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BY:- LAUKUSH KUMAR
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INTRODUCTION
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HISTORY
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WHY ARE THEY USED
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WHY ARE THEY USED
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HOW APPLIED
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CLASSIFICATION OF ADMIXTURES
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CHEMICAL ADMIXTURES 1.accelerators
2.retarders
3.water reducing admixtures 4.grouting admixtures
5.air-entraining admixtures
6.permeability reducing admixtures
7.plasticizers
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MINERAL ADMIXTURES 1.fly ash
2.blast furnace slag
3.rice husk ash 4.silica fumes
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Evolution of Chemical Admixtures Development of admixtures according to :
• Demands on concrete material properties • Changes in binder composition
• Evolution in construction technologies
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Demands on Concrete Properties • Higher moduli (compressive, tensile, flexural)
• Greater freeze-thaw resistance
• Improved durability • Minimum shrinkage cracking
• Minimum rebar corrosion
• No Alkali-Aggregate reaction
• Etc, …
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Increasing compressive strength Achieved through:
• Low W/C
• Effective WR • Superplasticizers
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Enhanced strength and durability Achieved through:
Using:
• Low w/c
• SCM‟s (SF)
• Superplasticizers
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Greater improving freeze-thaw
resistance Achieved through:
• Network of fine air voids
Using:
• Air-entraining agents
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Minimizing shrinkage-cracking Reduce drying
shrinkage cracking
through SRA ‟s
(shrinkage reducing
admixtures)
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Preventing rebar corrosion Achieved through:
• Low porosity
• Fine pore structure • And new admixtures :
corrosion inhibitors
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Minimize alkali-aggregate reactions
Mitigate with Lithium-based admixtures
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Changes in Binder Composition Due to incorporation of :
• Different forms of Ca-sulfate
• Fillers (e.g., limestone) • Supplementing cementitious materials (e.g.,
natural pozzolans, SF)
Others
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Changes in Binder Composition: Upon incorporation of
Fly Ash.
FA-carbon interferes with air-entrainingadmixtures.
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Evolution in Construction
Technologies Pumpable concrete
throughSuperplasticizers.
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Evolution in Construction
Technologies Cohesive, self-
consolidating concrete.
Achieved with :
Viscosity-Enhancing
Admixtures (VEA).
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Evolution in Construction
Technologies Admixtures impact on construction technologies:-
Chemical Admixtures enable
• Pumpable concrete• Self -levelling concrete
• Self -consolidating concrete
Leading to
• Reduced labour requirements
• Reduced construction time
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The Admixture Challenge Ahead Resolve fundamental issues:-
• Understand the chemistry and mode action
of each admixture. • Design molecular structure of admixtures for
specific function .
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Conclusions A First Conclusion:-
… the development of concrete materials
and technologies was largely supported anddriven by the timely introduction of multiple
new chemical admixtures
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Conclusions A Second Conclusion:-
Concrete chemical admixtures:
are essential components of quality concrete contribute directly to beneficiation of secondary
industrial materials or chemicals.