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Pozzolanic reactivity of fly ash – API method and K-value
Fuel 85 (2006) 2345–2351 www.fuelfirst.com
Pozzolanic reactivity of fly ash – API method and K-value Takeshi Yamamoto
a,*
, Tsutomu Kanazu a, Masateru Nambu b, Takao Tanosaki
c
a
Central Research Institute of Electric Power Industry, Civil Engineering Research Laboratory, 1646 Abiko, Abiko City, Chiba Prefecture, 270-1194, Japan b Tokyo University of Science, 2641, Yamazaki, Noda City, Chiba Prefecture, 278-8510, Japan c Research Center, Taiheiyo Cement Corp., 2-4-2, Osaku, Sakura City, Chiba Prefecture, 285-8655, Japan Received 5 March 2005; received in revised form 19 January 2006; accepted 19 January 2006 Available online 9 June 2006
Abstract The pozzolanic reaction of fly ash in mortar was primarily examined using a K-value from Fere´t’s law. As a result, the pozzolanic reaction would be mainly controlled by the diffusion kinetic, and the diffusion constant would increase with water content in the mortar. The K-value is useful to estimate the degree of the pozzolanic reaction of mortar. Secondly, the relation between K-value and assessed pozzolanic activity index derived from accelerated chemical test (API method) was inspected. It is concluded that the API is one of the useful acceleration methods to evaluate the degree of the pozzolanic activity, because API has a good relation with K-value. 2006 Elsevier Ltd. All rights reserved. Keywords: Fly ash; K-value; Pozzolanic reaction
1. Introduction Fly ash has pozzolanic activity in the presence of hydrating Portland cement to form compounds possessing cementitious properties [1]. It is generally accepted that the finer the grain sizes of the fly ash, the greater the pozzolanic activity [2–6]. The potential pozzolanic index (PPI) was proposed by Paya et al. [7]. Hubbard et al. [8] proposed a lime-reactivity by combination of the solubility of silica by hydrofluoric acid and specific surface area by Blaine, because silica components in fly ash are crystalline quartz and amorphous glass, and the latter is more soluble by acid. Ramezanianpour and Cabrera [9] showed that reaction quantity of Ca(OH)2 in concrete had a relation to the pozzolanic reaction by an experiment in which Ca(OH)2 and fly ash were mixed in the same ratio. Yamamoto and Kanazu [10,11,13] proposed an API (assessed pozzolanic-activity index) method that stands *
Corresponding author. E-mail address: [email protected] (T. Yamamoto).
0016-2361/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2006.01.034
for consuming quantity of Ca2+ in a suspension of which cement and fly ash is mixed, on the assumption that Na+ and K+ ions from Portland cement primarily dissolve the amorphous phase, and then the dissolved Si and Al ions react with Ca2+ which is derived from portlandite (Ca(OH)2). The main purpose of the API method is to complete a rapid and appropriate evaluation of the pozzolanic property of fly ash. It takes only two days to measure and calculate the API value. On the other hand, activity index (by ISO and JIS) needs 28 and 91 days to cure the test pieces. Unfortunately we cannot show any information of the activity index, until fly ash is shipped from a power plant. In Japan and many European countries, physical and chemical properties of fly ashes change in a few days, since the fuel coal is imported from many countries with changing in a few days. The objective of this study is to examine the API method using the K-value of Fere´t’s law (1892). This law states that the strength is proportional to [c/(c + w + a)]2 , where c, w and a are the volumes of cement, water and air, respectively.
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T. Yamamoto et al. / Fuel 85 (2006) 2345–2351
tar. The air contents were around 1%. Bleeding ratio of fly ash free mortar was 3.5%, but the ratios of fly ash containing mortar were from 4.4% to 7.0%. The mortar test piece was cured for 28, 91, 189 and 378 days.
2. Experiments 2.1. Materials Five fly ashes from different coal sources were collected from the same boiler (T) at a power station. The original fly ash samples were classified into two grades by use of an air stream classifier. The physical properties and chemical compositions of the fly ashes are given in Table 1. The characters BO, WA, MS, LI/BA, and WR stand for the source of coals, and the following letters Org, Fin, and Crs are the original, fine-grade and coarse-grade fly ashes, respectively. Content of over 45 lm measured by laser diffraction method is listed in Table 2.
2.3. Calculation of K-value and activity index The K-values were calculated from the following formula: S = K[(c + f)/(c + f + w + a)]2. Hereby, S is the compressive strength of mortar and f is volume of fly ash. Fly ash was counted as a cement material. To check the adequacy of the API method for the pozzolanic evaluation, the activity index was compared. The activity index was calculated from the strength of mortar according to EN 196-1.
2.2. Mix proportion for mortar 2.4. Accelerated chemical test For the purpose of the calculation of the K-value, two types of mortars mixed with different water ratios were made as shown in Table 3. Standard sand (ISO 679) was used as sand material. The water cement ratio 50% is according to JIS A 6201 and the 39% is a condition that does not cause the bleeding. In the latter case, superplasticizer and de-foaming agent were mixed to maintain a proper workability. The fresh mortar is vibrated by a table-vibrator for the purpose of decreasing the air in mor-
The testing method for API [11] is as follows: 1. (i) Mix 1.5 g of fly ash (FA) and 1.5 g of ordinary Portland cement (C) with 50 mL of purified water (fly ash– cement suspension), (ii) mix 1.5 g of OPC and 50 mL of purified water (cement suspension). Then, stir each sample contained in the sealed polypropylene vessels for 1 h by using a reciprocating machine at room temperature.
Table 1 Characteristics of fly ashes Materials
Chemical compositions
Density (g/cm3)
Blaine (cm2/g)
LOI
SiO2
Al2O3
Fe2O3
MgO
SO3
Na2O
K2O
BO
Org Fin Crs
0.9 1.8 0.8
42.8 43.3 45.6
29.6 28.4 28.6
9.0 9.3 8.6
5.0 5.2 4.9
1.4 2.0 1.7
0.43 0.69 0.25
1.3 1.1 0.9
1.1 1.6 1.4
2.41 2.57 2.32
2580 3860 1460
WA
Org Fin Crs
1.6 2.2 1.3
66.8 66.4 64.9
18.0 18.3 17.5
4.6 3.8 5.5
1.6 1.2 1.9
0.8 0.9 1.3
0.12 0.20 0.07
0.8 0.7 0.6
0.6 1.0 0.9
2.15 2.33 2.06
2850 4030 1800
MS
Org Fin Crs
1.6 2.6 1.6
56.6 54.4 56.0
20.6 20.4 20.3
6.1 6.0 6.1
7.9 8.4 8.5
0.6 1.3 1.2
0.41 0.73 0.23
0.9 0.3 0.2
0.8 0.8 0.8
2.30 2.42 2.20
3050 4370 1600
LI/BA
Org Fin Crs
1.8 3.2 1.4
68.8 63.2 67.0
21.8 21.9 21.1
1.3 1.1 1.2
0.3 0.5 0.4
0.2 0.3 0.3
0.05 0.09 0.02
0.2 0.1 0.0
1.6 1.8 1.5
2.07 2.27 2.04
2430 4700 1740
WR
Org Fin Crs
1.2 2.0 0.9
59.5 57.7 58.0
25.3 24.6 24.5
4.8 5.0 4.7
3.4 2.8 3.1
0.9 0.9 0.9
0.13 0.26 0.07
0.4 0.5 0.4
1.6 1.6 1.6
2.17 2.41 2.11
2640 3410 1570
0.5
21.0
5.3
2.6
64.6
2.1
2.00
0.3
0.6
3.17
3090
OPC
CaO
Org: original; Fin: fine; Crs: course.
Table 2 Content of over 45 lm of fly ash (measured by optical method) Sample
Over 45 lm
BO
WA
MS
L/BA
WR
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
26.3
0.2
43.6
28.3
0.1
46.1
29.6
0.1
46.0
40.0
0.5
51.0
34.6
0.0
46.2
Percentage remained over 45 lm.
T. Yamamoto et al. / Fuel 85 (2006) 2345–2351
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Table 3 Mixing conditions of mortars W/(C + F)
Sanda
OPC
Fly ash
Water
Superplasticizerb
De-foaming agentc
Bleeding ratio (%)
39% 39% 50% 50%
1350 1350 1350 1350
500 375 450 337.5
0 125 0 112.5
172.5 172.5 225 225
3 3(2)d – –
22.5 22.5 – –
0 0 4.4–7.0 3.5
a b c d
Standard sand (ISO 679). SP-8 N · 2 (no dilution). Micro-air 404 (100 times dilution). Two grams was used in fine grade.
2. Store the samples in sealed vessels at 80 C for 18 h. 3. Filter each suspension by using a 0.2 lm polyethylene membrane filter. 4. Measure the concentration of calcium ions in the filtrates; [Ca(FA + C)] and [Ca(C)], derived from fly ash–cement, and cement suspension, respectively. Determine the API of each fly ash by estimating the ratios of consumed calcium ion in the fly ash–cement suspension samples.
Table 4 Compressive strength of the mortar (N/mm2) W/(C + F) = 50%
Fig. 1 shows relation between Blaine specific surface area and K-values. These figures indicate that mortars containing finer fly ashes have higher strength during all curing ages. This would be the result of pozzolanic reaction, as mentioned above [2–7]. Exactly speaking, the linear relations break down from higher range of 3500 cm2/g. High-water mixed mortar (W/(C + F) = 50%) has a more
189 days
378 days
28 days
91 days
189 days
378 days
73.1 84.1 67.0
91.5 104.9 83.1
100.9 119.6 97.0
104.4 130.2 100.8
89.8 95.7 85.2
94.7 105.9 97.3
100.5 104.1 93.5
107.1 113.5 100.5
WA
Org Fin Crs
78.5 88.5 68.4
92.5 108.9 83.7
106.9 123.4 95.1
114.4 135.3 106.4
89.3 97.3 79.6
95.6 101.6 94.7
95.8 105.6 89.9
105.1 113.3 97.0
MS
Org Fin Crs
77.4 85.5 72.0
95.6 106.7 87.5
110.9 123.8 100.7
118.9 130.7 108.3
86.7 95.4 80.6
88.4 102.2 85.2
95.6 106.9 89.1
103.6 111.3 96.6
LI/BA
Org Fin Crs
75.5 89.1 73.4
90.7 106.4 87.4
107.1 122.3 99.0
111.8 130.0 105.1
85.8 91.1 86.2
95.8 96.5 88.4
95.1 102.8 88.7
101.6 111.3 94.9
WR
Org Fin Crs
70.7 90.6 70.3
91.8 110.9 84.8
105.8 123.2 95.7
113.1 134.7 102.5
85.7 94.4 82.8
99.3 107.6 93.1
98.2 105.9 88.9
106.4 111.6 100.1
3.1. Compressive strength of mortar and API
4.1. Effect of specific surface area of fly ash on pozzolanic reaction
91 days
Org Fin Crs
3. Experimental results
4. Discussion
28 days BO
API ¼ ðð½CaðCÞ ½CaðFA þ CÞÞ=½CaðCÞÞ 100 ð%Þ:
Results of the compressive strength of mortars related to curing time are listed in Table 4. The results show that the increase of strength in the fly ash containing mortars with curing time is bigger than that of fly ash free mortars (OPC in the table). API results are shown in Table 5. Finer fly ash has higher API value in each type of fly ash. Calculated results of the K-value and experimental results of activity index are shown in Tables 6 and 7, respectively.
W/(C + F) = 39%
acute gradient than low-water mixed mortar (W/(C + F) = 39%). These suggest that water content in mortar will control the rate of pozzolanic reaction. Joshi and Marsh [12] already pointed out that strength reaches the maximum when the Blaine surface area comes to more than 5000 cm2/g. But they did not mention the reason. The fineness from which the strength begins to break down would depend on the physical/chemical/mineralogical properties of fly ash. 4.2. Degree of pozzolanic reaction related to curing time Figs. 2 and 3 show the relations between curing time and the K-value of mortars. In these figures, x-axes (time) are logarithmic scales. The gradient of the K-value is linear to logarithmic time, as far as the curing time of this study
Table 5 Results of API value (%) Sample
BO
WA
MS
L/BA
WR
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
API (%)
46.5
85.8
35.9
41.4
79.3
20.5
35.4
73.1
22.6
25.1
67.2
19.1
39.0
81.1
22.2
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T. Yamamoto et al. / Fuel 85 (2006) 2345–2351
Table 6 Calculated results of K-value W/(C + F) = 50%
W/(C + F) = 39%
28 days
91 days
189 days
378 days
28 days
91 days
189 days
378 days
BO
Org Fin Crs
259.1 305.6 234.1
358.6 421.2 320.8
400.8 486.5 379.3
422.6 539.6 401.7
276.4 300.6 259.3
309.1 334.9 300.3
412.5 435.7 379.1
430.7 465.4 399.6
WA
Org Fin Crs
266.0 309.9 227.7
346.4 421.3 308.0
405.7 483.7 354.5
442.3 540.3 404.2
265.2 296.6 233.2
302.9 309.2 298.7
379.4 428.8 351.0
407.7 451.2 371.0
MS
Org Fin Crs
269.6 303.8 246.3
367.9 418.7 330.7
432.6 492.3 385.5
472.3 529.9 422.7
263.1 294.3 241.1
283.5 317.8 259.7
386.6 439.3 355.4
410.7 448.3 377.7
LI/BA
Org Fin Crs
251.7 308.6 243.3
334.4 407.3 320.4
400.0 474.4 367.4
425.7 513.8 397.6
251.7 275.4 251.5
301.0 292.8 273.7
371.8 414.1 345.2
389.4 439.5 362.0
WR
Org Fin Crs
240.5 321.4 246.7
345.1 434.8 328.9
402.9 489.3 375.8
438.9 545.2 410.3
255.2 290.7 244.4
317.8 330.1 322.3
390.0 434.7 349.8
414.1 449.1 386.0
507.8
561.2
568.5
579.3
332.9
344.3
443.6
434.8
OPC
Table 7 Activity indexes (%) W/(C + F) = 50%
W/(C + F) = 39%
28 days
91 days
189 days
378 days
28 days
91 days
189 days
378 days
BO
Org Fin Crs
73.1 84.1 67.0
91.5 104.9 83.1
100.9 119.6 97.0
104.4 130.2 100.8
89.8 95.7 85.2
94.7 105.9 97.3
100.5 104.1 93.5
107.1 113.5 100.5
WA
Org Fin Crs
78.5 88.5 68.4
92.5 108.9 83.7
106.9 123.4 95.1
114.4 135.3 106.4
89.3 97.3 79.6
95.6 101.6 94.7
95.8 105.6 89.9
105.1 113.3 97.0
MS
Org Fin Crs
77.4 85.5 72.0
95.6 106.7 87.5
110.9 123.8 100.7
118.9 130.7 108.3
86.7 95.4 80.6
88.4 102.2 85.2
95.6 106.9 89.1
103.6 111.3 96.6
LI/BA
Org Fin Crs
75.5 89.1 73.4
90.7 106.4 87.4
107.1 122.3 99.0
111.8 130.0 105.1
85.8 91.1 86.2
95.8 96.5 88.4
95.1 102.8 88.7
101.6 111.3 94.9
WR
Org Fin Crs
70.7 90.6 70.3
91.8 110.9 84.8
105.8 123.2 95.7
113.1 134.7 102.5
85.7 94.4 82.8
99.3 107.6 93.1
98.2 105.9 88.9
106.4 111.6 100.1
is concerned. This would suggest that the pozzolanic reaction would be mainly controlled by the diffusion kinetic. Pozzolanic reaction will be apparent, because K-value gradient of fly ash containing mortar is more acute than that of fly ash free mortar (OPC), especially in the case of high-water containing mortar. Furthermore, the diffusion constant would increase with water content in mortar, if the strength of mortar depends mainly on the degree of pozzolanic reaction. The porosity of mortar will increase with water content of mortar. The degree of chemical reaction/mineralization/pozzolanic reaction will also increase with water content, because degree of ion migration (diffusion) depends on the condition of porosity. As shown in Figs. 1–3, the K-value of W/(C + F) = 50% mortar is higher than W/(C + F) = 39% mortar, though the former strength of mortar is smaller than the latter. Therefore the K-value itself is not useful to compare among the different W/C mortars. In spite of this, the gradient of K-value is considered to be useful for estimating the characteristics of pozzolanic activity
700
700
600
600 500 R2 = 0.83
400
K-value
K-value
500 R2 = 0.87 300
2
R = 0.83 200
R = 0.83
0
1000 2000 3000 4000 Blaine surface area (cm2/g) (a) W/(C+F)=50%
400
R2 = 0.74
300 R2 = 0.74
28day 91day 189day 378day
2
100 0
28day 91day 189day 378day
200
R2 = 0.15
100 5000
0
R2 = 0.68 0
1000 2000 3000 4000 Blaine surface area (cm2/g) (b) W/(C+F)=39%
Fig. 1. K-value related to Blaine specific surface area.
5000
T. Yamamoto et al. / Fuel 85 (2006) 2345–2351 700
700
700
600
600
600
500
500
2
R = 0.96
K-value
400
R2 = 1.00 300
400
R2 = 1.00 300
WA-Fin (W/C=50%)
BO-Fin (W/C=50%)
200
BO-Org (W/C=50%) BO-Crs (W/C=50%)
100
OPC (W/C=50%)
100
OPC (W/C=50%)
0
0 10
100
10
1000
MS-Fin (W/C=50%) MS-Org (W/C=50%) MS-Crs (W/C=50%) OPC (W/C=50%)
200
WA-Org (W/C=50%) WA-Crs (W/C=50%)
100
0 10
1000
100
Curing time (day)
Curing time (day) 700
700
1000
Curing time (day) 700 R2 = 0.90
600
600
600 2
2
R = 1.00
R = 1.00 500
500
500 R2 = 0.99
2
R2 = 0.99 300
K-value
R = 0.99 400
400 R2 = 1.00 300 WR-Fin (W/C=50%) WR-Org (W/C=50%) WR-Crs (W/C=50%) OPC (W/C=50%)
LI/BA-Fin (W/C=50%) 200
200
LI/BA-Org (W/C=50%) LI/BA-Crs (W/C=50%)
100
100
OPC (W/C=50%)
K-value
K-value
R2 = 0.98 300
100
R2 = 0.99
R2 = 0.99
400
K-value
500
200
R2 = 0.99
R2 = 0.99
R2 = 1.00
K-value
2349
400 OPC (W/C=50%) 300 200 100
0
0 10
100
10
1000
Curing time (day)
100
0 10
1000
100
Curing time (day)
1000
Curing time (day)
Fig. 2. Relation between curing time and K-value of W/(C + F) = 50% mortars.
700
700
700
WA-Fin (W/C=39%)
BO-Fin (W/C=39%)
WA-Crs (W/C=39%)
R2 = 0.92
OPC (W/C=39%)
500
R2 = 0.94 300
500 R2 = 0.95
400 300
R2 = 0.98
100
100 0
0 10
1000
10
1000
700 WA-Fin (W/C=39%)
600
LI/BA-Org (W/C=39%)
WR-Org (W/C=39%)
500
2
R2 = 0.98
2
R = 0.90 300
K-value
R = 0.96
400
R2 = 0.99
300
400 300
200
200
200
100
100
100
100
1000
Curing time (day)
R2 = 0.77
500
R = 0.91
OPC (W/C=39%)
2
400
600 OPC (W/C=39%)
WR-Crs (W/C=39%)
R2 = 0.85
LI/BA-Crs (W/C=39%) OPC (W/C=39%)
0 10
100 Curing time (day)
700 LI/BA-Fin (W/C=39%)
500
100 Curing time (day)
Curing time (day)
600
R2 = 0.88
R2 = 0.87
100
700
R2 = 0.85
300 200
1000
MS-Crs (W/C=39%)
400
200
100
MS-Org (W/C=39%) OPC (W/C=39%)
200
0 10
K-value
R = 0.84
OPC (W/C=39%)
R2 = 0.90
400
600 2
K-value
BO-Crs (W/C=39%)
MS-Fin (W/C=39%)
WA-Org (W/C=39%)
K-value
K-value
500
600
BO-Org (W/C=39%)
K-value
600
0
0 10
100
1000
10
Curing time (day)
100
1000
Curing time (day)
Fig. 3. Relation between curing time and K-value of W/(C + F) = 39% mortars.
of fly ash. As shown below, we will clarify the relation between the K-value gradient and the degree of pozzolanic activity quantitatively.
As a reference of experimental data, the relations between curing time and activity index are shown in Figs. 4 and 5. The correlation coefficients are almost
2350
T. Yamamoto et al. / Fuel 85 (2006) 2345–2351
Fig. 4. Relation between curing time and activity index of W/(C + F) = 50% mortars.
Fig. 5. Relation between curing time and activity index of W/(C + F) = 39% mortars.
same as those of Figs. 2 and 3. This occurs because the K-value and activity index are obtained by the strength of mortar. 4.3. API method to evaluate the pozzolanic grade of fly ash As mentioned in the above section, the K-value is considered to be useful for estimating the degree of the pozzolanic activity of fly ash in mortar. From this view point, the relation of the API value to the K-value is plotted in Fig. 6.
As shown from the gradient of the slope in Fig. 6(a), we can find a good relation of the API value to the K-value. On the other hand, the slope decreases at W/ (C + F) = 39% mortar (Fig. 6(b)). This is considered to be derived from the insufficient water in mortar, which would decrease the rate of the chemical reaction. Judging from high correlation coefficient in Fig. 6(a), API has a good relation to the K-value during all curing ages, compared to the relation between specific surface area and K-value (Fig. 1). Therefore, the API is considered to be
T. Yamamoto et al. / Fuel 85 (2006) 2345–2351 700
700 R2 = 0.89 600 R = 0.90 500 K-v al ue
500
400 300 200
378 days 189 days 91 days 28 days
R2 = 0.93
100
2
R = 0.87 0 0
20
40
60
80
100
R2 = 0.79
378 days 189 days 91 days 28 days
600
2
K -v al u e
2351
R2 = 0.78
400 300 200
R2 = 0.36
100
R2 = 0.71
0 0
20
40
60
API (%)
API (%)
(a) W/(C+F)=50%
(b) W/(C+F)=39%
80
100
Fig. 6. Relation between API (%) and K-value.
one of the most useful and rapid methods to evaluate a degree of the pozzolanic activity of fly ash. We have already obtained a good relation of the API value to the pozzolanic reaction of fly ashes that were collected from 30 boilers of 24 electric power stations [13]. 5. Conclusion Yamamoto and Kanazu [10,11,13] proposed the API method, for the purpose of rapid and appropriate evaluation of the pozzolanic property of fly ash. It has been necessary to prove the applicability of this method. The K-value of Fere´t’s law was inspected primarily, and the correlation between K-value and API value was considered in this study. The conclusions are as follows: 1. Fine fly ash containing mortars have higher strength during all curing ages. This is the result of high amount of pozzolanic reaction in unit volume of mortar. 2. High-water mixed mortar has more acute gradient than low-water mixed mortar. This suggests that water content in mortar controls the rate of pozzolanic reaction of fly ash and even the hydration of cement grain. 3. The gradient of the K-value is liner to logarithmic time. This would suggest that the pozzolanic reaction would be mainly controlled by diffusion kinetic, and the diffusion coefficient would increase with water content in mortar. 4. The K-value is useful to estimate the degree of the pozzolanic activity of fly ash in mortar. 5. The API method is one of the most useful and rapid methods to evaluate the degree of pozzolanic activity of fly ash, because API has a good relation to the Kvalue.
References [1] Ogawa K, Uchikawa H, Takemoto K. The mechanism of the hydration in the system C3S-pozzolan. Cem Concr Res 1980;10: 683–96. [2] Ravina D. Optimized determination of PFA (fly ash) fineness with reference to pozzolanic activity. Cem Concr Res 1980;10:573–80. [3] Ranganath RV, Sharmw RC, Krishnamoorthy S. Influence of fineness and soluble silica content of fly ash on their strength development with respect to age. In: Malhotra VM, editor. Proceedings of the fifth international conference on fly ash, silica fume, slag, and natural pozzolans in concrete; 1995. p. 355–66. [4] Hall D, Mehta PK. Testing and correlation of fly ash properties with respect to pozzolanic behavior. EPRI CS-3314 Project 1260-26 Final Report, 1984. [5] Mehta PK. Influence of fly ash characteristics on the strength of Portland-fly ash mixtures. Cem Concr Res 1985;15:669–74. [6] Monzo J, Paya J, Peris-Mora E. A preliminary study of fly ash granulometric influence on mortar strength. Cem Concr Res 1994;24: 791–6. [7] Paya J, Monzo J, Peris-Mora E, Borrachero MV, Tercero R, Pinillos C. Early-strength development of Portland cement mortars containing air classified fly ash. Cem Concr Res 1995;25:449–56. [8] Hubbard FH, Dhir RK, Ellis MS. Pulverized-fuel ash for concrete – compositional characterization of United Kingdom PFA. Cem Concr Res 1985;15:185–98. [9] Ramezanianpour A, Cabrera JG. The measurement of lime reactivity of natural and artificial pozzolans. In: Second Int Sem Cem Build Mater, vol. 4; 1989. p. 81–8. [10] Yamamoto T, Kanazu T. Chemical assessment method for the preventive effect of fly ash on alkali–silica reaction. In: Proceedings of 11th Int Conf AAR; 2000. p. 801–10. [11] Yamamoto T, Kanazu T. Investigation on the pozzolanic reaction of fly ash. Central research institute of electric power industry report 2004, No. N04008 [in Japanese]. [12] Joshi RC, Marsh BK. Some physical, chemical and mineralogical properties of some Canadian fly ash. Material Research Society, Proceeding, vol. 86, Pittsburgh, USA. 1987. p. 113–26. [13] Yamamoto T, Kanazu T. Accelerated chemical assessing method for pozzolanic activity of fly ash. CRIEPI Abiko Research Laboratory Rep. No. U98047, 1999 [in Japanese].
Pozzolanic reactivity of fly ash – API method and K-value Takeshi Yamamoto
a,*
, Tsutomu Kanazu a, Masateru Nambu b, Takao Tanosaki
c
a
Central Research Institute of Electric Power Industry, Civil Engineering Research Laboratory, 1646 Abiko, Abiko City, Chiba Prefecture, 270-1194, Japan b Tokyo University of Science, 2641, Yamazaki, Noda City, Chiba Prefecture, 278-8510, Japan c Research Center, Taiheiyo Cement Corp., 2-4-2, Osaku, Sakura City, Chiba Prefecture, 285-8655, Japan Received 5 March 2005; received in revised form 19 January 2006; accepted 19 January 2006 Available online 9 June 2006
Abstract The pozzolanic reaction of fly ash in mortar was primarily examined using a K-value from Fere´t’s law. As a result, the pozzolanic reaction would be mainly controlled by the diffusion kinetic, and the diffusion constant would increase with water content in the mortar. The K-value is useful to estimate the degree of the pozzolanic reaction of mortar. Secondly, the relation between K-value and assessed pozzolanic activity index derived from accelerated chemical test (API method) was inspected. It is concluded that the API is one of the useful acceleration methods to evaluate the degree of the pozzolanic activity, because API has a good relation with K-value. 2006 Elsevier Ltd. All rights reserved. Keywords: Fly ash; K-value; Pozzolanic reaction
1. Introduction Fly ash has pozzolanic activity in the presence of hydrating Portland cement to form compounds possessing cementitious properties [1]. It is generally accepted that the finer the grain sizes of the fly ash, the greater the pozzolanic activity [2–6]. The potential pozzolanic index (PPI) was proposed by Paya et al. [7]. Hubbard et al. [8] proposed a lime-reactivity by combination of the solubility of silica by hydrofluoric acid and specific surface area by Blaine, because silica components in fly ash are crystalline quartz and amorphous glass, and the latter is more soluble by acid. Ramezanianpour and Cabrera [9] showed that reaction quantity of Ca(OH)2 in concrete had a relation to the pozzolanic reaction by an experiment in which Ca(OH)2 and fly ash were mixed in the same ratio. Yamamoto and Kanazu [10,11,13] proposed an API (assessed pozzolanic-activity index) method that stands *
Corresponding author. E-mail address: [email protected] (T. Yamamoto).
0016-2361/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2006.01.034
for consuming quantity of Ca2+ in a suspension of which cement and fly ash is mixed, on the assumption that Na+ and K+ ions from Portland cement primarily dissolve the amorphous phase, and then the dissolved Si and Al ions react with Ca2+ which is derived from portlandite (Ca(OH)2). The main purpose of the API method is to complete a rapid and appropriate evaluation of the pozzolanic property of fly ash. It takes only two days to measure and calculate the API value. On the other hand, activity index (by ISO and JIS) needs 28 and 91 days to cure the test pieces. Unfortunately we cannot show any information of the activity index, until fly ash is shipped from a power plant. In Japan and many European countries, physical and chemical properties of fly ashes change in a few days, since the fuel coal is imported from many countries with changing in a few days. The objective of this study is to examine the API method using the K-value of Fere´t’s law (1892). This law states that the strength is proportional to [c/(c + w + a)]2 , where c, w and a are the volumes of cement, water and air, respectively.
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T. Yamamoto et al. / Fuel 85 (2006) 2345–2351
tar. The air contents were around 1%. Bleeding ratio of fly ash free mortar was 3.5%, but the ratios of fly ash containing mortar were from 4.4% to 7.0%. The mortar test piece was cured for 28, 91, 189 and 378 days.
2. Experiments 2.1. Materials Five fly ashes from different coal sources were collected from the same boiler (T) at a power station. The original fly ash samples were classified into two grades by use of an air stream classifier. The physical properties and chemical compositions of the fly ashes are given in Table 1. The characters BO, WA, MS, LI/BA, and WR stand for the source of coals, and the following letters Org, Fin, and Crs are the original, fine-grade and coarse-grade fly ashes, respectively. Content of over 45 lm measured by laser diffraction method is listed in Table 2.
2.3. Calculation of K-value and activity index The K-values were calculated from the following formula: S = K[(c + f)/(c + f + w + a)]2. Hereby, S is the compressive strength of mortar and f is volume of fly ash. Fly ash was counted as a cement material. To check the adequacy of the API method for the pozzolanic evaluation, the activity index was compared. The activity index was calculated from the strength of mortar according to EN 196-1.
2.2. Mix proportion for mortar 2.4. Accelerated chemical test For the purpose of the calculation of the K-value, two types of mortars mixed with different water ratios were made as shown in Table 3. Standard sand (ISO 679) was used as sand material. The water cement ratio 50% is according to JIS A 6201 and the 39% is a condition that does not cause the bleeding. In the latter case, superplasticizer and de-foaming agent were mixed to maintain a proper workability. The fresh mortar is vibrated by a table-vibrator for the purpose of decreasing the air in mor-
The testing method for API [11] is as follows: 1. (i) Mix 1.5 g of fly ash (FA) and 1.5 g of ordinary Portland cement (C) with 50 mL of purified water (fly ash– cement suspension), (ii) mix 1.5 g of OPC and 50 mL of purified water (cement suspension). Then, stir each sample contained in the sealed polypropylene vessels for 1 h by using a reciprocating machine at room temperature.
Table 1 Characteristics of fly ashes Materials
Chemical compositions
Density (g/cm3)
Blaine (cm2/g)
LOI
SiO2
Al2O3
Fe2O3
MgO
SO3
Na2O
K2O
BO
Org Fin Crs
0.9 1.8 0.8
42.8 43.3 45.6
29.6 28.4 28.6
9.0 9.3 8.6
5.0 5.2 4.9
1.4 2.0 1.7
0.43 0.69 0.25
1.3 1.1 0.9
1.1 1.6 1.4
2.41 2.57 2.32
2580 3860 1460
WA
Org Fin Crs
1.6 2.2 1.3
66.8 66.4 64.9
18.0 18.3 17.5
4.6 3.8 5.5
1.6 1.2 1.9
0.8 0.9 1.3
0.12 0.20 0.07
0.8 0.7 0.6
0.6 1.0 0.9
2.15 2.33 2.06
2850 4030 1800
MS
Org Fin Crs
1.6 2.6 1.6
56.6 54.4 56.0
20.6 20.4 20.3
6.1 6.0 6.1
7.9 8.4 8.5
0.6 1.3 1.2
0.41 0.73 0.23
0.9 0.3 0.2
0.8 0.8 0.8
2.30 2.42 2.20
3050 4370 1600
LI/BA
Org Fin Crs
1.8 3.2 1.4
68.8 63.2 67.0
21.8 21.9 21.1
1.3 1.1 1.2
0.3 0.5 0.4
0.2 0.3 0.3
0.05 0.09 0.02
0.2 0.1 0.0
1.6 1.8 1.5
2.07 2.27 2.04
2430 4700 1740
WR
Org Fin Crs
1.2 2.0 0.9
59.5 57.7 58.0
25.3 24.6 24.5
4.8 5.0 4.7
3.4 2.8 3.1
0.9 0.9 0.9
0.13 0.26 0.07
0.4 0.5 0.4
1.6 1.6 1.6
2.17 2.41 2.11
2640 3410 1570
0.5
21.0
5.3
2.6
64.6
2.1
2.00
0.3
0.6
3.17
3090
OPC
CaO
Org: original; Fin: fine; Crs: course.
Table 2 Content of over 45 lm of fly ash (measured by optical method) Sample
Over 45 lm
BO
WA
MS
L/BA
WR
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
26.3
0.2
43.6
28.3
0.1
46.1
29.6
0.1
46.0
40.0
0.5
51.0
34.6
0.0
46.2
Percentage remained over 45 lm.
T. Yamamoto et al. / Fuel 85 (2006) 2345–2351
2347
Table 3 Mixing conditions of mortars W/(C + F)
Sanda
OPC
Fly ash
Water
Superplasticizerb
De-foaming agentc
Bleeding ratio (%)
39% 39% 50% 50%
1350 1350 1350 1350
500 375 450 337.5
0 125 0 112.5
172.5 172.5 225 225
3 3(2)d – –
22.5 22.5 – –
0 0 4.4–7.0 3.5
a b c d
Standard sand (ISO 679). SP-8 N · 2 (no dilution). Micro-air 404 (100 times dilution). Two grams was used in fine grade.
2. Store the samples in sealed vessels at 80 C for 18 h. 3. Filter each suspension by using a 0.2 lm polyethylene membrane filter. 4. Measure the concentration of calcium ions in the filtrates; [Ca(FA + C)] and [Ca(C)], derived from fly ash–cement, and cement suspension, respectively. Determine the API of each fly ash by estimating the ratios of consumed calcium ion in the fly ash–cement suspension samples.
Table 4 Compressive strength of the mortar (N/mm2) W/(C + F) = 50%
Fig. 1 shows relation between Blaine specific surface area and K-values. These figures indicate that mortars containing finer fly ashes have higher strength during all curing ages. This would be the result of pozzolanic reaction, as mentioned above [2–7]. Exactly speaking, the linear relations break down from higher range of 3500 cm2/g. High-water mixed mortar (W/(C + F) = 50%) has a more
189 days
378 days
28 days
91 days
189 days
378 days
73.1 84.1 67.0
91.5 104.9 83.1
100.9 119.6 97.0
104.4 130.2 100.8
89.8 95.7 85.2
94.7 105.9 97.3
100.5 104.1 93.5
107.1 113.5 100.5
WA
Org Fin Crs
78.5 88.5 68.4
92.5 108.9 83.7
106.9 123.4 95.1
114.4 135.3 106.4
89.3 97.3 79.6
95.6 101.6 94.7
95.8 105.6 89.9
105.1 113.3 97.0
MS
Org Fin Crs
77.4 85.5 72.0
95.6 106.7 87.5
110.9 123.8 100.7
118.9 130.7 108.3
86.7 95.4 80.6
88.4 102.2 85.2
95.6 106.9 89.1
103.6 111.3 96.6
LI/BA
Org Fin Crs
75.5 89.1 73.4
90.7 106.4 87.4
107.1 122.3 99.0
111.8 130.0 105.1
85.8 91.1 86.2
95.8 96.5 88.4
95.1 102.8 88.7
101.6 111.3 94.9
WR
Org Fin Crs
70.7 90.6 70.3
91.8 110.9 84.8
105.8 123.2 95.7
113.1 134.7 102.5
85.7 94.4 82.8
99.3 107.6 93.1
98.2 105.9 88.9
106.4 111.6 100.1
3.1. Compressive strength of mortar and API
4.1. Effect of specific surface area of fly ash on pozzolanic reaction
91 days
Org Fin Crs
3. Experimental results
4. Discussion
28 days BO
API ¼ ðð½CaðCÞ ½CaðFA þ CÞÞ=½CaðCÞÞ 100 ð%Þ:
Results of the compressive strength of mortars related to curing time are listed in Table 4. The results show that the increase of strength in the fly ash containing mortars with curing time is bigger than that of fly ash free mortars (OPC in the table). API results are shown in Table 5. Finer fly ash has higher API value in each type of fly ash. Calculated results of the K-value and experimental results of activity index are shown in Tables 6 and 7, respectively.
W/(C + F) = 39%
acute gradient than low-water mixed mortar (W/(C + F) = 39%). These suggest that water content in mortar will control the rate of pozzolanic reaction. Joshi and Marsh [12] already pointed out that strength reaches the maximum when the Blaine surface area comes to more than 5000 cm2/g. But they did not mention the reason. The fineness from which the strength begins to break down would depend on the physical/chemical/mineralogical properties of fly ash. 4.2. Degree of pozzolanic reaction related to curing time Figs. 2 and 3 show the relations between curing time and the K-value of mortars. In these figures, x-axes (time) are logarithmic scales. The gradient of the K-value is linear to logarithmic time, as far as the curing time of this study
Table 5 Results of API value (%) Sample
BO
WA
MS
L/BA
WR
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
Org
Fin
Crs
API (%)
46.5
85.8
35.9
41.4
79.3
20.5
35.4
73.1
22.6
25.1
67.2
19.1
39.0
81.1
22.2
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T. Yamamoto et al. / Fuel 85 (2006) 2345–2351
Table 6 Calculated results of K-value W/(C + F) = 50%
W/(C + F) = 39%
28 days
91 days
189 days
378 days
28 days
91 days
189 days
378 days
BO
Org Fin Crs
259.1 305.6 234.1
358.6 421.2 320.8
400.8 486.5 379.3
422.6 539.6 401.7
276.4 300.6 259.3
309.1 334.9 300.3
412.5 435.7 379.1
430.7 465.4 399.6
WA
Org Fin Crs
266.0 309.9 227.7
346.4 421.3 308.0
405.7 483.7 354.5
442.3 540.3 404.2
265.2 296.6 233.2
302.9 309.2 298.7
379.4 428.8 351.0
407.7 451.2 371.0
MS
Org Fin Crs
269.6 303.8 246.3
367.9 418.7 330.7
432.6 492.3 385.5
472.3 529.9 422.7
263.1 294.3 241.1
283.5 317.8 259.7
386.6 439.3 355.4
410.7 448.3 377.7
LI/BA
Org Fin Crs
251.7 308.6 243.3
334.4 407.3 320.4
400.0 474.4 367.4
425.7 513.8 397.6
251.7 275.4 251.5
301.0 292.8 273.7
371.8 414.1 345.2
389.4 439.5 362.0
WR
Org Fin Crs
240.5 321.4 246.7
345.1 434.8 328.9
402.9 489.3 375.8
438.9 545.2 410.3
255.2 290.7 244.4
317.8 330.1 322.3
390.0 434.7 349.8
414.1 449.1 386.0
507.8
561.2
568.5
579.3
332.9
344.3
443.6
434.8
OPC
Table 7 Activity indexes (%) W/(C + F) = 50%
W/(C + F) = 39%
28 days
91 days
189 days
378 days
28 days
91 days
189 days
378 days
BO
Org Fin Crs
73.1 84.1 67.0
91.5 104.9 83.1
100.9 119.6 97.0
104.4 130.2 100.8
89.8 95.7 85.2
94.7 105.9 97.3
100.5 104.1 93.5
107.1 113.5 100.5
WA
Org Fin Crs
78.5 88.5 68.4
92.5 108.9 83.7
106.9 123.4 95.1
114.4 135.3 106.4
89.3 97.3 79.6
95.6 101.6 94.7
95.8 105.6 89.9
105.1 113.3 97.0
MS
Org Fin Crs
77.4 85.5 72.0
95.6 106.7 87.5
110.9 123.8 100.7
118.9 130.7 108.3
86.7 95.4 80.6
88.4 102.2 85.2
95.6 106.9 89.1
103.6 111.3 96.6
LI/BA
Org Fin Crs
75.5 89.1 73.4
90.7 106.4 87.4
107.1 122.3 99.0
111.8 130.0 105.1
85.8 91.1 86.2
95.8 96.5 88.4
95.1 102.8 88.7
101.6 111.3 94.9
WR
Org Fin Crs
70.7 90.6 70.3
91.8 110.9 84.8
105.8 123.2 95.7
113.1 134.7 102.5
85.7 94.4 82.8
99.3 107.6 93.1
98.2 105.9 88.9
106.4 111.6 100.1
is concerned. This would suggest that the pozzolanic reaction would be mainly controlled by the diffusion kinetic. Pozzolanic reaction will be apparent, because K-value gradient of fly ash containing mortar is more acute than that of fly ash free mortar (OPC), especially in the case of high-water containing mortar. Furthermore, the diffusion constant would increase with water content in mortar, if the strength of mortar depends mainly on the degree of pozzolanic reaction. The porosity of mortar will increase with water content of mortar. The degree of chemical reaction/mineralization/pozzolanic reaction will also increase with water content, because degree of ion migration (diffusion) depends on the condition of porosity. As shown in Figs. 1–3, the K-value of W/(C + F) = 50% mortar is higher than W/(C + F) = 39% mortar, though the former strength of mortar is smaller than the latter. Therefore the K-value itself is not useful to compare among the different W/C mortars. In spite of this, the gradient of K-value is considered to be useful for estimating the characteristics of pozzolanic activity
700
700
600
600 500 R2 = 0.83
400
K-value
K-value
500 R2 = 0.87 300
2
R = 0.83 200
R = 0.83
0
1000 2000 3000 4000 Blaine surface area (cm2/g) (a) W/(C+F)=50%
400
R2 = 0.74
300 R2 = 0.74
28day 91day 189day 378day
2
100 0
28day 91day 189day 378day
200
R2 = 0.15
100 5000
0
R2 = 0.68 0
1000 2000 3000 4000 Blaine surface area (cm2/g) (b) W/(C+F)=39%
Fig. 1. K-value related to Blaine specific surface area.
5000
T. Yamamoto et al. / Fuel 85 (2006) 2345–2351 700
700
700
600
600
600
500
500
2
R = 0.96
K-value
400
R2 = 1.00 300
400
R2 = 1.00 300
WA-Fin (W/C=50%)
BO-Fin (W/C=50%)
200
BO-Org (W/C=50%) BO-Crs (W/C=50%)
100
OPC (W/C=50%)
100
OPC (W/C=50%)
0
0 10
100
10
1000
MS-Fin (W/C=50%) MS-Org (W/C=50%) MS-Crs (W/C=50%) OPC (W/C=50%)
200
WA-Org (W/C=50%) WA-Crs (W/C=50%)
100
0 10
1000
100
Curing time (day)
Curing time (day) 700
700
1000
Curing time (day) 700 R2 = 0.90
600
600
600 2
2
R = 1.00
R = 1.00 500
500
500 R2 = 0.99
2
R2 = 0.99 300
K-value
R = 0.99 400
400 R2 = 1.00 300 WR-Fin (W/C=50%) WR-Org (W/C=50%) WR-Crs (W/C=50%) OPC (W/C=50%)
LI/BA-Fin (W/C=50%) 200
200
LI/BA-Org (W/C=50%) LI/BA-Crs (W/C=50%)
100
100
OPC (W/C=50%)
K-value
K-value
R2 = 0.98 300
100
R2 = 0.99
R2 = 0.99
400
K-value
500
200
R2 = 0.99
R2 = 0.99
R2 = 1.00
K-value
2349
400 OPC (W/C=50%) 300 200 100
0
0 10
100
10
1000
Curing time (day)
100
0 10
1000
100
Curing time (day)
1000
Curing time (day)
Fig. 2. Relation between curing time and K-value of W/(C + F) = 50% mortars.
700
700
700
WA-Fin (W/C=39%)
BO-Fin (W/C=39%)
WA-Crs (W/C=39%)
R2 = 0.92
OPC (W/C=39%)
500
R2 = 0.94 300
500 R2 = 0.95
400 300
R2 = 0.98
100
100 0
0 10
1000
10
1000
700 WA-Fin (W/C=39%)
600
LI/BA-Org (W/C=39%)
WR-Org (W/C=39%)
500
2
R2 = 0.98
2
R = 0.90 300
K-value
R = 0.96
400
R2 = 0.99
300
400 300
200
200
200
100
100
100
100
1000
Curing time (day)
R2 = 0.77
500
R = 0.91
OPC (W/C=39%)
2
400
600 OPC (W/C=39%)
WR-Crs (W/C=39%)
R2 = 0.85
LI/BA-Crs (W/C=39%) OPC (W/C=39%)
0 10
100 Curing time (day)
700 LI/BA-Fin (W/C=39%)
500
100 Curing time (day)
Curing time (day)
600
R2 = 0.88
R2 = 0.87
100
700
R2 = 0.85
300 200
1000
MS-Crs (W/C=39%)
400
200
100
MS-Org (W/C=39%) OPC (W/C=39%)
200
0 10
K-value
R = 0.84
OPC (W/C=39%)
R2 = 0.90
400
600 2
K-value
BO-Crs (W/C=39%)
MS-Fin (W/C=39%)
WA-Org (W/C=39%)
K-value
K-value
500
600
BO-Org (W/C=39%)
K-value
600
0
0 10
100
1000
10
Curing time (day)
100
1000
Curing time (day)
Fig. 3. Relation between curing time and K-value of W/(C + F) = 39% mortars.
of fly ash. As shown below, we will clarify the relation between the K-value gradient and the degree of pozzolanic activity quantitatively.
As a reference of experimental data, the relations between curing time and activity index are shown in Figs. 4 and 5. The correlation coefficients are almost
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T. Yamamoto et al. / Fuel 85 (2006) 2345–2351
Fig. 4. Relation between curing time and activity index of W/(C + F) = 50% mortars.
Fig. 5. Relation between curing time and activity index of W/(C + F) = 39% mortars.
same as those of Figs. 2 and 3. This occurs because the K-value and activity index are obtained by the strength of mortar. 4.3. API method to evaluate the pozzolanic grade of fly ash As mentioned in the above section, the K-value is considered to be useful for estimating the degree of the pozzolanic activity of fly ash in mortar. From this view point, the relation of the API value to the K-value is plotted in Fig. 6.
As shown from the gradient of the slope in Fig. 6(a), we can find a good relation of the API value to the K-value. On the other hand, the slope decreases at W/ (C + F) = 39% mortar (Fig. 6(b)). This is considered to be derived from the insufficient water in mortar, which would decrease the rate of the chemical reaction. Judging from high correlation coefficient in Fig. 6(a), API has a good relation to the K-value during all curing ages, compared to the relation between specific surface area and K-value (Fig. 1). Therefore, the API is considered to be
T. Yamamoto et al. / Fuel 85 (2006) 2345–2351 700
700 R2 = 0.89 600 R = 0.90 500 K-v al ue
500
400 300 200
378 days 189 days 91 days 28 days
R2 = 0.93
100
2
R = 0.87 0 0
20
40
60
80
100
R2 = 0.79
378 days 189 days 91 days 28 days
600
2
K -v al u e
2351
R2 = 0.78
400 300 200
R2 = 0.36
100
R2 = 0.71
0 0
20
40
60
API (%)
API (%)
(a) W/(C+F)=50%
(b) W/(C+F)=39%
80
100
Fig. 6. Relation between API (%) and K-value.
one of the most useful and rapid methods to evaluate a degree of the pozzolanic activity of fly ash. We have already obtained a good relation of the API value to the pozzolanic reaction of fly ashes that were collected from 30 boilers of 24 electric power stations [13]. 5. Conclusion Yamamoto and Kanazu [10,11,13] proposed the API method, for the purpose of rapid and appropriate evaluation of the pozzolanic property of fly ash. It has been necessary to prove the applicability of this method. The K-value of Fere´t’s law was inspected primarily, and the correlation between K-value and API value was considered in this study. The conclusions are as follows: 1. Fine fly ash containing mortars have higher strength during all curing ages. This is the result of high amount of pozzolanic reaction in unit volume of mortar. 2. High-water mixed mortar has more acute gradient than low-water mixed mortar. This suggests that water content in mortar controls the rate of pozzolanic reaction of fly ash and even the hydration of cement grain. 3. The gradient of the K-value is liner to logarithmic time. This would suggest that the pozzolanic reaction would be mainly controlled by diffusion kinetic, and the diffusion coefficient would increase with water content in mortar. 4. The K-value is useful to estimate the degree of the pozzolanic activity of fly ash in mortar. 5. The API method is one of the most useful and rapid methods to evaluate the degree of pozzolanic activity of fly ash, because API has a good relation to the Kvalue.
References [1] Ogawa K, Uchikawa H, Takemoto K. The mechanism of the hydration in the system C3S-pozzolan. Cem Concr Res 1980;10: 683–96. [2] Ravina D. Optimized determination of PFA (fly ash) fineness with reference to pozzolanic activity. Cem Concr Res 1980;10:573–80. [3] Ranganath RV, Sharmw RC, Krishnamoorthy S. Influence of fineness and soluble silica content of fly ash on their strength development with respect to age. In: Malhotra VM, editor. Proceedings of the fifth international conference on fly ash, silica fume, slag, and natural pozzolans in concrete; 1995. p. 355–66. [4] Hall D, Mehta PK. Testing and correlation of fly ash properties with respect to pozzolanic behavior. EPRI CS-3314 Project 1260-26 Final Report, 1984. [5] Mehta PK. Influence of fly ash characteristics on the strength of Portland-fly ash mixtures. Cem Concr Res 1985;15:669–74. [6] Monzo J, Paya J, Peris-Mora E. A preliminary study of fly ash granulometric influence on mortar strength. Cem Concr Res 1994;24: 791–6. [7] Paya J, Monzo J, Peris-Mora E, Borrachero MV, Tercero R, Pinillos C. Early-strength development of Portland cement mortars containing air classified fly ash. Cem Concr Res 1995;25:449–56. [8] Hubbard FH, Dhir RK, Ellis MS. Pulverized-fuel ash for concrete – compositional characterization of United Kingdom PFA. Cem Concr Res 1985;15:185–98. [9] Ramezanianpour A, Cabrera JG. The measurement of lime reactivity of natural and artificial pozzolans. In: Second Int Sem Cem Build Mater, vol. 4; 1989. p. 81–8. [10] Yamamoto T, Kanazu T. Chemical assessment method for the preventive effect of fly ash on alkali–silica reaction. In: Proceedings of 11th Int Conf AAR; 2000. p. 801–10. [11] Yamamoto T, Kanazu T. Investigation on the pozzolanic reaction of fly ash. Central research institute of electric power industry report 2004, No. N04008 [in Japanese]. [12] Joshi RC, Marsh BK. Some physical, chemical and mineralogical properties of some Canadian fly ash. Material Research Society, Proceeding, vol. 86, Pittsburgh, USA. 1987. p. 113–26. [13] Yamamoto T, Kanazu T. Accelerated chemical assessing method for pozzolanic activity of fly ash. CRIEPI Abiko Research Laboratory Rep. No. U98047, 1999 [in Japanese].