Use of wood waste as a resource for structural wood-concrete compounds

Niccolò Macchi1, Daia Zwicky2

1 Boulevard de Pérolles 80, 1700 Fribourg, Switzerland College of Engineering and Architecture - Fribourg, niccolo.macchi@hefr.ch

2 Boulevard de Pérolles 80, 1700 Fribourg, Switzerland College of Engineering and Architecture - Fribourg, daia.zwicky@hefr.ch

Keywords: wood-concrete compound, structural properties, wood waste valorization

Wood-concrete compounds as structural materials

Construction and operation of buildings has an important environmental impact. Today the most widely used construction material is concrete; which is heavy, has rather high embedded energy, strongly draws upon non-renewable resources, is challenging to re-use, and exhibits rather poor properties with regard to thermal insulation and storage capacity, and acoustic insulation. Last but not least, the concrete types used today in mid-size building construction are essentially far too good from a structural point of view. Mixes of concrete with wood components, so-called wood-concrete compounds (WCC), may be one of the answers to the challenge of a more sustainable evolution of concrete-based construction. First WCC materials have already been developed at the beginning of the 20th century. Until today, they are mainly used as non-structural finishing layers where their good fire resistance, thermic and acoustic insulation properties are combined with a relatively low and thus, beneficial density. From a structural point of view, the main impact of this new material is the potential for creating very light-weight pourable concrete; but, due to their current application, their mechanical properties are not well known or optimized, respectively.

Mechanical properties of WCC

Sawdust and mineralized wood fiber concrete compositions were analyzed, including a commercially available product (Agreslith®). Different binders (standard Portland cement and aluminate cement) and wood/cement ratios (t/c) were considered. To improve compatibility of Portland cement and wooden aggregates, active charcoal has been added to certain recipes, see Table 1.

Table 1: Recipe and average material properties of WCC

Recipe t/c Humid density a COV in brackets

Compressive strength b COV in brackets

Tensile strength c COV in brackets

1: Sawdust, portland cement 0.33 1125 kg/m3 (0.4%) 2.1 MPa (0.3%) 0.3 MPa (7.0%) 2: Sawdust, portland cement, active charcoal

0.33 1209 kg/m3 (1.1%) 3.3 MPa (4.5%) 0.4 MPa (4.0%)

3:Sawdust, aluminate cement 0.33 1184 kg/m3 (0.6%) 1.0 MPa (18%) 0.1 MPa (15%) 4: Sawdust, portland cement (70%), aluminate cement (30%)

0.33 989 kg/m3 (5.7%) 0.2 MPa (4.5%) --1

5: Sawdust, portland cement 0.2 1149 kg/m3 (0.4%) 4.9 MPa (6.4%) 0.5 MPa (5%) 6: Sawdust, portland cement, active charcoal

0.2 1324 kg/m3 (1.1%) 6.8 MPa (5.5%) 0.8 MPa (2.0%)

7: Sawdust, aluminate cement 0.2 1233 kg/m3 (1.4%) 1.2 MPa (3.1%) 0.2 MPa (1.0%) 8: Mineralized fibers, portland cement

1385 kg/m3 (2.5%) 4.9 MPa (20%) 0.8 MPa (12%)

a The humid densities of the tested WCC compositions roughly are between 1000 to 1400 kg/m3. Dry densities are considerably lower (450 to 1100 kg/m3) depending on the content of organic material. b Tested according to SN EN SN EN 12 390-3 on cylinders with 150 mm diameter and 300 mm height c Tested in indirect double punch test proposed by Chen (1972)

Use in hybrid composite Timber-WCC construction

WCCs alone, as non-reinforced concrete, are of little potential for load-bearing elements. To overcome the lack in tensile strength, a tensile reinforcement is needed. Different timber-concrete composite systems can be adapted to the new structural material. Currently under development are multilayer sections with glulam tension layers and either directly a Compression layer of WCC or a shear layer of WCC plus a thin compression layer out of highly resistant WCC (or alternatively out of traditional structural concrete), Macchi (2014). By using a composite layered structure we can benefit of the numerous secondary benefits of this material, mainly:

• WCCs are difficultly inflammable.

• WCCs are good thermal and acoustic insulators.

• Pourable WCC can be used as active thermal inertia volume.

• Timber-WCC composite structures are light-weight.

• Timber-WCC can be burned to valorize the calorific energy contained

References

SN EN 12 390-3 Testing hardened concrete - Part 3: compressive strength of test specimens CHEN W. 1972, Double-punch test and tensile strength of concrete, Journal of Materials, vol. 7, n 12,

pp. 43-50 MACCHI N. and ZWICKY D., 2014, Development of wood-based concrete for building construction, in: Concrete

Innovation Conference 2014, Oslo, Norway, 2014

Acknowledgments:

This research project is funded as part of the national research program 66 “Resource Wood” of the Swiss National Science Foundation [“Verfügung 406640_136918/1”]. It is a collaborative effort of CEA-FR and Vienna University of Technology.

USE OF WOOD WASTE AS ARESOURCE FOR STRUCTURALWOOD CONCRETE COMPOUNDSNICCOLÒ MACCHI / DAIA ZWICKY

COST FP1303 meeting in Kranjska Gora • Octobre 2014

Institute of Construction and Environmental Technology iTEC

• interdisciplinary approach to the wood resource– from wood-chemistry to wooden buildings

• making wood more competitive compared to other materials

www.nrp66.ch

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Module 5:Wood-basedstructuresand buildings

Project Zwicky:Wood andwood-based concrete

Why use timber in urban construction?

• Speed of construction• Clean building site

– Less interference in Urban environment

• High quality control in timber prefabrication• Problems with fire safety codes & some

building physical problems

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What we want to achieve• Replacement of traditional concrete in (prefabricated)

timber structures with wood-concrete compounds• Benefits :

– Optimization of “waste” management in timber construction– Thermal and sound insulation – Fire protection– Light weight– Partially combustible material (recycling)

• resource for clinker production?

Hybrid, multi-layer construction system with wood-concrete compounds and timber

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What are WCC

Wood based concretes, or wood-concrete compounds (WCC) • minerally-bonded (cement, magnesit…)• important part of wooden aggregates

– sawdust, woodchips or wooden fibers – in natural or mineralized form

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Problems of existing WCC

• Usually in form of prefabricated boards• Board sizes around 3.5 m x 1.25 m• Structural connections between multiple

layers of boards difficult, expensive and environmentally challenging – (epoxies, steel screws…)

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• Untreated sawdust – economically

advantageous– Sawdust from industrial

processes can be used• Good workability• Current development :

self-compacting WCC

Sawdust-based castable WCC

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Sawdust-based WCC

• Tested WCC compositions* with sawdust

• Active charcoal added for better compatibility of sawdust with Portland cement

*Inspired by: Urbonas, H. «TP 16: Holzbeton» Technical Univ. Munich TUM, Germany

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Saw dust CEM I 52.5 Aluminate cement t/c Active charcoal Water1 105 kg 340 kg -- 0.33 -- 190 kg2 105 kg 340 kg -- 0.33 17 kg 190 kg3 105 kg -- 340 kg 0.33 -- 190 kg4 105 kg 240 kg 100 kg 0.33 -- 190 kg5 110 kg 540 kg -- 0.20 -- 190 kg6 110 kg 540 kg -- 0.20 27 kg 190 kg7 110 kg -- 540 kg 0.20 -- 190 kg

Castable WCC

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Synopsis of WCC properties

Average Min. fibers 1 2 3 4 5 6 7

fc [MPa] 4.9 2.1 3.3 1.0 0.2 4.9 6.8 1.2

ft [MPa] 0.8 0.26 0.38 0.13 -- 0.52 0.8 0.18

Humiddensity[kg/m3]

1’385 1’125 1’209 1’184 989 1’149 1’324 1’233

Dry density[kg/m3] -- 451 -- -- -- 783 866 --

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Synopsis of WCC properties

0

1

2

3

4

5

6

7

8

900 1000 1100 1200 1300 1400 1500

Com

pres

sive

str

engt

h [M

Pa]

Humid density [kg/m3]

1 (PC)

2 (PC,AC)

3 (AlC)

4 (PC,AlC)

5 (PC)

6 (PC,AC)

7 (AlC)

Min. fibers

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WCC 1, 5 & 6 – % in weight

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43%

36%

21%

WCC recipe 1

37%

45%

18%

WCC recipe 5

41%

41%

16%

2%WCC recipe 6

Water

Cement

Sawdust

Charcoal

WCC 1, 5 & 6 – Vol.-%

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17%

47%

37%

WCC recipe 1

31%

57%

13%

WCC recipe 5

29%

53%

15%

3%WCC recipe 6

Mineral Phase

Sawdust

Porosity

Charcoal

Long-term mechanical behavior• Creep and shrinkage tests were

conducted on WCCs 1, 5 & 6

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0

1

2

3

4

5

6

7

8

9

0 28 56 84 112 140 168 196 224 252 280 308 336 364

Defo

rmat

ion

[‰]

Age [d]

Shrinkage

1

5

6

Long-term mechanical behavior

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0

1

2

3

4

5

6

0 28 56 84 112 140 168 196 224 252 280 308 336

Defo

rmat

ion

[‰]

Age [d]

Creep

1

5

6

Recipe Initial displacement

Final displacement

ϕ

WCC 1 -70 µm -372 µm 5.32

WCC 5 -85 µm -556 µm 6.48

WCC 6 -169 µm -647 µm 3.82

Other benefits of WCC materials

WCC have additional benefits, since they• considerably contribute to thermal insulation• show considerable thermal storage capacity• are good for extrinsic noise protection

– but are (alone) insufficient for intrinsic noise and impact sound protection

• are combustible but difficultly inflammable

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Conclusions

• Timber-WCC composite construction offers interesting opportunities for light-weight structural elements – for residential, school and office buildings

• Shrinkage of WCCs is difficult• Mechanical performance is sufficient for

intended use

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