الفهرس 
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Abstract
Admixtures for concrete are defined as materials other than hydraulic
cement, water, or aggregates that are added immediately before or during
the mixing. Admixtures are added to modify the properties of fresh or
hardened concrete in such away to be more suitable or economic for the
job.
Chemical admixtures are classified into: water reducers, retarders,
accelerators and superplastizers.
Admixtures are very important in industry because they increase the
workability (water reducing agent), while other kinds increase or decrease
the setting time which give more freedom for the transportation of the
concrete or cement pastes.
In this investigation the MSF was prepared according to the four steps
method. In this method the polymers were formed through (a)
hydroxymethyltion of melamine by formaldehyde giving trimethylol
melamine; (b) sulfonation of one methylol group of the product by sodium
bisulfite giving sulfonated methylol melamine; (c) low pH condensation;
(d) highpH rearrangement givingmelamineformaldehyde sulfonate .
The MUSF was prepared by the same manner where the melamine
molecule replaced by melamine/urea, (111) in the first step, then the
sulfonation occurred in the second step. The product is undergoing low pH
condensation and high pH rearrangement at the same vessel and
conditions.
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__________________ Summary and Conclusion
Cement pastes were made, using different admixtures dosages such as,
0.00, 0.25, 0.50, 0.75 and 1.00 mass% of cement. These admixtures were
prepared in laboratory such as;
melamine sulfonate formaldehyde (MSFj) (M : S03 : F; I : 1.22 : 2.58),
melamine sulfonate formaldehyde (MSF2) (M : S03 : F; 1 : 1.22 : 5.56),
melamine sulfonate formaldehyde (MSF3) (M : S03 : F; 1 : 0.4 : 1.4),
melamine sulfonate formaldehyde (MSF4) (M : S03 : F; 1 : 0.5 : 4) and
melamine urea sulfonate formaldehyde (MUSF).
The water of consistency, initial and final setting time, rheological
properties, electrical conductivity, compressive strength, bulk density,
chemical combined water content, gel/space ratio, DTA and IRspectroscopy
were under taken.
The main conclusions derived from this investigation can be
summarized as the following:
1- The reduction in the water of consistency increases in presence of
different dosage of the admixture, this reduction was 33.33, 34.33,
14.33, 8.9 and 7.67% for 1.00% dose of (MSF[), (MSF2), (MSF3),
(MSF4) and (MUSF), respectively. At 0.25 mass% dosage, the
reduction in the water of consistency was 11,6.67,4.33, I and 2.23%
for the above admixture respectively. All prepared admixtures act as
water reducing agents.
In respect of initial and final setting time of cement paste admixed with
melamine sulfonate formaldehyde (MSF1), it is found that the initial
setting time is retarded with the admixture content. The amount of the
melamine sulfonate formaldehyde (MSF I) reduces the final setting time, it
acts as accelerating admixture and superplasticiser.
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__________________ Summary and Conclusion
The initial and final setting time of the cement pastes using different
dosages of melamine formaldehyde sulfonate (MSF2) show retardation
effect.
It can be concluded that the prepared (MSF2) is retarding as well as
water reducer.
The initial and final setting time are retarded by the addition of
melamine sulfonate formaldehyde (MSF3). Also, as the amount of (MSF3)
increases up to 0.50% the initial setting time is accelerated and then
retarded at 0.75% and 1.00%. So, it is concluded that (MSF3) is acted as
retarder and water reducer. MSF4 shows the same trend of (MSF2).
The initial setting time is accelerated by the addition of melamine urea
sulfonate formaldehyde (MUSF). As the dosage of admixture increases
the initial setting time decreases. By increasing the amount of (MUSF) the
final setting time is elongated. Also, it can be concluded that (MUSF) is
acted as retarder and water reducer.
2- It is found that as the amount of admixtures increases the fluidity of
pastes sharply increases. Also, it is found that (MSF2) gives the
highest fluidity of cement pastes at all dosages. This means that
(MSF2) is the optimum superplasticizer which gives higher fluidity of
cement pastes than the other superplasticizers.
3- The combined water contents of the cement pastes mcrease with
curing time for all admixtures dosages, due to the continuous
hydration. As the amount of (MSFj), (MSF2), (MSF3) and (MSF4)
increases the combined water content decreases, this is mainly due to
the reduction of mixing water which effects the rate of hydration.
1.00% (MUSF) gives the highest combined water contents at all ages.
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__________________ Summary and Conclusion
This means that 1.00% is the optimum dose of this admixture which
gives higher rate of hydration but lower than the control cement
sample.
4- The gel/space ratio of the cement pastes increase with curing time for
all admixtures dosages. This is due to the increase of the amount of
hydration products. Increase of the dosages of MSF] and MSF2 the
gel/space ratio increases. As the dosages of MSF] and MSF2 increase
the water of consistency and the total porosity decrease. MSF2 gives
higher gel/space ratio values than those with MSF 1, these results are in
a good agreement with the amount of water reduction. The gel/space
ratio of MSF3 and MSF4 decreases consequently the compressive
strength values. 0.5% of MSF3 is higher than 1.0%, this is due to the
retardation effect MSF3. As the hydration time increases the gel/space
ratio increases up to 1.0 mass% at 90 days. At early ages (15 min up to
one day) it was shown that the gel/space decreases with the amount of
MUSF dosages. At later ages (3 days up to 90 days) it was shown that
the gel/space ratio increases with the dosages of MUSF. This is due to
the production of more dense and close-textured structure of the
cement pastes.
5- The bulk density of the cement pastes increases with curing time for
all admixture dosages. Obviously, as the amount of (MSF]), (MSF2),
(MSF3) and (MSF4) increases the bulk density increases. Also, the
0.25% and 0.75% (MUSF) have higher bulk density than the other
dosages.
6- The compressive strength of the cement pastes increases with curing
time for all admixtures dosages. This mainly due to the increase of the
amount of hydration products especially Tobermorite - like gel
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___________________ Summary and Conclusion
(CSH). As the amount of MSFj, MSFz and MSF4 increases the
compressive strength increases due to the decrease of the mixing
water. The decrease in mixing water decreases the total porosity and
improves the compressive strength. 0.75% MSF3 gives the higher
values of the compressive strength at all ages. As the content of MSF3
increases the compressive strength decreases. 0.50% MUSF gives
higher values of compressive strength than the cement pastes
containing higher dosages. Therefore, 0.50% MUSF is the optimum
values of MUFS to be added as a water reducer and accelerator. The
increase of the dosage up to 0.5% retarded the hydration at early ages
(1-3 days), due to the retardation effect ofMUSF.
7- The change in the electrical conductivity reflects the physico-chemical
changes in the cement pastes and it can be used to monitor setting and
hardening processes. Significant changes in electrical conductivity
occur when the paste gains its rigidity. On increasing the amount of
polymeric materials, the conductivity maximum was found to have
shifted to longer hydration times.