Construction and Building Materials 35 (2012) 84–91

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Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

New approach for shrinkage prediction of high-strength lightweightaggregate concrete

Hugo Costa a,b,⇑, Eduardo Júlio b, Jorge Lourenço a

a Department of Civil Engineering, Polytechnic Institute of Coimbra, Rua Pedro Nunes – Quinta da Nora, 3030-199 Coimbra, Portugalb ICIST, Department of Civil Engineering and Architecture, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

a r t i c l e i n f o a b s t r a c t

Article history:Received 4 March 2011Received in revised form 9 January 2012Accepted 25 February 2012

Keywords:ShrinkageHigh-strengthLightweight aggregate concrete (LWAC)

0950-0618/$ - see front matter � 2012 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2012.02.052

⇑ Corresponding author at: Department of Civil Engiof Coimbra, Rua Pedro Nunes – Quinta da Nora, 3030+351 960 071 786; fax: +351 239 790 311.

E-mail addresses: hcosta@isec.pt (H. Costa), ejujl@isec.pt (J. Lourenço).

The use of saturated lightweight aggregates (LWAs) on concrete provides an efficient internal curing,resulting in reduced shrinkage. Codes predict concrete shrinkage based on concrete strength, type ofcement, geometry and curing conditions, being mixture design parameters neglected. Herein, an exper-imental study is presented, considering several high-strength lightweight aggregate concrete (HSLWAC)mixtures with different densities and compressive strengths. Compared to codes prediction, significantlylower shrinkage values were measured. It was concluded that, besides the parameters considered bycodes, HSLWAC shrinkage also depends on the type, dosage and moisture of LWA. A new approach forshrinkage prediction of HSLWAC is presented.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The recent production of lightweight aggregates (LWAs) withhigh mechanical strength, associated with the use of more efficientbinders and third generation superplasticizers, allowed the devel-opment of high strength lightweight aggregate concrete (HSLWAC)[1]. Depending on the specified density, generally between 1500and 2000 kg/m3, it is possible to produce HSLWAC with compres-sive strength varying from 40 to 90 MPa [2].

The improved high-strength is usually obtained by designingbinding paste matrixes with reduced water/binder (W/B) massratio and considering pozzolanic additions, e.g. silica fume [3].However, due to the higher sensitivity to self-desiccation of thebinding matrix, these design options lead to higher shrinkage ofhigh performance concrete, produced with normal weight aggre-gates, and therefore to an increased risk of early-age cracking[4–6]. Nevertheless, this risk can be reduced using an efficientshrinkage-reducing admixture (SRA) [7,8].

When compared to normal weight concrete (NWC), differentstudies [9–14] proved that shrinkage in HSLWAC is usually lower.This happens when saturated LWA are used, since an efficientinternal curing is promoted by an uninterrupted hydration of thebinding paste, as a result of a continuous flow of LWA moisturestored in its alveolar internal structure, avoiding self-desiccation

ll rights reserved.

neering, Polytechnic Institute-199 Coimbra, Portugal. Tel.:

lio@civil.ist.utl.pt (E. Júlio),

[1,9,10,15,16]. This gives rise to expansive autogenous deforma-tions [10,12,15] and thus to reduced total shrinkage. Also improvedtransition zone between the LWA and the binding matrix is ob-served, reducing its permeability [1,17,18].

Despite the enhanced internal curing of HSLWAC, there is aremaining risk of superficial micro-cracking at early ages, due todifferential shrinkage between the cover mortar matrix and theinterior of the concrete element. Therefore, special care on superfi-cial concrete curing is needed and the use of a curing membrane orof an SRA admixture is mostly recommended.

The effectiveness of internal curing and shrinkage reduction ofHSLWAC is influenced by several factors: LWA proportioning;LWA saturation degree; specimen size; starting age of dryingshrinkage and type of cement and additions [10,12,15].

2. Design codes

According to Eurocode 2 (EC2) and Model Code 2010 (MC10)[19,20], the total shrinkage of NWC, ecs, is the sum of drying shrink-age, ecd, with autogenous shrinkage, eca. In line with these codes,shrinkage of both LWAC and HSLWAC is predicted based onexpressions developed for NWC, adjusted using a corrective coeffi-cient g.

However, that sum is a simplification, since both parameters aredue to the reduction of the relative humidity (RH) of the concrete,which in the case of drying shrinkage occurs due to evaporation atthe concrete’s surface, while in the case of autogenous deformationis caused by partial emptying of the gel pores as a consequence ofcement hydration [18,21]. If the concrete has a low RH, due to

Table 1Characterized properties of the Leca LWA.

LWA qP0 (kg/dm3) p0 (kg/dm3) HP (%) AS (%) AN (%) fCr (MPa)

HD2/4 1.33 0.74 9.6 11.5 1.6 11.0HD4/12 1.09 0.60 19.1 19.7 0.5 6.8MD 0.83 0.46 0.6 11.4 10.3 3.7XS 1.02 0.58 6.1 12.9 6.0 5.2

H. Costa et al. / Construction and Building Materials 35 (2012) 84–91 85

self-desiccation, it has a reduced shrinkage when submitted to dry-ing, but if it has high internal RH due to internal curing (using wetLWA) it will have a reduced shrinkage in autogenous conditions, oreven an expansion. This autogenous deformation is uniform in theconcrete element, occurring mainly in the first month, while dryingshrinkage is non-uniform in the cross-section, with higher shrink-age in the exposed surfaces than inside the element, dependingmainly on the moisture transport to the drying surfaces [21].Therefore, autogenous and drying shrinkage are not independentand their sum does not correspond, in reality, to total shrinkage.

For both EC2 and MC10, the evolution of ecd with age dependson concrete strength, cement type, geometry, curing conditionsand starting age of drying shrinkage, whereas the evolution of eca

with age only depends on the concrete strength, for EC2, and onconcrete strength and cement type, for MC10. Although both EC2and MC10 state that eca is significantly reduced for LWAC producedwith saturated LWA, due to internal curing provided by the aggre-gates’ moisture, this reduction is not quantified.

The approach of ACI [22,23] for shrinkage prediction is ad-dressed using a different expression for the evolution of ecd withage. According to this, besides the parameters considered on EC2and MC10, the evolution of ecd also depends on some propertiesof the concrete mixture, such as slump, air content, fine aggregatespercentage and cement dosage.

Design codes do not consider the LWA moisture to predict theshrinkage. However, it is known that to produce an HSLWAC, par-tially or totally saturated LWA must be used, and that it is essentialto accurately quantify and control the LWA absorption water in themixture design [24]. Dry LWA can also be used, considering addi-tional absorption water, which should be added during the mixing,but this will result on a mixture with partially saturated aggre-gates. Thus, it is better to previously mix this water with LWA dur-ing about 2 min. Otherwise, these will absorb the effective waterfrom the binding matrix, compromising the concrete workabilityand the specified properties [2]. For this reason, the beneficial ef-fect of the LWA moisture to the internal curing and to the expan-sive autogenous deformation needs to be considered.

Since EC2 and MC10 shrinkage predictions for HSLWAC lead tovalues higher than those measured in practice, presented in Sec-tion 4.2 ahead, and ACI prediction leads, in some cases, to evenhigher values, there is an obvious need to further investigate thisissue.

The study herein presented was conducted aiming to improvecodes prediction. Given that both the compressive strength andthe Young’s modulus of HSLWAC depend essentially on the bindingpaste and on the LWA type and dosage [2,24–26], an experimentalstudy was conducted considering several HSLWAC mixtures toquantify the influence of these parameters on drying shrinkageand on autogenous deformation.

3. Materials and methods

According to the wanted properties both in fresh and hardened states, namely,consistency, density and compressive strength, the HSLWAC mixtures were de-signed by adopting optimized proportions of cement, pozzolanic addition, light-weight and/or normal weight sand and coarse LWA. With this aim, thegranulometric adjustment was performed using Faury’s reference curve[24,26,27]. The adequate dosage of water was quantified for each mixture, provid-ing hydration of the binding powder and simultaneously ensuring the requestedconsistency and workability, taking into account the adopted superplasticizer.

3.1. Materials

The following constituents were adopted for the binding paste: cement CEM II/A-L 42.5R, an addition of silica fume, a third generation superplasticizer and water.Two types of normal weight sand, 0/2 mm (FS) and 0/4 mm (MS), and lightweightexpanded clay aggregate (Leca) sand, 0.5/3 mm (XS), were used. Three types of Lecawere adopted as coarse aggregates: structural Leca 2/4 mm (HD2/4), structural Leca4/12 mm (HD4/12) and structural Leca 4/10 mm (MD). Besides the granulometric

analysis of these aggregates, the following properties were also characterized (Table1): dry particle density, qP0; dry bulk density, p0; interior moisture, HP; absorptionfrom natural stocking state, AN; total absorption to saturated state, AS; and crushingstrength, fCr. First, saturated particle density was characterized, followed by the to-tal absorption (percentage of water by mass of the dry LWA), and then the dry par-ticle density was calculated. Total absorption corresponds to the total water insidethe LWA, in saturated state, and this is the responsible for the internal curing ofLWAC. Afterwards, the interior moisture was determined on stocking state, beingthis used in mixture design to quantify the mass dosage of each LWA. Since LWAsare not usually saturated in stock conditions, absorption from stocking state (per-centage of absorption water by mass of LWA in stocking state) was calculated, inorder to quantify the absorption water of the mixture [2]. However, the interiormoisture of the LWA, as well as the absorption water, is not considered neitherfor the effective water of the binding paste nor for the W/B ratio.

3.2. Mixture design method for HSLWAC

A mixture design method was specifically developed for HSLWAC [28], based onFaury’s method [27] and on Feret’s expression [24]. The desired density for concreteis assured by an appropriate selection of LWA and by adjusting the granulometriccurve of the mixture to Faury’s reference curve. The aimed compressive strength,flc,p, is obtained based on Feret́s expression, (1), by first estimating the strength ofthe binding paste, fc,b, which depends on the paste compactness, c, and on the Fer-et’s coefficients, kj, and by multiplying this by a corrective coefficient, Cf, that de-pends on the LWA strength and dosage [2,26]. The expression (2), proposed topredict Cf, was adjusted based on correlations defined between the density, qP0,and the crushing strength, fCr, of the LWA and on the corresponding reduction instrength of the HSLWAC [2,26]

fc;b ¼ kj � c2 ð1Þ

Cf ¼Yn

i¼1

1� Vabs;i

100� 0:2� 0:51q2:9

P0;i

� �ð2Þ

where Cf is the strength reducing coefficient of the LWA blend; Vabs,i is the absolutevolume dosage, in dm3, of LWA i; qP0,i is the dry particle density, in kg/dm3, of LWA i;and n is the number of different types of LWA used in the mixture.

3.3. HSLWAC produced mixtures

Several mixtures of HSLWAC were produced (Table 2) by considering differentaggregates and proportions and by varying the cement dosage, with 5% silica fumeaddition. First, the mixture compactness (relation between the volume of the solidconstituents and the total volume of the HSLWAC) and the water and admixturedosages were adjusted to the wanted density and consistency. Afterwards, thesewere combined with the remaining parameters, as coarse/fine volumetric relationand as fine and coarse aggregates pre-blends. The main parameters of the HSLWACmixtures, such as LWA and air proportions, W/B ratio and the predicted strengths(fc,b and flc,p), are presented in Table 2.

4. Shrinkage results and discussion

Shrinkage was measured not only for all the produced HSLWACmixtures, but also for most representative mortar matrixes ofHSLWAC, in order to assess the influence of mortar shrinkage onthe corresponding HSLWAC shrinkage. Both HSLWAC and mortarspecimens were stocked in a thermo-hygrometric chamber, at20 �C and 50% R.H., 24 h after its production.

4.1. Mortar matrixes

For each of the HSLWAC adopted mixtures (types B and E, withS5 slump class, and types C and F, with S4 slump class), mortar ma-trix specimens were produced. The constituents’ proportions foreach mortar were obtained by multiplying the proportions of the

Table 2Types of produced HSLWAC mixtures.

HSLWAC Density (kg/m3) Cement (kg/m3) Fine aggreg. Coarse LWA W/B Air (%) fc,b (MPa) flc,p (MPa) Slump class

Type (dm3/m3)

B500.S4 1950 500 FS + MS HD2/4 315 0.29 0.25 87 75 S4B500.S5 500 308 0.32 0.25 80 69 S5B425.S5 425 309 0.36 0.25 81 61 S5

E425.S4 1800 425 FS + XS HD2/4 354 0.32 0.25 77 57 S4E500.S5 500 350 0.32 0.25 80 61 S5E425.S5 425 338 0.36 0.25 81 53 S5

D425.S4 1800 425 FS + MS MD 326 0.32 0.20 79 45 S4

C500.S4 1800 500 FS + MS HD4/12 423 0.29 0.20 89 59 S4C425.S4 425 426 0.32 0.20 79 52 S4C350.S4 350 431 0.37 0.20 69 46 S4C500.S5 500 402 0.33 0.20 79 53 S5

F500.S4 1600 500 FS + XS HD4/12 423 0.29 0.20 89 51 S4F425.S4 425 426 0.32 0.20 79 45 S4F350.S4 350 429 0.37 0.20 69 40 S4F500.S5 500 415 0.33 0.20 79 46 S5

86 H. Costa et al. / Construction and Building Materials 35 (2012) 84–91

corresponding concrete mixture by the volumetric proportion ofthe mortar. The mortar mixtures type E and type F contain LWAsand with the respective absorption water; however, due to its re-duced particle size, the interior moisture will fast flow to the bind-ing matrix. The corresponding shrinkage, ems, was assessed bymeasuring the deformations on three prismatic specimens with40 � 40 � 160 mm3, starting at 24 h of age (after demoulding), un-til no significant evolution was detected. In Fig. 1, the evolution ofems with age of the produced mortar mixtures is presented. It wasregistered that the analysed mortars exhibit similar evolution forshrinkage curves, although presenting different amplitudes.Approximately 80% of the measured ems occurred during the first28 days of age. The obtained results proved that ems increases withthe following parameters: (i) increase of cement dosage; (ii) use ofLWA sand blended with FS (mixtures E and F), instead of the blendof FS and MS (mixtures B and C); (iii) decrease of sand dosage (mix-tures C and F) and, thus, with the increase of coarse LWA dosage.

4.2. HSLWAC mixtures

Both total shrinkage, ecs, and autogenous deformation, eca, wereexperimentally assessed using two pairs of prismatic specimens

0

200

400

600

800

1000

0 28 56 84 112 140 168 196

εε ms

(×10

-6)

Age (days)

0 28 56 84 112 140 168 196

Age (days)

B500.S5

B425.S5

0

200

400

600

800

1000

ε ms

( ×10

-6)

C500.S4

C425.S4

C350.S4

Fig. 1. Evolution of mortar shrinkage, em

with 150 � 150 � 600 mm3, starting at 24 h of age (after demoul-ding), according to the standard [28]. The specimens used to mea-sure eca were appropriately sealed with a triple layer of plastic filmand hot glue, and no mass variations were registered, assuring thatno evaporation occurred. In Fig. 2, the evolution of total shrinkage,ecs, for each HSLWAC mixture, as well as the corresponding EC2prediction, is presented. The shrinkage curves proposed by MC10and by ACI are also presented, and compared with the measuredvalues, in Figs. 3 and 4, respectively.

Shrinkage expressions proposed by EC2 and MC10, althoughdifferent, result in similar curves. Neither strength nor densityare considered in ACI for shrinkage prediction, but mixture param-eters, such as slump, fine aggregates percentage and air content,resulting when compared to EC2 in higher shrinkage values, fortypes B and E mixtures, and in lower values, for types C and Fmixtures.

For the mixtures produced with LWA with higher particle den-sity, qP0, (B, C, E and F), the experimental results showed that: (i)mixtures with higher W/B ratio, and consequently within S5 con-sistency class (fluid), exhibit higher shrinkage, ecs, than those with-in lower W/B ratio (and S4 consistency class); (ii) measured valuesof the total shrinkage, ecs, are less than 20% of EC2 predictions, for

0 28 56 84 112 140 168 196

Age (days)

0 28 56 84 112 140 168 196

Age (days)

0

200

400

600

800

1000

1200

E500.S5

E425.S5

ε ms

(×10

-6)

ε ms

(×10

-6)

0

200

400

600

800

1000

1200

F500.S4

F425.S4

F350.S4

s, with age for the tested mixtures.

-1000

100200300400500600700800900

1000

εε cs(×

10-6

)

Age (days)

B500.S5 B500.S5_EC2B425.S5 B425.S5_EC2B500.S4 B500.S4_EC2

-1000

100200300400500600700800900

1000

ε cs(×

10-6

)

Age (days)

E500.S5 E500.S5_EC2E425.S5 E425.S5_EC2E425.S4 E425.S5_EC2D425.S4 D425.S4_EC2

-1000

100200300400500600700800900

ε cs(×

10-6

)

Age (days)

C500.S5 C500.S5_EC2C500.S4 C500.S4_EC2C425.S4 C425.S4_EC2C350.S4 C350.S4_EC2

-1000

100200300400500600700800900

0 112 224 336 448 560 672 0 112 224 336 448 560 672

0 112 224 336 448 560 672 0 112 224 336 448 560 672

ε cs(×

10-6

)Age (days)

F500.S5 F500.S5_EC2F500.S4 F500.S4_EC2F425.S4 F425.S4_EC2F350.S4 F350.S4_EC2

Fig. 2. Evolution of measured values of total shrinkage, ecs, and corresponding EC2 curves.

-1000

100200300400500600700800900

1000

εε cs(×

10-6

)

Age (days)

B500.S5 B500.S5_MC10B425.S5 B425.S5_MC10B500.S4 B500.S4_MC10

-1000

100200300400500600700800900

1000

ε cs(×

10-6

)

Age (days)

E500.S5 E500.S5_MC10E425.S5 E425.S5_MC10E425.S4 E425.S5_MC10D425.S4 D425.S4_MC10

-1000

100200300400500600700800900

ε cs( ×

10-6

)

Age (days)

C500.S5 C500.S5_MC10C500.S4 C500.S4_MC10C425.S4 C425.S4_MC10C350.S4 C350.S4_MC10

-1000

100200300400500600700800900

0 112 224 336 448 560 672 0 112 224 336 448 560 672

0 112 224 336 448 560 672 0 112 224 336 448 560 672

ε cs(×

10-6

)

Age (days)

F500.S5 F500.S5_MC10F500.S4 F500.S4_MC10F425.S4 F425.S4_MC10F350.S4 F350.S4_MC10

Fig. 3. Evolution of measured values of total shrinkage, ecs, and corresponding MC10 curves.

H. Costa et al. / Construction and Building Materials 35 (2012) 84–91 87

S4 mixtures, and less than 30% of EC2 predictions, for S5 mixtures.For mixture produced with LWA with lower qP0 (mixture D), themeasured value of ecs is approximately 40% of the correspondingEC2 prediction. The codes predictions are in average 10 times high-er than the measured values, with minimum and maximum ratiosof 3 and 16, respectively.

4.2.1. Autogenous deformationFrom the results analysis, it was possible to assess the efficiency

of each LWA to stock internal moisture and to verify its transferrate with age to the binding paste, thus influencing autogenous

deformation in expansion. Aiming to quantify these deformations,the evolution of autogenous deformation, eca, was measured formost mixtures, being results presented in Fig. 5. Since it is assumedthat concrete shrinks, autogenous expansion due to internal curingprovided by LWA moisture is assumed as a negative shrinkage.This effect was also observed in other studies [11,15]. Since thedevelopment of eca is similar for all mixtures, independently ofusing saturated or quasi-saturated LWA, it can be concluded thatdrying shrinkage, ecd, is responsible for the main observed differ-ences in total shrinkage, thus having the type of LWA a significantinfluence. This influence can be explained taking into account that

-1000

100200300400500600700800900

1000

εε cs(×

10-6

)

Age (days)

B500.S5 B500.S5_ACIB425.S5 B425.S5_ACIB500.S4 B500.S4_ACI

-1000

100200300400500600700800900

1000

ε cs( ×

10-6

)

Age (days)

E500.S5 E500.S5_ACIE425.S5 E425.S5_ACIE425.S4 E425.S5_ACID425.S4 D425.S4_ACI

-1000

100200300400500600700800900

ε cs(×

10-6

)

Age (days)

C500.S5 C500.S5_ACIC500.S4 C500.S4_ACIC425.S4 C425.S4_ACIC350.S4 C350.S4_ACI

-1000

100200300400500600700800900

0 112 224 336 448 560 672 0 112 224 336 448 560 672

0 112 224 336 448 560 672 0 112 224 336 448 560 672

ε cs(×

10-6

)Age (days)

F500.S5 F500.S5_ACIF500.S4 F500.S4_ACIF425.S4 F425.S4_ACIF350.S4 F350.S4_ACI

Fig. 4. Evolution of measured values of total shrinkage, ecs, and corresponding ACI curves.

-120

-100

-80

-60

-40

-20

0

B500 B425E500 E425Ref. curve

Age (days)

εε ca

(×10

-6)

-140

-120

-100

-80

-60

-40

-20

00 14 28 42 56 70 84 98 112 126 140 0 14 28 42 56 70 84 98 112 126 140

C500 C425F500 F425D425 Ref. curve

Age (days)

ε ca

(×10

-6)

Fig. 5. Evolution of autogenous shrinkage, eca, for the HSLWAC and of the estimated reference curve.

88 H. Costa et al. / Construction and Building Materials 35 (2012) 84–91

LWA with higher density and stiffness has higher capacity to pre-vent drying shrinkage. Additionally, the alveolar internal structureof the LWA is related with its density and has high influence on itscapacity to release water to the binding paste. Thus, and despitethe common variance of the LWA’s open porosity, the saturatedLWA with high density and strength have high efficiency to slowlyhydrate the binding matrix. Consequently, and due to this internalcuring, an enhanced transition zone, between the saturated LWAand the surrounding paste, is obtained, also with reduced porosityand permeability [1]. Therefore, the influence of the LWA densityon the drying shrinkage is performed: (i) directly, whenever theLWA with higher density oppose, through the higher stiffness,the drying shrinkage; (ii) indirectly, whenever the saturated LWAwith higher density promote a more efficient internal curing,reducing the permeability of the binding matrix, and reducingthe drying shrinkage. When partially saturated LWA are used[10,13,15], the internal curing is less efficient, and the expansiveautogenous deformation is lower, so that parameter must beconsidered.

To conservatively predict the autogenous deformation, eca,p, anenvelope was established with expression (3), as a function of bothtime and parameter cas, the latter depending on the coarse LWA.Two different values were estimated for cas: 110, for mixtures (Band E), and 130, for mixtures (C, F, D), resulting into the referencecurves of Fig. 5.

eca;p ¼ �cas � ð1� expð�0:35� ðt � t0Þ0:5ÞÞ ð3Þ

The production of HSLWAC should not be conducted using dryLWA, since these will absorb effective water from the mixture,therefore changing the concrete properties, both in fresh and hard-ened states. Even so, if reduced LWA’s moisture is considered inHSLWAC production, expansive autogenous deformation will occur[6,10]. Nevertheless, the advisable situation corresponds to adoptpartially or totally saturated LWA, resulting on expansive autoge-nous deformations. Based on the results of the present study, aswell as on the results obtained by other authors [10,13,15], newrecommendations to predict the autogenous deformation, depend-ing on those parameters, are presented ahead.

4.2.2. Drying shrinkageAlthough drying shrinkage, ecd, cannot be measured on real sys-

tems, thus being difficult to quantify it individually, as explained inSection 2, a simplified approximation to its evolution was com-puted for each mixture, by subtracting the estimated values of eca,p,in expression (3), to the measured values of ecs, resulting in theevolution curves presented in Fig. 6. This simplification was con-sidered to follow the approach in codes, allowing to quantify theinfluence of the design parameters on the shrinkage behaviour ofHSLWAC.

-100

0

100

200

300

400

500

εε c(×

10-6

)

Age (days)

B500.S5_cs B500.S5_cdB425.S5_cs B425.S5_cdB500.S4_cs B500.S4_cd

-100

0

100

200

300

400

500

600

ε c(×

10-6

)

Age (days)

E500.S5_cs E500.S5_cdE425.S5_cs E425.S5_cdE425.S4_cs E425.S4_cdD425.S4_cs D425.S4_cd

-100

0

100

200

300

400

500

ε c(×

10-6

)

Age (days)

C500.S5_cs C500.S5_cdC500.S4_cs C500.S4_cdC425.S4_cs C425.S4_cdC350.S4_cs C350.S4_cd

-100

0

100

200

300

400

500

0 112 224 336 448 560 672 0 112 224 336 448 560 672

0 112 224 336 448 560 672 0 112 224 336 448 560 672

ε c( ×

10-6

)Age (days)

F500.S5_cs F500.S5_cdF500.S4_cs F500.S4_cdF425.S4_cs F425.S4_cdF350.S4_cs F350.S4_cd

Fig. 6. Evolution of shrinkage, ec (drying, ecd, and total, ecs), of the produced HSLWAC.

H. Costa et al. / Construction and Building Materials 35 (2012) 84–91 89

Analysing the experimental results and comparing these withcodes predictions, three main aspects were identified as having asignificant influence on HSLWAC shrinkage: (i) the binding pastestrength; (ii) the type and dosage of LWA and its saturation degree,corroborating the conclusions of other studies [6,10]; and (iii) theW/B ratio, which is also related with the HSLWAC’s consistencyand workability.

Hence, it is proposed that the average value of concrete com-pressive strength, fcm, currently used to determine the evolutionof ecd, be replaced by the value of the compressive strength ofthe HSLWAC binding paste, fc,b. This is justified by the fact thatan HSLWAC with a high-strength binding paste and a high volumeof LWA will have reduced density and a significant reduction ofcompressive strength, although presenting reduced shrinkage. Thisparameter, fc,b, can be predicted by the Feret’s expression (1). Alter-natively, this value can be also obtained by dividing the compres-sive strength of the HSLWAC, flcm, by the strength reductioncoefficient (2), Cf, intrinsic to the type and dosage of the used LWA.

Type and dosage of LWA used in each mixture proved to havesignificant influence on HSLWAC drying shrinkage. In fact, high

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500

HD2/4HD4/12XSMDM

Csh

V (dm 3/m 3)

Fig. 7. Coefficient Csh, function of type and dosage of LWA, for shrinkage prediction.

dosage of LWA with lower density (and consequently less stiffness)has less efficiency on opposing to the high shrinkage of the mortarmatrix (Fig. 1). In order to quantify this behaviour, a coefficient, Csh,presented ahead, was determined by first analysing individuallythe type and dosage of each LWA with the increase of ecd and thenby adjusting the linear functions that can be observed in Fig. 7.Afterwards, a correlation between the module of the derivative ofeach linear function, msh, and the LWA particle density, qP0, couldbe obtained (Fig. 8), similarly to the procedure adopted in thestudy conducted to predict HSLWAC’s strength and modulus ofelasticity [2,26].

The consistency of HSLWAC is related mainly with the W/B ratioand with the admixture’s type and dosage. With the decrease ofthe W/B ratio, the drying shrinkage also decreases, mainly due towater reduction in the binding matrix but also due to the reductionof its permeability. By studying the influence of W/B ratio on dryingshrinkage, between mixtures with similar LWA type and dosageand equal cement dosage and air content, a correction coefficient,CW/B, ahead presented, could be obtained.

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.4 0.6 0.8 1 1.2 1.4 1.6

msh

ρρ P0 (kg/dm3)

msh=0.13×0.25ρP015

(R2=0.98)

Fig. 8. Correlation between dry particle density, qP0, and the coefficient msh of theLWA.

Table 3Proposal for autogenous deformation of HSLWAC.

LWA saturationdegree (%)

Autogenousdeformation

Recommendation for eca

[0; 30] Shrinkage EC2 expression[30; 40] �Null 0[40; 60] Expansion Expression (3), with cas = 40[60; 100] Expansion Expression (3), with cas = 80

90 H. Costa et al. / Construction and Building Materials 35 (2012) 84–91

Finally, drying shrinkage can be predicted for HSLWAC, consid-ering the corrections proposed in this study together with EC2expressions.

5. New approach for shrinkage prediction of HSLWAC

Based on the study herein presented, the following changes toEC2 are suggested to improve the prediction of drying shrinkage,ecd,c:

(i) To replace the concrete compressive strength, fcm, by thebinding paste strength, fc,b, in the expression (Eq. B.11) ofAnnex B.2.1 used to determine ecd,0.

(ii) To replace the coefficient g3, defined according to theSection 11.3.3 (2) of EC2, to correct ecd, by expression (4),where the effect of the W/B ratio and of the type and dosageof LWA are considered, through the respective coefficientsCW/B and Csh, given by expressions (5) and (6).

g3 ¼ CW=B=Csh ð4Þ

CW=B ¼ 1:7� ðW=BÞ0:8 ð5Þ

Csh ¼Yn

i¼1

1� Vabs;i

100� 0:13� 0:25q15

P0;i

� �ð6Þ

Based on the results of the present study, as well as on otherstudies [10,13,15], the recommendations presented in Table 3can be used to predict autogenous deformation, eca, dependingon LWA saturation degree.

0

100

200

300

400

500

εε cd

(×10

-6)

Age (days)

B500.S5_cd B500.S5_cd.cB425.S5_cd B425.S5_cd.cB500.S4_cd B500.S4_cd.c

0

100

200

300

400

500

ε cd

(×10

-6)

Age (days)

C500.S5_cd C500.S5_cd.cC500.S4_cd C500.S4_cd.cC425.S4_cd C425.S4_cd.cC350.S4_cd C350.S4_cd.c

0 112 224 336 448 560 672

0 112 224 336 448 560 672

Fig. 9. Evolution of drying shrinkage, ecd, and of the corrected pr

With the proposed corrections, the drying shrinkage predictionpresents a good approximation to the experimental results ob-tained for the HSLWAC produced with Leca LWA (Fig. 9). Compar-ing to EC2, predictions reduce in average from 10 to just 1.5 timesthe measured values.

6. Conclusions

Total shrinkage considered by concrete design codes usuallycomprehends both drying and autogenous shrinkage, which de-pend essentially on: the concrete compressive strength, the ce-ment type, the geometry and the curing conditions.

Shrinkage measured on HSLWAC specimens showed that codespredictions are not accurate in this case, presenting significantlyhigh values, on average 10 times higher than the correspondingexperimental results. This is mainly due to the fact that codes donot consider the favourable effect of the internal moisture ofLWA on autogenous deformation. In fact, for HSLWAC producedwith saturated LWA, the autogenous deformation is expansive,due to internal curing, thus opposing to drying shrinkage.

Also drying shrinkage predicted by codes is much higher thanmeasured values in HSLWAC specimens. The study herein pre-sented proves that this is mainly due to neglected factors in shrink-age prediction, namely: the binding paste strength; the water/binder ratio; the type and dosage of LWA.

A new approach is presented, where corrections are proposed,using the factors previously mentioned, to improve EC2 shrinkageprediction. With those corrections, EC2 predictions exhibited agood approximation to measured values, reducing from 10 to 1.5the ratio between predicted and measured values. However, andsince this study was developed using Leca LWA, further researchis previewed to adjust corrections to other types of manufacturedLWA, such as sintered fly ash or expanded shale.

Acknowledgments

The authors acknowledge: (i) the financial support of the Portu-guese Science and Technology Foundation (FCT) through the PhDGrant number SFRH/BD/44217/2008; (ii) the material supply madeby the companies Sain-Gobain Webber, Secil, Sika and Argilis.

0

100

200

300

400

500

600

ε cd

(×10

-6)

Age (days)

E425.S4_cd E425.S4_cd.cE500.S5_cd E500.S5_cd.cE425.S5_cd E425.S5_cd.cD425.S4_cd D425.S4_cd.c

0

100

200

300

400

500

0 112 224 336 448 560 672

0 112 224 336 448 560 672

ε cd

(×10

-6)

Age (days)

F500.S5_cd F500.S5_cd.cF500.S4_cd F500.S4_cd.cF425.S4_cd F425.S4_cd.cF350.S4_cd F350.S4_cd.c

ediction of drying shrinkage, ecd,c, of the produced HSLWAC.

H. Costa et al. / Construction and Building Materials 35 (2012) 84–91 91

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