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The use of cubic shaped sawdust in heavy clay products
119
CERAMURGla INTERNATIONAL, Vol. 4. n. 3, ,978
The Use of Cubic Shaped Sawdust lay Products in Heav I_~-_”
-_^__
CI
.-~_-YU~~
M.J. MURRAY uilding
and
. UVERSIDGE
Research,
The effect of the addition of sawdust on the of extruded heavy clay bodies before and after firing is described. It was found that sawdust particles of cubic shape, produced by swage-set band saws, could be added in greater quantities and had less adverse effect on the physical properties than the elongated particles produced by spring-set circular saws.
1 - INTRODUCTION
With improved production technology the strength of extruded clay building bricks is nowadays generally much higher than is required for their application, and Aust,ralian standards are easily met. Australian Standard A-21 calls for a brick with a minimum compressive strength of 10.4 MPa and a modulus of rupture of 2.77 MPa to satisfy class I( C 15requirements, which is used for most building purposes. The unnecessarily high strength of bricks produced in Australia h’as enabled brilck manufacturers to reduce the load-bearing area in a brick by introducing holes in the bed face or broad plane of the brick. This has the advantage of reducing the quantity of clay used to make a brick and also increases the total surface area of the brick, enabling faster drying and firing. A limitation on the maximum area of the holes is irnpo~, sed by the problem of mortar loss into these cavities when the bricks are laid into a wall. This problem can be partly offset by increasing the number of holes and reducing the cross-sectional area of each hole to a size which will enable the mortar to bridge the cavity. This solution, however, introduces engineering problems with extruder die construction and increased power requirements at the extruder. Another technique for reducing the clay content of a brick is to introduce into the bo organic particles cavities which will burn out on firing and I ve closed within. This technique is widely used in the ~rod~~~io~ of refractory i~s~~a~~~~ bricks. From a stress distribution aspect these cavities should be spherical or near spherical in shape, however the availability of low-cost spherical organic particles is limited. Recent success has been claimed by a process which uses expanded polystyrene beads ‘, but the process is covered by patent, there was difficulty in obtaining large quantities of the material in Australia, and the polystyrene produces a pungent odour upon decomposition in firing. The utilization of waste products has been attracting greater interest from research organizations and industry, and it was .in this area that a search was made for a spherical or approximately spherical particle. In Australian one of the largest sources of organic waste is the sawmilling industry where sawdusts constitute a waste output of approximately 3 x IO 6 cubic metr
CSlRB,
Australia
difficulty in disposing of sawdust residues. ~~v~ro~rne~~ tal authorities are imposing .sZrict control on emissions from combustion and are also watchful of the Black liquor run-off psoduced by sawdust dumps. The technique of introducing sawdust in heavy clay buildin manufacture has been tried in the past, but unsatisfaetory sawdusts, unsuitable kilns, and the state of the technology at that time prevented its acceptance. The aim of this investigation was to determine whether sawdust could be utilised if it is processed or produced as a I( near spherical )) particle, and whether, with modern technology, it could now be more successfully incorporated in clay building products. An examination of sawdusts produced from various milling techniques suggested that the ct cubic type 1~ sawdust produced by swage-set band saws would have a high likelihood of meeting the desired requirements.
2.1 ^ A white burning clay was selected for the initial investigation and a commercial red brick body was used for subsequent trials. A chemical analysis of these materials is given in Table I. The white burning clay was initially chosen for its low FeL3 content in order to minimize the influence of black coring on the physical properties of the fired samples. Three sawdusts were chosen for the study, an elongatad particle sawdust which was obtained from sawdust produced by a circular saw and two sawdusts with cubic-shaped particles, which were obtained from bandsaws. The use of bandsaws which have swage-set teeth is a relatively recent log conversion technique in ~~~stralia~ sawmills. andsaws are being used in an increasing number of millls and are ~~placi~~ the circular saws
LE I - Chemical
__I-SiO, ALO,
analysis
of clays.
White burning clay (%I 60.92 25.43 0.36 0.26 0.20 0.19 0.39 0.55 12.11
FezOl WC’
CaO iVESlO GO
TiO, MnO Loss on ignition
100.42 m
.i~,_j__
Red commercial brick clay (O/o) ---. 67.90 18.00 2.15 1.25 0.40 0.12 2.70 1.08 0.03 6.35 “_1___ 99.98 ._~_~_.~_
-=
M.J.
120 .-.
_Silvertop [band-saw)
Sieve range nominal aperture size
%
MURRAY
II = Analysis Sieve analysis Messmate (band-saw) [R) % % Cumulative
ash
$,M)
Cumulative
and R.M.
of
LIVERSIDGE
sawdusts.
Silvertop ash (circular saw) (K) % Cumulative %
-.2
.2
0
1.4
1.6
.6
.6
+3.35 mm
1.70mm
-3.35
mm +
-1.70
mm + 1.00
-
.3
.3
9.4
9.7 46.5
5.2
6.8
36.8
43.8
50.6
4.3 51.6
4.9
--I .OOmm + 500 urn
56.5
44.0
90.5
-500
38.0
88.6
34.4
90.9
a.3
98.8
mm
urn + 250 urn pm (Pan)
-250
11.4
100
9.1
55.3%
400
62.7%
_p._~__l__yI__,__.~_~,~~_._.-~~~~~~~-~~..”-”.._-
analysis
Caiorific
analysis
15.4%
greatly whh species. of wood are shown
Typical below,
[dry wood) 74-63 % 17-24% 1%
Volatile matter Fixed carbon [charcoal) Ash Ultimate Carbon Hydrogen Oxygen Ash
100
._--rr_._=_ ._.~ I,,_l-_I^“~.~_*--j__l_TLn”l___ix ___xI_-
oes not vary irhe elemental ~~rnp~s~t~o~ of wood average figures for proximate and ultimate analysis expressed as a percentage by weight’. Proximate
1.2
(dry
wood] 52% 6% 41% 1%
Value
a
(dry wood)
Calorific values for Australian hardwoods are generally in the range 19,200-20,500 kJ/kg while the values for softwoods are generally of the order of 20,500-22,600 kJ/kg the variations being due mainly to the presence of resins, oils or other flarnmable matter.
^ ._
._L1_l
.
I _..._ _.~___._._ _“__“ __..” ^__=__ll_rm_l
-____
Sawdust
additive
made
As a portion
Volume (cm31
Species
Weight kJl
--
Control
body K1 K2 Lz
iIll1 PI2
M3 M4 Note: A white
S
--
Silvertop ash from saw circular
Silve~o~ ash from band-saw burning
clay
was
”
of test
bodiea
clay.
W
0
-
0
0
12.2 30.6 61.2 48.0
100 250 500 400
5.0 12.5 25.0 20.0
4.3 10.8 21.7 17.3
367 890 1310 1837
12.2 29.7 43.7 61.2
125 294 435 612
6.3 14.7 21.7 30.6
3. 9.0 13.4 18.8
330 900 1290
21.0
65
30.0 43.0
442
15.5 22.1
10.0 14.2
1837
61.2
633
31.6
20.4
these
burning
sawdust 6%I
-
for
Compositions white
.__-.
Green
367 918 1837 1440
used
111 from
As a portion of dryI weioht _
sawdust (QI Body
TA
2
tests.
which usually have spring-set teeth, for many operations. The band-saw sawdusts were obtained from mills in the Orbost, Victoria area and were identified as Messmate (eucalyptus ~b~~~ua9 (Fig. l(a)9 and Siivertop ash (Eucalyptus sieberi) (Fig. i(b]). The circular saw sawdust was obtained from a mill at Cabbage Tree Creek near
Each of the sawdusts, in turn, was measured out by volume and the weight noted. It was slowly addad to a measured quantity of dry control clay body whilst mixing took place in a sigma mixer. Water was then added and fifteen minutes mixing given to each batch to ensure b0mo~ene~ty. The ~~rn~~s~t~~~s of each test III. atch are ~resent~d in ach
batch
was
then
into
a
THE
USE
OF
CUBIC
SHAPED
SAWDUST
IN
HEAVY
CLAY
121
PRODUCTS
section was produced. The extrusion marked with shrinkage measurement cut into 120 mm lengths.
was immediately indentations and
An assessment was made of the ease or otherwise of extrusion of the clay-sawdust body from a de-airing extruder. In addition the total length of body extruded at constant cross-section was measured for each come position. The weight of clay used was kept constant but the quantities of sawdust were varied.
FIGURE Ifa) - Messmate Satch 3’. (x 7).
(E.
obliqua)
sawdust
from
band-saw.
I’he extruded bars were dried in an evironment cabinet’ with a drying atrnosphere initially of 95% relative humidity at 40°C. After 8 h the temperature was gradually increased to llO”C and the relative humidity reduced to below 30 per cent and maintained until drying was completed. Firing took place in a gas-fired shuttle kiln heated at a rate of 150”C/h. Two firings in different kiln atmospheres were carried out: firstly, a reducing atmosphere and secondly an oxidizing atmosphere. Bars from both atmosphere trials were cross-sectioned and examined for evidence of carbon or black core.
2.5 - ‘~~~r~~~ra~~~@~ri~
a~~~~§~
TGA’s of the sawdusts were carried their behaviour during heating.
out to determine
Phe bars were measured for length and weight after drying and after firing. binear shrinkage and weight loss were determined. Dry bars and fired bars were also tested for modulus of rupture, and compressive strength. Five samples were used in every test and the average results were recorded. Standard deviation and standard error statistical determinations were also ap. plied to the results. FIGURE l(b) - Silvertop Batch ‘M’. (x 7).
ash
(E. sieberi)
sawdust
from
band-saw.
i’he irrfluer~ce of the cubic: particle sawdusts on the e’x, trudability of the product was minimal. The e~o~~ate~ sawdust however tended to clog the small screen leading into the de-airing chamber of the laboratory extru” der and it required frequent cleaning. The elongated sawdust also increased the resistance to wire-cutting of the extruded column. Less resistance to cutting was experienced from bodies containing CD bit sawdust. A significant increase was achieved in the volume of freshly extruded body for a given quantity of clay by the addition of sawdust in the body - see Table IV.
FlGURE 1 (c)
- Silvertop
ash
(E.
sieberi)
sawdust
from
eircukr
The water content at extrusion for a given volume of body was reduced by increased sawdust content. The control body without sawdust required 34.5% of water for satisfactory extrusion, whereas for example the body M4 required 23.6% water for an equi\/a~e~~ output volume, ie. 47.7% water was used ~~~c~ud~~~ the r~o~st~re in the sawdust] but relative v~i~~~~ was in
122
M.J. ^__I__c_I_____IIc-
-
_ --l___l----
._IL___I-_
-11-
. “-.-_-_-.-~“-“--.
-___LII-l----~-
-
LE Iv
Batch
Water required to achieve extrudability [WA (% of dry clay weight)
No.
Control
body
Body
Kl ::
S
Water content in added sawdust (W,) (“/a of dry clay weight)
Relative W, i- W, (% of dry clay weight]
volume of extruded
Total water content of body (~o,~~~~~t
product (%I
--
IbWHHAY
and
R.,M.
LlVERSlUCi~
---_I
_ Water
volume
of test
burning
clay.
content bodies made
and output from white
-~~
34.5
0
34.5
100
34.5
33.1 33.2 36.0 38.1
0.7 1.7 2.7 3.3
33.8 34.9 38.7 41.4
111.8
154.1 190.0 201.3
30.2 22.6 20.4 20.6
34.0 35.0 35.7 36.6
2.5 5.7 8.3 11.8
36.5 40.7 44.0 46.4
145.4 170.3 186.0 197.3
25.1 23.9 23.7 24.5
34.6 37.4 36.8 36.5
2.3 5.5 a9 11.2
36.9 42.9 44.7 47.7
142.8 160.3 172.9 202.2
25.6 26.8 25.8 23.6
&I increasing addition of sawdust into the body brought about a progressive reduction in drying shrinkage (Ta’ ble VI. The transverse strength of dry bars was in most cases increased by the addition of sawdust (Fig. 21.
‘G4 curves of the sawdusts and the white clay body (Fig. 31, together with firing trials showed that a slow rate of temperature rise between 230 and 500°C was required for the distillation of volatiles from the saw. dust. A t~r~~~e~t ox~‘~~~i~g atrn~s~~~re From ~~~rox~rn~., tely 780 to 880°C ensured complete oxidation of the carbonaceous residue and prevented black coring. This temperature range could vary slightly according to the type of clay. The wbi~e”b~r~ir~~ clay samples which were bred un reducing conditions I6.5% 60, flue gas content) produ.ted heavily carbon-impregnated interiors. Heavier addi~ -tions of sawdust, above about II % dry weight, opened the bodies and allowed some of the products of com-
__ 1..-.
Batch No.
___lc_l__l”~l--~
~-I~
Linear drying shrinkage %
.,I.-. .,--
-~--l..ll^__--_r
Total fired shrinkage
yll
Fired weight lOSS
%
%
Fired density g/cm3
s
9.0
17.3
10.1
2‘05
K1 K2 K3 K4
7.5 6.6 5.2 5.3
16.0 15.3 13.9 14.0
14.2 17‘5 23.5 26.1
1.82 1.69 1.46 1.33
RI R2 R3 H4
8.1 7.6 7.3 6,6
16.6 16.l 1S.6 45.2
13.2 17.2 20.1 23.5
1.65 1.67
Ml rm
8.2 7.3 6S 6.2 . --
16.7 15.9 15.4 24.7
13.8 18.2 19.9
:l
~I
I.~L.._,--I;x.-,;^I”.~~.
1.61 1.42
IHE
USE
OF
CUBIC
SHAPED
SAWDUST
IN
HEAVY
CLAY
PHODUCTS
123
.
.._1._-_.
.A
1-
A-..
i.__
.1--.
1..
_..A.
m
10
of
tb
FBGURE
UW) (Centrel [Bottom]
4
fired
w~it~~c~~y bodies.
of sectioned red-clay bodie?l without sawdust originally containing band-saw sawdust originally containing circular-saw sawdust. _ hterior
bustion to escape, reducing the quantity of carbon. Sectioned samples of the white body fired under oxi dizing conditions (9% CO) flue gas content) showed no sign of black coring. Similar firings with red clay bodies likewise produced no entrapped carbon or black coring under these firing conditions despite the higher Fe0 content (Fig. 4). The interior of the sectioned red clay bodies also srrowed (Fig. 4) the contrast between a body produced without sawdust (top) and bodies made from sawdust from a swage-set band-saw (centre) and a spring-set circular saw (bottom). The total fired shrinkage (Table IV) in all cases was decreased by the introduction of sawdust. The modulus of rupture strength of the fired samples Fig. 5) was in most cases increased by sawdust addition. The compressive strengths of the fired bodies are shown in Figure 6. With the exception of the elongated sawdust samples the strengths of the white clay bodies increased with increased sawdust content up to appro ximately 14% dry weight. The control body without additives had a fired density of 2.05 g/cm’ (Fig. 7). The addition of both types of sawdust reduced the fired density by approximately the same amount for equal weights of dry sawdust. A 230 x 110 x 76 mm brick with a density of 2.05 would weigh about 4 kg. That same brick would be reduced in weight to 2.7 kg by introducing 20% by weight of dry sawdust. y extruding that same brick with holes e~u~va~e~t to 32% of its total volume the weight could be further reduced to a~~rox~rnste~y 1.9 kg. The type of clay and the ~ern~er~t~r~ of hrrng are different in each plant and the ~~a~~it~ of to ~~aj~t~i~ brick ~~~~lity within the stan ~va~~a~~~ ~~~~vi~~a~~y~
0
10
a0
i’ElT (X by ~~~U~~
7
1
Densities
of
fired
bodies
after
dqj
wei&t)
various
~~~~~s~
M.J. MURRAY
124
__“__
___~..._
._I________.____.p.wV-----
were rnade on commercially produced bricks were lower in the light weight bricks than in the standard brick. or movement of water through light The pc!rmeability brick may be reduced by firing to a slightly weight than would be the case for the higher temperature same body without sawdust. ,Efflorescence caused by the movement of soluble salts to a drying surface and frost resistance should no% be influenced, provided a brick is adequately fired and capillaries have been closed off or reduced to a minimum. However in the situation where a brick has been underfired and water can penetrate and be contained in s cavity close to the surface, spalling due to freezing and efflorescence could occur. Bricks made with sawdust erefore be used cautiously above the snowshoul line or on the sea coast. An improvement in packing can occur with the add~%~or~ of sawdust, and should be of particular benefit with clays vuhich are considered too plastic on i-heir own or clays which are considered unsuitable for commercial use because of high levels of shrinkage. As a consequence the amount of interstitial water cont’ained in a body should decrease, with an overall reduction in water content on a volume basis. This was verified in the results. Tannin is well known and used as an organic deflocculant. The tannins contained in sawdust could also achieve a deflocculating effect on some clay bodies, and bring about improvements in plasticity. A contribution to the energy requirements for firing is made by combustion of sawdust within the brick, and savings with fuel consumption should be achieved. The energy liberated by the complete combustion of 1 kg of dry sawdust is between 18 and 22 megajoules3, de’pending upon species. In a modern tunnel kiln with an energy requirement of 2300 kJ/kg of ware the addition of only 12% by weight of dry sawdust to a body would provide more than enough energy to fire the kiln. In practice however, the loss of some of the ~~~~bust~ble volatiles before ignition can occur and the necessity for an oxidizing atmQspbere during part of the firing would bring about losses and lower this figure, e of the advantages of i~%Kod~~~~g sawdust into a ick: -Poflutron problems from some presen% a~~~~~% disposal methods would be reduced. - The brick maker would use less clay per brick. - Quicker drying is possible. _I The reduced water requirements in forming a saw,. dust brick should enable savings to be made in the energy used for drying. reen ~tre~gtb$ of bricks ee ~re=f~~~~g losses. the ~~lri~ka~e
containing and
sawdust
R.M.
LIVERSIDGE
and as a consequence inertia of a dwelling would be reduced.
of reduced constructed
mass the thermal with the material
- Additional benefits such as nailability and easier cutting would be advantages, particularly for electrlcians, carpenters and plumbers involved in internal wall construction. Disadvantages that can be imposed by the i~corporation of sawdust in bricks are: - A greater resistance to wire cutting of the extruded column can be experienced. Although the use of purely cubical sawdust, not contaminated with fibrous particles and the use of only fine sawdust [below 2.5 mm diameter) will minimise this problem. - The release of volatiles from the saw preheating can create a G(wood fire )) odour if leakages around the exhaust stack exist. Future tunnel kilns which are planned for firing sawdust bricks should incorporate a due% for recycling the volatiles into the combustion zone where the thermal energy liberated by their combustion would be utilized.
The aim of the study was to demonstrate that waste sawdust could be used to advantage by incorporating it in heavy clay products. It was shown that fresh cubic shaped sawdust was more suitable for this for this purpose because it affected the strength of the purpose because it affected the strength of the product to a smaller degree than an equivalent quantity of the splintery sawdust. More sawdust could therefore be added than was previously possible and enhance the benefits that could be derived from this action. The wide distribution of the sawmilling and brickmaking industries throughout Australia and the common location of both of these i~d~~~ries in many reentry towns should provide country brickmakers with a greater portunity to benefit from sawdust additions than t city ~Q~nterparts. The commercial production of lightweight bricks has now commenced at a large country brickworks and extruded bricks made with 1 par% of sawdust by bulk volume to 2 parts clay have been successfully produced. The bricks have a fired weight of 2.3 kg and a compressive strength of approximately 20 MPa. A peach-bloom colour in the centre of the brick face has been imparted on a normally cream firing body by exploiting the reducing effect of the sawdust combustion. a brick ~fld~s%ry
~~~%a~ni~~gsawdust
of the brick al accuracy
~~ri~~g ~~~~~~ Is from the fired
.- The contribution to the energy requirements made by the combustion of sawdust could e~~bie ~av~~~~ in fuel. In addition the firing load in a kiln would be reduced as a consequence of the lighter weight products and further add to fuel savings. A light-weight brick would be an advantage in transportation and could be of particular benefit to country bri~kma~ers who market over greater distances. The bricklayer would also benefit from ba~dling a lighter brick. ckwork loads on f~~~da%~orls would bodies latterly
and
__________
roofing weight
tile which is thermally insulating an could be a means of wj~~~~~ back lost markets.
1. R. HIEBEL, Produits alleges de terre cuite ajout de polystyrene expanse. Terre Cuite 4 (1969) 21-31. 2. M.J. MURRAY, ccAn Environment Generator far Ce’ramic Drying Studies )), CSIHO Aust. Div. Bldg. Res. Report CT. 2, (1972). 3. C.B. PRAKASH and F.E. MUR’RAV, 11A Review on Wood Waste Burning I), Pulp and Paper Magazine of Canada, 73 (1972). Timbers of New South Wales 4. I<.R. BOOTCE. I%The Commercial and their Use 11, Angus and Robertson, P/L, Sydney (1971).
CERAMURGla INTERNATIONAL, Vol. 4. n. 3, ,978
The Use of Cubic Shaped Sawdust lay Products in Heav I_~-_”
-_^__
CI
.-~_-YU~~
M.J. MURRAY uilding
and
. UVERSIDGE
Research,
The effect of the addition of sawdust on the of extruded heavy clay bodies before and after firing is described. It was found that sawdust particles of cubic shape, produced by swage-set band saws, could be added in greater quantities and had less adverse effect on the physical properties than the elongated particles produced by spring-set circular saws.
1 - INTRODUCTION
With improved production technology the strength of extruded clay building bricks is nowadays generally much higher than is required for their application, and Aust,ralian standards are easily met. Australian Standard A-21 calls for a brick with a minimum compressive strength of 10.4 MPa and a modulus of rupture of 2.77 MPa to satisfy class I( C 15requirements, which is used for most building purposes. The unnecessarily high strength of bricks produced in Australia h’as enabled brilck manufacturers to reduce the load-bearing area in a brick by introducing holes in the bed face or broad plane of the brick. This has the advantage of reducing the quantity of clay used to make a brick and also increases the total surface area of the brick, enabling faster drying and firing. A limitation on the maximum area of the holes is irnpo~, sed by the problem of mortar loss into these cavities when the bricks are laid into a wall. This problem can be partly offset by increasing the number of holes and reducing the cross-sectional area of each hole to a size which will enable the mortar to bridge the cavity. This solution, however, introduces engineering problems with extruder die construction and increased power requirements at the extruder. Another technique for reducing the clay content of a brick is to introduce into the bo organic particles cavities which will burn out on firing and I ve closed within. This technique is widely used in the ~rod~~~io~ of refractory i~s~~a~~~~ bricks. From a stress distribution aspect these cavities should be spherical or near spherical in shape, however the availability of low-cost spherical organic particles is limited. Recent success has been claimed by a process which uses expanded polystyrene beads ‘, but the process is covered by patent, there was difficulty in obtaining large quantities of the material in Australia, and the polystyrene produces a pungent odour upon decomposition in firing. The utilization of waste products has been attracting greater interest from research organizations and industry, and it was .in this area that a search was made for a spherical or approximately spherical particle. In Australian one of the largest sources of organic waste is the sawmilling industry where sawdusts constitute a waste output of approximately 3 x IO 6 cubic metr
CSlRB,
Australia
difficulty in disposing of sawdust residues. ~~v~ro~rne~~ tal authorities are imposing .sZrict control on emissions from combustion and are also watchful of the Black liquor run-off psoduced by sawdust dumps. The technique of introducing sawdust in heavy clay buildin manufacture has been tried in the past, but unsatisfaetory sawdusts, unsuitable kilns, and the state of the technology at that time prevented its acceptance. The aim of this investigation was to determine whether sawdust could be utilised if it is processed or produced as a I( near spherical )) particle, and whether, with modern technology, it could now be more successfully incorporated in clay building products. An examination of sawdusts produced from various milling techniques suggested that the ct cubic type 1~ sawdust produced by swage-set band saws would have a high likelihood of meeting the desired requirements.
2.1 ^ A white burning clay was selected for the initial investigation and a commercial red brick body was used for subsequent trials. A chemical analysis of these materials is given in Table I. The white burning clay was initially chosen for its low FeL3 content in order to minimize the influence of black coring on the physical properties of the fired samples. Three sawdusts were chosen for the study, an elongatad particle sawdust which was obtained from sawdust produced by a circular saw and two sawdusts with cubic-shaped particles, which were obtained from bandsaws. The use of bandsaws which have swage-set teeth is a relatively recent log conversion technique in ~~~stralia~ sawmills. andsaws are being used in an increasing number of millls and are ~~placi~~ the circular saws
LE I - Chemical
__I-SiO, ALO,
analysis
of clays.
White burning clay (%I 60.92 25.43 0.36 0.26 0.20 0.19 0.39 0.55 12.11
FezOl WC’
CaO iVESlO GO
TiO, MnO Loss on ignition
100.42 m
.i~,_j__
Red commercial brick clay (O/o) ---. 67.90 18.00 2.15 1.25 0.40 0.12 2.70 1.08 0.03 6.35 “_1___ 99.98 ._~_~_.~_
-=
M.J.
120 .-.
_Silvertop [band-saw)
Sieve range nominal aperture size
%
MURRAY
II = Analysis Sieve analysis Messmate (band-saw) [R) % % Cumulative
ash
$,M)
Cumulative
and R.M.
of
LIVERSIDGE
sawdusts.
Silvertop ash (circular saw) (K) % Cumulative %
-.2
.2
0
1.4
1.6
.6
.6
+3.35 mm
1.70mm
-3.35
mm +
-1.70
mm + 1.00
-
.3
.3
9.4
9.7 46.5
5.2
6.8
36.8
43.8
50.6
4.3 51.6
4.9
--I .OOmm + 500 urn
56.5
44.0
90.5
-500
38.0
88.6
34.4
90.9
a.3
98.8
mm
urn + 250 urn pm (Pan)
-250
11.4
100
9.1
55.3%
400
62.7%
_p._~__l__yI__,__.~_~,~~_._.-~~~~~~~-~~..”-”.._-
analysis
Caiorific
analysis
15.4%
greatly whh species. of wood are shown
Typical below,
[dry wood) 74-63 % 17-24% 1%
Volatile matter Fixed carbon [charcoal) Ash Ultimate Carbon Hydrogen Oxygen Ash
100
._--rr_._=_ ._.~ I,,_l-_I^“~.~_*--j__l_TLn”l___ix ___xI_-
oes not vary irhe elemental ~~rnp~s~t~o~ of wood average figures for proximate and ultimate analysis expressed as a percentage by weight’. Proximate
1.2
(dry
wood] 52% 6% 41% 1%
Value
a
(dry wood)
Calorific values for Australian hardwoods are generally in the range 19,200-20,500 kJ/kg while the values for softwoods are generally of the order of 20,500-22,600 kJ/kg the variations being due mainly to the presence of resins, oils or other flarnmable matter.
^ ._
._L1_l
.
I _..._ _.~___._._ _“__“ __..” ^__=__ll_rm_l
-____
Sawdust
additive
made
As a portion
Volume (cm31
Species
Weight kJl
--
Control
body K1 K2 Lz
iIll1 PI2
M3 M4 Note: A white
S
--
Silvertop ash from saw circular
Silve~o~ ash from band-saw burning
clay
was
”
of test
bodiea
clay.
W
0
-
0
0
12.2 30.6 61.2 48.0
100 250 500 400
5.0 12.5 25.0 20.0
4.3 10.8 21.7 17.3
367 890 1310 1837
12.2 29.7 43.7 61.2
125 294 435 612
6.3 14.7 21.7 30.6
3. 9.0 13.4 18.8
330 900 1290
21.0
65
30.0 43.0
442
15.5 22.1
10.0 14.2
1837
61.2
633
31.6
20.4
these
burning
sawdust 6%I
-
for
Compositions white
.__-.
Green
367 918 1837 1440
used
111 from
As a portion of dryI weioht _
sawdust (QI Body
TA
2
tests.
which usually have spring-set teeth, for many operations. The band-saw sawdusts were obtained from mills in the Orbost, Victoria area and were identified as Messmate (eucalyptus ~b~~~ua9 (Fig. l(a)9 and Siivertop ash (Eucalyptus sieberi) (Fig. i(b]). The circular saw sawdust was obtained from a mill at Cabbage Tree Creek near
Each of the sawdusts, in turn, was measured out by volume and the weight noted. It was slowly addad to a measured quantity of dry control clay body whilst mixing took place in a sigma mixer. Water was then added and fifteen minutes mixing given to each batch to ensure b0mo~ene~ty. The ~~rn~~s~t~~~s of each test III. atch are ~resent~d in ach
batch
was
then
into
a
THE
USE
OF
CUBIC
SHAPED
SAWDUST
IN
HEAVY
CLAY
121
PRODUCTS
section was produced. The extrusion marked with shrinkage measurement cut into 120 mm lengths.
was immediately indentations and
An assessment was made of the ease or otherwise of extrusion of the clay-sawdust body from a de-airing extruder. In addition the total length of body extruded at constant cross-section was measured for each come position. The weight of clay used was kept constant but the quantities of sawdust were varied.
FIGURE Ifa) - Messmate Satch 3’. (x 7).
(E.
obliqua)
sawdust
from
band-saw.
I’he extruded bars were dried in an evironment cabinet’ with a drying atrnosphere initially of 95% relative humidity at 40°C. After 8 h the temperature was gradually increased to llO”C and the relative humidity reduced to below 30 per cent and maintained until drying was completed. Firing took place in a gas-fired shuttle kiln heated at a rate of 150”C/h. Two firings in different kiln atmospheres were carried out: firstly, a reducing atmosphere and secondly an oxidizing atmosphere. Bars from both atmosphere trials were cross-sectioned and examined for evidence of carbon or black core.
2.5 - ‘~~~r~~~ra~~~@~ri~
a~~~~§~
TGA’s of the sawdusts were carried their behaviour during heating.
out to determine
Phe bars were measured for length and weight after drying and after firing. binear shrinkage and weight loss were determined. Dry bars and fired bars were also tested for modulus of rupture, and compressive strength. Five samples were used in every test and the average results were recorded. Standard deviation and standard error statistical determinations were also ap. plied to the results. FIGURE l(b) - Silvertop Batch ‘M’. (x 7).
ash
(E. sieberi)
sawdust
from
band-saw.
i’he irrfluer~ce of the cubic: particle sawdusts on the e’x, trudability of the product was minimal. The e~o~~ate~ sawdust however tended to clog the small screen leading into the de-airing chamber of the laboratory extru” der and it required frequent cleaning. The elongated sawdust also increased the resistance to wire-cutting of the extruded column. Less resistance to cutting was experienced from bodies containing CD bit sawdust. A significant increase was achieved in the volume of freshly extruded body for a given quantity of clay by the addition of sawdust in the body - see Table IV.
FlGURE 1 (c)
- Silvertop
ash
(E.
sieberi)
sawdust
from
eircukr
The water content at extrusion for a given volume of body was reduced by increased sawdust content. The control body without sawdust required 34.5% of water for satisfactory extrusion, whereas for example the body M4 required 23.6% water for an equi\/a~e~~ output volume, ie. 47.7% water was used ~~~c~ud~~~ the r~o~st~re in the sawdust] but relative v~i~~~~ was in
122
M.J. ^__I__c_I_____IIc-
-
_ --l___l----
._IL___I-_
-11-
. “-.-_-_-.-~“-“--.
-___LII-l----~-
-
LE Iv
Batch
Water required to achieve extrudability [WA (% of dry clay weight)
No.
Control
body
Body
Kl ::
S
Water content in added sawdust (W,) (“/a of dry clay weight)
Relative W, i- W, (% of dry clay weight]
volume of extruded
Total water content of body (~o,~~~~~t
product (%I
--
IbWHHAY
and
R.,M.
LlVERSlUCi~
---_I
_ Water
volume
of test
burning
clay.
content bodies made
and output from white
-~~
34.5
0
34.5
100
34.5
33.1 33.2 36.0 38.1
0.7 1.7 2.7 3.3
33.8 34.9 38.7 41.4
111.8
154.1 190.0 201.3
30.2 22.6 20.4 20.6
34.0 35.0 35.7 36.6
2.5 5.7 8.3 11.8
36.5 40.7 44.0 46.4
145.4 170.3 186.0 197.3
25.1 23.9 23.7 24.5
34.6 37.4 36.8 36.5
2.3 5.5 a9 11.2
36.9 42.9 44.7 47.7
142.8 160.3 172.9 202.2
25.6 26.8 25.8 23.6
&I increasing addition of sawdust into the body brought about a progressive reduction in drying shrinkage (Ta’ ble VI. The transverse strength of dry bars was in most cases increased by the addition of sawdust (Fig. 21.
‘G4 curves of the sawdusts and the white clay body (Fig. 31, together with firing trials showed that a slow rate of temperature rise between 230 and 500°C was required for the distillation of volatiles from the saw. dust. A t~r~~~e~t ox~‘~~~i~g atrn~s~~~re From ~~~rox~rn~., tely 780 to 880°C ensured complete oxidation of the carbonaceous residue and prevented black coring. This temperature range could vary slightly according to the type of clay. The wbi~e”b~r~ir~~ clay samples which were bred un reducing conditions I6.5% 60, flue gas content) produ.ted heavily carbon-impregnated interiors. Heavier addi~ -tions of sawdust, above about II % dry weight, opened the bodies and allowed some of the products of com-
__ 1..-.
Batch No.
___lc_l__l”~l--~
~-I~
Linear drying shrinkage %
.,I.-. .,--
-~--l..ll^__--_r
Total fired shrinkage
yll
Fired weight lOSS
%
%
Fired density g/cm3
s
9.0
17.3
10.1
2‘05
K1 K2 K3 K4
7.5 6.6 5.2 5.3
16.0 15.3 13.9 14.0
14.2 17‘5 23.5 26.1
1.82 1.69 1.46 1.33
RI R2 R3 H4
8.1 7.6 7.3 6,6
16.6 16.l 1S.6 45.2
13.2 17.2 20.1 23.5
1.65 1.67
Ml rm
8.2 7.3 6S 6.2 . --
16.7 15.9 15.4 24.7
13.8 18.2 19.9
:l
~I
I.~L.._,--I;x.-,;^I”.~~.
1.61 1.42
IHE
USE
OF
CUBIC
SHAPED
SAWDUST
IN
HEAVY
CLAY
PHODUCTS
123
.
.._1._-_.
.A
1-
A-..
i.__
.1--.
1..
_..A.
m
10
of
tb
FBGURE
UW) (Centrel [Bottom]
4
fired
w~it~~c~~y bodies.
of sectioned red-clay bodie?l without sawdust originally containing band-saw sawdust originally containing circular-saw sawdust. _ hterior
bustion to escape, reducing the quantity of carbon. Sectioned samples of the white body fired under oxi dizing conditions (9% CO) flue gas content) showed no sign of black coring. Similar firings with red clay bodies likewise produced no entrapped carbon or black coring under these firing conditions despite the higher Fe0 content (Fig. 4). The interior of the sectioned red clay bodies also srrowed (Fig. 4) the contrast between a body produced without sawdust (top) and bodies made from sawdust from a swage-set band-saw (centre) and a spring-set circular saw (bottom). The total fired shrinkage (Table IV) in all cases was decreased by the introduction of sawdust. The modulus of rupture strength of the fired samples Fig. 5) was in most cases increased by sawdust addition. The compressive strengths of the fired bodies are shown in Figure 6. With the exception of the elongated sawdust samples the strengths of the white clay bodies increased with increased sawdust content up to appro ximately 14% dry weight. The control body without additives had a fired density of 2.05 g/cm’ (Fig. 7). The addition of both types of sawdust reduced the fired density by approximately the same amount for equal weights of dry sawdust. A 230 x 110 x 76 mm brick with a density of 2.05 would weigh about 4 kg. That same brick would be reduced in weight to 2.7 kg by introducing 20% by weight of dry sawdust. y extruding that same brick with holes e~u~va~e~t to 32% of its total volume the weight could be further reduced to a~~rox~rnste~y 1.9 kg. The type of clay and the ~ern~er~t~r~ of hrrng are different in each plant and the ~~a~~it~ of to ~~aj~t~i~ brick ~~~~lity within the stan ~va~~a~~~ ~~~~vi~~a~~y~
0
10
a0
i’ElT (X by ~~~U~~
7
1
Densities
of
fired
bodies
after
dqj
wei&t)
various
~~~~~s~
M.J. MURRAY
124
__“__
___~..._
._I________.____.p.wV-----
were rnade on commercially produced bricks were lower in the light weight bricks than in the standard brick. or movement of water through light The pc!rmeability brick may be reduced by firing to a slightly weight than would be the case for the higher temperature same body without sawdust. ,Efflorescence caused by the movement of soluble salts to a drying surface and frost resistance should no% be influenced, provided a brick is adequately fired and capillaries have been closed off or reduced to a minimum. However in the situation where a brick has been underfired and water can penetrate and be contained in s cavity close to the surface, spalling due to freezing and efflorescence could occur. Bricks made with sawdust erefore be used cautiously above the snowshoul line or on the sea coast. An improvement in packing can occur with the add~%~or~ of sawdust, and should be of particular benefit with clays vuhich are considered too plastic on i-heir own or clays which are considered unsuitable for commercial use because of high levels of shrinkage. As a consequence the amount of interstitial water cont’ained in a body should decrease, with an overall reduction in water content on a volume basis. This was verified in the results. Tannin is well known and used as an organic deflocculant. The tannins contained in sawdust could also achieve a deflocculating effect on some clay bodies, and bring about improvements in plasticity. A contribution to the energy requirements for firing is made by combustion of sawdust within the brick, and savings with fuel consumption should be achieved. The energy liberated by the complete combustion of 1 kg of dry sawdust is between 18 and 22 megajoules3, de’pending upon species. In a modern tunnel kiln with an energy requirement of 2300 kJ/kg of ware the addition of only 12% by weight of dry sawdust to a body would provide more than enough energy to fire the kiln. In practice however, the loss of some of the ~~~~bust~ble volatiles before ignition can occur and the necessity for an oxidizing atmQspbere during part of the firing would bring about losses and lower this figure, e of the advantages of i~%Kod~~~~g sawdust into a ick: -Poflutron problems from some presen% a~~~~~% disposal methods would be reduced. - The brick maker would use less clay per brick. - Quicker drying is possible. _I The reduced water requirements in forming a saw,. dust brick should enable savings to be made in the energy used for drying. reen ~tre~gtb$ of bricks ee ~re=f~~~~g losses. the ~~lri~ka~e
containing and
sawdust
R.M.
LIVERSIDGE
and as a consequence inertia of a dwelling would be reduced.
of reduced constructed
mass the thermal with the material
- Additional benefits such as nailability and easier cutting would be advantages, particularly for electrlcians, carpenters and plumbers involved in internal wall construction. Disadvantages that can be imposed by the i~corporation of sawdust in bricks are: - A greater resistance to wire cutting of the extruded column can be experienced. Although the use of purely cubical sawdust, not contaminated with fibrous particles and the use of only fine sawdust [below 2.5 mm diameter) will minimise this problem. - The release of volatiles from the saw preheating can create a G(wood fire )) odour if leakages around the exhaust stack exist. Future tunnel kilns which are planned for firing sawdust bricks should incorporate a due% for recycling the volatiles into the combustion zone where the thermal energy liberated by their combustion would be utilized.
The aim of the study was to demonstrate that waste sawdust could be used to advantage by incorporating it in heavy clay products. It was shown that fresh cubic shaped sawdust was more suitable for this for this purpose because it affected the strength of the purpose because it affected the strength of the product to a smaller degree than an equivalent quantity of the splintery sawdust. More sawdust could therefore be added than was previously possible and enhance the benefits that could be derived from this action. The wide distribution of the sawmilling and brickmaking industries throughout Australia and the common location of both of these i~d~~~ries in many reentry towns should provide country brickmakers with a greater portunity to benefit from sawdust additions than t city ~Q~nterparts. The commercial production of lightweight bricks has now commenced at a large country brickworks and extruded bricks made with 1 par% of sawdust by bulk volume to 2 parts clay have been successfully produced. The bricks have a fired weight of 2.3 kg and a compressive strength of approximately 20 MPa. A peach-bloom colour in the centre of the brick face has been imparted on a normally cream firing body by exploiting the reducing effect of the sawdust combustion. a brick ~fld~s%ry
~~~%a~ni~~gsawdust
of the brick al accuracy
~~ri~~g ~~~~~~ Is from the fired
.- The contribution to the energy requirements made by the combustion of sawdust could e~~bie ~av~~~~ in fuel. In addition the firing load in a kiln would be reduced as a consequence of the lighter weight products and further add to fuel savings. A light-weight brick would be an advantage in transportation and could be of particular benefit to country bri~kma~ers who market over greater distances. The bricklayer would also benefit from ba~dling a lighter brick. ckwork loads on f~~~da%~orls would bodies latterly
and
__________
roofing weight
tile which is thermally insulating an could be a means of wj~~~~~ back lost markets.
1. R. HIEBEL, Produits alleges de terre cuite ajout de polystyrene expanse. Terre Cuite 4 (1969) 21-31. 2. M.J. MURRAY, ccAn Environment Generator far Ce’ramic Drying Studies )), CSIHO Aust. Div. Bldg. Res. Report CT. 2, (1972). 3. C.B. PRAKASH and F.E. MUR’RAV, 11A Review on Wood Waste Burning I), Pulp and Paper Magazine of Canada, 73 (1972). Timbers of New South Wales 4. I<.R. BOOTCE. I%The Commercial and their Use 11, Angus and Robertson, P/L, Sydney (1971).