ndi A

he ps, anretee sttoin cingermica

been uof LWCthat oftechniqht aggarticiand sestablicondites andce of l

material in structural design [612].Lightweight aggregate (LWA), can be used for making masonry

blocks, wall panels, precast concrete elements, structural in situconcrete, screeding and cladding. Its presence in concrete reducesthe dead weight of structure. The cellular structure of the aggre-gate gives thermal insulation properties. One of the main problems

slate and shale in concrete is that these porous aggregates absorb

The experimental program focused on investigating the properties of fresh andhardened concretes containing locally available natural lightweight aggregates, andmineral admixtures. A total of ninety-nine 100 mm cubes, and sixty-six100 200 mm cylinders were cast to measure the density, compressive and split-ting tensile strengths, and stressstrain diagram in compression.

2.1. Materials

The materials used in this investigation include lightweight aggregates (LWA),cement, silica sand, and admixtures. The LWAs were volcanic tuffs of scoria originavailable in the outskirts of Al-Madina, Saudi Arabia. Fig. 1 shows enlarged photosfor the natural LWA used in this investigation. The physical properties of the aggre-

* Tel.: +966 1 467 6928; fax: +966 1 467 7008.E-mail addresses: mjshanag@ksu.edu.sa, mmshannag@just.edu.jo

Construction and Building Materials 25 (2011) 658662

Contents lists availab

Construction and B

ev1 On leave from Jordan University of Science and Technology, Jordan.gates [15]. The demand for lightweight concrete in many applica-tions of modern construction is increasing, owing to the advantagethat lower density results in a signicant benet in terms of load-bearing elements of smaller cross sections and a correspondingreduction in the size of the foundation. However, despite the ef-forts to improve the strength/weight ratio and versatility of struc-tural lightweight concrete (SLWC), more research is needed forexploring the potential application of this important building

tions using locally available materials, (2) studying the propertiesof the LWC mixes developed, including workability, density, com-pressive and tensile strength, and (3) studying the compressivestressstrain behavior of the LWC mixes developed.

2. Experimental programLightweight concrete (LWC) hasposes for many years. The density1400 to 2000 kg/m3 compared withweight concrete (NWC). Some of theLWC include using natural lightweigdiatomite, and volcanic cinders, orperlite, expanded shale, clay, slate,ash (PFA). Lightweight concrete hasconstruction material whenever theings in the dead-loads in structurand whenever there is an abundan0950-0618/$ - see front matter 2010 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2010.07.025sed for structural pur-typically ranges from2400 kg/m3 for normalues used for producingregates such as pumice,al by-products such asintered pulverized fuelshed itself as a suitableions require strict sav-energy conservations

ocal lightweight aggre-

a very large quantity of the mixing water [5]. The presence of ashell structure on the LWA signicantly inuences the mechanicalproperties of the lightweight concrete. When the lightweightaggregate concrete is constituted with stiff aggregates, stressesare transmitted between cement phases. Failure cracks will extendalong the shells of the aggregates similar to that of the normalweight aggregates. For the soft aggregates or the aggregates with-out the shell, failure mechanism can be totally different sincecracks will pass right through the aggregates [6].

The main objectives of this investigation include: (1) developinglightweight concrete (LWC) mixes suitable for structural applica-1. Introduction associated with the use of conventional LWA produced from clay,Characteristics of lightweight concrete co

M.J. Shannag *,1

Department of Civil Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Sau

a r t i c l e i n f o

Article history:Received 4 April 2010Received in revised form 19 July 2010Accepted 28 July 2010Available online 21 August 2010

Keywords:Lightweight concreteMineral admixturesStressStrain

a b s t r a c t

This research investigates tural lightweight aggregatestructural lightweight conc14% increase in compressivsilica fume. But, adding upcaused about 18% decreasemixes without y ash. Addmixes perform better, in tsame contents of either sil

journal homepage: www.elsll rights reserved.rabia

roperties of fresh and hardened concretes containing locally available nat-d mineral admixtures. Test results indicated that replacing cement in thedeveloped, with 515% silica fume on weight basis, caused up to 57% andrength and modulus of elasticity, respectively, compared to mixes without10% y ash, as partial cement replacement by weight, to the same mixes,ompressive strength, with no change in modulus of elasticity, compared to10% or more of silica fume, and 5% or more y ash to lightweight concretes of strength and stiffness, compared to individual mixes prepared usingfume or y ash.

2010 Elsevier Ltd. All rights reserved.taining mineral admixtures

ier .com/locate /conbui ldmatle at ScienceDirect

uilding Materials

gates were determined following ACI and ASTM standards [1,13], as shown in Table1a. A brief summary of the properties of other materials used, is presented in Table1b.

2.2. Mix proportions

The absolute volume method, ACI 211 [3], was used for designing the basic con-crete mix. The nal mix was optimized for workability, density and strength, usingthe following ingredients: cement, silica sand, natural lightweight coarse and neaggregates, silica fume, y ash, high range water reducers, and water. After castingmany trial mixes, and making necessary adjustments, the concrete mix thatachieved relatively a good degree of workability, minimum density and an accept-able level of strength was considered as a basis for further investigation of the effectof mineral admixtures on the behavior of SLWC. The concrete mixes designed in thisinvestigation were of similar workability and water to cementitious materials ratio.They consisted of about 400 kg/m3 of Portland cement with the addition of 0%, 5%,10% and 15% of silica fume and y ash by weight of cement. The details of thesemixes are listed in Table 2.

2.3. Mixing and casting

The concrete mixes were prepared using a tilting drum mixer of 0.05 m3 capac-ity. The interior of the drum was initially washed with water to prevent waterabsorption. The coarse and medium aggregate fractions were mixed rst, followedby adding the amount of water absorbed by the aggregates and allowed to rest for30 min to minimize the variation in the initial slump caused by the high waterabsorption of lightweight aggregates; then silica sand was added, followed by add-ing cement, y ash, silica fume, and the water containing about 75% of the superp-lasticizer. One-fourth of the superplasticizer was always retained to be addedduring the last 3 min of mixing period. The concrete mixes were poured in cubicand cylindrical molds, and compacted using a vibration table at low speed. Aftereach mold was properly lled the vibration speed was increased to medium speedto ensure sufcient compaction.

Fig. 1. Natural lightweight aggregates used in this investigation.

Table 1aPhysical properties of lightweight aggregates used.

LWCA (Madina) LWFA (Madina)

Density (kg/m3)Loose 965 996Rodded 1071 1040

Density (gm/cm3)Dry 2.04 2.10SSD 2.1 2.15

Water absorption (%) LWCA LWFA

Time10 min 3.2 2.830 min 3.7 3.51 h 4.2 3.92 h 4.7 4.34 h 5.1 5.624 h 6.9 6.3

Cylinder compressive strength of LWA 4.5 MPa

Table 1bPhysical properties of cement, sand, and admixtures used.

Type of material Density(gm/cm3)

Specic surface area (m2/kg)

Portland cement (type I) ASTM C 150 [14]

3.15 300

Silica fume (powder form) 2.2 2000Fly ash (powder form) 2.3 500Superplasticizer ASTM

494-type D [14] (liquidform)

1.21

Silica sand (natural) 2.6 Fineness modulus: 1.65, waterabsorption: 0.5%, density: 1620 kg/m3

Table 2Concrete mix proportions in kg/m3 using natural lightweight aggregates from Madina reg

Mix no. Cement Fly ash Silica fume Silica sand

1 400 0 0 2002 380 0 20 199.33 360 0 40 198.64 340 0 60 2005 380 20 0 199.26 360 40 0 198.77 360 20 20 198.68 340 40 20 1989 340 20 40 197.9

10 320 40 40 197.311 320 20 60 199.2

M.J. Shannag / Construction and Building Materials 25 (2011) 658662 6592.4. Curing and casting

After casting, the specimens were covered with wet burlap and stored in thelaboratory at 23 C and 65% relative humidity for 24 h and then demoulded andplaced under water. Each specimen was labeled as to the date of casting, mix usedand serial number. The specimens were then taken out of water a day before testingand dried in air.

ion.

LWCA LWFA Water Superplasticizer (L)

550 350 250 1548 348.7 249.1 3546 347.4 248.2 3550 350 250 4548.2 348.9 249.2 2546.6 347.8 248.4 1.5546.3 347.6 248.3 3544.6 346.5 247.5 2544.3 346.4 247.4 4

Table 3Slump and density of LWC determined in this investigation.

Mix no. Slump (mm) Density (kg/m3)

Fresh Air dry Oven dry

1 160 2050 1950 18472 150 2040 1971 18523 90 2025 1946 18544 110 2032 1995 18785 130 2066 1968 18986 180 2050 1958 18967 180 2053 1947 18548 155 2060 1970 18349 150 2039 1947 1851

10 160 2032 1954 182011 160 2030 1935 1817542.6 345.3 246.6 4548.2 348.9 249.2 3

3. Results and discussion

The performance of the LWC mixes developed in this investiga-tion was evaluated by determining the following properties: den-sity, workability, compressive strength, splitting tensile strength,and stressstrain diagram.

3.1. Workability

The workability of the concrete mixes cast in this investigationwas measured using the slump test. The slump test results listed inTable 3 indicate that most of the LWC mixes showed a slump val-ues ranging from 90 mm to 180 mm immediately after mixing. The

lightweight aggregates, LWA, and mineral admixtures seems tobe feasible. The concrete produced possesses 28 days compressivestrength of about 22.543 MPa with a corresponding air dry den-sity of about 19351995 kg/m3 which falls slightly above the ACIrequirements of 1850 kg/m3.

3.4. Splitting tensile strength

The 28 days splitting tensile strengths and the correspondingcompressive strengths at the same age, for the lightweight con-crete mixes cast in this investigation are listed in Table 4. Majorityof the splitting tensile strength test results for air dried LWC shownin the table were about 89% of the corresponding compressivestrength. This is slightly below the standard range reported inthe literature of 10% for normal weight structural concrete [3]. Thiscould be due to the cellular structure of light weight concrete thatenhanced the initiation and growth of microcracks under tensile

660 M.J. Shannag / Construction and Building Materials 25 (2011) 658662larger slump for LWC is desirable in order to account for the grad-ual loss in workability, caused by the high water absorption of theaggregates, which may occur 12 h after mixing, i.e. at the begin-ning of pouring the concrete in the formwork. To be within thescope of this investigation, the workability of all the LWC mixescast, was kept almost the same by changing the dosage of superp-lasticizer whenever needed, in particular for the mixes containingrelatively high percentages of silica fume and y ash.

3.2. Density

In this investigation, the densities of all the LWC mixes cast,including fresh, air dry and oven dry were determined and pre-sented in Table 3. The fresh densities shown in Table 3 indicatedthat most of the LWC mixes made, showed a density varying from2025 kg/m3 to 2066 kg/m3. Since the aggregates in the fresh statewere completely saturated with water, therefore the fresh densi-ties were considerably higher than the corresponding air dry andoven dry densities as shown in Table 3. Most of the specicationstandards classify structural lightweight concrete based on airdry density not exceeding 2000 kg/m3 [2]. The air dry densityshown in the table varied from 1935 to 1995 kg/m3. It can be no-ticed that the range of air dry density complies with the Europeanspecications for structural LWC of air dry density not exceeding2000 kg/m3, but does not meet ACI requirements of air dry densitynot exceeding 1850 kg/m3. It should be noted that the air dry den-sities can be reduced to meet ACI requirements by making someadjustments on the composition of the mixes without sacricingthe structural strength required at 28 days. It can be observed fromTable 3 that the oven dry unit weights of the LWC mixes developedvaried from 1817 to 1898 kg/m3.

3.3. Compressive strength

The test results listed in Table 4, indicate that producing struc-tural lightweight concrete, SLWC, using locally available natural

Table 4Compressive strength, splitting tensile strength, and modulus of elasticity, of LWCmixes at 28 days.

Mixno.

Compressivestrength (MPa)

Splitting tensilestrength (MPa)

Modulus ofelasticity (MPa)

1 29.3 2.75 19,7882 28.8 3.15 19,3433 38.0 3.47 20,4134 43.2 3.18 22,4775 27.7 2.68 20,7956 22.5 2.76 19,7517 32.2 2.91 18,6968 32.4 2.39 17,457

9 39.0 3.44 20,213

10 33.7 2.86 18,69411 36.7 2.64 18,587loading, and thus resulted in larger decrease in tensile strengthcompared to normal weight concrete.

3.5. Stressstrain diagrams in compression

The compressive behavior of the LWC mixes proposed in thisinvestigation can best be understood by plotting the completestressstrain response. All specimens were tested under uniaxialcompression as shown in Fig. 2, by applying a vertical load gradu-ally until they reached complete failure. During the test, the dis-placement readings of the vertical LVDTs were recorded with thecorresponding load. The readings of the vertical LVDTs attachedto the specimen sides with a gage length of 120 mm were usedto record the axial deformation and axial strains at the surface ofthe specimen. The axial strains determined were also doublechecked by pasting two electrical strain gages of 60 mm gagelength on the sides of each specimen. The results of all tested spec-imens were recorded and analyzed in terms of their axial stressstrain curves as shown Figs. 36.

The shape of the stressstrain curves of the LWC tested, can becharacterised with a linear elastic response up to about 4050% ofits ultimate load carrying capacity; a curvilinear response up to thepeak followed by a post peak curvilinear segment of decreasingslope. Close to the peak load, vertical hairline cracks startedappearing on the surface of the specimen. The number and widthof these cracks kept on increasing with further increase in axialload until they formed a major shear crack at an angle of 45 withthe longitudinal axis of the cylinder. Because of the porous natureof LWA, the vertical cracks passed through the aggregates, and thusFig. 2. Test setup and instrumentation of the specimen used for determining thecomplete stressstrain diagram.

uilding Materials 25 (2011) 658662 66145

505% Silica Fume10% Silica Fume

M.J. Shannag / Construction and Bforced longitudinal pieces of the cylinder to split apart. Typical fail-ure modes of some of the LWC specimens tested are shown inFig. 7.

Fig. 3 illustrates that by adding up to 15% of silica fume, to themixes containing LWA, caused a signicant increase of 57% and

Fig. 4. Effect of y ash on the compressive behavior of LWC.

Fig. 5. Effect of silica fume, and y ash on the compressive behavior of LWC.

0

5

10

15

20

25

30

35

40

0 2000 4000 6000 8000 10000

Com

pres

sive

Stre

ss (M

Pa)

Strain mm/mm (10-6)

15% Silica Fume0% Silica Fume

Fig. 3. Effect of silica fume on the compressive behavior of LWC.14% in compressive strength and modulus of elasticity respectivelycompared to mixes without silica fume. But, adding up to 10% yash, to the same mixes, caused about 18% decrease in compressivestrength, with no change in modulus of elasticity, compared tomixes without y ash. The mixes containing 10% or more of silicafume, and 5% or more y ash, Figs. 5 and 6, exhibited a considerableincrease in compressive strength and modulus of elasticity com-pared to individual mixes containing same content of either silicafume or y ash.

The increase in the strength of the LWC due to the addition ofsilica fume and y ash may be attributed to the improved aggre-gatematrix bond associated with the formation of a less poroustransition zone and a better interlock between the paste and theaggregate [15,16]. The aggregatematrix bond improvement in-duced by these admixtures is probably the result of a combined l-ler and pozzolanic effect. The ller effect leads to reduction inporosity of the transition zone and provides a dense microstructureand thus increases the strength of the system. The pozzolanic effecthelps in the formation of bonds between the densely packed parti-cles in the transition zone through the pozzolanic reaction with thecalcium hydroxide liberated during the hydration of Portland ce-ment [15,16]. Therefore, it is recommended to use silica fume, y

Fig. 6. Effect of silica fume, and y ash on the compressive behavior of LWC.ash blends in producing structural LWC without sacricingstrength and workability by incorporating the required dosage ofsuperplasticizer.

Fig. 7. Typical failure modes of LWC cylinders tested under axial compression.

4. Conclusions

Based on the test results of this investigation, the following con-clusions can be drawn:

1. Lightweight concrete (LWC) mixes suitable for structural appli-cations were developed using locally available natural light-weight coarse and ne aggregates. The mixes developed had acompressive strength range of 22.543 MPa; an air dry densityof 19351995 kg/m3; and a high degree of workability.

2. The stressstrain diagrams plotted for the structural LWCmixesdeveloped were comparable to typical stressstrain diagramsfor normal weight concrete with relatively larger strain capacityat failure in case of LWC.

3. Replacing cement with 515% silica fume on weight basis forLWC, caused up to 57% and 14% increase in compressivestrength and modulus of elasticity respectively compared tomixes without silica fume. But, adding up to 10% y ash, as par-tial cement replacement by weight, to the same mixes, causedabout 18% decrease in compressive strength, with no changein modulus of elasticity, compared to mixes without y ash.Adding 10% or more of silica fume, and 5% or more y ashcaused a considerable increase in compressive strength andmodulus of elasticity compared to individual mixes containingsame contents of either silica fume or y ash.

Acknowledgements

tories for their assistance during the execution of the experimentalprogram.

References

[1] ACI 213-8. Guide for structural lightweight aggregate concrete. ACI 213-87.Manual of concrete practice, part 1. American Concrete Institute, Detroit,Michigan; 1995. p. 27.

[2] Neville AM. Properties of concrete. 4th ed. New York: JohnWiley and Sons Inc.;1996. p. 844.

[3] Mindess S, Young F, Darwin D. Concrete. 2nd ed. New Jersey: Prentice-Hall;1996. p. 644.

[4] Zhang MH, Gjorv OE. Characteristics of lightweight aggregate for high strengthconcrete. ACI Mater J 1991;88(2):1508.

[5] Hossain KMA. Properties of volcanic pumice based cement and lightweightconcrete. Cem Concr Res 2004;34:28391.

[6] Chi JM, Huang R, Yang CC, Chang JJ. Effect of aggregate properties on thestrength and stiffness of lightweight concrete. Cem Concr Compos2003;25(2):197205.

[7] Teo DC, Mannan MA, Kurian VJ, Ganapathy C. Lightweight concrete made fromoil palm shell (OPS): structural bond and durability properties. Build Environ2007;42:261421.

[8] Babu KG, Babu DS. Behavior of lightweight expanded polystyrene concretecontaining silica fume. Cem Concr Res 2003;33:75562.

[9] Chen B, Liu J. Experimental application of mineral admixtures in lightweightconcrete with high strength and workability. Constr Build Mater2008;22(4):6559.

[10] Waldron CJ. Demonstration of use of high-performance lightweight concretein bridge superstructure in Virginia. J Perform Constr Facil 2005;19(2):14654.

[11] Delsye CL, Abdul Mannan MD, Kurian JV. Flexural behavior of reinforcedlightweight concrete beams made with oil palm shell (OPS). J Adv ConcrTechnol 2006;4(3):110.

[12] Kayali O, Haque M, Zhu B. Some characteristics of high strength berreinforced lightweight aggregate concrete. ACI Mater J 1990;81(2):199204.

[13] ASTM C 33-97. Standard specication for concrete aggregates. Annual Book of

662 M.J. Shannag / Construction and Building Materials 25 (2011) 658662The author wishes to acknowledge the nancial support pro-vided by the Research Center at the College of Engineering of KingSaud University. He is also grateful to the engineers and the tech-nicians at the research center, and concrete and structural labora-ASTM Standards, vol. 4.02. p. 106.[14] ASTM C 150-97a. Standard specication for Portland cement. Annual Book of

ASTM Standards, vol. 4.01. p. 1347.[15] Malhotra VM, Carette GG, Sivasundaram V. Role of silica fume in concrete. In:

Proceedings of the international conference on advances in concretetechnology, CANMET, Ottawa, Canada; 1992.

[16] Popovics S. Portland cement-y ash silica fume systems in concrete. Adv CemBased Mater J 1993;1:8391.

Characteristics of lightweight concrete containing mineral admixturesIntroductionExperimental programMaterialsMix proportionsMixing and castingCuring and casting

Results and discussionWorkabilityDensityCompressive strengthSplitting tensile strengthStressstrain diagrams in compression

ConclusionsAcknowledgementsReferences