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Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams
Construction and Building Materials xxx (2015) xxx–xxx
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Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams Sung-Won Yoo a, Gum-Sung Ryu b, Jinkyo F. Choo c,⇑ a
Department of Civil and Environmental Engineering, Woosuk University, Jinchon 355-803, Republic of Korea Structural Engineering Research Division, Korea Institute of Civil engineering and building Technology, Goyang 411-712, Republic of Korea c Department of Civil Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 143-701, Republic of Korea b
h i g h l i g h t s Flexural tests on reinforced concrete beams with 0–50% FA replacement ratios are presented. Objective evaluation of the effects of HVFA on the flexural performance of RC beams. Proposal of a nonlinear analysis model for flexural behavior based upon experimental data. Strain compatibility condition and elasticity loss of concrete are considered in the model. Accurate prediction of flexural behavior of RC beams with various contents in FA.
a r t i c l e
i n f o
a b s t r a c t
Article history: Received 19 January 2015 Received in revised form 19 March 2015 Accepted 1 May 2015 Available online xxxx
High-volume fly ash (HVFA) concrete represents a promising solution for the construction industry to deal with the issues related to the global emissions of greenhouse gases. Although numerous studies were dedicated on the material properties of HVFA concrete, need is to study the flexural behavior and performance of structures using HVFA concrete in order to promote further field applications. Therefore, this study presents the results of a series of tests conducted on reinforced concrete beam specimens with various fly ash replacement ratios of 0%, 35% and 50%, various tensile steel ratios and concrete compressive strengths to evaluate their flexural behavior. Moreover, based upon the experimental results, an analysis model is proposed to predict the behavior of the reinforced concrete beams. The comparison with the test data verifies that the analytic results predict accurately the behavior of the beams for all the considered replacement ratios in fly ash. Ó 2015 Elsevier Ltd. All rights reserved.
Keywords: High-volume fly ash (HFVA) Reinforced concrete beam Replacement ratio Flexural behavior Structural performance
1. Introduction Under the Kyoto protocol most developed nations committed themselves to targets for cutting or slowing their emissions of greenhouse gases like carbon dioxide (CO2) that cause climate change. In response to such societal concern, the concrete industry and construction sector concentrated efforts in two major directions to reduce the amount of the highly CO2 producing-cement in the manufacture of concrete. One direction is the geopolymer concrete which exploits cement-free material as binder. This promising and innovative concrete relies on minimally processed natural materials or industrial byproducts to reduce drastically its carbon footprint [1–3]. However, the development of this ⇑ Corresponding author. Tel.: +82 2 2049 6246; fax: +82 2 2201 0783. E-mail addresses: [email protected] (G.-S. Ryu), [email protected] (J.F. Choo).
(S.-W.
Yoo),
[email protected]
material is still in its infancy, and further advancements are still needed to cope with the safety risk associated with the high alkalinity of the activating solution and the extreme sensitivity of the polymerization reaction to temperature [4–6]. The other direction is the concretes using high volume of replacement materials to substitute partially cement like high-volume fly ash (HVFA) concrete. Noting that a 25% fly ash replacement of cement reduces the CO2 exhaust to about 300 kg/m3, the adoption of higher volume of fly ash larger than 50% is indeed potentially interesting as an alternative to deal with environmental concerns. Following, the use of HVFA concrete has gained popularity as a sustainable option to many types of Portland cement concrete applications [7]. Fly ash is an industrial byproduct generated by the electric power industry that was formerly discarded in landfills but is today partially recycled as supplementary cementitious material in the production of Portland cement concrete. Fly ash content less than 25% of the total cementitious content is now commonly used
http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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in concrete owing to its ability to provide significant benefits to concrete such as a gain in long-term strength, reduced hydration heat, improved resistance to chloride attack, and enhanced workability [8,9]. Besides, there are shortcomings like the difficulty in quality control and the low early-age strength when using fly ash content larger than 30% in the production of large quantities of ready mixed concrete. Most of the previous studies focused nearly exclusively on the material properties of HVFA concrete using replacement ratios of 50–70% by HVFA [7,10]. Siddique [11] discussed on the performance characteristics of HVFA concrete and concluded that fly ash instead of cement can be used up to a 50% level replacement ratio for application in precast elements and reinforced concrete members but his study was limited to tests on concrete cubes without considering actual members. Reports were published by several institutions like the National Ready Mixed Concrete Association [7] and National Institute of Standards and Technology [12] to promote the application of HVFA on field but focused essentially on the mix proportions of HVFA concrete mixtures for acceptable performance. However, there is still no established study providing appropriate analysis technique for the evaluation of the structural behavior of structures using HVFA concrete applicable for further field applications. Following, this paper presents the results of a series of tests conducted on reinforced concrete beams using HVFA and proposes an analysis model to predict the behavior of the reinforced concrete beams according to the content in HVFA. To that goal, 18 test members were manufactured considering fly ash replacement ratios of 0%, 35% and 50%, concrete compressive strengths of 20, 40 and 60 MPa and two different levels of tensile steel ratio, and subjected to loading tests to evaluate their flexural behavior. Moreover, based upon the experimental results, an analysis model is proposed to predict the nonlinear behavior of the reinforced HVFA concrete beams. The comparison with the test results verifies the accuracy of the proposed analysis model regardless of the replacement ratio of HVFA.
Table 2 Physical properties of aggregates. Aggregates
Max. grain size (mm)
Density (g/cm3)
Absorption (%)
Fineness modulus
River sand Crushed gravel
– 25
2.58 2.64
1.01 0.82
2.90 6.87
Table 3 lists the mix proportions of the 9 types of mixes used in the material tests. In Table 3, fck, W/B, and S/a indicate respectively the compressive strength of concrete, the water-to-binder ratio, and the proportion of sand to total aggregate. The W/B ratios were adjusted appropriately to favor the development of strength. The averaged results of the compressive strength test and derived elastic moduli are plotted in Fig. 1 for the concrete design compressive strength of 40 MPa with respect to the duration of curing. Table 4 lists the material test results measured in the 9 types of mixes. The results are presented in terms of the compressive strength measured after 14, 28 and 91 days of curing, and the elastic modulus derived from the measurements. In Table 4, as compared to the design strengths of 20, 40 and 60 MPa, the strengths after 91 days of curing are 32.3, 35.9 and 48.8 MPa for the specimens without HVFA, and these values become 33.6, 45.8 and 51.3 MPa for the specimens with replacement ratio of 35% in HVFA, and 24.4, 22.3 and 49.2 MPa for the specimens with replacement ratio of 50% in HVFA. As expected, there is slight loss of compressive strength with larger replacement ratio of HVFA. Despite of the variability of the results induced by unavoidable test errors, there was practically no difference in the compressive strength with respect to the content in fly ash. With regard to the ultimate strains measured in the tests, the variation was observed according to the augmentation of the replacement ratio of HVFA. The averages of the ultimate strains according to the replacement ratio remained bounded between 0.0025 and 0.003. This observation differs slightly with the well-known Hognestad’s nonlinear model [15,16], which predicts the decrease of the ultimate strength with larger replacement ratio in Eq. (1) (Fig. 1).
2. Material properties Prior to the test on reinforced beam structures, preliminary experiments were conducted to identify the material properties of HVFA concrete. To that goal, 9 mixes were manufactured without alkali activator and with replacement ratios of 0%, 35% and 50% using 3 different concrete mixes with design compressive strengths of 20, 40 and 60 MPa. The tests were performed on eighty-one 100 200-mm cylinders made from the 9 mixes and the elastic modulus and compressive strength were evaluated in compliance with the method suggested by FHWA for high strength concretes and considering curing ages of 14, 28 and 91 days [13,14]. In this method, the modulus of elasticity is measured based on the values at 10% and 30% of the ultimate strength. For the tests, ordinary Portland cement (OPC) and fly ash from power plant S in Korea are adopted. Table 1 arranges the properties of OPC and fly ash. River sand and crushed gravels are used as fine and coarse aggregates of which physical properties are arranged in Table 2.
fc ¼
00 fc
2e
e0
2 !
e e0
00
where
e0 ¼ 2
fc 00 ; f ¼ 0:85f ck Ec c
ð1Þ
where fc = concrete stress; e = concrete strain corresponding to fc; 00 f c = peak concrete stress (MPa); e0 = ultimate strain or strain corre00 sponding to f c ; and, Ec = initial elastic modulus of concrete (MPa). In concern with the modulus of elasticity, the Concrete Design Code of the Korea Concrete Institute [17] specifies the following formula:
Ec ¼ 0:077 c1:5 c
qffiffiffiffiffiffi 3 f cu
ð2Þ
where Ec = elastic modulus (MPa); cc = density (kg/m3); and, fcu = reference compressive strength at 28 days. The comparison of the values predicted by Eq. (2) and test data in Fig. 2 reveals good agreement in the elastic modulus for HVFA concrete with density ranging between 2200 and 2300 kg/m3 and
Table 1 Properties of OPC and fly ash used in this study. Material
OPC Fly ash
Chemical composition
Physical properties
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
Ig. loss
Density (g/cm3)
Blaine (cm2/g)
21.96 55.66
5.27 27.76
3.44 7.04
63.41 2.70
2.13 1.14
1.96 0.49
0.79 4.3
3.16 2.19
3214 3621
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx Table 3 Mix proportions of the mixes used in the material tests. Mix
Fly ash (%)
fck (MPa)
W/B
S/a
00–20 00–40 00–60 35–20 35–40 35–60 50–20 50–40 50–60
0 0 0 35 35 35 50 50 50
20 40 60 20 40 60 20 40 60
0.58 0.45 0.35 0.44 0.35 0.30 0.40 0.48 0.33
0.47 0.42 0.42 0.42 0.42 0.42 0.45 0.45 0.45
Unit weight (kg/m3) Water
Cement
Fly ash
Sand
Gravel
185 170 165 185 150 150 125 208 242
319 380 471 273 277 320 156 216 368
– – – 147 149 172 156 216 368
812 719 694 673 707 684 827 681 509
946 1028 991 962 1012 975 1047 861 647
(a) Predicted and measured stress-strain curves
Water-reducing agent (%) 0.5 0.5 1.5 0.5 0.5 0.5 0.5 0.5 0.5
(b) Predicted and measured ultimate strains according to replacement ratio
Fig. 1. Comparison of measurement and Hognestad’s prediction.
Table 4 Material test results of 9 types of mixes according to duration of curing. Mix
00–20 00–40 00–60 35–20 35–40 35–60 50–20 50–40 50–60
14 days of curing
28 days of curing
91 days of curing
Compr. strength (MPa)
Elastic modulus (MPa)
Compr. strength (MPa)
Elastic modulus (MPa)
Compr. strength (MPa)
Elastic modulus (MPa)
22.4 28.2 40.2 22.0 28.2 36.4 14.5 12.9 32.1
19,266 21,195 25,300 19,590 21,195 24,755 17,329 14,081 24,167
24.4 30.8 46.2 31.7 39.8 44.9 25.6 23.9 50.5
19,866 23,062 28,853 25,044 28,314 32,064 24,273 20,046 26,641
32.3 35.9 48.8 33.6 45.8 51.3 24.4 22.3 49.2
32,821 28,340 34,969 22,767 28,325 34,841 28,981 19,850 29,163
the necessity to consider a modification factor for HVFA concrete with density falling out of this range. 3. Flexural test of reinforced concrete beams using HVFA 3.1. Test variables and test members Eighteen test members were manufactured considering fly ash replacement ratios of 0%, 35% and 50%, and concrete compressive strengths of 20, 40 and 60 MPa, as selected in the material test. In addition, two different levels of tensile steel ratio (L-series: low, H-series: high) were also considered. These tensile steel ratios
Slump (mm)
Air amount (%)
122 121 119 116 117 114 120 122 114
4.2 3.8 3.3 4.0 3.4 3.7 3.9 3.8 3.6
correspond to the requirements of the Concrete Design Code [17] that are (minimum steel ratio + maximum steel ratio)/3 and 2 (minimum steel ratio + maximum steel ratio)/3. The selection of these two levels of tensile steel ratio was dictated by the will to induce ductile failure within the range of the tensile reinforcement. Table 5 arranges the specifications of the 18 test members. The mix proportions are identical to those listed in Table 3. Fig. 3 illustrates the dimensions of the test members and arrangement of reinforcement. Shear reinforcement is arranged at more than 100% of the design code to prevent shear failure and induce failure through bending. The adopted reinforcing rebar are made of SD400 steel with average yield strength of 412 MPa
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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Fig. 4. Flexural test of reinforced beam member using HVFA.
Fig. 2. Comparison between predicted and measured elastic moduli.
Table 5 Specifications of test members. Test member
Fly ash (%)
fck (MPa)
Tensile steel ratio
Tensile reinforcement
00–20-L 00–20-H 00–40-L 00–40-H 00–60-L 00–60-H 35–20-L 35–20-H 35–40-L 35–40-H 35–60-L 35–60-H 50–20-L 50–20-H 50–40-L 50–40-H 50–60-L 50–60-H
0 0 0 0 0 0 35 35 35 35 35 35 50 50 50 50 50 50
20 20 40 40 60 60 20 20 40 40 60 60 20 20 40 40 60 60
0.00794 0.01548 0.01548 0.02570 0.02027 0.03176 0.00794 0.01548 0.01548 0.02570 0.02027 0.03176 0.00794 0.01548 0.01548 0.02570 0.02027 0.03176
D16-2EA D22-2EA D22-2EA D29-2EA D25-2EA D32-2EA D16-2EA D22-2EA D22-2EA D29-2EA D25-2EA D32-2EA D16-2EA D22-2EA D22-2EA D29-2EA D25-2EA D32-2EA
Fig. 3. Details of test members (unit: mm).
obtained through direct tensile test. Note that compressive steel is also adopted with a ratio of about half of that of the tensile ratio, which corresponds to the common ratio used in general.
3.2. Flexural test results Flexural test was conducted on the 18 test members (Fig. 4) and the crack load, yield load and ultimate load were measured as listed in Table 6. All the test members failed through flexure as induced. As shown in Table 6, the results correspond to the behavior generally observed in reinforced concrete beams. The ultimate load-to-yield load ratio (Pu/Py) ranges between 1.10 and 1.46. The crack load occurs nearly proportionally to the compressive
strength of concrete. And, the H-series members exhibiting larger tensile steel ratio than the L-series members develop better load resistance. In general, the ductility of a concrete structure can be quantified by the ductility index expressed in terms of the deformation characteristics like the deflection, rotational angle or curvature [13,18]. In this study, the ductility index is defined as follows in terms of the deflection:
l¼
Du Dy
ð3Þ
where l = ductility index of member; Du = deflection at ultimate load; and, Dy = deflection at yield load. This ductility index is calculated for each of the member and the corresponding values are listed in Table 6. With regard to the results of a previous study on the flexural ductility of high strength concrete [19], a minimum ductility index of 4.0 is necessary to prevent the brittle failure of the high strength concrete member. In view of the experimental data in Table 6, the ductility index of L-series members with small tensile steel ratio is always larger than 4.0, which indicates that these members can prevent brittle failure. Besides, even if some members show ductility index smaller than 4.0, most of the H-series members have ductility index larger than 4.0 but relatively smaller than the L-series members. Moreover, the ductility index is seen to decrease with higher compressive strength. This phenomenon can be observed in all sets of members regardless of the content in fly ash. Accordingly, it can be stated that the structural behavior of the test members with fly ash replacement ratio of 35% and 50% is similar to that of the member made of ordinary concrete. This statement will be corroborated through the following observation of the load–deflection curves of the members, the load–strain curves of the steel reinforcement, and the load–strain curves of concrete. The results of the survey of the cracks observed in the test members are also arranged in Table 6. All the cracks corresponded to flexural cracks with a number varying between 14 and 26 cracks and spacing ranging between 115 mm and 214 mm. Such number and spacing of cracks are seen to be practically indifferent to the compressive strength of concrete. In addition, even if there is no clear relationship with the tensile steel ratio, the number of cracks seems to increase and the spacing to reduce slightly with smaller tensile steel ratio. Fig. 5 plots the load–deflection curves measured in the test members. The deflection of all the members increases linearly until the crack load after which the increase becomes nonlinear until the ultimate load. Even if the overall behavior depends on the compressive strength of concrete, it appears that tensile steel ratio has larger influence on the flexural behavior of the members. Nevertheless, here also the flexural behavior of the test members
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx Table 6 Crack, yield and ultimate loads measured in test members. Test member
Crack load (kN)
Yield load, Py (kN)
Yield displ., Dy (mm)
Ultimate load, Pu (kN)
Ultimate displ., Du (mm)
Pu/Py
Du/Dy
Number of cracks (crack spacing in mm)
00–20-L 00–20-H 00–40-L 00–40-H 00–60-L 00–60-H 35–20-L 35–20-H 35–40-L 35–40-H 35–60-L 35–60-H 50–20-L 50–20-H 50–40-L 50–40-H 50–60-L 50–60-H
6.1 8.9 9.0 10.7 12.6 21.1 6.1 11.9 9.5 12.4 13.3 16.2 6.8 8.6 9.2 18.4 16.2 22.1
61.5 92.9 94.8 135.2 108.8 147.9 55.1 86.9 99.6 144.6 103.1 167.1 64.3 92.4 95.9 136.4 98.8 168.0
11.2 13.8 10.5 12.8 12.2 11.2 8.0 9.4 10.7 11.2 8.0 10.6 8.2 11.1 11.7 11.8 9.8 11.3
72.5 103.7 108.1 157.5 125.1 182.2 75.1 102.1 113.0 160.4 123.6 183.4 74.6 101.7 110.2 154.6 144.2 197.9
47.8 55.5 46.3 68.9 61.2 46.0 52.2 52.0 48.4 45.0 31.8 41.9 47.4 49.6 59.1 42.5 61.1 40.1
1.18 1.12 1.14 1.16 1.15 1.23 1.36 1.17 1.13 1.11 1.20 1.10 1.16 1.10 1.15 1.13 1.46 1.18
4.22 4.02 4.42 5.38 5.03 4.11 6.52 5.53 4.53 4.02 4.00 3.95 5.79 4.47 5.04 3.61 6.23 3.55
18 21 14 26 19 23 18 19 24 21 20 25 16 19 25 20 24 21
(a) L-series, 40-MPa beams
(c) L-series, 60-MPa beams
(167) (143) (214) (115) (158) (130) (167) (156) (125) (143) (150) (120) (188) (158) (120) (150) (125) (143)
(b) H-series, 40-MPa beams
(d) H-series, 60-MPa beams
Fig. 5. Comparison of load–displacement curves of test members.
with fly ash replacement ratio of 35% and 50% appears to be similar to that of the member made of ordinary concrete without replacement of cement by fly ash. Fig. 6 compares the load-steel strain curves measured in the tensile reinforcement. The behavior of the tensile reinforcement
is seen to be similar to that commonly observed in normal concrete. The strain in the steel reinforcement appears to be relatively small before cracking and experiences clear increase with larger loading after cracking. For the post-yielding behavior of the reinforcement, very large increase of the strain is observed even under
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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(a) L-series, 40-MPa beams
(b) H-series, 40-MPa beams
(c) L-series, 60-MPa beams
(d) H-series, 60-MPa beams
Fig. 6. Comparison of load–steel strain curves of test members.
minimal augmentation of the load. Here also, the strain of the tensile reinforcement exhibits similar pattern regardless of the content in fly ash. Fig. 7 compares the load-concrete strain curves measured at the top surface of the test members. The concrete strain is seen to range between 0.0035 and 0.0055 without typical difference caused by the content in fly ash. These comparisons (Figs. 5–7) verify that the flexural behavior of the test members with fly ash replacement ratio of 35% and 50% is similar to that of the member without fly ash. The density of fly ash being 25% lighter than cement, the unit weight of concrete with HVFA is known to reduce by 2–3%. Such reduction of the unit weight of concrete results in slight loss of the elastic modulus and in the increase of the deflection of the member made with HVFA [20] as can be observed in Fig. 5.
is used for the reinforcement so as to consider the post-yielding elastic modulus of the tensile steel. With regard to the strain compatibility conditions, the strain in the compressive zone of the section is increased stepwise from early loading to failure and, the corresponding stresses in steel and concrete, the flexural strength, the curvature and the deflection are computed at each step. The concept is illustrated in Fig. 8 and formulated in the following equations. For the reinforced concrete cross section of height h and width b shown in Fig. 8, the strain of the tensile steel, es, can be determined iteratively through equilibrium by assuming the strain at the top of the compressive zone of concrete, ec. The distance x between the crack and the neutral axis, and the relation between es and the strain at the crack, ecr, are expressed as follows:
x¼ 3.3. Flexural behavior analysis of reinforced HVFA concrete beams This study intends to propose an analysis model to evaluate the nonlinear flexural behavior of the reinforced HVFA concrete members using the strain compatibility conditions. 3.4. Proposed nonlinear flexural behavior analysis model The concrete model adopted here is the nonlinear model proposed by Hognestad [15,16] as expressed in Eq. (1). Bilinear model
ecr kd ec
ð4Þ
d kd ec kd
ð5Þ
es ¼
where d = depth of tensile steel from top of cross section; and, kd = depth of neutral axis from top of cross section. The resultants of the compressive force C, the tension force Ts in steel, and the tensile force Tc in concrete can be calculated by the following Eqs. (6)–(8). For a given strain, the stress in concrete is obtained using the concrete model of Hognestad in Eq. (1) and
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) L-series, 40-MPa beams
(b) H-series, 40-MPa beams
(c) L-series, 60-MPa beams
(d) H-series, 60-MPa beams
7
Fig. 7. Comparison of load–concrete strain curves measured at top face of test members.
Fig. 8. Strain compatibility of cross section for analysis.
the stress in the tensile steel can be obtained using the bilinear behavioral model.
C¼
Z A0
Ts ¼
Z
f c dAc
ð6Þ
f s dAs ¼ As f s
ð7Þ
Tc ¼
Z At
f t dAt ¼
1 ðEc ecr Þ xb 2
ð8Þ
where A0 = area up to ec under the Hognestad model’s f–e curve of concrete; As and fs correspond to es in f–e curve of steel; and, At = area up to ecr under the Hognestad model’s f–e curve of concrete assuming linear relationship.
As
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) Member 00-20-H
Fig. 9. Flowchart of proposed nonlinear flexural behavior analysis.
Accordingly, the resultant N of the compressive force C, the tension force Ts in steel, and the tensile force Tc is
N¼
Z
1 f c dAc As f s ðEc ecr Þ xb ¼ 0 2
A0
ð9Þ
(b) Member 35-20-H
Moreover, the resisting moment M of the cross section can be obtained by means of the moment in the tensile reinforcement using the compressive force and tensile forces expressed above in Eqs. (6)–(8).
x þ Cðd c kdÞ M ¼ T c d kd 3
ð10Þ
where c = centroid factor of concrete stress distribution. Finally, the curvature /, deflection D and load P can be obtained as follows using the span length L and the flexural strength.
/¼
ec
ð11Þ
kd 1
D ¼ sin
P¼
4M L
L/ 2
ð12Þ
(c) Member 50-20-H ð13Þ
Fig. 10. Comparison of predicted and measured load–deflection curves (H-series, 20 MPa).
qffiffiffiffi 0 where the cracking load Pcr = 0:63 f c the yield strain of the reinforcement es ¼ f y =Es ; and, the elastic modulus of steel reinforcement Es = 200,000 MPa. In addition, the ultimate load Pu is defined as the largest value among those computed by Eq. (13). The flowchart of the proposed analysis process for the flexural behavior is arranged in Fig. 9. The symbols used in the flowchart correspond to those defined in Fig. 8 and Eqs. (4)–(13). As a technique among others, the analysis model proposed in this study makes use of the strain compatibility condition in the concrete cross-section by adopting a bilinear model for the tensile steel and the Hognestad’s model for concrete. The most important improvement achieved by this approach is the possibility to
conduct nonlinear analysis considering the effect of the loss in the elastic modulus of concrete. Besides, the proposed method cannot represent the behavior of the whole member. 3.5. Comparison of analysis and experimental results This section compares the results of the analysis using the strain compatibility conditions exposed in the precedent section with the experimental data in terms of the load–deflection curves and loadstrain curves for all the 18 test members considered in Chapter 3.
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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(a) Member 00-40-H
(a) Member 00-60-H
(b) Member 35-40-H
(b) Member 35-60-H
(c) Member 50-40-H Fig. 11. Comparison of predicted and measured load–deflection curves (H-series, 40 MPa).
Figs. 10–12 compare the analysis and experimental load–deflection curves for the H-series specimens. A slight difference in the estimation of the elastic modulus can be observed in some cases but the evaluation can reproduce the crack load with good accuracy. At the whole, the analysis is seen to be in good agreement with the experimental data regardless of the replacement ratio of fly ash. The same observations hold for the L-series specimens. Figs. 13–15 compare the analysis and experimental results in term of the load-steel strain curves and Figs. 16–18 in term of the load-concrete strain curves. Here also, the analysis is in fair
9
(c) Member 50-60-H Fig. 12. Comparison of predicted and measured load–deflection curves (H-series, 60 MPa).
agreement with the measured values and the same observations hold for the L-series specimens. In view of the comparisons conducted in Figs. 10–18, the proposed nonlinear model using the strain compatibility conditions was able to reflect the slight variation of the elastic modulus caused by the density of fly ash. The analysis model enabled to consider quantitatively this variation to produce results in good agreement with the flexural test results performed on the 18 test members with varying tensile steel ratio, replacement ratio of fly ash and compressive strength of concrete.
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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(a) Member 00-20-H
(a) Member 00-40-H
(b) Member 35-20-H
(b) Member 35-40-H
(c) Member 50-20-H
(c) Member 50-40-H
Fig. 13. Comparison of predicted and measured load–steel strain curves (H-series, 20 MPa).
Fig. 14. Comparison of predicted and measured load–steel strain curves (H-series, 40 MPa).
Table 7 summarizes the results predicted by the analysis in terms of the crack, yield and ultimate loads for all the test members. The error is calculated with the corresponding measured values listed in Table 6. From the values of Table 7, the errors in the analytically predicted crack load, yield load and ultimate load as compared to the test results remain on the whole smaller than 10% except for a very few cases. For the crack load, the largest error in the prediction is seen to be 9.84% but it should be noted that the experimental values are not absolute since they depend on visual observations and skill of the technician. For the yield load, the
largest prediction error appears to be 15.15% for the member without fly ash and 12.65% for member 50–60-L. For the ultimate load, the largest prediction error is 14.89% for member 35–60-L. Apart from these largest errors, the remaining errors for the predicted crack load, yield load and ultimate load are practically all below 10%. Therefore, the analytic results can be considered as predicting the test values with very good accuracy. Here also, similarly to the conclusions drawn from the observation of Figs. 9–17, it can be stated that proposed nonlinear model using the strain compatibility conditions generates predictions in good agreement with the test results for the considered tensile steel ratios, replacement ratios of fly ash and compressive strengths of concrete.
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) Member 00-60-H
(b) Member 35-60-H
(c) Member 50-60-H
11
(a) Member 00-20-H
(b) Member 35-20-H
(c) Member 50-20-H
Fig. 15. Comparison of predicted and measured load–steel strain curves (H-series, 60 MPa).
Fig. 16. Comparison of predicted and measured load–concrete strain curves (H-series, 20 MPa).
Consequently, the proposed analysis model using the strain compatibility conditions can be used to evaluate and predict with satisfactory accuracy the flexural behavior of reinforced concrete beam members with various contents in fly ash and tensile steel ratios.
18 test beams fabricated with fly ash replacement ratios of 0%, 35% and 50%, two levels of tensile steel ratios and concrete compressive strengths of 20, 40 and 60 MPa. The following conclusions can be derived from the experimental and analytic results.
4. Conclusions This study evaluated experimentally and analytically the effects of high-volume fly ash (HVFA) on the flexural performance of reinforced concrete beams based upon the results of flexural tests on
(1) The ultimate load-to-yield load ratio of the test members ranged between 1.10 and 1.46, and the crack load was quasi-proportional to the compressive strength of concrete. Moreover, the members with high tensile steel ratio (H-series) developed naturally better load resistance than the members with low tensile steel ratio (L-series).
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) Member 00-40-H
(a) Member 00-60-H
(b) Member 35-40-H
(b) Member 35-60-H
(c) Member 50-40-H
(c) Member 50-60-H
Fig. 17. Comparison of predicted and measured load–concrete strain curves (H-series, 40 MPa).
(2) The ductility index defined as the ratio of the ultimate deflection to the yield deflection appeared to be larger than 4.0 for the L-series members, which indicated that these members could prevent brittle failure. Besides, the H-series members exhibited ductility index relatively smaller than the L-series members. The ductility index was seen to decrease with higher compressive strength regardless of the content in fly ash. (3) The deflection, strain, crack load, yield load and ultimate load observed in the members were seen to be practically indifferent to the content in fly ash since the structural
Fig. 18. Comparison of predicted and measured load–concrete strain curves (H-series, 60 MPa).
behavior of the test members with fly ash replacement ratio of 35% and 50% was quasi-similar to that of the members without fly ash. (4) The prediction of the elastic modulus revealed good agreement in the elastic modulus for HVFA concrete with density ranging between 2,200 and 2,300 kg/m3 and the necessity to consider a modification factor for HVFA concrete with density falling out of this range. Consequently, the present study could evaluate objectively the effects of HVFA on the flexural performance of reinforced concrete beams and propose an accurate analysis model enabling to predict
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx Table 7 Predicted crack, yield and ultimate loads of test members and corresponding errors. Test member
Crack load (kN)
Error in predicted crack load (%)
Yield load, Py (kN)
Error in predicted yield load (%)
Ultimate load, Pu (kN)
Error in predicted yield load (%)
00–20-L 00–20-H 00–40-L 00–40-H 00–60-L 00–60-H 35–20-L 35–20-H 35–40-L 35–40-H 35–60-L 35–60-H 50–20-L 50–20-H 50–40-L 50–40-H 50–60-L 50–60-H
5.7 8.7 8.9 10.7 12.4 22.9 6.7 12.8 9.6 13.1 13.3 15.4 6.8 8.0 9.0 19.2 17.3 23.3
6.56 2.25 1.11 0.00 1.59 8.53 9.84 7.56 1.05 5.65 0.00 4.94 0.00 6.98 2.17 4.35 6.79 5.43
56.0 96.7 103.5 151.3 113.7 170.3 56.2 84.1 87.7 140.4 113.2 172.2 72.3 98.4 88.2 126.2 111.3 155.9
8.94 4.09 9.18 11.91 4.50 15.15 2.00 3.22 11.95 2.90 9.80 3.05 12.44 6.49 8.03 7.48 12.65 7.20
66.5 107.3 117.7 168.0 143.7 197.0 74.2 104.1 124.3 165.0 142.0 201.0 81.4 110.4 110.3 149.0 134.8 184.3
8.28 3.47 8.88 6.67 14.87 8.12 1.20 1.96 10.00 2.87 14.89 9.60 9.12 8.55 0.09 3.62 6.52 6.87
the behavior of the reinforced concrete beams with various contents in fly ash. Acknowledgements This work was supported by the Nuclear Research & Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No. 20111010100030). References [1] Lloyd NA, Rangan BV. Geopolymer concrete: a review of development and opportunities. In: 35th conference in our world in concrete & structures, 25–27 August 2010, Singapore. Article Online ID: 100035037. [2] Fernández-Jiménez A, Palomo A, López-Hombrados C. Some engineering properties of alkali activated fly ash concrete. ACI Mater J 2006;103(2):106–12. [3] Delair E, Prud’homme E, Peyratout C, Smith A, Michaud P, Eloy L, et al. Durability of inorganic foam in solution: The role of alkali elements in the geopolymer network. Corros Sci 2012;59:213–21. [4] Federal Highway Administration (FHWA). Geopolymer concrete. CPTP TechBrief FHWA-HIF-10-014, March 2010. [5] Mustafa Al Bakri AM, Kamarudin H, Bnhussain M, Khairul Nizar I, Rafiza AR, Zarina Y. The processing, characterization, and properties of fly ash based geopolymer concrete. Rev Adv Mater Sci 2012;30:90–7. [6] Ryu GS, Lee YB, Koh KT, Chung YS. The mechanical properties of fly ash-based geopolymer concrete with alkaline activators. Constr Build Mater 2013;47:409–18. [7] Obla K, Upadhyaya S, Goulias D, Schindler AK, Carino NJ. New technologybased approach to advance higher volume fly ash concrete with acceptable performance. Final Report of RMC Research & Education Foundation Project No. 07-09, National Ready Mixed Concrete Association 2008.
[8] Thomas MDA, Bamforth PB. Modelling chloride diffusion in concrete: effect of fly ash and slag. Cem Concr Res 1999;29(4):487–95. [9] Song HW, Kwon SJ. Evaluation of chloride penetration in high performance concrete using neural network algorithm and micro pore structure. Cem Concr Res 2009;39(9):814–24. [10] Crouch LK, Hewitt R, Byard B. High volume fly ash concrete. 2007 World of Coal Ash (WOCA), 7–10 May, Northern Kentucky, USA. 2007. [11] Siddique R. Performance characteristics of high-volume class F fly ash concrete. Cem Concr Res 2004;34:487–93. [12] Bentz DP, Ferraris CF, Snyder KA. Best practices guide for high-volume fly ash concrete: Assuring properties and performance. National Institute of Standards and Technology (NIST) Technical Note 1812, US Department of Commerce. September 2013. [13] Graybeal BA. Material property characterization of ultra-high performance concrete. Report No. FHWA-HRT-06-103. August 2006. [14] Popovics JS, Ham S, Garrett S. State of practice for concrete cylinder match curing and effect of test cylinder size. Report No. FHWA-ICT-14-003. January 2014. [15] Hognestad E. Ultimate strength of reinforced concrete in American design practice. In: Proc. symposium on the strength of concrete structures, London, UK. May 1956. [16] Abbasi AF, Siess CP. Effect of stress-strain characteristics of high-strength reinforcement on the behavior of reinforced concrete beam-columns. In: Civil Engineering Studies, Structural Research Series, vol. 354, September 1969. [17] Korea Concrete Institute. Concrete Design Code and Commentary, Korea Concrete Institute; 2007. [18] Yang IH. An experimental study on flexural behavior of steel fiber reinforced ultra high performance concrete. J Korea Concr Inst 2009;21(6):737–44. [19] Shin SW, Ghosh SK, Moreno J. Flexural ductility of ultra high strength concrete members. ACI Struct J 1989;86(4):394–400. [20] Yoon S, Monteiro PJM, Macphee DE, Glasser FP, Imambi MSE. Statistical evaluation of the mechanical properties of high-volume class F fly ash concretes. Constr Build Mater 2014;54:432–42.
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Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams Sung-Won Yoo a, Gum-Sung Ryu b, Jinkyo F. Choo c,⇑ a
Department of Civil and Environmental Engineering, Woosuk University, Jinchon 355-803, Republic of Korea Structural Engineering Research Division, Korea Institute of Civil engineering and building Technology, Goyang 411-712, Republic of Korea c Department of Civil Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 143-701, Republic of Korea b
h i g h l i g h t s Flexural tests on reinforced concrete beams with 0–50% FA replacement ratios are presented. Objective evaluation of the effects of HVFA on the flexural performance of RC beams. Proposal of a nonlinear analysis model for flexural behavior based upon experimental data. Strain compatibility condition and elasticity loss of concrete are considered in the model. Accurate prediction of flexural behavior of RC beams with various contents in FA.
a r t i c l e
i n f o
a b s t r a c t
Article history: Received 19 January 2015 Received in revised form 19 March 2015 Accepted 1 May 2015 Available online xxxx
High-volume fly ash (HVFA) concrete represents a promising solution for the construction industry to deal with the issues related to the global emissions of greenhouse gases. Although numerous studies were dedicated on the material properties of HVFA concrete, need is to study the flexural behavior and performance of structures using HVFA concrete in order to promote further field applications. Therefore, this study presents the results of a series of tests conducted on reinforced concrete beam specimens with various fly ash replacement ratios of 0%, 35% and 50%, various tensile steel ratios and concrete compressive strengths to evaluate their flexural behavior. Moreover, based upon the experimental results, an analysis model is proposed to predict the behavior of the reinforced concrete beams. The comparison with the test data verifies that the analytic results predict accurately the behavior of the beams for all the considered replacement ratios in fly ash. Ó 2015 Elsevier Ltd. All rights reserved.
Keywords: High-volume fly ash (HFVA) Reinforced concrete beam Replacement ratio Flexural behavior Structural performance
1. Introduction Under the Kyoto protocol most developed nations committed themselves to targets for cutting or slowing their emissions of greenhouse gases like carbon dioxide (CO2) that cause climate change. In response to such societal concern, the concrete industry and construction sector concentrated efforts in two major directions to reduce the amount of the highly CO2 producing-cement in the manufacture of concrete. One direction is the geopolymer concrete which exploits cement-free material as binder. This promising and innovative concrete relies on minimally processed natural materials or industrial byproducts to reduce drastically its carbon footprint [1–3]. However, the development of this ⇑ Corresponding author. Tel.: +82 2 2049 6246; fax: +82 2 2201 0783. E-mail addresses: [email protected] (G.-S. Ryu), [email protected] (J.F. Choo).
(S.-W.
Yoo),
[email protected]
material is still in its infancy, and further advancements are still needed to cope with the safety risk associated with the high alkalinity of the activating solution and the extreme sensitivity of the polymerization reaction to temperature [4–6]. The other direction is the concretes using high volume of replacement materials to substitute partially cement like high-volume fly ash (HVFA) concrete. Noting that a 25% fly ash replacement of cement reduces the CO2 exhaust to about 300 kg/m3, the adoption of higher volume of fly ash larger than 50% is indeed potentially interesting as an alternative to deal with environmental concerns. Following, the use of HVFA concrete has gained popularity as a sustainable option to many types of Portland cement concrete applications [7]. Fly ash is an industrial byproduct generated by the electric power industry that was formerly discarded in landfills but is today partially recycled as supplementary cementitious material in the production of Portland cement concrete. Fly ash content less than 25% of the total cementitious content is now commonly used
http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
in concrete owing to its ability to provide significant benefits to concrete such as a gain in long-term strength, reduced hydration heat, improved resistance to chloride attack, and enhanced workability [8,9]. Besides, there are shortcomings like the difficulty in quality control and the low early-age strength when using fly ash content larger than 30% in the production of large quantities of ready mixed concrete. Most of the previous studies focused nearly exclusively on the material properties of HVFA concrete using replacement ratios of 50–70% by HVFA [7,10]. Siddique [11] discussed on the performance characteristics of HVFA concrete and concluded that fly ash instead of cement can be used up to a 50% level replacement ratio for application in precast elements and reinforced concrete members but his study was limited to tests on concrete cubes without considering actual members. Reports were published by several institutions like the National Ready Mixed Concrete Association [7] and National Institute of Standards and Technology [12] to promote the application of HVFA on field but focused essentially on the mix proportions of HVFA concrete mixtures for acceptable performance. However, there is still no established study providing appropriate analysis technique for the evaluation of the structural behavior of structures using HVFA concrete applicable for further field applications. Following, this paper presents the results of a series of tests conducted on reinforced concrete beams using HVFA and proposes an analysis model to predict the behavior of the reinforced concrete beams according to the content in HVFA. To that goal, 18 test members were manufactured considering fly ash replacement ratios of 0%, 35% and 50%, concrete compressive strengths of 20, 40 and 60 MPa and two different levels of tensile steel ratio, and subjected to loading tests to evaluate their flexural behavior. Moreover, based upon the experimental results, an analysis model is proposed to predict the nonlinear behavior of the reinforced HVFA concrete beams. The comparison with the test results verifies the accuracy of the proposed analysis model regardless of the replacement ratio of HVFA.
Table 2 Physical properties of aggregates. Aggregates
Max. grain size (mm)
Density (g/cm3)
Absorption (%)
Fineness modulus
River sand Crushed gravel
– 25
2.58 2.64
1.01 0.82
2.90 6.87
Table 3 lists the mix proportions of the 9 types of mixes used in the material tests. In Table 3, fck, W/B, and S/a indicate respectively the compressive strength of concrete, the water-to-binder ratio, and the proportion of sand to total aggregate. The W/B ratios were adjusted appropriately to favor the development of strength. The averaged results of the compressive strength test and derived elastic moduli are plotted in Fig. 1 for the concrete design compressive strength of 40 MPa with respect to the duration of curing. Table 4 lists the material test results measured in the 9 types of mixes. The results are presented in terms of the compressive strength measured after 14, 28 and 91 days of curing, and the elastic modulus derived from the measurements. In Table 4, as compared to the design strengths of 20, 40 and 60 MPa, the strengths after 91 days of curing are 32.3, 35.9 and 48.8 MPa for the specimens without HVFA, and these values become 33.6, 45.8 and 51.3 MPa for the specimens with replacement ratio of 35% in HVFA, and 24.4, 22.3 and 49.2 MPa for the specimens with replacement ratio of 50% in HVFA. As expected, there is slight loss of compressive strength with larger replacement ratio of HVFA. Despite of the variability of the results induced by unavoidable test errors, there was practically no difference in the compressive strength with respect to the content in fly ash. With regard to the ultimate strains measured in the tests, the variation was observed according to the augmentation of the replacement ratio of HVFA. The averages of the ultimate strains according to the replacement ratio remained bounded between 0.0025 and 0.003. This observation differs slightly with the well-known Hognestad’s nonlinear model [15,16], which predicts the decrease of the ultimate strength with larger replacement ratio in Eq. (1) (Fig. 1).
2. Material properties Prior to the test on reinforced beam structures, preliminary experiments were conducted to identify the material properties of HVFA concrete. To that goal, 9 mixes were manufactured without alkali activator and with replacement ratios of 0%, 35% and 50% using 3 different concrete mixes with design compressive strengths of 20, 40 and 60 MPa. The tests were performed on eighty-one 100 200-mm cylinders made from the 9 mixes and the elastic modulus and compressive strength were evaluated in compliance with the method suggested by FHWA for high strength concretes and considering curing ages of 14, 28 and 91 days [13,14]. In this method, the modulus of elasticity is measured based on the values at 10% and 30% of the ultimate strength. For the tests, ordinary Portland cement (OPC) and fly ash from power plant S in Korea are adopted. Table 1 arranges the properties of OPC and fly ash. River sand and crushed gravels are used as fine and coarse aggregates of which physical properties are arranged in Table 2.
fc ¼
00 fc
2e
e0
2 !
e e0
00
where
e0 ¼ 2
fc 00 ; f ¼ 0:85f ck Ec c
ð1Þ
where fc = concrete stress; e = concrete strain corresponding to fc; 00 f c = peak concrete stress (MPa); e0 = ultimate strain or strain corre00 sponding to f c ; and, Ec = initial elastic modulus of concrete (MPa). In concern with the modulus of elasticity, the Concrete Design Code of the Korea Concrete Institute [17] specifies the following formula:
Ec ¼ 0:077 c1:5 c
qffiffiffiffiffiffi 3 f cu
ð2Þ
where Ec = elastic modulus (MPa); cc = density (kg/m3); and, fcu = reference compressive strength at 28 days. The comparison of the values predicted by Eq. (2) and test data in Fig. 2 reveals good agreement in the elastic modulus for HVFA concrete with density ranging between 2200 and 2300 kg/m3 and
Table 1 Properties of OPC and fly ash used in this study. Material
OPC Fly ash
Chemical composition
Physical properties
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
Ig. loss
Density (g/cm3)
Blaine (cm2/g)
21.96 55.66
5.27 27.76
3.44 7.04
63.41 2.70
2.13 1.14
1.96 0.49
0.79 4.3
3.16 2.19
3214 3621
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx Table 3 Mix proportions of the mixes used in the material tests. Mix
Fly ash (%)
fck (MPa)
W/B
S/a
00–20 00–40 00–60 35–20 35–40 35–60 50–20 50–40 50–60
0 0 0 35 35 35 50 50 50
20 40 60 20 40 60 20 40 60
0.58 0.45 0.35 0.44 0.35 0.30 0.40 0.48 0.33
0.47 0.42 0.42 0.42 0.42 0.42 0.45 0.45 0.45
Unit weight (kg/m3) Water
Cement
Fly ash
Sand
Gravel
185 170 165 185 150 150 125 208 242
319 380 471 273 277 320 156 216 368
– – – 147 149 172 156 216 368
812 719 694 673 707 684 827 681 509
946 1028 991 962 1012 975 1047 861 647
(a) Predicted and measured stress-strain curves
Water-reducing agent (%) 0.5 0.5 1.5 0.5 0.5 0.5 0.5 0.5 0.5
(b) Predicted and measured ultimate strains according to replacement ratio
Fig. 1. Comparison of measurement and Hognestad’s prediction.
Table 4 Material test results of 9 types of mixes according to duration of curing. Mix
00–20 00–40 00–60 35–20 35–40 35–60 50–20 50–40 50–60
14 days of curing
28 days of curing
91 days of curing
Compr. strength (MPa)
Elastic modulus (MPa)
Compr. strength (MPa)
Elastic modulus (MPa)
Compr. strength (MPa)
Elastic modulus (MPa)
22.4 28.2 40.2 22.0 28.2 36.4 14.5 12.9 32.1
19,266 21,195 25,300 19,590 21,195 24,755 17,329 14,081 24,167
24.4 30.8 46.2 31.7 39.8 44.9 25.6 23.9 50.5
19,866 23,062 28,853 25,044 28,314 32,064 24,273 20,046 26,641
32.3 35.9 48.8 33.6 45.8 51.3 24.4 22.3 49.2
32,821 28,340 34,969 22,767 28,325 34,841 28,981 19,850 29,163
the necessity to consider a modification factor for HVFA concrete with density falling out of this range. 3. Flexural test of reinforced concrete beams using HVFA 3.1. Test variables and test members Eighteen test members were manufactured considering fly ash replacement ratios of 0%, 35% and 50%, and concrete compressive strengths of 20, 40 and 60 MPa, as selected in the material test. In addition, two different levels of tensile steel ratio (L-series: low, H-series: high) were also considered. These tensile steel ratios
Slump (mm)
Air amount (%)
122 121 119 116 117 114 120 122 114
4.2 3.8 3.3 4.0 3.4 3.7 3.9 3.8 3.6
correspond to the requirements of the Concrete Design Code [17] that are (minimum steel ratio + maximum steel ratio)/3 and 2 (minimum steel ratio + maximum steel ratio)/3. The selection of these two levels of tensile steel ratio was dictated by the will to induce ductile failure within the range of the tensile reinforcement. Table 5 arranges the specifications of the 18 test members. The mix proportions are identical to those listed in Table 3. Fig. 3 illustrates the dimensions of the test members and arrangement of reinforcement. Shear reinforcement is arranged at more than 100% of the design code to prevent shear failure and induce failure through bending. The adopted reinforcing rebar are made of SD400 steel with average yield strength of 412 MPa
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Fig. 4. Flexural test of reinforced beam member using HVFA.
Fig. 2. Comparison between predicted and measured elastic moduli.
Table 5 Specifications of test members. Test member
Fly ash (%)
fck (MPa)
Tensile steel ratio
Tensile reinforcement
00–20-L 00–20-H 00–40-L 00–40-H 00–60-L 00–60-H 35–20-L 35–20-H 35–40-L 35–40-H 35–60-L 35–60-H 50–20-L 50–20-H 50–40-L 50–40-H 50–60-L 50–60-H
0 0 0 0 0 0 35 35 35 35 35 35 50 50 50 50 50 50
20 20 40 40 60 60 20 20 40 40 60 60 20 20 40 40 60 60
0.00794 0.01548 0.01548 0.02570 0.02027 0.03176 0.00794 0.01548 0.01548 0.02570 0.02027 0.03176 0.00794 0.01548 0.01548 0.02570 0.02027 0.03176
D16-2EA D22-2EA D22-2EA D29-2EA D25-2EA D32-2EA D16-2EA D22-2EA D22-2EA D29-2EA D25-2EA D32-2EA D16-2EA D22-2EA D22-2EA D29-2EA D25-2EA D32-2EA
Fig. 3. Details of test members (unit: mm).
obtained through direct tensile test. Note that compressive steel is also adopted with a ratio of about half of that of the tensile ratio, which corresponds to the common ratio used in general.
3.2. Flexural test results Flexural test was conducted on the 18 test members (Fig. 4) and the crack load, yield load and ultimate load were measured as listed in Table 6. All the test members failed through flexure as induced. As shown in Table 6, the results correspond to the behavior generally observed in reinforced concrete beams. The ultimate load-to-yield load ratio (Pu/Py) ranges between 1.10 and 1.46. The crack load occurs nearly proportionally to the compressive
strength of concrete. And, the H-series members exhibiting larger tensile steel ratio than the L-series members develop better load resistance. In general, the ductility of a concrete structure can be quantified by the ductility index expressed in terms of the deformation characteristics like the deflection, rotational angle or curvature [13,18]. In this study, the ductility index is defined as follows in terms of the deflection:
l¼
Du Dy
ð3Þ
where l = ductility index of member; Du = deflection at ultimate load; and, Dy = deflection at yield load. This ductility index is calculated for each of the member and the corresponding values are listed in Table 6. With regard to the results of a previous study on the flexural ductility of high strength concrete [19], a minimum ductility index of 4.0 is necessary to prevent the brittle failure of the high strength concrete member. In view of the experimental data in Table 6, the ductility index of L-series members with small tensile steel ratio is always larger than 4.0, which indicates that these members can prevent brittle failure. Besides, even if some members show ductility index smaller than 4.0, most of the H-series members have ductility index larger than 4.0 but relatively smaller than the L-series members. Moreover, the ductility index is seen to decrease with higher compressive strength. This phenomenon can be observed in all sets of members regardless of the content in fly ash. Accordingly, it can be stated that the structural behavior of the test members with fly ash replacement ratio of 35% and 50% is similar to that of the member made of ordinary concrete. This statement will be corroborated through the following observation of the load–deflection curves of the members, the load–strain curves of the steel reinforcement, and the load–strain curves of concrete. The results of the survey of the cracks observed in the test members are also arranged in Table 6. All the cracks corresponded to flexural cracks with a number varying between 14 and 26 cracks and spacing ranging between 115 mm and 214 mm. Such number and spacing of cracks are seen to be practically indifferent to the compressive strength of concrete. In addition, even if there is no clear relationship with the tensile steel ratio, the number of cracks seems to increase and the spacing to reduce slightly with smaller tensile steel ratio. Fig. 5 plots the load–deflection curves measured in the test members. The deflection of all the members increases linearly until the crack load after which the increase becomes nonlinear until the ultimate load. Even if the overall behavior depends on the compressive strength of concrete, it appears that tensile steel ratio has larger influence on the flexural behavior of the members. Nevertheless, here also the flexural behavior of the test members
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx Table 6 Crack, yield and ultimate loads measured in test members. Test member
Crack load (kN)
Yield load, Py (kN)
Yield displ., Dy (mm)
Ultimate load, Pu (kN)
Ultimate displ., Du (mm)
Pu/Py
Du/Dy
Number of cracks (crack spacing in mm)
00–20-L 00–20-H 00–40-L 00–40-H 00–60-L 00–60-H 35–20-L 35–20-H 35–40-L 35–40-H 35–60-L 35–60-H 50–20-L 50–20-H 50–40-L 50–40-H 50–60-L 50–60-H
6.1 8.9 9.0 10.7 12.6 21.1 6.1 11.9 9.5 12.4 13.3 16.2 6.8 8.6 9.2 18.4 16.2 22.1
61.5 92.9 94.8 135.2 108.8 147.9 55.1 86.9 99.6 144.6 103.1 167.1 64.3 92.4 95.9 136.4 98.8 168.0
11.2 13.8 10.5 12.8 12.2 11.2 8.0 9.4 10.7 11.2 8.0 10.6 8.2 11.1 11.7 11.8 9.8 11.3
72.5 103.7 108.1 157.5 125.1 182.2 75.1 102.1 113.0 160.4 123.6 183.4 74.6 101.7 110.2 154.6 144.2 197.9
47.8 55.5 46.3 68.9 61.2 46.0 52.2 52.0 48.4 45.0 31.8 41.9 47.4 49.6 59.1 42.5 61.1 40.1
1.18 1.12 1.14 1.16 1.15 1.23 1.36 1.17 1.13 1.11 1.20 1.10 1.16 1.10 1.15 1.13 1.46 1.18
4.22 4.02 4.42 5.38 5.03 4.11 6.52 5.53 4.53 4.02 4.00 3.95 5.79 4.47 5.04 3.61 6.23 3.55
18 21 14 26 19 23 18 19 24 21 20 25 16 19 25 20 24 21
(a) L-series, 40-MPa beams
(c) L-series, 60-MPa beams
(167) (143) (214) (115) (158) (130) (167) (156) (125) (143) (150) (120) (188) (158) (120) (150) (125) (143)
(b) H-series, 40-MPa beams
(d) H-series, 60-MPa beams
Fig. 5. Comparison of load–displacement curves of test members.
with fly ash replacement ratio of 35% and 50% appears to be similar to that of the member made of ordinary concrete without replacement of cement by fly ash. Fig. 6 compares the load-steel strain curves measured in the tensile reinforcement. The behavior of the tensile reinforcement
is seen to be similar to that commonly observed in normal concrete. The strain in the steel reinforcement appears to be relatively small before cracking and experiences clear increase with larger loading after cracking. For the post-yielding behavior of the reinforcement, very large increase of the strain is observed even under
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) L-series, 40-MPa beams
(b) H-series, 40-MPa beams
(c) L-series, 60-MPa beams
(d) H-series, 60-MPa beams
Fig. 6. Comparison of load–steel strain curves of test members.
minimal augmentation of the load. Here also, the strain of the tensile reinforcement exhibits similar pattern regardless of the content in fly ash. Fig. 7 compares the load-concrete strain curves measured at the top surface of the test members. The concrete strain is seen to range between 0.0035 and 0.0055 without typical difference caused by the content in fly ash. These comparisons (Figs. 5–7) verify that the flexural behavior of the test members with fly ash replacement ratio of 35% and 50% is similar to that of the member without fly ash. The density of fly ash being 25% lighter than cement, the unit weight of concrete with HVFA is known to reduce by 2–3%. Such reduction of the unit weight of concrete results in slight loss of the elastic modulus and in the increase of the deflection of the member made with HVFA [20] as can be observed in Fig. 5.
is used for the reinforcement so as to consider the post-yielding elastic modulus of the tensile steel. With regard to the strain compatibility conditions, the strain in the compressive zone of the section is increased stepwise from early loading to failure and, the corresponding stresses in steel and concrete, the flexural strength, the curvature and the deflection are computed at each step. The concept is illustrated in Fig. 8 and formulated in the following equations. For the reinforced concrete cross section of height h and width b shown in Fig. 8, the strain of the tensile steel, es, can be determined iteratively through equilibrium by assuming the strain at the top of the compressive zone of concrete, ec. The distance x between the crack and the neutral axis, and the relation between es and the strain at the crack, ecr, are expressed as follows:
x¼ 3.3. Flexural behavior analysis of reinforced HVFA concrete beams This study intends to propose an analysis model to evaluate the nonlinear flexural behavior of the reinforced HVFA concrete members using the strain compatibility conditions. 3.4. Proposed nonlinear flexural behavior analysis model The concrete model adopted here is the nonlinear model proposed by Hognestad [15,16] as expressed in Eq. (1). Bilinear model
ecr kd ec
ð4Þ
d kd ec kd
ð5Þ
es ¼
where d = depth of tensile steel from top of cross section; and, kd = depth of neutral axis from top of cross section. The resultants of the compressive force C, the tension force Ts in steel, and the tensile force Tc in concrete can be calculated by the following Eqs. (6)–(8). For a given strain, the stress in concrete is obtained using the concrete model of Hognestad in Eq. (1) and
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) L-series, 40-MPa beams
(b) H-series, 40-MPa beams
(c) L-series, 60-MPa beams
(d) H-series, 60-MPa beams
7
Fig. 7. Comparison of load–concrete strain curves measured at top face of test members.
Fig. 8. Strain compatibility of cross section for analysis.
the stress in the tensile steel can be obtained using the bilinear behavioral model.
C¼
Z A0
Ts ¼
Z
f c dAc
ð6Þ
f s dAs ¼ As f s
ð7Þ
Tc ¼
Z At
f t dAt ¼
1 ðEc ecr Þ xb 2
ð8Þ
where A0 = area up to ec under the Hognestad model’s f–e curve of concrete; As and fs correspond to es in f–e curve of steel; and, At = area up to ecr under the Hognestad model’s f–e curve of concrete assuming linear relationship.
As
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) Member 00-20-H
Fig. 9. Flowchart of proposed nonlinear flexural behavior analysis.
Accordingly, the resultant N of the compressive force C, the tension force Ts in steel, and the tensile force Tc is
N¼
Z
1 f c dAc As f s ðEc ecr Þ xb ¼ 0 2
A0
ð9Þ
(b) Member 35-20-H
Moreover, the resisting moment M of the cross section can be obtained by means of the moment in the tensile reinforcement using the compressive force and tensile forces expressed above in Eqs. (6)–(8).
x þ Cðd c kdÞ M ¼ T c d kd 3
ð10Þ
where c = centroid factor of concrete stress distribution. Finally, the curvature /, deflection D and load P can be obtained as follows using the span length L and the flexural strength.
/¼
ec
ð11Þ
kd 1
D ¼ sin
P¼
4M L
L/ 2
ð12Þ
(c) Member 50-20-H ð13Þ
Fig. 10. Comparison of predicted and measured load–deflection curves (H-series, 20 MPa).
qffiffiffiffi 0 where the cracking load Pcr = 0:63 f c the yield strain of the reinforcement es ¼ f y =Es ; and, the elastic modulus of steel reinforcement Es = 200,000 MPa. In addition, the ultimate load Pu is defined as the largest value among those computed by Eq. (13). The flowchart of the proposed analysis process for the flexural behavior is arranged in Fig. 9. The symbols used in the flowchart correspond to those defined in Fig. 8 and Eqs. (4)–(13). As a technique among others, the analysis model proposed in this study makes use of the strain compatibility condition in the concrete cross-section by adopting a bilinear model for the tensile steel and the Hognestad’s model for concrete. The most important improvement achieved by this approach is the possibility to
conduct nonlinear analysis considering the effect of the loss in the elastic modulus of concrete. Besides, the proposed method cannot represent the behavior of the whole member. 3.5. Comparison of analysis and experimental results This section compares the results of the analysis using the strain compatibility conditions exposed in the precedent section with the experimental data in terms of the load–deflection curves and loadstrain curves for all the 18 test members considered in Chapter 3.
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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(a) Member 00-40-H
(a) Member 00-60-H
(b) Member 35-40-H
(b) Member 35-60-H
(c) Member 50-40-H Fig. 11. Comparison of predicted and measured load–deflection curves (H-series, 40 MPa).
Figs. 10–12 compare the analysis and experimental load–deflection curves for the H-series specimens. A slight difference in the estimation of the elastic modulus can be observed in some cases but the evaluation can reproduce the crack load with good accuracy. At the whole, the analysis is seen to be in good agreement with the experimental data regardless of the replacement ratio of fly ash. The same observations hold for the L-series specimens. Figs. 13–15 compare the analysis and experimental results in term of the load-steel strain curves and Figs. 16–18 in term of the load-concrete strain curves. Here also, the analysis is in fair
9
(c) Member 50-60-H Fig. 12. Comparison of predicted and measured load–deflection curves (H-series, 60 MPa).
agreement with the measured values and the same observations hold for the L-series specimens. In view of the comparisons conducted in Figs. 10–18, the proposed nonlinear model using the strain compatibility conditions was able to reflect the slight variation of the elastic modulus caused by the density of fly ash. The analysis model enabled to consider quantitatively this variation to produce results in good agreement with the flexural test results performed on the 18 test members with varying tensile steel ratio, replacement ratio of fly ash and compressive strength of concrete.
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) Member 00-20-H
(a) Member 00-40-H
(b) Member 35-20-H
(b) Member 35-40-H
(c) Member 50-20-H
(c) Member 50-40-H
Fig. 13. Comparison of predicted and measured load–steel strain curves (H-series, 20 MPa).
Fig. 14. Comparison of predicted and measured load–steel strain curves (H-series, 40 MPa).
Table 7 summarizes the results predicted by the analysis in terms of the crack, yield and ultimate loads for all the test members. The error is calculated with the corresponding measured values listed in Table 6. From the values of Table 7, the errors in the analytically predicted crack load, yield load and ultimate load as compared to the test results remain on the whole smaller than 10% except for a very few cases. For the crack load, the largest error in the prediction is seen to be 9.84% but it should be noted that the experimental values are not absolute since they depend on visual observations and skill of the technician. For the yield load, the
largest prediction error appears to be 15.15% for the member without fly ash and 12.65% for member 50–60-L. For the ultimate load, the largest prediction error is 14.89% for member 35–60-L. Apart from these largest errors, the remaining errors for the predicted crack load, yield load and ultimate load are practically all below 10%. Therefore, the analytic results can be considered as predicting the test values with very good accuracy. Here also, similarly to the conclusions drawn from the observation of Figs. 9–17, it can be stated that proposed nonlinear model using the strain compatibility conditions generates predictions in good agreement with the test results for the considered tensile steel ratios, replacement ratios of fly ash and compressive strengths of concrete.
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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(a) Member 00-60-H
(b) Member 35-60-H
(c) Member 50-60-H
11
(a) Member 00-20-H
(b) Member 35-20-H
(c) Member 50-20-H
Fig. 15. Comparison of predicted and measured load–steel strain curves (H-series, 60 MPa).
Fig. 16. Comparison of predicted and measured load–concrete strain curves (H-series, 20 MPa).
Consequently, the proposed analysis model using the strain compatibility conditions can be used to evaluate and predict with satisfactory accuracy the flexural behavior of reinforced concrete beam members with various contents in fly ash and tensile steel ratios.
18 test beams fabricated with fly ash replacement ratios of 0%, 35% and 50%, two levels of tensile steel ratios and concrete compressive strengths of 20, 40 and 60 MPa. The following conclusions can be derived from the experimental and analytic results.
4. Conclusions This study evaluated experimentally and analytically the effects of high-volume fly ash (HVFA) on the flexural performance of reinforced concrete beams based upon the results of flexural tests on
(1) The ultimate load-to-yield load ratio of the test members ranged between 1.10 and 1.46, and the crack load was quasi-proportional to the compressive strength of concrete. Moreover, the members with high tensile steel ratio (H-series) developed naturally better load resistance than the members with low tensile steel ratio (L-series).
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx
(a) Member 00-40-H
(a) Member 00-60-H
(b) Member 35-40-H
(b) Member 35-60-H
(c) Member 50-40-H
(c) Member 50-60-H
Fig. 17. Comparison of predicted and measured load–concrete strain curves (H-series, 40 MPa).
(2) The ductility index defined as the ratio of the ultimate deflection to the yield deflection appeared to be larger than 4.0 for the L-series members, which indicated that these members could prevent brittle failure. Besides, the H-series members exhibited ductility index relatively smaller than the L-series members. The ductility index was seen to decrease with higher compressive strength regardless of the content in fly ash. (3) The deflection, strain, crack load, yield load and ultimate load observed in the members were seen to be practically indifferent to the content in fly ash since the structural
Fig. 18. Comparison of predicted and measured load–concrete strain curves (H-series, 60 MPa).
behavior of the test members with fly ash replacement ratio of 35% and 50% was quasi-similar to that of the members without fly ash. (4) The prediction of the elastic modulus revealed good agreement in the elastic modulus for HVFA concrete with density ranging between 2,200 and 2,300 kg/m3 and the necessity to consider a modification factor for HVFA concrete with density falling out of this range. Consequently, the present study could evaluate objectively the effects of HVFA on the flexural performance of reinforced concrete beams and propose an accurate analysis model enabling to predict
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S.-W. Yoo et al. / Construction and Building Materials xxx (2015) xxx–xxx Table 7 Predicted crack, yield and ultimate loads of test members and corresponding errors. Test member
Crack load (kN)
Error in predicted crack load (%)
Yield load, Py (kN)
Error in predicted yield load (%)
Ultimate load, Pu (kN)
Error in predicted yield load (%)
00–20-L 00–20-H 00–40-L 00–40-H 00–60-L 00–60-H 35–20-L 35–20-H 35–40-L 35–40-H 35–60-L 35–60-H 50–20-L 50–20-H 50–40-L 50–40-H 50–60-L 50–60-H
5.7 8.7 8.9 10.7 12.4 22.9 6.7 12.8 9.6 13.1 13.3 15.4 6.8 8.0 9.0 19.2 17.3 23.3
6.56 2.25 1.11 0.00 1.59 8.53 9.84 7.56 1.05 5.65 0.00 4.94 0.00 6.98 2.17 4.35 6.79 5.43
56.0 96.7 103.5 151.3 113.7 170.3 56.2 84.1 87.7 140.4 113.2 172.2 72.3 98.4 88.2 126.2 111.3 155.9
8.94 4.09 9.18 11.91 4.50 15.15 2.00 3.22 11.95 2.90 9.80 3.05 12.44 6.49 8.03 7.48 12.65 7.20
66.5 107.3 117.7 168.0 143.7 197.0 74.2 104.1 124.3 165.0 142.0 201.0 81.4 110.4 110.3 149.0 134.8 184.3
8.28 3.47 8.88 6.67 14.87 8.12 1.20 1.96 10.00 2.87 14.89 9.60 9.12 8.55 0.09 3.62 6.52 6.87
the behavior of the reinforced concrete beams with various contents in fly ash. Acknowledgements This work was supported by the Nuclear Research & Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No. 20111010100030). References [1] Lloyd NA, Rangan BV. Geopolymer concrete: a review of development and opportunities. In: 35th conference in our world in concrete & structures, 25–27 August 2010, Singapore. Article Online ID: 100035037. [2] Fernández-Jiménez A, Palomo A, López-Hombrados C. Some engineering properties of alkali activated fly ash concrete. ACI Mater J 2006;103(2):106–12. [3] Delair E, Prud’homme E, Peyratout C, Smith A, Michaud P, Eloy L, et al. Durability of inorganic foam in solution: The role of alkali elements in the geopolymer network. Corros Sci 2012;59:213–21. [4] Federal Highway Administration (FHWA). Geopolymer concrete. CPTP TechBrief FHWA-HIF-10-014, March 2010. [5] Mustafa Al Bakri AM, Kamarudin H, Bnhussain M, Khairul Nizar I, Rafiza AR, Zarina Y. The processing, characterization, and properties of fly ash based geopolymer concrete. Rev Adv Mater Sci 2012;30:90–7. [6] Ryu GS, Lee YB, Koh KT, Chung YS. The mechanical properties of fly ash-based geopolymer concrete with alkaline activators. Constr Build Mater 2013;47:409–18. [7] Obla K, Upadhyaya S, Goulias D, Schindler AK, Carino NJ. New technologybased approach to advance higher volume fly ash concrete with acceptable performance. Final Report of RMC Research & Education Foundation Project No. 07-09, National Ready Mixed Concrete Association 2008.
[8] Thomas MDA, Bamforth PB. Modelling chloride diffusion in concrete: effect of fly ash and slag. Cem Concr Res 1999;29(4):487–95. [9] Song HW, Kwon SJ. Evaluation of chloride penetration in high performance concrete using neural network algorithm and micro pore structure. Cem Concr Res 2009;39(9):814–24. [10] Crouch LK, Hewitt R, Byard B. High volume fly ash concrete. 2007 World of Coal Ash (WOCA), 7–10 May, Northern Kentucky, USA. 2007. [11] Siddique R. Performance characteristics of high-volume class F fly ash concrete. Cem Concr Res 2004;34:487–93. [12] Bentz DP, Ferraris CF, Snyder KA. Best practices guide for high-volume fly ash concrete: Assuring properties and performance. National Institute of Standards and Technology (NIST) Technical Note 1812, US Department of Commerce. September 2013. [13] Graybeal BA. Material property characterization of ultra-high performance concrete. Report No. FHWA-HRT-06-103. August 2006. [14] Popovics JS, Ham S, Garrett S. State of practice for concrete cylinder match curing and effect of test cylinder size. Report No. FHWA-ICT-14-003. January 2014. [15] Hognestad E. Ultimate strength of reinforced concrete in American design practice. In: Proc. symposium on the strength of concrete structures, London, UK. May 1956. [16] Abbasi AF, Siess CP. Effect of stress-strain characteristics of high-strength reinforcement on the behavior of reinforced concrete beam-columns. In: Civil Engineering Studies, Structural Research Series, vol. 354, September 1969. [17] Korea Concrete Institute. Concrete Design Code and Commentary, Korea Concrete Institute; 2007. [18] Yang IH. An experimental study on flexural behavior of steel fiber reinforced ultra high performance concrete. J Korea Concr Inst 2009;21(6):737–44. [19] Shin SW, Ghosh SK, Moreno J. Flexural ductility of ultra high strength concrete members. ACI Struct J 1989;86(4):394–400. [20] Yoon S, Monteiro PJM, Macphee DE, Glasser FP, Imambi MSE. Statistical evaluation of the mechanical properties of high-volume class F fly ash concretes. Constr Build Mater 2014;54:432–42.
Please cite this article in press as: Yoo S-W et al. Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams. Constr Build Mater (2015), http://dx.doi.org/10.1016/j.conbuildmat.2015.05.021