Construction and Building Materials 63 (2014) 234–241

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Construction and Building Materials

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Ductility performance of lightweight concrete element containingmassive palm shell clinker

http://dx.doi.org/10.1016/j.conbuildmat.2014.04.0220950-0618/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +60 193129194; fax: +60 379675318.E-mail address: zamin@um.edu.my (M.Z. Jumaat).

Rasel Ahmmad a, M.Z. Jumaat a,⇑, Syamsul Bahri a,b, A.B.M. Saiful Islam a

a Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysiab Lhokseumawe State Polytechnic, Lhokseumawe, Indonesia

h i g h l i g h t s

� Aggregate replacement up to 70.5% by agricultural waste materials.� Ecofriendly and economic concrete for heavily loaded structure.� Significantly higher modulus of resilience and toughness of PSC concrete than NWC.� Higher Displacement and torsional ductility of PSC concrete element compared to NWC element.� Torsional ductility always higher than displacement ductility of PSC concrete element.

a r t i c l e i n f o

Article history:Received 18 November 2013Received in revised form 7 March 2014Accepted 1 April 2014

Keywords:PSCDuctility indexTorsionDisplacementAgricultural wasteOPS

a b s t r a c t

Lightweight and high strength concrete are commonly needed for a variety of structural applications.Structure with lightweight concrete should assure adequate performance of member under heavy load-ing. In this study, experimental investigations have been conducted to study the displacement ductilityand torsional ductility of lightweight concrete element containing high volume of waste materials.Crushed oil palm shell (OPS) is used as coarse aggregate in different mixes and palm oil clinker (POC)as fine aggregate for sand replacement. In this experiment using those waste materials palm shell clinker(PSC) concrete has been produced. Furthermore modulus of elasticity, modulus of resilience, modulus oftoughness, stress–strain and torsional behavior of PSC concrete are obtained and compared with normalweight concrete (NWC) and POC lightweight concrete. The study reveals that PSC concrete, in contrast tovarious types of structural lightweight concrete (LWC) and NWC, is a ductile material in structural ele-ment. Though the modulus of elasticity of PSC concrete is 30% and 37% of NWC and POC lightweight con-crete respectively, its modulus of resilience and modulus of toughness are significantly higher. Thedisplacement ductility index of PSC concrete element is 2.8 times higher than NWC and POC lightweightconcrete. In contrast the torsional ductility index of PSC lightweight concrete element is obtained 3.3times higher than corresponding concretes. This study found that the torsional ductility of PSC concreteis higher than displacement ductility because of good interlocking properties yet for NWC, displacementductility is higher than torsional ductility. Furthermore the modulus of toughness of PSC concrete ishigher, more energy required to completely break this concrete containing high volume of waste mate-rials. Thus PSC lightweight concrete may be more suitable than NWC and POC lightweight concrete in theearthquake-resistance of concrete structures subjected to compressive and torsional loading structure.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In various structural application lightweight and high strengthconcrete are expected to reduce the weight and size of structuralelements. Those concrete are commonly used in slabs and joists

in high rise buildings and bridge decks in highway bridge struc-tures as well as offshore and marine structures. Knowledge onlightweight aggregate (LWA) concrete is inevitable [1] for advanta-geous construction of such structural elements. In design, astructural engineer should not afford only strength acceptabilitybut should also assure that the member shows acceptable ductilityunder heavy loading [2]. Though satisfactory ductility is vital forconstructions in high seismic areas, numerous and serious

R. Ahmmad et al. / Construction and Building Materials 63 (2014) 234–241 235

difficulties relating to the behavior of reinforced concrete struc-tures under severe seismic action can be traced to the poor charac-teristics of reinforced concrete when subjected to compression andtorsion. It is well recognized that the failure of concrete is suddenand brittle in nature in case of diagonal tension [2]. For example,the pattern of diagonal tension failure of torsion critical concreteelement is brittle and the element fails with little or no warningwhich is similar to the diagonal tension failure of shear criticalmember [2]. However, ductility of concrete ensures safe escapefrom a structure in the event of serious overstress, such as fromblast or earthquake. Khayat et al. [3] shows the RC columns sub-jected to concentric compression to be more ductile in the caseof self-compacting concrete (SCC), than in similar normal concrete(NC) columns. These observations can be usefully applied indesigning reinforced concrete (RC) compressed columns and tor-sional beam in seismic regions [4]. In fact, according to Eurocode8 [5], the lack of attaining required ductility causes a compensationfor the loss of resistance due to crushing.

Ductility of LWC is important because it gives desired warningbefore ruin of the structure. Recently several investigators [6–15]have carried out experiment on LWC using available local wastematerials. The country like Malaysia produces a lot of waste mate-rials in palm oil industries such as oil palm shell, and palm oil clin-ker. Malaysia is the second largest palm oil producing country inthe world and it produces more than half of world’s palm oil. Everyyears Malaysia produce 4.0 million ton oil palm shell and a hugeamount of palm oil clinker as waste materials. Oil palm shell(OPS) and palm oil clinker (POC) both are reusable source of light-weight aggregate (LWA) from the agricultural waste in palm oilindustries. Contemporary studies have shown that OPS and POCcan be used as LWA for producing structural LWC with compres-sive strength in the range of 17–53.6 MPa which is a range of nor-mal strength to high strength ranges of LWC. Although previousresearches have shown separately that OPS or POC can be success-fully used as structural LWC [6,12,14–18], the LWC is still not acommon construction material in the construction industry andthere has been some reticence concerning its use in concretestructures.

Teo et al. [17] have shown that the LWC beams containing 0.52%and 0.75% reinforcement ratios fulfilled the maximum tolerabledeflection as per BS 8110 [19] code requirement at service loads.Incorporation of a 1.13% reinforcement ratio noted deflectionexceeding the maximum limit. They suggested that larger beamcross-sections should be well-thought-out to satisfy the deflectioncriteria. Mohammed et al. [15] found that palm oil clinker concrete(POCC) beam satisfies the deflection criteria of BS8110 code up to0.54% of reinforcement. The Grade 30 OPS concrete shows 24%higher shear strength than normal weight concrete [20]. However,the ductility of those structures is very important to sustain in con-dition of earthquake and impact loading [21,22]. Even the torsionalductility of lightweight concrete was rarely studied in the previousliteratures. In this study, the displacement ductility and torsionalductility of PSC lightweight concrete have been studied for highvolume of waste materials replacement and compared to POClightweight concrete as well as normal weight concrete.

Hence the objective of the study is to investigate the ductilitybehavior of light weight concrete element containing high volumeof waste materials. Complete and stable stress–strain curves andtorque vs. angle of twist curves were obtained. The deformation

Table 1Chemical composition of POC and OPS waste materials.

Oxides SiO2 K2O CaO P2O5 MgO Fe2O

POC 59.63 11.66 8.16 5.37 5.01 4.62OPS 46.61 9.88 14.76 1.95 2.91 10.19

characteristics can be measured by the displacement ductilityindex and torsional ductility index, which is defined later in thepaper. For the range of variables tested, the results indicate thatincreasing POC as sand replacing materials decreases the displace-ment and torsional ductility index of compression critical andtorsion critical members as well as decreases compressivestrength. The PSC concrete shows better ductility than NWC andPOC lightweight concrete. On the other hand the torsional ductilityis constantly higher than displacement ductility for PSC light-weight concrete, though for NWC torsional ductility is less thanthe displacement ductility.

2. Methodology

In this study the displacement ductility and torsional ductility of structuralelement were investigated. To carry out the investigation, high volume of wastematerials as aggregate replacement was considered. Details of materials used andexperimental works are given in the following section.

2.1. Materials used

2.1.1. CementThe Ordinary Portland Cement (OPC) was used with a specific gravity of 3.14 g/

cm3 for all the specimens. The class of OPC was 45.9 MPa is type I OPC cement. TheBlaine’s specific surface area of the cement was 3510 cm2/g.

2.1.2. Superplasticizer (SP) and waterSika viscocrete

�-2199 as a high range water reducing admixture was used in the

study, supplied by Sika Kimia. This admixture is chloride free according to BS 5075and is compatible with all types of Portland Cement including Sulfate ResistantCement (SRC). The super plasticizer was used as 1% of cement weight.

2.1.3. AggregatesLocal mining sand with a specific gravity, fineness modulus, water absorption

and maximum grain size of 2.66, 2.89, 1.17% and 4.75 mm, respectively, was usedas fine aggregate. OPS and POC aggregates are considered as a renewable sourceof aggregate from waste materials which were collected from a local palm oil fac-tory. The POC was obtained in large chunks during the oil palm shell and fiber incin-eration process [23]. POC was washed and dry after collecting from the palm oilfactory. Then it was crushed with the stone crushing machine in the laboratory.The crushed POC was sieved with 9.5 mm and 4.75 mm sieve, then particles below4.75 mm is considered as fine aggregate, as well as above 4.75 mm particles isconsidered as coarse aggregate. Palm oil clinker was used as 25%, 37.5% and 50%by volume of sand replacement. Moreover, the POC fine aggregates have specificgravity, fineness modulus and water absorption of 2.08, 3.12 and 3.61% respec-tively. Also the chemical composition of POC and OPS waste materials is shownin Table 1.

Another two types of coarse aggregate used in the study are OPS and granite. Allthe aggregate ranges were considered in same size. As in previous researches [6–8,10,13,24] OPS in different shapes were used as the coarse aggregate. The OPS werecollected from a local crude palm oil producing mill. Then it is stored in an opentrain about six months to wash the oil and remove the ash from the shell. Theadvantages of using old OPS in concrete were reported by Shafigh et al. [13]. Themeasured ranges of shell thickness were 0.45–4.05 mm which is in the rangesshown by Shafigh et al. [11]. Its flakiness index is high, about 65% of that obtainedby Mannan and Ganapathy [9]. Flakiness of OPS is significantly decreased due tocrushing its larger sizes, which results in a better performance of coarse aggregateand consequently improved the compressive strength of concrete. After collectingOPS from the industry is keep in open train at least to remove the oil and fiber fromthe surface of OPS. Then it was washed and dried, after drying it was crushed withthe stone crushing machine in the laboratory. The crushed OPS was sieved with4.75 mm and 9.5 mm sieve. The particles in between the range of 4.75 mm and9.5 mm were considered as coarse aggregate as the same size of POC coarseaggregate. All the coarse aggregates were submerged under water for 30 min beforemixing because of those lightweight aggregates are high water absorbing materials.After that they were moved from the water and kept in open-air to remove free

3 Al2O3 SO3 Na2O TiO2 Cr2O3 Others

3.7 0.73 0.32 0.22 – 0.583.33 7.84 1.15 – 1.38 –

Fig. 1. SEM image of (a) POC sand and (b) normal sand.

Table 2Mix proportion (kg/m3) and basic properties of concrete.

Mix no. Cement Water W/C SP Fine aggregate Coarse aggregate Slump (mm) Density (kg/m3)

Normal sand POC sand OPS POC Granite

P0 500 164 0.328 5 980 – 310 – – 182 1932P25 500 164 0.328 5 736 193 310 – – 127 1913P37.5 500 164 0.328 5 613 289 310 – – 102 1902P50 500 164 0.328 5 491 385 310 – – 83 1889N0 482 160 0.331 4.82 801 – – – 881 196 2342PC0 482 160 0.331 4.82 801 – – 620 – 124 1948PH0 482 160 0.331 4.82 801 – 405 – – 93 1700

Table 3Mechanical properties of PSC concrete.

Mixno.

Compressivestrength(MPa)

Modulus ofelasticity, MOE(GPa)

Modulus oftoughness/rupture,MOT (J/m3)

Modulus ofresilience, MOR(J/m3)

P0 37.80 13.79 189,458 8237P25 37.40 12.64 181,207 10,484P37.5 35.90 12.44 135,631 9374P50 31.20 8.57 150,186 9102N0 48.23 28.34 67,488 6733PC0 44.89 22.95 38,465 2094PH0 27.40 9.37 174,168 10,709

236 R. Ahmmad et al. / Construction and Building Materials 63 (2014) 234–241

surface water to use it in the mix. OPS with specific gravity, compacted bulk densityand 24 h water absorption of 1.22, 683 kg/m3 and 18.7% respectively, were used ascoarse aggregate in a wet condition without free surface water.

2.2. Mix proportions

In actual field condition, trial mixes [9] are customarily used for the mix designof LWC. According to this scheme, the P0 mix was designed for grade 35 with a highworkability. Based on P0 mix, the palm oil clinker was used as a sand replacementby 25%, 37.5% and 50% by volume is indicated as P25, P37.5 and P50 mix. Herewaste is increased up to 25% of total aggregate volume by using palm oil clinkersand. By adopting the sand replacement, the workability of concrete was reducedbecause palm oil clinker was more porous than normal sand shown in Fig. 1. Forcomparison a NWC mix N0, POC lightweight concrete mix PC0 and mix PH0 wereproduced with high volume of coarse aggregate which were correspondingly madeby crushing granite, clinker and OPS. The details of the concrete mixes with theirproperties are presented in Table 2.

2.3. Test specimens

For displacement ductility due to compressive strength of column, cylinder[4,25–27] of 150 mm diameter and 300 mm length was considered. Moreover, toachieve torsional ductility, the torsion test uses 100 � 100 � 500 mm concreteelement.

3. Results and discussion

The mechanical properties of PSC concrete as well as ductilitycharacteristics obtained from the test results are presented inTables 3 and 4. Based on the variation of mix proportions, Table 3represents the modulus of elasticity, modulus of rupture and mod-ulus of toughness against corresponding compressive strength.Furthermore, the concept of modulus of toughness and modulusof resilience definition is graphically shown in Fig. 2. Ramanet al. [28] have shown that if modulus of resilience of a materialis less, it will yield at lower strain. Here modulus of resilience ofPOC lightweight concrete and NWC was lower compared to PSClightweight concrete. It can be seen that the strains at yield pointof those concrete are lower than PSC lightweight concrete due to

lower modulus of resilience. This observation agrees with theRaman et al. [28] study well.

Structural elements ductility being generally indicated as ‘thecapacity of the structural element to endure load though incurringextra distortion beyond the maximum load stage’ [2]. This explana-tion is qualitative and to quantify the displacement ductility ofcompression critical member and torsional ductility of torsion crit-ical concrete elements. The ratio of the area of the stress–strain ortorque-angle of twist response up to 5eo or 5£o to the area up to eo

or £o for displacement and torsion respectively was defined as theductility index (l or w) is shown in Fig. 3.

Evaluation of structural parameters of the displacement ductil-ity and the torsional ductility index is illustrated in Table 4 for thesimilar mix proportioning of light weight concrete. For betterunderstanding, the experimental results are presented here intwo categories; displacement ductility and torsional ductility. Sub-sequent section discusses these behaviors in detail.

3.1. Prediction of modulus of elasticity

Modulus of elasticity (MOE) plays an important role in concretebecause deflection directly depends on it. Generally, for LWAC withnatural and artificial LWA, the value of the static MOE ranges

Table 4Deflection ductility and torsional ductility of LWC containing high volumes of waste materials.

Mix no. Compressive strength fcu, MPa Displacement ductility Torsional ductility

Stress, rmax MPa Strain, e l smax, N-m £ at smax, Degree W

P0 37.80 26.81 0.00305 4.05 897 1.466 5.54P25 37.40 25.46 0.00330 3.85 795 1.213 4.94P37.5 35.90 22.77 0.00270 3.82 753 1.204 4.80P50 31.20 16.49 0.00358 3.78 506 1.591 4.30N0 48.23 42.83 0.00225 1.19 1280 1.820 1.00PC0 44.89 33.90 0.00205 1.00 826 1.016 1.00PH0 27.40 19.44 0.00370 3.81 952 2.520 4.78

Fig. 2. Diagram for description of modulus of toughness and modulus of resilience.

Fig. 3. Diagram for description of displacement ductility and torsional ductility.

Mod

ulus

of

elas

ticity

, MO

E (

MPa

)Compressive Strength, fc' (MPa)

Fig. 4. Compressive strength vs. modulus of elasticity curve.

R. Ahmmad et al. / Construction and Building Materials 63 (2014) 234–241 237

between 10 and 24 kN/mm2 [29]. With the increase of POC sandcontent in PSC lightweight concrete the modulus of elasticitydecreases gradually which is shown in Fig. 4. In this study up to37.5% sand replacement by volume the modulus of elasticityreduction is only 9.7% and the value of MOE is higher than thevalue predicted by Alengaram et al. [30] for OPS lightweight con-crete. However, at 50% sand replacement by POC sand the modulusof elasticity suddenly decreases by 37.9% then the control P0 mixwhich is lower than the value predicted by Eq. (1). As a result, upto 37.5% sand replacement by POC sand is beneficiary then theincreasing POC sand content in PSC lightweight concrete.

The MOE is related to the compressive strength of concrete [30].Fig. 4 shows a comparison of the E value of PSC LWC with the pre-dicted by equation given by Alengaram et al. [30] (Eq. (1)) for OPSconcrete,

EsðpreÞ ¼ ½q=2400�2 � ðfcuÞ1=3 � 5:0 ð1Þ

where Es(pre) (kN/mm2), fcu (N/mm2) and q (kg/m3) are the predictedelastic modulus, cube compressive strength and air-dry density,respectively.

From the figure it is seen Alengaram underestimate the MOE ofOPSC. As a result an equation is suggested from the existing exper-imental data in below

Es ¼ 0:0026F2:5546cu ð2Þ

where Es(pre) (kN/mm2), is the predicted elastic modulus, Fcu is cubecompressive strength.

3.2. Stress–strain behavior

Fig. 4 show the stress–strain curves for all the specimens ofNWC, POC and PSC lightweight concrete containing differentpercentages of waste. Both the vertical and lateral strains are pre-sented with the increase of compressive load. The vertical displace-ment is shown in positive X-axis and lateral displacement atnegative X-axis in Fig. 5. The NWC shows maximum strain 0.002same as shown different researchers [27,31]. On the other handthe lightweight PSC concrete shows highest strain which wasachieved by using FFRC [31], steel bars mats, carbon fiber [27]strengthened NWC element. The stress–strain curves of PSC spec-imens softened towards a rounded peak at the post-yield stageand a very slow dropping tendency after post yield, mainly becausethe PSC concrete had good interlocking [20] and a bilinear ductile[32] stress–strain behavior. Evidence indicated that the PSC con-crete specimen could undergo much greater deformation beforefailure, and such a failure was ductile and gave warning of theimpending failure is similar to steel bar mat and wire meshstrength specimen [27]. Classically LWAC shows linear stress–strain curves up to 90% of its ultimate strength [33]. On the otherhand Domagała [34] investigated that NWC shows linear stress–strain curves up to 30–45% of its ultimate strength. In the presentstudy, the stress–strain curve behaves linearly up to 60% of its ulti-mate strength. This indicates that the behavior of PSC concretestrength is in the middle of LWAC and NWC because of theelasto-plastic nature of PSC concrete than traditional lightweightconcrete. For PSC concrete, the strain at maximum stress was

Fig. 5. Stress–strain curves for vertical and lateral displacement.

Fig. 7. Measurement of vertical and lateral strain by compressometer.

238 R. Ahmmad et al. / Construction and Building Materials 63 (2014) 234–241

measured in a range of 0.0024 to 0.0034 from the experiment ishigher than the strain at peak stress of NWC element [35] is0.0015–0.002 and near to the range of lightweight concrete ele-ment [36] is 0.026–0.003. However, as the strain rate of the presentPSC concrete is higher than others, it assists to overcome the crack-ing [37] caused by temperature and shrinkage effect on structuralelement.

The illustration shows that the effectiveness of ultimate loadcarrying capacity decreases with the increase of waste content byincreasing POC as sand replacement materials. Up to 37.5% of sandreplacement by POC sand, the ultimate load carrying capacitydecreases only by 15.6%. However, at 50% of sand replacementby POC sand, the ultimate load carrying capacity suddenlydecreased by 38.2%. Therefore, the sand replacement up to 37.5%by POC sand is more convenient for the concrete strength due ofless reduction of compressive strength in concrete. The POC sandpore size is in the range of 10.4–1200 lm is shown in Fig. 6 whichis larger in than the cement particle [38]. So the amount of cementreduced by inserting into the POC sand pores cause reduction ofcement paste. For such lessening of cement paste the strength ofPSC concrete is gradually decreases with the increase of POC sandpercentage. Besides, mix no PC0 use a large amount of POC coarseaggregates. However, there is no decrease of strength because thecoarse aggregates were submerged under water before using in themix. Due to submergence under water, the inside porous is filledwith water. So the cement does not reduce by inserting into theporous and no lessening of strength was seen. It can be seen thatincreasing POC sand content decreases ultimate stress as well asthe slope of the stress vs. strain curves. However, e value increasesdue to increases of POC sand content up to 37.5% and afterward itis going to decrease. The ultimate strain (eu) of PSC concrete isalways higher than the NWC and POC lightweight concrete for uni-axial load is shown in Fig. 4. In experiments for design purpose ofNWC, the eu value is considered as 0.0035 [39] or 0.003 [40]. The

Fig. 6. Size of pores in

increase of OPS content in mix and reduction of cement content(mix PH0 and P0) in concrete have significant effect on stress–strain curve of PSC concrete, mainly on the strain at maximumstress and strain at breaking point. With the increase of OPS con-tent the strength and modulus of elasticity reduction is significantin mix PH0 because the density of concrete reduced significantlydue to more porous in this concrete as shown in Table 2. In thestress–strain diagram it is identified that the strain at failure pointof POC concrete and NWC mixes are very close to maximum stress.For the applied load up to ultimate strength, the specimen failedsuddenly in case of POC and NWC. Besides, for PSC concretes, thefailure occurs steadily which is reflected in the illustration.

3.3. Displacement ductility

The displacement ductility values stated in this study are strainductility of compression-critical member. The strain is measuredwith the dial gauze of compressometer with digital data logger isshown in Fig. 7 and the strain is obtained in the same techniqueof previous research [41] on column. Here eo, is the strain at peakstress (rmax) for the concrete element. The pick stress is calculatedfrom the average of three samples peak stress. The displacementductility index is quantified from the experimental results of theelements, and the results are exposed in Table 4. In addition, rmax

and the corresponding strain (eo) recorded during the tests areshown. The stress–strain curve of PSC concretes element (Fig. 5)

POC clinker sand.

Tor

que

(),

N-m

Angle of Twist ( ), Degree

Fig. 8. Torque vs. angle of twist curves.

R. Ahmmad et al. / Construction and Building Materials 63 (2014) 234–241 239

shows that it behaves as ductile structural element by use of OPSas ductile materials [32], in contrast to the NWC and POC light-weight concrete, even high volume of waste materials was used.Therefore, it can be concluded that even NWC and POC concretehave more compressive strength and modulus of elasticity, thePSC concrete has at least 2.8 times higher ductility performancethan those concrete. Simultaneously, PSC concrete’s modulus oftoughness is 2.2 and 3.9 times compared to NWC and POC

Fig. 9. Cracking pattern (a) NWC and POC lightweight concrete

Fig. 10. Relationship among compressive strength, ducti

lightweight concrete respectively. Furthermore, the modulus ofresilience of PSC concrete is 1.3 and 3.9 times compared to corre-sponding values of NWC and POC lightweight concrete.

3.4. Torque vs. angle of twist behavior

Fig. 8 reveals the torque vs. angle of twist curves for all the spec-imens of NWC, POC and PSC lightweight concrete having differentpercentages of waste materials. Chalioris and Karayannis [42] nar-rated that after reaching maximum torque point, the normalweight concrete abruptly fails due to torsion, which is similar tothe study of NWC and POC lightweight concrete element. ThroughFig. 8, it is also shown that the PSC concrete behaves as a ductilematerials in torsion likewise Chalioris and Karayannis [42]obtained this behavior by using steel fiber. The pattern of torquevs. angle of twist curves of the PSC lightweight concrete are linearto level approaching 95% of the ultimate torque, which is similar tothe NWC and POC lightweight concrete. The angle of twist at peaktorque for PSC concrete is in the range of 1.2–1.6 degree which islower than the normal weight concrete but higher than the POClightweight concrete. Usually LWAC tend to be more inelastic thanNWC which cause sudden failure after ultimate torque. From thisstudy, it can be seen that the effectiveness of ultimate torquecarrying capacity decreases with the increase of waste content byincreasing POC sands as a replacement of normal sand in PSC

failure and (b) PSC concrete failure due to torsional effect.

lity index and waste percentages use PSC concrete.

240 R. Ahmmad et al. / Construction and Building Materials 63 (2014) 234–241

concrete. Increase of POC sand content in the concrete decreasesultimate torque due to decrease in the strength of concrete. Theultimate angle of twist (u) of PSC concrete is always higher thanthe NWC and POC lightweight concrete for pure torsional load asshown in Fig. 5. The increase of OPS content in mix and reductionof cement content (mix PH0 and P0) in concrete have significanteffect on torque vs. angle of twist curve of PSC concrete, especiallyon the angle of twist at peak torque point. From the illustration it isshown that the end point of the torque vs. angle of twist relation-ship of POC and NWC mixes are nearby the peak torque. Again, atthe level of ultimate torque, the specimen failed abruptly. How-ever, for PSC concretes the failure occurs gradually.

3.5. Torsional ductility

Torsional ductility is customarily measured in angle of twistonly. In this study maximum angle of twist is used to define tor-sional ductility. The torsional ductility values have been presentedas the angle of twist ductility of torsion-critical member. There o, isindicated as angle of twist at peak torque (smax) for the concreteelements. The torsional ductility index were quantified from theexperimental study of the elements, and the results are presentedin Table 4. Moreover, smax and the corresponding angle of twist ()recorded during the tests are shown in Table 4. Similar to the dis-placement ductility, the torque-angle of twist curve of PSC con-cretes (Fig. 9) also indicates that it is a ductile element ratherthan the NWC and POC lightweight concrete element. Thoughthe NWC and POC have more compressive strength and modulusof elasticity, the PSC concrete has at least 3.3 times higher torsionalductility performance than those concretes. Therefore, it exhibitshigh energy absorption capacity under torsional load althoughhigh volume of waste materials is used. From Fig. 9, it is seen thatafter failure in concrete due to torsion on NWC and POC light-weight concrete, the parts of structural elements separate eachother. However, in case of PSC concrete the parts are not separatedin each mix where three specimens are tested. Only displacing a bitdistance is seen even one end is released from the member endbecause of good interlocking [20] on PSC concrete. The torsionalfailure of all PSC concrete elements is due to the crushing of aggre-gate and debonding on surface of aggregate both occurs.

3.6. Influence of compressive strength and waste percentage onductility

The influence of the compressive strength of concrete in the dis-placement ductility index (l) and torsional ductility index (w) ofstructural element containing high volume waste materials isshown in Fig. 10. With the increase of compressive strength, theductility index increases gradually though Ahmad et al. [2] showswith the increase of compressive strength ductility should bedecreased for normal weight concrete. This is because; in thisstudy POC is added as replacement of sand which is porous mate-rial and reduces the cement pastes by absorbing cement causingreduction of compressive strength. With the increase of POC sandcontent in concrete the displacement ductility and torsional ductil-ity of concrete element decreases because of decreasing strength ofconcrete, though those ductility of PSC lightweight concrete hasbeen always higher than NWC and POC lightweight concrete. Fur-thermore, from Fig. 10 it is clear that torsional ductility of PSC con-crete element is always better than its displacement ductility.

4. Conclusions

Experimental results of compression-critical and torsion-criticalfresh lightweight concrete are presented. Based on the detail study,the following conclusions can be drawn:

(1) The displacement ductility and torsional ductility of PSClightweight concrete elements are more than 2.8 times and3.3 times higher in comparison with NWC as well as POClightweight concrete respectively.

(2) The ductility index decreases due to increase in porouswaste materials which reduce the cement paste in concretewhen the sand content is replaced by POC.

(3) The strain at maximum stress of concrete with high volumeof waste materials is about 59% and 75% higher than NWCand POC lightweight concrete respectively.

(4) Though the modulus of elasticity of PSC concrete is 30% and37% of NWC and POC lightweight concrete respectively, butits modulus of resilience and modulus of toughness are sig-nificantly higher than NWC and POC lightweight concrete.

(5) The torsional ductility index is higher than displacementductility index of PSC concrete, although for NWC, displace-ment ductility is higher than torsional ductility. This isbecause of good interlocking properties of coarse aggregateused in PSC lightweight concrete.

(6) PSC concrete’s modulus of toughness is 2.2 and 3.9 timescompared to NWC and POC lightweight concrete respec-tively. Furthermore, the modulus of resilience of PSCconcrete is 1.3 and 3.9 times compared to the correspondingvalues of other concretes.

Acknowledgment

The authors would like to thank the University of Malaya (UM)for funding through High Impact Research Grant H-16001-00-D000036 to carry out the present research.

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