Short description on concrete admixture

1. AMAZE CONCRETE
PART - 1
ConCrete Admixtures

4. Fresh state Hardened state
 decrease water content
 increase workability
 reduce segregation
 reduce the rate of slump
loss
 retard or accelerate
setting time
 improve strength &
abrasion resistance
 improve frost resistance
 reduce permeability
higher durability
 reduce shrinkage cracking
 produce colored concrete
 produce cellular concrete

5.  Current Admixture standards - ASTM
 ASTM C 494
 ASTM C 260
 ASTM D 98
 ASTM C 869
 ASTM C 1141
 ASTM C 1017
 ASTM C 937
 ASTM C 979
 EN 934 xx
 Chemical Admixtures
 Air-entraining Admixtures
 Calcium Chloride
 Foaming Agents
 Admixture for Shortcrete
 Flowing Concrete
 Grout Fluidifier
 Pigments
 Concrete Admixtures

6.  Concrete Admixture standards ASTM 494
 Type A
 Type B
 Type C
 Type D
 Type E
 Type F
 Type G
 Water-reducing admixtures
 Retarding admixtures
 Accelerating admixtures
 Water-reducing and retarding
admixtures.
 Water-reducing and accelerating
admixtures
 High range water-reducing admixtures
 High range water-red. and retard.
Admixtures

7. B C D E F GA
-- -- 95 95 88 8895
1:00 later 1:00 earlier 1:00 later 1:00 earlier -- 1:00 later--
3:30 later 3:30 earlier 3:30 later 3:30 earlier
1:00 earlier
nor 1:30 later
3:00 later
1:00 earlier
nor 1:30 later
-- 1:00 earlier -- 1:00 earlier -- ----
3:30 later -- -- -- 1:00 earlier
nor 1:30 later
3:00 later
1:00 earlier
nor 1:30 later
-- -- -- -- 140 125-
90 125 110 125 125 125110
90 100 110 110 115 115110
90 100 110 110 100 110110
90 90 100 100 100 100100
At least
Not more
than
At least
Not more
than
1d
3d
7d
28d
1year
Compressive
strength, %
of control
min
Initial
Final
Time
of
setting
hr:min
Water content, % of control-max
Requirement
Type of Chemical Admixture - ASTM C494
Physical requirements of concrete treated with chemical
admixture

9.  Normal water reducer (decreases the water requirements by
about 5 – 10%)
 Ca or Na salts of lignosulfonic acid
 salts of hydroxycarboxylic acids
 Carbohydrate
 Mid-range water-reducing (decreases the water requirements
by about 6 – 12%)
 Complex aqueous solution of lignosulfonates with accelerating
admixtures
 Polycarboxylate ether with set and strength enhancing
ingredients
 Superplasticizer (decreases the water requirements by
about 12 - 30%)
 Sulfonated melamine formaldehyde
 Sulfonated naphtalene formaldehyde

Classification

10.  Cement particles in the absence of a dispersing admixture

11.  Cement particles in the presence of a
dispersing admixture
How They Work

12. Mode of Action of Dispersing Admixtures

13.  Surface adsorption and steric repulsion
Increasing with optimum molecular weight and
the presence of Ca+2
in solution
Increasing with polymer charge
 Electrostatic repulsion

14. Undesired side effects caused by water reducers:
 Influence on sulfate solubility  slump loss
 Higher air content  strength loss
 Over dosage  bleeding and segregation
Cement / Superplasticizers Interactions

15.  Because all kinds of fuels (more or less rich in sulfur) are burned in
cement kilns the SO3 content of a particular cement is no more
related to its calcium sulfate content because the SO3 content of the
clinker varies

16.  Normally, when a incompatibility between cement
and admixture results in a fast slump loss, it can be
solved by either:
 Replacing the admixture by other type / brand
 Extending the concrete mixing time
 Extending the premixing time or make delayed addition

17. How to overcome the slump loss problem
through the use of admixtures ??

18.  early strength
 incompatibility problem
 tricky

20.  Mini-slump flow: measure the “Flow resistance”

21. 40
50
60
70
80
90
100
110
120
0 1 2 3 4
%superplasticizer (by wt. solids)
Marshconeflowtime(sec)
5 min
60 min
W/C = 0.35
Saturation point