This document summarizes laboratory testing of chemical admixtures for use in the Zirdan RCC dam project in Iran. Various plasticizers and superplasticizers from different suppliers were tested through normal consistency tests of cement pastes and concrete mixture trials. The admixtures were evaluated based on their water reduction capabilities and effects on compressive strength. The two top performing admixtures were selected for further site testing to determine the best option for use in the dam.

1. Proceedings of the 1st
International Conference on Concrete Technology, Tabriz, Iran, 6-7 November 2009
Paper Code. No. CT0018
CT0018, Page 1
Laboratory Studies for Selection of a Suitable
Chemical Admixture in Zirdan RCC Dam
M.R. Sadri
Chief of laboratory of Zirdan RCC dam; Jahan Kowsar Construction Company
geosadry@yahoo.com
H.R. Araghian
Concrete technology advisor of Zirdan RCC dam; Jahan Kowsar Construction Company
hra@hra.ir
ABSTRACT
The use of chemical admixtures in hydraulic-cement concrete mixtures has been common in recent decades for
different purposes. Zirdan dam as the 2nd reservoir RCC dam in Iran has about 220,000 m3 conventional vibrated
concrete (CVC) –including mass and reinforced conventional concrete- and 280,000 m3 roller compacted concrete
(RCC). Due to the hot climate of Zirdan district, suitable admixtures should be used to prolong workability and reduce
the cementitious content and help prevent thermal problems. Some different kinds (brands & types) of plasticizers and
super-plasticizers were tested in the dam local laboratory. Retarding effects of admixtures were tested also.
The test program included normal consistency test of cement paste plus admixtures and making some trial
concrete mixtures to investigate water reducing effect and compressive strength. Eventually the selected admixtures due
to technical aspects had been compared economically. After the laboratory testing stage, the two top selected
admixtures have been brought to dam site and used in a site test to finalize the best option. In this paper the commercial
name of admixtures and their producers will not be mentioned and just be named A, B, C and etc.
Key Words: (Chemical Admixture, Normal Consistency, Water Reducing Effect, Zirdan RCC Dam)
1 INTRODUCTION
Due to the hot climate of Zirdan district, chemical admixtures should be used to prolong workability
and reduce the cementitious content and so help prevent thermal problems. Also the slump retention
as an important factor has been considered. When making high-performance concrete (HPC), the
selection of the super-plasticizer is a crucial step, just as crucial as the selection of the cement,
because not all commercial super-plasticizers have the same efficiency and react in the same way
with all cements [1].
Therefore primarily, the products of four well-known companies have been selected and their
admixture samples have been used to make trial mixtures. The performed tests consisted of Normal
consistency tests in accordance with ASTM C187 and also making some concrete trial mixtures. 34
trial mixtures have been prepared by using plasticizers and super-plasticizers and the properties of
fresh and hardened concrete have been determined. Those admixtures are named A to M in this
paper.
All of mixtures have been made of the same cementitious materials and the same gradation of
aggregates and tried to retain the slump constant to 12 cm.
The F super-plasticizer has not been used in concrete mixtures due to high PH amount -about
10- and also the B and D super-plasticizers due to proposing other counterpart and low-price

2. CT0018, Page 2
admixtures from their suppliers have just been used in normal consistency tests. Eventually 10 types
of admixtures have been used for concrete trial mixtures.
2 NORMAL CONSISTENCY TESTS
To investigate the water reducing effect of admixtures, some normal consistency tests have
been conducted; that is to say by increasing the dosage of admixtures, the water demand of cement
paste to achieve the normal consistency has been determined. Because of the plasticizing effect of
chemical admixtures is caused by the interaction of admixtures and cement particles, the normal
consistency test could be a suitable indicator of the effect of admixtures on concrete mixture.
The results of normal consistency tests and the specifications of admixtures are given in table
1 and figures 1 and 2.
Table 1 Results of Normal Consistency Tests and the Specifications of Admixtures
Admixture No A B C D E
Dosage (%) 0.00 0.50 0.80 1.40 2.00 0.40 0.80 1.20 0.19 0.40 0.65 0.90 0.40 0.80 1.20 0.40 0.70 1.10 1.50
NormalConsistency 25.7 25.1 24.0 23.2 23.4 25.0 23.1 22.6 25.0 24.7 23.7 23.5 23.2 22.0 21.5 25.5 24.7 23.9 23.8
Color --- Dark Brown Greenish Light Brown Brown Dark Brown
Density --- 1.18 kg/lit 1.10 kg/lit 1.07 kg/lit 1.11 kg/lit 1.12 kg/lit
Shelf Life --- 18 months 15 months 12 months 12 months 12 months
RecommendedDosage --- 0.8-2.5% 0.4-1.2% 0.4-0.9% 0.9-1.1% ---
Side Effect ---
Set Retarding, Long-Lasting
Slump
Set Retarding, Long-
Lasting Slump
Prolonged Workability SlightRetardation
Setting Retarded if Large
Amounts added at Low
Temperatures
Admixture F G H I J K L M
Dosage (%) 0.40 0.80 1.20 1.60 0.30 0.60 0.30 0.60 0.30 0.60 0.40 0.80 1.20 0.30 0.60 0.30 0.60 0.30 0.60
NormalConsistency 25.3 24.2 23.5 23.0 25.4 24.1 25.2 24.0 25.4 24.1 24.2 22.8 22.3 24.5 24.3 24.6 23.7 25.7 24.9
Color Brown Light Brown --- Brown Brown Brown Brown Brown
Density 1.15 kg/lit 1.13 kg/lit --- 1.22 kg/lit 1.19 kg/lit 1.14 kg/lit 1.19 kg/lit 1.15 kg/lit
Shelf Life --- 18 months --- 12 months 12 months 12 months 12 months 18 months
Recommended Dosage --- 0.2-0.8% --- 0.25-0.4% 1.2-3.0% 0.35-0.7% 0.25-0.85% 0.25-1.0%
Side Effect ---
Retarding
Effect if
Amounts
Added
Greater
than 0.35%
--- ---
Improve the
Workability and
Retention
Increase the
Workability
and Initial
and Final
Setting Time
Helping
Maintain
the
Workability,
Extend
Working
Time
Improvement
of
Workability,
Weak
Retarding
Action

3. CT0018, Page 3
Figure 1: Effect of Plasticizers on Water Demand of Cement Paste
Figure 2: Effect of Super-Plasticizers on Water Demand of Cement Paste
To compare the water reducing effect of plasticizers and super-plasticizers, the normal
consistencies of cement pastes containing admixtures have been compared with the paste having no
admixture and so a water reduction percent for each admixture was defined. Because of existence of
more variable materials in concrete, so tests on cement pastes may be more reliable. The plasticizers
have been compared in the dosage of 0.6% and the super-plasticizers in the dosage of 0.8%. The
water reduction percent of plasticizers is divided to 4 categories -0-2%, 2-4%, 4-6% and 6-8%- and
also the super-plasticizer’s to 4 categories -3-6%, 6-9%, 9-12% and 12-15%- the results are shown
in figures 3 and 4.
Plasticizers (0.6%)
water reductionamount admixture
6-8%
G
H
L
4-6% K
2-4% M
0-2% I
Figure 3: Water Reduction of Plasticizers with a Dosage of 0.6%
I
H
K
L
G
M
C
E
A
J
D
B
F
I M K G H L

4. CT0018, Page 4
Super-Plasticizers (0.8%)
water reductionamount admixture
12-15% D
9-12%
B
J
6-9%
A
C
3-6%
E
F
Figure 4: Water Reduction of Super-Plasticizers with a Dosage of 0.8%
3 CONCRETE TRIAL MIXTURES
In all of these concrete test mixtures was used 341 kg/m3
type II pozzolanic Portland cement
(containing 25% Khash Natural pozzolan), 24 kg/m3
Khash ground natural pozzolan, aggregates
with the MSA=25 mm containing 45% sand –except for mixtures 20, 21 and 22-. It should be
mentioned that the total pozzolan content is equal to 30% of cementitious material.
Aggregates have been placed into 50 °C oven to get a 30 °C fresh concrete after mixing all
components to simulate the actual condition for fresh concrete. Concrete trial mixtures have been
shown in table 2.
Table 2 Properties of Fresh and Hardened Concrete Mixtures
Mix No.
Natural
Sand
Crushed
Sand
Natural
5-25 mm
Crushed
5-25 mm
Blended
Cement
Ground
Pozzolan
Free
Water
Admixture Slump (cm)
W/C
Compressive Strength
(kg/cm²)
(kg/m³) (kg/m³) (kg/m³) (kg/m³) (kg/m³) (kg/m³) (kg/m³) % of (C+P) Type 5 min. 20 min. 7 day 28 day 90 day
280/25-11 559 285 629 419 341 24 167 0.8
A
10 5 0.46 299.3 335.2 394.7
280/25-12 562 287 633 422 341 24 161 1.2 10 3 0.44 286.7 351.5 442.4
280/25-13 564 287 634 423 341 24 158 1.6 11 3 0.43 --- 370.6 480.9
280/25-14 560 286 631 420 341 24 161 2.0 15 8 0.44 290.0 --- 469.4
280/25-15 540 275 608 405 341 24 193 0.0 10 7.5 0.53 --- 236.4 311.2
280/25-16 559 285 628 419 341 24 166 1.2 20 12 0.45 --- 339.8 439.0
280/25-17 555 283 624 416 341 24 172 0.8 20 11 0.47 --- 310.7 385.8
280/25-18 551 281 620 413 341 24 178 0.4
C
6.5 2.5 0.49 --- 275.4 352.0
280/25-19 563 287 633 422 341 24 162 0.8 11 3 0.44 --- 355.8 456.5
280/25-20 721 0 664 443 341 24 192 0.0
J
12 8.5 0.53 187.9 244.7 ---
280/25-21 746 0 687 458 341 24 165 1.2 Colps Colps 0.45 272.5 347.1 ---
280/25-22 754 0 695 463 341 24 157 1.2 Colps --- 0.43 320.6 378.2 ---
280/25-23 811 0 608 405 341 24 193 0.0 11 7 0.53 181.7 228.7 ---
280/25-24 808 0 606 404 341 24 195 0.0 12 9 0.53 182.5 233.9 ---
280/25-25 825 0 618 412 341 24 180 0.4 11 4.5 0.49 241.9 294.8 ---
280/25-26 838 0 628 419 341 24 167 0.8 12 6.5 0.46 268.4 334.0 ---
280/25-27 855 0 641 427 341 24 152 1.2 12 3.5 0.42 347.5 402.3 ---
280/25-28 830 0 623 415 341 24 175 0.4
A
12 7.5 0.48 254.6 283.3 ---
280/25-29 832 0 624 416 341 24 172 0.8 11 4.5 0.47 244.6 323.7 ---
280/25-30 841 0 631 421 341 24 163 1.2 16 6 0.45 285.0 354.1 ---
280/25-31 809 0 607 405 341 24 193 0.4
E
13 7 0.53 173.9 231.7 ---
280/25-32 832 0 624 416 341 24 172 0.8 13 6 0.47 243.7 319.3 ---
280/25-33 840 0 630 420 341 24 164 1.2 12 7 0.45 275.0 340.9 ---
280/25-34 819 0 614 409 341 24 185 0.3
K
13 7 0.51 224.8 269.1 ---
280/25-35 837 0 628 418 341 24 169 0.6 17 11 0.46 262.5 319.0 ---
280/25-36 843 0 632 421 341 24 164 0.6 12 8 0.45 269.8 347.3 ---
280/25-37 813 0 610 406 341 24 190 0.3
H
12 7 0.52 203.9 267.6 ---
280/25-38 825 0 619 413 341 24 178 0.6 12 5.5 0.49 233.4 297.0 ---
280/25-39 815 0 612 408 341 24 188 0.3 I 12 9 0.52 211.6 268.7 ---
280/25-40 826 0 620 413 341 24 179 0.3
G
12 9 0.49 216.3 310.3 ---
280/25-41 835 0 626 417 341 24 170 0.6 14 10 0.47 244.8 333.7 ---
280/25-42 813 0 610 407 341 24 189 0.6 M 12 7 0.52 203.7 277.0 ---
280/25-43 823 0 617 411 341 24 181 0.6 I 12 8 0.50 225.0 299.0 ---
280/25-44 827 0 621 414 341 24 177 0.6 L 12 5 0.48 231.5 308.7 ---
E F A C B J D

5. CT0018, Page 5
3.1 Water Reducibility
To compare the water reducing effect, the plasticizers have been tested in the dosage of 0.6%
and the super-plasticizers in the dosage of 0.8%. So the results of mixtures that have a slump of
12±1 cm were used for this comparison. The water reduction results are shown in table 3 and figure
5.
Table 3 Categorized Water Reduction of Admixtures in Concrete Mixtures
Plasticizers (0.6%) Super-Plasticizers (0.8%)
water reductionamount admixture water reductionamount admixture
10-15%
G
12-15%
C
K J
5-10%
I E
H 9-12% A
L
0-5% M
Figure 5: Water Reduction of Super-Plasticizers and Plasticizers in Concrete Mixtures
3.2 Slump Retention
The slump retention of admixture or in the other word their effect on slump loss of concrete is
an important parameter to transport, place and moulding the concrete. Therefore the slump of all
mixtures has been measured in 5 and 20 minutes after mixing of the cement and water. The slump
loss of all mixtures is shown in table 4 and figure 6. For mixtures that have no results in 0.6%
dosage, the slump loss has been interpolated from the results of dosage 0.4 and 0.8% -showed by *-.
Table 4 Slump Loss (%) of Concrete Mixtures within 15 Minutes after Mixing
Admixture
Dosage (%)
0.30 0.40 0.60 0.80 1.20
G 25 29
I 25 33
K 46 34
M 42
A 38 48* 59 63
E 46 50* 54 42
J 59 52* 46 71
H 42 54
L 58
C 62 67* 73
M I H L G K A E J C

6. CT0018, Page 6
Figure 6: Slump Loss of Concrete Mixtures with the Dosage of 0.6%
Also based on the results of super-plasticizer type A that is shown in figure 7 the more dosage
is used, the more slump loss rate will be attained.
Figure 7: Slump Loss vs. Dosage of Super-Plasticizer Type A
3.3 W/C vs. Compressive Strength
To verify the water content of mixtures, the correlation of W/C and compressive strength of
related specimens are shown in figure 8 at the ages of 7, 28 and 90 days.
Figure 8: Correlation of W/C and Compressive Strength of All Concrete Mixtures
G I K M A E J H L C
Dosage of super-plasticizer type A, (% of cementitious materials)

7. CT0018, Page 7
4 CONCLUSION
According to the slump retention results, all of used super-plasticizers with a dosage of 0.6%
show a slump loss rate more than 48% within 5-20 minutes after mixing and so the slump loss
could be much in real time period of construction; i.e. Mixtures have a high range water reduction
display a higher rate of slump loss [2] and the mixtures made with super-plasticizers that have an
initial slump of 12 cm are not applicable and must become much workable by increasing water or
dosage of admixture that has not economical preference; thus it’s been decided not to use super-
plasticizers.
- Based on the results of super-plasticizer type A, the more dosage is used, the more
slump loss rate will be attained.
- According to the normal consistency test, L, H, G and K plasticizers have the higher
rate of water reducibility respectively.
- According to the trial concrete mixtures, K and G plasticizers have the higher rate of
water reducibility respectively. According to the trial concrete mixtures, G, I, K and M
plasticizers have the minimum rate of slump loss respectively.
Eventually based on above results, G and K plasticizers as the most compatible chemical
admixtures have been brought to dam site and used in prototype concreting scale to finalize the best
option.
REFERENCES
[1] Pierre-Claude Aïtcin, Binders for Durable and Sustainable Concrete,-2008
[2] ASTM C494, Specification for Chemical Admixtures for Concrete,-2004