The Concrete Handbook

Segregation is the separation of coarse aggregates from the cement paste, leading to uneven strength and texture.

• Identification
• Visible coarse aggregates settling at the bottom or paste rising to the top.
• Causes
• Excessive water content.
• Poorly graded or oversized aggregates.
• Inadequate mixing or over-vibration.
• Prevention
• Use well-graded aggregates and proper water content.
• Avoid excessive handling and over-vibration.
• Repair
• Minor segregation can be corrected by remixing before placement.
• Severe segregation may require removal and replacement.

Bleeding is water rising to the surface of freshly placed concrete.

• Identification
• Pools of water or shiny surfaces during finishing.
• Causes
• High water-to-cement ratio.
• Poorly graded fine aggregates.
• Prevention
• Adjust mix design with air-entraining admixtures or reduce water content.
• Use a mix with appropriate cement and fine aggregate proportions.
• Repair
• Excess bleeding can be controlled by delaying finishing until water evaporates.
• Surface defects from excessive bleeding may require surface repair.

Blistering is the formation of raised areas on the concrete surface caused by trapped air or water.

• Identification
• Small, dome-like bubbles on the hardened surface.
• Causes
• Premature finishing while bleed water is still present.
• Low evaporation rates due to high humidity or wind.
• Prevention
• Avoid finishing the surface too early.
• Use evaporation retarders in hot or windy weather.
• Repair
• Remove blisters and patch with a polymer-modified repair compound.

Cracking refers to visible splits or fractures in the concrete.

• Identification
• Linear cracks that vary in size and depth.
• Causes
• Shrinkage due to moisture loss.
• Structural overload or improper reinforcement.
• Prevention
• Proper curing to minimize shrinkage.
• Adequate reinforcement and structural design.
• Repair
• Minor cracks can be filled with epoxy or polyurethane.
• Major structural cracks may require injection grouting or structural retrofitting.

Bugholes are small voids or holes on the surface caused by trapped air.

• Identification
• Pinholes or voids visible on formed surfaces after removal.
• Causes
• Poor vibration or consolidation.
• Overly viscous concrete mix.
• Excessive form oil, dirty form.
• Prevention
• Use proper vibration techniques during placement.
• Adjust mix design for improved flowability.
• Proper form oil application, form cleanliness.
• Repair
• Patch bugholes by filling with cementitious repair compounds.

Spalls are surface chipping or flaking.

• Identification
• Areas where surface layers break away, exposing aggregates.
• Causes
• Freeze-thaw damage.
• Corrosion of embedded reinforcement.
• Improper handling.
• Prevention
• Use air-entrained concrete in freeze-thaw environments.
• Ensure adequate cover over reinforcement.
• Do not prematurely remove formwork.
• Repair
• Patch spalled areas with epoxy or polymer-modified mortar.

Alkali-Silica Reaction (ASR) is the chemical reaction between alkalis in cement and reactive silica in aggregates, causing expansive cracking.

• Identification
• Map-like cracking with possible gel exuding from cracks.
• Causes
• Use of reactive aggregates with high alkali cement.
• Prevention
• Use low-alkali cement or supplementary cementitious materials like fly ash.
• Avoid reactive aggregates.
• Repair
• Manage cracks with epoxy injection.
• Prevent further damage with surface sealers or overlays.

Delayed Ettringite Formation (DEF) is the internal expansion caused by delayed formation of ettringite during curing.

• Identification
• Random cracking without clear external causes, often in high-temperature cured concrete.
• Causes
• High curing temperatures (>158°F or 70°C).
• High sulfate content in cement.
• Prevention
• Avoid high curing temperatures.
• Use sulfate-resistant cement.
• Repair
• Damage may require removal and replacement of affected sections.