ML12153A409

1500 - E117 - Concrete Technology and Codes - 28 - Troubleshooting Hardened Concrete Problems

ML12153A409
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Issue date:	06/01/2012
From:	Office of the Chief Human Capital Officer
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Download: ML12153A409 (68)

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Troubleshooting Hardened Concrete Techno ology and Codes Concrete Problems

z When troubleshooting concrete problems it is important to relate the symptom y p to causes of distress and deterioration.

Identify Concrete Surface Defects ACI 201.1 R z Dusting z Blisters z Delaminations z Crazing z Popouts z Mortar Flaking & Scaling z Spalling z Bugholes z Cold Joint z Discoloration z Efflorescence z Honeycombing (Internal?)

References z ACI 201- Condition Survey z PCA- IS177- Concrete Surface Defects z Corps of Engineers- Evaluation and Repair Guide

Surface Defects-Defects-Dusting z Development of a fine, powdery material at the surface of hardened concrete.

Use Ventilated Heaters Surface Defects-Defects-Blistering z The irregular raising of a thin layer at the surface of placed mortar or concrete duringg or soon after completion of the finishing operation.

Blisters Causes:

Too many fines Too much or too little vibration Early finishing

Blisters Prevention:

Avoid high slumps and excess fines Use appropriate cement content Warm subgrade in cold weather Do not place slab directly on vapor retarder

Blisters Prevention:

Do not overwork the concrete Do not seal (finish) the surface too soon Use proper finishing techniques and timing Reduce evaporation Avoid air contents of more than 3% for interior slabs

Surface Defects-Defects-Delamination z A separation along a plane parallel to a surface. In the case of a concrete slab, a horizontal splitting, p g cracking, g

or separation of a slab in a plane roughly parallel to, and generally near, the upper surface.

Sealing The Surface z Improper Tooling z Traps Bleed Water and Air Beneath Layer of Mortar

Surface Defects-Defects-Crazing z Fine, random cracks or fissures in the surface of plaster, cement paste, mortar, or concrete.

Crazing Causes:

Rapid surface drying after setting Applying dry cement to surface during finishing

Surface Defects-Defects-Popouts z Conical fragment that breaks from the concrete surface. A fractured aggregate gg g particle p is often at the bottom of the hole.

Popouts Causes:

z Porous rock with high absorption, low specific gravity:

Pyrite Hard-burned dolomite Coal Shale Soft, fine-grained limestone Chert z Alkali-aggregate reactivity

Popouts Prevention:

Use low slump, low water content mix Use durable crushed stone or beneficiated aggregate Slope the slab surface to drain water properly Use supplementary cementing materials to control ASR-induced popouts

Surface Defects-Defects-Mortar Flaking z A form of scaling over coarse aggregate (popoffs)

Surface Defects-Defects-Scaling z Local flaking or peeling away of the near-surface portion of concrete or mortar.

Surface Defects-Defects-Spalling z A fragment, usually in the shape of a flake, detached from a larger mass byy a blow, byy the action of weather, by pressure, or by expansion within the larger mass.

Surface Defects-Defects-Bugholes z Small regular or irregular cavities, usually not exceeding 15 mm in diameter, resultingg from entrapment p

of air bubbles in the surface of formed concrete during placement and compaction.

Surface Defects-Defects-Cold Joint z Visible lines on the surfaces of formed concrete indicating the presence of jjoints where one layer p y of concrete had hardened before subsequent concrete was placed.

Surface Defects-Defects-Discoloration z A departure of color from that which is normal or desired.

Surface Defects-Defects-Staining z Spotted or mottled light or dark blotches.

Surface Defects-Defects-Efflorescence z Deposit, usually white, formed on a surface, the substance having emerged g in solution from within concrete or masonry and subsequently having been precipitated by evaporation.

Surface (Internal?) Defects- Defects-Honeycombing z Voids left in concrete due to failure of the mortar to effectively fill the spaces p amongg course aggregate gg g particles.

Durability Chemical Attack

Durability Freeze--Thaw Failure Freeze

Durability Alkali--Aggregate Reactivity Alkali

Durability Corrosion

z When troubleshooting concrete problems it is important to relate the symptom y p to causes of distress and deterioration.