Building Materials, Third Edition

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Generally RMC is transported to sites which are located at long distances from the batching
plants. At the delivery point, concrete should be workable and plastic. The transit period is
sometimes four to five hours. The ordinary concrete will suffer slump loss due to the time lost
in transit and evaporation of water due to atmospheric conditions such as high temperature.
Therefore, admixtures will be required to extend the setting time and, retention of specified
slump of concrete. Superplasticizers are, therefore, used to assure quality, workability, and
strength of ready mixed concrete. Two types of admixtures are in use—the high performance
water reducing admixtures and a high range water-reducing super-plasticizers. High
performance water reducing admixtures have been specially designed to retain workability
even in high ambient temperature. The examples are conplast RMC P 333 and conplast RMC
P 505. The advantages of using high performance water reducing admixtures are:

1. Improved cohesion and reduced bleeding and segregation.


2. Makes the mix cohesive even if the aggregates are of slightly poor grading.


3. Since chloride free it is safe for use in reinforced and prestressed concrete.


4. Improved workability and workability retention with controlled extended setting time
   and hence ideal for use in hot weather condition.


5. Workability increases without extra water addition.


6. Assists in producing dense, close textured, low permeability concrete thus enhancing
   durability.


7. Water reduction helps in improvement of compressive strength at all ages.
   The high range water-reducing superplasticizers are designed to impart high workability
   and slump retention for low and medium grades of concrete. Some of the high range water-
   reducing superplasticizers are conplast RMC SP 444, conplast RMC SP 555. Another admixture,
   the high early strength superplasticizer, e.g., Zentrament FBV is used to impart high early
   strength to RMC. The concrete produced with this admixture is homogeneous and free from
   segregation and bleeding. Also a saving of 20% of cement is achieved for the same slump and
   strength. The advantages of using high range water-reducing super plasticizers are:

a) Speedy construction.

b) Increased workability and reduced segregation.

c) Longer placing time.

d) Improved pumpability.

e) Chloride free.

f) Safe for use in prestressed and marine structures.

g) Safe for use with sulphate resisting cement and marine aggregate.

h) Higher ultimate strength.

i) Improved workability.

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1. Enhanced quality and durability resulting in lower maintenance costs and increased
   speed of construction.


2. Ready mix concrete is consistently of the same quality and provides a high quality of
   construction material; construction time is also reduced.