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BESS-SB13 CALIFORNIA: Advancing Towards Net Zero. Pomona, California, USA. 24-25 June 2013
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Gypsum - Rubber from pipe foam insulation waste recycling:
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Thermal performance
JIMÉNEZ RIVERO, A., DE GUZMÁN BÁEZ, A., GARCÍA NAVARRO, J.
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ABSTRACT: The aim of this research work is to study the effect of different percentages of waste
rubber coming from pipe foam insulation addition in the thermal performance of a gypsum matrix.
Four particle size waste rubber: 1-2 mm, 2-4 mm, 4-6 mm and 20-25 mm, and different rates of waste
rubber addition: 1.25%; 2.50%; 5.00% and 7.50% were analyzed. After deciding the optimal size and
percentage of waste rubber, two combinations were chosen to carry out the thermal test.
Furthermore, in order to characterize its mechanical behavior, an experimental plan was elaborated to
study its density, flexure strength and compression strength.
This addition contributes to obtain a low density, lightweight, environmentally friendly material with
improved thermal performance.
Keywords: thermal performance, waste rubber, low density.
1. INTRODUCTION
Under the 2020 objectives on energy efficiency,
all new buildings shall be nearly zero-energy
consumption by 31 December 2020 and new
materials with improved thermal behaviour are a
key tool in order to obtain this target.
For this reason, the development of research
studies in this field has experienced a strong
growth in recent years and many works are
focusing on cement - concrete - gypsum matrixes
incorporating different additions to improve their
thermal conductivity. Recently, Bouvard et al
(2007) characterized and simulated an expanded
polystyrene (EPS) lightweight concrete and
Vejmelková et al (2012) analyzed the improved
thermal properties of concrete containing fineground ceramics, among other examples.
Moreover, due to the concern about the high rate
of waste disposal in landfill, the recycling of
industrial wastes in new materials would
contribute to valorise certain types of waste,
forming part of new materials with improved
thermal properties: Bederina et al (2007) studied
the effect of the addition of wood shavings on
thermal conductivity of sand concretes,
Corinaldesi et al (2011) tested the mechanical
behavior and thermal conductivity of mortars
containing waste rubber from used tires and
Panesar and Shindman (2012) analyzed the
mechanical and thermal properties of concrete
containing waste cork.
However, no previous experience about the
addition of pipe foam insulation waste rubber in
any matrix has been found. Only in Spain about
400 tons of this foam insulation are yearly sent to
landfill for only one manufacturer, meaning a
great amount of waste in volume due to its low
density.
This new material would contribute to pursue the
European Union targets set out for waste
recycling. (European Parliament and the Council
of the European Union, 2008)
2. MATERIALS AND METHODS
- Gypsum matrix E-35 plaster, Type B1 according
to UNE-EN 13279-2 Standard, and certified by N
mark from AENOR. (Fig.1)
TABLE 1: MATERIALS
Materials
Thermal
conductivity
Size
(mm)
E-35 Plaster
0.30
>0.2
Pipe foam insulation
≤ 0.036
1 - 25
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Departamento de Construcción y Vías Rurales, ETSIA - UPM, Madrid, Spain
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BESS-SB13 CALIFORNIA: Advancing Towards Net Zero. Pomona, California, USA. 24-25 June 2013
- Ground waste rubber coming from pipe foam
insulation,
received
from
a
Spanish
manufacturing plant as material rejected during
its production process. It is listed in the European
List of Waste (ELW) as 07 02 13: Waste Plastic.
(Fig. 1)
Its initial ground size, after being shredded by the
manufacturer, varies from 20 mm to 25 mm,
being subsequently mechanically shredded in
laboratory, to sizes from 25 mm to 1 mm.
obtaining a first approximation of the composite
heat conductivity.
To assess the heat conductivity rough value a
model house-box with replaceable side walls
(Fig. 2 and Fig 3) was used. The box had an
inside heat source and a temperature sensor
connected to the thermal control thermostat.
Three NiCr-Ni thermocouples connected to
temperature measurement tools and the software
Measure, to program the box and to export the
results, were used.
The temperatures were measured in the steady
state, at a constant interior and outer air
temperature. (Phywe Systeme GmbH & Co. KG,
2008)
Fig. 1: Waste rubber 20-25mm and plaster under study
3. TEST PIECES ELABORATION AND
METHODOLOGY
Test pieces series of 40 mm x 40 mm x 160 mm
(three per series) were produced in order to
assess the mechanical behavior. Furthermore,
230 mm x 230 mm x 25 mm wall test pieces were
prepared to assess thermal performance.
Sizes of crumbed rubber, 1-2 mm, 2-4 mm, 4-6
mm and 20-25 mm and percentages of 1.25%,
2.50%, 5.00% and 7.50% added by plaster
weight were studied.
The water/plaster (w/p) ratio was assessed
according to UNE-EN 13279-2 Standard, being
0.76 the value obtained.
Wet weight was recorded after the test pieces
were unmolded, then they were kept for 6 days in
laboratory atmosphere and later stored for 24
hours in a stove (CENTERM 150 model), at 40 ±
2 ºC (313 ± 279 K), to reach a constant mass and
in order to obtain the dry weight value.
Seven days later, the test pieces were cooled in
the desiccators in order to achieve the room
temperature
and
being
subsequently
mechanically and physically tested. The
reference standard for this process has been the
UNE-EN 13279-2.
In order to determine the thermal behavior a
simplified method was used, which allowed
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Fig. 2. Model house to study the heat conduction.
Fig.3. Interior of the model house: NiCr-Ni thermocouples
and rubber-gypsum wall test piece
An EPS board with known thermal conductivity
was fixed to the gypsum-rubber test piece, in
order to obtain the plaster-rubber λ value.
BESS-SB13 CALIFORNIA: Advancing Towards Net Zero. Pomona, California, USA. 24-25 June 2013
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The heat flow (Q) through the wall was
considered constant. The plaster-rubber λ value
was obtained according to a simplified Fourier
Equation:
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S is the wall surface (known value): 0.0441 m2
T1, T2 and T3 are the layers’ temperature (ºC)
h is each material thickness, being h1 0.035 m
and h2 0.019 m.
Fig. 5. Waste rubber percentage –density
4.2. Flexural strength test
It can be stated that the waste rubber addition
increases the composite plastic period: once the
breaking load is achieved there isn't a division
between both sides, remaining strongly joined in
most of the cases. (Fig.6). However, an important
strength loss is observed when increasing rubber
addition and as larger its size is. (Fig. 7)
Fig. 6. Waste rubber percentage -density
Fig. 4. Experiment scheme.
4. RESULTS AND DISCUSSION
4.1. Density
Waste rubber addition entails a density decrease
in the test pieces. The values obtained with 1-2
mm, 2-4 mm and 4-6 mm particle sizes, resulted
very similar varying between 0.90 and 1.00
g/cm3. Up to 48% of density lost is obtained in
20-25 mm test pieces, compared to reference
plaster, turning into a highly lightweight
composite. (Fig. 5)
Fig. 7. Flexural strength - waste rubber addition
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Where:
λ1 is the plaster-rubber composite thermal
conductivity (W/m∙K)
λ2 is the EPS thermal conductivity (known value):
0.041 W/m∙K
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BESS-SB13 CALIFORNIA: Advancing Towards Net Zero. Pomona, California, USA. 24-25 June 2013
4.3. Compressive strength
Once the breaking load is reached, the different
fragments are still linked, allowing the material
being deformed after exceeding its breaking load.
(Fig. 8)
The results are much smaller than the reference
ones, being under UNE-EN 13279 standard the
20-25 mm size from 5.00% percentage addition:
meaning a decrease of around 88% under the
reference results. (Fig.9)
TABLE 2. THERMAL TEST RESULTS
Wall test piece
Reference
1.25% 1-2 mm
7.5% 4-6 mm
Thermal conductivity, λ
(W/m∙K)
0.30
0.25
0.20
The minimum presence of rubber leads to an
increase of 17% of the thermal performance,
being 33% higher the improvement obtained with
7.5% of waste.
Due to the low density of both materials and the
low thermal conductivity of waste foam rubber, an
improvement in the thermal performance was
expected.
5. CONCLUSION
Fig. 8. Test piece after exceeding its breaking load.
This paper presents the results of an
investigation on the use of waste ground rubber,
from pipe insulation production, as addition in
gypsum-plaster matrix. Based on the results of
this study, the following conclusions can be
drawn:
1. The maximum waste weight percentage
accepted by the mixture, to make it
workable, is 7.50%
Fig. 9. Compressive strength - waste rubber content
4.4. Thermal behavior
Two rubber-gypsum composites were selected to
be tested in order to assess its thermal behavior:
- The 7.5% of 4-6 mm waste amount: because its
size is easy to obtain and its mechanical
performance fulfills the UNE-EN 13279-2
standard.
- The 1.25% of 1-2 mm waste amount: for being
the minimum content of waste in the series
studied meeting high mechanical strengths.
The average results are shown in the following
table (Table 3):
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2. There is a good compatibility between
waste rubber coming from pipe foam
insulation and the plaster matrix.
Despite the low density waste particles
present, the ground rubber is distributed
in a proper way inside the test pieces:
they don’t float in the mixture and
therefore an homogenous paste is
obtained.
3. Plaster-rubber composite is a lightweight
construction material: 48% weight
reduction is reached compared to the
reference samples.
4. Mechanical strength decreases with an
increase in waste rubber addition,
highlighting a higher decrease with the
larger size and waste amount added,
this happens because the matrix pores
compromise its strength. All the flexural
strength values obtained meet the UNEEN 13279 requirements. However, there
are two series which don’t meet the
compressive requirements: 5.00 and
7.50% with 20-25 mm rubber size.
5. An improved thermal behavior is
obtained, decreasing the new composite
thermal conductivity as far as the rubber
content increases.
For all these reasons, waste foam rubber could
be used forming part of core plasterboards,
achieving an environmental benefit as well as an
improved thermal performance. On the other
hand, the resulting lightweight drywall would be
easier to handle, making it easy to install too.
6. ACKNOWLEDGEMENTS
The authors would like to thank the Construction
Materials and Physics laboratory workers of the
School of Building Engineering - Technical
University of Madrid, for their assistance.
7. REFERENCES
AENOR, 2006. UNE-EN 13279-2. Yesos de
construcción y conglomerantes a base de yeso
para la construcción. Parte 2: Métodos de
ensayo. Norma Española. Madrid.
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