CVG 2141 Lecture Notes - Lecture 5: Epoxy, Concrete Cover, Stainless Steel
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9 Aug 2016
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Durability of Concrete:
Is the resistance to weathering by chemicals, abrasion, deterioration.
Permeability:
Porosity: Caused by improper consolidation and the evaporation of excess water unused for
hydration.
Influencing factors: w/c ratio, rate of hydration, curing, aggregate size, grading, shrinkage
deterioration.
Cement paste has a higher permeability coefficient than concrete. Permeability coeff. Increases
as w/c ration increases.
Causes of Deterioration:
Chemical: alkali-agg reactions (ASR or ACR, chem reaction b/w minerals in aggregates and alkalis
in PC), sulphate attack, reinforcement corrosion
oAlkali-Aggregate Reactions: needs reactive components in agg. And cement and
moisture
Physical: Freezing and thawing cycles, fire
Alkali Silica Reaction (ASR):
Causes cracking, pop-outs
Can be minimized by using non reactive aggregates and low alkali cement. Using mineral
admixes
Sulphate Attack:
Occurs when sulphate ions (from environment) penetrates the concrete and reacts with
hydrated C3A.
Causes volume expansion, internal stresses, scaling and cracking
Can be minimized by using cement with low C3A (MS or HS), low w/c, mineral admixtures (w/o
Cl)
Reinforcement Corrosion:
Caused by electrochemical processes with the presence of Oxygen and moisture
Causes Cracking in the concrete and mass loss (pitting) of the bar can also cause the bar to
rupture, spalling
Methods to reduce corrosion:
o reduce permeability of concrete, increase concrete cover.
o Epoxy coatings, galvanized steel, stainless steel.
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