This result is similar to that of Cabrera and Donza [27] who reported that when crushed sand was incorporated in concrete, the increase of water demand due to the shape and texture of the crushed sand can be mitigated by using a water reducing admixture. Fig. 3 shows the slump values of the Series II mixes were maintained at approximately the same value by reducing the added free water (Fig. 4) when FBA and FRA were used to replace river sand. However, for the case of the CFS mixes, more free water was needed to produce the same workability due to the angular shape of CFS.
3.2. Compressive strength Figs. 5–10 show the compressive strength results of the concrete mixes in Series I and II, respectively. It can be seen from Figs. 5 and 6 that when using the same W/C ratio, generally the compressive strength of the FBA and FRA concrete decreased at all the ages with an increase in the FBA and FRA contents. This may be due to the high initial free water content used in the mixes rendered bleeding and poorer interfacial bonding between the aggregates and the cement pastes. Moreover, it can be seen from Fig. 7 that at replacement levels of 75% and 100%, the compressive strength of the CFS concrete decreased when compared with the control. This was due to the decrease in slump when the angular CFS was used to replace sand. This is consistent with other researchers’ findings that the use of crushed sand in concrete would increase both the water and cement content in order to maintain an adequate workability [24– 27]. The amount of additional water and cement required was dependent on the shape, texture, grading and dust content of the crushed sand.
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210 180
Slump (mm )
150 120 90 60 30 0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
Mix notation Fig. 2. Slump values of fresh concrete in Series I.
90 80
Slump (mm)
70 60 50 40 30 20 10 0
Mix notation Fig. 3. Slump values of fresh concrete in Series II.
Free water content (kg/m3)
250
200
150
100
50
0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
Mix notation Fig. 4. Free water content of concrete in Series II.
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70
3-day
7-day
28-day
90-day
Compressive strength (MPa)
60 50 40 30 20 10 0 Control
FBA25
FBA50
FBA75
FBA100
Mix notation Fig. 5. Compressive strength of concrete mixes in Series I (FBA).
70
3-day
7-day
28-day
90-day
Compressive strength (MPa)
60 50 40 30 20 10 0 Control
FRA25
FRA50
FRA75
FRA100
Mix notation Fig. 6. Compressive strength of concrete mixes in Series I (FRA).
70
3-day
7-day
28-day
90-day
Compressive strength (MPa)
60 50 40 30 20 10 0 Control
CFS25
CFS50
CFS75
Mix notation Fig. 7. Compressive strength of concrete mixes in Series I (CFS).
CFS100
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80
3-day
7-day
28-day
90-day
Compressive strength (MPa)
70 60 50 40 30 20 10 0 Control
FBA25
FBA50
FBA75
FBA100
Mix notation Fig. 8. Compressive strength of concrete mixes in Series II (FBA).
70
3-day
7-day
28-day
90-day
Compressive strength (MPa)
60 50 40 30 20 10 0 Control
FRA25
FRA50
FRA75
FRA100
Mix notation Fig. 9. Compressive strength of concrete mixes in Series II (FRA).
Compressive strength (MPa)
70
3-day
7-day
28-day
90-day
60 50 40 30 20 10 0 Control
CFS25
CFS50
CFS75
Mix notation Fig. 10. Compressive strength of concrete mixes in Series II (CFS).
CFS100
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Fig. 8 indicates that for concrete designed with a fixed slump range, the compressive strength of the FBA concrete was higher than that of the control. The improved in compressive strength should be attributed to the decrease in free W/C due to the fact that for a given slump of concrete, the high water absorption properties of FBA would lead to a reduction of free water required (Fig. 4) to produce the target slump value. Fig. 9 shows the compressive strength of the concrete decreased with an increase in the FRA content at all the test ages. This is probably because similar to the case of FBA, the free water required for the fixed slump in the case of the FRA mixes was also decreased. But due to the water absorption value of FRA was a lot lower than that of FBA (see Table 2), the water reduction effect on FRA concrete was not as significant as that on the FBA concrete. Under such conditions, the effect of the relative weaker FRA on concrete strength would lead to an overall reduction of compressive strength. Moreover, it can also be seen from Fig. 10 that at replacement levels of 75% and 100%, the compressive strength of the CFS concrete decreased when compared with the control. This was due to the increase in free W/C ratio used (Table 3) to compensate
for the decrease in slump when the angular CFS was used to replace river sand. Figs. 11 and 12 show the comparison of the compressive strength of the concrete made with 100% FBA, 100% FRA and 100% CFS in Series I and II, respectively. Fig. 11 shows at all the test ages, when the W/C was kept constant, the compressive strength of FBA, FRA and CFS concrete was lower than that of the control. The concrete mixes with 100% FBA had the lowest compressive strength. However, Fig. 12 shows that when designing the concrete mixes at a fixed slump range, the concrete made with FBA had the highest compressive strength while the FRA concrete had the lowest compressive strength. The above results further illustrate how the water absorption properties of the different fine aggregates affected the free water required in the concrete mixes (hence W/C) which had direct bearings on the compressive strength. 3.3. Drying shrinkage The drying shrinkage results of the concrete mixes in Series I and II are presented in Figs. 13 and 14, respectively. Fig. 13 indi-
70
Compressive strength (MPa )
60 50
Control FBA100 FRA100 CFS100
40 30 20 10 0
3-day
7-day
28-day
90-day
Time (day) Fig. 11. Comparison of compressive strength of concrete mixes in Series I prepared with 100% FBA, FRA and CFS as fine aggregate.
80
Compressive strength (MPa)
70 60
Control FBA100 FRA100 CFS100
50 40 30 20 10 0
3-day
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7-day 28-day Mix notation
90-day
Fig. 12. Comparison of compressive strength of concrete mixes in Series II prepared with 100% FBA, FRA and CFS as fine aggregate.
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900
Drying shrinkage (Microstrain)
800 700 600 500 400 300 200 100 0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25
CFS50
CFS75 CFS100
Mix notation Fig. 13. Drying shrinkage of concrete mixes in Series I at 112 days.
900
Drying shrinkage (microstrain)
800 700 600 500 400 300 200 100 0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
Mix notation Fig. 14. Drying shrinkage of concrete mixes in Series II at 112 days.
cates that at the fixed W/C of 0.53, the drying shrinkage values of all FBA and CFS concretes are lower than that of the control concrete with the exception of the 100% FBA replacement level. The results agreed with the findings of Bai et al. [28] who suggested that with a fixed W/C of 0.45 and 0.50, the drying shrinkage of concrete could be reduced by using FBA to replace sand. This was due to with the use of FBA in the concrete mixes, moisture would be slowly released from the porous FBA particles during the drying of the concrete resulting in lower drying shrinkage values than that of the control concrete. But the drying shrinkage values of FRA concretes increased with an increase in FRA content due to the adhered old mortar in FRA. As shown in Fig. 14, at the fixed slump range, the drying shrinkage values of all the FBA concretes are lower than that of the control. This was due to the fact that with the increase in FBA content, the required free water content decreased (Table 3). However, Fig. 14 also shows the drying shrinkage of the FRA concrete increased with an increase in the FRA content probably due to the instability of the old adhered cement mortar in the FRA. Moreover, the drying shrinkage values of all the CFS concretes in both the fixed W/C and the fixed slump range mixtures were
lower than that of the control. This is probably due to the CFS used had larger particle sizes distribution and hence lower specific surface areas (SSA) than that of the river sand. It has been suggested that SSA of aggregates is one of the properties that affects concrete shrinkage [29], and in general a sample of aggregate with a lower SSA (i.e. larger particle size) would result in lower shrinkage of the concrete produced. 3.4. Chloride-ion penetration The test results of chloride-ion penetration of the concrete mixes in Series I and II are shown in Figs. 15 and 16, respectively. Fig. 15 shows at the same W/C, the resistance to chloride-ion penetration of the concrete mixes decreased with increasing percentages FBA, FRA and CFS replacement of river sand. This may be due to the FBA and FRA concretes had more free water than the control concrete which led to a looser microstructure. In the case of FRA concrete, the adhered mortar should lead to a worse microstructure too. For CFS, the decrease in slump of the CFS concrete might have rendered a poorer microstructure due to difficulty in compaction.
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7000
Total charge passed in coulombs
28-day
90-day
6000 5000 4000 3000 2000 1000 0
Mix notation Fig. 15. Total charge passed in coulombs of concrete mixes in Series I at 28 days and 90 days.
7000
28-day
90-day
Total charge passed in coulombs
6000 5000 4000 3000 2000 1000 0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
Mix notation Fig. 16. Total charge passed in coulombs of concrete mixes in Series II at 28 days and 90 days.
Moreover, at a fixed slump range (Series II, Fig. 16), due to the initial free water required was decreased (see Fig. 4), the resistance to chloride-ion penetration of all FBA, FRA and CFS concrete mixes was better than that of the control. Again, the effect was most significant for the FBA mixes due probably to the pozzolanic effect between the hydrated cement paste (i.e. calcium hydroxide) and the small FBA particles. 4. Conclusion Based on the present investigation, the following conclusions can be drawn: (1) At a fixed W/C, the compressive strength and the drying shrinkage decreased with the increase in the FBA content. FRA decreased the compressive strength and increased the drying shrinkage of the concrete. (2) At a fixed slump value, the use of FBA and FRA was able to reduce to free water requirement of the concrete mixes.
(3) For the mixes prepared with the same slump range and with the use of a lower free W/C ratio, the FBA concrete had the highest compressive strength values. (4) But the use of FRA led to a reduction in compressive strength despite the use of a lower free W/C. This might be due to the inherent weaker mechanical properties of FRA. (5) The drying shrinkage decreased with the increase of the FBA content. FRA increased the drying shrinkage of the concrete. (6) At a fixed slump value, the resistance to chloride-ion penetration of all FBA, FRA and CFS concretes was higher than that of the control concrete. (7) It is feasible to use FBA and FRA as fine aggregate in preparing concrete mixes.
Acknowledgements The authors would like to thank the Research Grants Council (PolyU 5259/06E) and the Hong Kong Polytechnic University for
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funding support. The FBA for this research was provided by the China Light and Power Co. Ltd. and the FRA was provided by the Civil Engineering Development Department of the Hong Kong SAR Government. References [1] Bai Y, Basheer PAM. Influence of furnace bottom ash on properties of concrete. Proc I Civil Eng Struct Build 2003;156(1):85–92. [2] Bai Y, Basheer PAM. Properties of concrete containing furnace bottom ash as a sand replacement material. In: Proceedings of structural faults and repair (CDROM), London, July 1–3; 2003. [3] Collins F, Sanjayan JG. Strength and shrinkage properties of alkali-activated slag concrete containing porous coarse aggregate. Cem Concr Res 1999;29:607–10. [4] Kohno K, Okamoto T, Isikawa Y, Sibata T, Mori H. Effects of artificial lightweight aggregate on autogenous shrinkage of concrete. Cem Concr Res 1999;29:611–4. [5] Weber S, Reinhardt HW. A new generation of high performance concrete: concrete with autogenous curing. Adv Cem Based Mater 1997;6:59–68. [6] Bentz DP, Snyder KA. Protected paste volume in concrete – extension to internal curing using saturated lightweight fine aggregate. Cem Concr Res 1999;29:1863–7. [7] Dhir RK, Limbachiya MC, Leelawat T. Suitability of recycled concrete aggregate for use in BS 5328 designated mixes. Proc ICE – Struct Build 1999;134:257–74. [8] Abou-Zeid MN, Shenouda MN, Mccabe S, El-Tawil FA. Reincarnation of concrete. Concr Int 2005;27(2):53–9. [9] Poon CS, Kou SC, Lam L. Use of recycled aggregates in moulded concrete bricks and blocks. Constr Build Mater 2002;16:281–9. [10] Eguchi K, Teranishi K, Nakagome A, Kishimoto H, Shinozaki K, Narikawa A. Application of recycled coarse aggregate by mixture to concrete construction. Constr Build Mater 2007;21:1542–51. [11] Evangelista L, De Brito J. Mechanical behaviour of concrete made with fine recycled concrete aggregates. Cem Concr Compos 2007;29:397–401. [12] Etxeberria M, Vázquez EA, Barra M. Influence of amount of recycled coarse aggregates and production process on properties of recycled aggregate concrete. Cem Concr Res 2007;37:735–42.
[13] Gomez-soberon JMV. Relationship between gas absorption and the shrinkage and creep of recycled aggregate concrete. Cem Concr Aggr 2003;25(2):42–8. [14] Lin YH, Tyan YY, Chang TP, Chang CY. An assessment of optimal mixture for concrete made with recycled concrete aggregates. Cem Concr Res 2004;34:1373–80. [15] Bairagi NK, Vidyadhara HS, Ravande K. Mix design procedure for recycled aggregate concrete. Constr Build Mater 1990;4(4):188–93. [16] Khatib JM. Properties of concrete incorporating fine recycled aggregate. Cem Concr Res 2005;35:763–9. [17] British Standards Institution. Cement – part 1: composition, specifications and conformity criteria for common cements. London: BSI, BS EN 197 – 1:2000. [18] British Standards Institution. Aggregates for concrete. London: BSI, BS EN 12620:2002. [19] British Standards Institution. Method of mixing and sampling fresh concrete in the laboratory. London: BSI, BS 1881: Part 125; 1986. [20] British Standards Institution. Method for determination of slump. London: BSI, BS 1881: Part 102; 1983. [21] British Standards Institution. Method for determination of compressive strength of concrete cubes. London: BSI, BS 1881: Part 116; 1983. [22] ASTM C490-07. Standard practice for use of apparatus for the determination of length change of hardened cement paste, mortar, and concrete. American Society of Testing Materials; 1997. [23] ASTM C 1202. Standard test method for electrical indication of concrete’s ability to resist chloride ion penetration. American Society of Testing Materials; 1997. [24] CIRSOC 201-82. Code for project, design and execution of reinforced and prestressed concrete structure. Argentina: INTI; 1982. [25] ACI Committee 363. State-of-the-art report on high strength concrete, manual of concrete practice. Farmington Hill (USA): ACI; 1984. [26] Kim J, Lee C, Park C, Eo S. The fracture characteristics of crushed limestone sand concrete. Cem Concr Res 1997;27(11):1719–29. [27] Cabrera O, Donza H. High strength concrete with crushed fine aggregate. In: XXVIII Jornadas Sul-Americanas de Engenharia Estrutural, San Carlos, Brazil, vol. 5; 1997. p. 2099–107. [28] Bai Y, Darcy F, Basheer PAM. Strength and drying shrinkage properties of concrete containing furnace bottom ash as fine aggregate. Constr Build Mater 2005;19:691–7. [29] Imamoto K, Arai M. Specific surface area of aggregate and its relation to concrete drying shrinkage. Mater Struct 2008;41:323–33.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Properties of concrete prepared with crushed fine stone, furnace bottom ash and fine recycled aggregate as fine aggregates Kou Shi-Cong, Poon Chi-Sun * Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China
a r t i c l e
i n f o
Article history: Received 4 August 2008 Received in revised form 29 December 2008 Accepted 8 February 2009 Available online 12 March 2009 Keywords: Fine aggregates Furnace bottom ash Fine recycled aggregate Crushed fine stone Concrete
a b s t r a c t This paper presents the results of a study to compare the properties of concretes prepared with the use river sand, crushed fine stone (CFS), furnace bottom ash (FBA), and fine recycled aggregate (FRA) as fine aggregates. Two methods were used to design the concrete mixes: (i) fixed water–cement ratio (W/C) and (ii) fixed slump ranges. The investigation included testing of compressive strength, drying shrinkage and resistance to chloride-ion penetration of the concretes. The test results showed that, at fixed water– cement ratios, the compressive strength and the drying shrinkage decreased with the increase in the FBA content. FRA decreased the compressive strength and increased the drying shrinkage of the concrete. However, when designing the concrete mixes with a fixed slump value, at all the test ages, when FBA was used as the fine aggregates to replace natural aggregates, the concrete had higher compressive strength, lower drying shrinkage and higher resistance to the chloride-ion penetration. But the use of FRA led to a reduction in compressive strength but increase in shrinkage values. The results suggest that both FBA and FRA can be used as fine aggregates for concrete production. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Natural materials such as river sand and crushed fine stone are generally used in concrete as fine aggregates. However, with the booming in urban infrastructure development and the increasing demand on protecting the natural environment, especially in build-up areas such as Hong Kong and some southern Chinese cities in the Pearl River Delta, the availability of the natural resources is diminishing rapidly. Other sources of fine aggregates are urgently needed. Furnace bottom ash (FBA) is a waste material generated from coal-fired thermal power plants. Unlike its companion – pulverised fuel ash (PFA), it usually has much lower pozzolanic property which makes it unsuitable to be used as a cement replacement material in concrete. However, as its particle distribution is similar to that of sand which makes it attractive to be used as a sand replacement material especially in concrete masonry block production. But few studies have been done on exploring the feasibility of using FBA for making concrete. Previous studies carried out by Bai et al. on using FBA as a natural sand replacement material in concrete indicated that, although FBA has no adverse effect on the strength of concrete, beyond 30% replacement level, the permeation properties of the concrete would be detrimentally affected [1,2]. The porous structure of the FBA particles has been considered to have caused the increase * Corresponding author. Tel.: +852 2766 6024; fax: +852 2334 6389. E-mail address: [email protected] (C.-S. Poon). 0950-0618/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2009.02.009
in the permeation properties. However, the porous nature of the aggregate is believed to be a benefit for reducing the shrinkage of concrete [3,4], which is considered to be due to its ‘‘internal curing effect’’ through slow release of moisture from the saturated porous particles [5,6]. Recycled aggregates are produced from the re-processing of mineral waste materials, with the largest source being construction and demolition (C&D) waste. The coarse portion of the recycled aggregates has been used as a replacement of the natural aggregates for concrete production. The potential benefits and drawbacks of using recycled aggregates in concrete are well understood and extensively documented [7–13]. In general, the quality of recycled aggregates is inferior to those of natural aggregates. The density of the recycled aggregates is lower than the natural aggregates and the recycled aggregates have a greater water absorption value compared to the natural aggregates. As a result, a proper mix design is required for obtaining the desired qualities for concrete made with recycled aggregates [14,15]. In addition to the coarse recycled aggregates, fine recycled aggregates (FRA, <5 mm) can also be used to replace natural fine aggregates in the production of concrete. Khatib [16] reported that when natural fine aggregates in concrete were replaced by 0%, 25%, 50%, 75% and 100% fine recycled aggregates and the free water/cement ratio was kept constant for all the mixes, the 28-day strength of the concrete developed at a slower rate. Furthermore, the concrete mixtures containing fine recycled aggregates had higher shrinkage than the natural aggregates concrete. Evangelista et al. [11] indicated that the use of fine recycled concrete aggregates
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up to 30% replacement ratios would not jeopardize the mechanical properties of concrete. This paper compares the properties of concretes that are prepared with the use river sand, crushed rock fine, furnace bottom ash, and recycled fine aggregates as fine aggregates. The mechanical properties, deformational behaviour and durability of the concrete were investigated by testing of compressive strength, drying shrinkage and resistance to chloride-ion penetration of the concretes, respectively.
2.2. Mixture proportions
2. Experimental details
2.3. Details of specimen
2.1. Materials
For each concrete mix, twelve 100 mm size cubes were cast to determine the compressive strength. Three 75 75 285 mm prisms with an indentation at the centre of the two ends were cast to determine the drying shrinkage. Two 100 200 cylindrical specimens were cast to determine the resistance to chloride-ion penetration. All concrete specimens were prepared in accordance with BS 1881: Part 125:1986 [19]. All specimens were cast in two layers and compacted on a vibrating table until no more air bubbles appeared. They were covered with a plastic sheet and left in the mould in the laboratory at 22(±1) °C for 24 h. After that, different curing regimes were used as described below: (1) The 100 mm cubes were cured in water 27(±1) °C until they were tested at 3, 7, 28 and 90 days to determine the compressive strength; (2) the concrete prisms were covered with a damp Hessian cloth and a plastic sheet. After 1 day, the covers were removed and the specimens were wiped clean, and then the initial length was measured. The prisms were then stored
The cement used was the ASTM Type I Portland cement complying with BS EN 197 – 1:2000 [17]. The coarse aggregate used was 10 and 20 mm crushed natural granite. The natural fine aggregates used were river sand sourced from the Pearl River and crushed fine stone (CFS, granite) obtained from a local quarry. Both materials comply with BS EN 12620:2002 [18]. The FBA used was obtained from a local coal-fired power plant. Before the FBA was used, it underwent a process of sieving so that all materials used in the experiment were <5 mm. The fine recycled aggregate (FRA) was obtained from a local C&D waste recycling plant. The physical and chemical properties of the materials used are shown in Tables 1 and 2. Fig. 1 shows the particle size distributions of the FBA, the CFS, the FRA and the river sand used in this study.
Two series of concrete mixes were prepared. In the concrete mixes, natural river sand was replaced by the FBA, CFS and FRA at replacement levels of 0%, 25%, 50%, 75% and 100% by mass, respectively, and the cement content was fixed at 386 kg/ m. In Series I, the concrete mixes were designed at fixed water–cement ratio of 0.53. In Series II, the concrete mixes were designed to have a near constant slump in the range of 60–80 mm; and as such, the free water content (and hence the water–cement ratio) varied. Table 3 shows the detailed mix proportions. The concrete mixes were designed based on the saturated surface dried condition as reflected in Table 3. Water compensation was made during concrete batching.
Table 1 Chemical composition (% by mass) of cement and FBA.
Cement FBA
SiO2
Al2O3
Fe2O3
MgO
CaO
Na2O
K2O
TiO2
SO3
Others
LOI
19.6 60.7
7.33 18.3
3.32 6.56
2.54 1.28
63.15 3.25
– 0.89
– 2.12
– 0.95
2.13 0.82
– 1.00
2.97 4.13
LOI: loss on ignition.
Table 2 Properties of aggregates. Property
Granite
Density (SSD) (kg/m3) Fineness modulus 1-h Water absorption (%)
10 mm
20 mm
2620 – 0.48
2620 – 0.47
CFS
River sand
FBA
FRA
2610 3.56 0.89
2620 2.18 0.38
2190 1.83 28.9
2310 3.18 2.38
Cumulative percentage passing (%)
120
100
80
60 FBA 40
River sand CFS
20
FRA
0 10
5
2.36
1.18
0.6
0.3
0.15
Size of test sieve (mm) Fig. 1. Comparison of particle size distributions of FBA, river sand, CFS and FRA.
0.075
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II
a
Mix notation
SRLa (%)
Cement
Free water
W/C
Sand
FBA
FRA
CFS
Coarse agg.
FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
0 25 50 75 100 25 50 75 100 25 50 75 100
386 386 386 386 386 386 386 386 386 386 386 386 386
205 205 205 205 205 205 205 205 205 205 205 205 205
0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53
652 457 262 67 – 473 293 114 – 489 325 162 –
– 163 326 489 545 – – – – – – – –
– – – – – 163 326 489 592 – – – –
– – – – – – – – – 163 326 489 650
1110 1110 1110 1110 1110 1110 1110 1110 1110 1110 1110 1110 1110
FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
25 50 75 100 25 50 75 100 25 50 75 100
386 386 386 386 386 386 386 386 386 386 386 386
190 170 150 130 200 195 190 185 208 211 214 217
0.49 0.44 0.39 0.34 0.52 0.51 0.49 0.48 0.54 0.55 0.56 0.57
494 318 138 – 490 307 130 – 487 322 161 –
167 343 529 725 – – – – – – – –
– – – – 164 331 500 671 – – – –
– – – – – – – – 162 323 482 640
1127 1126 1135 1184 1114 1086 1073 1086 1105 1099 1093 1087
SRL: sand replacement level.
in an environmental chamber at 23(±1) °C and 50(±1)% RH until the drying shrinkage was tested at the ages of 1, 4, 7, 14, 28, 90 and 112 days; (3) The concrete cylinders were cured in water at 27(±1) °C until the curing ages of 28 days and 90 days. The cylinders were then cut by a diamond saw to obtain 100 mm diameter 50 mm thick concrete discs for the chloride-ion penetration test. 2.4. Test procedures 2.4.1. Workability The workability of fresh concrete was measured by the slump test, in accordance with BS 1881: Part 102: 1983 [20]. 2.4.2. Compressive strength The compressive strength was measured by crushing 300 mm cubes in accordance with BS 1881: Part 116: 1983 [21] using a Denison compression machine with a capacity of 3000 kN. The loading rates were 200 kN/min for the compressive tests. The compressive strengths of the hardened concrete were determined at the ages of 3, 7, 28 and 90 days. 2.4.3. Drying shrinkage The drying shrinkage values were determined following ASTM C490-07 [22]. The prism specimen size was 75 75 285 mm. The specimens were demolded after curing for 24 h and the initial lengths of the specimens were measured. After the initial reading, the specimens were conveyed to a drying-chamber with a temperature of 23 °C and a relative humidity of 55% until the time when the next measurement at 1, 4, 7, 28, 56, 90 and 112 days was reached. The accuracy in the length change measurement was ±0.0025 mm. 2.4.4. Chloride-ion penetration The resistance to chloride penetrability of concrete was determined in accordance with ASTM C1202-94 [23]. The resistance of concrete against chloride-ion penetration is represented by the total charge passed in coulombs during a test period of 6 h.
3. Results and discussion 3.1. Property of fresh concrete The slump values of the fresh concretes in Series I and II are shown in Figs. 2 and 3, respectively. From Fig. 2, it can be seen that, at the fixed W/C ratio, the slump of the FBA and FRA concrete mixes was increased with an increase in FBA or FRA content. This
was due to FBA and FRA had higher water absorption values than that of river sand making more free water was made available to increase the fluidity of the fresh concrete. However, the slump of CFS concrete mixes was decreased with an increase in CFS content probably due to the angular shape of the CFS when compared to river sand. This result is similar to that of Cabrera and Donza [27] who reported that when crushed sand was incorporated in concrete, the increase of water demand due to the shape and texture of the crushed sand can be mitigated by using a water reducing admixture. Fig. 3 shows the slump values of the Series II mixes were maintained at approximately the same value by reducing the added free water (Fig. 4) when FBA and FRA were used to replace river sand. However, for the case of the CFS mixes, more free water was needed to produce the same workability due to the angular shape of CFS.
3.2. Compressive strength Figs. 5–10 show the compressive strength results of the concrete mixes in Series I and II, respectively. It can be seen from Figs. 5 and 6 that when using the same W/C ratio, generally the compressive strength of the FBA and FRA concrete decreased at all the ages with an increase in the FBA and FRA contents. This may be due to the high initial free water content used in the mixes rendered bleeding and poorer interfacial bonding between the aggregates and the cement pastes. Moreover, it can be seen from Fig. 7 that at replacement levels of 75% and 100%, the compressive strength of the CFS concrete decreased when compared with the control. This was due to the decrease in slump when the angular CFS was used to replace sand. This is consistent with other researchers’ findings that the use of crushed sand in concrete would increase both the water and cement content in order to maintain an adequate workability [24– 27]. The amount of additional water and cement required was dependent on the shape, texture, grading and dust content of the crushed sand.
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210 180
Slump (mm )
150 120 90 60 30 0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
Mix notation Fig. 2. Slump values of fresh concrete in Series I.
90 80
Slump (mm)
70 60 50 40 30 20 10 0
Mix notation Fig. 3. Slump values of fresh concrete in Series II.
Free water content (kg/m3)
250
200
150
100
50
0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
Mix notation Fig. 4. Free water content of concrete in Series II.
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70
3-day
7-day
28-day
90-day
Compressive strength (MPa)
60 50 40 30 20 10 0 Control
FBA25
FBA50
FBA75
FBA100
Mix notation Fig. 5. Compressive strength of concrete mixes in Series I (FBA).
70
3-day
7-day
28-day
90-day
Compressive strength (MPa)
60 50 40 30 20 10 0 Control
FRA25
FRA50
FRA75
FRA100
Mix notation Fig. 6. Compressive strength of concrete mixes in Series I (FRA).
70
3-day
7-day
28-day
90-day
Compressive strength (MPa)
60 50 40 30 20 10 0 Control
CFS25
CFS50
CFS75
Mix notation Fig. 7. Compressive strength of concrete mixes in Series I (CFS).
CFS100
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80
3-day
7-day
28-day
90-day
Compressive strength (MPa)
70 60 50 40 30 20 10 0 Control
FBA25
FBA50
FBA75
FBA100
Mix notation Fig. 8. Compressive strength of concrete mixes in Series II (FBA).
70
3-day
7-day
28-day
90-day
Compressive strength (MPa)
60 50 40 30 20 10 0 Control
FRA25
FRA50
FRA75
FRA100
Mix notation Fig. 9. Compressive strength of concrete mixes in Series II (FRA).
Compressive strength (MPa)
70
3-day
7-day
28-day
90-day
60 50 40 30 20 10 0 Control
CFS25
CFS50
CFS75
Mix notation Fig. 10. Compressive strength of concrete mixes in Series II (CFS).
CFS100
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Fig. 8 indicates that for concrete designed with a fixed slump range, the compressive strength of the FBA concrete was higher than that of the control. The improved in compressive strength should be attributed to the decrease in free W/C due to the fact that for a given slump of concrete, the high water absorption properties of FBA would lead to a reduction of free water required (Fig. 4) to produce the target slump value. Fig. 9 shows the compressive strength of the concrete decreased with an increase in the FRA content at all the test ages. This is probably because similar to the case of FBA, the free water required for the fixed slump in the case of the FRA mixes was also decreased. But due to the water absorption value of FRA was a lot lower than that of FBA (see Table 2), the water reduction effect on FRA concrete was not as significant as that on the FBA concrete. Under such conditions, the effect of the relative weaker FRA on concrete strength would lead to an overall reduction of compressive strength. Moreover, it can also be seen from Fig. 10 that at replacement levels of 75% and 100%, the compressive strength of the CFS concrete decreased when compared with the control. This was due to the increase in free W/C ratio used (Table 3) to compensate
for the decrease in slump when the angular CFS was used to replace river sand. Figs. 11 and 12 show the comparison of the compressive strength of the concrete made with 100% FBA, 100% FRA and 100% CFS in Series I and II, respectively. Fig. 11 shows at all the test ages, when the W/C was kept constant, the compressive strength of FBA, FRA and CFS concrete was lower than that of the control. The concrete mixes with 100% FBA had the lowest compressive strength. However, Fig. 12 shows that when designing the concrete mixes at a fixed slump range, the concrete made with FBA had the highest compressive strength while the FRA concrete had the lowest compressive strength. The above results further illustrate how the water absorption properties of the different fine aggregates affected the free water required in the concrete mixes (hence W/C) which had direct bearings on the compressive strength. 3.3. Drying shrinkage The drying shrinkage results of the concrete mixes in Series I and II are presented in Figs. 13 and 14, respectively. Fig. 13 indi-
70
Compressive strength (MPa )
60 50
Control FBA100 FRA100 CFS100
40 30 20 10 0
3-day
7-day
28-day
90-day
Time (day) Fig. 11. Comparison of compressive strength of concrete mixes in Series I prepared with 100% FBA, FRA and CFS as fine aggregate.
80
Compressive strength (MPa)
70 60
Control FBA100 FRA100 CFS100
50 40 30 20 10 0
3-day
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7-day 28-day Mix notation
90-day
Fig. 12. Comparison of compressive strength of concrete mixes in Series II prepared with 100% FBA, FRA and CFS as fine aggregate.
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900
Drying shrinkage (Microstrain)
800 700 600 500 400 300 200 100 0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25
CFS50
CFS75 CFS100
Mix notation Fig. 13. Drying shrinkage of concrete mixes in Series I at 112 days.
900
Drying shrinkage (microstrain)
800 700 600 500 400 300 200 100 0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
Mix notation Fig. 14. Drying shrinkage of concrete mixes in Series II at 112 days.
cates that at the fixed W/C of 0.53, the drying shrinkage values of all FBA and CFS concretes are lower than that of the control concrete with the exception of the 100% FBA replacement level. The results agreed with the findings of Bai et al. [28] who suggested that with a fixed W/C of 0.45 and 0.50, the drying shrinkage of concrete could be reduced by using FBA to replace sand. This was due to with the use of FBA in the concrete mixes, moisture would be slowly released from the porous FBA particles during the drying of the concrete resulting in lower drying shrinkage values than that of the control concrete. But the drying shrinkage values of FRA concretes increased with an increase in FRA content due to the adhered old mortar in FRA. As shown in Fig. 14, at the fixed slump range, the drying shrinkage values of all the FBA concretes are lower than that of the control. This was due to the fact that with the increase in FBA content, the required free water content decreased (Table 3). However, Fig. 14 also shows the drying shrinkage of the FRA concrete increased with an increase in the FRA content probably due to the instability of the old adhered cement mortar in the FRA. Moreover, the drying shrinkage values of all the CFS concretes in both the fixed W/C and the fixed slump range mixtures were
lower than that of the control. This is probably due to the CFS used had larger particle sizes distribution and hence lower specific surface areas (SSA) than that of the river sand. It has been suggested that SSA of aggregates is one of the properties that affects concrete shrinkage [29], and in general a sample of aggregate with a lower SSA (i.e. larger particle size) would result in lower shrinkage of the concrete produced. 3.4. Chloride-ion penetration The test results of chloride-ion penetration of the concrete mixes in Series I and II are shown in Figs. 15 and 16, respectively. Fig. 15 shows at the same W/C, the resistance to chloride-ion penetration of the concrete mixes decreased with increasing percentages FBA, FRA and CFS replacement of river sand. This may be due to the FBA and FRA concretes had more free water than the control concrete which led to a looser microstructure. In the case of FRA concrete, the adhered mortar should lead to a worse microstructure too. For CFS, the decrease in slump of the CFS concrete might have rendered a poorer microstructure due to difficulty in compaction.
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7000
Total charge passed in coulombs
28-day
90-day
6000 5000 4000 3000 2000 1000 0
Mix notation Fig. 15. Total charge passed in coulombs of concrete mixes in Series I at 28 days and 90 days.
7000
28-day
90-day
Total charge passed in coulombs
6000 5000 4000 3000 2000 1000 0 Control FBA25 FBA50 FBA75 FBA100 FRA25 FRA50 FRA75 FRA100 CFS25 CFS50 CFS75 CFS100
Mix notation Fig. 16. Total charge passed in coulombs of concrete mixes in Series II at 28 days and 90 days.
Moreover, at a fixed slump range (Series II, Fig. 16), due to the initial free water required was decreased (see Fig. 4), the resistance to chloride-ion penetration of all FBA, FRA and CFS concrete mixes was better than that of the control. Again, the effect was most significant for the FBA mixes due probably to the pozzolanic effect between the hydrated cement paste (i.e. calcium hydroxide) and the small FBA particles. 4. Conclusion Based on the present investigation, the following conclusions can be drawn: (1) At a fixed W/C, the compressive strength and the drying shrinkage decreased with the increase in the FBA content. FRA decreased the compressive strength and increased the drying shrinkage of the concrete. (2) At a fixed slump value, the use of FBA and FRA was able to reduce to free water requirement of the concrete mixes.
(3) For the mixes prepared with the same slump range and with the use of a lower free W/C ratio, the FBA concrete had the highest compressive strength values. (4) But the use of FRA led to a reduction in compressive strength despite the use of a lower free W/C. This might be due to the inherent weaker mechanical properties of FRA. (5) The drying shrinkage decreased with the increase of the FBA content. FRA increased the drying shrinkage of the concrete. (6) At a fixed slump value, the resistance to chloride-ion penetration of all FBA, FRA and CFS concretes was higher than that of the control concrete. (7) It is feasible to use FBA and FRA as fine aggregate in preparing concrete mixes.
Acknowledgements The authors would like to thank the Research Grants Council (PolyU 5259/06E) and the Hong Kong Polytechnic University for
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funding support. The FBA for this research was provided by the China Light and Power Co. Ltd. and the FRA was provided by the Civil Engineering Development Department of the Hong Kong SAR Government. References [1] Bai Y, Basheer PAM. Influence of furnace bottom ash on properties of concrete. Proc I Civil Eng Struct Build 2003;156(1):85–92. [2] Bai Y, Basheer PAM. Properties of concrete containing furnace bottom ash as a sand replacement material. In: Proceedings of structural faults and repair (CDROM), London, July 1–3; 2003. [3] Collins F, Sanjayan JG. Strength and shrinkage properties of alkali-activated slag concrete containing porous coarse aggregate. Cem Concr Res 1999;29:607–10. [4] Kohno K, Okamoto T, Isikawa Y, Sibata T, Mori H. Effects of artificial lightweight aggregate on autogenous shrinkage of concrete. Cem Concr Res 1999;29:611–4. [5] Weber S, Reinhardt HW. A new generation of high performance concrete: concrete with autogenous curing. Adv Cem Based Mater 1997;6:59–68. [6] Bentz DP, Snyder KA. Protected paste volume in concrete – extension to internal curing using saturated lightweight fine aggregate. Cem Concr Res 1999;29:1863–7. [7] Dhir RK, Limbachiya MC, Leelawat T. Suitability of recycled concrete aggregate for use in BS 5328 designated mixes. Proc ICE – Struct Build 1999;134:257–74. [8] Abou-Zeid MN, Shenouda MN, Mccabe S, El-Tawil FA. Reincarnation of concrete. Concr Int 2005;27(2):53–9. [9] Poon CS, Kou SC, Lam L. Use of recycled aggregates in moulded concrete bricks and blocks. Constr Build Mater 2002;16:281–9. [10] Eguchi K, Teranishi K, Nakagome A, Kishimoto H, Shinozaki K, Narikawa A. Application of recycled coarse aggregate by mixture to concrete construction. Constr Build Mater 2007;21:1542–51. [11] Evangelista L, De Brito J. Mechanical behaviour of concrete made with fine recycled concrete aggregates. Cem Concr Compos 2007;29:397–401. [12] Etxeberria M, Vázquez EA, Barra M. Influence of amount of recycled coarse aggregates and production process on properties of recycled aggregate concrete. Cem Concr Res 2007;37:735–42.
[13] Gomez-soberon JMV. Relationship between gas absorption and the shrinkage and creep of recycled aggregate concrete. Cem Concr Aggr 2003;25(2):42–8. [14] Lin YH, Tyan YY, Chang TP, Chang CY. An assessment of optimal mixture for concrete made with recycled concrete aggregates. Cem Concr Res 2004;34:1373–80. [15] Bairagi NK, Vidyadhara HS, Ravande K. Mix design procedure for recycled aggregate concrete. Constr Build Mater 1990;4(4):188–93. [16] Khatib JM. Properties of concrete incorporating fine recycled aggregate. Cem Concr Res 2005;35:763–9. [17] British Standards Institution. Cement – part 1: composition, specifications and conformity criteria for common cements. London: BSI, BS EN 197 – 1:2000. [18] British Standards Institution. Aggregates for concrete. London: BSI, BS EN 12620:2002. [19] British Standards Institution. Method of mixing and sampling fresh concrete in the laboratory. London: BSI, BS 1881: Part 125; 1986. [20] British Standards Institution. Method for determination of slump. London: BSI, BS 1881: Part 102; 1983. [21] British Standards Institution. Method for determination of compressive strength of concrete cubes. London: BSI, BS 1881: Part 116; 1983. [22] ASTM C490-07. Standard practice for use of apparatus for the determination of length change of hardened cement paste, mortar, and concrete. American Society of Testing Materials; 1997. [23] ASTM C 1202. Standard test method for electrical indication of concrete’s ability to resist chloride ion penetration. American Society of Testing Materials; 1997. [24] CIRSOC 201-82. Code for project, design and execution of reinforced and prestressed concrete structure. Argentina: INTI; 1982. [25] ACI Committee 363. State-of-the-art report on high strength concrete, manual of concrete practice. Farmington Hill (USA): ACI; 1984. [26] Kim J, Lee C, Park C, Eo S. The fracture characteristics of crushed limestone sand concrete. Cem Concr Res 1997;27(11):1719–29. [27] Cabrera O, Donza H. High strength concrete with crushed fine aggregate. In: XXVIII Jornadas Sul-Americanas de Engenharia Estrutural, San Carlos, Brazil, vol. 5; 1997. p. 2099–107. [28] Bai Y, Darcy F, Basheer PAM. Strength and drying shrinkage properties of concrete containing furnace bottom ash as fine aggregate. Constr Build Mater 2005;19:691–7. [29] Imamoto K, Arai M. Specific surface area of aggregate and its relation to concrete drying shrinkage. Mater Struct 2008;41:323–33.