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 SpecifierR/M SupplierContractor 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 SpecifierR/M SupplierContractor 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 SpecifierR/M SupplierContractor 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 SpecifierR/M SupplierContractor 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 SpecifierR/M SupplierContractor 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 Problems SpecifierR/M SupplierContractor 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 SpecifierR/M SupplierContractor 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 SpecifierR/M SupplierContractor Mandating the timing of finishing Ignoring atmospheric conditions Allowing surface drying & crusting