Chemical Admixtures for Concrete Design and Control of

Overview n Air-entraining admixtures n Coloring admixtures n Water-reducing admixtures n Pumping Aids n

Control of Air Content n Dosage depends on: n Materials n Proportions n Batching

Water-Reducing Admixtures n Normal – 5%-10% water reduction n Mid-range – 6%-12% water reduction

Impact of Water Reducers on Properties of Concrete

Set Retarding Admixtures n Used to delay the rate of setting – initial and

Set Accelerating Admixtures n Accelerates hydration and strength development n Calcium chloride – most

Set Accelerating Admixtures n Calcium chloride effects on concrete n Increase corrosion n Discoloration

Hydration-Control Admixtures n Two-part system: n Stabilizer/retarder that stops hydration n Activator that restarts

Workability-Retaining Admixtures n Provide workability retention without affecting set times or early-age strength n

Permeability Reducing Admixtures n Two water penetration mechanisms: n Capillary absorption (wicking) n Direct

Miscellaneous Admixtures n Pumping aids n Bonding admixtures and agents n Grouting admixtures n

Admixture Compatibility n Cement-admixture or admixture-admixture incompatibilities are encountered n Slump loss, air loss,

Less Than Expected Water Reduction n Composition of cementitious materials n Presence of other

Less Than Expected Retardation n May be caused by increase in C A 3

Storing and Dispensing Chemical Admixtures

Summary n Air-entraining admixtures n Coloring admixtures n Water-reducing admixtures n Pumping Aids n

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Chemical Admixtures for Concrete Design and Control of Concrete Mixtures – Chapter 7

Overview n Air-entraining admixtures n Coloring admixtures n Water-reducing admixtures n Pumping Aids n Set retarding admixtures n Bonding admixtures and agents n Set accelerating admixtures n Grouting admixtures n Hydration-control admixtures n Gas-forming admixtures n Workability-retaining admixtures n Air-detrainers n Corrosion inhibitors n Fungicidal, germicidal, and insecticidal admixtures n Shrinkage-reducing admixtures n Viscosity modifying admixtures n Permeability reducing admixtures n Admixture compatibility n Alkali-aggregate reactivity inhibitors n Storing and dispensing chemical admixtures

Chemical Admixtures

Air-Entraining Admixtures

Mechanism of Air Entrainment

Entrained Air

Control of Air Content n Dosage depends on: n Materials n Proportions n Batching order and transport n Placing and finishing n Curing n Defoaming agents are available if air is excessive

Impact of Air on Concrete Properties

Water-Reducing Admixtures

Water-Reducing Admixtures n Normal – 5%-10% water reduction n Mid-range – 6%-12% water reduction n High-range – 12%-40% water reduction n Superplasticizers

High-Range Water Reducers

Flowing Concrete

Mechanisms of Water Reducers

Polycarboxylate Technology

Impact of Water Reducers on Properties of Concrete

Set Retarding Admixtures n Used to delay the rate of setting – initial and final n Offset accelerating effects n Enable special placing/finishing techniques n Lower early-age strength, but higher longterm strength n Effects on other properties may be unpredictable

Set Accelerating Admixtures n Accelerates hydration and strength development n Calcium chloride – most common n Up to 2% by mass of cementing material n Triethanolamine (TEA), inorganic salts – alternatives n Mechanism depends on admixture chemistry

Set Accelerating Admixtures n Calcium chloride effects on concrete n Increase corrosion n Discoloration n Increased shrinkage n Long-term strength reduction n Reduced durability

Hydration-Control Admixtures n Two-part system: n Stabilizer/retarder that stops hydration n Activator that restarts hydration n Allows for suspending overnight or for long hauls

Workability-Retaining Admixtures n Provide workability retention without affecting set times or early-age strength n Can be used with water-reducing admixtures n Reduces the need for slump adjustments

Corrosion Inhibitors

Shrinkage-Reducing Admixtures

Permeability Reducing Admixtures n Two water penetration mechanisms: n Capillary absorption (wicking) n Direct ingress under pressure n Two types of PRA: n Non-hydrostatic (PRAN) n Hydrostatic (PRAH) n Not a replacement for quality concrete

Alkali-Aggregate Reactivity Inhibitors

Coloring Admixtures (Pigments)

Miscellaneous Admixtures n Pumping aids n Bonding admixtures and agents n Grouting admixtures n Gas-forming admixtures n Air detrainers n Fungicidal, germicidal, and insecticidal admixtures n Viscosity modifying admixtures

Admixture Compatibility n Cement-admixture or admixture-admixture incompatibilities are encountered n Slump loss, air loss, early stiffening, and other fresh and hardened concrete properties may be affected n Solved by: n Dosage rate or sequence n Altering cement or admixture composition

Less Than Expected Water Reduction n Composition of cementitious materials n Presence of other set-control admixtures n Temperature n Clay minerals n Admixture dosage n Slump loss n Can be attributed to temperature, reactivity of cement, dispersion and availability of admixture, expansive clays n Typically avoided by delaying addition of water -reducer

Less Than Expected Retardation n May be caused by increase in C A 3 n Too much retardation caused by: n Low C 3 A n Low cement reactivity n Excessive admixture n High levels of SCMs n Low temperatures

Storing and Dispensing Chemical Admixtures

Summary n Air-entraining admixtures n Coloring admixtures n Water-reducing admixtures n Pumping Aids n Set retarding admixtures n Bonding admixtures and agents n Set accelerating admixtures n Grouting admixtures n Hydration-control admixtures n Gas-forming admixtures n Workability-retaining admixtures n Air-detrainers n Corrosion inhibitors n Fungicidal, germicidal, and insecticidal admixtures n Shrinkage-reducing admixtures n Viscosity modifying admixtures n Permeability reducing admixtures n Admixture compatibility n Alkali-aggregate reactivity inhibitors n Storing and dispensing chemical admixtures

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