Chemical attack Flashcards
Acid attack mechanism (4)
Acid in contract with surface
React with hydrates in cement past
Microstructure of cement paste is concreted to more permeable matrix
Products removed by dissolution or abrasion
Sources of acids
Agri, industrial, sewers, exhausts
Factors for acid attack
strength of pH
Solubility of resulting salt
Type
Availability
Minimising acid attack
pH < 3
PFA, GGBS, silica fume
What for PFA, GGBS, silica fume do to minimise acid attack?
Improve penetration properties
Mechanism for sulphate attack
sulfate ions + aluminate + calcium hydroxide
MAP CRACKING!
Expansive ettringite and gypsum
Forms of sulfur
Groundwater
fertilizers
Factors for sulfate attack (7)
Type- magnesium bad
Concentration
Permeation properties - sulfates DIFFUSE
Cement type
Mobility rate
Section sizes
Environment - temp
Combatting sulfate attack
Sulfate resistant cements
Physical barrier - bitumen
What is thaumasite attack
destroys the cementitious binding ability for cement matrix
Factors for thaumastie attack
Temp - low!
Sulfates
Groundwater
Carbonate from aggregates
Combatting thaumasite attack
Limit PC
PFA, GGBS good!
Avoid carbonaceous aggregates
Physical barrier
