How to Cause Scaling

• Two primary mechanisms and manifestations– Freeze-Thaw /

Deicer Scaling– Sealed Surface

Blistering and Delamination

Key Players

• Specifier

• Ready Mix Concrete Producer

• Concrete Contractor

Scaling from Freeze/Thaw Cycles and Deicers

• Disintegration of paste caused by:– the hydraulic

pressures from water in saturated pores and capillaries turning to ice.

– the osmotic pressures developed in the paste by the differential concentrations of alkali solutions as produced from the use of deicer salts.

Key Factors Related to Freeze-Thaw & Deicer Scaling

• Entrained Air

• Paste Permeability (& Strength) Characteristics

• Degree of Pore Saturation

• Deicer Chemicals & Use

Entrained Air

Contributors to Improper Entrained Air

Specifier R/M Supplier Contractor

Specify inadequate air content limits

Failure to ask appropriate questions when receiving order

Failure to properly order

Omitting or putting inadequate Air-Entrainment dosage during batching

Adding water to surface and/or over-finishing surface (driving air out of surface)

Paste Permeability (& Strength) Characteristics

Cement Particles

Mix Water Concentration (or Dilution) of Cement Particles in Paste

• W/C Ratio

•Space between cement particles directly determines paste pore structure and strength

Paste Permeability (& Strength) Characteristics

Early Hydration

C-S-H Crystal Growth (Critical)

Later Hydration

CH Crystals (potential pores)

Pores and Capillaries

Contributors to Poor Paste Characteristics

Specifier R/M Supplier Contractor

Failure to address issue-ACI- NMDOT

Failure to ask appropriate questions when receiving order

Failure to properly order

Disallow or inappropriately limit Supplementary Cementitious Materials (SCM’s)

Supply inappropriate mix

Add excessive water to mix at site

Deliver mix with excessive amount of mix water

Work bleed water or surface applied water into the surface

Inadequate curing requirements

Inadequate curing procedures

Degree of Pore Saturation

• Reduced saturation lessens potential for expansive pressures– “Dry concrete doesn’t care about freezing

temperatures”

Contributors to Undesirable Pore Saturation

Specifier R/M Supplier Contractor

Design site conditions with no or inadequate drainage off and away from concrete

Construct concrete members with no or inadequate drainage

Failure to address “Drying” period

Failure to assure drying conditions

Deicer Chemicals & Use

• Frequently used deicers:– Sodium chloride (rock salt)– Calcium chloride– Urea– Magnesium chloride

• Magnesium chloride deicers have come under recent criticism for aggravating scaling.

• Deicers containing ammonium nitrate and ammonium sulfate rapidly attack and disintegrate concrete.

• Deicing chemicals should not be applied during first winter season.

Contributors to Problems from Deicer Use

Specifier R/M Supplier Contractor

Failure to address the use and application of deicers

Failure to adequately instruct owner on the use and application of deicers

Failure to address “Drying” period

Failure to assure drying conditions

Blisters and Delaminations

• Result from bleed water and bleed air being trapped below the prematurely closed (densified) mortar surface

Key Factors Related to Blisters & Delaminations

• Surface Finish

• Bleeding

• Consolidation

• Finishing Conditions and Procedures

Surface Finish

• Stainless Steel finishing tools close or seal a concrete surface

• Many (most) applications do not need a steel trowel surface

Contributors to Problem of Finish

Specifier R/M Supplier Contractor

Requiring Steel Trowel Finish when unnecessary

Applying steel trowel finish when unnecessary

Bleeding/Bleed Water

• Bleed capacity and bleed rate affect timing of finishing.

• Bleeding affected by:– Water content– Fine particles content

(Cement, SCM’s, and sand)

– Air content– Some admixtures– Slab thickness

Contributors to Bleeding ProblemsSpecifier R/M Supplier Contractor

Requiring high cementitious content

Supplying concrete with excessive cementitious content

Requiring high sand content

Using sand with excessive amount of -#30 particles and/or having over-sanded mix

Requiring air content above 3% when not necessary

Entraining excessive air in concrete (Intentionally or inadvertantly)

Providing high water content

Having water added at site

Consolidation

• Insufficient amount leaves entrapped air in which a portion becomes bleed air

• Too much brings excessive fines to surface– Inviting crusting and

premature finishing

Contributors to Consolidation Problems

Specifier R/M Supplier Contractor

Supplying a mix with poor composite aggregate gradation

Insufficient consolidation efforts

Supply of too wet of a mix

Overuse of vibrating screed on wetter mixes

Use of jitterbug

Finishing Conditions & Procedures

• Applying stainless steel tools to the surface at the right time (at the right concrete conditions) is crucial– When bleeding has

ceased– Not necessarily when

surface seems to be hardening (Spongy)

Surface Crusting

Still plastic

Contributors to Inappropriate Finishing Conditions & Procedures

Specifier R/M Supplier Contractor

Mandating the timing of finishing

Ignoring atmospheric conditions

Allowing surface drying & crusting