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Properties and structure of oil shale ash pastes I: Composition and physical features
CEMENT and CONCRETE RESEARCH. Vol. 15, pp. 303-314, 1985. Printed in the U S A 0008-8846/85 $3.00+00. Copyright (c) 1985 Pergamon Press, Ltd.
PROPERTIES AND STRUCTURE OF OIL SHALE ASH PASTES I: COMPOSITION AND PHYSICAL FEATURES H. Baum, I. Soroka and A. Bentur Building Research Station - Faculty of Civil Engineering Technion, Israel Institute of Technology Haifa, Israel
(Communicated by J. Skalny) (Received Aug. 6, 1984)
ABSTRACT The composition and physical features of oil shale ash pastes were determined and compared with the corresponding properties of portland cement paste. In the first part presented here, the composition, chemically combined water, porosity (total, capillary and gel porosity), pore-slze and pore-slze distribution, and specific surface area were determined by water vapor adsorption, mercury penetration and X-ray diffraction . It was established that the structural features and the factors which control and determine these features, are essentially the same in both the ash and the portland cement pastes. In the ash paste, however, total porosity remained virtually unchanged with time. This aspect, as well as the mechanical properties of the ash paste, are presented and discussed in the second part of the paper.
Introduction The utilization of oil shale as a source of energy has been given serious consideration in recent years. In many oil shales, however, the content of the organic matter is rather low (i.e. only about 15%-30%) and its use as fuel is associated with generation of large quantities of by-product which constitutes an ecological problem. The by-product can be in the form of ash in the case of direct burning of the oil shales, or spent shale in the case of retorting processes which are used to extract liquid fuels from the oll shale. The economic use of such a low-calory source of energy is highly dependent on whether or not, if at all, some economic use can be made of the by-product (I). Hence, the economic use of large quantities of the byproduct is a decisive prerequisite for the successful and economic use of oll shales as a fuel. Usually the inorganic portion of the oil shale is high in silica and in such cases the by-product may possess pozzolanlc properties and, consequently, most of the relevant research has been associated with the utilization of the latter properties (1-4). The local Israeli oil shale, however, 303
304
Vol. 15, No. 2 H. Baum, et al.
is comparatively rich in lime and, under certain burning conditions, the resulting ash has cementitious properties (5)(6), probably due to the presence of reactive dicalcium silicate (7)(8). Indeed, earlier studies have shown that the ash in question can be used to produce concrete blocks and mortars for plastering and rendering (9)(10). Information with respect to oil-shale ash which possess cementitious properties is limited and only few publications dealt with this material (5)-(8). Hence, the present study was undertaken in order to determine the properties of such an ash, to establish the factors which determine its properties, and possibly to suggest a model by which the mechanical properties of the set ash can be explained and related to its physical structure.
Experimental The tests included oil-shale ash pastes having water/ash ratio of 0.8, 0.9 and 1.0, and a portland cement paste with a water/cement ratio of 0.4. Materials Only one type of ash was used in this work, being the by-product of burning local ell shale in a fluldlzed bed at a temperature of 850°C. Chemical composition of the ash is presented in Table I. The specific gravity of the ash was 2.68 and its Blaine specific surface area (ASTM C204) was 1134 m2/kg. Table i Chemical composition of the oil-shale ash and the portland cement (weight percentage)
Material
CaO Ca0 (total) (free)
Si02[AI203 Fe203
MgO
Na20
K20
0.58
P205
Oil Shale ash
45.50
9.00
21.40
8.50 3.60
0.70 0.58
2.70
Portland cement
63.66
2.14
20.98
5.74 2.94
1.58 nd (3) nd (3) nd (3)
SO 3 (total)
L.O.I.
10.20 (1) 5.50 (2)
1.81
2.65
i) including 9.7% soluble SO 3 (2) including 3.80% CO 2 (3) not determined
It should be pointed out that the high specific surface area of the ash resulted in a high water requirement and the ash pastes prepared were therefore of a high water/ash ratio. It is to be expected that such high ratios would result in pastes of a low strength. Such fineness is, however, a characteristic property of the ash in question and, at this stage at least, cannot be avoided (5). The cement was ordinary portland cement having specific gravity of 3.04, specific surface area (ASTM C204) of 307 m2/kg and chemical composition which is given in Table I.
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305 OIL SHALE, ASH PASTES, COMPOSITION,
PORE STRUCTURE
Mixing procedure complied with ASTM C305. 25 mm cubes were prepared from all the mixes. Prisms of 25x25x160 mm were prepared only from the portland cement paste and the ash paste having the water/ash ratio of 0.8. Specimens were continuously cured in water at 20°±I°C. Testing was carried out at ages of i to 180 days. Testing Procedures
(a)
Total porosity was determined on 25 mm cubes from the weight of the evaporable water, i.e. from the difference in the weight of the saturated surface-dry cube and its corresponding oven-dry weight (24 hrs at I05°C), and assuming that the specific gravity of the evaporable water is I. Accordingly, the total porosity given in col. 3 of Table 2 is the volume percentage of the evaporable water with respect to the volume of the test specimen.
(b)
Degree of hydration. The chemically combined water was considered to measure the extent of hydration, and was determined on fragments which remained from the compression test of the 25 mm cubes. The fragments were pestled to the fineness of 75-200 mesh, washed with acetone to stop hydration, and then dried in a desicator over magnesium perchlorate for at least I0 days, to give their "P-dry weight", Gp (ii). The chemically combined water, Wn, was calculated from the loss on ignition of the P-drled samples corrected for the loss on ignition of the unhydrated ash. Accordingly, the chemically combined water, expressed as percentage of the weight of the ignited sample is given in col. 6 of Table 2.
(c)
Water vapour adsorption. Tests were carried out on P-dried samples, conditioned to a constant weight at different relative pressures, P/Po' ranging from 0.ii to 1.00, to give the complete adsorption isotherm. Sulphurlc acid solutions of different concentrations were used to control the relative pressure in the conditioning desicators. Typical adsorption isotherms of the portland cement and the ash pastes are given in Fig. i. It can be seen that the resulting isotherms are of type IV and exhibit a distinct "B-point" (12,13). Hence, the adsorption data was utilized to determine (a) the specific surface area of the pastes by the BET method; (b) the pore size distribution in the pastes and the specific surface area using the Kelvin equation; and, (c) the specific surface area of the pastes from the "V-t" curves.
(d)
BET surface area (SBET) was determined from the adsorption isotherm in the range of 0.05 < P/Po < 0.30 in accordance with the well established procedure of Brunauer, Emmett and Teller (12,14), and assuming that the area covered by one molecule of adsorbed water is IO.6A 2 (15). 0.5
I
I
I
I
I
I
]
I
I
E~0.4
Fig. I Typical adsorption isotherms of oll shale ash (full line) and portland cement (dotted llne) pastes.
w
~o0.2 o.
>~Eo.I w
0o
0.1
0.2
0,3
0.4
0.5 0.6 P/Po
0.7
0.8
0.9
1.0
306
Vol. 15, No. 2 H. Baum, et al.
The specific surface area was calculated with respect to the ignited weight of the sample, S ~ T , and with respect to its P-dried weight, S ~ T. Accordingly, the data are presented in cols. 7 and 8 of Table 2.
(e)
Pore-slze distribution was determined from the water adsorption isotherm in the range of 0.30 g P/Po g 1.00, using the Kelvin equation (assuming contact angle of 0 ° and surface energy of 73.5 dyne/cm) and correcting for the thickness, t, of the adsorbed water film (13, 15, 17).
Table 2 Physical features of the set portland cement and ash pastes
W/A or W/C Age Ratio
Days I
2
pd
Total Capillary Gel Chemically Porosity Porosity Porosity Combined d>30A d<30A Water % Volume 3
SBET
pd Spp
SVt
m2/g
% Wt.
4
pd
Scp
5
6
7
8
9
I0
II
.,I
0.8
0.9
1.O
Portland Cement 0.4
(f)
I 3 7 28 60 180
70.06 70.53 70.16 69.43 69.19 71.65
54.72 53.39 53.09 51.70 50.90 46.65
15.54 17.14 17.07 17.73 19.00 25.00
9.50 12.58 13.64 20.98 22.62 23.00
31 46 55 83 63 79
30 36 48 68 51 64
81 115 125 143 I01 I01
45 54 92 99 96 86
28 36 45 68 50 64
i 3 7 28 60 180
78.62 78.20 78.52 77.68 77.49 78.85
72.32
6.3
65.09 55.23 54.00
12.59 22.26 24.85
II .46 II .75 14.18 21.00 22.11 23.25
29 54 54 82 71 94
26 44 44 68 58 77
106 73 126 129 1271102 137 98 105 91 102 93
26 48 47 68 60 78
I 3 7 28 60 180
84.30 83.61 84.92 83.95 82.39 84.59
40
36
I00 105
36
65.63 64.59 61.40
18.32 16.90 23.19
12.00 13.16 15.00 21.43 22.92 23.66
70 69 90
64 65 93
109 119 97
88 94 88
64 62 77
1 3 7 28 60 180
29.67 28.64 27.87 25.94 25.31 23.23
21.45
8.22
15.98 II.01
9.33 12.22
6.36 12.18 16.32 18.30 21.23 22.08
45 59 57 60 84 108
42 52 64 58 69 77
58 55 61 74 74 -
53 55 59 71 73 -
40 50 60 60 62 77
Specific surface area from pore-slze distribution, S pd. On the b a s i s of the analysis of the pore-size distribution, i.e. the volume of the pores in each of the radius intervals, the surface area of the pores can be
Vol. 15, No. 2
307 OIL SHALE, ASH PASTES, COMPOSITION,
PORE STRUCTURE
determined on the assumption that the pores are either cylindrical or sllt shaped. The specific surface area, with respect to the P-drled weight of the samples, was determined for_= both assumptions and, accordingly, the data in col. g of Table 2, S ~ , are based on the assumption of cylindrical pores and those in col. ~0, S ~ , on sllt shaped pores with parallel walls.
(g)
Specific surface area from V-t curves. Knowing the amount, V, of the adsorbed water and the corresponding thickness, t, of the water layer, the adsorbent surface area, SVt , is given by V/t, i.e. by the slope of the V-t curve. It was shown (18), and demonstrated again in the present study, that the lower part of the curve is a straight line passing through the origin. Hence, the slope of this straight part of the curve gave the specific surface area SVt of the adsorbent (col. Ii of Table
2). (h)
Mercury penetration. Pore-size distribution was determined on P-drled samples using a porosimeter with a pressuring capacity of 422.5 MPa. The calculation was based on the Washburn equation assuming a surface tension of 47.3 dyne/cm 2, and a contact angle of the mercury with the pore walls of 130 °. Results and Discussion
Composition of the Ash X-ray diffraction of the oil-shale ash (Fig. 2) indicates that 8C2S is one of the ash constituents, with the remaining ones being CaO, CaSOg and CaCO 3. The presence of the same constituents was observed by others (5,7,19) and it was suggested that the 8C2S is much more reactive than that present in
%s+%s
j
C3S 3.0~
Fig. 2 X-ray diffraction patterns of the portland cement and of oil shale ash.
OIL SHALE ASH
39
37
II ~
35
33 31 2 8°
337
A 29
27
308
Vol. 15, No. 2 H. Baum, et al.
portland cement (7)(8). This was confirmed in the present work, which showed a similar increase in chemically combined water and BET surface area with hydration of the ash and the portland cement pastes. The main constituent of portland cement is, of course, C3S , which is not present in the ash. Nevertheless, as the hydration of both silicates, C3S and BC2S , results in essentially the same CSH gel, and as the properties of the set cement are mainly determined by the properties of the gel, it may be further expected that the behavlour and the properties of the set ash will be similar to those of the set portland cement. It will be seen later that, indeed, such a similarity was observed in most cases, but not necessarily without exception. Hydrationland surface area development Considering the chemically combined water, Wn, to measure the extent of hydration (col. 6, Table 2), it can be seen that at ages greater than about 3 days, the hydration of the oil-shale ash proceeded essentially at the same rate as that of the portland cement (Fig. 3). At earlier ages, however, the amount of the chemically combined water was greater in the ash pastes than in the portland cement pastes. This greater amount can be attributed to the greater amount of ettringite formed in the ash pastes (7) and to the much greater fineness of the ash, i.e. 1134 vs. 307 m2/kg. On the other hand, in view of the fact that 6-C2S will hydrate at a slower rate than C3S , it was to be expected that the ash will hydrate at a slower rate than the portland cement. The essentially same rate of hydration may be attributed, again, to the greater fineness of the ash on one hand, and to the greater reactivity of the 6C2S formed under conditions in hand, on the other. Indeed, it was suggested (20,21) that the 6C2S formed at about 800°C is more reactive and that this greater reactivity stems from its imperfect crystallization. The oil shale ash studied here was burned at 850°C. Hence, this explanation may be considered valid for the present tests. As the hydration proceeds, the BET surface area (col. 7, Table 2) increases, and the nature of this increase is, again, essentially similar in both the ash and the portland cement pastes (Fig. 4). Moreover, in both pastes the relation between the BET surface area and the chemically combined water was of a linear nature (Fig. 5). Such a linear relation in portland cement pastes was observed, of course, by others (II). Finally, for a given age (Fig. 4), or alternatively for the same amount of chemically combined water (Fig. 5) the BET surface area of the portland cement paste was somewhat greater than the surface area of the ash pastes. This difference may be expected to be reflected in the strength of the pastes, but this aspect will be discussed at a later stage.
rr ~ 2 5 | 20 I-
I
I
o
.......
i
o=
4
,
0°
0 I I
I $
,
I 7 AGE
Fig. 3
(log
,
I I 28 60 scale) , DAYS
-I
I 180
Chemlcally-comblned water vs. age in oll shale ash (full llne) and portland cement (dotted line) pastes.
Vol. 15, No. 2
309 OIL SHALE, ASH PASTES, COMPOSITION,
I
I
I
PORE STRUCTURE
I
I00
120
I
I
I
I x/1 i
lO0
*~°'° ~ _ ~ j l
E
~
80
~
~..~
-
%
.%/~
-60
.
6O G
Hu,~=40
~
20
20 I
5
[
L
I
7 28 60 AGE ( Io0 scole) , DAYS
Fig. 4 Development of BET surface area with time in oll shale ash (full line) and portland cement (dotted llne) pastes.
180
I
I
I
I
5
I0
15
20
WnlA
,%
WnlC
or
J 25
Fig. 5 BET surface area vs chemically combined water in oll shale ash (full line) and portland cement (dotted llne) pastes.
As mentioned earlier, the surface area, sPd, was also determined from the adsorption tests, assuming both cylindrical or silt-shaped pores with parallel walls (cols. 9 and i0, respectively, in Table 2). There exist some data (13,22,23) which indicate that the surface area S pd is greater than the BET surface area when the sample contains large pores and smaller when the sample contains ~mall pores. It was suggested (13) that this difference occurs because the S p° surface area excludes the volume of the pores smaller than approximately 20A which are included in the BET surface area. In the ash pastes, the S pd surface area was much greater in all cases than the corresponding area determined by the BET method. Hence, it may be concluded that such pastes were characterized bY relatively high content of large pores. In the portland cement paste S pa surface area was greater in most cases than the BET surface area, but the difference between the two was much smaller. In the ash pastes the S ~ surface area was, in most cases, smaller than S ~ surface area, and closer To the BET area. It is implied, therefore, that the shape of the pores in the ash paste is rather more sllt-llke in shape than cylindrical. In the portland cement paste the S pd and the S~ d were P P virtually the same, implying that both shapes occured ~o the same extent. Finally, the specific surface area, SVt , from the V-t curves (Fig. 6) is given in col. ii of Table 2, and it can be seen that in the ash pastes, and in most cases in the portland cement pastes, this method gave the closest values to the BET method. The V-t curves were straight lines passing through the origin, and implied, therefore, a material with silt-shaped large pores where the layer of the adsorbed water vapour can be built up unhindered. Porosity (a)
Total porosity. Generally speaking, due to the much higher water/ash ratio, the total porosity, Pt, of the ash pastes was much greater than
310
Vol. 15, No. 2 H. Baum, et al.
04
[
'
I
I
J
I
[
I
2S OArS 0.3
WZA,O - -
I
t
7
S
q
O.Z
2
[°' ~.
~-
o
o,~
Fig. 6 ,
,
i
,
,
i
i
i
i
i
,
6o DAYS
w/A-o.9
3
o4
V-t curves of the ash pastes.
os
oz
o.L
°o
zo
4o
so
• 80
ioo
the porosity of the portland cement pastes (col. 3, Table 2), i.e. 85% in the ash pastes versus, depending on the age, from 23 to 30% the portland cement pastes. It is to be expected, therefore, that strength of the ash pastes will be much lower than the strength of portland cement pastes. It will be shown later that, indeed, this the case here.
70 to in the the was
In the portland cement pastes total porosity decreases with age, as the hydration proceeds, because the volume of the hydration products is greater than the volume of reacting cement (II). In view of the similarity in the behavlour of the portland cement and the ash pastes, it was totally unexpected to find that the porosity of the ash pastes remained virtually unchanged with age and with the increase in the amount of hydration. The average total porosity of the ash pastes was approximately, regardless of age, 70%, 78% and 84% for the water/ash ratios of 0.8, 0.9 and 1.0, respectively. This particular observation warrants a suitable explanation and will be dealt with at a later stage. The decrease in total porosity, Pt, with the decrease in the water/ binder ratio characterizes both the portland cement and the ash pastes. In the portland cement paste, however, total porosity is also dependent on the degree of hydration (i.e. age) whereas, as pointed out earlier, in the ash paste total porosity remained unchanged and therefore independent on the latter. Accordingly, a linear relationship Pt = 14.3 + 70 W/A, which was independent of age, was established in the ash pastes between total porosity, Pt, and the corresponding water/ash ratio, W/A. Extrapolating and solving the total porosity expression for W/A = 0.40 give Pt = 42% which, with due reservation, constitutes a rough estimate of the total porosity of the ash paste, were it possible to produce such a paste with a W/A ratio of 0.4. This estimated porosity of 42% is rather high in comparison with the porosity of 23 to 30% observed in the portland cement paste with a corresponding water/cement ratio. It was suggested (24) that the hydration of 6C2S results in a more porous structure than the hydration of C3S. Hence, the former silicate, being the main cementitlous constituent of the ash, may explain the higher porosity of the ash paste. In any case, if this estimated value represents the true porosity, it is to be expected that for the same water/blnder ratio the portland cement paste will be stronger than its ash counterpart. It will be seen later that estimating the strength from the water/blnder ratio substantiated this conclusion.
Vol. 15, No. 2
311 OIL SHALE, ASH PASTES, COMPOSITION,
PORE STRUCTURE
E 0.3 , uJ ~L
~,g o.2
-
t
W/A=O 8
a- w
•~u j
o~' -
~
"~'~.
~
W/C=O.
= E _<
=
• o
Effect of age on (a) mean pore diameter, and (b) threshold diameter of oll shale ash (full llne) and portland cement (dotted line) pastes.
W/A=O.8
"
u~ w O . 4 ocw I- < 0.2
I 5
....."h. . . .
[
7
28 AGE
"P---4
60
. . . .
90
Fig. 7
180
, DAYS
(b)
Capillary porosity. Applying the maximum pressure of 422.5 MPa, the mercury penetrates into the pores down to the size of approximately 30A, but not into those of a smaller diameter. Hence, the porosity determined accordingly was considered to represent the capillary porosity, i.e. the fraction of the bigger-size pores. Relevant data are given in col. 4 of Table 2, and it can be seen that, although the total porosity remained unchanged, the capillary porosity of the ash pastes decreased with age, similarly to the decrease in the portland cement paste.
(c)
Gel porosity (col. 5, Table 2). The difference between total and capillary porosities measures the volume of the pores smaller than about 30A, which might be defined as gel pores. As the amount of the gel increases with age and hydration, the volume of the gel pores is expected to increase simultaneously. Indeed, this was the case for both the portland cement and the ash pastes.
(d)
Pore size. It was shown earlier that in both the portland cement and the ash pastes, the increase in gel porosity with time involves a simultaneous decrease in capillary porosity, i.e. the increase in the volume of the smaller pores corresponds to a decrease in the volume of the bigger pores. It is to be expected, therefore, that the mean pore diameter will also decrease with time. The latter diameter was determined from the adsorption data using the expression d = 4V/SBE T (13) (V amount of evaporable water), and is presented accordingly in Fig. 7a. It is clearly evident that the mean diameter decreases with the age of the pastes. In the ash paste of the water/ash ratio of 0.8, the mean diameter at the age of one day was 0.28 ~m, decreasing to 0.08 ~m at the age of 7 days, and further decreasing, at a slower rate, to less than 0.01 ~m at the age of 180 days. The mean diameter in the portland cement paste, although being smaller, similarly decreased from 0.12 Bm at the age of one day to about 0.01 ~m at 180 days. The decrease in the size of the portland cement pores with age was also reported elsewhere (25).
3L2
Vol. 15, No. 2 H. Baum, et al.
The pore-size can also be considered with respect to the "threshold diameter". The threshold diameter is the diameter which corresponds to the turning point of the cumulative pore size distribution curve (Figs. 8 and 9), and as such constitutes a measure of the size of the biggest pores in the paste. The change in the threshold diameter with time is presented in Fig. 7b, from which it is clearly evident that this diameter decreases with time. Again, it may be concluded that, in both the portland cement and the ash pastes, pore-slze decreases with time. Likewise, it can be concluded that the threshold diameter decreases with the decrease in the W/A ratio. It can be seen from Fig. 8 that the threshold diameter decreased from approximately 0.8 to 0.3 ~m with the decrease in the W/A ratio from 1.0 to 0.8, and further decreased to 0.07 ~m for the portland cement paste having the w/c ratio of 0.4.
(e)
Pore-size distribution data, as determined from mercury penetration, are presented in Figs. 8 and 9. Generally speaking, the nature of the ash and the portland cement curves are essentially the same once allowance is made for the difference in the porosity of the two types of paste. In fact, noting the effect of the water/ash ratio on pore-size distribution curves (Fig. 8), it is rather likely that, if it was possible to produce an ash paste with a water/ash ratio of 0.4, its poredistribution curve would not be very much different from that of portland cement paste. Normalized pore-slze distribution, determined from water adsorption tests, is presented in Fig. I0. It is clearly evident that all the ash pastes, irrespective of their W/A ratio and age, as well as the portland cement paste, exhibited a mode at P/Po = 0.65, which is equivalent to a pore radius of approximately 50A.
0.7
I
I
]
I
|
0.6
-T
.,,.-, 0.5 E o
Fig. 8
uaO.4 "
>0.3
g
Mercury penetration pore size distribution curves of oil shale ash (full line) and portland cement (dotted llne) pastes.
W / A = I. 0
\L
~
\
\
0.9
\
0.8
0.2
'-,, 0.0 0.001
I
I
I
I
0.01
0.1
I
I0
EQUIVALENT
PORE
DIAMETER
I00 , /u. m
Conclusions BC~S is the constituent which imparts the oll shale ash its cementltious properties. Apparently the reactivity of the 8C2S of the ash is greater than that of the portland cement, and the ash pastes hydrate at essentally the
Vol. 15, No. 2
313 OIL SHALE, ASH PASTES, COMPOSITION, PORE STRUCTURE
same rate as their portland cement counterparts. As hydration proceeds with time, the surface a r e a of the set ash increases in a similar way to the increase in the set portland cement. For a given age, or chemically combined water, however, the surface area of the portland cement paste is greater by about 20% t h a n the surface area of the ash paste. Similarly to the portland cement paste, the volume of the gel pores in the ash paste increases with time at the expense of the volume of the capillary pores. Likewise, total porosity of the ash pastes increases with 0.7
~
i
T
0.6
I
-I
~
T
W/A = 0.8
UO.5
7
0.4
o
T
i
T
i
W/A: 1.0 28 D~YS-
W/A=O'9
I DAY
.=
l
28 DAYS
77
60
~-o
180 28
z) 0.5 - -
60 180
.
~0.2
0.0 0.0001
O.OI
0.1
I
I0
0.01
0.1
EQUIVALENT
I
I0
0.01
0.1
I
I0
PORE DIAMETER , ~ m
Fig. 9 Effect of age on pore size distribution of ash pastes of different water/ash ratios.
w.Li2!
I
I
8 0 -- A ~
I
WlA=I.O
60
,
I
I
AGE
2 8 DAYS
I
W / A = O. 8
40
~ 2o >
WIA=O 8 60
Fig. i0
3 DAYS
o
O"
I 0"651
0.3
0.4
0.5
0.6
0.7
0.8
0.9-
P/Po
I
I
I
I
I
I,.5
20
50
50
70
%.i
I 120
1.0
Normalized pore size distribution of pastes of (a) ash with different water/ash ratios (0.8, 0.9, 1.0) and portland cement with water/cement ratio of 0.4, and (b) ash at different ages.
314
Vol. 15, No. 2 H. Baum, et al.
the W/A ratio. However, whereas total porosity in the portland cement paste decreases with time, the total porosity in the ash paste remains virtually unchanged. This particular property, which eonstltutes the main difference Between the ash and the portland cement pastes, will he discussed in some detail in the second part of the paper. Nevertheless, with the remaining structural features being essentially the same, it is to be expected that the same factors determine and control the physical properties and hehavlour of both the portland cement and the ash pastes. The physical properties of the pastes with respect to their structural features are discussed in the second part of the paper.
References I. 2. 3. 4. 5. 6. 7. 8. 9.
I0. II. 12.
R. Rohrbach, Zement-Kalk-Gips, 2, 293 (1969). M. Lawson and P.J. Nixon, Building Research Establishment Current Paper, CP50/78, pp. 11-19 (1978). G.J. Gromko, Trans. Res. Rec. 549, 47 (1975). P.K. Metha, Cem. Contr. Res. i0, 545 (1980). M. Ish-Shalom, A. Bentur and T. Grlnberg, Cem. Concr. Res. IO, 799 (1980). A. Bentur, M. Ish-Shalom and T. Grinberg, Cem. Concr. Res. ii, 175 (1981). A. Bentur and T. Grinberg, Amer. Ceram. Soc. Bull. 61, 1296 (1982). A. Bentur and T. Grinberg, Amer. Ceram. Soc. Bull. 63, 290 (1984). M. Ish-Shalom, A. Bentur and T. Grinberg, "Application of Oil Shale Ash From Zefa Ere", Israel Ceramic and Silicate Institute, Report to the Ministry of Energy and Infrastructure, The Government of Israel, Haifa (1979). A. Bentur, Silicate Industrials, XLVII, 163 (1982). T.C. Power and T.L. Brownyard, Amer. Concr. Inst. Proc. 43, i01 (1947). S. Brunauer, L.S. Demig, W.S. Demig and E. Teller, J. Amer. Chem. Soc.
6!2, 1723 (1940). 13. 14. 15. 16. 17. 18. 19.
S.J. Gregg and K.S.W. Sing, "Adsorption, Surface Area and Porosity", pp. 121-189, Academic Press, London (1967). S. Brunauer, P.H. Emmet and E. Teller, J. Amer. Chem. Soc. 60, 309 (1938). H.K. L i v i n g s t o n , J . Amer. Chem. Soc. 6 6 , 69 ( 1 9 4 4 ) . C. P i e r c e , J . Amer. Chem. Soc. 57, 149 ( 1 9 5 3 ) . C. Orr and J.M. Dalla Valle "Fine Particle Measurements", pp. 256-271 (1959). B.C. Lippens, B.G. Linsen and J.H. de Boer, J. Catal. ~, 32 (1964). I. Natan, A. Zevln and S.H. Gross, "Oil Shale Ash - Mineralogical Tests", Geological Institute Report No. M.G./5/81, Jerusalem, Israel
(1981). 20. 21. 22. 23. 24. 25.
D.M. Roy, T.P. O'Holleram and R.N. Neurgankar, II Cemento, 75, 337 (1978). R. Struillon and M. Arnould, pp. V-75 - V-79 in 7th Int. Symp. Chem. of Cements, Vol. 3, Paris (1980). K.S.W. Slng J.D. Madeley, J. Appl. Chem. 3, 549 (1953). M.R. Harris and G. Whltaker, J. Appl. Chem. 13, 349 (1963). J. Hagumassy, S. Brunauer and R. Mikhail, J. Coll. Inter. Sol. 29, 485 (1969). D.N. Winslow and S. Diamond, J. Mater. ~, 564 (1970).
PROPERTIES AND STRUCTURE OF OIL SHALE ASH PASTES I: COMPOSITION AND PHYSICAL FEATURES H. Baum, I. Soroka and A. Bentur Building Research Station - Faculty of Civil Engineering Technion, Israel Institute of Technology Haifa, Israel
(Communicated by J. Skalny) (Received Aug. 6, 1984)
ABSTRACT The composition and physical features of oil shale ash pastes were determined and compared with the corresponding properties of portland cement paste. In the first part presented here, the composition, chemically combined water, porosity (total, capillary and gel porosity), pore-slze and pore-slze distribution, and specific surface area were determined by water vapor adsorption, mercury penetration and X-ray diffraction . It was established that the structural features and the factors which control and determine these features, are essentially the same in both the ash and the portland cement pastes. In the ash paste, however, total porosity remained virtually unchanged with time. This aspect, as well as the mechanical properties of the ash paste, are presented and discussed in the second part of the paper.
Introduction The utilization of oil shale as a source of energy has been given serious consideration in recent years. In many oil shales, however, the content of the organic matter is rather low (i.e. only about 15%-30%) and its use as fuel is associated with generation of large quantities of by-product which constitutes an ecological problem. The by-product can be in the form of ash in the case of direct burning of the oil shales, or spent shale in the case of retorting processes which are used to extract liquid fuels from the oll shale. The economic use of such a low-calory source of energy is highly dependent on whether or not, if at all, some economic use can be made of the by-product (I). Hence, the economic use of large quantities of the byproduct is a decisive prerequisite for the successful and economic use of oll shales as a fuel. Usually the inorganic portion of the oil shale is high in silica and in such cases the by-product may possess pozzolanlc properties and, consequently, most of the relevant research has been associated with the utilization of the latter properties (1-4). The local Israeli oil shale, however, 303
304
Vol. 15, No. 2 H. Baum, et al.
is comparatively rich in lime and, under certain burning conditions, the resulting ash has cementitious properties (5)(6), probably due to the presence of reactive dicalcium silicate (7)(8). Indeed, earlier studies have shown that the ash in question can be used to produce concrete blocks and mortars for plastering and rendering (9)(10). Information with respect to oil-shale ash which possess cementitious properties is limited and only few publications dealt with this material (5)-(8). Hence, the present study was undertaken in order to determine the properties of such an ash, to establish the factors which determine its properties, and possibly to suggest a model by which the mechanical properties of the set ash can be explained and related to its physical structure.
Experimental The tests included oil-shale ash pastes having water/ash ratio of 0.8, 0.9 and 1.0, and a portland cement paste with a water/cement ratio of 0.4. Materials Only one type of ash was used in this work, being the by-product of burning local ell shale in a fluldlzed bed at a temperature of 850°C. Chemical composition of the ash is presented in Table I. The specific gravity of the ash was 2.68 and its Blaine specific surface area (ASTM C204) was 1134 m2/kg. Table i Chemical composition of the oil-shale ash and the portland cement (weight percentage)
Material
CaO Ca0 (total) (free)
Si02[AI203 Fe203
MgO
Na20
K20
0.58
P205
Oil Shale ash
45.50
9.00
21.40
8.50 3.60
0.70 0.58
2.70
Portland cement
63.66
2.14
20.98
5.74 2.94
1.58 nd (3) nd (3) nd (3)
SO 3 (total)
L.O.I.
10.20 (1) 5.50 (2)
1.81
2.65
i) including 9.7% soluble SO 3 (2) including 3.80% CO 2 (3) not determined
It should be pointed out that the high specific surface area of the ash resulted in a high water requirement and the ash pastes prepared were therefore of a high water/ash ratio. It is to be expected that such high ratios would result in pastes of a low strength. Such fineness is, however, a characteristic property of the ash in question and, at this stage at least, cannot be avoided (5). The cement was ordinary portland cement having specific gravity of 3.04, specific surface area (ASTM C204) of 307 m2/kg and chemical composition which is given in Table I.
Vol. 15, No. 2
305 OIL SHALE, ASH PASTES, COMPOSITION,
PORE STRUCTURE
Mixing procedure complied with ASTM C305. 25 mm cubes were prepared from all the mixes. Prisms of 25x25x160 mm were prepared only from the portland cement paste and the ash paste having the water/ash ratio of 0.8. Specimens were continuously cured in water at 20°±I°C. Testing was carried out at ages of i to 180 days. Testing Procedures
(a)
Total porosity was determined on 25 mm cubes from the weight of the evaporable water, i.e. from the difference in the weight of the saturated surface-dry cube and its corresponding oven-dry weight (24 hrs at I05°C), and assuming that the specific gravity of the evaporable water is I. Accordingly, the total porosity given in col. 3 of Table 2 is the volume percentage of the evaporable water with respect to the volume of the test specimen.
(b)
Degree of hydration. The chemically combined water was considered to measure the extent of hydration, and was determined on fragments which remained from the compression test of the 25 mm cubes. The fragments were pestled to the fineness of 75-200 mesh, washed with acetone to stop hydration, and then dried in a desicator over magnesium perchlorate for at least I0 days, to give their "P-dry weight", Gp (ii). The chemically combined water, Wn, was calculated from the loss on ignition of the P-drled samples corrected for the loss on ignition of the unhydrated ash. Accordingly, the chemically combined water, expressed as percentage of the weight of the ignited sample is given in col. 6 of Table 2.
(c)
Water vapour adsorption. Tests were carried out on P-dried samples, conditioned to a constant weight at different relative pressures, P/Po' ranging from 0.ii to 1.00, to give the complete adsorption isotherm. Sulphurlc acid solutions of different concentrations were used to control the relative pressure in the conditioning desicators. Typical adsorption isotherms of the portland cement and the ash pastes are given in Fig. i. It can be seen that the resulting isotherms are of type IV and exhibit a distinct "B-point" (12,13). Hence, the adsorption data was utilized to determine (a) the specific surface area of the pastes by the BET method; (b) the pore size distribution in the pastes and the specific surface area using the Kelvin equation; and, (c) the specific surface area of the pastes from the "V-t" curves.
(d)
BET surface area (SBET) was determined from the adsorption isotherm in the range of 0.05 < P/Po < 0.30 in accordance with the well established procedure of Brunauer, Emmett and Teller (12,14), and assuming that the area covered by one molecule of adsorbed water is IO.6A 2 (15). 0.5
I
I
I
I
I
I
]
I
I
E~0.4
Fig. I Typical adsorption isotherms of oll shale ash (full line) and portland cement (dotted llne) pastes.
w
~o0.2 o.
>~Eo.I w
0o
0.1
0.2
0,3
0.4
0.5 0.6 P/Po
0.7
0.8
0.9
1.0
306
Vol. 15, No. 2 H. Baum, et al.
The specific surface area was calculated with respect to the ignited weight of the sample, S ~ T , and with respect to its P-dried weight, S ~ T. Accordingly, the data are presented in cols. 7 and 8 of Table 2.
(e)
Pore-slze distribution was determined from the water adsorption isotherm in the range of 0.30 g P/Po g 1.00, using the Kelvin equation (assuming contact angle of 0 ° and surface energy of 73.5 dyne/cm) and correcting for the thickness, t, of the adsorbed water film (13, 15, 17).
Table 2 Physical features of the set portland cement and ash pastes
W/A or W/C Age Ratio
Days I
2
pd
Total Capillary Gel Chemically Porosity Porosity Porosity Combined d>30A d<30A Water % Volume 3
SBET
pd Spp
SVt
m2/g
% Wt.
4
pd
Scp
5
6
7
8
9
I0
II
.,I
0.8
0.9
1.O
Portland Cement 0.4
(f)
I 3 7 28 60 180
70.06 70.53 70.16 69.43 69.19 71.65
54.72 53.39 53.09 51.70 50.90 46.65
15.54 17.14 17.07 17.73 19.00 25.00
9.50 12.58 13.64 20.98 22.62 23.00
31 46 55 83 63 79
30 36 48 68 51 64
81 115 125 143 I01 I01
45 54 92 99 96 86
28 36 45 68 50 64
i 3 7 28 60 180
78.62 78.20 78.52 77.68 77.49 78.85
72.32
6.3
65.09 55.23 54.00
12.59 22.26 24.85
II .46 II .75 14.18 21.00 22.11 23.25
29 54 54 82 71 94
26 44 44 68 58 77
106 73 126 129 1271102 137 98 105 91 102 93
26 48 47 68 60 78
I 3 7 28 60 180
84.30 83.61 84.92 83.95 82.39 84.59
40
36
I00 105
36
65.63 64.59 61.40
18.32 16.90 23.19
12.00 13.16 15.00 21.43 22.92 23.66
70 69 90
64 65 93
109 119 97
88 94 88
64 62 77
1 3 7 28 60 180
29.67 28.64 27.87 25.94 25.31 23.23
21.45
8.22
15.98 II.01
9.33 12.22
6.36 12.18 16.32 18.30 21.23 22.08
45 59 57 60 84 108
42 52 64 58 69 77
58 55 61 74 74 -
53 55 59 71 73 -
40 50 60 60 62 77
Specific surface area from pore-slze distribution, S pd. On the b a s i s of the analysis of the pore-size distribution, i.e. the volume of the pores in each of the radius intervals, the surface area of the pores can be
Vol. 15, No. 2
307 OIL SHALE, ASH PASTES, COMPOSITION,
PORE STRUCTURE
determined on the assumption that the pores are either cylindrical or sllt shaped. The specific surface area, with respect to the P-drled weight of the samples, was determined for_= both assumptions and, accordingly, the data in col. g of Table 2, S ~ , are based on the assumption of cylindrical pores and those in col. ~0, S ~ , on sllt shaped pores with parallel walls.
(g)
Specific surface area from V-t curves. Knowing the amount, V, of the adsorbed water and the corresponding thickness, t, of the water layer, the adsorbent surface area, SVt , is given by V/t, i.e. by the slope of the V-t curve. It was shown (18), and demonstrated again in the present study, that the lower part of the curve is a straight line passing through the origin. Hence, the slope of this straight part of the curve gave the specific surface area SVt of the adsorbent (col. Ii of Table
2). (h)
Mercury penetration. Pore-size distribution was determined on P-drled samples using a porosimeter with a pressuring capacity of 422.5 MPa. The calculation was based on the Washburn equation assuming a surface tension of 47.3 dyne/cm 2, and a contact angle of the mercury with the pore walls of 130 °. Results and Discussion
Composition of the Ash X-ray diffraction of the oil-shale ash (Fig. 2) indicates that 8C2S is one of the ash constituents, with the remaining ones being CaO, CaSOg and CaCO 3. The presence of the same constituents was observed by others (5,7,19) and it was suggested that the 8C2S is much more reactive than that present in
%s+%s
j
C3S 3.0~
Fig. 2 X-ray diffraction patterns of the portland cement and of oil shale ash.
OIL SHALE ASH
39
37
II ~
35
33 31 2 8°
337
A 29
27
308
Vol. 15, No. 2 H. Baum, et al.
portland cement (7)(8). This was confirmed in the present work, which showed a similar increase in chemically combined water and BET surface area with hydration of the ash and the portland cement pastes. The main constituent of portland cement is, of course, C3S , which is not present in the ash. Nevertheless, as the hydration of both silicates, C3S and BC2S , results in essentially the same CSH gel, and as the properties of the set cement are mainly determined by the properties of the gel, it may be further expected that the behavlour and the properties of the set ash will be similar to those of the set portland cement. It will be seen later that, indeed, such a similarity was observed in most cases, but not necessarily without exception. Hydrationland surface area development Considering the chemically combined water, Wn, to measure the extent of hydration (col. 6, Table 2), it can be seen that at ages greater than about 3 days, the hydration of the oil-shale ash proceeded essentially at the same rate as that of the portland cement (Fig. 3). At earlier ages, however, the amount of the chemically combined water was greater in the ash pastes than in the portland cement pastes. This greater amount can be attributed to the greater amount of ettringite formed in the ash pastes (7) and to the much greater fineness of the ash, i.e. 1134 vs. 307 m2/kg. On the other hand, in view of the fact that 6-C2S will hydrate at a slower rate than C3S , it was to be expected that the ash will hydrate at a slower rate than the portland cement. The essentially same rate of hydration may be attributed, again, to the greater fineness of the ash on one hand, and to the greater reactivity of the 6C2S formed under conditions in hand, on the other. Indeed, it was suggested (20,21) that the 6C2S formed at about 800°C is more reactive and that this greater reactivity stems from its imperfect crystallization. The oil shale ash studied here was burned at 850°C. Hence, this explanation may be considered valid for the present tests. As the hydration proceeds, the BET surface area (col. 7, Table 2) increases, and the nature of this increase is, again, essentially similar in both the ash and the portland cement pastes (Fig. 4). Moreover, in both pastes the relation between the BET surface area and the chemically combined water was of a linear nature (Fig. 5). Such a linear relation in portland cement pastes was observed, of course, by others (II). Finally, for a given age (Fig. 4), or alternatively for the same amount of chemically combined water (Fig. 5) the BET surface area of the portland cement paste was somewhat greater than the surface area of the ash pastes. This difference may be expected to be reflected in the strength of the pastes, but this aspect will be discussed at a later stage.
rr ~ 2 5 | 20 I-
I
I
o
.......
i
o=
4
,
0°
0 I I
I $
,
I 7 AGE
Fig. 3
(log
,
I I 28 60 scale) , DAYS
-I
I 180
Chemlcally-comblned water vs. age in oll shale ash (full llne) and portland cement (dotted line) pastes.
Vol. 15, No. 2
309 OIL SHALE, ASH PASTES, COMPOSITION,
I
I
I
PORE STRUCTURE
I
I00
120
I
I
I
I x/1 i
lO0
*~°'° ~ _ ~ j l
E
~
80
~
~..~
-
%
.%/~
-60
.
6O G
Hu,~=40
~
20
20 I
5
[
L
I
7 28 60 AGE ( Io0 scole) , DAYS
Fig. 4 Development of BET surface area with time in oll shale ash (full line) and portland cement (dotted llne) pastes.
180
I
I
I
I
5
I0
15
20
WnlA
,%
WnlC
or
J 25
Fig. 5 BET surface area vs chemically combined water in oll shale ash (full line) and portland cement (dotted llne) pastes.
As mentioned earlier, the surface area, sPd, was also determined from the adsorption tests, assuming both cylindrical or silt-shaped pores with parallel walls (cols. 9 and i0, respectively, in Table 2). There exist some data (13,22,23) which indicate that the surface area S pd is greater than the BET surface area when the sample contains large pores and smaller when the sample contains ~mall pores. It was suggested (13) that this difference occurs because the S p° surface area excludes the volume of the pores smaller than approximately 20A which are included in the BET surface area. In the ash pastes, the S pd surface area was much greater in all cases than the corresponding area determined by the BET method. Hence, it may be concluded that such pastes were characterized bY relatively high content of large pores. In the portland cement paste S pa surface area was greater in most cases than the BET surface area, but the difference between the two was much smaller. In the ash pastes the S ~ surface area was, in most cases, smaller than S ~ surface area, and closer To the BET area. It is implied, therefore, that the shape of the pores in the ash paste is rather more sllt-llke in shape than cylindrical. In the portland cement paste the S pd and the S~ d were P P virtually the same, implying that both shapes occured ~o the same extent. Finally, the specific surface area, SVt , from the V-t curves (Fig. 6) is given in col. ii of Table 2, and it can be seen that in the ash pastes, and in most cases in the portland cement pastes, this method gave the closest values to the BET method. The V-t curves were straight lines passing through the origin, and implied, therefore, a material with silt-shaped large pores where the layer of the adsorbed water vapour can be built up unhindered. Porosity (a)
Total porosity. Generally speaking, due to the much higher water/ash ratio, the total porosity, Pt, of the ash pastes was much greater than
310
Vol. 15, No. 2 H. Baum, et al.
04
[
'
I
I
J
I
[
I
2S OArS 0.3
WZA,O - -
I
t
7
S
q
O.Z
2
[°' ~.
~-
o
o,~
Fig. 6 ,
,
i
,
,
i
i
i
i
i
,
6o DAYS
w/A-o.9
3
o4
V-t curves of the ash pastes.
os
oz
o.L
°o
zo
4o
so
• 80
ioo
the porosity of the portland cement pastes (col. 3, Table 2), i.e. 85% in the ash pastes versus, depending on the age, from 23 to 30% the portland cement pastes. It is to be expected, therefore, that strength of the ash pastes will be much lower than the strength of portland cement pastes. It will be shown later that, indeed, this the case here.
70 to in the the was
In the portland cement pastes total porosity decreases with age, as the hydration proceeds, because the volume of the hydration products is greater than the volume of reacting cement (II). In view of the similarity in the behavlour of the portland cement and the ash pastes, it was totally unexpected to find that the porosity of the ash pastes remained virtually unchanged with age and with the increase in the amount of hydration. The average total porosity of the ash pastes was approximately, regardless of age, 70%, 78% and 84% for the water/ash ratios of 0.8, 0.9 and 1.0, respectively. This particular observation warrants a suitable explanation and will be dealt with at a later stage. The decrease in total porosity, Pt, with the decrease in the water/ binder ratio characterizes both the portland cement and the ash pastes. In the portland cement paste, however, total porosity is also dependent on the degree of hydration (i.e. age) whereas, as pointed out earlier, in the ash paste total porosity remained unchanged and therefore independent on the latter. Accordingly, a linear relationship Pt = 14.3 + 70 W/A, which was independent of age, was established in the ash pastes between total porosity, Pt, and the corresponding water/ash ratio, W/A. Extrapolating and solving the total porosity expression for W/A = 0.40 give Pt = 42% which, with due reservation, constitutes a rough estimate of the total porosity of the ash paste, were it possible to produce such a paste with a W/A ratio of 0.4. This estimated porosity of 42% is rather high in comparison with the porosity of 23 to 30% observed in the portland cement paste with a corresponding water/cement ratio. It was suggested (24) that the hydration of 6C2S results in a more porous structure than the hydration of C3S. Hence, the former silicate, being the main cementitlous constituent of the ash, may explain the higher porosity of the ash paste. In any case, if this estimated value represents the true porosity, it is to be expected that for the same water/blnder ratio the portland cement paste will be stronger than its ash counterpart. It will be seen later that estimating the strength from the water/blnder ratio substantiated this conclusion.
Vol. 15, No. 2
311 OIL SHALE, ASH PASTES, COMPOSITION,
PORE STRUCTURE
E 0.3 , uJ ~L
~,g o.2
-
t
W/A=O 8
a- w
•~u j
o~' -
~
"~'~.
~
W/C=O.
= E _<
=
• o
Effect of age on (a) mean pore diameter, and (b) threshold diameter of oll shale ash (full llne) and portland cement (dotted line) pastes.
W/A=O.8
"
u~ w O . 4 ocw I- < 0.2
I 5
....."h. . . .
[
7
28 AGE
"P---4
60
. . . .
90
Fig. 7
180
, DAYS
(b)
Capillary porosity. Applying the maximum pressure of 422.5 MPa, the mercury penetrates into the pores down to the size of approximately 30A, but not into those of a smaller diameter. Hence, the porosity determined accordingly was considered to represent the capillary porosity, i.e. the fraction of the bigger-size pores. Relevant data are given in col. 4 of Table 2, and it can be seen that, although the total porosity remained unchanged, the capillary porosity of the ash pastes decreased with age, similarly to the decrease in the portland cement paste.
(c)
Gel porosity (col. 5, Table 2). The difference between total and capillary porosities measures the volume of the pores smaller than about 30A, which might be defined as gel pores. As the amount of the gel increases with age and hydration, the volume of the gel pores is expected to increase simultaneously. Indeed, this was the case for both the portland cement and the ash pastes.
(d)
Pore size. It was shown earlier that in both the portland cement and the ash pastes, the increase in gel porosity with time involves a simultaneous decrease in capillary porosity, i.e. the increase in the volume of the smaller pores corresponds to a decrease in the volume of the bigger pores. It is to be expected, therefore, that the mean pore diameter will also decrease with time. The latter diameter was determined from the adsorption data using the expression d = 4V/SBE T (13) (V amount of evaporable water), and is presented accordingly in Fig. 7a. It is clearly evident that the mean diameter decreases with the age of the pastes. In the ash paste of the water/ash ratio of 0.8, the mean diameter at the age of one day was 0.28 ~m, decreasing to 0.08 ~m at the age of 7 days, and further decreasing, at a slower rate, to less than 0.01 ~m at the age of 180 days. The mean diameter in the portland cement paste, although being smaller, similarly decreased from 0.12 Bm at the age of one day to about 0.01 ~m at 180 days. The decrease in the size of the portland cement pores with age was also reported elsewhere (25).
3L2
Vol. 15, No. 2 H. Baum, et al.
The pore-size can also be considered with respect to the "threshold diameter". The threshold diameter is the diameter which corresponds to the turning point of the cumulative pore size distribution curve (Figs. 8 and 9), and as such constitutes a measure of the size of the biggest pores in the paste. The change in the threshold diameter with time is presented in Fig. 7b, from which it is clearly evident that this diameter decreases with time. Again, it may be concluded that, in both the portland cement and the ash pastes, pore-slze decreases with time. Likewise, it can be concluded that the threshold diameter decreases with the decrease in the W/A ratio. It can be seen from Fig. 8 that the threshold diameter decreased from approximately 0.8 to 0.3 ~m with the decrease in the W/A ratio from 1.0 to 0.8, and further decreased to 0.07 ~m for the portland cement paste having the w/c ratio of 0.4.
(e)
Pore-size distribution data, as determined from mercury penetration, are presented in Figs. 8 and 9. Generally speaking, the nature of the ash and the portland cement curves are essentially the same once allowance is made for the difference in the porosity of the two types of paste. In fact, noting the effect of the water/ash ratio on pore-size distribution curves (Fig. 8), it is rather likely that, if it was possible to produce an ash paste with a water/ash ratio of 0.4, its poredistribution curve would not be very much different from that of portland cement paste. Normalized pore-slze distribution, determined from water adsorption tests, is presented in Fig. I0. It is clearly evident that all the ash pastes, irrespective of their W/A ratio and age, as well as the portland cement paste, exhibited a mode at P/Po = 0.65, which is equivalent to a pore radius of approximately 50A.
0.7
I
I
]
I
|
0.6
-T
.,,.-, 0.5 E o
Fig. 8
uaO.4 "
>0.3
g
Mercury penetration pore size distribution curves of oil shale ash (full line) and portland cement (dotted llne) pastes.
W / A = I. 0
\L
~
\
\
0.9
\
0.8
0.2
'-,, 0.0 0.001
I
I
I
I
0.01
0.1
I
I0
EQUIVALENT
PORE
DIAMETER
I00 , /u. m
Conclusions BC~S is the constituent which imparts the oll shale ash its cementltious properties. Apparently the reactivity of the 8C2S of the ash is greater than that of the portland cement, and the ash pastes hydrate at essentally the
Vol. 15, No. 2
313 OIL SHALE, ASH PASTES, COMPOSITION, PORE STRUCTURE
same rate as their portland cement counterparts. As hydration proceeds with time, the surface a r e a of the set ash increases in a similar way to the increase in the set portland cement. For a given age, or chemically combined water, however, the surface area of the portland cement paste is greater by about 20% t h a n the surface area of the ash paste. Similarly to the portland cement paste, the volume of the gel pores in the ash paste increases with time at the expense of the volume of the capillary pores. Likewise, total porosity of the ash pastes increases with 0.7
~
i
T
0.6
I
-I
~
T
W/A = 0.8
UO.5
7
0.4
o
T
i
T
i
W/A: 1.0 28 D~YS-
W/A=O'9
I DAY
.=
l
28 DAYS
77
60
~-o
180 28
z) 0.5 - -
60 180
.
~0.2
0.0 0.0001
O.OI
0.1
I
I0
0.01
0.1
EQUIVALENT
I
I0
0.01
0.1
I
I0
PORE DIAMETER , ~ m
Fig. 9 Effect of age on pore size distribution of ash pastes of different water/ash ratios.
w.Li2!
I
I
8 0 -- A ~
I
WlA=I.O
60
,
I
I
AGE
2 8 DAYS
I
W / A = O. 8
40
~ 2o >
WIA=O 8 60
Fig. i0
3 DAYS
o
O"
I 0"651
0.3
0.4
0.5
0.6
0.7
0.8
0.9-
P/Po
I
I
I
I
I
I,.5
20
50
50
70
%.i
I 120
1.0
Normalized pore size distribution of pastes of (a) ash with different water/ash ratios (0.8, 0.9, 1.0) and portland cement with water/cement ratio of 0.4, and (b) ash at different ages.
314
Vol. 15, No. 2 H. Baum, et al.
the W/A ratio. However, whereas total porosity in the portland cement paste decreases with time, the total porosity in the ash paste remains virtually unchanged. This particular property, which eonstltutes the main difference Between the ash and the portland cement pastes, will he discussed in some detail in the second part of the paper. Nevertheless, with the remaining structural features being essentially the same, it is to be expected that the same factors determine and control the physical properties and hehavlour of both the portland cement and the ash pastes. The physical properties of the pastes with respect to their structural features are discussed in the second part of the paper.
References I. 2. 3. 4. 5. 6. 7. 8. 9.
I0. II. 12.
R. Rohrbach, Zement-Kalk-Gips, 2, 293 (1969). M. Lawson and P.J. Nixon, Building Research Establishment Current Paper, CP50/78, pp. 11-19 (1978). G.J. Gromko, Trans. Res. Rec. 549, 47 (1975). P.K. Metha, Cem. Contr. Res. i0, 545 (1980). M. Ish-Shalom, A. Bentur and T. Grlnberg, Cem. Concr. Res. IO, 799 (1980). A. Bentur, M. Ish-Shalom and T. Grinberg, Cem. Concr. Res. ii, 175 (1981). A. Bentur and T. Grinberg, Amer. Ceram. Soc. Bull. 61, 1296 (1982). A. Bentur and T. Grinberg, Amer. Ceram. Soc. Bull. 63, 290 (1984). M. Ish-Shalom, A. Bentur and T. Grinberg, "Application of Oil Shale Ash From Zefa Ere", Israel Ceramic and Silicate Institute, Report to the Ministry of Energy and Infrastructure, The Government of Israel, Haifa (1979). A. Bentur, Silicate Industrials, XLVII, 163 (1982). T.C. Power and T.L. Brownyard, Amer. Concr. Inst. Proc. 43, i01 (1947). S. Brunauer, L.S. Demig, W.S. Demig and E. Teller, J. Amer. Chem. Soc.
6!2, 1723 (1940). 13. 14. 15. 16. 17. 18. 19.
S.J. Gregg and K.S.W. Sing, "Adsorption, Surface Area and Porosity", pp. 121-189, Academic Press, London (1967). S. Brunauer, P.H. Emmet and E. Teller, J. Amer. Chem. Soc. 60, 309 (1938). H.K. L i v i n g s t o n , J . Amer. Chem. Soc. 6 6 , 69 ( 1 9 4 4 ) . C. P i e r c e , J . Amer. Chem. Soc. 57, 149 ( 1 9 5 3 ) . C. Orr and J.M. Dalla Valle "Fine Particle Measurements", pp. 256-271 (1959). B.C. Lippens, B.G. Linsen and J.H. de Boer, J. Catal. ~, 32 (1964). I. Natan, A. Zevln and S.H. Gross, "Oil Shale Ash - Mineralogical Tests", Geological Institute Report No. M.G./5/81, Jerusalem, Israel
(1981). 20. 21. 22. 23. 24. 25.
D.M. Roy, T.P. O'Holleram and R.N. Neurgankar, II Cemento, 75, 337 (1978). R. Struillon and M. Arnould, pp. V-75 - V-79 in 7th Int. Symp. Chem. of Cements, Vol. 3, Paris (1980). K.S.W. Slng J.D. Madeley, J. Appl. Chem. 3, 549 (1953). M.R. Harris and G. Whltaker, J. Appl. Chem. 13, 349 (1963). J. Hagumassy, S. Brunauer and R. Mikhail, J. Coll. Inter. Sol. 29, 485 (1969). D.N. Winslow and S. Diamond, J. Mater. ~, 564 (1970).