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Effect of polymerization conditions of sulfonated-melamine formaldehyde superplasticizers on concrete
CEMENT and CONCRETE RESEARCH. Vol. 18, pp. 513-531, 1988. Printed in the USA. 0008-8846/88 $3.00+00. Copyright (c) 1988 Pergamon Press plc
E F F E C T OF P O L Y M E R I Z A T I O N C O N D I T I O N S OF S U L F O N A T E D - M E L A M I N E FORMALDEHYDE S U P E R P L A S T I C I Z E R S CONCRETE
ON
Shawqul M. L a h a l l h , M. A b s I - H a l a b l and A l l M. A l l Kuwait Institute for Scientific R e s e a r c h , P . O . B o x 24885,
13109-Safat-Kuwalt
(Refereed) (Received July 16, 1987; in final form March 30, 1988) ABSTRACT The e f f e c t o f polymerization conditions o f sulfonated-melamlne formaldehyde superplastlcizers on the workability, mechanical p r o p e r t i e s and setting o f concrete and mortar was Investigated. Over twenty s u p e r - plasticizers were prepared according t o a novel procedure. It was found that reaction conditions have a significant e f f e c t on the p r o p e r t i e s o f the superplasticlzers and the interaction between them and concrete. The f o u r - s t e p r e a c t i o n p r o d u c t s gave 30-40% b e t t e r performance than the t h r e e - s t e p process. The f o u r t h step conditions o f time and temperature a f f e c t the stability o f the p r o d u c t s , but have no significant e f f e c t on workability. The e f f e c t o f reaction conditions on the performance of melamine- based superplastictzers Is discussed In terms o f molecular theory.
Introduction
In the past two decades, a new group o f c o n c r e t e admixtures, termed "superplasticizers", was Introduced to the c o n c r e t e industry. They have gained wide acceptance because o f their many advantages. The addition o f superplasticlzers t o c o n c r e t e mixes Improves the concrete's workability and Increases Its compressive strength. The three major types o f superplastlcizing admixtures commercially available are modified Ilgnosulfonates, sulfonated naphthalene-formaldehyde resins, and sulfonated melamine-formaldehyde resins (1). The use o f superplastlclzers In concrete and their Interaction with concrete have been extensively r e p o r t ed by researchers In the field (1,2,3,4). The Influence o f polymerization o f sulfonated naphthalene condensate and Its Interaction with cement was r e p o r t e d by Collepardi et al. (5). However, no studies were r e p o r t e d regarding the Influence o f polymerization conditions o f these admixtures on their superplasticizing efficiency when added t o c o n c r e t e or mortar mixes. The authors were able t o develop a novel f o u r - s t e p process, accepted t o p a t e n t by U.S. Department o f Commerce, Patent and Trademark Office, where significant Improvements In the synthetic superplasticlzers were obtained (6,7) when compared t o superplasticlzers prepared in accordance with the p a t e n t literature (8,9). This paper p r e s e n t s and discusses the results obtained on the e f f e c t o f various reaction conditions In the preparation o f s u l f o n a t e d melamine formaldehyde resins and the influence they have on c o n c r e t e workability and mechanical p r o p e r t i e s when they are added to the concrete.
513
4.0 4.0
4.0 4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
3.0
3.0 3.0
3.0 3.0
3.0
3.0
3.0
I 2
3 4
5
6
7
8
9
10
II
12
13
14 15
16 ]7
]8
19
20
11.35
11.35
11.35
II.35 II.35
11.35 11.35
11.35
11.35
11.35
11.35
11.35
11.35
11.35
11.35
11.35
11.35 11.35
11.35 11.35
pHI
M = melamine,
0.5
0.5
0.5
0.5 0.5
0.5 0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5 0.5
0.5 0.5
S/M+U
* F = formaldehyde,
F/M+U
Sample No.
U = urea.
50
50
50
75 50
50 55
50
50
50
50
50
50
50
50
75
50 50
45 50
.
11.35
11.35
I1.35
.
.
80
80
80
. 80
80 80
80
80
80
80
80
80
80
80
.
.
.
t2
60
60
60
60
60 60
60
60
60
60
60
60
60
60
60 60
60 60
(min)
3.5
3.5
3.5
3.5 3.5
3.5 3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5 "%.5
3.5 3.5
PH3
55
55
55
55 55
50 55
50
60
60
60
60
60
60
60
55
55 55
55 55
(°0
T3
t3
7.0
7.0
9.0
8.0 8.0
7.O 7.0
7.0
7.0
7.0
7.0
7.0
9.0
8.0
8.0
7.0
7.O 7.0
7.0 7.0
PH4
80
80
80
80 80
80 80
80
]OO
iOO
90
90
80
80
80
80
80 80
80 80
(°C)
T4
60
60
60
60 60
60 60
60
180
60
180
60
60
60
60
60
60 60
60 60
(min)
t4
Step 4 H i g h pH c o n d e n s a t i o n
Conditions.
4.82
3.58
5.01
3.86 4.56
4.15 3.87
4.09
3.31
3.41
3.54
3.50
4.48
4.00
4.00
5.60
4.42 4.O1
4.34 4.29
(cP)
Viscosity a t 20°C
temperature and time of reaction.
90
60
90
70 90
90 70
90
ii0
ii0
llO
llO
iiO
ii0
110
105
90 90
90 90
(min)
Step 3 Low pH c o n d e n s a t i o n
** pH, T and t refer the alkalinity,
. . . 11.35
11.35 11.35
11.35
I1.35
11.35
11.35
11.35
11.35
11.35
11.35
.
80 80
80 80
(°C)
T2
Step 2 Sulfonation
11.35 11.35
.
TABLE1 for Testing with Hortar and Concrete and their Reaction
11.35 11.35
PH2
S = sulfite;
15
15
15
30 15
15 15
15
15
15
15
15
15
15
15
30
15 15
15 15
tI
(n/n)
TI
(°c)
Step 1"* Hydroxymethylation
Samples Selected
lab
the
)atetxt
(30
O
Same as 18 except NaOH used in step 4.
~c-
O
pitt,. Same a s 13 e x c e p t t 3•
m
CD ct
D"
m me m
oD
PH 4 • Same as 12 except
Patent procedure. Same as 12 except
S4me a s ~3 e x c e p t VIM r a t i o . Same a s 13. Same a s 13 e x c e p t T I , T 3 and t .
Same as 2 except T and t .
Sa4me a s 2 except T 4
except T 4 Same as 2 e x c e p t T and t 4
pH 4 and t Same a s 24
pll4 and t 4 Same as 2 e x c e p t
procedure Same a s 2 e x c e p t pH 4 . Same a s 2 e x c e p t
except
Sample a s 2 plus aging at 90°C f o r two h. Same a s 2
Standard sample.
Remarks
&'-
Vol. 18, No. 4
515 POLYMERIZATION, SUPERPLASTICIZERS, CONCRETE, WORKABILITY
Exper" Imental
Method
Materials The sulfonated-melamine formaldehyde was synthesized according t o a f o u r - s t e p process that was developed In the author's l a b o r a t o r y (6,7). The f o u r steps are: (a) hydroxymethylation (the addition reaction between melamine and formaldehyde), (b) sulfonatlon (the product o f step (a) Is sulfonated), (c) low pH condensation (the p r o d u c t o f step (b) Is polymerlzed), and (d) high pH rearrangement (molecules rearranged t o give a more stable product). In each o f the f o u r steps, time, temperature and pH were varied to develop an optimum product. Sample nos. 1 - 2 0 are shown In Table 1 with their reaction conditions. Commercial sulphonated melamine superplastlclzer was obtained In powder form. The commercial superplasticlzer, manufactured by Suddeutsche K a l k s t i c k s t o f f - W e r k e Aktiengesellschaft (SKW), Germany, Is labeled Melment F - I O in the powder form and Meiment L - I O In the liquid form o f 20% solid content. Ordinary Portland cement (Type I) was used In this study. cement are shown In Table 2.
Detailed analyses o f
Sand with standard specifications (ASTM C - l O g ) was used f o r this study. water was used In the mixes and in the melamine solution.
the
Filtered tap
Equl/~nent Standard equipment, rectangle multiflow mixers models 2228 CL and 2283 manufactured by Edward Benton Co. Ltd., England, was used f o r the d i f f e r e n t t e s t s . Consistency was measured by a Vicat apparatus manufactured by Soiltest Inc., USA, according t o ASTM C-187 standard. Setting times were measured using the same Vlcat appar a t u s except that a d i f f e r e n t needle size was used. Flow p r o p e r t i e s o r spread was measured using a standard flow table as specified In ASTM C87. The flow table Is manufactured by Soilt e s t Inc., USA. Finally creep was measured by Creep Apparatus Model CT-180, manufactured by Solltest Inc., USA.
Procedure For all the c o n c r e t e t e s t s , the c o n s t i t u e n t s In the control mix has the following p r o p o r tions:
Cement: W a t e r : 385: 205:
Sand: 625:
10 mm a g g r e g a t e : 395:
20 mm a g g r e g a t e 759
The mix has a compressive s t r e n g t h (28 days) o f 350 kg/cm 2 and a slump o f 6 0 - 1 2 0 mm. The admixtures, cement, sand, and the a g g r e g a t e s were f i r s t mixed dry, then water was added with continuous mixing and finally, the admixture solution was slowly added. The avallable sand Is zone 3 and the gravel Is single and 20 mm maximum size. Water s u b s t i t u t e d f o r a g g r e gate absorption was 1.7~ o f sand weight, 1.6~ o f 10 mm gravel weight and 1.2~ o f 20 mm gravel weight.
Slump. The slump o f c o n c r e t e (plain and t r e a t e d with admixtures) was determined according t o ASTM C143. In each slump t e s t , the slump conical mold was placed on a metal t r a y and filled with the c o n c r e t e mtx In three equal layers and each layer was given 25 s t r o k e s with the tamping rod. The c o n c r e t e s u r f a c e In the mold was then s t r u c k o f f by a screening and rolling motion o f the tamping rod. The mold was vertically raised carefully, then the slump was measured by determining the vertical d i f f e r e n c e between the top o f the mold and the displaced original c e n t e r o f the t o p s u r f a c e o f the specimen.
(air permeability
test)
(Vicat test)
Strength
Strength 2 3 d not less than 1200 Ib/i N Z 7 d not less than 200 ib/in
Concrete Compressive
3 d not less than 2200 Ib/in 2 3 d not less than 3400 ib/in 2
Mortar Compressive
4820 Ib/in~ 6180 Ib/in
2668 lb/in~ 3890 Ib/in
140 min 3 h 15 min
2950 cm2/g
1.5
3
Min. 0.66 Max. 1.20 Min. 0.66
Max.
Max. 4
Max.
Content
AI203/Fe203
Lime saturation
factor
1.45
0.91
Silica 21.40 Inso]ub]e residue 0.24 A1um~na (A1203) 5.45 Ferric oxide (Fe203) 3.75 Lime (CaO) 14.O5 Magnesia (MgO) 2.O2 Sulphuric anhydride (SO3) 1.96 Loss on ignition 0.74 Undetermined O.41
Analysis
(Type I)
Chemical
Cement
Specification
of Ordinary Portland
Tested Cement
Expansion as received not more than IO mm After 7 days aeration, not more than 5 mm
Soundness
Initial not less than 45 min Final not more than I0 h
Tinm of setting
Average value minimum 2250 cm2/g
Fineness
Specification
Mechanical Tests (according to BS12:17)
Properties
TABLE 2
(%)
~D c~
~r
Oq
O
© p~
Vol. 18, No. 4
517 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORKABILITY
The slump t e s t was made on plain c o n c r e t e , c o n c r e t e t r e a t e d with commercial admixture and c o n c r e t e t r e a t e d with l a b o r a t o r y prepared admixtures. The studies included variation o f admixture dose, v a r i a t i o n o f water r e d u c t i o n and loss o f slump with time.
C o n s i s t e n c y (ASTM C187-79). This determines the amount o f water required to p r e p a r e hydraulic cement p a s t e s f o r testing. The Vicar a p p a r a t u s Is used t o determine the w a t e r / c e m e n t (W/C) r a t i o o f normal c o n s i s t e n c y . It Is measured by the amount o f p e n e t r a t i o n o f a 10 mm diameter rod t o a point 10+1 mm below the original s u r f a c e o f the specimen 30 s a f t e r the rod Is released. S e t t i n g Time (ASTM C191-79). This determines the cement by the Vicat a p p a r a t u s needle. Initial s e t t i n g time is f o u n d mm diameter p e n e t r a t e s the specimen t o a point o f 25 mm o r less. when the 5 turn cap ring diameter leaves no mark when r e s t e d on the
s e t t i n g time o f hydraulic when a Vlcat needle o f 1 Final s e t t i n g time is found s u r f a c e o f the sample.
D e t e r m i n a t i o n o f Flow (ASTM CI09 and C230). This determines flow and how well the cement paste spreads using the flow table. The flow Is the resulting increase in a v e r a g e base diameter o f the p a s t e mass, measured on at least f o u r diameters at a p p r o x i mately equlspaced Intervals, e x p r e s s e d as a p e r c e n t a g e o f the original base diameter. All W/C r a t i o s were the same as in the c o n s i s t e n c y determination. Compressive S t r e n g t h (ASTM C109). This determines the compressive s t r e n g t h o f hydraulic cement mortars using 50 mm cube specimens. Cement mortar specimens are molded and k e p t In 100% humidity in the case o f 24 h curing o r b e f o r e demolding, otherwise specimens are k e p t in s t o r a g e w a t e r f o r curing, at a t e m p e r a t u r e o f 23+2°C, until testing. Mortar c o n t e n t p r o p o r t i o n s are 2.75, 1, and 0.485 (sand,cement,water) r e s p e c t i v e l y . Compressive s t r e n g t h Is measured by an Instron Universal Testing Machine Model 1195. S p l i t t i n g T e n s i l e S t r e n g t h . The splitting tensile s t r e n g t h o f molded c o n c r e t e cylinder was determined according t o ASTM C496. Cylinders 15 cm x 30 cm were molded and c u r e d in water f o r 28 days. The t e s t s were carried o u t on plain c o n c r e t e , c o n c r e t e t r e a t e d with 3~ commercial admixture Melment L - 1 0 , and c o n c r e t e t r e a t e d with 3% prepared admixture. F l e x u r a l S t r e n g t h . The flexural s t r e n g t h o f c o n c r e t e specimens was determined according t o ASTM C293, using simple beams with c e n t e r point loading. The t e s t s were carried o u t on beams 50 cm long, 10 cm wide, and 10 cm deep, with a s u p p o r t span o f 42 cm, cast and cured from plain c o n c r e t e , c o n c r e t e plus 3% commercial Melment L - 1 0 , and c o n c r e t e plus 3~ p r e p a r e d admixtures. Using an Instron Universal t e s t i n g machine Type 1195, the beams were loaded till r u p t u r e o c c u r r e d . The flexural s t r e n g t h (or modulus o f r u p t u r e ) was then c a l culated. Creep. The creep o f molded c o n c r e t e cylinders s u b j e c t e d t o substantial longitudinal compressive loads was determined according t o ASTM C512. Cubes (100 m m x 100 mm x 100 ram) and cylinders (15 c m x 30 cm) o f plain c o n c r e t e and c o n c r e t e t r e a t e d with 3% commercial admixture and with sample 1 were c o n c u r r e n t l y molded and s t o r e d in humid conditions at 23°C f o r 28 days. The compressive s t r e n g t h o f each mix was determined using the cubes. Specimens were loaded in the creep a p p a r a t u s at a s t r e s s level equal t o 30% o f the compressive s t r e n g t h . Strain readings were t a k e n immediately b e f o r e and a f t e r loading and at s e v e r a l time intervals afterwards.
Results
Physical
T e s t i n g o f S u p e r p l a s t i c l z e r s In C e m e n t ,and C o n c r e t e Several samples p r e p a r e d in the l a b o r a t o r y were t e s t e d against samples o f a commercialIX available p r o d u c t , Melment L - 1 0 . The e f f e c t o f the p r o d u c t on m o r t a r and c o n c r e t e mixes was comprehensively e v a l u a t e d . As r e g a r d s m o r t a r mixes, the e f f e c t o f admixture addition on w a t e r r e d u c t i o n and s e t t i n g times was studied, and with r e s p e c t t o c o n c r e t e mixes, the e f f e c t
2.75
4.88
3.50
4.42
4. Ol
3.44
4. O0
Melment L-IO (aged)*
No. 1 (fresh)
No. 1 (aged)**
No. 3 (normal)
No. 4
No. 6
No. 7
30 30 15 30 15 15 15 45 30 O0 45
oo 15 OO OO oo oo OO 30 15 45 30
6.52 26.09 32.09 6.52 21.72 6.52 21.74 32.61 6.52 21.74 32.61
O.215 O.170 O.155 O.215 O.180 O.215 O.180 O.155 O.215 0.180 0.155
3 5 I
1
3O 45 45 3O 30 45
15 30 I0 15 15 30
19.60 28.30 4.35 19.60 28.30 6.50
0.185 O.165 0.220 O.185 O.165 O.215
Final min
3 5
h
OO 3O 15 OO 45
Initial min
O0 O0 45 OO 30
h
O.0 4.35 21.74 30.43 6.50
(z)
Water Reduction
Setting Time
230 O. 220 O. 180 O. 160 O. 215 O.
WaterCement Ratio
0.0 1 3 5 1
(%)
(cp)
-4.36
Dose
Viscosity at 20°C
Neat Melment L-IO (Fresh)
Sample*
Admixture
TABLE 3 Water Reduction andSetting Times for Mortar Mixes Treated with Various Admixtures Prepared Under Different Conditions
Like 3 except pH 4 = 8 t4 = 3 h
Like 4 except pH 4 = 8 instead of 7.
Like 3 plus 2 h of heating at 90°C.
Aged at 60°C for 15 days.
Aged at 60°C for 15 days.
Remarks**
r
Lo
o
E
o
OO
h~
Ii
12
13
17
18
19 20
No.
No.
No.
No.
No.
No. No.
O.180 O.180
3 3
21.74 21.74
21.74
21.74
6.52 21.74 32.61 6.52 21.74 30.43 4 30 21 74 32 61 6 52 21 74 3O 43 6 52 21 74 3O 43 21 74
(~)
Water Reduction
5 4
4
4
3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 4
h
aging
OO 45
45
45
15 30 30 OO O0 30 O0 15 30 15 O0 45 O0 O0 30 15
Initial min
test
5 5
5
5
3 4 5 3 4 5 3 4 5 3 4 6 3 4 5 4
to
15 OO
O0
OO
30 45 45 O0 15 45 30 30 45 30 15 O0 15 15 45 45
3
shelf
life of the
PH4 = 7, t 3 = 90 F/M 3:1 p H 4 = 8, F / M = 3 t~ = 90 F/M = 3:1, pll4 = 90 t~ = 90 F : M = 3:1, t 3 = 60 pH = 7, F / M = 3:1 N a O H used in step 4.
T 4 = IO0 t4 = 3 h
T 4 = 1OO t4 = I h
T 4 = 90 t4 = 3 h
except
Remarks
pH 4 = 9 t4 = 3 h T4 90 t4 = 1 h
Like
represent
Final h min
S e t t i n g Time
(1-20), see Table i. for two w e e k s as an a c c e l e r a t e d
0.180
O.180
0.215 O. 180 0.155 0.215 O. 180 O. 160 O. 220 0.180 0.155 0.215 O. 180 O. 160 0.215 O. 180 0.160 O. 180
WaterCement Ratio
3
3
I 3 5 I 3 5 I 3 5 1 3 5 1 3 5 3
* For more details on the samples ** The samples were stored at 60°C aqueous product.
3.85 4.80
5 .OO
4.56
4 09
3 31
3 41
3 54
I0
No.
4.48
3 50
8
No. 9
No.
Dose (%)
Admixture
Viscosity at 20°C (cp)
3 (cont'd)
Sample**
Table
t~
o
trt ,-t trl
f'3 0 C"I
u~
t~
t'rl
0
>
O
L~
O
Oo
o
520
Vol. 18, No. S.M. Lahalih, et al.
o f admixture addition on flowability and workability (i.e., water reduction, slump and loss of slump) were evaluated. Various e f f e c t s were analyzed in view o f the reaction conditions o f the samples tested. The various laboratory prepared samples are shown In Table 1 along with their r e s p e c t i v e reaction conditions. Effects of Various Reaction Conditions on W a t e r R e d u c t i o n and Setting Time of Mortar Table 3 shows the water reduction and setting times f o r mortar mixes t r e a t e d with v a r i ous admixtures prepared under d i f f e r e n t conditions. A selected sample (Sample 1) was aged at 60°C f o r two weeks with the commercial sample (Melment L - I O ) . Water reduction and setting times were evaluated b e f o r e and a f t e r aging f o r d i f f e r e n t p e r c e n t doses o f the admixtures ranging from 1-5%. The results show that with Me[ment L - I O , there was a huge drop In viscosity upon aging, a slight drop In water reduction capacity and a significant r e t a r d a t i o n o f mortar setting times, especially at high dosage (5%). The laboratory prepared sample, however, showed a much smaller viscosity drop upon aging and a slight Improvement In water reduction and a slight r e t a r d a t i o n In mortar setting time. Table 3 shows no significant e f f e c t from the various r e a c tion conditions on water reduction. For example, the e f f e c t o f the f o u r t h step o f the r e a c tion mechanism Is exemplified in samples 12 and 3. Sample 12 was prepared at a f o u r t h step temperature o f 100°C f o r three hours whereas sample 3 was prepared at a f o u r t h step tempe r a t u r e o f 80°C f o r 1 h, y e t there was no significant change In their e f f e c t on the mortar water reduction or setting time. However, there is a significant e f f e c t on the stability o f these samples from s t o r a g e aging as can be seen from the large viscosity drop upon aging (Table 3). Table 3 also gives the e f f e c t o f formaldehyde to melamine ratio, the pH o f the f o u r t h step, and the reaction time of the third step, as r e p r e s e n t e d by sample nos. 19, 18, 17, 20 and 13. The only e f f e c t observed was the r e t a r d a t i o n o f the setting times o f mortar mixes. Flowablllty of Cement Paste. The flowability o f the cement paste Is determined by a flow table diameter spread. When 3% by weight o f cement admixture Is used, the same flowability ls obtained a f t e r a water reduction o f 19.56% in the case o f Melment L - I O and 21.74% In case o f sample no. 1 (Table 4). This shows that c o n c r e t e t r e a t e d with the l a b o r a t o ry prepared sample has b e t t e r flowability than concrete t r e a t e d with the commercial admixture.
Flowablllty Sample
Neat Melment L-IO No. 1
of
Admixture (%) -3 3
TABLE 4 Admixture Treated W/C R a t i o
0.230 0.185 0.180
Effect of Various Laboratory Prepared Workability" of Concrete Mixes
Cement P a s t e
Water Reduction
(~)
0 19.56 21.74
Superplasticlzers
Flow Table D i a m e t e r (cm) 13.3 13.0 13.1
on t h e
Water Reduction. When superplastlclzers are added to c o n c r e t e they tend to improve Its flow c h a r a c t e r i s t i c s , which are generally r e f e r r e d t o as their "workability". This e f f e c t Is thought t o be due to the ability o f these admixtures t o encapsulate the cement p a r t i t l e s thus forming a microfilm that Is negatively charged because o f sulfonatlon o f these p r o d u c t s . Because o f the negative charge, the particles tend t o disperse more homogeneously, and due to the lubricity o f these p r o d u c t s , the flow characteristics and morphological s t r u c t u r e s are both improved (1). To malntaln a desirable and predeslgned flow characterlstlc, the amount o f water that is normally added to the c o n c r e t e mix has to be reduced to maintain a certain consistency. This consistency is normally r e f e r r e d to as the slump o f concrete. Table 5 shows the e f f e c t o f some selected admixtures doses on water reduction o f concrete
Vol. 18, No. 4
521 POLYMERIZATION, SUPERPLASTICIZERS, CONCRETE, WORKABILITY
mixes t o maintain a slump o f 5 0 ± 5 ram. A commercial sample (Melment L - 1 0 ) was compared with two l a b o r a t o r y p r e p a r e d samples (nos. 2 and 11, Table 1). Sample no. 2 r e p r e s e n t s a normal running cycle and sample no. 11 r e p r e s e n t s the ultimate Optimized cycle t h a t p r o v e d t o be the most stable p r o d u c t under a c c e l e r a t e d aging conditions. The d a t a o f Table 5 are r e p r e s e n t e d graphically In Flgure 1. The data show t h a t l a b o r a t o r y p r e p a r e d samples are more e f f i c i e n t in reducing the amount o f w a t e r required t o o b t a i n the mix slump o f 5 0 ¢ 5 mm. The normal dose o f admixture usually a d o p t e d in practice is between 1 and 2% o f the dry weight o f cement. Table 5 and Figure 1 show t h a t f o r this p e r c e n t a g e , the l a b o r a t o r y prepared samples are s u p e r i o r t o the commercial sample by 31-45~; in their ability t o r e d u c e the amount o f water r e q u i r e d t o o b t a i n the desired slump.
Effect
TABLE 5 A d m i x t u r e Dose on W a t e r R e d u c t i o n o f M a i n t a i n a Slump o f 50±5 mm
of
Water
Concrete
Reduction
Mixes
to
(%)
Sample
Melment L-10 No. 2 No. 11 = % dose of
admixture
1=
2*
3*
4*
5=
9 13 13
19 25 24
29 35 34
36 38 37
38 41 40
b a s e d on d r y
weight
of
cement used
In t h e m i x .
S l u mp a n d F l o w t a b l e o f F l o w i n g C o n c r e t e . The e f f e c t o f admixture dose on the slump o f c o n c r e t e is shown in Table 6 and Figure 2. The samples r e p r e s e n t d i f f e r e n t r e a c t i o n conditions. Comparison o f the results o f the commercial sample (Melment L - 1 0 ) and the s t a n d a r d l a b o r a t o r y prepared sample (no. 2) shows t h a t a 1~ dose o f sample 2 gives the same r e s u l t as a 1.3~ dose o f Melment L - 1 0 . This means t h a t the l a b o r a t o r y prepared sample Is more e f f e c t i v e In Its plasticizing e f f e c t by almost 30%, t o achieve a c o n c r e t e slump o f
Effect
of
TABLE 6 A d m i x t u r e Dose on Slump o f C o n c r e t e w i t h an Slump o f 50±5 mm ( C o n t r o l M i x S l u m p )
Initial
Slump (mm) Sample =*
Melment L-IO No. 2 No. 5 No. 11 No. 14 No. 16 • • dose • = Sample Sample Sample
0.3 =
0,5 =
85
93
87 84 75 87 97
108 100 105 120 110
0.6 =
0.7 =
0.8*
0.9*
1.0"
1.2 =
1.3 =
120
--
125
--
150
183
200
135 135 122 140 120
175 -125 ---
185 145 -155 150
190 -170 ---
200 170 180 185 180
. . . . 187 210 195 215 200 -195 --
o f a d m i x t u r e b a s e d on d r y w e i g h t o f c e m e n t u s e d In t h e m i x . melment L-IO: Commercial sample Melment L-10 2: N o r m a l r u n n i n g c y c l e ( s e e T a b l e 1) 5 : Was p r e p a r e d a c c o r d i n g to patent disclosure with formaldehyde/melamine (F/M) ratio - 4:1 S a m p l e 1 1 : Same as 2 e x c e p t f o r s t e p 4 ( s e e T a b l e 1) S a m p l e 14: Same as 2 e x c e p t f o r F/M - 3 : 1 S a m p l e 16: Same as 5 e x c e p t f o r F/M - 3:1
522
Vo[. S.M. Lahalih,
1,3, .';o. i
e~ al.
40
30
20-
I0
1
i
i
~
i
L
1
~
3
4
)
6
Dose
(%)
FIG.
1
Effect o f a d m i x t u r e d o s e on w a t e r r e d u c t i o n of concrete mixes to maintain a s l u m p o f 50±5 mm. Sample 2 (--Q--) s a m p l e 11 ( - - 0 - - ) and c o m m e r c i a l s a m p l e M e l m e n t L - I O (--A--).
200+5 ram. Figure 2 shows the slump-dose relationship f o r c o n c r e t e t r e a t e d with Melment L - I O and the l a b o r a t o r y p r e p a r e d sample nos. 2,11 and 5. The f i g u r e shows t h a t sample no. 2 is best, followed by 11 and 5 and Melment L - I O in t h a t o r d e r . Sample 5 was prepared according t o a t h r e e - s t e p p a t e n t p r o c e d u r e (8) t h a t is a p r o c e s s with a formaldehyde t o melamine ratio o f 4:1, similar t o sample no. 2; but 2 was p r e p a r e d In a f o u r - s t e p p r o c e s s t h a t we believe is the p r o p e r r e a c t i o n mechanism (Table 1). Similarly, sample 11 was p r e p a r e d according t o our p r o c e d u r e e x c e p t t h a t f u r t h e r r e a c t i o n s were i n t r o d u c e d t o achieve b e t t e r stability. The f o u r s t e p process a d o p t e d gives s u p e r i o r p r o d u c t s t h a t have b e t t e r plasticizing e f f e c t s (Figure 2). Table 7 shows the slump and flow table diameter o f t r e a t e d and u n t r e a t e d c o n c r e t e mixes when a 3% dose o f a commercial Melment L - I O and the one l a b o r a t o r y p r e p a r e d sample No. 1 was used. Both the slump and flow table diameter are higher f o r sample no. 1 than the commercial Melment L - I O e v e n when r e d u c t i o n was higher (i.e., 29% f o r sample no. 1 v e r s u s 28% f o r Melment L - I O ) .
Vol. 18, No. 4
523 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORKABILITY
200 -
180.
160
140
-g E ~. 120
E
100
80-
60-
40
o.'2
o.'4
J.6
0'.8
1.'o
1.'2
1.4
Admixture Dose (%) FIG.
2
Slump-dose relationship for concrete treated with admixtures (initial slump of control m i x Is 50+5 mm), Sample 2 (--t--) and c o m m e r c i a l s a m p l e M e l m e n t L - I O
(--A--). Slump and F l o w T a b l e o f with
Mix Neat 3~ L - I O 3% 1
Water Reduction 0 28 29
(~)
TABLE 7 Concrete Mixes for Treated S a m p l e s L - I O and 1 Slump (mm) 51 40 67
and U n t r e a t e d
Flow Table Diameter (mm) 35 34 40
SIumD L o s s o f F l o w i n g C o n c r e t e . Some o f the c o n c r e t e mixes p r e p a r e d with the d i f f e r e n t admixtures were l e f t t o r e c o v e r and their slump was monitored as a f u n c t i o n o f the elapsed time (Table 8). The experiment was c o n d u c t e d on c o n c r e t e mixes with 200+5 mm slump
524
Vol. 18, No. S.M. Lahalih,
Slump
Loss
of
et al.
TABLE 8 High WorKability Concrete Treated Admixtures Versus Elapsed Time.
with
Various
Slump (mm) Sample
Dose of
Admixture (%) 2 Melment 13 16 9 11
L-IO
1.0 1.3 1.0 1.2 1.2 1.2
Initial
1.5
200 200 200 195 200 205
164 175 175 105 135 170
h
1 h
1.25
97 125 100 80 65 105
---40 37 --
h
1.5
h
63 58 55 --65
E =
\
\
\
\ \
50-
o.~
1~o
1~
Time (h)
FIG. 3 Slump loss of high workability concrete versus tlme for various admixtures. Sample 2 (--e--), sample 13 (--0--), commercial sample Melment L-IO (--&--). S a m p l e 2 a n d 13 u s e d 1% d o s e w h i l e commercial M e l m e n t L - I O u s e d 1.3% d o s e .
1.75
5O 45
h
Vol. 18, No. 4
525 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORkaBILITY
a f t e r d i f f e r e n t doses o f admixtures were added and the slump was measured a f t e r a certain time had elapsed (Table 8 and Figure 3). The results show that a f t e r 1.75 h the slump dropped from 200+5 mm t o the original slump o f 50_+5 mm. This time is essential In the field, and the minimum standard time allowed is 45 rain. The samples t e s t e d exceed the standard time by a f a c t o r o f two. On the o t h e r hand, when a dose o f 3~ o f admixture was added, initial collapse slump was obtained. Loss r a t e o f slump o f mixes with 3~ commercial Melment L - I O and 3~ o f sample no. 1 was measured and It was found that f o r 3% Melment L - l 0, 3.5 h were needed t o g e t 50 mm slump a f t e r the mix was prepared. In the l a b o r a t o r y prepared sample no. 1, when 3~ was used, 4.5 h were needed t o g e t 50 mm slump a f t e r the mix was prepared.
C o m p r e s s i v e S t r e n g t h o f Cement M o r t a r . The compressive s t r e n g t h o f t r e a t e d and u n t r e a t e d mortar samples a f t e r 1, 3, 7 and 28 days o f aging Is shown In Table 5. In all t e s t s , except where Indicated otherwise, the flowability o f the mixes was maintained at the same flow table diameter o f 15.5_+0.5 cm. Compressive s t r e n g t h was increased by the Improved dispersion o f the cement caused by the admixture. Early s t r e n g t h development was also noticeable In l a b o r a t o r y prepared samples compared t o commercial samples. When superplasticlzers are used with no water reduction, i.e., W/C ,, 0.485, however, the high flow mortar still gives comparable compressive s t r e n g t h values. This shows that the improvement In the mortar's flowabllity Is n o t at the expense o f the mortar's compressive strength. Effect o f A d m i x t u r e D o s e on C o m p r e s s i v e S t r e n g t h o f C o n c r e t e . The e f f e c t s o f amount o f admixture dose on the compressive s t r e n g t h o f t r e a t e d c o n c r e t e mixes are shown In Figure 4. Figure 4 shows the e f f e c t o f sample 2 and Melment L - I O on the compressive s t r e n g t h o f c o n c r e t e with the proper water reduction t o maintain a slump o f 50+5
600
500 J=
03
=> ==
o o
400
300 0
L
[
1
2
I 3
A d m i x ~ m D ~ e (% m r dr y weight of cement)
FIG.
4
The e f f e c t o f a d m i x t u r e dose on t h e c o m p r e s s i v e s t r e n g t h o f c o n c r e t e m i x e s a f t e r 28 d a y s o f a g i n g . C o m m e r c i a l Melment L-10 (--,--) and s a m p l e 2 ( - - A - - ) .
526
Vol. S.M.
Lahaligh,
18,
No.
i
et al.
ram, I.e., equal t o that o f the control. As the dose Increases, the compressive strength o f c o n c r e t e also increases. In general, the l a b o r a t o r y prepared samples gave b e t t e r results than the commercial sample. The prepared samples improved the compressive s t r e n g t h by 70% over control whereas the commercial sample improved s t r e n g t h by 50~ when 3% doses were used. The formaldehyde to melamine ratio cloes not a f f e c t the mechanical p r o p e r t i e s significantly.
Comloresslve Strength
Sample
Admixture (%)
Neat Melment L-IO
0 3
No.
3
1
of
TABLE 9 T r e a t e d and U n t r e a t e d Aging Times
W/C r a t i o 0.485 0.420 0.485* 0.420 0.485*
* Complete flow
where flow
at
Different
Average Compressive Strength
( k g / c m 2)
1 day 85.0 171.9 82.2 129.7 105.6 table
diameter
Mortar
3 days
7 days
166.5 245.5 171.6 275.6 201.0
228.0 288.4 231.4 345.0 258.4
> 22.0
28 days 303.0 412.7 283.9 427.5 336.4
cm
600
..........................................................
500
"4"
/ I
A
E "~ 400
¢n 300
E ~ 200
100
!
r
l
t
I
0
1
3
7
28
Age (days) FIG.
5
EffeCt of different reaction t e m p e r a t u r e s In t h e f o u r t h s t e p on t h e c o m p r e s s i v e s t r e n g t h o f w a t e r r e d u c e d c o n c r e t e m i x e s t r e a t e d w i t h 3~ a d m i x t u r e and w i t h a s l u m p o f 50±5 mm. P l a i n ( - - i - - ) , commercial melment L-IO (..~..), sample 2 (--A--) sample 9 (--x--) and s a m p l e 11 ( - - e - - ) .
Vol. 18, No. 4
527 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORKABILITY
Effect o f F o u r t h S t e p R e a c t i o n C o n d i t i o n s on C o m p r e s s i v e S t r e n g t h of Concrete. Samples 2, 9 and 11 were prepared in the l a b o r a t o r y according t o o u r f o u r s t e p process. The r e a c t i o n conditions were Identical f o r all samples e x c e p t f o r the f o u r t h s t e p when the r e a c t i o n t e m p e r a t u r e s f o r samples 2, 9 and 11 were 80°C, 90°C and 100°C, r e s p e c t i v e l y . Figure 5 shows the e f f e c t o f these samples on the compressive s t r e n g t h o f c o n c r e t e when a 3~ dose was added t o c o n c r e t e t o o b t a i n a slump o f 50+5 mm with the p r o p er w a t e r reduction. Melment L - I O and plain c o n c r e t e are shown f o r comparison. The data show t h a t , as the t e m p e r a t u r e o f the f o u r t h step increases, the compressive s t r e n g t h increases. The l a b o r a t o r y prepared samples improve the s t r e n g t h o f plain c o n c r e t e by 70% compared with 50~ f o r Melment L - I O . The e f f e c t o f f o u r t h step conditions on the p r o p e r t i e s o f c o n c r e t e are n o t really v e r y significant. The tremendous e f f e c t o f these variables is on the stability o f the materials d u r ing s t o r a g e . The e f f e c t o f r e a c t i o n conditions on the s t o r a g e stability o f these materials was discussed In g r e a t detail in a p r e v i o u s publication (12) and the e f f e c t o f aging these admixt u r e s on the compressive s t r e n g t h o f c o n c r e t e was also studied (Table 10). It can be seen t h a t compressive s t r e n g t h drops a b o u t 5% when the admixtures are s t o r e d at 60°C f o r two weeks. Polymerization conditions such as the time and t e m p e r a t u r e o f the f o u r t h s t e p o f the r e a c t i o n p r o c e d u r e can be increased t o maximize the stability o f the p r o d u c t s and p r e s e r v e their e f f i c i e n c y as e f f e c t i v e superplasticizers. o f A d m i x t u r e s on O t h e r M e c h a n i c a l P r o p e r t i e s The e f f e c t o f admixtures on splitting tensile s t r e n g t h , flexural s t r e n g t h , modulus were also e v a l u a t e d with the following results. Effect
and elastic
j*
300
250
A
200
/ ,~
15o
100
50
0
I
I
I
I
4
8
12
16
f 20
I 24
I
I
28
32
Strain (mm/mrn) x 10-4
FIG. Stress-strain diagram concrete treated with sample 1 (--A--).
6
of plain concrete (--=--) and o f 3% M e l m e n t L - I O ( - - * - - ) and 3%
528
Vol. S.M.
Effect
Sample
of
Admixture Dose (%)
18,
No.
4
et al.
TABLE 10 Aglng Superplastlclzers
Water/ Cement Ratio
Plain Sample 1 (fresh) Sample 1 (aged)
Lahaligh,
Water Reduction (%)
on t h e i r
Efficiency
Average Compressive Strength o f Aged C o n c r e t e ( k g / c m 2) 1 d
3 d
7 d
28 d
0.54 0.38
0.0 3.0
0.0 29.0
126.0 258.0
239 403
268 467
357 565
0.38
3.0
29.0
129.7
328
389
534
Melment L-10 (fresh) 0.38 (aged) 0.38
3.0 3.0
28.0 28.0
241.0 150.0
373 350
457 380
531 503
S p l i t t i n g T e n s i l e Strength. The splitting tensile s t r e n g t h o f molded concrete cylinders was determined f o r u n t r e a t e d c o n c r e t e and f o r c o n c r e t e t r e a t e d with 3% o f admixtures. Sample 1, a prepared sample, was t e s t e d against a commercial sample (Melment L - l 0). The results are shown in Table 2. TABLE 11 Splitting Tensile Strength of Treated with Admixtures After Splitting Sample Plain Concrete C o n c r e t e + 3% L - 1 0 C o n c r e t e + 3% Sample 1
Concrete Samples 28 Days o f A g i n g Tensile Strength ( k g / c m 2) 30.58 38.68 37.06
Tensile s t r e n g t h Increased 20-25% with the addition o f admixture.
Flexural
Strength.
was also determined. L - I O were used.
The e f f e c t o f admixtures on the flexural s t r e n g t h o f concrete Table 3 shows the results obtained when 3% o f sample 1 and o f Melment
TABLE 12 Flexural Strength of Concrete Treated with A d m i x t u r e a f t e r 28 Days o f A g i n g
Sample Plain Concrete C o n c r e t e + 3% L - 1 0 C o n c r e t e + 3% Sample 1
Flexural Strength ( k g / c m 2) 52.12 54.86 56.37
Flexural s t r e n g t h Increased 5-8% when 3% o f an admixture was used.
Vol. 18, No. 4
529 POLYMERIZATION, SUPERPLASTICIZERS, CONCRETE, WORKABILITY
Elastic Modulus. Figure 6 is a s t r e s s - s t r a i n diagram o f plain c o n c r e t e and o f c o n c r e t e t r e a t e d with 3% o f sample 1 and 3~ o f Melment L - I O . The curves are highly non-linear, as expected. The tangent t o these curves give a tangent elastic modulus o f 1.88 x 105 k g / cm2 f o r both sample 1 and sample Melment L - I O compared with 1.67 x 105 f o r the untreated c o n c r e t e . The elastic modulus Improved by 1 2 - 1 3 ~ when 3~ o f admixture was used. Effect" of Admixture on C r e e p D e f o r m a t i o n of Concrete. Concrete, like o t h e r s t r u c t u r a l materials, creeps under load. The long term deformation o f c o n c r e t e under load Is a result o f the s t r u c t u r a l rearrangement o f the c o n c r e t e matrix. The internal morphological rearrangement Is a f f e c t e d by the degree o f homogeneity o f the original mix as well as such f a c t o r s as Intensity o f loading, temperature and hLu~ldity o f the environment among other things. Creep o f c o n c r e t e has been studied extensively and has been addressed fully In the l i t e r a t u r e , but the e f f e c t o f admixture addition t o c o n c r e t e on Its creep p r o p e r t i e s has not been extensively r e p o r t e d (1). More specifically, the e f f e c t o f reaction conditions of melamine-based superplasticlzers on the long term behavior o f c o n c r e t e has not been r e p o r t ed. Samples f o r a creep study were prepared from c o n c r e t e mixes t r e a t e d with prepared sample 1 and a commercially available sample Melment L - I O . The t e s t was carried o u t at room temperature In air. The s t r e s s e s applied were approximately o n e - t h i r d o f the ultimate compressive s t r e n g t h o f the t r e a t e d and u n t r e a t e d c o n c r e t e according t o the ASTM-C512 s t a n dard. Figure 7 shows the creep deformation o f loaded c o n c r e t e samples when 3% o f admixture is added. A f t e r one year o f c o n c r e t e creep, the deformation o f the t r e a t e d samples is less than that o f the control by 30%. The creep deformation o f samples t r e a t e d with the prepared sample 1 Is less than o f those t r e a t e d with Melment L - I O . For Infinitesimal deformation, the creep modulus can be calculated from Hook's law in which the modulus Is the ratio of s t r e s s to strain. From Figure 7, the creep modulus a f t e r
0.6
0.5 .°.°~°..._.°..-
......
-)~
.°.°°°~°°
0.4 E ~°.)~.o ° ° o
0.3
0.2
0.1
0.0
q
T
I
I
I
I
2
4
6
8
10
12
1 14
Time (months) FIG.
7
E f f e c t o f a d m i x t u r e a t 3% dose on c r e e p o f l o a d e d c o n c r e t e in a i r a t room t e m p e r a t u r e . Initial stress p l a i n c o n c r e t e = 83 k g / c m 2 and f o r a d m i x t u r e t r e a t e d c o n c r e t e = 127 kg/cm z. P l a i n ( m m ~ ) , commercial Melment L-IO (--~--) and s a m p l e 1 ( h A - - ) .
for
530
Vol. 18, No. 4 S.M. Lahaligh,
et al.
one year o f creep is 4.54 x 104 kg/cm 2 f o r the control, 8.30 x 104 kg/cm 2 f o r samples t r e a t e d with the commercially available Melment L - 1 0 , and 9.55 x 104 kg/cm 2 f o r samples t r e a t e d with prepared sample 1. A comparison o f the creep modulus data with the elastic modulus data r e p o r t e d earlier shows that the modulus o f the u n t r e a t e d c o n c r e t e or control dropped 72.8~ that o f c o n c r e t e treated with the commercial sample dropped 55.9%, and that of c o n c r e t e t r e a t e d with the prepared sample 1 dropped only 49.2~. The creep modulus r e p r e sents c o n c r e t e proPerties upon long term aging. More significantly, the creep modulus of c o n c r e t e t r e a t e d with admixtures a f t e r one year o f continuous deformation Is almost twice as much as the creep modulus f o r the u n t r e a t e d concrete o r the control sample. Discussion
The Increase in flowability o f c o n c r e t e with the addition o f superplastlclzers Is a result o f the dispersion ability these additives can Impart on the Inorganic materials. In their study o f the e f f e c t s o f superplasticlzers on viscosity and yield s t r e s s o f cement mixes, Asaga et al. (10) s u g g e s t e d that the theological p r o p e r t y changes In cement slurries are the result of changes In the dispersion s t r u c t u r e o f the particles In the slurries. They argued that as the suPerplastlclzer Is adsorbed on the surface o f the cement and Its hydrate, the zeta potential becomes s t r o n g l y negative, and the partlcle dispersion Is enhanced, resulting In a decrease in both viscosity and yield stress. The same o b s e r v a t i o n was found by us In an earlier study (11). We found that yield s t r e s s diminishes and viscosity decreases t o a low plateau as the dose o f the superplasticizer increases. Beyond a certain dose o f the superplastlclzer, however, the f u r t h e r drop In viscosity is not significant, which Indicates that there is a critical dose beyond which a f u r t h e r addition o f superplasticlzer will not significantly help the flow. This Is also obvious from the water reduction curve shown In Figure 1 as a function o f the superplastlclzer dose. The figure also shows that as the dose Increases the reduction In the amount o f water needed to maintain a predetermined flow parameter (I.e., slump) reaches a plateau. This again strongly suggest that the hypothesis o f adsorption o f the superplastlclzer by the cement particles and the repulsion and reordering In the mix matrix due t o the negative charges Is c o r r e c t . Because adsorption o f superplastlclzer by the cement particles g e t s p e r f e c t e d o r s a t u r a t e d when a certain dose (I.e., weight o f superplastlclzer t o dry weight of cement r a t i o ) Is applied, any additional dosage o f the superplastlclzer will have no significant e f f e c t on the dispersion and workability o f concrete. In t h e o r y , a water/cement ratio o f about 0.27 Is adequate f o r complete hydration o f the cement In any c o n c r e t e mix. Any additional water would tend t o reduce the potential compressive s t r e n g t h (1). Therefore, any attempt to reduce the amount o f water added to concrete mixes while maintaining the same degree o f flowability, among o t h e r things, would increase the compressive s t r e n g t h and the load carrying capacity o f c o n c r e t e s t r u c t u r e s . It was shown In the l i t e r a t u r e and in this paper that superplastlclzers based on melamine are e f f e c t i v e In Improving the compressive strength of c o n c r e t e because they can reduce the amount o f water needed t o a f f e c t a specified flow. More specifically, this paper showed that the specific r e a c t i o n conditions In the preparation o f these admixtures play a significant role. We believe that the reaction conditions are responsible f o r the p r o d u c t ' s final molecular weight and molecular weight distribution. The final rearrangement o f the polymer molecular chains and their Interrelationship with each o t h e r In the polymer matrix are a f f e c t e d by the preparation conditions (12). This is so significant because the performance o r Interaction of these polymers with cement and c o n c r e t e particles Is contingent on the polymer chain length, the degree o f cross linking, and the intensity o f temporary and permanent entangled Iocls o f the polymer chain. When these polymers are added to c o n c r e t e mixes, they tend to coat the various Inorganic particles. Because o f the negative charges they c a r r y due to sulfonatlon, they tend t o repel each other, resulting in a well dispersed mix. Because o f their lubrlclty and reduction o f s u r f a c e tension (1), they minimize Internal frictional f o r c e s thus Increasing the flow o f c o n c r e t e mixes. We believe that the action of melamine-based superplasticlzers ceases a f t e r the Initial dispersion and a f t e r hydration is completed. Therefore, the s t r u c t u r a l matrix resulting Is not only hydrated with less water but is more homogeneous. Therefore, the reduction In water
Vol. 18, No. 4
531 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORKABILITY
needed f o r hydration (lower water/cement ratio) and the Improved perfected morphology of the concrete matrix are responsible for improvements in concrete mechanical properties and in its long term performance, for example, creep. But water reduction and dispersion are strongly affected by the Interaction of concrete and the polymer. The polymer Is being affected by the different reaction conditions imposed during Its preparation. The significance of this study Is that It shows that, with the proper selection of reaction condltlons In the preparation of polymeric additives, one could make significant savings in materials used and better designs can be realized for the same cost. Acknowledgments
This research was supported in part by a grant from the Kuwait Foundation for the Advancement of Sciences (KFAS) under grant number 8 4 - 1 2 - 0 2 and by Kuwait Melamine Industries Company. This Is publication no. KISR 2333, Kuwait Institute for Scientific Research, Kuwait. References
1.
2. 3. 4. 5.
6.
7.
8.
9.
10. 11. 12. 13.
Joint Working Party, Superplasticizers In concrete, Cement Admixtures Assn. and the Cement and Concrete Assn., Wexham Springs, UK (1978). M.R. Rlxom, Chemical Admixtures for Concrete, p. 52-85, Halsted Press, London (1978). V.M. Malhotra, Superplastlcizers In concrete, American Concrete Inst., Publlcatlon SP-62, Detroit, Michigan, USA (1979). V~. Malhotra, Developments In the use of superplasticizers. American Concrete Inst., Publication SP-68, Detrolt, Michigan, USA (1981). M. Collepardl, M. Corradl and M. Valente, Influence of polymerization of sulfonated naphthalene condensate and Its interaction with cement, American Concrete Inst., Publication SP-68, Detroit, Michigan, USA (1981). S.M. Lahallh and M. AbsI-Halabl. A process for the synthesis of highly stable sulfonated melamine-formaldehyde condensates as superplastlclzing admixtures In concrete. U.S. Patent No. 4,677,159 (1987). M. AbsI-Halabl, S.M. Lahallh and T. AI-Khalid, J. of Polymer Scl., 33, 2975-1984 (1987). A. Algnesberger, P. Bornmann, H.G. Resenbaur and H. Thelsstg. Process of preparing aqueous solutions of melamine-formaldehyde condensation products having anionic sulfgroups. U.S. Patent No. 3,985,696 (1976). G.E. Sheldrlck, Low-salt containing aqueous solutions of melamine-formaldehyde resin. U.S, Patent No. 4,444,945 (1984). K. Asaga and D.M. Roy. Cement and Concrete Research, 10, 287 (1980). S.M. Lahalih, M. AbsI-Halabl and K.F. Shuhalbar, J.Polymer Sci., 33, 2997-3004 (1987). S.M. Lahalih and M. AbsI-Halabi, J. of Polymer Scl., 33, 3005-3017 (1987). P.J. Flory. Principles of polymer chemistry, Cornell University Press, Ithaca (1975).
E F F E C T OF P O L Y M E R I Z A T I O N C O N D I T I O N S OF S U L F O N A T E D - M E L A M I N E FORMALDEHYDE S U P E R P L A S T I C I Z E R S CONCRETE
ON
Shawqul M. L a h a l l h , M. A b s I - H a l a b l and A l l M. A l l Kuwait Institute for Scientific R e s e a r c h , P . O . B o x 24885,
13109-Safat-Kuwalt
(Refereed) (Received July 16, 1987; in final form March 30, 1988) ABSTRACT The e f f e c t o f polymerization conditions o f sulfonated-melamlne formaldehyde superplastlcizers on the workability, mechanical p r o p e r t i e s and setting o f concrete and mortar was Investigated. Over twenty s u p e r - plasticizers were prepared according t o a novel procedure. It was found that reaction conditions have a significant e f f e c t on the p r o p e r t i e s o f the superplasticlzers and the interaction between them and concrete. The f o u r - s t e p r e a c t i o n p r o d u c t s gave 30-40% b e t t e r performance than the t h r e e - s t e p process. The f o u r t h step conditions o f time and temperature a f f e c t the stability o f the p r o d u c t s , but have no significant e f f e c t on workability. The e f f e c t o f reaction conditions on the performance of melamine- based superplastictzers Is discussed In terms o f molecular theory.
Introduction
In the past two decades, a new group o f c o n c r e t e admixtures, termed "superplasticizers", was Introduced to the c o n c r e t e industry. They have gained wide acceptance because o f their many advantages. The addition o f superplasticlzers t o c o n c r e t e mixes Improves the concrete's workability and Increases Its compressive strength. The three major types o f superplastlcizing admixtures commercially available are modified Ilgnosulfonates, sulfonated naphthalene-formaldehyde resins, and sulfonated melamine-formaldehyde resins (1). The use o f superplastlclzers In concrete and their Interaction with concrete have been extensively r e p o r t ed by researchers In the field (1,2,3,4). The Influence o f polymerization o f sulfonated naphthalene condensate and Its Interaction with cement was r e p o r t e d by Collepardi et al. (5). However, no studies were r e p o r t e d regarding the Influence o f polymerization conditions o f these admixtures on their superplasticizing efficiency when added t o c o n c r e t e or mortar mixes. The authors were able t o develop a novel f o u r - s t e p process, accepted t o p a t e n t by U.S. Department o f Commerce, Patent and Trademark Office, where significant Improvements In the synthetic superplasticlzers were obtained (6,7) when compared t o superplasticlzers prepared in accordance with the p a t e n t literature (8,9). This paper p r e s e n t s and discusses the results obtained on the e f f e c t o f various reaction conditions In the preparation o f s u l f o n a t e d melamine formaldehyde resins and the influence they have on c o n c r e t e workability and mechanical p r o p e r t i e s when they are added to the concrete.
513
4.0 4.0
4.0 4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
3.0
3.0 3.0
3.0 3.0
3.0
3.0
3.0
I 2
3 4
5
6
7
8
9
10
II
12
13
14 15
16 ]7
]8
19
20
11.35
11.35
11.35
II.35 II.35
11.35 11.35
11.35
11.35
11.35
11.35
11.35
11.35
11.35
11.35
11.35
11.35 11.35
11.35 11.35
pHI
M = melamine,
0.5
0.5
0.5
0.5 0.5
0.5 0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5 0.5
0.5 0.5
S/M+U
* F = formaldehyde,
F/M+U
Sample No.
U = urea.
50
50
50
75 50
50 55
50
50
50
50
50
50
50
50
75
50 50
45 50
.
11.35
11.35
I1.35
.
.
80
80
80
. 80
80 80
80
80
80
80
80
80
80
80
.
.
.
t2
60
60
60
60
60 60
60
60
60
60
60
60
60
60
60 60
60 60
(min)
3.5
3.5
3.5
3.5 3.5
3.5 3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5 "%.5
3.5 3.5
PH3
55
55
55
55 55
50 55
50
60
60
60
60
60
60
60
55
55 55
55 55
(°0
T3
t3
7.0
7.0
9.0
8.0 8.0
7.O 7.0
7.0
7.0
7.0
7.0
7.0
9.0
8.0
8.0
7.0
7.O 7.0
7.0 7.0
PH4
80
80
80
80 80
80 80
80
]OO
iOO
90
90
80
80
80
80
80 80
80 80
(°C)
T4
60
60
60
60 60
60 60
60
180
60
180
60
60
60
60
60
60 60
60 60
(min)
t4
Step 4 H i g h pH c o n d e n s a t i o n
Conditions.
4.82
3.58
5.01
3.86 4.56
4.15 3.87
4.09
3.31
3.41
3.54
3.50
4.48
4.00
4.00
5.60
4.42 4.O1
4.34 4.29
(cP)
Viscosity a t 20°C
temperature and time of reaction.
90
60
90
70 90
90 70
90
ii0
ii0
llO
llO
iiO
ii0
110
105
90 90
90 90
(min)
Step 3 Low pH c o n d e n s a t i o n
** pH, T and t refer the alkalinity,
. . . 11.35
11.35 11.35
11.35
I1.35
11.35
11.35
11.35
11.35
11.35
11.35
.
80 80
80 80
(°C)
T2
Step 2 Sulfonation
11.35 11.35
.
TABLE1 for Testing with Hortar and Concrete and their Reaction
11.35 11.35
PH2
S = sulfite;
15
15
15
30 15
15 15
15
15
15
15
15
15
15
15
30
15 15
15 15
tI
(n/n)
TI
(°c)
Step 1"* Hydroxymethylation
Samples Selected
lab
the
)atetxt
(30
O
Same as 18 except NaOH used in step 4.
~c-
O
pitt,. Same a s 13 e x c e p t t 3•
m
CD ct
D"
m me m
oD
PH 4 • Same as 12 except
Patent procedure. Same as 12 except
S4me a s ~3 e x c e p t VIM r a t i o . Same a s 13. Same a s 13 e x c e p t T I , T 3 and t .
Same as 2 except T and t .
Sa4me a s 2 except T 4
except T 4 Same as 2 e x c e p t T and t 4
pH 4 and t Same a s 24
pll4 and t 4 Same as 2 e x c e p t
procedure Same a s 2 e x c e p t pH 4 . Same a s 2 e x c e p t
except
Sample a s 2 plus aging at 90°C f o r two h. Same a s 2
Standard sample.
Remarks
&'-
Vol. 18, No. 4
515 POLYMERIZATION, SUPERPLASTICIZERS, CONCRETE, WORKABILITY
Exper" Imental
Method
Materials The sulfonated-melamine formaldehyde was synthesized according t o a f o u r - s t e p process that was developed In the author's l a b o r a t o r y (6,7). The f o u r steps are: (a) hydroxymethylation (the addition reaction between melamine and formaldehyde), (b) sulfonatlon (the product o f step (a) Is sulfonated), (c) low pH condensation (the p r o d u c t o f step (b) Is polymerlzed), and (d) high pH rearrangement (molecules rearranged t o give a more stable product). In each o f the f o u r steps, time, temperature and pH were varied to develop an optimum product. Sample nos. 1 - 2 0 are shown In Table 1 with their reaction conditions. Commercial sulphonated melamine superplastlclzer was obtained In powder form. The commercial superplasticlzer, manufactured by Suddeutsche K a l k s t i c k s t o f f - W e r k e Aktiengesellschaft (SKW), Germany, Is labeled Melment F - I O in the powder form and Meiment L - I O In the liquid form o f 20% solid content. Ordinary Portland cement (Type I) was used In this study. cement are shown In Table 2.
Detailed analyses o f
Sand with standard specifications (ASTM C - l O g ) was used f o r this study. water was used In the mixes and in the melamine solution.
the
Filtered tap
Equl/~nent Standard equipment, rectangle multiflow mixers models 2228 CL and 2283 manufactured by Edward Benton Co. Ltd., England, was used f o r the d i f f e r e n t t e s t s . Consistency was measured by a Vicat apparatus manufactured by Soiltest Inc., USA, according t o ASTM C-187 standard. Setting times were measured using the same Vlcat appar a t u s except that a d i f f e r e n t needle size was used. Flow p r o p e r t i e s o r spread was measured using a standard flow table as specified In ASTM C87. The flow table Is manufactured by Soilt e s t Inc., USA. Finally creep was measured by Creep Apparatus Model CT-180, manufactured by Solltest Inc., USA.
Procedure For all the c o n c r e t e t e s t s , the c o n s t i t u e n t s In the control mix has the following p r o p o r tions:
Cement: W a t e r : 385: 205:
Sand: 625:
10 mm a g g r e g a t e : 395:
20 mm a g g r e g a t e 759
The mix has a compressive s t r e n g t h (28 days) o f 350 kg/cm 2 and a slump o f 6 0 - 1 2 0 mm. The admixtures, cement, sand, and the a g g r e g a t e s were f i r s t mixed dry, then water was added with continuous mixing and finally, the admixture solution was slowly added. The avallable sand Is zone 3 and the gravel Is single and 20 mm maximum size. Water s u b s t i t u t e d f o r a g g r e gate absorption was 1.7~ o f sand weight, 1.6~ o f 10 mm gravel weight and 1.2~ o f 20 mm gravel weight.
Slump. The slump o f c o n c r e t e (plain and t r e a t e d with admixtures) was determined according t o ASTM C143. In each slump t e s t , the slump conical mold was placed on a metal t r a y and filled with the c o n c r e t e mtx In three equal layers and each layer was given 25 s t r o k e s with the tamping rod. The c o n c r e t e s u r f a c e In the mold was then s t r u c k o f f by a screening and rolling motion o f the tamping rod. The mold was vertically raised carefully, then the slump was measured by determining the vertical d i f f e r e n c e between the top o f the mold and the displaced original c e n t e r o f the t o p s u r f a c e o f the specimen.
(air permeability
test)
(Vicat test)
Strength
Strength 2 3 d not less than 1200 Ib/i N Z 7 d not less than 200 ib/in
Concrete Compressive
3 d not less than 2200 Ib/in 2 3 d not less than 3400 ib/in 2
Mortar Compressive
4820 Ib/in~ 6180 Ib/in
2668 lb/in~ 3890 Ib/in
140 min 3 h 15 min
2950 cm2/g
1.5
3
Min. 0.66 Max. 1.20 Min. 0.66
Max.
Max. 4
Max.
Content
AI203/Fe203
Lime saturation
factor
1.45
0.91
Silica 21.40 Inso]ub]e residue 0.24 A1um~na (A1203) 5.45 Ferric oxide (Fe203) 3.75 Lime (CaO) 14.O5 Magnesia (MgO) 2.O2 Sulphuric anhydride (SO3) 1.96 Loss on ignition 0.74 Undetermined O.41
Analysis
(Type I)
Chemical
Cement
Specification
of Ordinary Portland
Tested Cement
Expansion as received not more than IO mm After 7 days aeration, not more than 5 mm
Soundness
Initial not less than 45 min Final not more than I0 h
Tinm of setting
Average value minimum 2250 cm2/g
Fineness
Specification
Mechanical Tests (according to BS12:17)
Properties
TABLE 2
(%)
~D c~
~r
Oq
O
© p~
Vol. 18, No. 4
517 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORKABILITY
The slump t e s t was made on plain c o n c r e t e , c o n c r e t e t r e a t e d with commercial admixture and c o n c r e t e t r e a t e d with l a b o r a t o r y prepared admixtures. The studies included variation o f admixture dose, v a r i a t i o n o f water r e d u c t i o n and loss o f slump with time.
C o n s i s t e n c y (ASTM C187-79). This determines the amount o f water required to p r e p a r e hydraulic cement p a s t e s f o r testing. The Vicar a p p a r a t u s Is used t o determine the w a t e r / c e m e n t (W/C) r a t i o o f normal c o n s i s t e n c y . It Is measured by the amount o f p e n e t r a t i o n o f a 10 mm diameter rod t o a point 10+1 mm below the original s u r f a c e o f the specimen 30 s a f t e r the rod Is released. S e t t i n g Time (ASTM C191-79). This determines the cement by the Vicat a p p a r a t u s needle. Initial s e t t i n g time is f o u n d mm diameter p e n e t r a t e s the specimen t o a point o f 25 mm o r less. when the 5 turn cap ring diameter leaves no mark when r e s t e d on the
s e t t i n g time o f hydraulic when a Vlcat needle o f 1 Final s e t t i n g time is found s u r f a c e o f the sample.
D e t e r m i n a t i o n o f Flow (ASTM CI09 and C230). This determines flow and how well the cement paste spreads using the flow table. The flow Is the resulting increase in a v e r a g e base diameter o f the p a s t e mass, measured on at least f o u r diameters at a p p r o x i mately equlspaced Intervals, e x p r e s s e d as a p e r c e n t a g e o f the original base diameter. All W/C r a t i o s were the same as in the c o n s i s t e n c y determination. Compressive S t r e n g t h (ASTM C109). This determines the compressive s t r e n g t h o f hydraulic cement mortars using 50 mm cube specimens. Cement mortar specimens are molded and k e p t In 100% humidity in the case o f 24 h curing o r b e f o r e demolding, otherwise specimens are k e p t in s t o r a g e w a t e r f o r curing, at a t e m p e r a t u r e o f 23+2°C, until testing. Mortar c o n t e n t p r o p o r t i o n s are 2.75, 1, and 0.485 (sand,cement,water) r e s p e c t i v e l y . Compressive s t r e n g t h Is measured by an Instron Universal Testing Machine Model 1195. S p l i t t i n g T e n s i l e S t r e n g t h . The splitting tensile s t r e n g t h o f molded c o n c r e t e cylinder was determined according t o ASTM C496. Cylinders 15 cm x 30 cm were molded and c u r e d in water f o r 28 days. The t e s t s were carried o u t on plain c o n c r e t e , c o n c r e t e t r e a t e d with 3~ commercial admixture Melment L - 1 0 , and c o n c r e t e t r e a t e d with 3% prepared admixture. F l e x u r a l S t r e n g t h . The flexural s t r e n g t h o f c o n c r e t e specimens was determined according t o ASTM C293, using simple beams with c e n t e r point loading. The t e s t s were carried o u t on beams 50 cm long, 10 cm wide, and 10 cm deep, with a s u p p o r t span o f 42 cm, cast and cured from plain c o n c r e t e , c o n c r e t e plus 3% commercial Melment L - 1 0 , and c o n c r e t e plus 3~ p r e p a r e d admixtures. Using an Instron Universal t e s t i n g machine Type 1195, the beams were loaded till r u p t u r e o c c u r r e d . The flexural s t r e n g t h (or modulus o f r u p t u r e ) was then c a l culated. Creep. The creep o f molded c o n c r e t e cylinders s u b j e c t e d t o substantial longitudinal compressive loads was determined according t o ASTM C512. Cubes (100 m m x 100 mm x 100 ram) and cylinders (15 c m x 30 cm) o f plain c o n c r e t e and c o n c r e t e t r e a t e d with 3% commercial admixture and with sample 1 were c o n c u r r e n t l y molded and s t o r e d in humid conditions at 23°C f o r 28 days. The compressive s t r e n g t h o f each mix was determined using the cubes. Specimens were loaded in the creep a p p a r a t u s at a s t r e s s level equal t o 30% o f the compressive s t r e n g t h . Strain readings were t a k e n immediately b e f o r e and a f t e r loading and at s e v e r a l time intervals afterwards.
Results
Physical
T e s t i n g o f S u p e r p l a s t i c l z e r s In C e m e n t ,and C o n c r e t e Several samples p r e p a r e d in the l a b o r a t o r y were t e s t e d against samples o f a commercialIX available p r o d u c t , Melment L - 1 0 . The e f f e c t o f the p r o d u c t on m o r t a r and c o n c r e t e mixes was comprehensively e v a l u a t e d . As r e g a r d s m o r t a r mixes, the e f f e c t o f admixture addition on w a t e r r e d u c t i o n and s e t t i n g times was studied, and with r e s p e c t t o c o n c r e t e mixes, the e f f e c t
2.75
4.88
3.50
4.42
4. Ol
3.44
4. O0
Melment L-IO (aged)*
No. 1 (fresh)
No. 1 (aged)**
No. 3 (normal)
No. 4
No. 6
No. 7
30 30 15 30 15 15 15 45 30 O0 45
oo 15 OO OO oo oo OO 30 15 45 30
6.52 26.09 32.09 6.52 21.72 6.52 21.74 32.61 6.52 21.74 32.61
O.215 O.170 O.155 O.215 O.180 O.215 O.180 O.155 O.215 0.180 0.155
3 5 I
1
3O 45 45 3O 30 45
15 30 I0 15 15 30
19.60 28.30 4.35 19.60 28.30 6.50
0.185 O.165 0.220 O.185 O.165 O.215
Final min
3 5
h
OO 3O 15 OO 45
Initial min
O0 O0 45 OO 30
h
O.0 4.35 21.74 30.43 6.50
(z)
Water Reduction
Setting Time
230 O. 220 O. 180 O. 160 O. 215 O.
WaterCement Ratio
0.0 1 3 5 1
(%)
(cp)
-4.36
Dose
Viscosity at 20°C
Neat Melment L-IO (Fresh)
Sample*
Admixture
TABLE 3 Water Reduction andSetting Times for Mortar Mixes Treated with Various Admixtures Prepared Under Different Conditions
Like 3 except pH 4 = 8 t4 = 3 h
Like 4 except pH 4 = 8 instead of 7.
Like 3 plus 2 h of heating at 90°C.
Aged at 60°C for 15 days.
Aged at 60°C for 15 days.
Remarks**
r
Lo
o
E
o
OO
h~
Ii
12
13
17
18
19 20
No.
No.
No.
No.
No.
No. No.
O.180 O.180
3 3
21.74 21.74
21.74
21.74
6.52 21.74 32.61 6.52 21.74 30.43 4 30 21 74 32 61 6 52 21 74 3O 43 6 52 21 74 3O 43 21 74
(~)
Water Reduction
5 4
4
4
3 4 5 3 4 5 3 4 5 3 4 5 3 4 5 4
h
aging
OO 45
45
45
15 30 30 OO O0 30 O0 15 30 15 O0 45 O0 O0 30 15
Initial min
test
5 5
5
5
3 4 5 3 4 5 3 4 5 3 4 6 3 4 5 4
to
15 OO
O0
OO
30 45 45 O0 15 45 30 30 45 30 15 O0 15 15 45 45
3
shelf
life of the
PH4 = 7, t 3 = 90 F/M 3:1 p H 4 = 8, F / M = 3 t~ = 90 F/M = 3:1, pll4 = 90 t~ = 90 F : M = 3:1, t 3 = 60 pH = 7, F / M = 3:1 N a O H used in step 4.
T 4 = IO0 t4 = 3 h
T 4 = 1OO t4 = I h
T 4 = 90 t4 = 3 h
except
Remarks
pH 4 = 9 t4 = 3 h T4 90 t4 = 1 h
Like
represent
Final h min
S e t t i n g Time
(1-20), see Table i. for two w e e k s as an a c c e l e r a t e d
0.180
O.180
0.215 O. 180 0.155 0.215 O. 180 O. 160 O. 220 0.180 0.155 0.215 O. 180 O. 160 0.215 O. 180 0.160 O. 180
WaterCement Ratio
3
3
I 3 5 I 3 5 I 3 5 1 3 5 1 3 5 3
* For more details on the samples ** The samples were stored at 60°C aqueous product.
3.85 4.80
5 .OO
4.56
4 09
3 31
3 41
3 54
I0
No.
4.48
3 50
8
No. 9
No.
Dose (%)
Admixture
Viscosity at 20°C (cp)
3 (cont'd)
Sample**
Table
t~
o
trt ,-t trl
f'3 0 C"I
u~
t~
t'rl
0
>
O
L~
O
Oo
o
520
Vol. 18, No. S.M. Lahalih, et al.
o f admixture addition on flowability and workability (i.e., water reduction, slump and loss of slump) were evaluated. Various e f f e c t s were analyzed in view o f the reaction conditions o f the samples tested. The various laboratory prepared samples are shown In Table 1 along with their r e s p e c t i v e reaction conditions. Effects of Various Reaction Conditions on W a t e r R e d u c t i o n and Setting Time of Mortar Table 3 shows the water reduction and setting times f o r mortar mixes t r e a t e d with v a r i ous admixtures prepared under d i f f e r e n t conditions. A selected sample (Sample 1) was aged at 60°C f o r two weeks with the commercial sample (Melment L - I O ) . Water reduction and setting times were evaluated b e f o r e and a f t e r aging f o r d i f f e r e n t p e r c e n t doses o f the admixtures ranging from 1-5%. The results show that with Me[ment L - I O , there was a huge drop In viscosity upon aging, a slight drop In water reduction capacity and a significant r e t a r d a t i o n o f mortar setting times, especially at high dosage (5%). The laboratory prepared sample, however, showed a much smaller viscosity drop upon aging and a slight Improvement In water reduction and a slight r e t a r d a t i o n In mortar setting time. Table 3 shows no significant e f f e c t from the various r e a c tion conditions on water reduction. For example, the e f f e c t o f the f o u r t h step o f the r e a c tion mechanism Is exemplified in samples 12 and 3. Sample 12 was prepared at a f o u r t h step temperature o f 100°C f o r three hours whereas sample 3 was prepared at a f o u r t h step tempe r a t u r e o f 80°C f o r 1 h, y e t there was no significant change In their e f f e c t on the mortar water reduction or setting time. However, there is a significant e f f e c t on the stability o f these samples from s t o r a g e aging as can be seen from the large viscosity drop upon aging (Table 3). Table 3 also gives the e f f e c t o f formaldehyde to melamine ratio, the pH o f the f o u r t h step, and the reaction time of the third step, as r e p r e s e n t e d by sample nos. 19, 18, 17, 20 and 13. The only e f f e c t observed was the r e t a r d a t i o n o f the setting times o f mortar mixes. Flowablllty of Cement Paste. The flowability o f the cement paste Is determined by a flow table diameter spread. When 3% by weight o f cement admixture Is used, the same flowability ls obtained a f t e r a water reduction o f 19.56% in the case o f Melment L - I O and 21.74% In case o f sample no. 1 (Table 4). This shows that c o n c r e t e t r e a t e d with the l a b o r a t o ry prepared sample has b e t t e r flowability than concrete t r e a t e d with the commercial admixture.
Flowablllty Sample
Neat Melment L-IO No. 1
of
Admixture (%) -3 3
TABLE 4 Admixture Treated W/C R a t i o
0.230 0.185 0.180
Effect of Various Laboratory Prepared Workability" of Concrete Mixes
Cement P a s t e
Water Reduction
(~)
0 19.56 21.74
Superplasticlzers
Flow Table D i a m e t e r (cm) 13.3 13.0 13.1
on t h e
Water Reduction. When superplastlclzers are added to c o n c r e t e they tend to improve Its flow c h a r a c t e r i s t i c s , which are generally r e f e r r e d t o as their "workability". This e f f e c t Is thought t o be due to the ability o f these admixtures t o encapsulate the cement p a r t i t l e s thus forming a microfilm that Is negatively charged because o f sulfonatlon o f these p r o d u c t s . Because o f the negative charge, the particles tend t o disperse more homogeneously, and due to the lubricity o f these p r o d u c t s , the flow characteristics and morphological s t r u c t u r e s are both improved (1). To malntaln a desirable and predeslgned flow characterlstlc, the amount o f water that is normally added to the c o n c r e t e mix has to be reduced to maintain a certain consistency. This consistency is normally r e f e r r e d to as the slump o f concrete. Table 5 shows the e f f e c t o f some selected admixtures doses on water reduction o f concrete
Vol. 18, No. 4
521 POLYMERIZATION, SUPERPLASTICIZERS, CONCRETE, WORKABILITY
mixes t o maintain a slump o f 5 0 ± 5 ram. A commercial sample (Melment L - 1 0 ) was compared with two l a b o r a t o r y p r e p a r e d samples (nos. 2 and 11, Table 1). Sample no. 2 r e p r e s e n t s a normal running cycle and sample no. 11 r e p r e s e n t s the ultimate Optimized cycle t h a t p r o v e d t o be the most stable p r o d u c t under a c c e l e r a t e d aging conditions. The d a t a o f Table 5 are r e p r e s e n t e d graphically In Flgure 1. The data show t h a t l a b o r a t o r y p r e p a r e d samples are more e f f i c i e n t in reducing the amount o f w a t e r required t o o b t a i n the mix slump o f 5 0 ¢ 5 mm. The normal dose o f admixture usually a d o p t e d in practice is between 1 and 2% o f the dry weight o f cement. Table 5 and Figure 1 show t h a t f o r this p e r c e n t a g e , the l a b o r a t o r y prepared samples are s u p e r i o r t o the commercial sample by 31-45~; in their ability t o r e d u c e the amount o f water r e q u i r e d t o o b t a i n the desired slump.
Effect
TABLE 5 A d m i x t u r e Dose on W a t e r R e d u c t i o n o f M a i n t a i n a Slump o f 50±5 mm
of
Water
Concrete
Reduction
Mixes
to
(%)
Sample
Melment L-10 No. 2 No. 11 = % dose of
admixture
1=
2*
3*
4*
5=
9 13 13
19 25 24
29 35 34
36 38 37
38 41 40
b a s e d on d r y
weight
of
cement used
In t h e m i x .
S l u mp a n d F l o w t a b l e o f F l o w i n g C o n c r e t e . The e f f e c t o f admixture dose on the slump o f c o n c r e t e is shown in Table 6 and Figure 2. The samples r e p r e s e n t d i f f e r e n t r e a c t i o n conditions. Comparison o f the results o f the commercial sample (Melment L - 1 0 ) and the s t a n d a r d l a b o r a t o r y prepared sample (no. 2) shows t h a t a 1~ dose o f sample 2 gives the same r e s u l t as a 1.3~ dose o f Melment L - 1 0 . This means t h a t the l a b o r a t o r y prepared sample Is more e f f e c t i v e In Its plasticizing e f f e c t by almost 30%, t o achieve a c o n c r e t e slump o f
Effect
of
TABLE 6 A d m i x t u r e Dose on Slump o f C o n c r e t e w i t h an Slump o f 50±5 mm ( C o n t r o l M i x S l u m p )
Initial
Slump (mm) Sample =*
Melment L-IO No. 2 No. 5 No. 11 No. 14 No. 16 • • dose • = Sample Sample Sample
0.3 =
0,5 =
85
93
87 84 75 87 97
108 100 105 120 110
0.6 =
0.7 =
0.8*
0.9*
1.0"
1.2 =
1.3 =
120
--
125
--
150
183
200
135 135 122 140 120
175 -125 ---
185 145 -155 150
190 -170 ---
200 170 180 185 180
. . . . 187 210 195 215 200 -195 --
o f a d m i x t u r e b a s e d on d r y w e i g h t o f c e m e n t u s e d In t h e m i x . melment L-IO: Commercial sample Melment L-10 2: N o r m a l r u n n i n g c y c l e ( s e e T a b l e 1) 5 : Was p r e p a r e d a c c o r d i n g to patent disclosure with formaldehyde/melamine (F/M) ratio - 4:1 S a m p l e 1 1 : Same as 2 e x c e p t f o r s t e p 4 ( s e e T a b l e 1) S a m p l e 14: Same as 2 e x c e p t f o r F/M - 3 : 1 S a m p l e 16: Same as 5 e x c e p t f o r F/M - 3:1
522
Vo[. S.M. Lahalih,
1,3, .';o. i
e~ al.
40
30
20-
I0
1
i
i
~
i
L
1
~
3
4
)
6
Dose
(%)
FIG.
1
Effect o f a d m i x t u r e d o s e on w a t e r r e d u c t i o n of concrete mixes to maintain a s l u m p o f 50±5 mm. Sample 2 (--Q--) s a m p l e 11 ( - - 0 - - ) and c o m m e r c i a l s a m p l e M e l m e n t L - I O (--A--).
200+5 ram. Figure 2 shows the slump-dose relationship f o r c o n c r e t e t r e a t e d with Melment L - I O and the l a b o r a t o r y p r e p a r e d sample nos. 2,11 and 5. The f i g u r e shows t h a t sample no. 2 is best, followed by 11 and 5 and Melment L - I O in t h a t o r d e r . Sample 5 was prepared according t o a t h r e e - s t e p p a t e n t p r o c e d u r e (8) t h a t is a p r o c e s s with a formaldehyde t o melamine ratio o f 4:1, similar t o sample no. 2; but 2 was p r e p a r e d In a f o u r - s t e p p r o c e s s t h a t we believe is the p r o p e r r e a c t i o n mechanism (Table 1). Similarly, sample 11 was p r e p a r e d according t o our p r o c e d u r e e x c e p t t h a t f u r t h e r r e a c t i o n s were i n t r o d u c e d t o achieve b e t t e r stability. The f o u r s t e p process a d o p t e d gives s u p e r i o r p r o d u c t s t h a t have b e t t e r plasticizing e f f e c t s (Figure 2). Table 7 shows the slump and flow table diameter o f t r e a t e d and u n t r e a t e d c o n c r e t e mixes when a 3% dose o f a commercial Melment L - I O and the one l a b o r a t o r y p r e p a r e d sample No. 1 was used. Both the slump and flow table diameter are higher f o r sample no. 1 than the commercial Melment L - I O e v e n when r e d u c t i o n was higher (i.e., 29% f o r sample no. 1 v e r s u s 28% f o r Melment L - I O ) .
Vol. 18, No. 4
523 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORKABILITY
200 -
180.
160
140
-g E ~. 120
E
100
80-
60-
40
o.'2
o.'4
J.6
0'.8
1.'o
1.'2
1.4
Admixture Dose (%) FIG.
2
Slump-dose relationship for concrete treated with admixtures (initial slump of control m i x Is 50+5 mm), Sample 2 (--t--) and c o m m e r c i a l s a m p l e M e l m e n t L - I O
(--A--). Slump and F l o w T a b l e o f with
Mix Neat 3~ L - I O 3% 1
Water Reduction 0 28 29
(~)
TABLE 7 Concrete Mixes for Treated S a m p l e s L - I O and 1 Slump (mm) 51 40 67
and U n t r e a t e d
Flow Table Diameter (mm) 35 34 40
SIumD L o s s o f F l o w i n g C o n c r e t e . Some o f the c o n c r e t e mixes p r e p a r e d with the d i f f e r e n t admixtures were l e f t t o r e c o v e r and their slump was monitored as a f u n c t i o n o f the elapsed time (Table 8). The experiment was c o n d u c t e d on c o n c r e t e mixes with 200+5 mm slump
524
Vol. 18, No. S.M. Lahalih,
Slump
Loss
of
et al.
TABLE 8 High WorKability Concrete Treated Admixtures Versus Elapsed Time.
with
Various
Slump (mm) Sample
Dose of
Admixture (%) 2 Melment 13 16 9 11
L-IO
1.0 1.3 1.0 1.2 1.2 1.2
Initial
1.5
200 200 200 195 200 205
164 175 175 105 135 170
h
1 h
1.25
97 125 100 80 65 105
---40 37 --
h
1.5
h
63 58 55 --65
E =
\
\
\
\ \
50-
o.~
1~o
1~
Time (h)
FIG. 3 Slump loss of high workability concrete versus tlme for various admixtures. Sample 2 (--e--), sample 13 (--0--), commercial sample Melment L-IO (--&--). S a m p l e 2 a n d 13 u s e d 1% d o s e w h i l e commercial M e l m e n t L - I O u s e d 1.3% d o s e .
1.75
5O 45
h
Vol. 18, No. 4
525 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORkaBILITY
a f t e r d i f f e r e n t doses o f admixtures were added and the slump was measured a f t e r a certain time had elapsed (Table 8 and Figure 3). The results show that a f t e r 1.75 h the slump dropped from 200+5 mm t o the original slump o f 50_+5 mm. This time is essential In the field, and the minimum standard time allowed is 45 rain. The samples t e s t e d exceed the standard time by a f a c t o r o f two. On the o t h e r hand, when a dose o f 3~ o f admixture was added, initial collapse slump was obtained. Loss r a t e o f slump o f mixes with 3~ commercial Melment L - I O and 3~ o f sample no. 1 was measured and It was found that f o r 3% Melment L - l 0, 3.5 h were needed t o g e t 50 mm slump a f t e r the mix was prepared. In the l a b o r a t o r y prepared sample no. 1, when 3~ was used, 4.5 h were needed t o g e t 50 mm slump a f t e r the mix was prepared.
C o m p r e s s i v e S t r e n g t h o f Cement M o r t a r . The compressive s t r e n g t h o f t r e a t e d and u n t r e a t e d mortar samples a f t e r 1, 3, 7 and 28 days o f aging Is shown In Table 5. In all t e s t s , except where Indicated otherwise, the flowability o f the mixes was maintained at the same flow table diameter o f 15.5_+0.5 cm. Compressive s t r e n g t h was increased by the Improved dispersion o f the cement caused by the admixture. Early s t r e n g t h development was also noticeable In l a b o r a t o r y prepared samples compared t o commercial samples. When superplasticlzers are used with no water reduction, i.e., W/C ,, 0.485, however, the high flow mortar still gives comparable compressive s t r e n g t h values. This shows that the improvement In the mortar's flowabllity Is n o t at the expense o f the mortar's compressive strength. Effect o f A d m i x t u r e D o s e on C o m p r e s s i v e S t r e n g t h o f C o n c r e t e . The e f f e c t s o f amount o f admixture dose on the compressive s t r e n g t h o f t r e a t e d c o n c r e t e mixes are shown In Figure 4. Figure 4 shows the e f f e c t o f sample 2 and Melment L - I O on the compressive s t r e n g t h o f c o n c r e t e with the proper water reduction t o maintain a slump o f 50+5
600
500 J=
03
=> ==
o o
400
300 0
L
[
1
2
I 3
A d m i x ~ m D ~ e (% m r dr y weight of cement)
FIG.
4
The e f f e c t o f a d m i x t u r e dose on t h e c o m p r e s s i v e s t r e n g t h o f c o n c r e t e m i x e s a f t e r 28 d a y s o f a g i n g . C o m m e r c i a l Melment L-10 (--,--) and s a m p l e 2 ( - - A - - ) .
526
Vol. S.M.
Lahaligh,
18,
No.
i
et al.
ram, I.e., equal t o that o f the control. As the dose Increases, the compressive strength o f c o n c r e t e also increases. In general, the l a b o r a t o r y prepared samples gave b e t t e r results than the commercial sample. The prepared samples improved the compressive s t r e n g t h by 70% over control whereas the commercial sample improved s t r e n g t h by 50~ when 3% doses were used. The formaldehyde to melamine ratio cloes not a f f e c t the mechanical p r o p e r t i e s significantly.
Comloresslve Strength
Sample
Admixture (%)
Neat Melment L-IO
0 3
No.
3
1
of
TABLE 9 T r e a t e d and U n t r e a t e d Aging Times
W/C r a t i o 0.485 0.420 0.485* 0.420 0.485*
* Complete flow
where flow
at
Different
Average Compressive Strength
( k g / c m 2)
1 day 85.0 171.9 82.2 129.7 105.6 table
diameter
Mortar
3 days
7 days
166.5 245.5 171.6 275.6 201.0
228.0 288.4 231.4 345.0 258.4
> 22.0
28 days 303.0 412.7 283.9 427.5 336.4
cm
600
..........................................................
500
"4"
/ I
A
E "~ 400
¢n 300
E ~ 200
100
!
r
l
t
I
0
1
3
7
28
Age (days) FIG.
5
EffeCt of different reaction t e m p e r a t u r e s In t h e f o u r t h s t e p on t h e c o m p r e s s i v e s t r e n g t h o f w a t e r r e d u c e d c o n c r e t e m i x e s t r e a t e d w i t h 3~ a d m i x t u r e and w i t h a s l u m p o f 50±5 mm. P l a i n ( - - i - - ) , commercial melment L-IO (..~..), sample 2 (--A--) sample 9 (--x--) and s a m p l e 11 ( - - e - - ) .
Vol. 18, No. 4
527 POLYMERIZATION,
SUPERPLASTICIZERS,
CONCRETE, WORKABILITY
Effect o f F o u r t h S t e p R e a c t i o n C o n d i t i o n s on C o m p r e s s i v e S t r e n g t h of Concrete. Samples 2, 9 and 11 were prepared in the l a b o r a t o r y according t o o u r f o u r s t e p process. The r e a c t i o n conditions were Identical f o r all samples e x c e p t f o r the f o u r t h s t e p when the r e a c t i o n t e m p e r a t u r e s f o r samples 2, 9 and 11 were 80°C, 90°C and 100°C, r e s p e c t i v e l y . Figure 5 shows the e f f e c t o f these samples on the compressive s t r e n g t h o f c o n c r e t e when a 3~ dose was added t o c o n c r e t e t o o b t a i n a slump o f 50+5 mm with the p r o p er w a t e r reduction. Melment L - I O and plain c o n c r e t e are shown f o r comparison. The data show t h a t , as the t e m p e r a t u r e o f the f o u r t h step increases, the compressive s t r e n g t h increases. The l a b o r a t o r y prepared samples improve the s t r e n g t h o f plain c o n c r e t e by 70% compared with 50~ f o r Melment L - I O . The e f f e c t o f f o u r t h step conditions on the p r o p e r t i e s o f c o n c r e t e are n o t really v e r y significant. The tremendous e f f e c t o f these variables is on the stability o f the materials d u r ing s t o r a g e . The e f f e c t o f r e a c t i o n conditions on the s t o r a g e stability o f these materials was discussed In g r e a t detail in a p r e v i o u s publication (12) and the e f f e c t o f aging these admixt u r e s on the compressive s t r e n g t h o f c o n c r e t e was also studied (Table 10). It can be seen t h a t compressive s t r e n g t h drops a b o u t 5% when the admixtures are s t o r e d at 60°C f o r two weeks. Polymerization conditions such as the time and t e m p e r a t u r e o f the f o u r t h s t e p o f the r e a c t i o n p r o c e d u r e can be increased t o maximize the stability o f the p r o d u c t s and p r e s e r v e their e f f i c i e n c y as e f f e c t i v e superplasticizers. o f A d m i x t u r e s on O t h e r M e c h a n i c a l P r o p e r t i e s The e f f e c t o f admixtures on splitting tensile s t r e n g t h , flexural s t r e n g t h , modulus were also e v a l u a t e d with the following results. Effect
and elastic
j*
300
250
A
200
/ ,~
15o
100
50
0
I
I
I
I
4
8
12
16
f 20
I 24
I
I
28
32
Strain (mm/mrn) x 10-4
FIG. Stress-strain diagram concrete treated with sample 1 (--A--).
6
of plain concrete (--=--) and o f 3% M e l m e n t L - I O ( - - * - - ) and 3%
528
Vol. S.M.
Effect
Sample
of
Admixture Dose (%)
18,
No.
4
et al.
TABLE 10 Aglng Superplastlclzers
Water/ Cement Ratio
Plain Sample 1 (fresh) Sample 1 (aged)
Lahaligh,
Water Reduction (%)
on t h e i r
Efficiency
Average Compressive Strength o f Aged C o n c r e t e ( k g / c m 2) 1 d
3 d
7 d
28 d
0.54 0.38
0.0 3.0
0.0 29.0
126.0 258.0
239 403
268 467
357 565
0.38
3.0
29.0
129.7
328
389
534
Melment L-10 (fresh) 0.38 (aged) 0.38
3.0 3.0
28.0 28.0
241.0 150.0
373 350
457 380
531 503
S p l i t t i n g T e n s i l e Strength. The splitting tensile s t r e n g t h o f molded concrete cylinders was determined f o r u n t r e a t e d c o n c r e t e and f o r c o n c r e t e t r e a t e d with 3% o f admixtures. Sample 1, a prepared sample, was t e s t e d against a commercial sample (Melment L - l 0). The results are shown in Table 2. TABLE 11 Splitting Tensile Strength of Treated with Admixtures After Splitting Sample Plain Concrete C o n c r e t e + 3% L - 1 0 C o n c r e t e + 3% Sample 1
Concrete Samples 28 Days o f A g i n g Tensile Strength ( k g / c m 2) 30.58 38.68 37.06
Tensile s t r e n g t h Increased 20-25% with the addition o f admixture.
Flexural
Strength.
was also determined. L - I O were used.
The e f f e c t o f admixtures on the flexural s t r e n g t h o f concrete Table 3 shows the results obtained when 3% o f sample 1 and o f Melment
TABLE 12 Flexural Strength of Concrete Treated with A d m i x t u r e a f t e r 28 Days o f A g i n g
Sample Plain Concrete C o n c r e t e + 3% L - 1 0 C o n c r e t e + 3% Sample 1
Flexural Strength ( k g / c m 2) 52.12 54.86 56.37
Flexural s t r e n g t h Increased 5-8% when 3% o f an admixture was used.
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529 POLYMERIZATION, SUPERPLASTICIZERS, CONCRETE, WORKABILITY
Elastic Modulus. Figure 6 is a s t r e s s - s t r a i n diagram o f plain c o n c r e t e and o f c o n c r e t e t r e a t e d with 3% o f sample 1 and 3~ o f Melment L - I O . The curves are highly non-linear, as expected. The tangent t o these curves give a tangent elastic modulus o f 1.88 x 105 k g / cm2 f o r both sample 1 and sample Melment L - I O compared with 1.67 x 105 f o r the untreated c o n c r e t e . The elastic modulus Improved by 1 2 - 1 3 ~ when 3~ o f admixture was used. Effect" of Admixture on C r e e p D e f o r m a t i o n of Concrete. Concrete, like o t h e r s t r u c t u r a l materials, creeps under load. The long term deformation o f c o n c r e t e under load Is a result o f the s t r u c t u r a l rearrangement o f the c o n c r e t e matrix. The internal morphological rearrangement Is a f f e c t e d by the degree o f homogeneity o f the original mix as well as such f a c t o r s as Intensity o f loading, temperature and hLu~ldity o f the environment among other things. Creep o f c o n c r e t e has been studied extensively and has been addressed fully In the l i t e r a t u r e , but the e f f e c t o f admixture addition t o c o n c r e t e on Its creep p r o p e r t i e s has not been extensively r e p o r t e d (1). More specifically, the e f f e c t o f reaction conditions of melamine-based superplasticlzers on the long term behavior o f c o n c r e t e has not been r e p o r t ed. Samples f o r a creep study were prepared from c o n c r e t e mixes t r e a t e d with prepared sample 1 and a commercially available sample Melment L - I O . The t e s t was carried o u t at room temperature In air. The s t r e s s e s applied were approximately o n e - t h i r d o f the ultimate compressive s t r e n g t h o f the t r e a t e d and u n t r e a t e d c o n c r e t e according t o the ASTM-C512 s t a n dard. Figure 7 shows the creep deformation o f loaded c o n c r e t e samples when 3% o f admixture is added. A f t e r one year o f c o n c r e t e creep, the deformation o f the t r e a t e d samples is less than that o f the control by 30%. The creep deformation o f samples t r e a t e d with the prepared sample 1 Is less than o f those t r e a t e d with Melment L - I O . For Infinitesimal deformation, the creep modulus can be calculated from Hook's law in which the modulus Is the ratio of s t r e s s to strain. From Figure 7, the creep modulus a f t e r
0.6
0.5 .°.°~°..._.°..-
......
-)~
.°.°°°~°°
0.4 E ~°.)~.o ° ° o
0.3
0.2
0.1
0.0
q
T
I
I
I
I
2
4
6
8
10
12
1 14
Time (months) FIG.
7
E f f e c t o f a d m i x t u r e a t 3% dose on c r e e p o f l o a d e d c o n c r e t e in a i r a t room t e m p e r a t u r e . Initial stress p l a i n c o n c r e t e = 83 k g / c m 2 and f o r a d m i x t u r e t r e a t e d c o n c r e t e = 127 kg/cm z. P l a i n ( m m ~ ) , commercial Melment L-IO (--~--) and s a m p l e 1 ( h A - - ) .
for
530
Vol. 18, No. 4 S.M. Lahaligh,
et al.
one year o f creep is 4.54 x 104 kg/cm 2 f o r the control, 8.30 x 104 kg/cm 2 f o r samples t r e a t e d with the commercially available Melment L - 1 0 , and 9.55 x 104 kg/cm 2 f o r samples t r e a t e d with prepared sample 1. A comparison o f the creep modulus data with the elastic modulus data r e p o r t e d earlier shows that the modulus o f the u n t r e a t e d c o n c r e t e or control dropped 72.8~ that o f c o n c r e t e treated with the commercial sample dropped 55.9%, and that of c o n c r e t e t r e a t e d with the prepared sample 1 dropped only 49.2~. The creep modulus r e p r e sents c o n c r e t e proPerties upon long term aging. More significantly, the creep modulus of c o n c r e t e t r e a t e d with admixtures a f t e r one year o f continuous deformation Is almost twice as much as the creep modulus f o r the u n t r e a t e d concrete o r the control sample. Discussion
The Increase in flowability o f c o n c r e t e with the addition o f superplastlclzers Is a result o f the dispersion ability these additives can Impart on the Inorganic materials. In their study o f the e f f e c t s o f superplasticlzers on viscosity and yield s t r e s s o f cement mixes, Asaga et al. (10) s u g g e s t e d that the theological p r o p e r t y changes In cement slurries are the result of changes In the dispersion s t r u c t u r e o f the particles In the slurries. They argued that as the suPerplastlclzer Is adsorbed on the surface o f the cement and Its hydrate, the zeta potential becomes s t r o n g l y negative, and the partlcle dispersion Is enhanced, resulting In a decrease in both viscosity and yield stress. The same o b s e r v a t i o n was found by us In an earlier study (11). We found that yield s t r e s s diminishes and viscosity decreases t o a low plateau as the dose o f the superplasticizer increases. Beyond a certain dose o f the superplastlclzer, however, the f u r t h e r drop In viscosity is not significant, which Indicates that there is a critical dose beyond which a f u r t h e r addition o f superplasticlzer will not significantly help the flow. This Is also obvious from the water reduction curve shown In Figure 1 as a function o f the superplastlclzer dose. The figure also shows that as the dose Increases the reduction In the amount o f water needed to maintain a predetermined flow parameter (I.e., slump) reaches a plateau. This again strongly suggest that the hypothesis o f adsorption o f the superplastlclzer by the cement particles and the repulsion and reordering In the mix matrix due t o the negative charges Is c o r r e c t . Because adsorption o f superplastlclzer by the cement particles g e t s p e r f e c t e d o r s a t u r a t e d when a certain dose (I.e., weight o f superplastlclzer t o dry weight of cement r a t i o ) Is applied, any additional dosage o f the superplastlclzer will have no significant e f f e c t on the dispersion and workability o f concrete. In t h e o r y , a water/cement ratio o f about 0.27 Is adequate f o r complete hydration o f the cement In any c o n c r e t e mix. Any additional water would tend t o reduce the potential compressive s t r e n g t h (1). Therefore, any attempt to reduce the amount o f water added to concrete mixes while maintaining the same degree o f flowability, among o t h e r things, would increase the compressive s t r e n g t h and the load carrying capacity o f c o n c r e t e s t r u c t u r e s . It was shown In the l i t e r a t u r e and in this paper that superplastlclzers based on melamine are e f f e c t i v e In Improving the compressive strength of c o n c r e t e because they can reduce the amount o f water needed t o a f f e c t a specified flow. More specifically, this paper showed that the specific r e a c t i o n conditions In the preparation o f these admixtures play a significant role. We believe that the reaction conditions are responsible f o r the p r o d u c t ' s final molecular weight and molecular weight distribution. The final rearrangement o f the polymer molecular chains and their Interrelationship with each o t h e r In the polymer matrix are a f f e c t e d by the preparation conditions (12). This is so significant because the performance o r Interaction of these polymers with cement and c o n c r e t e particles Is contingent on the polymer chain length, the degree o f cross linking, and the intensity o f temporary and permanent entangled Iocls o f the polymer chain. When these polymers are added to c o n c r e t e mixes, they tend to coat the various Inorganic particles. Because o f the negative charges they c a r r y due to sulfonatlon, they tend t o repel each other, resulting in a well dispersed mix. Because o f their lubrlclty and reduction o f s u r f a c e tension (1), they minimize Internal frictional f o r c e s thus Increasing the flow o f c o n c r e t e mixes. We believe that the action of melamine-based superplasticlzers ceases a f t e r the Initial dispersion and a f t e r hydration is completed. Therefore, the s t r u c t u r a l matrix resulting Is not only hydrated with less water but is more homogeneous. Therefore, the reduction In water
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531 POLYMERIZATION,
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needed f o r hydration (lower water/cement ratio) and the Improved perfected morphology of the concrete matrix are responsible for improvements in concrete mechanical properties and in its long term performance, for example, creep. But water reduction and dispersion are strongly affected by the Interaction of concrete and the polymer. The polymer Is being affected by the different reaction conditions imposed during Its preparation. The significance of this study Is that It shows that, with the proper selection of reaction condltlons In the preparation of polymeric additives, one could make significant savings in materials used and better designs can be realized for the same cost. Acknowledgments
This research was supported in part by a grant from the Kuwait Foundation for the Advancement of Sciences (KFAS) under grant number 8 4 - 1 2 - 0 2 and by Kuwait Melamine Industries Company. This Is publication no. KISR 2333, Kuwait Institute for Scientific Research, Kuwait. References
1.
2. 3. 4. 5.
6.
7.
8.
9.
10. 11. 12. 13.
Joint Working Party, Superplasticizers In concrete, Cement Admixtures Assn. and the Cement and Concrete Assn., Wexham Springs, UK (1978). M.R. Rlxom, Chemical Admixtures for Concrete, p. 52-85, Halsted Press, London (1978). V.M. Malhotra, Superplastlcizers In concrete, American Concrete Inst., Publlcatlon SP-62, Detroit, Michigan, USA (1979). V~. Malhotra, Developments In the use of superplasticizers. American Concrete Inst., Publication SP-68, Detrolt, Michigan, USA (1981). M. Collepardl, M. Corradl and M. Valente, Influence of polymerization of sulfonated naphthalene condensate and Its interaction with cement, American Concrete Inst., Publication SP-68, Detroit, Michigan, USA (1981). S.M. Lahallh and M. AbsI-Halabl. A process for the synthesis of highly stable sulfonated melamine-formaldehyde condensates as superplastlclzing admixtures In concrete. U.S. Patent No. 4,677,159 (1987). M. AbsI-Halabl, S.M. Lahallh and T. AI-Khalid, J. of Polymer Scl., 33, 2975-1984 (1987). A. Algnesberger, P. Bornmann, H.G. Resenbaur and H. Thelsstg. Process of preparing aqueous solutions of melamine-formaldehyde condensation products having anionic sulfgroups. U.S. Patent No. 3,985,696 (1976). G.E. Sheldrlck, Low-salt containing aqueous solutions of melamine-formaldehyde resin. U.S, Patent No. 4,444,945 (1984). K. Asaga and D.M. Roy. Cement and Concrete Research, 10, 287 (1980). S.M. Lahalih, M. AbsI-Halabl and K.F. Shuhalbar, J.Polymer Sci., 33, 2997-3004 (1987). S.M. Lahalih and M. AbsI-Halabi, J. of Polymer Scl., 33, 3005-3017 (1987). P.J. Flory. Principles of polymer chemistry, Cornell University Press, Ithaca (1975).