Transcript Document

4.2.4 Concrete Admixture
4.2.4.1 Chemical Admixture
 Introduction
 Water-Reducing Admixture
 Hardening Accelerator
 Air Entraining Admixture
 Set Retarding Admixture
 Flash Setting Admixture
 Expanding Admixture
 Frost-resistance Admixture
4.2.4.2 Mineral Admixture
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
Water-Reducing Admixture
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.
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%.
Water-Reducing Admixture
Classification by the effect on setting time
Three types
Standard type
Set retarder type
Coagulant type
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
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
Mechanism
hydrophobic
group
hydrophilic
group
Fig4.2.4 Sketch map of the structure of Water-reducing admixture
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.
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.
Technical and economic effects
Technical and economic effects of water-reducing
admixture are listed in Tab4.2.10
Tab4.2.10
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
300
0.62
100
38
3. Improving strength
300
0.56
50
46
4. Saving cement
270
0.62
50
37.5
Water-reducing admixture
in common use
Lignin sulfonate water-reducing admixture
Naphthalene sulfonate water-reducing
admixture
Resinous water-reducing admixture
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.
Lignin sulfonate
water-reducing admixture
Performance
The amount and its effects
 If 0.2-0.3% lignin sulfonate is added
 The water-reducing rate will be 10%
 Or increasing the slump by 10cm
 The strength increased by 10-20%
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.
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.
Lignin sulfonate
water-reducing admixture
Application
According to the performances, it applies to
large moulding
sliding formwork
mass concrete
concrete pumping
summer construction
Naphthalene sulfonate
water-reducing admixture
Brief Introduction
At present, there are varieties of
naphthalene sulfonate waterreducing admixtures in China.
The types in common use include
NF,NNO,FDN,UNF,MF,AF, and so on.
Performance
Adding 0.2-1.0%
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.
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
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.
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