ML12153A409
| ML12153A409 | |
| Person / Time | |
|---|---|
| Issue date: | 06/01/2012 |
| From: | Office of the Chief Human Capital Officer |
| To: | |
| References | |
| Download: ML12153A409 (68) | |
Text
ology and Codes ology and Codes Troubleshooting Hardened Concrete Problems Concrete Techno Concrete Techno
z When troubleshooting concrete problems it is important to relate the symptom to causes of distress y p and deterioration.
Identify Concrete Surface Identify Concrete Surface Defects Defects ACI 201.1 R 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 References z ACI 201-Condition Survey z PCA-IS177-Concrete Surface Defects z Corps of Engineers-Evaluation and Repair Guide
Surface Defects Surface Defects--
Dusting Dusting z Development of a fine, powdery material at the surface of hardened concrete.
Use Ventilated Heaters Use Ventilated Heaters
Surface Defects Surface Defects--
Blistering Blistering z The irregular raising of a thin layer at the surface of placed mortar or concrete during or soon after g
completion of the finishing operation.
Blisters Blisters Causes:
Too many fines Too much or too little vibration Too much or too little vibration Early finishing
Blisters Blisters Prevention:
Avoid high slumps and excess fines Use appropriate cement content Use appropriate cement content Warm subgrade in cold weather Do not place slab directly on vapor retarder
Blisters Blisters Prevention:
Do not overwork the concrete Do not seal (finish) the surface too soon 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 Surface Defects--
Delamination Delamination z A separation along a plane parallel to a surface. In the case of a concrete slab, a horizontal splitting, cracking, p
g g
or separation of a slab in a plane roughly parallel to, and generally near, the upper surface.
Sealing The Surface Sealing The Surface z Improper Tooling z Traps Bleed Water and Air Beneath Layer of Mortar
Surface Defects Surface Defects--
Crazing Crazing z Fine, random cracks or fissures in the surface of plaster, cement paste, mortar, or concrete.
Crazing Crazing Causes:
Rapid surface drying after setting Applying dry cement to surface during finishing
Surface Defects Surface Defects--
Popouts Popouts z Conical fragment that breaks from the concrete surface. A fractured aggregate particle is often at the gg g
p bottom of the hole.
Popouts 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 Popouts Prevention:
Use low slump, low water content mix Use durable crushed stone or beneficiated 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 Surface Defects--
Mortar Flaking Mortar Flaking z A form of scaling over coarse aggregate (popoffs)
Surface Defects Surface Defects--
Scaling Scaling z Local flaking or peeling away of the near-surface portion of concrete or mortar.
Surface Defects Surface Defects--
Spalling Spalling z A fragment, usually in the shape of a flake, detached from a larger mass by a blow, by the action of weather, y
y by pressure, or by expansion within the larger mass.
Surface Defects Surface Defects--
Bugholes Bugholes z Small regular or irregular cavities, usually not exceeding 15 mm in diameter, resulting from entrapment g
p of air bubbles in the surface of formed concrete during placement and compaction.
Surface Defects Surface Defects--
Cold Joint Cold Joint z Visible lines on the surfaces of formed concrete indicating the presence of joints where one layer of p
j y
concrete had hardened before subsequent concrete was placed.
Surface Defects Surface Defects--
Discoloration Discoloration z A departure of color from that which is normal or desired.
Surface Defects Surface Defects--
Staining Staining z Spotted or mottled light or dark blotches.
Surface Defects Surface Defects--
Efflorescence Efflorescence z Deposit, usually white, formed on a surface, the substance having emerged in solution from within g
concrete or masonry and subsequently having been precipitated by evaporation.
Surface (Internal?) Defects Surface (Internal?) Defects--
Honeycombing Honeycombing z Voids left in concrete due to failure of the mortar to effectively fill the spaces among course aggregate p
g gg g
particles.
Durability Durability Chemical Attack Chemical Attack
Durability Durability Freeze Freeze--Thaw Failure Thaw Failure
Durability Durability Alkali Alkali--Aggregate Reactivity Aggregate Reactivity
Durability Durability Corrosion Corrosion
z When troubleshooting concrete problems it is important to relate the symptom to causes of distress y p and deterioration.