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Structural Performance of Recycled Aggregate Concrete Confined by Spiral Reinforcement

Structural Performance of Recycled Aggregate Concrete Confined by Spiral Reinforcement This paper estimates the structural behavior of recycled aggregate concrete confined by spiral reinforcement. The main test parameters are designed to be the type of aggregates, replacement ratio of recycled aggregates, steel ratio and yield strength of spirals. Specimens subjected to concentrated axial load can be divided into two groups, natural and recycled aggregate specimens, based on the type of coarse aggregate used. The recycled aggregates are designed to be used from 0% to 100% in the specimens. Spiral reinforcement is varied up to 1.75% and 1,430 MPa for the steel ratio and yield strength of spiral, respectively. Furthermore, cover concrete and longitudinal reinforcement are neglected to estimate the pure capacity of recycled aggregate concrete confined by spiral reinforcement only. Test results showed that the structural performance of recycled aggregate concrete specimens confined by steel spirals was similar to that of natural aggregate concrete specimens, regardless of the replacement ratio of recycled aggregates, the steel ratio and the yield strength of the spirals. Keywords: recycled aggregate; confined concrete; spiral reinforcement; stress-strain relationship; ultra-high-strength reinforcement 1. Introduction to a lack of social recognition concerning their safety, Architectural activities have become more recycled aggregates have only been utilized as non- widespread with human development, and the number structural materials. of deteriorated buildings has increased in proportion. For recycled aggregates to be utilized as a structural When such buildings are demolished, vast amounts material, the structural performance of concrete with of construction waste are produced, and the quantity recycled aggregates must be verified, but the existing of this waste continues to rise each year. The burial of studies on recycled aggregates have focused on waste concrete, which accounts for the largest portion material properties. Recently, a few studies (Fathifazl of construction waste, has adverse effects on the et al. 2012; Kim et al. 2013; Rahal and Al-Khaleefi environment. An adequate solution, therefore, should 2015) have been carried out on the flexural, shear, be devised to recycle waste concrete. and shear-friction behaviors of reinforced recycled The recent shortage of natural aggregates has aggregate concrete members. However, such studies on resulted in growing interest in alternative aggregates. structural members are still scarce. Recycled aggregates can be obtained from the waste In general, to prevent the collapse of a whole concrete through crushing and abrasion processes. building, building codes demand high safety for Many studies have been conducted on the quality reinforced concrete columns, which are structural control and manufacturing process of recycled members subjected to high axial force. Columns aggregates to achieve environmental-friendly and without transverse reinforcement exhibit brittle failure higher value-added recycled aggregates. However, due after peak load, showing excessive lateral expansion and cracks. Since the brittle failure of reinforced concrete columns can be avoided through the use of *Contact Author: Kil-Hee Kim, Professor transverse reinforcement, it is necessary to estimate Kongju National University the structural performance of recycled aggregate 275 Budae-daong, Cheonan, 330-717, Republic of Korea concrete confined by transverse reinforcement. This Tel: +82-41-521-9335 Fax: +82-41-562-0310 research performs an experimental and analytical study E-mail: kimkh@kongju.ac.kr to provide a fundamental resource on the structural ( Received April 5, 2017 ; accepted July 23, 2018 ) performance of recycled aggregate concrete confined DOI http://doi.org/10.3130/jaabe.17.541 by spiral reinforcement. Journal of Asian Architecture and Building Engineering/September 2018/548 541 Table 1. Physical Properties of Aggregates Used in this Study Aggregates Maximum size (mm) Specific gravity (g/cm ) Absorption rate (%) Fineness modulus Natural 25 2.61 0.68 6.60 Coarse aggregate Recycled 25 2.53 2.55 6.58 Fine aggregate 5 0.64 2.39 2.94 Table 2. Concrete Mix Proportions Design strength W/C S/a Unit weight (kg/m ) Concrete (MPa) (%) (%) W C S G AD NA-series 61.9 257 891 898 2.00 R50-series 60.2 265 888 895 1.91 25 50 177 R75-series 60.2 265 888 895 1.91 R100-series 59.0 270 885 892 1.80 2. Experimental Program variables were the type of aggregate, the replacement 2.1 Materials ratio of recycled aggregate, the yield strength and Type 1 Portland cement was used to make ready- the steel ratio of the spirals. The replacement ratios mixed concrete. This study used two types of coarse of recycled aggregates were designed to be 0% and aggregates, natural and recycled, as described in Table 50% as well as 75% and 100%. In the names of the 1. The recycled coarse aggregate used in this study specimens, NA and R refer to natural and recycled obtained from waste concrete. The production process aggregates, respectively. The normal- and ultra-high- of recycled coarse aggregate is (1) the crushing of the strength steel bars had yield strengths of 472 MPa and waste concrete using jaw crusher, (2) the exclusion of 1,430 MPa, respectively. The steel ratios of the spirals impurities, (3) second crushing using cone crusher, were designed to be 1.75% and 1.0%, named S and M, impact crusher, and double log washer, and (4) the respectively, as seen in Fig.2. separation of crushed aggregates by size. Natural crushed coarse aggregates used in this test had a nominal maximum size of 25 mm, a specific gravity of 2.61 g/cm , and an absorption rate of 2.55%. Natural fine aggregates were used in all of specimens 20 and their physical properties are presented in Table 1. NA As can be seen in Table 2., four types of concrete were R50 R75 used in this study according to the replacement ratio R100 of recycled aggregates. The concrete was designed to -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 Strain have a design strength of 25 MPa, a water-to-cement (a) Concrete ratio of approximately 60%, and a sand percentage of 50%. The concrete used in this study showed similar slumps of 160~170 mm. Compression tests for cylindrical plain concrete specimens with a diameter of 150 mm and a height of 300 mm were performed to estimate the properties of the concrete. The compressive strengths of the f = 472 MPa concrete were measured from 26.1 to 29.7 MPa. The f = 1430 MPa compressive strength and axial strain at peak stress 0 0.000 0.005 0.010 0.015 0.020 0.025 0.030 Strain (peak axial strain) of each concrete are presented in Table 3. Fig.1.(a) shows the stress-strain relationships (b) Steel bars of the concrete used in this study. Fig. 1. Stress versus strain relationships of materials Fig.1. Stress Versus Strain Relationships of Materials This study used normal- and ultra-high-strength round bars with a diameter of 4.5 mm. Based on 150 150 the 0.2% off-set method, yield strengths of round Strain Strain bars were found to be 472 MPa and 1,430 MPa. All gauge gauge reinforcement showed the same elastic modulus of 2.0×10 MPa. The tensile stress-strain relationships of the steel reinforcement are presented in Fig.1.(b). 2.2 Specimen Details A total of 12 unconfined specimens and 30 spirally (a) S-series ( = 1.75%) (b) M-series ( = 1.00%) s s confined specimens, with a diameter of 150 mm and F Fig.2. Details of Specimens ig. 2. Details of specime(Unit: mm) ns (Unit: mm) a height of 300 mm, were designed to investigate the confined behavior of recycled aggregate concrete with spiral reinforcement. As seen in Table 3., the main test 542 JAABE vol.17 no.3 September 2018 Sang-Woo Kim - 1 - - 2 - Stress (MPa) 50 200 50 Stress (MPa) 50 200 50 43.4 To obtain the reliability of the experimental results, yield strength and reinforcement ratio of the spirals the same three specimens were designed for each increased. This tendency was similar to that of other series. Cover concrete and longitudinal reinforcement spirally confined specimens regardless of the aggregate were neglected to estimate the pure effect of spiral type and replacement ratio. As presented in Table 3., reinforcement. Fig.2. shows the positions of strain the spiral reinforcement of all specimens reached their gauges attached to steel spirals with intervals 120 yield strain before peak stress. This implies that the degrees at mid-height of the specimen. concrete can be fully confined by spiral reinforcement 2.3 Test Setup of Specimens even if the ratio of recycled aggregates is increased to The test setup of the specimens is presented in Fig.3. 100%. Three linear variable differential transformers (LVDTs) for longitudinal direction were installed between upper and lower circular steel frames fixed at a distance of 50 mm from the top and bottom of the specimen, respectively. Furthermore, three transverse LVDTs were installed at the mid-height of each specimen to measure the transverse deformation of specimens. A NA-P universal machine with a capacity of 2,000 kN was NA-NS NA-NM used for loading specimens. NA-US -0.04 -0.02 0.00 0.02 0.04 3. Experimental Results and Discussion Strain 3.1 General Behavior (a) NA-series Table 3. provides the experimental results for the peak stress, axial and lateral strains at peak stress, and the yielding point of the spiral reinforcement. Figs.4. and 5. show the crack patterns and stress versus strain relations of tested specimens. As shown in Table 3., plain concrete specimens had similar average peak stresses, f , of 26.9~29.4 MPa and average peak axial 20 co strains of 0.0021~0.0023. In this study, axial strain was R50-P R50-NS measured using the longitudinal LVDTs. The lateral R50-MN strain of unconfined specimens was obtained from -0.04 -0.02 0.00 0.02 0.04 Strain the transverse LVDTs, and that of spirally confined specimens from strain gauges. (b) R50-series The unconfined concrete specimens showed brittle failure after peak stress. On the other hand, spirally confined specimens showed ductile behavior after peak load, exhibiting increasing peak axial strain and 40 lateral strain at peak stress (peak lateral strain) as the R75-P R75-NS R75-NM -0.04 -0.02 0.00 0.02 0.04 Strain (c) R75-series Fig. 3. Test setup of specimen Fig.3. Test Setup of Specimen R100-P R100-NS R100-NM R100-US -0.04 -0.02 0.00 0.02 0.04 Strain (d) R100-series (a) R100-NS (b) R100-NM (c) R100-US Fig. 4. Crack patterns of typical specimens after failure Fig. 5. Experimental results of specimens Fig.5. Experimental Results of Specimens Fig.4. Crack Patterns of Typical Specimens After Failure JAABE vol.17 no.3 September 2018 Sang-Woo Kim 543 - 5 - - 3 - - 4 - Stress (MPa) Stress (MPa) Stress (MPa) Stress (MPa) Table 3. Specimen Details and Experimental Results of Tested Specimens Experimental results f f ' ρ co y s ' Specimens ε f Axial strain Axial strain Spiral co cc (MPa) (MPa) (%) (MPa) at peak load at yielding yielding 1 26.9 0.0021 472 1.75 35.3 0.0116 0.0061 pre-peak NA-NS 2 26.9 0.0021 472 1.75 34.8 0.0118 0.0060 pre-peak 3 26.9 0.0021 472 1.75 34.7 0.0120 0.0069 pre-peak 1 26.9 0.0021 472 1.01 28.4 0.0078 0.0041 pre-peak NA-NM 2 26.9 0.0021 472 1.01 28.7 0.0084 0.0047 pre-peak 3 26.9 0.0021 472 1.01 28.7 0.0073 0.0057 pre-peak 1 26.9 0.0021 1430 1.75 53.9 0.0271 - - NA-US 2 26.9 0.0021 1430 1.75 56.8 0.0303 0.0161 pre-peak 3 26.9 0.0021 1430 1.75 54.0 0.0277 0.0171 pre-peak 1 28.3 0.0022 472 1.75 37.0 0.0108 0.0052 pre-peak R50-NS 2 28.3 0.0022 472 1.75 37.6 0.0116 0.0057 pre-peak 3 28.3 0.0022 472 1.75 38.5 0.0129 0.0053 pre-peak 1 28.3 0.0022 472 1.01 29.3 0.0064 0.0044 pre-peak R50-NM 2 28.3 0.0022 472 1.01 29.9 0.0061 0.0049 pre-peak 3 28.3 0.0022 472 1.01 28.8 0.0080 0.0054 pre-peak 1 28.4 0.0023 472 1.75 38.1 0.0127 0.0052 pre-peak R75-NS 2 28.4 0.0023 472 1.75 39.3 0.0141 0.0057 pre-peak 3 28.4 0.0023 472 1.75 37.6 0.0132 0.0053 pre-peak 1 28.4 0.0023 472 1.01 29.3 0.0068 0.0044 pre-peak R75-NM 2 28.4 0.0023 472 1.01 30.0 0.0064 0.0049 pre-peak 3 28.4 0.0023 472 1.01 29.3 0.0077 0.0054 pre-peak 1 29.4 0.0022 472 1.75 38.2 0.0103 0.0051 pre-peak R100-NS 2 29.4 0.0022 472 1.75 37.5 0.0121 0.0057 pre-peak 3 29.4 0.0022 472 1.75 36.6 0.0107 0.0053 pre-peak 1 29.4 0.0022 472 1.01 30.4 0.0067 0.0043 pre-peak R100-NM 2 29.4 0.0022 472 1.01 29.0 0.0067 0.0053 pre-peak 3 29.4 0.0022 472 1.01 27.8 0.0056 0.0045 pre-peak 1 29.4 0.0022 1430 1.75 52.7 0.0358 0.0222 pre-peak R100-US 2 29.4 0.0022 1430 1.75 53.3 0.0340 0.0174 pre-peak 3 29.4 0.0022 1430 1.75 54.4 0.0356 0.0195 pre-peak Specimens previously tested by authors (Kim et al. 2011) The specimens failed with spalling of the concrete 5.6 times compared to those of unconfined specimens. between the spiral reinforcement. This spalling These results show that a superior lateral confinement increased with higher yield strength of spiral effect is achieved by using spiral reinforcement. As reinforcement due to the increasing lateral expansion shown in Figs.6. and 7., the R50-, R75-, and R100- of concrete at failure. The concrete spalling after NS specimens, having the same spiral reinforcement failure was remarkable as the steel ratio of spirals but different replacement ratios, improved 1.27~1.35 decreased because of the smaller effective areas of times and 5~5.8 times in strength and peak axial strain, lateral confinement, as seen in Fig.4. Based on the respectively. For the NS-series specimens, there was no experimental results, no differences were observed deterioration in strength with increasing replacement in crack patterns in relation to the replacement ratio of recycled aggregates, as seen in Fig.6. ratio of recycled aggregates. This demonstrates that recycled aggregates do not deteriorate the structural performance of spirally confined concrete. Further research, however, is needed on recycled aggregates with adsorption rates higher than 2.55%. 3.2 Strength and Ductility Enhancement The strength and ductility enhancements of specimens are shown in Figs.6. and 7., respectively. In this study, the ductility enhancement ratio was defined as the enhancement ratio of the peak axial strain of specimens. The strength and peak axial strain of NA- NS specimens, with natural aggregates and a spiral Fig.6. Strength Enhancement of Specimens Fig. 6. Strength enhancement of specimens reinforcement ratio of 1.75%, improved 1.3 times and 544 JAABE vol.17 no.3 September 2018 Sang-Woo Kim - 6 - '' f / f cc co lateral strain of unconfined specimens was obtained from transverse LVDTs, while those of the remaining specimens were obtained from strain gauges attached to the spiral reinforcement. As shown in Fig.8.(a), the lateral expansion ratio of unconfined specimens begins at approximately 0.15 and exceeds approximately 0.5 at peak stress. After peak load, the specimens exhibited brittle failure with rapid lateral expansion. It can be seen in Fig.8.(a) that lateral expansion behavior is hardly influenced by the aggregate type and the replacement ratio of recycled aggregates. Fig. 7. Fig.7. Axia Axial Strain Enhancement of Specimens l strain enhancement of specimens Fig.8. shows that spirally confined specimens have In the case of the NM-series specimens, with a yield less lateral expansion compared to unconfined P-series strength of 472 MPa and a steel ratio of 1.0%, NA- specimens. Spirally confined specimens exhibited NM specimens with natural aggregates had only a 6% an increase in lateral expansion after yielding of improvement in peak stress compared to unconfined spirals, and the decrease in lateral expansion became concrete due to their low lateral reinforcement ratio. more pronounced with increasing steel ratio and In terms of ductility, however, the peak axial strain yield strength of spiral reinforcement. In particular, increased by 3.7 times compared to that of unconfined the lateral expansion ratio significantly decreased specimens. This tendency was also observed in the when the yield strength of spiral reinforcement specimens with recycled aggregates. rose from normal- to ultra-high-strength. These When high-strength spiral reinforcement was used, experimental results indicate that the lateral expansion the peak stress and ductility of NA-US specimens with characteristics of specimens are unaffected by the use natural aggregates improved 2.04 times and 13.5 times, of recycled aggregates, and that the lateral expansion respectively, compared to the unconfined specimens. ratio decreases with the increasing lateral confinement As shown in Figs.6. and 7., the strength and ductility performance of spiral reinforcement. of the NA-US specimens are 1.57 and 2.4 times better, respectively, than those of the NA-NS specimens. In 4. Prediction of Stress Versus Axial Strain Relationship other words, improvements in strength and ductility 4.1 Analytical Model of spirally confined specimens can be achieved by In this study, experimental results for confined having higher yield strength of spiral reinforcement. concrete specimens with up to 100% replacement Since the lateral confinement performance of ratio of recycled aggregates are predicted using the spiral reinforcement decreases with increasing the analytical model proposed by Kim et al. (2016), which compressive strength of concrete (Martinez et al. predicts the stress versus axial strain relationship of 1984; Sheikh et al. 1994), further research should be confined concrete with spiral reinforcement using the conducted on the lateral confinement performance of relationship between axial and lateral strains at peak the recycled aggregate concrete with varying levels of load. This model is able to consider the confinement the compressive strength of concrete. effect of high-strength materials for strength and The strength of R100-US specimens with ultra- ductility enhancement of spirally confined concrete. high-strength spirals and 100% replacement ratio of Analytical results obtained from the model proposed recycled aggregates was 1.82 times better than that by Kim et al. were shown to be in good agreement of unconfined specimens, and 1.43 times better than with test results (Assa et al. 2001; Desayi et al. 1978; that of R100-NS specimens with normal-strength JICE 1990; Kim 2010; Muguruma et al. 1978) with spiral reinforcement. This was somewhat lower than the concrete compressive strengths of 18.9~120 MPa, NA-US specimens having natural aggregates, but the Equations (1) ~ (10) spiral yield strengths of 164~1,430 MPa, and spiral structural performance is comparable considering the ratios of 0.29~2.33%. 10% higher concrete compressive strength of R100- The model proposed by Kim et al. (2016) uses the US. In particular, as shown in Fig.7., the ductility of following equation proposed by Popovics (1973) for R100-US specimens was 16 times and 3.2 times higher the stress-axial strain relationship of spirally confined than those of unconfined specimens and R100-NS concrete. specimens with normal-strength spiral reinforcement, respectively. These results were superior to those for fn (/  ) c c cc  (1) (1) NA-US specimens. ' ' n fn 1( / ) cc c cc 3.3 Lateral Expansion Behavior Fig.8. shows the relationship between axial strain where f and f are the stress and peak stress of c cc and lateral expansion ratio of tested specimens. In confined concrete, respectively, ε and ε are the c cc this study, the lateral expansion ratio refers to the axial strain and peak axial strain of confined concrete, ratio of the lateral-to-axial strains of specimens. The - 7 - JAABE vol.17 no.3 September 2018 Sang-Woo Kim 545 - 1 - ''  / cc co 1. 1.75 75 1.75 respectively, and n is a coefficient affecting ascent and NA- NA-P P 1.75 NA-P NA-P R50 R50- -P P decent curves and is defined as follows: R50-P 1. 1.50 50 1.50 R50-P 1.50 R75 R75- -P P R75-P R75-P R10 R100- 0-P P 1. 1.25 25 R100-P 1.25 (2) nE /(E E ) (2) R100-P 1.25 Pe Pea ak k c c cc Peak Peak Equations (4) 1. 1.00 00 1.00 ' '' 1.00 (3) Ef  / (3) cc cc cc 0. 0.75 75 0.75 0.75 where E is the elastic modulus of concrete, taken as 0. 0.50 50 0.50 0.50 the following equation proposed by Carrasquillo et al. 0. 0.25 25 0.25 (1981). 0.25 0. 0.00 00 0.00 0.00 0 0..0 000 00 0. 0.005 005 0. 0.01 010 0 0. 0.01 015 5 0. 0.0 020 20 ' 0.000 0.005 0.010 0.015 0.020 (4) E 3320 f (MPa) 6900 (4) 0.000 0.005 0.010 0.015 0.020 Axial Strain Axial Strain c co Axial Strain Axial Strain (a) P-series (a) P-series (a) P-series (a) P-series Kim et al. proposed the following relationship (a) P-series between the axial and lateral strains at peak load 1. 1.75 75 1.75 1.75 NA- NA-NS NS NA-NS to estimate the peak stress and strain state of spiral NA-NS R50- R50-NS NS 1. 1.50 50 R50-NS 1.50 R50-NS 1.50 R75-NS R75-NS reinforcement. R75-NS R75-NS R100 R100-NS -NS 1.25 1.25 R100-NS 1.25 R100-NS 1.25 Pe Peak ak Peak ' Peak Yield 1.00 Yield l ' 1.00 Yield 1.00 (5)  0.75 0.0035 f 0.6 (5) Yield 1.00 co cc 0. 0.75 75 0.75 0.75 ' ' 0. 0.50 50 0.50 where ε and ε are the axial and lateral strains at peak cc l 0.50 stress, respectively, and f is the compressive strength 0. 0.25 25 co 0.25 0.25 of plain concrete. Once the peak axial strain ε is cc 0. 0.00 00 0.00 0.00 0 0..000 000 0. 0.005 005 0. 0.010 010 0. 0.015 015 0 0..020 020 determined, the peak lateral strain ε can be calculated 0.000 0.005 0.010 0.015 0.020 l 0.000 0.005 0.010 0.015 0.020 A Ax xi ia al l S St tra rai in n Axial Strain using Eq. (5). As the peak lateral strain represents Axial Strain the spiral stress and the lateral confinement pressure (b) NS-series (b) NS-series (b) NS-series (b) NS-series ' ' (b) NS-series at peak stress, f and f , the peak stress of confined sp l 1. 1.75 75 1.75 concrete can be obtained. 1.75 NA- NA-N NM M NA-NM NA-NM R50-NM R50-NM Kim et al. modified the formulas proposed by El- 1. 1.50 50 R50-NM 1.50 R50-NM 1.50 R75-NM R75-NM R75-NM Dash and Ahmad (1995) to calculate the peak axial R75-NM R100-NM R100-NM 1. 1.25 25 R100-NM 1.25 R100-NM 1.25 strain and peak stress of spirally confined concrete as Pe Peak ak Peak Peak Yi Yiel eld d 1. 1.00 00 Yield 1.00 follows: Yield 1.00 0. 0.75 75 0.75 ' ' ' 0.75 (6)   (6) cc co ce 0. 0.50 50 0.50 0.50 0. 0.25 25  6.0  f  0.25 0.25   (7)    ce 0.11 ' 1.15 ' (7) 0. 0.00 00 (sd / ) ( f ) f 0.00  s co  co  0.00 0. 0.000 000 0 0..0 005 05 0. 0.01 010 0 0. 0.01 015 5 0 0..020 020 0.000 0.005 0.010 0.015 0.020 0.000 0.005 0.010 0.015 0.020 A Ax xi ia al l S St tr rai ain n Axial Strain Axial Strain  1 s '' (c) NM-series (c) NM-series (c) NM-series (8) (c) NM-series ff  1 (8)  l s sp (c) NM-series  2 1.25D  1. 1.75 75 1.75 1.75 NA- NA-U US S NA-US NA-US ' '' R100-US R100-US (9) 1. 1.50 50 R100-US f ff (9) 1.50 R100-US cc co ce 1.50 Pe Peak ak Peak Peak Yi Yiel eld d 1. 1.25 25 Yield 1.25 Yield 1.25 0.5 0.25  '    1. 1.00 00 fd 1.00 '' co s   (10) 1.00 f  5.1 f (10) ce  l   f   0.75 0.75 sp s 0.75   0.75   0.50 0.50 0.50 0.50 where ε is the peak axial strain of plain concrete, co 0. 0.25 25 ' ' ' 0.25 taken as 0.001648+0.000016f , ε and f are the 0.25 co ce ce 0. 0.00 00 enhanced axial strain and stress at peak, s is the vertical 0.00 0.00 0. 0.000 000 0 0..0 005 05 0. 0.01 010 0 0. 0.01 015 5 0 0..020 020 0.000 0.005 0.010 0.015 0.020 0.000 0.005 0.010 0.015 0.020 A Ax xi ia al l S St tr rai ain n spacing of spiral reinforcement, d is the diameter of Axial Strain s Axial Strain a spiral, ρ is the steel ratio of spirals, f is the stress s sp (d) US-series (d) US-series (d) US-series (d) US-series of spiral reinforcement at peak load, and D is the (d) US-series Fig.8. Lateral Expansion Characteristics of Tested Specimens diameter of spiral between bar centers. Fig. 8. Lateral expansion ch Fig. 8. Lateral expansion charac aract te er ri is st ti ic cs s o of f t te es st te ed d sp spe ec ci im me en ns s Fig. 8. Lateral expansion characteristics of tested specimens Fig. 8. Lateral expansion characteristics of tested specimens - 2 - - 1 - - 3 - - - 8 8 - - - 8 - - 8 - 546 JAABE vol.17 no.3 September 2018 Sang-Woo Kim - 5 - - 7 - - 8 - - 6 - - 9 - - 10 - Late Late Late Late ral ex ral ex ral ex ral ex pa pa pa pa nsio nsio nsio nsio n ratio n ratio n ratio n ratio La La La La tera tera tera tera l e l e l e l e xp xx xp an p pan an an sion ss sion ion ion r r atio r ratio atio atio La La La La tera tera tera tera l e l e l e l e xp xx xp an p pan an an sion ss sion ion ion r r atio r ratio atio atio Lat Lat Lat Lat era ee era ra ra l e l e l e l e xpan xx xpan pan pan sisi on r si sion r on r on r aa ta a ito t tii io o o  T T able 4. Comparison between Experimental and able 4. Comparison between experimental and ana Analytical Results lytical results Experimental/Analytical Experimental results (average) El-Dash and Ahmad Mander et al. (1988) Kim et al. (2016) (1995) ' ' Specimens f f ' co cc  ' ' ' ' ' ' cc f  f  f  cc ,exp . cc ,exp . cc ,exp . cc ,exp . cc ,exp . cc ,exp . (MPa) (MPa) ' ' ' ' ' ' f  f  f  cc ,ana . cc ,ana . cc ,ana . cc ,ana . cc ,ana . cc ,ana . NA-NS 34.9 0.0118 0.74 1.19 0.89 1.83 0.89 0.90 NA-NM 26.9 28.6 0.0078 0.74 1.15 0.85 2.40 0.85 1.13 NA-US 54.9 0.0284 0.78 1.49 1.12 1.85 1.13 0.80 R50-NS 37.7 0.0118 0.78 1.21 0.92 1.99 0.92 0.98 28.3 R50-NM 29.4 0.0070 0.73 1.03 0.83 2.18 0.84 1.05 R75-NS 38.3 0.0133 0.79 1.37 0.93 2.26 0.93 1.11 28.4 R75-NM 29.5 0.0070 0.73 1.05 0.84 2.22 0.84 1.08 R100-NS 37.4 0.0110 0.75 1.15 0.88 1.98 0.89 0.98 29.4 R100-NM 29.1 0.0063 0.70 0.96 0.80 2.07 0.80 1.03 R100-US 53.5 0.0351 0.72 1.90 1.02 2.78 1.03 1.17 Mean 0.75 1.25 0.91 2.16 0.91 1.02 COV 3.6% 21.0% 10.2% 12.6% 10.3% 10.5% 4.2 Comparison of Experimental and Analytical Results Table 4. and Fig.9. provide a comparison of experimental and analytical results. In this study, existing models proposed by Mander et al. (1988) and El-dash and Ahmad (1995) are used in this study to verify the accuracy of the model by Kim et al. (2016). As seen in Table 4., the model proposed by Mander Test result Mander et al. et al. overestimates the test results for peak stress El-Dash and Ahmad Kim et al. with a mean experimental-to-analytical ratio of 0.75, 0.00 0.01 0.02 0.03 0.04 whereas it underestimates the peak axial stress with an Strain average of 1.25. The prediction results obtained using (a) R100-NS the model by Mander et al. for the peak stress had no significant effect on spiral properties, but the peak axial strain greatly deteriorated as the yield strength of the steel spirals increased. In the case of peak stress, Kim et al. modified the original equations proposed by El-Dash and Ahmad to consider the decrease of strength enhancement with lower peak stress of spiral reinforcement. In this test, Test result all specimens with spiral reinforcement yielded before Mander et al. El-Dash and Ahmad peak load, because normal-strength concrete was used. Kim et al. As seen in Table 4., therefore, models proposed by 0.00 0.01 0.02 0.03 0.04 Strain Kim et al. and El-Dash and Ahmad equally predict the (b) R100-NM real peak stress with a mean of 0.91 and a coefficient of variation (COV) of 10.3%. In addition, the prediction results show that neither model is affected by changing the spiral properties. In the case of peak axial strain, the model proposed by El-Dash and Ahmad greatly underestimated the experimental results by an average of 2.16 times. On the other hand, the model by Kim et al. provided good Test result accuracy for the real peak axial strain with an average Mander et al. of 1.02 and a COV of 10.5%. Furthermore, as seen in El-Dash and Ahmad Kim et al. Fig.9. for R100 series specimens, the model by Kim et 0.00 0.01 0.02 0.03 0.04 al. can successfully trace the stress versus axial strain Strain of natural and recycled aggregate concrete specimens (c) R100-US with spiral reinforcement. Comparison between Fig.9. Comparison of Analytical and Experimental Results Fig. 9. Comparison of analytical and experimental results JAABE vol.17 no.3 September 2018 Sang-Woo Kim 547 - 9 - Stress (MPa) Stress (MPa) Stress (MPa) analytical and experimental results showed that the References 1) Assa B, Nishiyama M and Watanabe F (2001) New approach model proposed by Kim et al. can be reasonably used for modeling confined concrete I: Circular columns. Journal of for the prediction of the behavior of spirally confined Structural Engineering, 127(7), pp.743-750. concrete, regardless of the replacement ratio of 2) Carrasquillo RL, Nilson AH and Slate FO (1981) Properties of recycled aggregates. high-strength concrete subjected to short term loads. ACI Journal, 78(3), pp.171-178. 3) Desayi P, Iyengar KTSR and Reddy TS (1978) Equation for stress- 5. Conclusions strain curve of concrete confined in circular steel spiral. Materials This study evaluated the behavior of spirally and Structures, 11(5), pp.339-345. confined recycled aggregate concrete with test variables 4) El-Dash KM and Ahmad SH (1995) A model for stress-strain of the replacement ratio of recycled aggregate, yield relationship of spirally confined normal and high-strength concrete strength and steel ratio of spiral reinforcement. Based columns. Magazine of Concrete Research, 47(171), pp.177-184. 5) Fathifazl G, Razaqpur AG, Isgor OB, Abbas A, Fournier B, and on this study, the following conclusions are drawn: Foo S (2012) Flexural performance of steel-reinforced recycled (1) The lateral confinement performance of spirally concrete beams. ACI Structural Journal, 109(6), pp.777-786. confined concrete with recycled aggregates improved 6) JICE (1990) High-strength concrete subcommittee report. Japan as the yield strength and steel ratio of the spiral Institute of Construction Engineering, 231pp. reinforcement increased. This tendency was observed 7) Kim S-W, Kim Y-S, Lee J-Y and Kim K-H (2016) Behavior of confined concrete with varying yield strengths of spirals. Magazine regardless of the aggregate type and replacement ratio of Concrete Research, 69(5), pp.217-229. of recycled aggregates. Furthermore, the use of 100% 8) Kim S-W, Jeong C-Y, Lee J-S, and Kim K-H (2013) Size effect in recycled aggregates with absorption rate of 2.55% did shear failure of reinforced concrete beams with recycled aggregate. not cause any deterioration of the strength and ductility Journal of Asian Architecture and Building Engineering, 12(2), of the spirally confined specimens. pp.323-330. 9) Kim S-W, Jung C-K, Lee S-H, Kim K-H (2011) Experimental (2) These experimental results for normal-strength study on structural performance of recycled coarse aggregate concrete demonstrated that all specimens, regardless concrete confined by steel spirals. Journal of the Korea Institute of aggregate type, showed the yielding of spirals for Structural Maintenance and Inspection, 15(1), pp.103-111. before peak stress and had similar lateral expansion 10) Kim Y-S (2010) Behavior of confined concrete with high-strength characteristics. This implies that steel spirals exhibit transverse reinforcement. Master Thesis, Kongju National University, Republic of Korea. their full performance before peak stress, and that 11) Mander JB, Priestley MJN and Park R (1988) Theoretical lateral confinement performance is unaffected by the stress-strain model for confined concrete. Journal of Structural use of recycled aggregates. Engineering, 114(8), pp.1804-1826. (3) Spirally confined specimens showed greater 12) Martinez S, Nilson AH and Slate FO (1984) Spirally reinforced spalling of concrete with an increase in the yield high-strength concrete columns. ACI Journal, 81(5), pp.431-442. 13) Muguruma H, Watanabe S, Tanaka S, Sakurai K and Nakamura E strength of spiral reinforcement due to the increase in (1978) A study on the improvement of bending ultimate strain of lateral expansion at failure. The spalling of concrete concrete. Journal of Structural Engineering, Tokyo 24, pp.109- also increased with decreasing spiral reinforcement ratio because of the smaller effective areas of lateral 14) Popovics S (1973) A numerical approach to the complete stress- confinement. The crack patterns of specimens with strain curves for concrete. Cement and Concrete Research, 3(5), pp.583-599. recycled aggregates were similar to those of specimens 15) Rahal KN and Al-Khaleefi A-L (2015) Shear-friction behavior with natural aggregates, regardless of aggregate type of recycled and natural aggregate concrete-An experimental and the replacement ratio of recycled aggregates. investigation. ACI Structural Journal, 112(6), pp.725-733. (4) From a comparison of experimental and 16) Sheikh SA, Shah DV and Khoury SS (1994) Confinement of high- analytical results, it is shown that the analytical model strength concrete columns. ACI Structural Journal, 91(1), pp.100- proposed by Kim et al. has sufficient accuracy in predicting the behavior of spirally confined concrete with recycled aggregates. Acknowledgments This research was supported by the International Science and Business Belt Program through the Ministry of Science, ICT and Future Planning (2017K000488). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. NRF- 2018R1A2B3001656). 548 JAABE vol.17 no.3 September 2018 Sang-Woo Kim http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Asian Architecture and Building Engineering Taylor & Francis

Structural Performance of Recycled Aggregate Concrete Confined by Spiral Reinforcement

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Taylor & Francis
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© 2018 Architectural Institute of Japan
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1347-2852
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1346-7581
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10.3130/jaabe.17.541
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Abstract

This paper estimates the structural behavior of recycled aggregate concrete confined by spiral reinforcement. The main test parameters are designed to be the type of aggregates, replacement ratio of recycled aggregates, steel ratio and yield strength of spirals. Specimens subjected to concentrated axial load can be divided into two groups, natural and recycled aggregate specimens, based on the type of coarse aggregate used. The recycled aggregates are designed to be used from 0% to 100% in the specimens. Spiral reinforcement is varied up to 1.75% and 1,430 MPa for the steel ratio and yield strength of spiral, respectively. Furthermore, cover concrete and longitudinal reinforcement are neglected to estimate the pure capacity of recycled aggregate concrete confined by spiral reinforcement only. Test results showed that the structural performance of recycled aggregate concrete specimens confined by steel spirals was similar to that of natural aggregate concrete specimens, regardless of the replacement ratio of recycled aggregates, the steel ratio and the yield strength of the spirals. Keywords: recycled aggregate; confined concrete; spiral reinforcement; stress-strain relationship; ultra-high-strength reinforcement 1. Introduction to a lack of social recognition concerning their safety, Architectural activities have become more recycled aggregates have only been utilized as non- widespread with human development, and the number structural materials. of deteriorated buildings has increased in proportion. For recycled aggregates to be utilized as a structural When such buildings are demolished, vast amounts material, the structural performance of concrete with of construction waste are produced, and the quantity recycled aggregates must be verified, but the existing of this waste continues to rise each year. The burial of studies on recycled aggregates have focused on waste concrete, which accounts for the largest portion material properties. Recently, a few studies (Fathifazl of construction waste, has adverse effects on the et al. 2012; Kim et al. 2013; Rahal and Al-Khaleefi environment. An adequate solution, therefore, should 2015) have been carried out on the flexural, shear, be devised to recycle waste concrete. and shear-friction behaviors of reinforced recycled The recent shortage of natural aggregates has aggregate concrete members. However, such studies on resulted in growing interest in alternative aggregates. structural members are still scarce. Recycled aggregates can be obtained from the waste In general, to prevent the collapse of a whole concrete through crushing and abrasion processes. building, building codes demand high safety for Many studies have been conducted on the quality reinforced concrete columns, which are structural control and manufacturing process of recycled members subjected to high axial force. Columns aggregates to achieve environmental-friendly and without transverse reinforcement exhibit brittle failure higher value-added recycled aggregates. However, due after peak load, showing excessive lateral expansion and cracks. Since the brittle failure of reinforced concrete columns can be avoided through the use of *Contact Author: Kil-Hee Kim, Professor transverse reinforcement, it is necessary to estimate Kongju National University the structural performance of recycled aggregate 275 Budae-daong, Cheonan, 330-717, Republic of Korea concrete confined by transverse reinforcement. This Tel: +82-41-521-9335 Fax: +82-41-562-0310 research performs an experimental and analytical study E-mail: kimkh@kongju.ac.kr to provide a fundamental resource on the structural ( Received April 5, 2017 ; accepted July 23, 2018 ) performance of recycled aggregate concrete confined DOI http://doi.org/10.3130/jaabe.17.541 by spiral reinforcement. Journal of Asian Architecture and Building Engineering/September 2018/548 541 Table 1. Physical Properties of Aggregates Used in this Study Aggregates Maximum size (mm) Specific gravity (g/cm ) Absorption rate (%) Fineness modulus Natural 25 2.61 0.68 6.60 Coarse aggregate Recycled 25 2.53 2.55 6.58 Fine aggregate 5 0.64 2.39 2.94 Table 2. Concrete Mix Proportions Design strength W/C S/a Unit weight (kg/m ) Concrete (MPa) (%) (%) W C S G AD NA-series 61.9 257 891 898 2.00 R50-series 60.2 265 888 895 1.91 25 50 177 R75-series 60.2 265 888 895 1.91 R100-series 59.0 270 885 892 1.80 2. Experimental Program variables were the type of aggregate, the replacement 2.1 Materials ratio of recycled aggregate, the yield strength and Type 1 Portland cement was used to make ready- the steel ratio of the spirals. The replacement ratios mixed concrete. This study used two types of coarse of recycled aggregates were designed to be 0% and aggregates, natural and recycled, as described in Table 50% as well as 75% and 100%. In the names of the 1. The recycled coarse aggregate used in this study specimens, NA and R refer to natural and recycled obtained from waste concrete. The production process aggregates, respectively. The normal- and ultra-high- of recycled coarse aggregate is (1) the crushing of the strength steel bars had yield strengths of 472 MPa and waste concrete using jaw crusher, (2) the exclusion of 1,430 MPa, respectively. The steel ratios of the spirals impurities, (3) second crushing using cone crusher, were designed to be 1.75% and 1.0%, named S and M, impact crusher, and double log washer, and (4) the respectively, as seen in Fig.2. separation of crushed aggregates by size. Natural crushed coarse aggregates used in this test had a nominal maximum size of 25 mm, a specific gravity of 2.61 g/cm , and an absorption rate of 2.55%. Natural fine aggregates were used in all of specimens 20 and their physical properties are presented in Table 1. NA As can be seen in Table 2., four types of concrete were R50 R75 used in this study according to the replacement ratio R100 of recycled aggregates. The concrete was designed to -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 Strain have a design strength of 25 MPa, a water-to-cement (a) Concrete ratio of approximately 60%, and a sand percentage of 50%. The concrete used in this study showed similar slumps of 160~170 mm. Compression tests for cylindrical plain concrete specimens with a diameter of 150 mm and a height of 300 mm were performed to estimate the properties of the concrete. The compressive strengths of the f = 472 MPa concrete were measured from 26.1 to 29.7 MPa. The f = 1430 MPa compressive strength and axial strain at peak stress 0 0.000 0.005 0.010 0.015 0.020 0.025 0.030 Strain (peak axial strain) of each concrete are presented in Table 3. Fig.1.(a) shows the stress-strain relationships (b) Steel bars of the concrete used in this study. Fig. 1. Stress versus strain relationships of materials Fig.1. Stress Versus Strain Relationships of Materials This study used normal- and ultra-high-strength round bars with a diameter of 4.5 mm. Based on 150 150 the 0.2% off-set method, yield strengths of round Strain Strain bars were found to be 472 MPa and 1,430 MPa. All gauge gauge reinforcement showed the same elastic modulus of 2.0×10 MPa. The tensile stress-strain relationships of the steel reinforcement are presented in Fig.1.(b). 2.2 Specimen Details A total of 12 unconfined specimens and 30 spirally (a) S-series ( = 1.75%) (b) M-series ( = 1.00%) s s confined specimens, with a diameter of 150 mm and F Fig.2. Details of Specimens ig. 2. Details of specime(Unit: mm) ns (Unit: mm) a height of 300 mm, were designed to investigate the confined behavior of recycled aggregate concrete with spiral reinforcement. As seen in Table 3., the main test 542 JAABE vol.17 no.3 September 2018 Sang-Woo Kim - 1 - - 2 - Stress (MPa) 50 200 50 Stress (MPa) 50 200 50 43.4 To obtain the reliability of the experimental results, yield strength and reinforcement ratio of the spirals the same three specimens were designed for each increased. This tendency was similar to that of other series. Cover concrete and longitudinal reinforcement spirally confined specimens regardless of the aggregate were neglected to estimate the pure effect of spiral type and replacement ratio. As presented in Table 3., reinforcement. Fig.2. shows the positions of strain the spiral reinforcement of all specimens reached their gauges attached to steel spirals with intervals 120 yield strain before peak stress. This implies that the degrees at mid-height of the specimen. concrete can be fully confined by spiral reinforcement 2.3 Test Setup of Specimens even if the ratio of recycled aggregates is increased to The test setup of the specimens is presented in Fig.3. 100%. Three linear variable differential transformers (LVDTs) for longitudinal direction were installed between upper and lower circular steel frames fixed at a distance of 50 mm from the top and bottom of the specimen, respectively. Furthermore, three transverse LVDTs were installed at the mid-height of each specimen to measure the transverse deformation of specimens. A NA-P universal machine with a capacity of 2,000 kN was NA-NS NA-NM used for loading specimens. NA-US -0.04 -0.02 0.00 0.02 0.04 3. Experimental Results and Discussion Strain 3.1 General Behavior (a) NA-series Table 3. provides the experimental results for the peak stress, axial and lateral strains at peak stress, and the yielding point of the spiral reinforcement. Figs.4. and 5. show the crack patterns and stress versus strain relations of tested specimens. As shown in Table 3., plain concrete specimens had similar average peak stresses, f , of 26.9~29.4 MPa and average peak axial 20 co strains of 0.0021~0.0023. In this study, axial strain was R50-P R50-NS measured using the longitudinal LVDTs. The lateral R50-MN strain of unconfined specimens was obtained from -0.04 -0.02 0.00 0.02 0.04 Strain the transverse LVDTs, and that of spirally confined specimens from strain gauges. (b) R50-series The unconfined concrete specimens showed brittle failure after peak stress. On the other hand, spirally confined specimens showed ductile behavior after peak load, exhibiting increasing peak axial strain and 40 lateral strain at peak stress (peak lateral strain) as the R75-P R75-NS R75-NM -0.04 -0.02 0.00 0.02 0.04 Strain (c) R75-series Fig. 3. Test setup of specimen Fig.3. Test Setup of Specimen R100-P R100-NS R100-NM R100-US -0.04 -0.02 0.00 0.02 0.04 Strain (d) R100-series (a) R100-NS (b) R100-NM (c) R100-US Fig. 4. Crack patterns of typical specimens after failure Fig. 5. Experimental results of specimens Fig.5. Experimental Results of Specimens Fig.4. Crack Patterns of Typical Specimens After Failure JAABE vol.17 no.3 September 2018 Sang-Woo Kim 543 - 5 - - 3 - - 4 - Stress (MPa) Stress (MPa) Stress (MPa) Stress (MPa) Table 3. Specimen Details and Experimental Results of Tested Specimens Experimental results f f ' ρ co y s ' Specimens ε f Axial strain Axial strain Spiral co cc (MPa) (MPa) (%) (MPa) at peak load at yielding yielding 1 26.9 0.0021 472 1.75 35.3 0.0116 0.0061 pre-peak NA-NS 2 26.9 0.0021 472 1.75 34.8 0.0118 0.0060 pre-peak 3 26.9 0.0021 472 1.75 34.7 0.0120 0.0069 pre-peak 1 26.9 0.0021 472 1.01 28.4 0.0078 0.0041 pre-peak NA-NM 2 26.9 0.0021 472 1.01 28.7 0.0084 0.0047 pre-peak 3 26.9 0.0021 472 1.01 28.7 0.0073 0.0057 pre-peak 1 26.9 0.0021 1430 1.75 53.9 0.0271 - - NA-US 2 26.9 0.0021 1430 1.75 56.8 0.0303 0.0161 pre-peak 3 26.9 0.0021 1430 1.75 54.0 0.0277 0.0171 pre-peak 1 28.3 0.0022 472 1.75 37.0 0.0108 0.0052 pre-peak R50-NS 2 28.3 0.0022 472 1.75 37.6 0.0116 0.0057 pre-peak 3 28.3 0.0022 472 1.75 38.5 0.0129 0.0053 pre-peak 1 28.3 0.0022 472 1.01 29.3 0.0064 0.0044 pre-peak R50-NM 2 28.3 0.0022 472 1.01 29.9 0.0061 0.0049 pre-peak 3 28.3 0.0022 472 1.01 28.8 0.0080 0.0054 pre-peak 1 28.4 0.0023 472 1.75 38.1 0.0127 0.0052 pre-peak R75-NS 2 28.4 0.0023 472 1.75 39.3 0.0141 0.0057 pre-peak 3 28.4 0.0023 472 1.75 37.6 0.0132 0.0053 pre-peak 1 28.4 0.0023 472 1.01 29.3 0.0068 0.0044 pre-peak R75-NM 2 28.4 0.0023 472 1.01 30.0 0.0064 0.0049 pre-peak 3 28.4 0.0023 472 1.01 29.3 0.0077 0.0054 pre-peak 1 29.4 0.0022 472 1.75 38.2 0.0103 0.0051 pre-peak R100-NS 2 29.4 0.0022 472 1.75 37.5 0.0121 0.0057 pre-peak 3 29.4 0.0022 472 1.75 36.6 0.0107 0.0053 pre-peak 1 29.4 0.0022 472 1.01 30.4 0.0067 0.0043 pre-peak R100-NM 2 29.4 0.0022 472 1.01 29.0 0.0067 0.0053 pre-peak 3 29.4 0.0022 472 1.01 27.8 0.0056 0.0045 pre-peak 1 29.4 0.0022 1430 1.75 52.7 0.0358 0.0222 pre-peak R100-US 2 29.4 0.0022 1430 1.75 53.3 0.0340 0.0174 pre-peak 3 29.4 0.0022 1430 1.75 54.4 0.0356 0.0195 pre-peak Specimens previously tested by authors (Kim et al. 2011) The specimens failed with spalling of the concrete 5.6 times compared to those of unconfined specimens. between the spiral reinforcement. This spalling These results show that a superior lateral confinement increased with higher yield strength of spiral effect is achieved by using spiral reinforcement. As reinforcement due to the increasing lateral expansion shown in Figs.6. and 7., the R50-, R75-, and R100- of concrete at failure. The concrete spalling after NS specimens, having the same spiral reinforcement failure was remarkable as the steel ratio of spirals but different replacement ratios, improved 1.27~1.35 decreased because of the smaller effective areas of times and 5~5.8 times in strength and peak axial strain, lateral confinement, as seen in Fig.4. Based on the respectively. For the NS-series specimens, there was no experimental results, no differences were observed deterioration in strength with increasing replacement in crack patterns in relation to the replacement ratio of recycled aggregates, as seen in Fig.6. ratio of recycled aggregates. This demonstrates that recycled aggregates do not deteriorate the structural performance of spirally confined concrete. Further research, however, is needed on recycled aggregates with adsorption rates higher than 2.55%. 3.2 Strength and Ductility Enhancement The strength and ductility enhancements of specimens are shown in Figs.6. and 7., respectively. In this study, the ductility enhancement ratio was defined as the enhancement ratio of the peak axial strain of specimens. The strength and peak axial strain of NA- NS specimens, with natural aggregates and a spiral Fig.6. Strength Enhancement of Specimens Fig. 6. Strength enhancement of specimens reinforcement ratio of 1.75%, improved 1.3 times and 544 JAABE vol.17 no.3 September 2018 Sang-Woo Kim - 6 - '' f / f cc co lateral strain of unconfined specimens was obtained from transverse LVDTs, while those of the remaining specimens were obtained from strain gauges attached to the spiral reinforcement. As shown in Fig.8.(a), the lateral expansion ratio of unconfined specimens begins at approximately 0.15 and exceeds approximately 0.5 at peak stress. After peak load, the specimens exhibited brittle failure with rapid lateral expansion. It can be seen in Fig.8.(a) that lateral expansion behavior is hardly influenced by the aggregate type and the replacement ratio of recycled aggregates. Fig. 7. Fig.7. Axia Axial Strain Enhancement of Specimens l strain enhancement of specimens Fig.8. shows that spirally confined specimens have In the case of the NM-series specimens, with a yield less lateral expansion compared to unconfined P-series strength of 472 MPa and a steel ratio of 1.0%, NA- specimens. Spirally confined specimens exhibited NM specimens with natural aggregates had only a 6% an increase in lateral expansion after yielding of improvement in peak stress compared to unconfined spirals, and the decrease in lateral expansion became concrete due to their low lateral reinforcement ratio. more pronounced with increasing steel ratio and In terms of ductility, however, the peak axial strain yield strength of spiral reinforcement. In particular, increased by 3.7 times compared to that of unconfined the lateral expansion ratio significantly decreased specimens. This tendency was also observed in the when the yield strength of spiral reinforcement specimens with recycled aggregates. rose from normal- to ultra-high-strength. These When high-strength spiral reinforcement was used, experimental results indicate that the lateral expansion the peak stress and ductility of NA-US specimens with characteristics of specimens are unaffected by the use natural aggregates improved 2.04 times and 13.5 times, of recycled aggregates, and that the lateral expansion respectively, compared to the unconfined specimens. ratio decreases with the increasing lateral confinement As shown in Figs.6. and 7., the strength and ductility performance of spiral reinforcement. of the NA-US specimens are 1.57 and 2.4 times better, respectively, than those of the NA-NS specimens. In 4. Prediction of Stress Versus Axial Strain Relationship other words, improvements in strength and ductility 4.1 Analytical Model of spirally confined specimens can be achieved by In this study, experimental results for confined having higher yield strength of spiral reinforcement. concrete specimens with up to 100% replacement Since the lateral confinement performance of ratio of recycled aggregates are predicted using the spiral reinforcement decreases with increasing the analytical model proposed by Kim et al. (2016), which compressive strength of concrete (Martinez et al. predicts the stress versus axial strain relationship of 1984; Sheikh et al. 1994), further research should be confined concrete with spiral reinforcement using the conducted on the lateral confinement performance of relationship between axial and lateral strains at peak the recycled aggregate concrete with varying levels of load. This model is able to consider the confinement the compressive strength of concrete. effect of high-strength materials for strength and The strength of R100-US specimens with ultra- ductility enhancement of spirally confined concrete. high-strength spirals and 100% replacement ratio of Analytical results obtained from the model proposed recycled aggregates was 1.82 times better than that by Kim et al. were shown to be in good agreement of unconfined specimens, and 1.43 times better than with test results (Assa et al. 2001; Desayi et al. 1978; that of R100-NS specimens with normal-strength JICE 1990; Kim 2010; Muguruma et al. 1978) with spiral reinforcement. This was somewhat lower than the concrete compressive strengths of 18.9~120 MPa, NA-US specimens having natural aggregates, but the Equations (1) ~ (10) spiral yield strengths of 164~1,430 MPa, and spiral structural performance is comparable considering the ratios of 0.29~2.33%. 10% higher concrete compressive strength of R100- The model proposed by Kim et al. (2016) uses the US. In particular, as shown in Fig.7., the ductility of following equation proposed by Popovics (1973) for R100-US specimens was 16 times and 3.2 times higher the stress-axial strain relationship of spirally confined than those of unconfined specimens and R100-NS concrete. specimens with normal-strength spiral reinforcement, respectively. These results were superior to those for fn (/  ) c c cc  (1) (1) NA-US specimens. ' ' n fn 1( / ) cc c cc 3.3 Lateral Expansion Behavior Fig.8. shows the relationship between axial strain where f and f are the stress and peak stress of c cc and lateral expansion ratio of tested specimens. In confined concrete, respectively, ε and ε are the c cc this study, the lateral expansion ratio refers to the axial strain and peak axial strain of confined concrete, ratio of the lateral-to-axial strains of specimens. The - 7 - JAABE vol.17 no.3 September 2018 Sang-Woo Kim 545 - 1 - ''  / cc co 1. 1.75 75 1.75 respectively, and n is a coefficient affecting ascent and NA- NA-P P 1.75 NA-P NA-P R50 R50- -P P decent curves and is defined as follows: R50-P 1. 1.50 50 1.50 R50-P 1.50 R75 R75- -P P R75-P R75-P R10 R100- 0-P P 1. 1.25 25 R100-P 1.25 (2) nE /(E E ) (2) R100-P 1.25 Pe Pea ak k c c cc Peak Peak Equations (4) 1. 1.00 00 1.00 ' '' 1.00 (3) Ef  / (3) cc cc cc 0. 0.75 75 0.75 0.75 where E is the elastic modulus of concrete, taken as 0. 0.50 50 0.50 0.50 the following equation proposed by Carrasquillo et al. 0. 0.25 25 0.25 (1981). 0.25 0. 0.00 00 0.00 0.00 0 0..0 000 00 0. 0.005 005 0. 0.01 010 0 0. 0.01 015 5 0. 0.0 020 20 ' 0.000 0.005 0.010 0.015 0.020 (4) E 3320 f (MPa) 6900 (4) 0.000 0.005 0.010 0.015 0.020 Axial Strain Axial Strain c co Axial Strain Axial Strain (a) P-series (a) P-series (a) P-series (a) P-series Kim et al. proposed the following relationship (a) P-series between the axial and lateral strains at peak load 1. 1.75 75 1.75 1.75 NA- NA-NS NS NA-NS to estimate the peak stress and strain state of spiral NA-NS R50- R50-NS NS 1. 1.50 50 R50-NS 1.50 R50-NS 1.50 R75-NS R75-NS reinforcement. R75-NS R75-NS R100 R100-NS -NS 1.25 1.25 R100-NS 1.25 R100-NS 1.25 Pe Peak ak Peak ' Peak Yield 1.00 Yield l ' 1.00 Yield 1.00 (5)  0.75 0.0035 f 0.6 (5) Yield 1.00 co cc 0. 0.75 75 0.75 0.75 ' ' 0. 0.50 50 0.50 where ε and ε are the axial and lateral strains at peak cc l 0.50 stress, respectively, and f is the compressive strength 0. 0.25 25 co 0.25 0.25 of plain concrete. Once the peak axial strain ε is cc 0. 0.00 00 0.00 0.00 0 0..000 000 0. 0.005 005 0. 0.010 010 0. 0.015 015 0 0..020 020 determined, the peak lateral strain ε can be calculated 0.000 0.005 0.010 0.015 0.020 l 0.000 0.005 0.010 0.015 0.020 A Ax xi ia al l S St tra rai in n Axial Strain using Eq. (5). As the peak lateral strain represents Axial Strain the spiral stress and the lateral confinement pressure (b) NS-series (b) NS-series (b) NS-series (b) NS-series ' ' (b) NS-series at peak stress, f and f , the peak stress of confined sp l 1. 1.75 75 1.75 concrete can be obtained. 1.75 NA- NA-N NM M NA-NM NA-NM R50-NM R50-NM Kim et al. modified the formulas proposed by El- 1. 1.50 50 R50-NM 1.50 R50-NM 1.50 R75-NM R75-NM R75-NM Dash and Ahmad (1995) to calculate the peak axial R75-NM R100-NM R100-NM 1. 1.25 25 R100-NM 1.25 R100-NM 1.25 strain and peak stress of spirally confined concrete as Pe Peak ak Peak Peak Yi Yiel eld d 1. 1.00 00 Yield 1.00 follows: Yield 1.00 0. 0.75 75 0.75 ' ' ' 0.75 (6)   (6) cc co ce 0. 0.50 50 0.50 0.50 0. 0.25 25  6.0  f  0.25 0.25   (7)    ce 0.11 ' 1.15 ' (7) 0. 0.00 00 (sd / ) ( f ) f 0.00  s co  co  0.00 0. 0.000 000 0 0..0 005 05 0. 0.01 010 0 0. 0.01 015 5 0 0..020 020 0.000 0.005 0.010 0.015 0.020 0.000 0.005 0.010 0.015 0.020 A Ax xi ia al l S St tr rai ain n Axial Strain Axial Strain  1 s '' (c) NM-series (c) NM-series (c) NM-series (8) (c) NM-series ff  1 (8)  l s sp (c) NM-series  2 1.25D  1. 1.75 75 1.75 1.75 NA- NA-U US S NA-US NA-US ' '' R100-US R100-US (9) 1. 1.50 50 R100-US f ff (9) 1.50 R100-US cc co ce 1.50 Pe Peak ak Peak Peak Yi Yiel eld d 1. 1.25 25 Yield 1.25 Yield 1.25 0.5 0.25  '    1. 1.00 00 fd 1.00 '' co s   (10) 1.00 f  5.1 f (10) ce  l   f   0.75 0.75 sp s 0.75   0.75   0.50 0.50 0.50 0.50 where ε is the peak axial strain of plain concrete, co 0. 0.25 25 ' ' ' 0.25 taken as 0.001648+0.000016f , ε and f are the 0.25 co ce ce 0. 0.00 00 enhanced axial strain and stress at peak, s is the vertical 0.00 0.00 0. 0.000 000 0 0..0 005 05 0. 0.01 010 0 0. 0.01 015 5 0 0..020 020 0.000 0.005 0.010 0.015 0.020 0.000 0.005 0.010 0.015 0.020 A Ax xi ia al l S St tr rai ain n spacing of spiral reinforcement, d is the diameter of Axial Strain s Axial Strain a spiral, ρ is the steel ratio of spirals, f is the stress s sp (d) US-series (d) US-series (d) US-series (d) US-series of spiral reinforcement at peak load, and D is the (d) US-series Fig.8. Lateral Expansion Characteristics of Tested Specimens diameter of spiral between bar centers. Fig. 8. Lateral expansion ch Fig. 8. Lateral expansion charac aract te er ri is st ti ic cs s o of f t te es st te ed d sp spe ec ci im me en ns s Fig. 8. Lateral expansion characteristics of tested specimens Fig. 8. Lateral expansion characteristics of tested specimens - 2 - - 1 - - 3 - - - 8 8 - - - 8 - - 8 - 546 JAABE vol.17 no.3 September 2018 Sang-Woo Kim - 5 - - 7 - - 8 - - 6 - - 9 - - 10 - Late Late Late Late ral ex ral ex ral ex ral ex pa pa pa pa nsio nsio nsio nsio n ratio n ratio n ratio n ratio La La La La tera tera tera tera l e l e l e l e xp xx xp an p pan an an sion ss sion ion ion r r atio r ratio atio atio La La La La tera tera tera tera l e l e l e l e xp xx xp an p pan an an sion ss sion ion ion r r atio r ratio atio atio Lat Lat Lat Lat era ee era ra ra l e l e l e l e xpan xx xpan pan pan sisi on r si sion r on r on r aa ta a ito t tii io o o  T T able 4. Comparison between Experimental and able 4. Comparison between experimental and ana Analytical Results lytical results Experimental/Analytical Experimental results (average) El-Dash and Ahmad Mander et al. (1988) Kim et al. (2016) (1995) ' ' Specimens f f ' co cc  ' ' ' ' ' ' cc f  f  f  cc ,exp . cc ,exp . cc ,exp . cc ,exp . cc ,exp . cc ,exp . (MPa) (MPa) ' ' ' ' ' ' f  f  f  cc ,ana . cc ,ana . cc ,ana . cc ,ana . cc ,ana . cc ,ana . NA-NS 34.9 0.0118 0.74 1.19 0.89 1.83 0.89 0.90 NA-NM 26.9 28.6 0.0078 0.74 1.15 0.85 2.40 0.85 1.13 NA-US 54.9 0.0284 0.78 1.49 1.12 1.85 1.13 0.80 R50-NS 37.7 0.0118 0.78 1.21 0.92 1.99 0.92 0.98 28.3 R50-NM 29.4 0.0070 0.73 1.03 0.83 2.18 0.84 1.05 R75-NS 38.3 0.0133 0.79 1.37 0.93 2.26 0.93 1.11 28.4 R75-NM 29.5 0.0070 0.73 1.05 0.84 2.22 0.84 1.08 R100-NS 37.4 0.0110 0.75 1.15 0.88 1.98 0.89 0.98 29.4 R100-NM 29.1 0.0063 0.70 0.96 0.80 2.07 0.80 1.03 R100-US 53.5 0.0351 0.72 1.90 1.02 2.78 1.03 1.17 Mean 0.75 1.25 0.91 2.16 0.91 1.02 COV 3.6% 21.0% 10.2% 12.6% 10.3% 10.5% 4.2 Comparison of Experimental and Analytical Results Table 4. and Fig.9. provide a comparison of experimental and analytical results. In this study, existing models proposed by Mander et al. (1988) and El-dash and Ahmad (1995) are used in this study to verify the accuracy of the model by Kim et al. (2016). As seen in Table 4., the model proposed by Mander Test result Mander et al. et al. overestimates the test results for peak stress El-Dash and Ahmad Kim et al. with a mean experimental-to-analytical ratio of 0.75, 0.00 0.01 0.02 0.03 0.04 whereas it underestimates the peak axial stress with an Strain average of 1.25. The prediction results obtained using (a) R100-NS the model by Mander et al. for the peak stress had no significant effect on spiral properties, but the peak axial strain greatly deteriorated as the yield strength of the steel spirals increased. In the case of peak stress, Kim et al. modified the original equations proposed by El-Dash and Ahmad to consider the decrease of strength enhancement with lower peak stress of spiral reinforcement. In this test, Test result all specimens with spiral reinforcement yielded before Mander et al. El-Dash and Ahmad peak load, because normal-strength concrete was used. Kim et al. As seen in Table 4., therefore, models proposed by 0.00 0.01 0.02 0.03 0.04 Strain Kim et al. and El-Dash and Ahmad equally predict the (b) R100-NM real peak stress with a mean of 0.91 and a coefficient of variation (COV) of 10.3%. In addition, the prediction results show that neither model is affected by changing the spiral properties. In the case of peak axial strain, the model proposed by El-Dash and Ahmad greatly underestimated the experimental results by an average of 2.16 times. On the other hand, the model by Kim et al. provided good Test result accuracy for the real peak axial strain with an average Mander et al. of 1.02 and a COV of 10.5%. Furthermore, as seen in El-Dash and Ahmad Kim et al. Fig.9. for R100 series specimens, the model by Kim et 0.00 0.01 0.02 0.03 0.04 al. can successfully trace the stress versus axial strain Strain of natural and recycled aggregate concrete specimens (c) R100-US with spiral reinforcement. Comparison between Fig.9. Comparison of Analytical and Experimental Results Fig. 9. Comparison of analytical and experimental results JAABE vol.17 no.3 September 2018 Sang-Woo Kim 547 - 9 - Stress (MPa) Stress (MPa) Stress (MPa) analytical and experimental results showed that the References 1) Assa B, Nishiyama M and Watanabe F (2001) New approach model proposed by Kim et al. can be reasonably used for modeling confined concrete I: Circular columns. Journal of for the prediction of the behavior of spirally confined Structural Engineering, 127(7), pp.743-750. concrete, regardless of the replacement ratio of 2) Carrasquillo RL, Nilson AH and Slate FO (1981) Properties of recycled aggregates. high-strength concrete subjected to short term loads. ACI Journal, 78(3), pp.171-178. 3) Desayi P, Iyengar KTSR and Reddy TS (1978) Equation for stress- 5. Conclusions strain curve of concrete confined in circular steel spiral. Materials This study evaluated the behavior of spirally and Structures, 11(5), pp.339-345. confined recycled aggregate concrete with test variables 4) El-Dash KM and Ahmad SH (1995) A model for stress-strain of the replacement ratio of recycled aggregate, yield relationship of spirally confined normal and high-strength concrete strength and steel ratio of spiral reinforcement. Based columns. Magazine of Concrete Research, 47(171), pp.177-184. 5) Fathifazl G, Razaqpur AG, Isgor OB, Abbas A, Fournier B, and on this study, the following conclusions are drawn: Foo S (2012) Flexural performance of steel-reinforced recycled (1) The lateral confinement performance of spirally concrete beams. ACI Structural Journal, 109(6), pp.777-786. confined concrete with recycled aggregates improved 6) JICE (1990) High-strength concrete subcommittee report. Japan as the yield strength and steel ratio of the spiral Institute of Construction Engineering, 231pp. reinforcement increased. This tendency was observed 7) Kim S-W, Kim Y-S, Lee J-Y and Kim K-H (2016) Behavior of confined concrete with varying yield strengths of spirals. Magazine regardless of the aggregate type and replacement ratio of Concrete Research, 69(5), pp.217-229. of recycled aggregates. Furthermore, the use of 100% 8) Kim S-W, Jeong C-Y, Lee J-S, and Kim K-H (2013) Size effect in recycled aggregates with absorption rate of 2.55% did shear failure of reinforced concrete beams with recycled aggregate. not cause any deterioration of the strength and ductility Journal of Asian Architecture and Building Engineering, 12(2), of the spirally confined specimens. pp.323-330. 9) Kim S-W, Jung C-K, Lee S-H, Kim K-H (2011) Experimental (2) These experimental results for normal-strength study on structural performance of recycled coarse aggregate concrete demonstrated that all specimens, regardless concrete confined by steel spirals. Journal of the Korea Institute of aggregate type, showed the yielding of spirals for Structural Maintenance and Inspection, 15(1), pp.103-111. before peak stress and had similar lateral expansion 10) Kim Y-S (2010) Behavior of confined concrete with high-strength characteristics. This implies that steel spirals exhibit transverse reinforcement. Master Thesis, Kongju National University, Republic of Korea. their full performance before peak stress, and that 11) Mander JB, Priestley MJN and Park R (1988) Theoretical lateral confinement performance is unaffected by the stress-strain model for confined concrete. Journal of Structural use of recycled aggregates. Engineering, 114(8), pp.1804-1826. (3) Spirally confined specimens showed greater 12) Martinez S, Nilson AH and Slate FO (1984) Spirally reinforced spalling of concrete with an increase in the yield high-strength concrete columns. ACI Journal, 81(5), pp.431-442. 13) Muguruma H, Watanabe S, Tanaka S, Sakurai K and Nakamura E strength of spiral reinforcement due to the increase in (1978) A study on the improvement of bending ultimate strain of lateral expansion at failure. The spalling of concrete concrete. Journal of Structural Engineering, Tokyo 24, pp.109- also increased with decreasing spiral reinforcement ratio because of the smaller effective areas of lateral 14) Popovics S (1973) A numerical approach to the complete stress- confinement. The crack patterns of specimens with strain curves for concrete. Cement and Concrete Research, 3(5), pp.583-599. recycled aggregates were similar to those of specimens 15) Rahal KN and Al-Khaleefi A-L (2015) Shear-friction behavior with natural aggregates, regardless of aggregate type of recycled and natural aggregate concrete-An experimental and the replacement ratio of recycled aggregates. investigation. ACI Structural Journal, 112(6), pp.725-733. (4) From a comparison of experimental and 16) Sheikh SA, Shah DV and Khoury SS (1994) Confinement of high- analytical results, it is shown that the analytical model strength concrete columns. ACI Structural Journal, 91(1), pp.100- proposed by Kim et al. has sufficient accuracy in predicting the behavior of spirally confined concrete with recycled aggregates. Acknowledgments This research was supported by the International Science and Business Belt Program through the Ministry of Science, ICT and Future Planning (2017K000488). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. NRF- 2018R1A2B3001656). 548 JAABE vol.17 no.3 September 2018 Sang-Woo Kim

Journal

Journal of Asian Architecture and Building Engineering – Taylor & Francis

Published: Sep 1, 2018

Keywords: recycled aggregate; confined concrete; spiral reinforcement; stress-strain relationship; ultra-high-strength reinforcement

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