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Development of calcium silicate thermal insulator in Saudi Arabia
CEMENT and CONCRETE RESEARCH, Vol. 20, pp. 767-777, 1990. Printed in the USA. 0008-8846/90. $3.00+00. Copyright (c) 1990 Pergamon Press plc.
DEVELOPMENT OF CALCIUM SILICATE THERMAL INSULATOR IN SAUDI ARABIA
A.J. AI-Tayyib I, H.J. Jung 2 and M. Shamim Khan 3 l'3Manager and Engineer-II , respectively Materials and Building Technology Program Research Institute King Fahd University of Petroleum and Minerals Dhahran 31261, Saudi Arabia 2Korea Advanced Institute for Science and Technology Seoul, South Korea
(Communicated by C.D. Pome~oy) (Received March 8, 1990)
ABSTRACT Th~s paper presents an experimental study on the development of calcium silicate thermal insulator (CSTI) using the raw materials locally available in Saudi Arabia. Several parameters have been considered to optimize the synthetic conditions and batch composition of CSTI. These include autoclaving temperature and time, SiO 2 content of sand, fineness of sand, lime to silica ratio, water to solid ratio and fiber reinforcement. The measured properties of the product include bulk density, bending strength, linear dimensional chan~e and thermal conductivity. A CSTI with a bulk density of 400 kg/m ~, bending strength of 3.92 MPa and thermal conductivity of 0.083 W/m.k has been developed, which is comparable to ASTH C-656 class A material.
Introduction Calcium silicate is a commercially important inorganic thermal insulation material that is principally composed of hydrous calcium silicate and sometimes contains reinforcing fibers (I). It is produced by autoclaving a slurry of lime and silica powder, adding some fibrous filler such as asbestos fiber or pu]p fiber in it, and then forming the resulting mixture into desired shapes such as sheets, pipe covers, blocks, panels, etc. (2). Calcium silicate thermal insulator (CSTI) has several industrial applications such as in the manufacture of ovens and dryers for temperatures up to 650vC, 767
768
A.J. AI-Tayyib, et al.
Vol. 20. No. 5
and in fireproofing applications (i). In the hot climate of Saudi Arabia, CSTI can be potentially utilized in various forms such as ceiling tiles for protecting the houses from outside environment and heat insulator pipe covers for air cooling systems. Since lime and sand, the major raw materials of CSTI, are abundantly available in Saudi Arabia, the industrialization of CSTI could be very economical in this part of the world. This study was carried out with an objective to assess the suitability of the locally available raw materials, particularly sand, in the production of CSTI.
Materials A total of six sand samples collected from different areas of the Eastern Province of Saudl Arabia have been considered in this test program as silica sources. In general, the silicious material used in the production of CSTI has at least 92% of SiO 2 and maximum 1% of [Na20+K20 ] (3). The location of various sand sources along with their chemical composition in terms of Si02, Na20 and K20 contents is given in Table I.
TABLE I Sand Samples* Used in the Development of CSTI
Sample No.
Location
SiO 2 (wt.%)
(Na20+K20) (wt.%)
S-i S-2 S-3 S-4
Half-Moon Beach Dhahran Abqalq Road Zilfi-Medlnah Road
88 0
1.29 1.66 2.01 1.26 1.40 0.07
S-5
Half-Moon
S-6
Rlyadh-Dammam Road
Beach
79 7 82 92 89 98
2 5 7 2
* For detailed identification and characterization tests, refer to (3).
The lime used in this study was a commercial grade hydrated lime obtained from Saudl Arabian Sand, Lime and Brick Factory, Jeddah. The reinforcing fiber used was an insulation grade asbestos fiber.
Experimental Program Attempts have been made in this study to optimize the autoclaving conditions and batch composition of CSTI in terms of bulk density, bending strength and linear dimensional change. The different variables included in the study are autoclaving temperature and time, silica (Si02) content of the sand, fineness of sand, lime to silica ratio (CaO/SiO 2 mole ratio), water to solid ratio and fiber reinforcement. A total of 33 batches of CSTI have been prepared. Table II shows the experimental design of the test program. Specimen Preparation In the laboratory preparation of CSTI, the following steps were followed:
Vol. 20. No. 5
Ca SILICATE, THERMAL INSULATOR
769
TABLE II Experimental Design of the Test Program
Batch No.
Parameter studied
Details of autoclaving conditions and hatch composition Lutoclaving ;emp.
Sand type X weight of Si02)
(*cl
cs-1 lutoclavics-2 '18tempercs-3 nture
i-1 ((88.0)
cs-4 \utoclavics-5 lg time CS-6 cs-7
b Weight Lime/silica Jater/ Asbestos ratio )f sand golid fiber :CaO/Si03 finer ratio :x wt.) mole ratio) than 10 pm
0.975
0.0
11
12.0 1, 11
i-1 (88.0) 11 ,l 11
0.975 II l, I,
12.0 11 ,, I,
0.0
CS-8 silica cs-9 :ontent of cs-10 nand cs-11 cs-12 cs-13
1-l (88.0) i-2 (79.7) 1-3 (82.2) i-4 (92.5) i-5 (89.7) ;-6 (98.2)
5
cs-14 ?ineness cs-15 Jf CS-16 sand cs-17
i-6 (98.2) ,t 11 1,
12.0
0.0 ,t
CS-18 cs-19 cs-20 cs-21 es-22 CS-23 CS-24 CS-25 CS-26 CS-27 CS-28 cs-29
11
I,
;ime/ silica ratio and Eiber reiiforcement
cs-30 Jater/ cs-31 solid CS-32 ratio cs-33
7.9 12.6 54.8 94.7
11 II
0.800 II
11
11 ,l t1
11 II
0.0
10.7 0.0 10.7 0.0 10.7 0.0 10.7 -0.0 10.7 0.0 10.7
0.830 I, 0.922 ,I 0.975 11
1.200 11 1.500 ,,
i-6 (98.2) 1, I, II
11
10.0 12.0 15.0 20.0
0.0 II 11 11
770
A.J. AI-Tayyib, et al.
Vol. 20, N¢~.
i.
The sand was ground to the required
fineness.
2.
Sand and lime were thoroughly mixture and a slurry was made.
3.
The slurry and steam stirring.
4.
The autoclaved slurry was discharged into a container, reinforcing fibers, if used, were added and thoroughly mixed.
5.
The mixture obtained from the preceding step was filtered in a centrifugal or aspirator filter to drain out as much water as possible. The resulting product was a white calcium silicate cake.
6.
The white calcium silicate cake was placed into the molds and forming pressure of 2.75 HPa was applied for a short period of time.
7.
The specimens were removed f~om the molds hours at a temperature of 100uC.
mixed,
tap
water
was
added
in
the
was poured in an autoclave set at a selected temperature pressure, and was left for few hours with continuous
and
and then oven dried
the
a
for 24
Specimen Testing Bulk density, bending strength and linear dimensional change measurements were carried out according to the specifications of ASTH C-303, ASTH C-203 and ASTH C-356, respectively. Thermal conductivity measurements, on selected number of batches, were carried out according to ASTH C-518 specifications. X-ray diffraction (XRD) analysis as described in reference (4) was used for the identification of various phase formations.
Test Results and Discussion Autoclaving
Temperature
Figure 1 shows the variation of bulk density with three different autoclaving temperatures of 175, 191 and 2000C. It is observed that the minimum bulk density is obtained at a temperature of 1910C. The variation of linear dimensional change at varying autoclaving temperatures (Fig. 2) indicates that the linear dimensional change is quite high when the temperature exceeds 1910C. XRD analysis of CSTI specimens prepared at different autoclaving temperatures (Fig. 3) indicates that at lower temperature (175vC), there are traces of unreacted lime [Ca(OH)2]. Calcium orthosi]icate hydrate, the major crystalline phase of CSTI converts to tobermorite and xonolite on increasing the autoclaving temperature. Autoclaving
Time
The variation of bulk density with the reaction time of the slurry in the autoclave is shown in Fig. 4. Bulk density decreases with the increase in autoclaving time up to 4 hours and after that no reduction is observed and it remains almost constant up to 8 hours. XRD analysis of CSTI specimens prepared at two autoclaving times of 4 hours and 8 hours (Fig. 5) indicates the absence of any unreacted llme.
Vol. 20, No. 5
Ca SILICATE,THERMAl, INSULATOR
771
1000
Sand S-I
~6
_800 E
Sand S-I
CU
Cn
600
r'-
"r_. tU'I
g ~oo
Crt
~2 m200 I
170
1
I
180
190
I
I
200
170
180
190
Autoclaving Temperature (, C )
Autoclaving Temperature {oc)
FIG. 1 Variation of b u l k density of calcium silicate thermal insulator with autoclaving temperature
FIG. 2 Variation of linear drying shrinkage of calcium silicate thermal insulator with autoclaving temperature
[ : Calcium Orthosilicafe Hydrate
13. : I~uartz H : Calcium Silicate Hydrate ITobermorite 9A ° ) T : Tobermorite 11A° H X : Xono|ite ~X
0 : Calcium Hydroxide lea IOH}2]
Ca 0 I
60
50
200
a C C~C cC i
&O
O.
C
I
2000 C
a 0
1750[
I
i
I
I
30
20
10
&
20 FIG. 3 Comparison of x-ray diffraction patterns of calcium silicate thermal insulator specimens prepared at different autoclaving temperatures
i
772
A.J. At-Tayyib, et al.
Silica (Si02) Content of the Sand
Vol. 20. No. 5
1000
Figure 6 shows the variation of bulk density and bending strength of CSTI against silica content of different sand samples. The bulk density is found to be almost constant for different silica content of the sands, but the bending strength increases exponentially with the increase of silica content. The highest bending strength results from the sand sample S-6 containing the highest silica content (98.2%).
7so
.~_>~500 f-
C3 250 col
Fineness of Sand To observe the effect of the fineness of sand on various properties of CSTI, sand was ground for different durations of 24, 36, 60 and 82 hours in a ball mill. Percentage weight (wt.%) of particles less than i0 ~m in size was considered a measure of fineness. The bulk density and bending strength are plotted against respectively. The minimum bulk density obtained for the sand having about corresponding to a grinding time of fineness, the bending strength decreases
I
I
I
I
2
4
6
8
Autodaving Time (Hours) FIG. 4 Variation of bulk density of calcium silicate thermal insulator with autoclaving time
the sand fineness in Figs. 7 and 8, and maximum bending strength have been 55 wt.% particles less than I0 pm 60 hours. With further increase in drastically.
Lime to Silica Ratio (CaO/SiO 2 mole Ratio) The variations
of bulk density,
[ Cl H T
: : : :
bending strength and linear dimenslonal
Calcium Orthosilicate Hydrate 0.uartz Calcium Silicate Hydrate (Tobermorite Tobermorife 11A ° . T
.
60
C .._~1~
-
9A e)
(1
/,Hours
I
I
I
I
I
50
~,0
30
20
10
l
--.----20 FIG. 5 Comparison of x-ray diffraction patterns of calcium silicate thermal insulator •speclmens prepared at different autoclaving times
change
CaSILICATE,THERMALINSULATOR
Vol, 20, No. 5
773
6 1200
% 1000 \
w
'-4 FIG.6
~ BS-6 - u ~k Strength Bending 800 -d-->,
i-
V a r i a t i o n s of bending strength and
,I
600 =
bulk density of calcium s i l i c a t e thermal insulator wlth s i l i c a content of the sand.
~2
on
Density
° ~ S - 4 ,
S-2
S-5
80
90
400
~ 200
100
SiLica Content of the Sand (%)
1200
Hrs.
Sand 5-6
'~E 1000 J< 800 600
Hrs.
c~ 400
o0 Hrs.
82 Hrs O--
a~ 200 I
I
I
I
20
40
60
80
FIG. 7 V a r i a t i o n of bulk density of calcium s i l i c a t e thermal i n s u l a t o r with the fineness of sand.
100
% Weight of Particles Less then lOp, m
6
C.s
Sand S-6
"-4 t-
FIG. 8 V a r i a t i o n of bending strength of calcium s i l i c a t e thermal i n s u ] a t o r with the fineness of sand.
.=3
60Hrs.
V1
a~2 -a
20
40
60
80
% Weight of ParticLes Less then lOFm
100
774
A.J. A1-Tayyib, et al.
Vol. 20, No 5
Sand S-I Sa
1.5
600
rt~ O-
T" r..
r-
~400
1.0
r
rt-" OJ
200
.-j
oo 0.5 o |
I
0.6
10.7% Fiber o No Fiber I
0.9
1.2
~
I
I
CaO/SiO z MoLe Ratio
I
I
0.6
1.5
10.7O/oFiber o o No Fiber 0.9
1.2
I
1.5
CaO/SiO z Mote Ratio
FIG. 9 Variation of bulk density of calcium silicate thermal insulator with CaO/SiO 2 mole ratio
FIG. I0 Variation of bending strength of calcium silicate thermal insulator with CaO/SiO 2 mole ratio
with different CaO/SiO 2 mole ratios are shown in Figs. 9, I0, and 11, respectively. The bulk aensity is found to be minimum at a CaO/SiO 2 mole ratio of 0.90 (Fig. 9). The maximum bending strength is obtained at a CaO/SiO 2 mole ratio of 1.2 (Fig. 10).
o~
600
• - - 4 10.7% Fiber o o No Fiber
~J
~+2.0 "Sand
I'D rL.J
Sand S-6 r,%
E
~.00
"N r-
. o ÷1.0
tn
t~ r-
r-
zoo
E
~,
0
e~
e.-
-- -0.5
0'.9 1.2 ' 1.5 ' CaO/SiO z MoLe Ratio
0.6 '
FIG. ii Variation of linear dimensional change of calcium sillcate thermal insulator with CaO/SiO 2 mole ratio
10
5
20
Water/Sotid Ratio FIG. 12 Variation of bulk density of calcium silicate thermal insulator with water/ solid ratio
Vol. 20, No, 5
Ca SILICATE, THERMAL INSULATOR
775
Fiber Reinforcement The effect of the addition of reinforcing fibers on bulk density, bending strength and linear dimensional change has been investigated while studying the effect of CaO/SiO 2 mole ratio (batches CS-18 to CS-29, Table II). For each CaO/SIO 2 mole ratio, two batches were prepared; one without fiber and the other with i0.7 wt.% of asbestos fiber. The results are shown in Figs. 9, I0 and Ii. It is noticed that the addition of fiber has a beneflcJal effect on bending strength and linear dimensional change, but it increases the bulk density. The bulk density of CSTI specimens with fiber is 5-25Z higher than those without fiber (Fig. 9). The improvement in bending strength is of the order of 15-30Z (Fig. i0). The linear dimensional change of the CSTI specimens with fiber is negligible as compared to 1.75% in specimens without fiber (Fig. Ii). Water to Solid Ratio The bulk density and bending strength are plotted for different water to solid ratios in Figs. 12 and 13, respectively. The lowest bulk density and highest bending strength are obtained at a water to solid ratio of 12. Comparison of the Properties with ASTM Specifications
4 --
n~
Sand S-6
Q. Properties of six batches of CSTI have been compared with ASTM C-656 rspecifications in Table III. For these six batches, thermal C ~2 conductivity has also been measured in addition to bulk density, bending strength, and linear dimensional cchange measurements. It may be tnoticed that all the batches satisfy en the bulk density, linear dimensional change and thermal conductivity 0 .A I I I 10 15 20 requirements of both the ASTM C-656 class A and ASTH C-656 class B Water/Solid Ratio materlals. However, the bending strength requirement has only been FIG. 13 satisfied by the batch CS-13, and Variation of bending strength that too of ASTM C-656 class A of calcium silicate thermal material only. The addition of insulator with water/solld fiber in batch CS-13 might have ratio yielded a bending strength comparable to that of ASTM C-656 class B material. Batch CS-13 is the one which contains the sand of highest SiO 2 content (98.2Z). Thus it seems that the strength requirements of ASTM C,656 materials could only be met wlth hlgh silica sands llke S-6. It is to be noted here that ASTH class A material is specified for use where thermal insulation properties are primary and strength properties are secondary In importance. While, ASTH class B materlal is specified for use where a balance between physical strength and themal insulation properties is required.
Conclusions The following study:
conclusions
can be drawn
from the results
of this experimental
776
A.J. Al-Tayyib. et al.
Voh 20, No. 5
TABLE III Comparison of the Properties of Some CSTI Specimens With the Specifications of ASTM
Batch No.
CS-13 CS'17 CS-22 CS-23 CS-24 CS-25
Bulk density (kg/m ~)
Bending strength (MPa)
Linear dimensional change
Thermal conductivity
(%)
(W/m.k)
3.92
1.080 1.190 0.987 0.254 0.275 1.302
400 230 290
0.73 0.59 0.88 0.95 1.25
375 275 450
ASTM C-656 Class A
417
ASTM C-656 Class B
< 609
>
2.93
>_6.89
0.083 0.054 0.060 0.078 0.057 0.093
0.094
<
1.500
<
<
1.500
< 0.124
i.
The optimum autoclaving temperature and autoclaving time are about 1900C and 4 hours, respectively.
2.
The minimum bulk density and maximum bending strength are obtained when the sand particles less than 10 ~m size are 55 wt.%, the CaO/SiO 2 mole ratio is in the range of 0.9-1.2, and the water to solid ratio is 12.
3.
The SiO7 content of the sand does not appear to affect the bulk density of C S T ~ significantly, but it has a profound impact on the bending strength. The bending strength of CSTI increases with the increase in silica content. The strength requirement of ASTM C-656 class A material has only been met by sand S-6 having 98.2 wt.% of SiO 2.
4.
The addition of 10.7 wt.% of asbestos fiber improves the bending strength by 15 to 30%, but yields a heavier product. The increase in bulk density has been found to be in the range of 5 to 25%.
Acknowledgements The financial support (Grant No. AR4-Bldg) of King Abdulaziz City for Science and Technology (KACST) for this research is greatly acknowledged. The authors also acknowledge the Civil Engineering Department at King Fahd University of Petroleum and Minerals (KFUPM), Saudi Arabia, where the research was conducted. The first and third authors were associate professor and graduate student, respectively, at the Civil Engineering Department of KFUPM at the time of this research.
,I
.
VOL
20.No. 5
CaSILlCATE.THERMALINSULA'I'CR
777
References 1. Standard Specification for Structural Insulating Board, Calcium Silicate (ASTM C 656-79a), In: Annual Book of ASTM Standards, Vol. 4.06, ASTM, Philadelphia, 335 (1986). 2. E.C. Shuman, The Petroleum Engineer, 4, C-55 (1952). 3. A.J. Al-Tayyib, A.F. Abbasi; Mirxa, S.D. Jang, H.J. Jung, Construction Materials Using I), Final Report, Vols. I and
A.K. Axad, M.H. Baluch, M.F. Tewfik, W.H. and Y.H. Kim, Development of Building and Available Resources in Saudi Arabia (Phase II, KACST, Riyadh (1985).
4. H.P. Klug and L.E. Alexender, X-ray Diffraction Procedures, John Wiley and Sons, Inc., New York, N.Y. (1967).
DEVELOPMENT OF CALCIUM SILICATE THERMAL INSULATOR IN SAUDI ARABIA
A.J. AI-Tayyib I, H.J. Jung 2 and M. Shamim Khan 3 l'3Manager and Engineer-II , respectively Materials and Building Technology Program Research Institute King Fahd University of Petroleum and Minerals Dhahran 31261, Saudi Arabia 2Korea Advanced Institute for Science and Technology Seoul, South Korea
(Communicated by C.D. Pome~oy) (Received March 8, 1990)
ABSTRACT Th~s paper presents an experimental study on the development of calcium silicate thermal insulator (CSTI) using the raw materials locally available in Saudi Arabia. Several parameters have been considered to optimize the synthetic conditions and batch composition of CSTI. These include autoclaving temperature and time, SiO 2 content of sand, fineness of sand, lime to silica ratio, water to solid ratio and fiber reinforcement. The measured properties of the product include bulk density, bending strength, linear dimensional chan~e and thermal conductivity. A CSTI with a bulk density of 400 kg/m ~, bending strength of 3.92 MPa and thermal conductivity of 0.083 W/m.k has been developed, which is comparable to ASTH C-656 class A material.
Introduction Calcium silicate is a commercially important inorganic thermal insulation material that is principally composed of hydrous calcium silicate and sometimes contains reinforcing fibers (I). It is produced by autoclaving a slurry of lime and silica powder, adding some fibrous filler such as asbestos fiber or pu]p fiber in it, and then forming the resulting mixture into desired shapes such as sheets, pipe covers, blocks, panels, etc. (2). Calcium silicate thermal insulator (CSTI) has several industrial applications such as in the manufacture of ovens and dryers for temperatures up to 650vC, 767
768
A.J. AI-Tayyib, et al.
Vol. 20. No. 5
and in fireproofing applications (i). In the hot climate of Saudi Arabia, CSTI can be potentially utilized in various forms such as ceiling tiles for protecting the houses from outside environment and heat insulator pipe covers for air cooling systems. Since lime and sand, the major raw materials of CSTI, are abundantly available in Saudi Arabia, the industrialization of CSTI could be very economical in this part of the world. This study was carried out with an objective to assess the suitability of the locally available raw materials, particularly sand, in the production of CSTI.
Materials A total of six sand samples collected from different areas of the Eastern Province of Saudl Arabia have been considered in this test program as silica sources. In general, the silicious material used in the production of CSTI has at least 92% of SiO 2 and maximum 1% of [Na20+K20 ] (3). The location of various sand sources along with their chemical composition in terms of Si02, Na20 and K20 contents is given in Table I.
TABLE I Sand Samples* Used in the Development of CSTI
Sample No.
Location
SiO 2 (wt.%)
(Na20+K20) (wt.%)
S-i S-2 S-3 S-4
Half-Moon Beach Dhahran Abqalq Road Zilfi-Medlnah Road
88 0
1.29 1.66 2.01 1.26 1.40 0.07
S-5
Half-Moon
S-6
Rlyadh-Dammam Road
Beach
79 7 82 92 89 98
2 5 7 2
* For detailed identification and characterization tests, refer to (3).
The lime used in this study was a commercial grade hydrated lime obtained from Saudl Arabian Sand, Lime and Brick Factory, Jeddah. The reinforcing fiber used was an insulation grade asbestos fiber.
Experimental Program Attempts have been made in this study to optimize the autoclaving conditions and batch composition of CSTI in terms of bulk density, bending strength and linear dimensional change. The different variables included in the study are autoclaving temperature and time, silica (Si02) content of the sand, fineness of sand, lime to silica ratio (CaO/SiO 2 mole ratio), water to solid ratio and fiber reinforcement. A total of 33 batches of CSTI have been prepared. Table II shows the experimental design of the test program. Specimen Preparation In the laboratory preparation of CSTI, the following steps were followed:
Vol. 20. No. 5
Ca SILICATE, THERMAL INSULATOR
769
TABLE II Experimental Design of the Test Program
Batch No.
Parameter studied
Details of autoclaving conditions and hatch composition Lutoclaving ;emp.
Sand type X weight of Si02)
(*cl
cs-1 lutoclavics-2 '18tempercs-3 nture
i-1 ((88.0)
cs-4 \utoclavics-5 lg time CS-6 cs-7
b Weight Lime/silica Jater/ Asbestos ratio )f sand golid fiber :CaO/Si03 finer ratio :x wt.) mole ratio) than 10 pm
0.975
0.0
11
12.0 1, 11
i-1 (88.0) 11 ,l 11
0.975 II l, I,
12.0 11 ,, I,
0.0
CS-8 silica cs-9 :ontent of cs-10 nand cs-11 cs-12 cs-13
1-l (88.0) i-2 (79.7) 1-3 (82.2) i-4 (92.5) i-5 (89.7) ;-6 (98.2)
5
cs-14 ?ineness cs-15 Jf CS-16 sand cs-17
i-6 (98.2) ,t 11 1,
12.0
0.0 ,t
CS-18 cs-19 cs-20 cs-21 es-22 CS-23 CS-24 CS-25 CS-26 CS-27 CS-28 cs-29
11
I,
;ime/ silica ratio and Eiber reiiforcement
cs-30 Jater/ cs-31 solid CS-32 ratio cs-33
7.9 12.6 54.8 94.7
11 II
0.800 II
11
11 ,l t1
11 II
0.0
10.7 0.0 10.7 0.0 10.7 0.0 10.7 -0.0 10.7 0.0 10.7
0.830 I, 0.922 ,I 0.975 11
1.200 11 1.500 ,,
i-6 (98.2) 1, I, II
11
10.0 12.0 15.0 20.0
0.0 II 11 11
770
A.J. AI-Tayyib, et al.
Vol. 20, N¢~.
i.
The sand was ground to the required
fineness.
2.
Sand and lime were thoroughly mixture and a slurry was made.
3.
The slurry and steam stirring.
4.
The autoclaved slurry was discharged into a container, reinforcing fibers, if used, were added and thoroughly mixed.
5.
The mixture obtained from the preceding step was filtered in a centrifugal or aspirator filter to drain out as much water as possible. The resulting product was a white calcium silicate cake.
6.
The white calcium silicate cake was placed into the molds and forming pressure of 2.75 HPa was applied for a short period of time.
7.
The specimens were removed f~om the molds hours at a temperature of 100uC.
mixed,
tap
water
was
added
in
the
was poured in an autoclave set at a selected temperature pressure, and was left for few hours with continuous
and
and then oven dried
the
a
for 24
Specimen Testing Bulk density, bending strength and linear dimensional change measurements were carried out according to the specifications of ASTH C-303, ASTH C-203 and ASTH C-356, respectively. Thermal conductivity measurements, on selected number of batches, were carried out according to ASTH C-518 specifications. X-ray diffraction (XRD) analysis as described in reference (4) was used for the identification of various phase formations.
Test Results and Discussion Autoclaving
Temperature
Figure 1 shows the variation of bulk density with three different autoclaving temperatures of 175, 191 and 2000C. It is observed that the minimum bulk density is obtained at a temperature of 1910C. The variation of linear dimensional change at varying autoclaving temperatures (Fig. 2) indicates that the linear dimensional change is quite high when the temperature exceeds 1910C. XRD analysis of CSTI specimens prepared at different autoclaving temperatures (Fig. 3) indicates that at lower temperature (175vC), there are traces of unreacted lime [Ca(OH)2]. Calcium orthosi]icate hydrate, the major crystalline phase of CSTI converts to tobermorite and xonolite on increasing the autoclaving temperature. Autoclaving
Time
The variation of bulk density with the reaction time of the slurry in the autoclave is shown in Fig. 4. Bulk density decreases with the increase in autoclaving time up to 4 hours and after that no reduction is observed and it remains almost constant up to 8 hours. XRD analysis of CSTI specimens prepared at two autoclaving times of 4 hours and 8 hours (Fig. 5) indicates the absence of any unreacted llme.
Vol. 20, No. 5
Ca SILICATE,THERMAl, INSULATOR
771
1000
Sand S-I
~6
_800 E
Sand S-I
CU
Cn
600
r'-
"r_. tU'I
g ~oo
Crt
~2 m200 I
170
1
I
180
190
I
I
200
170
180
190
Autoclaving Temperature (, C )
Autoclaving Temperature {oc)
FIG. 1 Variation of b u l k density of calcium silicate thermal insulator with autoclaving temperature
FIG. 2 Variation of linear drying shrinkage of calcium silicate thermal insulator with autoclaving temperature
[ : Calcium Orthosilicafe Hydrate
13. : I~uartz H : Calcium Silicate Hydrate ITobermorite 9A ° ) T : Tobermorite 11A° H X : Xono|ite ~X
0 : Calcium Hydroxide lea IOH}2]
Ca 0 I
60
50
200
a C C~C cC i
&O
O.
C
I
2000 C
a 0
1750[
I
i
I
I
30
20
10
&
20 FIG. 3 Comparison of x-ray diffraction patterns of calcium silicate thermal insulator specimens prepared at different autoclaving temperatures
i
772
A.J. At-Tayyib, et al.
Silica (Si02) Content of the Sand
Vol. 20. No. 5
1000
Figure 6 shows the variation of bulk density and bending strength of CSTI against silica content of different sand samples. The bulk density is found to be almost constant for different silica content of the sands, but the bending strength increases exponentially with the increase of silica content. The highest bending strength results from the sand sample S-6 containing the highest silica content (98.2%).
7so
.~_>~500 f-
C3 250 col
Fineness of Sand To observe the effect of the fineness of sand on various properties of CSTI, sand was ground for different durations of 24, 36, 60 and 82 hours in a ball mill. Percentage weight (wt.%) of particles less than i0 ~m in size was considered a measure of fineness. The bulk density and bending strength are plotted against respectively. The minimum bulk density obtained for the sand having about corresponding to a grinding time of fineness, the bending strength decreases
I
I
I
I
2
4
6
8
Autodaving Time (Hours) FIG. 4 Variation of bulk density of calcium silicate thermal insulator with autoclaving time
the sand fineness in Figs. 7 and 8, and maximum bending strength have been 55 wt.% particles less than I0 pm 60 hours. With further increase in drastically.
Lime to Silica Ratio (CaO/SiO 2 mole Ratio) The variations
of bulk density,
[ Cl H T
: : : :
bending strength and linear dimenslonal
Calcium Orthosilicate Hydrate 0.uartz Calcium Silicate Hydrate (Tobermorite Tobermorife 11A ° . T
.
60
C .._~1~
-
9A e)
(1
/,Hours
I
I
I
I
I
50
~,0
30
20
10
l
--.----20 FIG. 5 Comparison of x-ray diffraction patterns of calcium silicate thermal insulator •speclmens prepared at different autoclaving times
change
CaSILICATE,THERMALINSULATOR
Vol, 20, No. 5
773
6 1200
% 1000 \
w
'-4 FIG.6
~ BS-6 - u ~k Strength Bending 800 -d-->,
i-
V a r i a t i o n s of bending strength and
,I
600 =
bulk density of calcium s i l i c a t e thermal insulator wlth s i l i c a content of the sand.
~2
on
Density
° ~ S - 4 ,
S-2
S-5
80
90
400
~ 200
100
SiLica Content of the Sand (%)
1200
Hrs.
Sand 5-6
'~E 1000 J< 800 600
Hrs.
c~ 400
o0 Hrs.
82 Hrs O--
a~ 200 I
I
I
I
20
40
60
80
FIG. 7 V a r i a t i o n of bulk density of calcium s i l i c a t e thermal i n s u l a t o r with the fineness of sand.
100
% Weight of Particles Less then lOp, m
6
C.s
Sand S-6
"-4 t-
FIG. 8 V a r i a t i o n of bending strength of calcium s i l i c a t e thermal i n s u ] a t o r with the fineness of sand.
.=3
60Hrs.
V1
a~2 -a
20
40
60
80
% Weight of ParticLes Less then lOFm
100
774
A.J. A1-Tayyib, et al.
Vol. 20, No 5
Sand S-I Sa
1.5
600
rt~ O-
T" r..
r-
~400
1.0
r
rt-" OJ
200
.-j
oo 0.5 o |
I
0.6
10.7% Fiber o No Fiber I
0.9
1.2
~
I
I
CaO/SiO z MoLe Ratio
I
I
0.6
1.5
10.7O/oFiber o o No Fiber 0.9
1.2
I
1.5
CaO/SiO z Mote Ratio
FIG. 9 Variation of bulk density of calcium silicate thermal insulator with CaO/SiO 2 mole ratio
FIG. I0 Variation of bending strength of calcium silicate thermal insulator with CaO/SiO 2 mole ratio
with different CaO/SiO 2 mole ratios are shown in Figs. 9, I0, and 11, respectively. The bulk aensity is found to be minimum at a CaO/SiO 2 mole ratio of 0.90 (Fig. 9). The maximum bending strength is obtained at a CaO/SiO 2 mole ratio of 1.2 (Fig. 10).
o~
600
• - - 4 10.7% Fiber o o No Fiber
~J
~+2.0 "Sand
I'D rL.J
Sand S-6 r,%
E
~.00
"N r-
. o ÷1.0
tn
t~ r-
r-
zoo
E
~,
0
e~
e.-
-- -0.5
0'.9 1.2 ' 1.5 ' CaO/SiO z MoLe Ratio
0.6 '
FIG. ii Variation of linear dimensional change of calcium sillcate thermal insulator with CaO/SiO 2 mole ratio
10
5
20
Water/Sotid Ratio FIG. 12 Variation of bulk density of calcium silicate thermal insulator with water/ solid ratio
Vol. 20, No, 5
Ca SILICATE, THERMAL INSULATOR
775
Fiber Reinforcement The effect of the addition of reinforcing fibers on bulk density, bending strength and linear dimensional change has been investigated while studying the effect of CaO/SiO 2 mole ratio (batches CS-18 to CS-29, Table II). For each CaO/SIO 2 mole ratio, two batches were prepared; one without fiber and the other with i0.7 wt.% of asbestos fiber. The results are shown in Figs. 9, I0 and Ii. It is noticed that the addition of fiber has a beneflcJal effect on bending strength and linear dimensional change, but it increases the bulk density. The bulk density of CSTI specimens with fiber is 5-25Z higher than those without fiber (Fig. 9). The improvement in bending strength is of the order of 15-30Z (Fig. i0). The linear dimensional change of the CSTI specimens with fiber is negligible as compared to 1.75% in specimens without fiber (Fig. Ii). Water to Solid Ratio The bulk density and bending strength are plotted for different water to solid ratios in Figs. 12 and 13, respectively. The lowest bulk density and highest bending strength are obtained at a water to solid ratio of 12. Comparison of the Properties with ASTM Specifications
4 --
n~
Sand S-6
Q. Properties of six batches of CSTI have been compared with ASTM C-656 rspecifications in Table III. For these six batches, thermal C ~2 conductivity has also been measured in addition to bulk density, bending strength, and linear dimensional cchange measurements. It may be tnoticed that all the batches satisfy en the bulk density, linear dimensional change and thermal conductivity 0 .A I I I 10 15 20 requirements of both the ASTM C-656 class A and ASTH C-656 class B Water/Solid Ratio materlals. However, the bending strength requirement has only been FIG. 13 satisfied by the batch CS-13, and Variation of bending strength that too of ASTM C-656 class A of calcium silicate thermal material only. The addition of insulator with water/solld fiber in batch CS-13 might have ratio yielded a bending strength comparable to that of ASTM C-656 class B material. Batch CS-13 is the one which contains the sand of highest SiO 2 content (98.2Z). Thus it seems that the strength requirements of ASTM C,656 materials could only be met wlth hlgh silica sands llke S-6. It is to be noted here that ASTH class A material is specified for use where thermal insulation properties are primary and strength properties are secondary In importance. While, ASTH class B materlal is specified for use where a balance between physical strength and themal insulation properties is required.
Conclusions The following study:
conclusions
can be drawn
from the results
of this experimental
776
A.J. Al-Tayyib. et al.
Voh 20, No. 5
TABLE III Comparison of the Properties of Some CSTI Specimens With the Specifications of ASTM
Batch No.
CS-13 CS'17 CS-22 CS-23 CS-24 CS-25
Bulk density (kg/m ~)
Bending strength (MPa)
Linear dimensional change
Thermal conductivity
(%)
(W/m.k)
3.92
1.080 1.190 0.987 0.254 0.275 1.302
400 230 290
0.73 0.59 0.88 0.95 1.25
375 275 450
ASTM C-656 Class A
417
ASTM C-656 Class B
< 609
>
2.93
>_6.89
0.083 0.054 0.060 0.078 0.057 0.093
0.094
<
1.500
<
<
1.500
< 0.124
i.
The optimum autoclaving temperature and autoclaving time are about 1900C and 4 hours, respectively.
2.
The minimum bulk density and maximum bending strength are obtained when the sand particles less than 10 ~m size are 55 wt.%, the CaO/SiO 2 mole ratio is in the range of 0.9-1.2, and the water to solid ratio is 12.
3.
The SiO7 content of the sand does not appear to affect the bulk density of C S T ~ significantly, but it has a profound impact on the bending strength. The bending strength of CSTI increases with the increase in silica content. The strength requirement of ASTM C-656 class A material has only been met by sand S-6 having 98.2 wt.% of SiO 2.
4.
The addition of 10.7 wt.% of asbestos fiber improves the bending strength by 15 to 30%, but yields a heavier product. The increase in bulk density has been found to be in the range of 5 to 25%.
Acknowledgements The financial support (Grant No. AR4-Bldg) of King Abdulaziz City for Science and Technology (KACST) for this research is greatly acknowledged. The authors also acknowledge the Civil Engineering Department at King Fahd University of Petroleum and Minerals (KFUPM), Saudi Arabia, where the research was conducted. The first and third authors were associate professor and graduate student, respectively, at the Civil Engineering Department of KFUPM at the time of this research.
,I
.
VOL
20.No. 5
CaSILlCATE.THERMALINSULA'I'CR
777
References 1. Standard Specification for Structural Insulating Board, Calcium Silicate (ASTM C 656-79a), In: Annual Book of ASTM Standards, Vol. 4.06, ASTM, Philadelphia, 335 (1986). 2. E.C. Shuman, The Petroleum Engineer, 4, C-55 (1952). 3. A.J. Al-Tayyib, A.F. Abbasi; Mirxa, S.D. Jang, H.J. Jung, Construction Materials Using I), Final Report, Vols. I and
A.K. Axad, M.H. Baluch, M.F. Tewfik, W.H. and Y.H. Kim, Development of Building and Available Resources in Saudi Arabia (Phase II, KACST, Riyadh (1985).
4. H.P. Klug and L.E. Alexender, X-ray Diffraction Procedures, John Wiley and Sons, Inc., New York, N.Y. (1967).