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Journal of Cleaner Production 112 (2016) 690e701

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

Development of Ultra-Lightweight Fibre Reinforced Concrete applyingexpanded waste glass

R. Yu a, *, D.V. van Onna a, P. Spiesz a, b, Q.L. Yu a, H.J.H. Brouwers a

a Department of the Built Environment, Eindhoven University of Technology, The Netherlandsb ENCI HeidelbergCement Benelux, The Netherlands

a r t i c l e i n f o

Article history:Received 18 December 2014Received in revised form16 June 2015Accepted 14 July 2015Available online 21 July 2015

Keywords:Ultra-Lightweight Fibre Reinforced Concrete(ULFRC)Expanded waste glassPolypropylene fibresDensityThermal conductivityMechanical properties

* Corresponding author. Tel.: þ31 (0) 40 247 5469;E-mail address: r.yu@tue.nl (R. Yu).

http://dx.doi.org/10.1016/j.jclepro.2015.07.0820959-6526/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

This paper presents the development of Ultra-Lightweight Fibre Reinforced Concrete (ULFRC) applyingexpanded waste glass in form of lightweight aggregates. The modified Andreasen & Andersen particlepacking model and an optimal amount of polypropylene fibres are utilized in the design and productionof ULFRC. The density, mechanical properties and thermal conductivity of the developed ULFRC aremeasured and analyzed. The ULFRC with a dry density of 750 kg/m3 is produced. It is found that hy-bridization and an optimized amount of polypropylene fibres are beneficial for improving the mechanicalproperties of ULFRC. Moreover, compared to the other lightweight concretes with the same density, theULFRC developed in this study has improved mechanical properties and lower thermal conductivity,therefore it can be utilized as a new material for the production of floating structures, insulating ele-ments or even for load bearing applications. As sustainable development is currently a crucial globalissue and various industries are striving to save the energy and lower the environmental impact, thedeveloped ULFRC has a good prospect in the near future.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Concrete is one of the most widely used building materialsthroughout the world. Nevertheless, due to the fact that the sus-tainable development is currently a crucial global issue and variousindustries are striving to save the energy and lower the environ-mental impact, also concrete is more frequently required to possessmore advanced characteristics, such as low cost, low density, lowthermal conductivity, good mechanical properties and eco-friendliness (Yang et al., 2013, 2014; Yu and Shui, 2013; Yu et al.,2014b; Bravo et al., 2015). Lightweight concrete (LWC) is one typeof concrete having a dry density of not less than 800 kg/m3 and notmore than 2000 kg/m3 (EN 206-1, 2001), which can be traced backto around 3000 years ago (Chandra and Berntsson, 2003). Someinvestigations have demonstrated that the thermal insulation andfire resistance capacities of LWC are much better than for normalweight concrete (NWC), and LWC is suitable to be applied as bothstructural and non-structural material (Pelisser et al., 2012; Shafighet al., 2014). In general, the methods of LWC production can be

fax: þ31 (0) 40 243 8595.

mainly summarized as follows (Chandra and Berntsson, 2003): 1)Adding lightweight aggregates (LWA) into concrete mixtures,replacing partially or completely conventional normal density ag-gregates; 2) Adding a foaming or air-entraining agent into themixture in order to introduce a certain volume of air voids into thematrix of concrete; 3) Gap grading (poor packing density of thesolid ingredients) of themixture (e.g. applying no fine aggregates inthe concrete mixture). Nevertheless, due to the use of variousLWAs, foaming agents and applied production methods, it ispossible to obtain a large variety of the properties (density, me-chanical properties, thermal properties and durability) of LWCs(Chandra and Berntsson, 2003; Topçu et al., 2010; Neville, 2011;Schauerte and Trettin, 2012). Additionally, experimental in-vestigations (Neville, 2011) showed that both thermal conductivityand mechanical properties of LWC are strongly linked with itsdensity. Neville (2011) reported that there is a linear correlationbetween the thermal conductivity and the density of LWC producedwith different types of LWAs, such as pumice, vermiculite, cinders,expanded shale and expanded slag. Chandra and Berntsson (2003)presented a relationship between the compressive strength anddensity of LWC applying expanded clay as LWA, for which thecompressive strength of LWC increases from 7 to 16 MPa as itsdensity increases from 1000 to 1500 kg/m3. Therefore, it is difficult

Delta:1_given nameDelta:1_surnameDelta:1_given nameDelta:1_surnameDelta:1_given namemailto:r.yu@tue.nlhttp://crossmark.crossref.org/dialog/?doi=10.1016/j.jclepro.2015.07.082&domain=pdfwww.sciencedirect.com/science/journal/09596526http://www.elsevier.com/locate/jcleprohttp://dx.doi.org/10.1016/j.jclepro.2015.07.082http://dx.doi.org/10.1016/j.jclepro.2015.07.082http://dx.doi.org/10.1016/j.jclepro.2015.07.082

Table 1Chemical composition of the used cement and LWA.

Substance Cement (mass %) LWAa (mass %)

CaO 64.60 8 ± 2SiO2 20.08 71 ± 2Al2O3 4.98 2 ± 0.3Fe2O3 3.24 0.5 ± 0.2K2O 0.53 1 ± 0.2Na2O 0.27 13 ± 1SO3 3.13 eMgO 1.98 2 ± 1TiO2 0.30 eMn3O4 0.10 eP2O5 0.74 eCl� 0.05

Fig. 1. Utilized lightweight aggregates (LWA) (expanded waste glass).

Table 2Physical properties of the used light-weight aggregates (LWA).

Materials sizerange (mm)

Bulkdensity(kg/m3)

Specificdensity(kg/m3)

Crushingresistance(N/mm2)

1 h waterabsorption(wt.%)

24 h waterabsorption(wt.%)

LWA 0.1-0.3 450 810 >3.5 1.06 2.81LWA 0.25-0.5 300 540 >2.9 0.88 3.90LWA 0.5-1.0 350 450 >2.6 1.59 8.50LWA 1.0-2.0 220 350 >2.4 1.71 7.63LWA 2.0-4.0 190 310 >2.2 0.55 7.80LWA 4.0-8.0 170 300 >2.0 1.30 9.11

(Part of the data is obtained from (Yu et al., 2015a)).

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701692

Larrard and Sedran (1994, 2002) postulated different approaches todesign concrete: the Linear Packing Density Model (LPDM), SolidSuspension Model (SSM) and Compressive Packing Model (CPM).Fennis et al. (2009) developed a concrete mix design method basedon the concepts of De Larrard and Sedran. To consider the influenceof fine particles on the particle packing skeleton, Funk and Dinger(1994) proposed a modified model based on the Andreasen andAndersen equation In this study, the so-called modified Andreasenand Andersen particle packing model is utilized to design theconcrete mixture, which is shown as follows (Andreasen andAndersen, 1930; Funk and Dinger, 1994; Brouwers and Radix,2005):

PðDÞ ¼ Dq � Dqmin

Dqmax � Dqmin(1)

where D is the particle size (mm), P(D) is the fraction of the totalsolids smaller than size D, Dmax is the maximum particle size (mm),Dmin is the minimum particle size (mm) and q is the distributionmodulus.

The modified Andreasen and Andersen particle packing modelhas already been successfully employed in optimization algorithmsfor the design of different types of concrete (Hüsken and Brouwers,2008; Yu et al., 2014c, 2014d, 2014e, 2015b; Quercia et al., 2014).Different types of concrete can be designed using Eq. (1) byapplying different values of the distribution modulus q, as it de-termines the proportion between the fine and coarse particles inthe mixture. In this study, based on the recommendations given byHunger (2010) and Yu et al. (2015a), the value of q is fixed at 0.35.The modified Andreasen and Andersen model (Eq. (1)) acts as atarget function for the optimization of the composition of mixtureof granular materials. The proportions of each individual materialin themix are adjusted until an optimum fit between the composedmix and the target curve is reached, using an optimization algo-rithm based on the Least Squares Method (LSM), as presented asfollows:

RSS ¼Pn

i¼1�Pmix

�Diþ1i

�� Ptar

�Diþ1i

��2

n(2)

where Pmix is the composed mix, and the Ptar is the target gradingcalculated from Eq. (1).

As commonly accepted, the quality of the curve fit is assessed bythe coefficient of determination (R2), since it gives a value for thecorrelation between the grading of the target curve and thecomposed mix. Therefore, the coefficient of determination (R2) isutilized in this study to obtain the optimized mixture given by:

R2 ¼ 1�Pn

i¼1�Pmix

�Diþ1i

�� Ptar

�Diþ1i

��2

Pni¼1

�Pmix

�Diþ1i

�� Pmix

�2 (3)

Fig. 2. SEM pictures of the utilized light weight aggregates (LWA).

Fig. 3. Utilized polypropylene fibres: a) Length ¼ 18 mm, diameter ¼ 22 mm, b) Length ¼ 45 mm, diameter ¼ 0.5 mm.

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701 693

Where Pmix ¼ 1nPn

i¼1PmixðDiþ1i Þ, which represents the mean of theentire distribution.

Additionally, the water and SP amounts are very important toproduce the ULFRC. As shown in Table 2, the applied LWAs have avery low particle density, ranging from 300 to 810 kg/m3, whichindicates the possibility of segregation of cement paste and theLWA in fresh concrete state, if the amount of water and SP amountare not properly selected. However, due to the fact that the

polypropylene fibres can reduce the workability of concrete, the SPand water amount should be appropriately adjusted compared tothe ULWC mixtures without fibres. Hence, to simultaneously avoidthe appearance of segregation and mostly improve the workabilityof ULFRC, a water/cement ratio of 0.4 and added SP amount of 0.5%by the mass of cement are determined in this study. The compo-sitions of the ULFRC mixtures developed based on the optimizedparticle packing model are listed in Table 3. The resulting integral

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701694

grading curve of the composite mixes is shown in Fig. 4 (thecalculated R2 is about 0.999). In total, 1 reference mixture (withoutfibres) and 9 ULFRC mixtures are designed in this study. Accordingto the recommendation of polypropylene fibre amount from thefibre supplier, ULFRC mixtures No. 1e3 (with only LPF) aredesigned. Then, to evaluate the hybrid polypropylene fibres influ-ence on the properties of ULFRC, the LPF and SPF are simultaneouslyadded into the concretematrix, while the total fibre amount is fixedat 0.2% (vol.). Finally, to further analyze the influence of the higherfibre content on the characteristics of ULFRC, the LPF is added intothe concrete matrix at 0.6%, 0.9% and 1.2% (vol.), respectively.

2.2.2. Mixing procedures and fresh behaviourIn this study, the cement and LWA are firstly mixed in the mixer

in dry state for about 1min. Then, around 75% of water is added andmixed with the cement and LWA for about 2 min. Afterwards, theSP and remaining water are added into the mixer and mixed foradditional two minutes. Subsequently, the polypropylene fibres areslowly added into themixer until the end of the mixing procedures.The mixing process takes about 7 min in total. The mixing is alwaysexecuted under laboratory conditions with dried and temperedaggregates and powder materials. The room temperature duringthe mixing and testing is constant, around 21 �C. Following theEuropean standard BS EN 12350-5 (2009), the slump and flow ofthe fresh ULFRC are about 135 mm and 348 mm (corresponding toS3 and F2 classes, according to EN 206-1), respectively.

2.2.3. Hardened densityAfter mixing, the fresh ULFRC is cast into molds of with different

sizes: 100 mm� 100 mm� 100 mm,150 mm� 150 mm� 150 mmand 100 mm � 100 mm � 500 mm, and compacted on a vibrationtable for about 1 min. Subsequently, the cubes and beams arestripped from the moulds after 24 h from casting, and stored in aclimate chamber with a relative humidity of over 95%, at roomtemperature (around 20 �C), following EN 12390-2 (2000). Aftercuring for 28 days, the small cubes (100 mm � 100 mm � 100 mm)are utilized to determine the density of ULFRC, following EN 12390-7(2009). In this study, two types of densities are measured: apparentwet and dry density. For the wet density, the sample is measureddirectly with dry surface after curing for 28 days. Prior to the dry-density measurement, the samples are dried in a ventilated ovenat 105 �C until a constant mass is reached.

2.2.4. Mechanical propertiesThe cubes (150mm� 150mm� 150mm) are used to determine

the compressive strength of ULFRC after 28 days, following EN12390-3 (2009), while the beams (100 mm � 100 mm � 500 mm)are subjected to the 4-point bending test, as described in EN 12390-5(2009). For the 4-point bending test, the span between the two

Table 3Recipes of the developed ULFRC.

No. C kg/m3 LWA-1 kg/m3 LWA-2 kg/m3 LWA-3 kg/m3 LWA-4 kg/m3

Ref. 350.0 92.2 16.1 35.4 31.71 350.0 92.2 16.1 35.4 31.72 350.0 92.2 16.1 35.4 31.73 350.0 92.2 16.1 35.4 31.74 350.0 92.2 16.1 35.4 31.75 350.0 92.2 16.1 35.4 31.76 350.0 92.2 16.1 35.4 31.77 350.0 92.2 16.1 35.4 31.78 350.0 92.2 16.1 35.4 31.79 350.0 92.2 16.1 35.4 31.7

(C: Cement, LWA-1: 0.1e0.3, LWA-2: 0.25e0.5, LWA-3: 0.5e1.0, LWA-4: 1.0e2.0, LWA-5fibre, SPF: Short polypropylene fibre, Ref.: reference sample).

supported points at the bottom is 400 mm. To obtain the flexuralload over the middle displacement curve, a Linear Variable Differ-ential Transformer (LVDT) mounted on the surface of the testedsamples is utilized to record the displacement. During the test, theset-up is running in a displacement control mode, which is set at0.1mm/min. Before the test, the calibration of the used LVDT is done.

2.2.5. Thermal conductivitySimilar to the density measurements, for the thermal conduc-

tivity test, the samples (100 mm � 100 mm � 100 mm) are dried ina ventilated oven at 105 �C until a constant mass following EN12390-7 (2009). Afterwards, the samples are cooled down to theroom temperature. Finally, the thermal conductivity is measured bya heat transfer analyzer (ISOMET model, 2014). This analyzer ap-plies a dynamic measurement method to determine simulta-neously the volumetric heat capacity (J/(m3$K)) and the thermalconductivity (W/(m K)) of materials with a measurement time ofabout 15 min. The measurement is based on the analysis of thetemperature response of the tested sample to heat flow impulses,while the heat flow is excited by the electrical heating of a resistorheater inserted into the probe, which is in direct contact with thetested samples.

3. Results and discussion

3.1. Densities

The apparent wet and dry densities of ULFRC are illustrated inFig. 5. It is important to notice that the dry densities of all thedesigned ULFRC are less than 800 kg/m3, which is out of the rangeof LWC defined by the standard e EN 206-1 (2001). Therefore, itcan be stated that the concrete developed in this study is an ultra-lightweight concrete. Due to the very low density, the developedULFRC has an ability to float on the water, which could besignificantly beneficial for its wider application in practice. Forinstance, the developed ULFRC can be applied in the production ofmarine and floating constructions, since the available lands areprominently decreasing and there is a strong demand for devel-oping new building types. Moreover, due to the fact that lowdensity normally means relatively low thermal conductivity, thedeveloped ULFRC may also be utilized as thermal insulatingbuilding material.

From Fig. 5, it can also noticed that the dry densities of themixtures No.1e7 fluctuate around 750 kg/m3, while the densities ofthe mixtures No. 8 and No. 9 are relatively smaller than those ofother mixtures. Particularly, for the concrete mixture No. 9, whosedry and wet densities are around 720 and 790 kg/m3, respectively.This should be attributed to the effect of large amount of fibres onthe internal structure of ULFRC. As shown in Table 3, around 1.2%

LWA-5 kg/m3 LWA-6 kg/m3 W kg/m3 SP kg/m3 LPF vol.% SPF vol.%

54.6 68.9 140 1.75 0 054.6 68.9 140 1.75 0.1 054.6 68.9 140 1.75 0.2 054.6 68.9 140 1.75 0.3 054.6 68.9 140 1.75 0.15 0.0554.6 68.9 140 1.75 0.1 0.154.6 68.9 140 1.75 0.05 0.1554.6 68.9 140 1.75 0.6 054.6 68.9 140 1.75 0.9 054.6 68.9 140 1.75 1.2 0

: 2.0e4.0, LWA-6: 4.0e8.0, W: Water, SP: Superplasticizer, LPF: Long polypropylene

0

20

40

60

80

100

0.01 0.1 1 10 100 1000 10000 100000Particle size (μm )

Cum

ulat

ive

curv

e (%

)CEM I 52.5 R

LWA 0.1-0.3

LWA 0.25-0.5

LWA 0.5-1

LWA 1-2

LWA 2-4

LWA 4-8

Target curve

Composed curve

Fig. 4. PSDs of the ingredients, the target curve and the resulting integral grading curve of the composed mixture.

600

700

800

900

Ref. No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 No. 9

ULFRC mixtures

Den

sity

( kg/m3)

Wet densityDry density

Fig. 5. Densities of the designed ULFRC.

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701 695

LPF (vol.) is added in the mixture No. 9. Due to the fact that theutilized LPF is relatively stiff, it can push the surrounding particles(mainly low density LWA) and alter the structure of the granularskeleton. Therefore, when the additional fibre content is relativelyhigh, a number of air voids will be entrapped into the ULFRC, whichcause that the concrete is more porous (as shown in Fig. 6) and itsdensity is decreased. The porous structure of ULFRC (as shown inFig. 6) may cause a negative influence on its mechanical properties,which is elaborated in the following part.

3.2. Mechanical properties

3.2.1. Compressive behaviourFig. 7 reveals the compressive strength of the developed ULFRC

at 28 days. It is clear that the addition of polypropylene fibres

improves the compressive strength of ULWC, which is similar to theeffect of steel fibres on the mechanical properties of normal densityconcrete. Moreover, the results for mixtures No. 1e3 (with rec-ommended fibre amount by the supplier, 0.1%, 0.2% and 0.3% vol.)show that with an increase of the LPF amount, the compressivestrength of ULFRC at 28 days gradually increases from 11.8 to13.1 MPa. These results are in accordance with the phenomenaobserved by other researchers (Kayali et al., 2003; Mazaheripouret al., 2011; Libre et al., 2011). The polypropylene fibers couldrestrict the crack formation and development and thus lead to anincrease of the compressive strength. Moreover, in this study, it canbe noticed that the utilized long polypropylene fibre has a relativelyrough surface (as shown in Fig. 3), which can strengthen theadhesion between the concrete matrix and fibres, and is beneficialfor improving the compressive strength of ULFRC.

Fig. 6. Lightweight aggregates distribution in ULFRC cross-section, (a): without fibres (reference), (b): with 0.6% LPF, (c): with 0.9% LPF, (d): with 1.2% LPF.

0

3

6

9

12

15

18

Ref. No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 No. 9

ULFRC mixtures

Com

pres

sive

stre

ngth

at 2

8 da

ys (MPa

)

Fig. 7. Compressive strength (28 days) of the designed ULFRC.

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701696

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701 697

The results for mixtures No. 4e6 (with hybrid fibres) showthat the compressive strength strongly depends on the propor-tion of long fibres (LPF) and short fibres (SPF). For instance, whenthe hybrid fibres are composed of 75% of LPF and 25% of SPF, thecompressive strength of ULFRC is around 13.0 MPa, which ishigher than that for the sample with only 0.2% LPF (vol.)(12.1 MPa). Then, with an increasing SPF amount, the compres-sive strength slightly decreases to 11.9 MPa. This phenomenonshould be attributed to the different reinforcing functions thatLPF and SPF play in concrete. As already demonstrated byMarkovic (2006), SPF can efficiently bridge micro-cracks, whilethe LPF is more efficient in resisting the development of macro-cracks. Hence, when the micro-cracks are just generated in theconcrete specimen, the SPF can effectively bridge them. As themicro-cracks grow and merge into larger macro-cracks, the LPFbecomes increasingly active in the crack bridging. Hence,appropriate hybridization of LPF and SPF is beneficial for furtherimprovement of the compressive strength of ULFRC.

To clarify the effect of relatively high fibre dosages (compared tothe amount recommended by the fibre supplier), the compressivestrengths of the concrete mixtures with 0.6%, 0.9% and 1.2% (vol.) ofLPF are tested, as shown in Fig. 7 (mixtures No. 7e9). It is importantto notice that the compressive strength of the mixture with 0.6%(vol.) of LPF is the highest among all the mixtures. However, with afurther increase of LPF amount, the compressive strength of ULFRCslightly decreases, which is contrary to the results observed formixtures No. 1e3. This should be attributed to the effect of LPF onthe internal structure of ULFRC. As mentioned before, due to thefact that the utilized LWAs have very low densities (300e800 kg/m3), it is relatively easy for the LPF to push apart the big particlesand disturb the structure of the granular skeleton. When the LPFcontent is relatively high, more air voids will be entrapped into theULFRC (as presented in Fig. 6), which is negative for the strengthimprovement of concrete. This can also be demonstrated by thedensity results shown in Fig. 5 and cross section of the ULFRCshown in Fig. 6. Although the addition of polypropylene fibres isbeneficial for improving the compressive strength of ULFRC, theexcessive LPF can significantly disturb the internal structure ofconcrete, which simultaneously decreases the density andcompressive strength of ULFRC. Hence, it can be concluded that anappropriate LPF amount is crucial to produce ULFRC with anoptimal compressive strength.

The relationship between the compressive strength and drydensity for different types of LWC retrieved from the literatureand for ULFRC developed here is shown in Fig. 8. A clear increasetrend of the compressive strength can be observed when the drydensities of LWCs increase from about 400 kg/m3 to around2000 kg/m3. Moreover, it is important to notice that thecompressive strengths of ULFRC are higher than those of otherLWCs (from the literature) with the same density, which impliesthat the developed ULFRC can bear higher loads withoutincreasing its density range. This specific characteristic is veryimportant to widen the application of ULFRC in practice. Forinstance, for the production of floating structures, the developedULFRC can simultaneously fulfill the low density and load bearingrequirements, which can effectively simplify the operation pro-cedures and reduce the energy and labor demand. Hence, basedon the method proposed in this study, it is possible to produce aLWC with a very low density and relatively good compressivestrength simultaneously.

3.2.2. Flexural behaviourFig. 9 presents the 4-point bending test results of ULFRC with

0.1%, 0.2% and 0.3% (vol.) of LPF. It is clear that with an increase ofdisplacement, the load firstly increases and then sharply decreases.

Then, the residual load of all the tested samples remains relativelystable with an increase of the displacement, which represents aslow fibre pull out process. Furthermore, it can also be found thatthe first crack load of the mixtures with 0.1%, 0.2% and 0.3% of LPF is3.0, 3.3 and 3.6 kN, respectively. As can be found in the literature(Grünewald, 2004; Markovic, 2006), the load development of fibrereinforced concrete in bending test largely depends on the fibretype and amount. At the beginning of the 4-point bending test, theconcrete matrix will endure the applied load. With an increase ofthe load, the used fibres will becomemore active and sustain part ofthe load. Afterwards, when the fibres and concrete matrix can notendure the applied load, the first crack will appear, and theendurable load will simultaneously reduce. After that, the fibreswill be pulled out, and the development of the residual load willdepend on the fibre type and amount. In this study, after theappearance of the first crack, the residual load of ULFRC (mixturesNo. 1e3) remains relatively stable, which implies that to furtherimprove the flexural properties of ULFRC, the utilized fibre amountshould be appropriately increased.

The effect of hybrid polypropylene fibres on the flexuralbehaviour of ULFRC is illustrated in Fig. 10, which shows similarphenomenon as that presented in Fig. 9. Although the hybrid fibrecan simultaneously restrict the development of micro and macro-cracks, the relatively low fibre amount causes that the residualload (after the appearance of the first crack) can not be furtherenhanced. Consequently, combining the results shown in Figs. 9and 10, it can be concluded that to obtain a better post-crackresponse, more fibres should be appropriately added into theULFRC mixture.

Fig. 11 shows the 4-point bending test results of ULFRC mixtureswith relatively high fibre amount. It is noteworthy that theseULFRCs show substantially different post-crack response comparedto the ULFRC mixtures with relatively low fibre amount (about 0.2%vol.). The loadedisplacement curves of themixtures with 0.6%, 0.9%and 1.2% (vol.) of LPF can be mainly divided into three parts: elasticsection, strain hardening section and strain softening section. Afterthe first crack appears, their endurable loads firstly decrease andthen gradually increase to a value (peak load) larger than the firstcrack load. In this study, the peak loads are enhanced with anincreasing amount of the utilized LPF. However, it can also be foundthat the first crack load of the mixtures with 0.6%, 0.9% and 1.2% vol.of LPF reduces with an increase of the utilized LPF amount, whichshould be attributed to the influence of the high amount of fibres onthe structure of the granular skeleton (in linewith the effect of fibreamount on compressive strength), as discussed in the previoussection.

In summary, based on the obtained results, it can be concludedthat an optimized hybridization of fibres and an appropriate in-crease of the utilized LPF amount are beneficial for improving themechanical properties of ULFRC. In practice, when the developedULFRC is applied in elements with high toughness requirements,then a relatively high dosage of LFP should be added.

3.3. Thermal conductivity

The thermal conductivities of all the designed ULFRCs areillustrated in Fig. 12. It can be found that the thermal conductivityof ULFRC remains stable with the variation of fibre amount andhybridization, and all the tested thermal conductivities fluctuatearound 0.165 W/(m K). For instance, the highest thermal con-ductivity is about 0.171 W/(m K) (No. 7), while the lowest one isaround 0.160 W/(m K) (No. 9). The small differences between themeasurements are probably caused by internal or surface locatedair voids. Nevertheless, for the mixture No. 9, the effect of a highernumber of long polypropylene fibres on the internal structure

0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500

Dry density (kg/m 3 )

Com

pres

sive

stre

ngth

(MPa

)

[8] [56]

[57] [19] Porous concrete

[19] UHPC foam concrete [19] Foam concrete

[18] [58]

[59] This study

Fig. 8. Relationship between the compressive strength and dry density for different types of lightweight concrete.

0

1

2

3

4

0.0 0.2 0.4 0.6 0.8 1.0

Displacement (mm )

Load

(kN

)

Fibre amount - 0.1% vol.

Fibre amount - 0.2% vol.

Fibre amount - 0.3% vol.

Fig. 9. 4-point bending test results of ULFRC with relatively low fibre amount (0.1%, 0.2% and 0.3% vol.).

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701698

should also be a reason for the relatively low thermal conductivity.Normally, a dense granular structure results in better mechanicalproperties and a higher thermal conductivity. In this study, due tothe fact that the relatively large amount of fibres can increase theentrapped air voids in ULFRC and reduce the ULFRC density, thethermal conductivity of ULFRC is simultaneously decreased.

The relationship between the compressive strength and thermalconductivity for different types of LWC retrieved from the literatureand for ULFRC developed here are shown in Fig. 13. In general, it canbe noticed that the thermal conductivity of LWC increases with anincrease of its compressive strength. Due to the difference betweenthe utilized raw materials and casting methods, the increasingtrends of compressive strength alongwith the thermal conductivityvaries for different types of LWCs. Moreover, it is important to findthat the data points representing ULFRC are all above the points

representing other LWCs, which means that the developed ULFRChas a higher compressive strength than the other LWCs with thesame thermal conductivity range. Therefore, when the developedULFRC is applied in the insulating elements, monolithic designconcept can be utilized instead of multilayers design, which cansignificantly simplify the construction procedures and reduce thelabor and energy cost.

In general, due to the low density, low thermal conductivity andacceptable mechanical properties, the developed ULFRC can beutilized as a new material for the production of floating structures,insulating elements or even load bearing elements. As the sus-tainable development is currently a crucial global issue and variousindustries are striving in saving energy and lowering the environ-mental impact, the developed ULFRC is a good candidate to bewidely applied in the near future.

0

1

2

3

4

5

0.0 0.2 0.4 0.6 0.8 1.0

Displacement (mm )

Load

(kN

)

75% LPF + 25% SPF

50% LPF + 50% SPF

25% LPF + 75% SPF

100% LPF

Fig. 10. 4-point bending test results of ULFRC with hybrid fibres (total fibre amount is fixed at 0.2% vol.).

0

1

2

3

4

5

6

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Displacement (mm )

Load

(kN

)

Fibre amount - 0.30% vol.

Fibre amount - 0.60% vol.

Fibre amount - 0.90% vol.

Fibre amount - 1.20% vol.

Fig. 11. 4-point bending test results of ULFRC with relatively high fibre content.

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701 699

4. Conclusions

This paper addresses the development of Ultra-LightweightFibre Reinforced Concrete (ULFRC) applying expanded waste glass(lightweight aggregates). From the obtained results the followingconclusions can be drawn:

� The dry density and thermal conductivity of the developedULFRC are about 750 kg/m3 and 0.165W/(m K), respectively. Theused lightweight aggregates (LWA) homogeneously distribute inthe concrete matrix. Compared to the other lightweight con-cretes (LWCs) with the same density or thermal conductivity,the developed ULFRC has significantly higher compressivestrength (about 16 MPa).

� An optimized amount and hybridization of polypropylene fi-bres are crucial in improving the mechanical properties ofULFRC. To obtain a good post-crack response in the 4-pointbending test, the added long polypropylene fibres (LPF)amount in the ULFRC mixture should be more than 0.6% (vol.)in this study, which can significantly improve the toughness ofULFRC. Hence, based on the different requirements frompractice, the polypropylene fibre amount and type should betailored.

� The relatively high LPF amount (about 1.2% vol.) can significantlyinfluence the density and mechanical properties of ULFRC. Dueto the fact that the utilized LWAs have very low density(300e800 kg/m3), it is relatively easy for the LPF to push apartthe big particles and disturb the structure of the granular

0.00

0.05

0.10

0.15

0.20

Ref. No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 No. 9

ULFRC mixtures

Ther

mal

con

duct

ivity

(w/(m·K))

Fig. 12. Thermal conductivity of the designed ULFRC.

0

10

20

30

40

0.0 0.2 0.4 0.6 0.8

Thermal conductivity (W/(m·K) )

Com

pres

sive

stre

ngth

(MPa

)

[49] [19] UHPC foam concrete

[19] Porous concrete [19] Foam concrete

[18] [59]

This study

Fig. 13. Relationship between the compressive strength and the thermal conductivity for different types of lightweight concrete.

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701700

skeleton. Hence, when the additional LPF amount is relativelyhigh, the density and mechanical properties of ULFRC can besimultaneously decreased.

� The low density, low thermal conductivity and acceptable me-chanical properties of the developed ULFRC are beneficial forwidening its application range in the practice. Since the avail-able lands are prominently decreasing and there is a strongdemand for the development of new building types, thedeveloped ULFRC can be applied in the marine and floatingconstrictions. Moreover, due to the low thermal conductivity, itis also possible to utilize the ULFRC as a thermal insulatingbuilding material to design monolithic structures.

� The main raw material in ULFRC is the expanded glass aggre-gates, produced from expanded waste glass. Hence, the

application of ULFRC provides a new method to efficientlyreuse the waste glass, which is in line with the sustainabledevelopment.

Acknowledgements

The authors wish to express their gratitude to M.Sc. X. Gao forsupporting the experimental work, and to the following sponsors ofthe Building Materials research group at TU Eindhoven: Graniet-Import Benelux, Kijlstra Betonmortel, Struyk Verwo, Attero, ENCIHeidelbergCement, Provincie Overijssel, Rijkswaterstaat Zee enDelta e District Noord, Van Gansewinkel Minerals, BTE, V.d. BoschBeton, Selor, Twee “R” Recycling, GMB, Schenk Concrete Consul-tancy, Geochem Research, Icopal, BN International, Eltomation,

R. Yu et al. / Journal of Cleaner Production 112 (2016) 690e701 701

Knauf Gips, Hess ACC Systems, Kronos, Joma, CRH Europe Sus-tainable Concrete Centre, Cement&BetonCentrum, Heros andInashco (in chronological order of joining).

List of symbols and abbreviations

SymbolsD Particle size (mm)Dmax Maximum particle size (mm)Dmin Minimum particle size (mm)Pmix Composed mix (e)Ptar Target curve (e)P(D) Fraction of the total solids being smaller than size D (e)q Distribution modulus (e)RSS Sum of the squares of the residuals (e)

AbbreviationsCPM Compressive Packing ModelLPDM Linear Packing Density ModelLPF Long polypropylene fibresLWA Lightweight AggregateLWC Lightweight ConcreteOPC Ordinary Portland CementSPF Short polypropylene fibresULFRC Ultra-Lightweight Fibre Reinforced Concrete

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Development of Ultra-Lightweight Fibre Reinforced Concrete applying expanded waste glass1. Introduction2. Materials and methods2.1. Materials2.2. Experimental methodology2.2.1. Mix design of ULFRC2.2.2. Mixing procedures and fresh behaviour2.2.3. Hardened density2.2.4. Mechanical properties2.2.5. Thermal conductivity

3. Results and discussion3.1. Densities3.2. Mechanical properties3.2.1. Compressive behaviour3.2.2. Flexural behaviour

3.3. Thermal conductivity

4. ConclusionsAcknowledgementsList of symbols and abbreviationsReferences