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Proceedings of CIVIL2011@UNILORIN 3rd Annual Conference of Civil Engineering 6 - 8 July, 2011
209
The Effect of Contact Between Strawbale Wall Composition and
Glass Cement Plaster.
S D Olayemi and A A Adedeji
Department of Civil Engineering, Faculty of Engineering and Technology,
University of Ilorin, Nigeria
Abstract
The response of the contact between plaster and strawbale wall composition for the
wall optimal design has been observed and simulated in this work using SAP2000. In
the laboratory, glass cement plastered strawbale wall has shown adequate resistance
against vertical loading when the mix ratio was varied to 1:2:2 (cement:glass:sand).
The results have shown that the cement plastered wall has much more stresses under
load than the wall plastered with only glass for both single course and double courses
(i.e. maximum stress for only cement plastered strawbale wall is 2.82N/mm2 and that
of glass only is 2.20N/mm2 for single coarse). Also obtained is the maximum predicted
stress of 3.38N/mm2 obtained from SAP2000 using the value obtained from the
observed maximum stress of 2.96 for the plastered strawbale wall. Although the
predicted and the observed values are close, the predicted values is higher than the
observed value which indicates that the stress stability, in general, of the plastered
strawbale wall are satisfactory.
Keywords; Strawbale, wall prism, glass, plaster
1. Introduction
Straw is a flexible (non-rigid) material that is sustainable, plentiful and non-expensive
as a building material which requires people to work with somewhat differently than if
it was rigid. Straws are originated from leftovers stem of harvested grain that are of
different types depending on the type of grain they are derived from e.g. from rice,
wheat, maize, millet, elephant grass, e.t.c. It is important to recognize that straws are
dry plant material or stack in the field after a plant has matured, been harvested for
seed (Jones, 1999). These straws are baled together and compressed to bear loading
when being used as post and beam system or structural bale system.
According to Lerner (2003), in strawbale wall, the relatively strong, stiff plaster
plays a significant role as it works together with the ductile strawbale come to function
as a stress skin panel. Plastering materials used for strawbale structures are of different
types like earth/laterite plaster, lime plaster, cement plaster, e.t.c. These plastering
materials make the wall strong and prevent the strawbale from fire when plastered on
both interior and exterior part, creating a wall system that is strong, resilient and very
attractive. Some of the properties of straw are: Sustainability, Sound insulation,
Proceedings of CIVIL2011@UNILORIN 3rd Annual Conference of Civil Engineering 6 - 8 July, 2011
210
Thermal insulation, Pest resistance, Fire resistance, Structural sound, Durability,
Simplicity. The final strength of these wall systems depends both on plasters and
strawbale . Plasters serve many functions in a wall system. They are:
Protect the underlying surface
Permit or prevent the migration of vapor or liquid moisture
Prevent the migration of air currents
Can carry structural loads.
Benefits of plastered walls also include sound proofing not present with regular
dry wall. Glass as an aggregate blend is one of the most durable materials known
because it has basically zero water absorption with current emphasis. Durability of high
performance is only natural to rely on extremely durable ingredient. Glass serve as a
potential environmental benefits, serve as recycling purpose, it is economical, conserve
energy and material resources. The effect of contact between the strawbale structures
and plastering materials and addition of glass cement as an aggregates blend is to
obtain the response of such structure to compressive loadings. This project will also
show the effectiveness of contact between strawbale and plaster composition in
different mix ratio.
The objectives of this paper to determine the effects of contact between strawbale
and glass-cement plaster composition involve the assessment of their material
properties by experimental tests and the analyzes of the composite wall for its stresses
using finite element method (FEM).
2. Plaster/Render and Stucco
Plaster starts as a dry matrix that is mixed with water to form a paste which liberates
heat and then hardens. Unlike mortar and cement, plaster remains quite soft after
setting, and can manipulated with metal tools or even sandpaper. These characteristics
make plaster suitable for a finishing rather than a load-bearing material. However, the
term mortar implies a plastic mixture of a cementing materials, fine aggregates and
water regardless of plaster while the mixture is known as stucco/render when used on
the exterior surface.
In load-bearing straw bale systems, the relatively strong, stiff plaster plays a
significant role as it works together with the strawbale to function as a stress skin
panel, resisting compressive, in-plane and out-of plane loading. the plaster can act as a
shear wall, resisting in-plane lateral loads.
3 Glass Cement
Waste glass is one of the most solid pollutants from industrial and civilian uses, which
are contaminated by some hazard substance, so it is very important to reuse these
wastes for reducing the pollution created from accumulation of several tons of these
materials.
Proceedings of CIVIL2011@UNILORIN 3rd Annual Conference of Civil Engineering 6 - 8 July, 2011
211
Different percentages of glass grains with similar grain sizes is used instead of sand as
fine aggregate in preparation of plasters made from ordinary Portland cement. The
characteristics of prepared mortars and cement glass bond will be investigated by
determination of compressive strength and bulk density.
Glass that has been reduced to a fine aggregate size fraction less than 4.75mm in
size exhibits properties similar to that of fine aggregate or sandy material with relative
high stability, due to the angular nature of crushed glass particles. Glass-cement plaster
is a mixture of suitable plaster sand, broken glass, Portland cement and water which is
normally applied to walls interiors and exteriors to achieve a smooth surface.
4. Loadings on Strawbale Wall
It is important to note that un-plastered walls can carry a very small load before
compressing beyond acceptability or buckling. Plastered walls, on the other hand,
increase drastically in strength, especially if they are detailed to carry vertical loads
through the skin or plaster. Strawbale can bear load either flat or on edge.
5. Methodology
5.1 Production Of Strawbale Block Specimens
Selection of materials and dimension: This experimental programme covered the
model of strawbale block units (sizes: 160mm x85mmx90mm). In constructing the
strawbale wall, materials needed for the construction has to be selected such as
portland cement(OPC), getting fine aggregates which is clean, natural, hard sand (free
from chalk and clay) of 100% passing through sieve no 5mm was employed in the mix,
water and powder glass. A steel mould of 160x85x90mm was fabricated for moulding
the strawbale block units. Also maize stem was gotten and cut into 5cm sizes and
glasses was crushed to powder form and then sieve with 4mm sieve.
Particle size distribution: Commercially available clean, natural hard sand (free from
chalk and clay) of 100% passing sieve no 5mm and which complies with BS882:1201
is employed in the mix. The sand was well graded to conform to the limit given in the
table 1 of BS882:1201 for the maximum size aggregate to the strawbale mix.
The grading test results are shown in table 3.1 for the determination of the
distribution for the number of different sized particles present. Maximum sieve
(BS410:1976) size of 5mm was employed for the production of the block specimens.
Table.1 Grading of sand for strawbale block.
Sieve size (mm) 5.0 4.0 2.0 1.0 0.5 0.4 0.25 0.125 0.063
Weight of sieve (g) 1535 654 555 531 503 485 480 459 444
Sieve +retained (g) - 586 668 673 713 565 661 635 540
Retained weight (g) - 22.5 114 142 211 81 181 176 60
Percentage retained (%) - 2.3 11.4 14.2 21.1 8.1 18.1 17.6 6.1
Cummulative % passing 100 97.7 86.3 72.1 51.0 42.9 24.8 7.2 1.1
Proceedings of CIVIL2011@UNILORIN 3rd Annual Conference of Civil Engineering 6 - 8 July, 2011
212
Weight of the pan =267g weight of sample = 500g Weight of pan + sample = 767g;
Time of shaking = 20 minutes.
Batching, Mixing, Moulding, and Curing of Blocks: In moulding the block, after
cement and aggregates have been acquired, then following the mix ratio of 1:6 (cement
to fine aggregates) for moulding the block, thorough mixing was done for the cement
and sand, this was poured into the mould say to one third of the mould, then using
maize stem as our bale which has been cut into moderate sizes of 5cm was arranged
into the mould and then fill up the mould which is then compacted. After the block has
been moulded it was allowed to cure for twenty eight days of which the first three days
of curing was very important until sufficient strength is gained for 28 days. After
curing has been done, some of the block was joined together as double coarse using
mortar ratio of 1:3, and some left as a single block.
Plastering of the constructed strawbale: The materials used for plastering include
cement, fine sand and powdered glass. In this project, during plastering the mix ratio
was varied in other to look for the ratio that can blend with the strawbale wall. The
crushed glass was varied with the plaster sand in certain proportion as the proportion of
cement remain constant. These are the mix ratio used for the plastering 1:0:4, 1:1:3,
1:2:2, 1:3:1, 1:4:0 of cement to sand to crushed glass respectively. This mix ratio was
used to plaster on both the single and double layer. After plastering has been done, it
was allowed to set and dry before testing.
Compressive strength test: Compressive strength test was conducted for plastered
strawbale wall, using the same block specimens of size (170mm x 95mm ). A vertical
load was applied to each wall specimen, by means of a compressive strength test
machine, which was sufficiently stiff in flexure to ensure that the top and bottom of the
panel were restrained against rotation. The magnitude of the axial load applied to the
panel was read off the pressure gauge. The appropriate value of the wall characteristic
strength was obtained using gross sectional area of the wall.
Proceedings of CIVIL2011@UNILORIN 3rd Annual Conference of Civil Engineering 6 - 8 July, 2011
213
(a) One block (b) Two-block prism
Figure 1 Set-up of experimental test for compression
Table 3.2 Results of compressive strength of plastered strawbale
wall for single and double coarse.
The compressive strength results were calculated using equation (1).
σv = W/A (1)
From the above equation, σv is the vertical stress, W = applied load
and A =cross sectional are
5.2 Documentation
Compressive strength (N/mm2) = crushing load (N) / plan area (mm2)
Where; area = length x breadth
Length (plastered) = 170mm, breadth (plastered) = 95mm
Length (unplastered) = 160mm, breadth (unplastered) = 85mm.
From the table above;
Laboratory investigations carried out to assess the potential of the crushed recycled
glass as natural sand replacement using ratios of 25%, 50% and 75% shows that with
the incorporation of 50% (i.e ratio 1:2:2) of crushed glass as a natural sand
replacement, the compressive strength have marginally increased.
5.3 Stresses analysis using SAP2000
Specim
en
Plaster
ratio
(Cement
:sand:gl
ass)
Plan
e
area
(mm2)
Crushing load
(N)
Compressive
Strength
(N/mm2)
Single
coarse
Double
coarse
Single
coarse
Double
coarse
1
1:0:4
16150
35530
34722
2.20
2.15
2
1:1:3
16150
42313
39083
2.62
2.42
3
1:2:2
16150
47804
45543
2.96
2.82
4
1:3:1
16150
36660
36014
2.27
2.23
5
1:4:0
16150
45543
43120
2.82
2.67
Unplast
ered
___
13600
29648
27880
2.18
2.05
Proceedings of CIVIL2011@UNILORIN 3rd Annual Conference of Civil Engineering 6 - 8 July, 2011
214
The figure below shows the maximum stresses for the glass-cement plastered strawbale
wall using SAP2000.
Figure 2 applied load on strawbale wall Figure 3 Deflected shape of the glass
cement strawbale wall.
Proceedings of CIVIL2011@UNILORIN 3rd Annual Conference of Civil Engineering 6 - 8 July, 2011
215
Figure 4 Maximum stress of a glass cement plastered strawbale wall
6. Discussion of Results
In the laboratory for strength analysis of a strawbale wall when plastered with glass
cement as an aggregate blend, it shows that the mix proportion of 50%(1:2:2) has the
maximum shear strength. That is, the laboratory investigation carried out to access the
potential of the crushed recycled glass as natural sand replacement using ratios of 25%,
50%, and 75% shows that the incorporation of 50% of crushed glass as a natural sand
replacement, the compressive and flexural strength have marginally increased, while
the indirect tensile strength marginally decreased.
For the height of the strawbale wall = 80mm and thickness, t = 95mm, and plaster
thickness of 5mm, the predicted maximum stresses is 3.38N/mm2 using SAP2000 and
that of the maximum observed stresses in the laboratory is 2.96N/mm2 which shows
that they are so close and that the predicted value is greater than that of the observed
value. Also it is noted that the stresses at the face of contact between lass cement
plaster and strawbale wall, from the compression zone, the values of the stresses keep
on reducing to the tension zone (3.38N/mm2 to 0.78N/mm2) respectively. This implies
that the stress stability of the plastered strawbale wall are okay. The maximum stresses
calculated using SAP 2000 is shown in the table 4.1 below for both glass-cement
plastered and cement plastered strawbale wall.
Proceedings of CIVIL2011@UNILORIN 3rd Annual Conference of Civil Engineering 6 - 8 July, 2011
216
Table 4.1: Differences between the predicted and observed s
tresses for both plaster composition.
Wall composition
Maximum predicted
stress using Sap2000
Max
imum observed
stress in the laboratory
Glass cement plastered
strawbale wall
3.38N/mm
2
2.96N/mm
2
7. Conclusion And Recommendation
Glass-cement plastered strawbale wall has shown an adequate resistance against
vertical loading, as shown by the results obtained between predicted and observed
maximum stresses. (i.e. maximum stress for glass-cement plastered strawbale wall is
3.38N/mm2 for predicted using SAP2000 and 2.96N/mm2 as observed in the
laboratory). Laboratory investigations carried out to assess the potential of crushed
recycled glass as natural sand replacement using ratios of 25%, 50% and 75% shows
that with the incorporation of 50% (1:2:2) of crushed glass as a natural sand
replacement in plastering, the compressive strength have marginally increased.
Also it is noted that the stresses at the face of contact between lass cement plaster
and strawbale wall, from the compression zone, the values of the stresses keep on
reducing to the tension zone (3.38N/mm2 to 0.78N/mm2) respectively. This implies that
the stress stability of the plastered strawbale wall are okay. From this experiment, it
could be recommended that 50% of crushed glass as a natural sand aggregates blends
be introduced in plastering for wall design.
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