Placing and Finishing Concrete
Design and Control of Concrete Mixtures – Chapter 14

Overview
 Preparation before placing
 Depositing concrete
 Consolidation
 Finishing
 Jointing
 Patching and cleaning concrete

Moisture Control

Moisture Testing

Formwork and Reinforcement
 Forms:

Proper alignment, clean, tight, braced

Proper materials for finished look
 Reinforcement:

Clean of debris and excessive rust/mill scale

Remove loose, dry mortar from previous lifts

Depositing Concrete

Depositing Concrete

Depositing
Concrete

Placing Concrete Underwater

Placing on Hardened Concrete
 Surface must be prepared

Mechanical cleaning, roughening

Walls and columns have weaker tops

Form-cured elements may still have weak tops

Preparing
Hardened
Concrete

Bonding New to Existing Concrete

Special Placing Techniques

Consolidation

Vibration

Vibration

External Vibration

External Vibration

External Vibration

Finishing
 Finishes can be customized – colors, textures
 Basic steps:

Strikeoff/screeding

Floating

Trowling

Texturing
 Timing is important

Screeding/Strikeoff
 Process of cutting off excess concrete

Straightedge or screed
 Straightedges used in sawing motion

Surcharge of concrete fills low spots

Bullfloating/Darbying

Edging/Jointing
 Edging required along edge forms and formed joints in slabs

Densifies concrete where troweling is less effective
 First pass before bleeding
 Subsequent passes after each finishing operation
 Contraction joints can be formed with groovers or inserts

Floating

Troweling

Brooming/Tining

Formed
Surfaces

Special Surface Finishes

Exposed-Aggregate Concrete
 Rugged, attractive surface texture
 Special aggregates chosen

Embedded by tapping or integrally mixed
 Surface mortar is worn away to expose aggregate

Brushing and flushing, may require acid

Abrasive blasting or water blasting

Tooling/bushhammering

Grinding and polishing
 Mock-up is necessary

Colored
Finishes

Stain, Paints, and
Clear Coatings

Curing and Protection

Isolation Joints

Contraction Joints

Contraction Joints

Construction
Joints

Horizontal Construction Joints

Horizontal Construction Joints

Joint Layout

Filling Floor Joints
 Three options for joints:

Filling

Sealing

Left open
 Fillers provide more edge support than sealers

Used for heavy-traffic areas

Unjointed Floors
 Three suggested methods:

Post-tensioning

High reinforcement levels

Concrete made with expansive cement

Removing Forms
 Ideally forms left on as long as possible
 Realistically, forms must come off

Rubbed finishes

Form reuse
 Minimum time to form removal based on strength
 Forms should be removed gently

Patching and Cleaning Concrete
 Bulges, fins, projections chipped off
 Undesired metal cut back
 Surface can be rubbed
 Repairs are easier the younger the concrete
 Patches tend to be darker

White cement is used to lighten color

Patching and Cleaning Concrete

Patching and Cleaning Concrete

Curing Patches

Cleaning Concrete Surfaces
 Water methods

Low-pressure, moderate- to high-pressure

Steam
 Chemical methods

Surfactants

Acids/alkalis
 Mechanical methods

Sandblasting, shotblasting, scarification, power chipping, grinding

Precautions
 Protect your head and eyes

Full-cover goggles, safety glasses with side shields, NIOSH-approved respirators
 Protect your back

Lift with legs, not back

Use mechanical means as much as possible
 Working safely with concrete

Wet concrete is caustic and abrasive

Avoid prolonged exposure to skin

Summary
 Preparation before placing
 Depositing concrete
 Consolidation
 Finishing
 Jointing
 Patching and cleaning concrete

Questions