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Evaluation of blended cement, mortar and concrete made from type III cement and kiln dust
Evaluation of B l e n d e d C e m e n t , Mortar and C o n c r e t e m a d e from Type I11 C e m e n t and Kiln Dust M.L. Wang', V. Ramakrlahnan b
Abstract A study was conducted to determine the effects of using kiln dust (a pozzolonic waste by.product of cement manufacture) as a cost reducing additive in blended cements. Cement quality, properties of mortar and properties of fresh and hardened concrete were investigatged in the laboratory. Shrinkage, creep and durabillity were also examined. The test results show that replacing 5 percent of cement by weight with kiln dust produces a mix exhibiting slightly greater shrinkage and creep and greater setting time than plain concrete but does not adversely affect other properties of mortar or concrete.
Introduction This report presents the results of an investigation into the effects of using kiln dust as a pozzolon in blended cement. The benefits of using pozzolonic materials are both economical and technical. Replacing a portion of cement with a pozzoion, reduces the cost of a mix and, for mixtures deficient in fine materials, may serve as a corrective in fresh concrete. Pozzolons, especially fly ash, have been used and stL'~diedfor decades, both here and abroad. The first reported data on the use of fly ash in concrete in the United States was in 19371 . Since then numerous studies have been published 1, 2. Reports have also been published detailing the decades of experience with fly ash as an additive in blended cements 3 - 5. The microstructural and chemical effects of cement additives are not easily directly investigated and, therefore, only recently have researchers begun to report on the chemical processes and microstructural effects of using fly ash6 - 8. ER Giasser, et al6 state that the presence of fine particles may influence the flocculation behaviour of the system and thus the packing properties. This could affect the pore size distribution and the pore interconnectivity. They also state that the blending agent "may act as preferential sites for the nucleation of cement hydration products". There is reason to believe that kiln dust, a product similar to fly ash and of the same order of fineness as fly ash, may have similar effects when used as a blending agent. However, although a wealth of information exists on fly ash, we have been unable to find any published data on kiln dust. Historically the effects of blending cement with various agents have been determined by studying the properties of materials made with the blended product. This investigation was undertaken to determine the suitability of blending kiln dust with Type !11 Portland cement. The objective of the research programme was to a Profesor, Civil EngineeringDepartment, University of New Mexico,Albuquerque,NM 87131. b Protesaor, Civil Engineering Department, South Dakota School of Mines & Technology, Rapid City, SD 57701.
78
0950 - 0618/90/020079 -
08 © 1990 Butterworfh-Heinemann Ltd
determine the properties of fresh and hardened concrete made with Type I!1 Portland cement blended with kiln dust.
Research significance Using waste by.products in the manufacture of construction materials has a two-fold benefit. The cost of the material is reduced and the burden of disposal of the waste is decreased. Before such products can be used in the field, extensive tests must be conducted to ensure the serviceability of projects made using the new materials. This investigation examines the effects of using kiln dust (a waste by-product of the cement manufacturing process) as a pozzolon in blended ce. ments. The ready availability of kiln dust in cement processing plants suggests an opportunity for the production of blended cement using this by-product. Test p r o g r a m
In order to determine the effects of adding kiln dust to cement, tests were conducted on blended cement, on cement without kiln dust (plain cement), and on mortar and concrete specimens (cylinders and cubes) cast with both blended cement and plain cement. The cement tests measured fineness, composition, normal consistency and setting time. The tests on mortar compared unit weight, compressive strength and splitting tensile strength. The concrete tests included compressive strength, unit weight, durability, pulse velocity, shrinkage and creep. Where applicable, all tests were conducted according to ASTM specifications. All tests used Type Iii, Portland cement produced by the South Dakota State Cement Plant. The chemical and physical properties of the cement are given in Table 1. The kiln dust was also supplied by the SD State Cement Plant. it was produced during the burning of Type II clinker and collected from the precipitators of kilns fired with coal and natural gas. The fine aggregate was natural sand with a fineness modulus of 3.04. The coarse aggregate used was crushed limestone. Sieve analyses for fine and coarse aggregate are given in
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
Table !
Chemical analysis and physical properties of Type III cement
PHYSICAL
CHEMICAL
5.82
Fineness, Blaine Fineness Meter, sq. cm. 1 gram
Ferric Oxide (Fe203)
2.88
Soundness, Autoclave Expansion
0.00
Magnesium Oxide (MgO)
Time.of Setting (GiUmore Test) Initial (Hr.:Min.)
2:20
1.44
Sulfur Trioxide (SOs) when 3CaO.AI203 is 8% or less
_
Final (Hr.:Min.)
3:50
When 3CaO.AI203 is more than 8%
4.27
Time of Setting (Vicar Test)
1:25
Ignition Loss
1.84
Compressive Strength (psi) 1 day
Insoluble Residue
0.54
5 days
4951
Tricalcium aluminate (3CaO.AI2'o3)
10.55
7 days
5796
Tricalcium silicate & Tricalcium atuminate (3CaO.SiO2 + 3CaO.AI203)
62.91
28 days
Tetracalcium aluminoferrite + 2X Tricalcium /4CaO.AI303.Fe203} + 2 (3CaO,AI203)
29.84
Alumina (AI203)
Alkalies (Na20 + .658 x K220)
0.45
Table I! Sieve analysis - Fine aggregates
5397
2936
Air Cement of Mortar
93%
False Set Ratio of Final to Initial Penetration
53.1o/0
Table I!i Sieve analysis - Coarse aggregates Percent
Percent Sieve Size
Sieve Size Passing through
by
by Retained on
Weight
Weight
Passing through
Retained on
11/2 in.
1 in.
1.0
¼in.
#
4
0
#4
#
8
14.30
I in.
~4 in.
28.8
#8
# 16
24.94
3/4 in.
1/2 in.
50.8
# 16
# 3o
28.87
V2 in.
3/8 in.
15.3
# 30
# 5o
17.88
% in.
1/4 in.
3.0
# 4
0.5
# 50
#100
10.55
¼ in.
#100
# 200
2.80
# 4
# 8
0.3
# 8
Pan
0.3
#2~
Pan
0.66
Tables 2 and 3, respectively. The water used was tap water. Neutralised vinsol resin (Protex) was used as an air entraining agent. Mortars were proportioned according to ASTM C
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No, 2 JUNE 1990
109. The sand.cement ratio of 2.75 and water-cement ratio of 0.485 by weight were used throughout. The mortar mixes numbered WP] and WB1 are plain cement mix for ] day test and blended cement mix for
79
Table IV Type of • mix
Cement Content iblyd 3 kg/m 3
W/C Ratio
Concrete mix details
Aggregate Cement Ratio
Ratio of Coarse: Fine Aggregate by weight
Air Entraining Agent % of cement
Mix No. 1 WB 1 WP 3 WB,~ 3 WP~, 4 WB 4 WP
Type Ill Cement
' 650
385
0.45
4.4
60:40
0.13
Type III Blended
650
385
0,45
4.4
60:40
0.13
Type III Cement
564
335
0.55
5.8
60:40
NO
5 WB 5 WP
Type Ill
564
335
0.55
5.8
60:40
NO
6 WB 6 WP
564
335
0.52
5.2
60:40
013
2 WB+
564
335
0.52
5.2
60:40
0.13
2 WP+
Blended
Type Ill Cement Type III Blended Note:
~r These mixes were tested for creep & shrinkage also + These mixes were tested for freezing and thawing
1 day test, respectively. The mortar was mixed per ASTM C 305. The mortar cube specimens were mould. .=.d and tested per ASTM C 109. The mortar cylinder specimens were cast in steel moulds, compacted in two layers by rodding with the fiat end of a 3ram (1/8 inch) diameter rod. The details of the concrete mixes are given in Table 4. The mixed specified as lWP and ]WB are plain concrete mix ] and blended concrete mix 1, respectively. The concrete was batched in accordance with ASTM C192. T h e following tests were performed:
Cement and blended cement Fineness - ASTM C 184 Normal consistency - ASTM C 187 Setting time - ASTM C 4 0 3 Mortar Compressive strength - ASTM C 109 Tensile strength - ASTM C 4 9 6 (specification for concrete Unit weight Fresh concrete S l u m p test - ASTM C 143 Vebe c o n s i s t o m e t e r - U.S. Army Corps of En gineers C RD-C2-75 and AC! Standard 211-65 Air content - ASTM C 231 Pressure Method Plastic unit weight - ASTM C 138 Concrete t e m p e r a t u r e and a m b i e n t t e m p e r a t u r e and humidity were recorded. Hardened Concrete Compression test - cylinder s p e c i m e n s - ASTM C 39 Dry unit weight Static m o d u l u s of elasticity - ASTM C 4 6 9 Pulse velocity - ASTM C 5 9 7
80
Fiexural strength (Modulus of rupture) ASTM C 215 Setting time - ASTM C 4 0 3 D y n a m i c m o d u l u s of elasticty - ASTM C 2 1 5 Freeze thaw test - ASTM C 6 6 6 Shrinkage - ASTM C 157 Creep - ASTM C 512
Results Cement Tests Fineness: The fineness of kiln dust, plain and blended cements using No. 100 and 200 sieves. The kiln dust was finer than the cement, but there was no apreciable difference between the fineness of the plain and blended cements. Normal consistency: The amount of mixing water specified is related to the water content required to bring the paste to a standard condition of wetness called nor. mall consistency. The normal consistencies for the plain and blended cement were 27 percent and 28 percent, respectively. Time of setting: It is customary to refer to initial setting, defined as the beginning of stiffening, and final setting, marked by the disappearance of plasticity. The cement paste tested for setting time was the same mix as that used for the normal consistency test. The initial set and final set of the plain and blended cement pastes are shown in Figure 1. Both initial and final setting time were greater for the blended cement paste than for the plain cement paste. Mortar Tests T h e mortar s p e c i m e n s (2 inch c u b e s and 3 inch diameter by 6 inch cylinders) were tested for unit weight,
compressive strength and splitting tensile strength at ages of 1, 3, 7, 14, 28 and 90 days.
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
Table V Plastic properties of concrete Slump
Air
Mix in
Vehe
Concrete
Time
Temperature
Room Temperature
oC
OF
oC
mm
%
sec
OF
Relative Humidity
Unit Weight
%
tblft3
W/C kg/m 3
ratio
lWP
21/,=
57.2
3.0
4
72
22
75
24
40
147.9
2371
0.45
lWB
2
50.8
2.8
4
79
26
77
25
40
147.9
2371
0.45
2WP
3
76.2
5.0
2
75
24
72
22
39
145.2
2328
0.52
2WB
31/o
79.4
5.1
2
75
24
71
22
39
144.6
2318
0.52
3WP
2
50.8
3.2
4
74
23
60
16
49
147.9
2371
0.45
3WB
21/o
54.0
3.0
4
72
22
58
15
56
147.7
2368
0.45
4WP
31/,=
82.6
4.9
2
66
19
60
16
47
143.4
2298
0.45
4WB
3
76.2
4.3
2
66
19
63
17
48
144.7
2320
0.45
5WP
3~
95.3
1.5
2
71
22
65
18
31
149.5
2398
0.55
5WB
2¥4
69.9
1.6
3
74
23
74
25
30
148.8
2385
0.55
6WP
21/4
57.2
1.5
3
66
19
66
19
40
148.8
2385
0.55
6WB
17/s
47.6
1.8
4
66
19
63
17
40
148.8
2385
0.55
100 7O
6O
Normal consistency :
50 40
Plain cement, W I C = 0 . 2 7 Blended cement, W l C = 0.28 - - O - - Plain cement Blended cement
i
0.
~
50 -
~ 30
L
Initial set
.• 40-
A
Z~
~
A
z~ o
20
OPlain cylinders
~
15
ABlended cylinders • Plain cubes
E ~
10
~
o 30_o
o
Q.
E o u Initial set, h r : m i n u t e s Plain 2:02 Blended 2:49
o
~
7
5
I
i
i
l
I .5
2
Final set
~
3
i
,
I
4
6
10
Time ( h o u r s )
20
l
0
l
l
l
l
20
,
J
I
,
~
,
I
40 60 Age ( d a y s )
,
,
~
]
80
l
l
I
100
F g. 2 Mortar compressive strength as function of age.
Final set Plain 2:35 Blended 3:28
0) Q,.
A Blended cubes
[log scale]
F g.l Curves of uicat penetration for plain cement and blended cement paste setting at room temperature
Compressive strength: The pattern of compressive strength development with age is shown in Figure 2. in general, there was no signficant difference in the com. pressive strengths of blended cement mortar and plain cement mortar for either cube or cylinder specimens. Most of the blended cement mortar strengths fell
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
within plus or minus 1-4 percent of the strength of plain cement mortar. Tensile strength: The pattern of splitting tensile strength development with age is shown in Figure 3. The 14 day tensile strength of the blended cement mortar was 10 percent higher than for the plain cement mor. tar. At 28 and 90 days, however, there was no significant difference in the tensile strengths of the plain cement and blended cement specimens. Unit weight: The unit weights for the mortar specimens are given in Table 5. There was no significant difference in unit weight between plain and blended cement at any age. The lower unit weight of cylinder specimens than corresponding cube specimens can be attributed to the different compacting methods used for cylinder and cube specimens. The unit weight was approximately the same for comparable specimens compacted by the same method. Also, there was no appreciable change in unit weight after 7 days.
81
7
¢! A 0
=~ 5D~
~ 4 c
0 Plain m o r t a r
3
Z~Blended m o r t a r
~- 2 1
,
,,
,
I
,
i
,
20
I
,
,
,
I
J
,
~
40 60 Age ( d a y s ]
,
,
,
80
100
F g.a Mortar tensile strength as a function of age.
I n i t i a l s e t t i n g time, h o u r s : m i n u t e s Plain 5:05 Blended 5:25 Final s e t t i n g time Plain 6:45 Blended 7:15
6000 -
-~ 4500 -
~--I--~
Final set
//
3000 -'0"-Plain
9/ /
cement c o n c r e t e B l e n d e d cement c o n c r e t e I
,?'/
1500
122.222
,,,
2
-
4
/ /
I
6
Time ( h o u r s )
F0.4 Comparison of setting time for plain cement concrete and blended cement concrete.
Plastic properties of concrete The plastic properties of the fresh concretes are presented in Table 5. There was no significantdifference in the slump and vebe time between the plain and blended cement concretes. W h e n an air entraining agent was used, the amount of air entrained in blended cement concrete was approximately 0.2 percent less than that of plain cement con. crete. W h e n no air entraining agent was used, the air entrapped in both the plain and blended cement concretes was the same. Both concretes showed the same ease of placement and finishability. The effect of blended cement on the initialand final setting times of concrete as determined by penetration resistance (AS'I'M C 403) is illustratedin Figure 4. Both inRial and final set of blended cement concrete occur 30 minutes later than for plain cement concrete. Behaviour of hardened concrete The following properties were studied to evaluate the effect of kiln dust on hardened concrete. Compressive strength: The pattern of compressive strength development with age is shown in figure 5. Most of the strengths for blended cement concrete were 4 percent higher in the earlier tests and 3-5 percent lower at 28 days than for the plain cement concrete. Unit weight: The unit weights were essentially the same for plain and blended cement concretes for all ages. The unit weight of the blended cement concrete, mix 4, was 1-2 pcf more than that of the plain cement concrete at all ages. This discrepancy may be due to the 0.6 percent more entrained air in the plain cement concrete, Pulse velocity: The development of pulse velocity with age is shown in Figure 6. The pulse velocity com. padson is similar to that for compressive strength. The pulse velocity of blended cement concrete was approx, imately 1-3 percent less than that for plain cement concrete except for mix 4. For mix 4, the pulse velocity of the blended cement concrete was 2 percent higher than for plain cement concrete. Similar results were obtained for the dynamic modulus of elasticity. Flexural strength: The results of flexure strength tests at ages of 28 and 90 days are shown in Table 6. The
50
5000
40
._-----------4
4800
(-O D~ C
~
E 30
m
•~
4600
~
4400
mixes 5 t 0
o_ 20 E
I
A B l e n d e d mixes 5 & 6
o
10
,
I
10
L
I
20
,
30
Age ( d a y s )
Y
4200
• Blended mixes 5 & 6
,
0
I
,
10
l
20
,
30
Age (days]
F g. 5 Concrete compressive strength as a function of age.
Fig. 6
Pulse velocity of concrete as a function of age.
Table VI Comparison of flexural strength Specimen
Modulus of Rupture
Age
Days
No, 1PC #4 1PC #5 1PC # 6
Loss 0.2
--0--
Plain concrete, f r eeze- t haw c u r i n g jlp-~l Blended concrete, f r e e z e - t h a w c u r i n g J ~ , / - - O - - Plain concrete, st andar d c u r i n g j l , 1 ~ Blended concrete, st andar d ,-~ .J curing lil'~
Oo
Average
psi
28
710 715 660
28
680 730 640
psi
MPa
695
4.8
o
O, O.
1BC #4 1BC #5 1BC #6 1PC # 1 1PC # 2 1PC # 3
90
1BC # 1
1BC # 2 1BC #3
90
680
4.7
O. ]in
730 790 690
740
820 740 750
770
I
"I
I
I
I
I
40
80
120
160
200
240
5.1
Cycles
Weight loss v. cycles.
9 5.3
--0--
17000
Plain concrete, st andar d curing Blended concrete, st andar d curing Plain concrete, f r eeze- t haw curing Blended concrete, f r eeze- t haw c u r i n g
--41--
E
8
400
~1650C
o Plain mix 2 Blended mix 2 300
• Plain mix 3.
I
280 300
~,._...__...--~
0
~16000
x
E
u
200
155oi 3 to
I00 15000
r-
'Z .c u~
0
0
-100
i
I
i
150
200
250
300
Fig. 10 Pulse velocity v. number of freeze.thaw cycles. 0
20
40 60 Age (days)
80
100
0.4
0.3
o
0.2
~ --O-t~ @
I
100
Cycles
Fig. 7 Drying shrinkage with age.
•-
I
50
Blended concrete Plain concrete
0.1
u
F g. 8
S t r e s s - s t r e n g t h : 30% I
I
I
I
I
I
I
1o
2o
3o
40
5o
60
70
80
Comparison of creep strains for plain and blended concretes.
strengths of blended cement concrete were within a range of plus or minus 4 percent of those of the plain cement concrete and, therefore, not significant. Shrinkage: Two different mixes (mix 2 and mix 3) were tested for shrinkage. The mix details and the test results are shown in Table 7. The measured shrinkage deformations are given plotted in Figure 7. The mixes
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
compared had the same maximum coarse aggregate size but different w/c ratios and aggregate-cement ratios. As shown in Figure 7, the shrinkage deformation of blended cement concrete for mix 2 was considerably more (22 percent) than for plain cement concrete. For mix 3, however, the shrinkage deformation was approximately the same for both blended and plain cement concretes. The reason for the difference is not known. Creep: Two mixes with the same proportions were made with plain and blended cement. From each batch, three specimens were made. After curing for 28 days, the specimens were arranged in series and loaded to a stress level equal to 30 percent of the 28 day strength using constant pressure hydraulic rams. Strain measurements were taken immediately after loading and at fie. quent intervals thereafter. The average of the measured strains on two faces of the specimens were recorded for both the plain and blended cement specimens. Measured creep strains are plotted in Figure 8 for both blended and plain cement concretes. The plotted values are average strains for three cylinders. Figure 8 indicates that for the same maximum aggregate size and the same strength.stress ratio, the blended cement concrete exhibits more creep than the plain cement concrete (14 percent greater at 60 days).
83
Table VII Details of mixes used for creep and shrinkage specimens Maximum Aggregate Size in.
Mix No.
WIC
NC
2 WP
0.52
5.2
2 WB
0.52
5.2
3 WP
0.45
4.4
3 WB
0.45
4.4
Vebe Time $ec.
Slump in.
3~
2~
28-Day Strength psi
Modulus of Elasticity psi x 10s
5093
5.25
4790
5.42
5453
5.33
306 x 10 - s at 1635 psi
5285
5.39
291 x 10 -6 at 1569 psi
Table VIii
Elastic Strain
Chemical analysis
>.
.'~ 120, Kiln Dust
Type I Cement
Cement & Kiln Dust
SiO 2%
15.78
20.98
20.36
Fe20s
1,09
2.61
2,17
AI20 3 %
3.95
6.13
6.03
CaO %
45.71
63.05
62.77
SO s %
2.32
2.50
2.50
MgO %
0.98
1.39
1.37
Volatile
27.83
3.39
4.10
Total %
97.66
100.05
99.30
5.04
Compound
-~ 1~0
"----------'--'--'--'--'-
100 ~ ' - - - 4 " - - ~ b ~ . ~ A E "E
l 901-
co
|
.~
| 80 1
-~
--O'~ --O-~ I 40
.
"-,m- . . . . . .
Plain c o n c r e t e , f r e e z e - t h a w c u r i n g Blended c o n c r e t e , f r e e z e - t h a w c u r i n g Plain c o n c r e t e , s t a n d a r d c u r i n g Blended c o n c r e t e , s t a n d a r d c u r i n g ,I I I I I 80 120 160 200 240
I [ I I I 300
Number o f f r e e z e - t h a w cycles
8,74
8.20
F-CaO %
0.43
0.54
Insoluble %
0.48
1.12
C4AF %
7.94
R20~ %
F/g. 11 Relatiue dynamic modulus at different freeze. thaw cycles. Durability: Freeze-thaw performance was evaluated using two sets of two specimens for each type of mix. One set was exposed to the conditions specified in ASTM C 666 (rapid freezing and thawing in water), the other was used as a reference. In addition to monitoring changes in fundamental transverse frequency to calculate durability factors, changes in length and weight were also monitored. The results are presented graphically in Figures 10 and 11 and listed in Table 13. The change in weight of both sets are plotted in Figure 10. The weights of the reference specimens increased up to 120 cycles (84 days) and then remained approximately constant. The weights of the specimens subjected to freeze-thaw cycles increased up to 120 cycles due to absorption and then decreased due to deterioration of the surface of the specimens. The weight gained or lost by blended and plain cement concretes is, more or less, equal. The development of pulse velocity and the relative dynamic modulus of elasticity are shown in Figures 10 and 11, respectively. The pulse velocity increased in reference specimens and decreased in freeze.thaw specimens. There was no difference in pulse velocity between plain and blended cement concretes for either freeze-thaw or standard cured specimens. The blended cement concrete showed an earlier decrease in rela-
C3A %
11.83
C3S %
45.19
C2S %
26.06
A/F
2,35
C3S/C2S
1.73
6.01 1.82
S/(A+F)
2.40
2.48
tive dynamic modulus than did the plain cement concrete. As mentioned above, additional methods of detecting damage were employed. The data for changes were recorded. The blended cement concrete showed more expansion than did the plain cement concrete. The expansion indicates internal structural damage caused by the freezing and thawing process. C h e m i c a l properties of kiln dust Dust collected from the gases emanating from rotary kiln is specially known as Cement Kiln Dust (CKD). This dust is entrained in large volumes of hot exhaust gases. More often it contains unacceptably high concentrations of alkalies (Sodium and Potassium) which make it unsuitable for return to the cement making process, This dust also contains sulfate salts and partly calcined
material which Causes some hydraulics and cementious properties. The presence of water soluble alkalies in CKD can cause pollution of surface or ground waters. Chemical analysis is shown in Table 8. Many types of dust collectors are used in cement industry. They are cyclones, Electrostatic Precipitators, Baghouses, Wet Scrubbers, and Settling Chambers. They are used independently or in combination. At present 98 to 100% of the dust is collected. The cement kiln dust used in this investigation was collect. ed by the electrostatic precipitator. The chemical and physical properties of dusts vary from plant to plant. The variation is due to the variation in the raw materials used, and due to the type of col. lection used. There is also great variation in the dusts collected in the after compartments of a precipitator is considerably different from dust collected in the forward compartments. Furthermore, dust collected in baghouses is different from a given kiln and from a given plant. Dust shows a wide range of particle sizes ranging from less than 6 microns to 100 microns in diameter as shown in Table 9. Presently the cement kiln dust collected is a big solid waste disposal problem for the cement manufacturers. This paper reports the results of an investigation into the effects of partial replacement of cement (5% by weight) with cement kiln dust on the properties of concrete. The kiln dust used in this investigation was collected consistently from the s a m e location in the precipitator. This particular dust had lower alkali and chloride con. tents than generally found in this location and in other plants. Discussion
of test results
The following results are based on the use of 5 percent kiln dust by weight in the blended cement. They are not necessarily valid for other proportions. ] The kiln dust was finer than both plain and blended cement. There was no appreciable difference in fineness between plain and blended cements. 2 The water content required for normal consistency was one percent higher for blended cement than for plain cement. This does not necessarily mean that blended cement needs a higher water content to produce the same slump as plain cement. The Vicar test measures viscosity whereas the slump test indicates lubricating ability of the paste. 3 Due to the higher water content at normal consistency the setting time for blended cement was longer than that for plain cement (45 minutes). 4 There were no significant differences in dry unit weight, compressive strength and splitting tensile strength of blended c e m e n t and plain cement mortar specimens. 5 Most properties of the fresh blended cement concrete were the s a m e as those of the plain cement concrete. The exception was setting time. The blended c e m e n t concrete had 30 minutes longer initial and final setting times
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
Table IX
F i n e n e s s test results
Sieve Size No.
Total Weight of Sample g
Plain Cement
100 200
Blend Cement
100 200
Cement
Residue g
Fineness % Passing
50 50
0.30 2.25
99.4 95.5*
50 50
0.28 2.20
99.44 95.6.
Note: , The Sieve Correction (c) to be calculated as per ASTM C 184 Sec. 6.1.2. is assumed as zero.
than the plain cement concrete. 6 The hardened concrete properties of blended cement concrete were comparable to those of plain cement concrete at all ages. 7 The blended cement concrete experienced greater shrinkage and creep than the plain cement concrete. 8 The blended cement concrete did not show inferior resistance to rapid freezing and thawing up to 120 cycles but experienced a little more weight loss thereafter.
Conclusions Where slightly increased shrinkage and creep and in. creased setting time can be tolerated, replacement of 5 percent by weight of cement with kiln dust produces a blended cement which can be used to make mortar and concrete with good serviceability properties for any application. A preliminary test result for 7% by weight of cement replacement indicate no difference to 5% one. Further research is needed to determine the effects of replacement at greater proportions and of mixing kiln dust with other pozzolons such as fly ash. References 1 V.M. Malhotra (1987). "Superplasticizers, Pozzolans and Granulated Blast.FurnaceSlagsin Concretes: A Review:' Lewis H. Tuthill International Symposium on Concrete and Concrete Construction, ACI SP.I04, G.T. Halvorsen, Ed., Amer. Concrete Inst., 63.88.
2
P.K.Melht~ (1983). "Pozzolonicand CementitiousByproducts as Mineral Admixtures for Concrete - A Critical Review:'F/y Ash, Silica Fume, Slag E, Other Mineral By~Products in Concrete Vol. I, ACI SP.79, 1.46.
3 4 5 6
J.F. Lamond (1983). "Twenty-FiveYears'ExperienceUsing Fly Ash in Concrete:' Ibid Ref. 2, 47.69. A. Samarin, R.L Munn and J.B. Ashby (1983). "The Use of Fly Ashy in Concrete - Australian Experience/'Ibid Ref. 2, 143.172. V. Korac and V. Ukraincik (1983). "Studies into the Use of Fly Ash in Concrete for Water Dam Structures" Ibid Ref. 2, 173.185. F.P. Glasser, S. Diamond and D.M. Roy (1986). Hydration
Reactions in Cement PastesIncorporating Fly Ash and Other Pozzolonic Materials:' Materials Research Society Symposia Proceedings, 86, 139-158.
7
8
N. Tenoutmme and A.M. Marion (1986). "Mechansim of Hydrationof Cement Blendedwith Fly Ashes:'BlendedCements, ASTM STP 897, G. Frohnsdorff, Ed., ASTM, Philadelphia, Pa, 65.85. S. Chatterji, M. Collepardi and G. Moriconi (1983). "Poz. zolonic Propertyof Natural and SyntheticPozzolans:a Comparative Study;' Ibid Re[. 2, 221.233.
85
Abstract A study was conducted to determine the effects of using kiln dust (a pozzolonic waste by.product of cement manufacture) as a cost reducing additive in blended cements. Cement quality, properties of mortar and properties of fresh and hardened concrete were investigatged in the laboratory. Shrinkage, creep and durabillity were also examined. The test results show that replacing 5 percent of cement by weight with kiln dust produces a mix exhibiting slightly greater shrinkage and creep and greater setting time than plain concrete but does not adversely affect other properties of mortar or concrete.
Introduction This report presents the results of an investigation into the effects of using kiln dust as a pozzolon in blended cement. The benefits of using pozzolonic materials are both economical and technical. Replacing a portion of cement with a pozzoion, reduces the cost of a mix and, for mixtures deficient in fine materials, may serve as a corrective in fresh concrete. Pozzolons, especially fly ash, have been used and stL'~diedfor decades, both here and abroad. The first reported data on the use of fly ash in concrete in the United States was in 19371 . Since then numerous studies have been published 1, 2. Reports have also been published detailing the decades of experience with fly ash as an additive in blended cements 3 - 5. The microstructural and chemical effects of cement additives are not easily directly investigated and, therefore, only recently have researchers begun to report on the chemical processes and microstructural effects of using fly ash6 - 8. ER Giasser, et al6 state that the presence of fine particles may influence the flocculation behaviour of the system and thus the packing properties. This could affect the pore size distribution and the pore interconnectivity. They also state that the blending agent "may act as preferential sites for the nucleation of cement hydration products". There is reason to believe that kiln dust, a product similar to fly ash and of the same order of fineness as fly ash, may have similar effects when used as a blending agent. However, although a wealth of information exists on fly ash, we have been unable to find any published data on kiln dust. Historically the effects of blending cement with various agents have been determined by studying the properties of materials made with the blended product. This investigation was undertaken to determine the suitability of blending kiln dust with Type !11 Portland cement. The objective of the research programme was to a Profesor, Civil EngineeringDepartment, University of New Mexico,Albuquerque,NM 87131. b Protesaor, Civil Engineering Department, South Dakota School of Mines & Technology, Rapid City, SD 57701.
78
0950 - 0618/90/020079 -
08 © 1990 Butterworfh-Heinemann Ltd
determine the properties of fresh and hardened concrete made with Type I!1 Portland cement blended with kiln dust.
Research significance Using waste by.products in the manufacture of construction materials has a two-fold benefit. The cost of the material is reduced and the burden of disposal of the waste is decreased. Before such products can be used in the field, extensive tests must be conducted to ensure the serviceability of projects made using the new materials. This investigation examines the effects of using kiln dust (a waste by-product of the cement manufacturing process) as a pozzolon in blended ce. ments. The ready availability of kiln dust in cement processing plants suggests an opportunity for the production of blended cement using this by-product. Test p r o g r a m
In order to determine the effects of adding kiln dust to cement, tests were conducted on blended cement, on cement without kiln dust (plain cement), and on mortar and concrete specimens (cylinders and cubes) cast with both blended cement and plain cement. The cement tests measured fineness, composition, normal consistency and setting time. The tests on mortar compared unit weight, compressive strength and splitting tensile strength. The concrete tests included compressive strength, unit weight, durability, pulse velocity, shrinkage and creep. Where applicable, all tests were conducted according to ASTM specifications. All tests used Type Iii, Portland cement produced by the South Dakota State Cement Plant. The chemical and physical properties of the cement are given in Table 1. The kiln dust was also supplied by the SD State Cement Plant. it was produced during the burning of Type II clinker and collected from the precipitators of kilns fired with coal and natural gas. The fine aggregate was natural sand with a fineness modulus of 3.04. The coarse aggregate used was crushed limestone. Sieve analyses for fine and coarse aggregate are given in
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
Table !
Chemical analysis and physical properties of Type III cement
PHYSICAL
CHEMICAL
5.82
Fineness, Blaine Fineness Meter, sq. cm. 1 gram
Ferric Oxide (Fe203)
2.88
Soundness, Autoclave Expansion
0.00
Magnesium Oxide (MgO)
Time.of Setting (GiUmore Test) Initial (Hr.:Min.)
2:20
1.44
Sulfur Trioxide (SOs) when 3CaO.AI203 is 8% or less
_
Final (Hr.:Min.)
3:50
When 3CaO.AI203 is more than 8%
4.27
Time of Setting (Vicar Test)
1:25
Ignition Loss
1.84
Compressive Strength (psi) 1 day
Insoluble Residue
0.54
5 days
4951
Tricalcium aluminate (3CaO.AI2'o3)
10.55
7 days
5796
Tricalcium silicate & Tricalcium atuminate (3CaO.SiO2 + 3CaO.AI203)
62.91
28 days
Tetracalcium aluminoferrite + 2X Tricalcium /4CaO.AI303.Fe203} + 2 (3CaO,AI203)
29.84
Alumina (AI203)
Alkalies (Na20 + .658 x K220)
0.45
Table I! Sieve analysis - Fine aggregates
5397
2936
Air Cement of Mortar
93%
False Set Ratio of Final to Initial Penetration
53.1o/0
Table I!i Sieve analysis - Coarse aggregates Percent
Percent Sieve Size
Sieve Size Passing through
by
by Retained on
Weight
Weight
Passing through
Retained on
11/2 in.
1 in.
1.0
¼in.
#
4
0
#4
#
8
14.30
I in.
~4 in.
28.8
#8
# 16
24.94
3/4 in.
1/2 in.
50.8
# 16
# 3o
28.87
V2 in.
3/8 in.
15.3
# 30
# 5o
17.88
% in.
1/4 in.
3.0
# 4
0.5
# 50
#100
10.55
¼ in.
#100
# 200
2.80
# 4
# 8
0.3
# 8
Pan
0.3
#2~
Pan
0.66
Tables 2 and 3, respectively. The water used was tap water. Neutralised vinsol resin (Protex) was used as an air entraining agent. Mortars were proportioned according to ASTM C
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No, 2 JUNE 1990
109. The sand.cement ratio of 2.75 and water-cement ratio of 0.485 by weight were used throughout. The mortar mixes numbered WP] and WB1 are plain cement mix for ] day test and blended cement mix for
79
Table IV Type of • mix
Cement Content iblyd 3 kg/m 3
W/C Ratio
Concrete mix details
Aggregate Cement Ratio
Ratio of Coarse: Fine Aggregate by weight
Air Entraining Agent % of cement
Mix No. 1 WB 1 WP 3 WB,~ 3 WP~, 4 WB 4 WP
Type Ill Cement
' 650
385
0.45
4.4
60:40
0.13
Type III Blended
650
385
0,45
4.4
60:40
0.13
Type III Cement
564
335
0.55
5.8
60:40
NO
5 WB 5 WP
Type Ill
564
335
0.55
5.8
60:40
NO
6 WB 6 WP
564
335
0.52
5.2
60:40
013
2 WB+
564
335
0.52
5.2
60:40
0.13
2 WP+
Blended
Type Ill Cement Type III Blended Note:
~r These mixes were tested for creep & shrinkage also + These mixes were tested for freezing and thawing
1 day test, respectively. The mortar was mixed per ASTM C 305. The mortar cube specimens were mould. .=.d and tested per ASTM C 109. The mortar cylinder specimens were cast in steel moulds, compacted in two layers by rodding with the fiat end of a 3ram (1/8 inch) diameter rod. The details of the concrete mixes are given in Table 4. The mixed specified as lWP and ]WB are plain concrete mix ] and blended concrete mix 1, respectively. The concrete was batched in accordance with ASTM C192. T h e following tests were performed:
Cement and blended cement Fineness - ASTM C 184 Normal consistency - ASTM C 187 Setting time - ASTM C 4 0 3 Mortar Compressive strength - ASTM C 109 Tensile strength - ASTM C 4 9 6 (specification for concrete Unit weight Fresh concrete S l u m p test - ASTM C 143 Vebe c o n s i s t o m e t e r - U.S. Army Corps of En gineers C RD-C2-75 and AC! Standard 211-65 Air content - ASTM C 231 Pressure Method Plastic unit weight - ASTM C 138 Concrete t e m p e r a t u r e and a m b i e n t t e m p e r a t u r e and humidity were recorded. Hardened Concrete Compression test - cylinder s p e c i m e n s - ASTM C 39 Dry unit weight Static m o d u l u s of elasticity - ASTM C 4 6 9 Pulse velocity - ASTM C 5 9 7
80
Fiexural strength (Modulus of rupture) ASTM C 215 Setting time - ASTM C 4 0 3 D y n a m i c m o d u l u s of elasticty - ASTM C 2 1 5 Freeze thaw test - ASTM C 6 6 6 Shrinkage - ASTM C 157 Creep - ASTM C 512
Results Cement Tests Fineness: The fineness of kiln dust, plain and blended cements using No. 100 and 200 sieves. The kiln dust was finer than the cement, but there was no apreciable difference between the fineness of the plain and blended cements. Normal consistency: The amount of mixing water specified is related to the water content required to bring the paste to a standard condition of wetness called nor. mall consistency. The normal consistencies for the plain and blended cement were 27 percent and 28 percent, respectively. Time of setting: It is customary to refer to initial setting, defined as the beginning of stiffening, and final setting, marked by the disappearance of plasticity. The cement paste tested for setting time was the same mix as that used for the normal consistency test. The initial set and final set of the plain and blended cement pastes are shown in Figure 1. Both initial and final setting time were greater for the blended cement paste than for the plain cement paste. Mortar Tests T h e mortar s p e c i m e n s (2 inch c u b e s and 3 inch diameter by 6 inch cylinders) were tested for unit weight,
compressive strength and splitting tensile strength at ages of 1, 3, 7, 14, 28 and 90 days.
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
Table V Plastic properties of concrete Slump
Air
Mix in
Vehe
Concrete
Time
Temperature
Room Temperature
oC
OF
oC
mm
%
sec
OF
Relative Humidity
Unit Weight
%
tblft3
W/C kg/m 3
ratio
lWP
21/,=
57.2
3.0
4
72
22
75
24
40
147.9
2371
0.45
lWB
2
50.8
2.8
4
79
26
77
25
40
147.9
2371
0.45
2WP
3
76.2
5.0
2
75
24
72
22
39
145.2
2328
0.52
2WB
31/o
79.4
5.1
2
75
24
71
22
39
144.6
2318
0.52
3WP
2
50.8
3.2
4
74
23
60
16
49
147.9
2371
0.45
3WB
21/o
54.0
3.0
4
72
22
58
15
56
147.7
2368
0.45
4WP
31/,=
82.6
4.9
2
66
19
60
16
47
143.4
2298
0.45
4WB
3
76.2
4.3
2
66
19
63
17
48
144.7
2320
0.45
5WP
3~
95.3
1.5
2
71
22
65
18
31
149.5
2398
0.55
5WB
2¥4
69.9
1.6
3
74
23
74
25
30
148.8
2385
0.55
6WP
21/4
57.2
1.5
3
66
19
66
19
40
148.8
2385
0.55
6WB
17/s
47.6
1.8
4
66
19
63
17
40
148.8
2385
0.55
100 7O
6O
Normal consistency :
50 40
Plain cement, W I C = 0 . 2 7 Blended cement, W l C = 0.28 - - O - - Plain cement Blended cement
i
0.
~
50 -
~ 30
L
Initial set
.• 40-
A
Z~
~
A
z~ o
20
OPlain cylinders
~
15
ABlended cylinders • Plain cubes
E ~
10
~
o 30_o
o
Q.
E o u Initial set, h r : m i n u t e s Plain 2:02 Blended 2:49
o
~
7
5
I
i
i
l
I .5
2
Final set
~
3
i
,
I
4
6
10
Time ( h o u r s )
20
l
0
l
l
l
l
20
,
J
I
,
~
,
I
40 60 Age ( d a y s )
,
,
~
]
80
l
l
I
100
F g. 2 Mortar compressive strength as function of age.
Final set Plain 2:35 Blended 3:28
0) Q,.
A Blended cubes
[log scale]
F g.l Curves of uicat penetration for plain cement and blended cement paste setting at room temperature
Compressive strength: The pattern of compressive strength development with age is shown in Figure 2. in general, there was no signficant difference in the com. pressive strengths of blended cement mortar and plain cement mortar for either cube or cylinder specimens. Most of the blended cement mortar strengths fell
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
within plus or minus 1-4 percent of the strength of plain cement mortar. Tensile strength: The pattern of splitting tensile strength development with age is shown in Figure 3. The 14 day tensile strength of the blended cement mortar was 10 percent higher than for the plain cement mor. tar. At 28 and 90 days, however, there was no significant difference in the tensile strengths of the plain cement and blended cement specimens. Unit weight: The unit weights for the mortar specimens are given in Table 5. There was no significant difference in unit weight between plain and blended cement at any age. The lower unit weight of cylinder specimens than corresponding cube specimens can be attributed to the different compacting methods used for cylinder and cube specimens. The unit weight was approximately the same for comparable specimens compacted by the same method. Also, there was no appreciable change in unit weight after 7 days.
81
7
¢! A 0
=~ 5D~
~ 4 c
0 Plain m o r t a r
3
Z~Blended m o r t a r
~- 2 1
,
,,
,
I
,
i
,
20
I
,
,
,
I
J
,
~
40 60 Age ( d a y s ]
,
,
,
80
100
F g.a Mortar tensile strength as a function of age.
I n i t i a l s e t t i n g time, h o u r s : m i n u t e s Plain 5:05 Blended 5:25 Final s e t t i n g time Plain 6:45 Blended 7:15
6000 -
-~ 4500 -
~--I--~
Final set
//
3000 -'0"-Plain
9/ /
cement c o n c r e t e B l e n d e d cement c o n c r e t e I
,?'/
1500
122.222
,,,
2
-
4
/ /
I
6
Time ( h o u r s )
F0.4 Comparison of setting time for plain cement concrete and blended cement concrete.
Plastic properties of concrete The plastic properties of the fresh concretes are presented in Table 5. There was no significantdifference in the slump and vebe time between the plain and blended cement concretes. W h e n an air entraining agent was used, the amount of air entrained in blended cement concrete was approximately 0.2 percent less than that of plain cement con. crete. W h e n no air entraining agent was used, the air entrapped in both the plain and blended cement concretes was the same. Both concretes showed the same ease of placement and finishability. The effect of blended cement on the initialand final setting times of concrete as determined by penetration resistance (AS'I'M C 403) is illustratedin Figure 4. Both inRial and final set of blended cement concrete occur 30 minutes later than for plain cement concrete. Behaviour of hardened concrete The following properties were studied to evaluate the effect of kiln dust on hardened concrete. Compressive strength: The pattern of compressive strength development with age is shown in figure 5. Most of the strengths for blended cement concrete were 4 percent higher in the earlier tests and 3-5 percent lower at 28 days than for the plain cement concrete. Unit weight: The unit weights were essentially the same for plain and blended cement concretes for all ages. The unit weight of the blended cement concrete, mix 4, was 1-2 pcf more than that of the plain cement concrete at all ages. This discrepancy may be due to the 0.6 percent more entrained air in the plain cement concrete, Pulse velocity: The development of pulse velocity with age is shown in Figure 6. The pulse velocity com. padson is similar to that for compressive strength. The pulse velocity of blended cement concrete was approx, imately 1-3 percent less than that for plain cement concrete except for mix 4. For mix 4, the pulse velocity of the blended cement concrete was 2 percent higher than for plain cement concrete. Similar results were obtained for the dynamic modulus of elasticity. Flexural strength: The results of flexure strength tests at ages of 28 and 90 days are shown in Table 6. The
50
5000
40
._-----------4
4800
(-O D~ C
~
E 30
m
•~
4600
~
4400
mixes 5 t 0
o_ 20 E
I
A B l e n d e d mixes 5 & 6
o
10
,
I
10
L
I
20
,
30
Age ( d a y s )
Y
4200
• Blended mixes 5 & 6
,
0
I
,
10
l
20
,
30
Age (days]
F g. 5 Concrete compressive strength as a function of age.
Fig. 6
Pulse velocity of concrete as a function of age.
Table VI Comparison of flexural strength Specimen
Modulus of Rupture
Age
Days
No, 1PC #4 1PC #5 1PC # 6
Loss 0.2
--0--
Plain concrete, f r eeze- t haw c u r i n g jlp-~l Blended concrete, f r e e z e - t h a w c u r i n g J ~ , / - - O - - Plain concrete, st andar d c u r i n g j l , 1 ~ Blended concrete, st andar d ,-~ .J curing lil'~
Oo
Average
psi
28
710 715 660
28
680 730 640
psi
MPa
695
4.8
o
O, O.
1BC #4 1BC #5 1BC #6 1PC # 1 1PC # 2 1PC # 3
90
1BC # 1
1BC # 2 1BC #3
90
680
4.7
O. ]in
730 790 690
740
820 740 750
770
I
"I
I
I
I
I
40
80
120
160
200
240
5.1
Cycles
Weight loss v. cycles.
9 5.3
--0--
17000
Plain concrete, st andar d curing Blended concrete, st andar d curing Plain concrete, f r eeze- t haw curing Blended concrete, f r eeze- t haw c u r i n g
--41--
E
8
400
~1650C
o Plain mix 2 Blended mix 2 300
• Plain mix 3.
I
280 300
~,._...__...--~
0
~16000
x
E
u
200
155oi 3 to
I00 15000
r-
'Z .c u~
0
0
-100
i
I
i
150
200
250
300
Fig. 10 Pulse velocity v. number of freeze.thaw cycles. 0
20
40 60 Age (days)
80
100
0.4
0.3
o
0.2
~ --O-t~ @
I
100
Cycles
Fig. 7 Drying shrinkage with age.
•-
I
50
Blended concrete Plain concrete
0.1
u
F g. 8
S t r e s s - s t r e n g t h : 30% I
I
I
I
I
I
I
1o
2o
3o
40
5o
60
70
80
Comparison of creep strains for plain and blended concretes.
strengths of blended cement concrete were within a range of plus or minus 4 percent of those of the plain cement concrete and, therefore, not significant. Shrinkage: Two different mixes (mix 2 and mix 3) were tested for shrinkage. The mix details and the test results are shown in Table 7. The measured shrinkage deformations are given plotted in Figure 7. The mixes
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
compared had the same maximum coarse aggregate size but different w/c ratios and aggregate-cement ratios. As shown in Figure 7, the shrinkage deformation of blended cement concrete for mix 2 was considerably more (22 percent) than for plain cement concrete. For mix 3, however, the shrinkage deformation was approximately the same for both blended and plain cement concretes. The reason for the difference is not known. Creep: Two mixes with the same proportions were made with plain and blended cement. From each batch, three specimens were made. After curing for 28 days, the specimens were arranged in series and loaded to a stress level equal to 30 percent of the 28 day strength using constant pressure hydraulic rams. Strain measurements were taken immediately after loading and at fie. quent intervals thereafter. The average of the measured strains on two faces of the specimens were recorded for both the plain and blended cement specimens. Measured creep strains are plotted in Figure 8 for both blended and plain cement concretes. The plotted values are average strains for three cylinders. Figure 8 indicates that for the same maximum aggregate size and the same strength.stress ratio, the blended cement concrete exhibits more creep than the plain cement concrete (14 percent greater at 60 days).
83
Table VII Details of mixes used for creep and shrinkage specimens Maximum Aggregate Size in.
Mix No.
WIC
NC
2 WP
0.52
5.2
2 WB
0.52
5.2
3 WP
0.45
4.4
3 WB
0.45
4.4
Vebe Time $ec.
Slump in.
3~
2~
28-Day Strength psi
Modulus of Elasticity psi x 10s
5093
5.25
4790
5.42
5453
5.33
306 x 10 - s at 1635 psi
5285
5.39
291 x 10 -6 at 1569 psi
Table VIii
Elastic Strain
Chemical analysis
>.
.'~ 120, Kiln Dust
Type I Cement
Cement & Kiln Dust
SiO 2%
15.78
20.98
20.36
Fe20s
1,09
2.61
2,17
AI20 3 %
3.95
6.13
6.03
CaO %
45.71
63.05
62.77
SO s %
2.32
2.50
2.50
MgO %
0.98
1.39
1.37
Volatile
27.83
3.39
4.10
Total %
97.66
100.05
99.30
5.04
Compound
-~ 1~0
"----------'--'--'--'--'-
100 ~ ' - - - 4 " - - ~ b ~ . ~ A E "E
l 901-
co
|
.~
| 80 1
-~
--O'~ --O-~ I 40
.
"-,m- . . . . . .
Plain c o n c r e t e , f r e e z e - t h a w c u r i n g Blended c o n c r e t e , f r e e z e - t h a w c u r i n g Plain c o n c r e t e , s t a n d a r d c u r i n g Blended c o n c r e t e , s t a n d a r d c u r i n g ,I I I I I 80 120 160 200 240
I [ I I I 300
Number o f f r e e z e - t h a w cycles
8,74
8.20
F-CaO %
0.43
0.54
Insoluble %
0.48
1.12
C4AF %
7.94
R20~ %
F/g. 11 Relatiue dynamic modulus at different freeze. thaw cycles. Durability: Freeze-thaw performance was evaluated using two sets of two specimens for each type of mix. One set was exposed to the conditions specified in ASTM C 666 (rapid freezing and thawing in water), the other was used as a reference. In addition to monitoring changes in fundamental transverse frequency to calculate durability factors, changes in length and weight were also monitored. The results are presented graphically in Figures 10 and 11 and listed in Table 13. The change in weight of both sets are plotted in Figure 10. The weights of the reference specimens increased up to 120 cycles (84 days) and then remained approximately constant. The weights of the specimens subjected to freeze-thaw cycles increased up to 120 cycles due to absorption and then decreased due to deterioration of the surface of the specimens. The weight gained or lost by blended and plain cement concretes is, more or less, equal. The development of pulse velocity and the relative dynamic modulus of elasticity are shown in Figures 10 and 11, respectively. The pulse velocity increased in reference specimens and decreased in freeze.thaw specimens. There was no difference in pulse velocity between plain and blended cement concretes for either freeze-thaw or standard cured specimens. The blended cement concrete showed an earlier decrease in rela-
C3A %
11.83
C3S %
45.19
C2S %
26.06
A/F
2,35
C3S/C2S
1.73
6.01 1.82
S/(A+F)
2.40
2.48
tive dynamic modulus than did the plain cement concrete. As mentioned above, additional methods of detecting damage were employed. The data for changes were recorded. The blended cement concrete showed more expansion than did the plain cement concrete. The expansion indicates internal structural damage caused by the freezing and thawing process. C h e m i c a l properties of kiln dust Dust collected from the gases emanating from rotary kiln is specially known as Cement Kiln Dust (CKD). This dust is entrained in large volumes of hot exhaust gases. More often it contains unacceptably high concentrations of alkalies (Sodium and Potassium) which make it unsuitable for return to the cement making process, This dust also contains sulfate salts and partly calcined
material which Causes some hydraulics and cementious properties. The presence of water soluble alkalies in CKD can cause pollution of surface or ground waters. Chemical analysis is shown in Table 8. Many types of dust collectors are used in cement industry. They are cyclones, Electrostatic Precipitators, Baghouses, Wet Scrubbers, and Settling Chambers. They are used independently or in combination. At present 98 to 100% of the dust is collected. The cement kiln dust used in this investigation was collect. ed by the electrostatic precipitator. The chemical and physical properties of dusts vary from plant to plant. The variation is due to the variation in the raw materials used, and due to the type of col. lection used. There is also great variation in the dusts collected in the after compartments of a precipitator is considerably different from dust collected in the forward compartments. Furthermore, dust collected in baghouses is different from a given kiln and from a given plant. Dust shows a wide range of particle sizes ranging from less than 6 microns to 100 microns in diameter as shown in Table 9. Presently the cement kiln dust collected is a big solid waste disposal problem for the cement manufacturers. This paper reports the results of an investigation into the effects of partial replacement of cement (5% by weight) with cement kiln dust on the properties of concrete. The kiln dust used in this investigation was collected consistently from the s a m e location in the precipitator. This particular dust had lower alkali and chloride con. tents than generally found in this location and in other plants. Discussion
of test results
The following results are based on the use of 5 percent kiln dust by weight in the blended cement. They are not necessarily valid for other proportions. ] The kiln dust was finer than both plain and blended cement. There was no appreciable difference in fineness between plain and blended cements. 2 The water content required for normal consistency was one percent higher for blended cement than for plain cement. This does not necessarily mean that blended cement needs a higher water content to produce the same slump as plain cement. The Vicar test measures viscosity whereas the slump test indicates lubricating ability of the paste. 3 Due to the higher water content at normal consistency the setting time for blended cement was longer than that for plain cement (45 minutes). 4 There were no significant differences in dry unit weight, compressive strength and splitting tensile strength of blended c e m e n t and plain cement mortar specimens. 5 Most properties of the fresh blended cement concrete were the s a m e as those of the plain cement concrete. The exception was setting time. The blended c e m e n t concrete had 30 minutes longer initial and final setting times
CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990
Table IX
F i n e n e s s test results
Sieve Size No.
Total Weight of Sample g
Plain Cement
100 200
Blend Cement
100 200
Cement
Residue g
Fineness % Passing
50 50
0.30 2.25
99.4 95.5*
50 50
0.28 2.20
99.44 95.6.
Note: , The Sieve Correction (c) to be calculated as per ASTM C 184 Sec. 6.1.2. is assumed as zero.
than the plain cement concrete. 6 The hardened concrete properties of blended cement concrete were comparable to those of plain cement concrete at all ages. 7 The blended cement concrete experienced greater shrinkage and creep than the plain cement concrete. 8 The blended cement concrete did not show inferior resistance to rapid freezing and thawing up to 120 cycles but experienced a little more weight loss thereafter.
Conclusions Where slightly increased shrinkage and creep and in. creased setting time can be tolerated, replacement of 5 percent by weight of cement with kiln dust produces a blended cement which can be used to make mortar and concrete with good serviceability properties for any application. A preliminary test result for 7% by weight of cement replacement indicate no difference to 5% one. Further research is needed to determine the effects of replacement at greater proportions and of mixing kiln dust with other pozzolons such as fly ash. References 1 V.M. Malhotra (1987). "Superplasticizers, Pozzolans and Granulated Blast.FurnaceSlagsin Concretes: A Review:' Lewis H. Tuthill International Symposium on Concrete and Concrete Construction, ACI SP.I04, G.T. Halvorsen, Ed., Amer. Concrete Inst., 63.88.
2
P.K.Melht~ (1983). "Pozzolonicand CementitiousByproducts as Mineral Admixtures for Concrete - A Critical Review:'F/y Ash, Silica Fume, Slag E, Other Mineral By~Products in Concrete Vol. I, ACI SP.79, 1.46.
3 4 5 6
J.F. Lamond (1983). "Twenty-FiveYears'ExperienceUsing Fly Ash in Concrete:' Ibid Ref. 2, 47.69. A. Samarin, R.L Munn and J.B. Ashby (1983). "The Use of Fly Ashy in Concrete - Australian Experience/'Ibid Ref. 2, 143.172. V. Korac and V. Ukraincik (1983). "Studies into the Use of Fly Ash in Concrete for Water Dam Structures" Ibid Ref. 2, 173.185. F.P. Glasser, S. Diamond and D.M. Roy (1986). Hydration
Reactions in Cement PastesIncorporating Fly Ash and Other Pozzolonic Materials:' Materials Research Society Symposia Proceedings, 86, 139-158.
7
8
N. Tenoutmme and A.M. Marion (1986). "Mechansim of Hydrationof Cement Blendedwith Fly Ashes:'BlendedCements, ASTM STP 897, G. Frohnsdorff, Ed., ASTM, Philadelphia, Pa, 65.85. S. Chatterji, M. Collepardi and G. Moriconi (1983). "Poz. zolonic Propertyof Natural and SyntheticPozzolans:a Comparative Study;' Ibid Re[. 2, 221.233.
85