1. 4.2.4.1 Chemical Admixture 4.2.4.2 Mineral Admixture
4.2.4 Concrete Admixture
Chemical Admixture
Introduction
Water-Reducing Admixture
Hardening Accelerator
Air Entraining Admixture
Set Retarding Admixture
Flash Setting Admixture
Expanding Admixture
Frost-resistance Admixture
Mineral Admixture

2. Water-Reducing Admixture
Definition
Classification
Water-reducing admixture in common use
Lignin sulfonate water-reducing admixture
Naphthalene sulfonate water-reducing admixture
Resinous water-reducing admixtures
Mechanism
Technical and economic effects

3. Water-Reducing Admixture
Definition
Water-reducing admixture permits less amount of water at the same of workability or the increase of the mobility at the same amount of water.
Water-reducing admixtures increase workability and quality by use of water more efficiently in a concrete mixture. By reducing the water, these admixtures densify the concrete and decrease capillary voids and permeability.

4. Classification by effect
Water-Reducing Admixture
Classification by effect
It can be classified into two types by effect:
Ordinary water-reducing admixture
Super plasticizer
The water-reducing rate of Ordinary water-reducing admixture is less than 10%.
The water-reducing rate of Super plasticizer ,also called super plasticizer or fluid concrete is more than 10%.

5. Water-Reducing Admixture
Classification by the effect on setting time
Three types
Standard type
Set retarder type
Coagulant type

6. Water-Reducing Admixture
Classification by the effect on air content
Two types by the effect on air content
Air entraining type
Non air entraining type

7. Mechanism Water-reducing admixture (surfactant) is composed of
hydrophilic group-polar group
hydrophobic group -nonpolar group
When mixed with water
hydrophobic group attaches to cement particle
hydrophilic group attaches to water

8. Mechanism hydrophobic group hydrophilic group
Fig4.2.4 Sketch map of the structure of Water-reducing admixture

10. Mechanism
Mechanism of water-reducing admixture is reflected in the apparent active reaction.
Cement paste flocculation structure is wrapped to reduce the mobility of the admixture.
But water-reducing admixtures make flocculation structure dissolve so as to improve the mobility and strength.

11. Mechanism
The flocculation structure dissolves in the following three ways:
Disassemble cement flocculation by electron repelling from the surface of cement particle
Improve the fluidity of paste by forming a solvate membrane on the particle surface
Extend the hydrating area by improving the dispersity of the cement particles
Mobility is improved.

12. Technical and economic effects
Technical and economic effects of water-reducing admixture are listed in Tab4.2.10
Tab Technical and economic effects of water-reducing admixture
Group
effects
Cement content （Kg/m3）
W/C
Slump
（mm）
fcu,k
(Mpa)
1.Base concrete( not of water-reducing admixture)
300
0.62 50 37
2. Improving mobility
100 38
3. Improving strength
0.56 46
4. Saving cement
270
37.5

13. Water-reducing admixture in common use
Lignin sulfonate water-reducing admixture
Naphthalene sulfonate water-reducing admixture
Resinous water-reducing admixture

14. Lignin sulfonate water-reducing admixture
Definition
Lignin sulfonate(M) is the most common in use.
It is made by wood pulp through sulfonation and dryness.
Definition

15. Lignin sulfonate water-reducing admixture
Performance
The amount and its effects
If % lignin sulfonate is added
The water-reducing rate will be 10%
Or increasing the slump by 10cm
The strength increased by 10-20%
Performance

16. Lignin sulfonate water-reducing admixture
Performance
Set retarder activity
Delay the setting time 1-3hours, and add 0.25% Minto lignin sulfonate water-reducing admixture.
Thus, it must be used with the mixture of hardening accelerator in winter.
Performance

17. Lignin sulfonate water-reducing admixture
Performance
Air entraining activity
To increase the air content from 2% to 3.6%
So that the strength is reduced, while the durability is improved.
Performance

18. Lignin sulfonate water-reducing admixture
Application
According to the performances, it applies to
large moulding
sliding formwork
mass concrete
concrete pumping
summer construction
Application

19. Naphthalene sulfonate water-reducing admixture
Brief Introduction
At present, there are varieties of naphthalene sulfonate water-reducing admixtures in China.
The types in common use include NF,NNO,FDN,UNF,MF,AF, and so on.
Brief introduction

20. Performance
Adding %
It has advantages over lignin sulfonate water-reducing admixture for its violent dispersion
water-reducing rate >15%
reinforcing rate >20%
saving cement 10-20%
Minor set retarder activity doesn’t affect the strength
Most of them are non air entraining.

21. Naphthalene sulfonate water-reducing admixture
Application
Naphthalene sulfonate water-reducing admixture can be used in
High strength concrete
High performance concrete
Liquid concrete
Concrete pumping
Winter construction concrete
Application

22. Resinous water-reducing admixtures
Introduction
Resinous water-reducing admixtures are one of superplasticizer.
In China, as the main type of resinous water-reducing admixtures, SM has the perfect water-reducing effect.

23. Resinous water-reducing admixtures
Advantages
It is better than naphthalene sulfonate in dispersion, water reducing, and reinforcing.
The 7d strength is the same with 28d strength of ordinary ones.
The 28d strength can increase by 30-60%.
Disadvantages
The cost is high