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4.2.4.1 Chemical AdmixtureIntroductionWater-Reducing AdmixtureHardening AcceleratorAir Entraining AdmixtureSet Retarding AdmixtureFlash Setting AdmixtureExpanding AdmixtureFrost-resistance Admixture
4.2.4 Concrete Admixture
4.2.4.2 Mineral Admixture
Water-Reducing AdmixtureDefinition
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 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 effectClassification by effect
It can be classified into two types by effect:Ordinary water-reducing admixtureSuper 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
Water-Reducing Admixture
Three types Standard type
Set retarder type
Coagulant type
Classification by the effect on setting timeClassification by the effect on setting time
Two types by the effect on air content
Air entraining type
Non air entraining type
Water-Reducing Admixture
Classification by the effect on air Classification by the effect on air contentcontent
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 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 repelli
ng from the surface of cement particle– Improve the fluidity of paste by forming a solvate m
embrane on the particle surface– Extend the hydrating area by improving the dispers
ity of the cement particles
Mobility is improved.
Mechanism
Technical and economic effects
Group effects
Cement content ( Kg/m
3)
W/CSlump(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
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
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
• Lignin sulfonate(M) is the most common in use.
• It is made by wood pulp through sulfonation and dryness.
Definition
Lignin sulfonate water-reducing admixture
The amount and its effects If 0.2-0.3% lignin sulfonate is addedThe water-reducing rate will be 10% Or increasing the slump by 10cmThe strength increased by 10-20%
PerformancePerformance
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
PerformancePerformance
Lignin sulfonate water-reducing admixture
Air entraining activityTo increase the air content from 2% to 3.6%So that the strength is reduced, while the
durability is improved.
PerformancePerformance
Lignin sulfonate water-reducing admixture
According to the performances, it applies to
large moulding
sliding formwork
mass concrete
concrete pumping
summer construction
ApplicationApplication
Naphthalene sulfonate water-reducing admixture
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 IntroductionBrief Introduction
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.
PerformancePerformancePerformancePerformance
Naphthalene sulfonate water-reducing admixture
Naphthalene sulfonate water-reducing admixture
can be used in
High strength concreteHigh strength concrete
High performance concrete High performance concrete
Liquid concrete Liquid concrete
Concrete pumping Concrete pumping
Winter construction concreteWinter construction concrete
ApplicationApplication
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.
IntroductionIntroduction
Resinous water-reducing admixtures
• 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%.
AdvantagesAdvantagesAdvantagesAdvantages
DisadvantagesDisadvantagesDisadvantagesDisadvantages
The cost is highThe cost is high
Resinous water-reducing admixtures