454
Table 4 lists main experimental results. Theoretical value o f ultimate load is calc;il;iti;i| h-means o f equilibrium and strain compatibility equations according to the usual hypothesv:s ui'\\^^. l i m i t state approach, and according to Eurocode 2 relations. A n increase o f ultimate iK-xui-ii capacity is observed f o r all the beams w i t h E A F slag w i t h respect to beams w i t h traditional conglomerate; furthermore, any significant difference i n structural behaviour i n lenns oj-cracking pattern and failure mode is noted. The value o f the first oj-cracking moment is h\u.hy:f Linj the crack widths are lower for the beams w i t h recycled concrete, probably due to mofg pronounced cohesion i n the matrix w i t h slag w i t h respect to that o f traditional concrete. In Un; beams failing i n shear, the typical failure w i t h development o f diagonal cracks was obser\\;i| Particularly f o r B l elements (without shear reinforcement), the experimental ultimate loiid was higher than the theoretical one, both for traditional and recycled concrete, showiim the conservative nature o f Eurocode 2.
4. C O N C L U S I O N S
Concerning the results obtained i n this work, the f o l l o w i n g conclusion can be syiiiliclieiilly drawn:
1. Slag used i n this experimental investigation showed a high crystalline nature and the presfnuL-o f a lpresfnuL-ot presfnuL-o f mineralpresfnuL-ogical phases, thus increasing the stability presfnuL-o f the material. Oxides arc nniinly bounded i n other compounds, and problems due to expansion or disintegration seem to be not relevant. Leachate d i d not present concentration o f unhealthy material over reasonable limits. 2. The high angularity and the particular shape o f this slag promote an increase i n com|ii e.-isiv\:. tensile strength and elastic modulus, other than specific weight.
3. The use o f E A F slag increases water demand, reducing the w o r k a b i l i t y o f fresh concrete. This is not a significant problem because o f the possibility o f using plasticizers, whose quantity conid be adjusted to obtain the required fluidity o f t h e mixture.
4. B o t h ultimate flexural and shear capacity o f t h e beams made w i t h recycled concicle uciv higher than the corresponding traditional beams, w i t h generally reduced crack widths and similar crack patterns. This behaviour is probably due to higher cohesion between cementitious matrix and E A F aggregates.
5. The use o f steel slag as aggregate i n R C structural elements, i n principle, is possible, iiiul ilk-rate o f substitution could reach the whole part o f coarse aggregates. Benefits can be obtained both from an economical and environmental point o f view: re-use, prevention i n discarding materials and saving natural resources are the main issues that could be reached.
R E F E R E N C E S
Exteberria M . , Vazquez E., "Influence o f amount o f recycled coarse aggregates and production on properties o f recycled aggregate concrete", Cement and Concrete Research, V . 37, 2007, pp. 735-742
Manso J.M., Polanco J.A., Losanez M . , Gonzalez J.J., "Durability o f concrete made with EAf slag as aggregate". Cement and Concrete Composites, V . 28, 2006; pp. 528 - 534
Papayianni I . , Anastasiou E.,"Production o f high-strength concrete using high volume of industrial by-products", Construction and B u i l d m g Materials, V . 24, 2010, pp. 1412 - 1417 Pellegrmo C , Gaddo V . , "Mechanical and durability characteristics o f concrete containing EAF
slag as aggregate", Cement and Concrete Composites, V . 3 1 , 2009, pp. 663 - 671
Oilconomou N . D . , "Recycled concrete aggregates", Cement & Concrete Composites, V. 27, 2005, pp. 315-318
W u W . , Zhang W . , M a G., " O p t i m u m content o f copper slag as a f m e aggregate i n high strength concrete", Materials and Design, V . 3 1 , 2010, pp. 2878 - 2883.
Yang K . - H . , Chung H.-S., Ashour A . F . , "Influence o f type and replacement level o f rccycid aggregates on concrete properties", A C I Materials Joumal, V.105, N o . 3, 2008, pp. 289-2')fi.
455
Intliience of Particle Packing Densii
Content Concrete
pr. ir. S.A-A-M. Fennis
Pelft University o f Technology, C i T G Stevinweg 1
•^L 2628 C N D e l f t
E-mail: S.A.A.M.Fennis@tudelft.nl I'rn;'. ilr. ir. J-C Wahaven
Delft University o f Technology, C i T G Stevinweg 1
K L - 2 6 2 8 C N D e l f t
on the Rheology of Low Cement
Dr. ir. S. G r ü n e w a l d
Hurks beton bv / D U T , C i T G Locht 126
N L - 5504 RP Veldhoven E-mail: S.Grunewald@tudelft.nl Ir. J.A. den U i j l
D e l f t University o f Technology, C i T G Stevmweg 1
N L - 2628 C N D e l f t V B S n U C T
Optimizing concrete mixtures w i t h regard to cement content is one o f the most important solutions i n sustainable concrete design. Workability o f these l o w cement content or ecological mixtures is very important. Eleven mortar mixtures are presented, w h i c h show how a higher packing density can be used to obtain mixtures that require less water. Higher packuig densities reduce the void volume between the particles and therefore decrease the amount o f water neces-sary to fill this void volume. The reduced amount o f water and lower water/cement ratio can be used to save a certain amount o f cement when concrete is designed f o r a fixed strength class. Ki'j words: Cement, Concrete, Cyclic design. Ecology, Particle packing. Water demand 1. I N T R O D U C T I O N
The environmental impact o f concrete can be decreased i n several ways, f o r instance b y creating slender concrete structures, m i n i m i z i n g material transports or by using recycled materials. However, about 50% o f the total C02-emmissions w h i c h are emitted during the building o f a concrete structure comes from the use o f Portland cement. Therefore, optimizing concrete mixtures w i t h regard to cement content is one o f the most important solutions i n sustainable concrete design. Lowering the cement content i n concrete is possible without changing concrete properties i n a negative w a y b y making use o f particle packing optimization /Dhir et al. 2005/.
When reducing the cement content i n concrete, various types o f fillers or binders can be used combined w i t h different types o f admixtures. Using particle packing technology is an effective way o f selecting the right type o f cement replacing material i n combination w i t h a certain type of superplasticizer. This is because o f the relationship between packing density and water demand o f mixtures. Increased packing density reduces the water demand and thus improves concrete performance and allows f o r cement reduction. Therefore, the key to design ecological concrete is to control the water demand and workability. I n this paper it is presented i n what way particle packing density and water demand are related and how this can be used to design concrete with lower cement contents.
2. P A R T I C L E P A C K I N G D E N S I T Y A N D W A T E R D E M A N D
The particle packing density o f an ecological concrete mixture has an important influence on its water demand. The definition o f particle packing density is the solid volume o f particles i n a unit volume. However, distinction should be made between a stable particle structure and the sohd content cp„,;x o f a real concrete mixture. I n a stable particle stmcture all particles are i n contact w i t h each other. I n such a stable structure, the particles are packed w i t h certain packing
456
Stable particle structure Mixture fmix'^i [ ™ ' ]
Figure 1 - The volume of a stable particle structure (left Figure 2 - The flow value as a function of hand side) compared to the volume occupied by a flowable (pmiJaifor mortar mixtures,
mixture containing the same particles (right hand side).
density a,. This paclcing density is higher than the solid content (p„,/.v o f a real concrete mixture contaiiung these particles. This is shown i n F i g . 1, where the same amount o f particles in a stable particle structure is packed closer than m a real mixture. I n a real concrete mixture p.iri oT the water is used to f i l l the voids between the particles, w h i l e the rest o f the water is regarded as excess water. This excess water provides the f l o w a b i l i t y o f the misture. Flowability increases w i t h a higher amount o f excess water i n the mixture. I n that case, the solid content o f the mixture <^„,a decreases.
Increasmg the packmg density improves the w o r k a b i l i t y o f a mixture, w h i c h is very useful in the design o f ecological concrete mixtures. I f the particle composition o f a concrete nuxture is optimized i n such a w a y that the particle packing density increases, less v o i d water is necessary. I f i n this optimized mixture the water dosage w o u l d be kept constant, the water that fu-st filled up the voids between the particles now becomes available as excess water and provides more flowability. I n Fennis /2011/ a good relation was f o u n d between f l o w value and packing density o f the tested mortar mixtures. The results are presented i n F i g . 2 as a function o f the solid volume i n the real mixtures (p„,iv over the m a x i m u m calculated packing density a^.
3. D E S I G N M E T H O D F O R E C O L O G I C A L C O N C R E T E
The relation between packing density and water demand can be used to predict the reii'.nicd amount o f water o f a mixture. As described i n section 2, the water demand o f a mistui'e dcpcmis on the required amount o f v o i d and excess water. Increasing the packing density lowers the required amount o f v o i d water. For instance, i n mixtures B l and B10-B13 (Table 1) packing density increased and less v o i d water was required. Since the amount o f water i n the mixtures was kept constant, the water became available as excess water and the f l o w a b i l i t y o f these mixtures increased. The other w a y around, mixtures B14 and B15 were designed to have the same f l o w a b i l i t y as the reference mixture B l . Because B14 and B15 have a higher packing density, they require less (void) water f o r this flowability. Therefore, the mixtures could be designed w i t h less water and the possibility was created to maintain a constant water/cement ratio while replacing cement.
Optimizing the packmg density is not only beneficial for the water demand, but it can also decrease the space between the cement particles. This space between the cement particles depends on the particle structure o f the mixture. I n ecological concrete this factor is important because the cement is replaced b y fillers (or binders). Dependmg o n the particle size o f the used filler, the space between the cement particles w i l l vary, as is shovm i n Fig. 3.
457
fable 1 - Mixture compositions and test results of mortars series B /Fennis 2011/.
CEiVl 1 42.5 N Quartz Sand Water SP WCR WPR Clt Slump Slump Flow Comp. strength powder 51 Kt=9 flow value 7-day 28 day [g] [g] [g] [g] [g] [-] [-] [-] [mm] [mm] [mm] [N/mm^] [N/mm^] Bl ClOO 900 - 2700 326 10.8 0.37 0.37 0.803 2 83 95 49.6 55.5 33 C80-[V16 720 180 2700 326 10.8 0.46 0.37 0.798 5 83 95 36.8 49.0 ; B C60-M6 540 360 2700 326 10.8 0.62 0.37 0.793 12 89 102 24.1 34.7 B7 C80-M300 720 180 2700 325 10.8 0.46 0.37 0.798 3 87 97 37.7 48.6 B9 C60-IVI300 540 360 2700 326 10.8 0.62 0.37 0.792 15 93 113 27.8 38.5 BlO C90-M600 810 90 2700 326 10.8 0.41 0.37 0.813 15 90 97 47.8 52.6 •111 C80-M600 720 180 2700 326 10.8 0.46 0.37 0.821 27 92 140 47 60.4 812 C70-IV1600 630 270 2700 326 10.8 0.53 0.37 0.827 39 134 177 38.9 52.5 B13 C60-M600 540 360 2700 326 10.8 0.52 0.37 0.829 48 159 202 35.9 50.0 B14 C90-IV1600 810 90 2700 293 10.8 0.37 0.33 0.813 4 86 96 54.9 68.0 B15 C80-iV1600 720 180 2700 259 10.8 0.37 0.30 0.821 2 85 94 57.5 74.4
Replacing cement b y coarse fillers, such as quartz powder M 6 and M 3 0 0 (Sibelco), increases the spacing between the cement particles. This can be explained b y considering a container filled by cement particles. I f 2 0 % o f the cement is replaced b y a filler o f similar size, the packing density remains constant. I n total the same volume percentage o f the container is still occupied b y the particles, however, now only 80% o f the original cement particles are present in that container. Thus the cement particles are relatively farther away from each other (Fig. 3 left hand side). However, when cement is replaced b y fmer particles (M600) the packing density increases. I n that case, the 80%) cement particles w i l l fit i n a smaller container (Fig. 3) and therefore the space between the cement particles is smaller than w i t h the coarse filler.
The relations between packing density and water demand, and between particle structure and cement spacing can be used i n the design o f ecological concrete. Figure 4 presents the cyclic design procedure f o r ecological concrete based on these t w o relations. This design procedure starts b y determining the packing density at o f the particles i n a concrete mixture b y calculations based on the Compressible Packing M o d e l /Larrard 1999/. The new Compaction Interaction Packing M o d e l ( C I P M ) /Fennis 2 0 1 1 / was developed and tested to include wet packings o f microparticles i n combination w i t h superplasticizer Glenium 5 1 . The result o f this first design step is a knovm particle size distribution w i t h its corresponding packing density. I n the next step the water demand o f the mixture is determined by using the ratio f ma/a,, see also Fig. 2. This ratio cprna/a/ is directly related to the flowability o f a mixture, so (p,„,j and thus the volume o f
Figure 3 -The volume occupied by a stable particle structure Figure 4 - Cyclic design procedure for with coarse filler (F) compared to the volume occupied by a ecological concrete,
458
water can be adjusted to the required consistency. I n the f o l l o w i n g step the strength is predi^i.-j on the basis o f this mixture composition, its packing density and its particle structure. Tl>(; strength prediction is based on the assumption that i n low strength ecological concrete -li] aggregates are stronger than the produced concrete. I n that case, the cement glues the aggix-^ai-^ together and the strength depends on the spacings to be bridged to cormect all aggregates. AVid, •\ high packmg density m the mixture, cement particles and other particles are close to each oihcr reducing the space that needs to be filled b y hydration products, w h i c h leads to higher stren"ihs" W i t h higher amounts o f water and higher water/cement ratios, the cement particles are filnil^..'. apart, eventually leadmg to lower strengths. W i t h this concept, expressed by the cement spafing factor (CSF), the strength o f a mixture can be predicted /Permis 2011/.
Atter the strength prediction, adjustments can be made to the mixture composition to coinp|., w i t h user defmed requirements. For instance, when the strength is still higher than reqniix-j' cement can be replaced by inert filler i n order to create a more ecological mixture. Change of the mixture composition may involve change o f the particle size distribution and the cyclic design procedure should be repeated until the mixture meets all requirements.
4. C O N C L U S I O N S A N D F U T U R E P R O S P E C T S
The workability o f ecological concrete is very important i n the design o f these types o f concrete mixtures. The flow value is related to the packing density and the amount o f water in the mixture. Higher packing densities decrease the v o i d volume between the particles and therefore decrease the amount o f water necessary to fill this void volume. I n a real mixture, part o f the added amount o f water is used to fill voids, while the rest is used to lubricate the particles and provide flowability. I t is important to control this amount o f water because the excess water pushes the cement particles hirther away from each other, thus increasing the volumetric distance between the cement particles. I n that case, a higher water/cement ratio and lower partial volume o f t h e cement, lead to larger distances between the cement particles and thus, eventually, to a lower strength due to the fact that the hydration products o f the cement particles need to bridge larger spacmgs. I n ecological concrete w i t h h i g h amounts o f cement replacing materials, this effect is even more important than i n ordinary concrete. This is because a slight increase in water demand o f mixtures w i t h l o w cement content has a larger effect on the water/cement ratio than i n mixtures w i t h high cement content. A n increased water/cement ratio w i l l decrease strength and durability. Thus, i n the future, it w i l l be very important to use particle packing models to control the water demand and workability o f ecological concrete. This can be done by using the cyclic design method. W i t h this method, the amount o f water i n concrete mixtures can be reduced. The reduced amount o f water and l o w water/cement ratio can be used to save a certain amount o f cement when concrete is designed f o r a f i x e d strength class. I n the present project on ecological concrete the only controlling parameter i n the design procedure was the strength requirement. However, the set-up o f the cyclic procedure allows also f o r concrete mixture design based o n mixture composition restrictions, or mixture design based on defined performance requirements.
R E F E R E N C E S
D h h , R.K., McCarthy, M . J . , & Paine K . A . , 2005
"Engineering property and structural design relationships f o r new and developing concretes". Materials and Structures 38 (275), pp. 1-9.
Fennis, S . A . A . M . . , 2011
"Design o f Ecological Concrete by Particle Packing Optimization", PhD Thesis, Delft: D e l f t University o f Technology.
Larrard, F. de, 1999
"Concrete mixture proportioning, A scientific approach", EF & Spon, London.
459
l eeze-Thavv Effect on the Flexural Behaviour of Plain Concrete Beams w i t h
Layer of Sustainable Strain-Hardening Cement Composite (2SHCC)
Professor, Dr. Keitetsu Rokugo Department o f C i v i l Engineering G i f i i University
G i f i i Japan
E-mail: rk@gifu-u.ac.jp
M r . Young Jae Song, Seok Jun Jang, Zhong Jie Y u
Department o f Architectural Engineerkig Chungnam National University
Daejeon
Republic o f Korea, 305-764 E-mail: sinkinto@hanmail.net
M i S T R A C T . Freeze-thaw influence on the cracldng and flexural behaviour of plain concrete beams with a sustamable
fiber reinforced stram-hardening cement composite (2SHCC) layer were investigated experimentally. Alternative recycled materials - recycled sand from demohshed concrete, fly ash, and polyethylene terephthalate (PET) fibres - are used to partially replace silica sand, cement, and polyvinyl alcohol (PVA) fibres, respectively, in 2SHCC material. Concrete beams with 40mm of 2SHCC layer thickness, which had 100 x 100 mm rectangular cross section and 300mm span length, were tested in four-point bending. Freezing and thawing tests of SHCC materials and SHCC-layered concrete beams followed ASTM C 666 Procedure B.
Key words: Stram-hardenuig cement composite (SHCC), freeze-thaw action, flexural behaviour, layered concrete beam
1. I N T R O D U C T I O N
The behavior o f s t r a i n - h a r d e n i n g cement composite ( S H C C ) has been studied considerably over the last f e w years. However, compared to normal concrete mix, SHCC mixtures are energy intensive and rich. Such high cement content usually creates negative envhonmental knpacts due to the associated carbon dioxide emissions. Approximately one t o n o f cement produces a nearly equal amount o f carbon dioxide [Yang et al., 2007].
A possible solution is to replace the cement w i t h mdustrial by-products, such as silica fiime and fly ash. I n the fib2011, Y u n , Rolcugo, and Park (2011) presented a paper w h i c h described the frost resistance and mechanical properties o f sustainable S H C C ( 2 S H C C ) after rapid freezing and thawing exposure. The long-term performance o f 2SHCC-layered plaui concrete beams i n aggressive environment such as freeze-thaw actions was investigated i n this study.
2. M E C H A N I C A L P R O P E R T I E S O F 2 S H C C 2.1 M a t e r i a l s
Table 1 shows the detailed m i x proportion o f proposed 2SHCC material. Typical Portland cement was used, and Class F fly ash was used to replace the cement. P V A fiber (REC-15, Japan) and PET fibers from recycled bottles were used f o r the reinforcmg fiber. Silica sand (specific gravity o f 2.61, ^ o f 105 - 120|im) and recycled aggregate (maximum size o f aggregate 2.5 mm) also were used i n this study.
Professor, Dr. H y u n D o Y u n
|),-partment o f Architectural Engineering Chungnam National University
Daejeon Republic o f Korea, 305-764 E-mail: wiseroad@cnu.ac.kr Professor, Dr. Chang Süc C h o i Division o f Architecture Hanyang University Seoul Kepubhc o f Korea E-mail: ccs5530@hanyang.ac.kr
