CONCRETE RESTORATION-

A PRACTICAL APPROACH

Surface Preparation

Saw-cut edges to a minimum ¼”. Mechanically abrade / remove unsound

& contaminated concrete. Pre-dampen repair zone to a Saturated,

Surface Dry (SSD) condition. Prime with slurry coat as directed Clean reinforcing steel to a white metal

finish.

Understanding & Controlling Cracks

Causations and On-site Modifications

Good Water, Bad Water

Bad - All water prior to final set Controls porosity and shrinkage.

Good - All water after final set Ensures complete hydration of all cement

particles.

Types of Shrinkage

Plastic Shrinkage Shrinkage / Cracks which form prior to final

set.

Drying Shrinkage Shrinkage / Cracks which form after final

set.

Plastic Shrinkage

Plastic Shrinkage cracks occur when water evaporates from the surface faster than water can appear at the surface during the bleeding process.

Mortars by nature do not bleed and therefore, are more likely to Plastic Shrink, but this can be easily minimized by proper and immediate curing.

Drying Shrinkage

Drying shrinkage cracks occur when the Internal Stress Forces caused by shrinkage (evaporation of water and cement hydration) are greater than the strength developed for the corresponding Strength Vector at a given time.

What Governs the Internal Stress Force? The Mortar will crack when the Internal

Stress Forces > Strength Vector Internal Stress Force is similar to the

(Shrinkage - Relaxation). The extent of Relaxation is mostly controlled

by Creep Extent of creep is mostly controlled by

Modulus of Elasticity

W/C Ratio Governs the Following Properties: Shrinkage Strength development and Ultimate

Strength Porosity Bond Strength Set Time Trowelability

Why Extend with Aggregate? Minimize Cracking

Reduces Shrinkage

Lower Cost per Unit Lower Heat of Hydration

Extension Extend with 3/8” pea gravel.

Washed Dried Minimum size

Poor aggregate can and will lead to a severe reduction in physical properties. Up to 40%

Extension Requirements

Depth 2”- 4” 25% by Weight

Greater than 4” 50% by weight

Larger aggregate may be used in thicker patches.

Patch Sizing As with concrete, jointing is necessary topromote cracking in a desirable form.

The identical requirements apply for a repairmortar.

Therefore, with the proper allowance for control& expansion joints, mortars can be placed overlarge areas.

Do NOT apply a repair mortar to a POST- TENSION structure covering more than a couple sq. ft.

Why Cure?

Minimize Evaporation - Water Loss When Relative Humidity of cementitious products

drops below 80%, hydration and therefore, strength gain stops.

Minimize Shrinkage Vs. Time The longer you maintain water in the bulk mix, the

lower your shrinkage is Vs. time and the greater your strength gain and relaxation factor, thereby minimizing the propensity to crack.

Improper Curing

Plastic Shrinkage Cracks Drying Shrinkage Low Strengths Poor Bonding Poor Abrasion Resistance

Polymer Modification

Dramatic increases in Flexural & Tensile Strength

Imparts greater Bond Strength Greater Durability

Lower Porosity Improved Freeze-Thaw Resistance Lowers Propensity to Crack

High Tensile Strength / Lower Modulus

Limitations for Polymer-Modified Products Do NOT apply when temperature is

expected to be below 45 °F for two days. Minimum Film Forming Temperature. Polymer Micelles will break below 32 °F. Efflorescence

Do NOT apply when rain is imminent.

Restoration Projects

A repair project is more likely to experience cost overruns (extras) since the extent of deterioration is very difficult to determine prior to break-out.

Success is strongly tied to the experience of the restoration contractor as relating to the specified application method.

Especially true with spray applied mortars. ACI & ASTM both require pre-testing

nozzle men prior to start of project.

Carbonation

Carbonation of the mortar / concrete is the reduction in pH.

Freshly placed mortar has a pH in the range of 12-13.

Mortar / Concrete having a pH of 9.5 passivates the steel – corrosion can not take place.

CORTEC-Migrating Corrosion Inhibitor

Corrosion of the reinforcing steel is caused by Electro-Chemical Reaction – much like a battery.

The CORTEC – MCI will dramatically reduce the potential for incipient anodes.

CORTEC – MCI protects the reinforcing steel through anodic & cathodic processes.

Failure Analysis

Understanding the initial causation Premature failure of new repair

Surface preparation Loss of bond

Too much water (High shrinkage / porous) cracks low strengths poor / loss of bond

Failure Analysis Cont. Improper Curing (Early water loss / Rapid

Shrinkage) Cracks low strength poor abrasion resistance

Improper extension (Increased shrinkage / Weak matrix) low strength dry shrinkage cracks Poor or loss of bond

Cost Comparison

Direct bag cost comparison, even with equal weights doesn’t work.

Direct comparison of associated costs must be determined based on bag yields in cost per Cubic Foot.

Determination of $ / Cu. Ft. for Two Products Designed for the Same Application

Actual Product #1 Weight: 55 lbs. Cost: $22.75 Yield of 0.62 has a $ /

Cu. Ft. of: $22.75 / 0.62 Cu. Ft. = $36.69/Cu. Ft.

Actual Product # 2 Weight: 55 lbs. Cost: $14.75 Yield of 0.40 has a $/Cu. Ft. of:

$14.75 / 0.40 Cu. Ft. = $36.87/Cu. Ft.

Therefore, a bag costing $8.00 more has actually a lower cost.

Thank You

Any Question please