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Durability
Categories: Chemical and Physical Mechanisms
Deterioration Mechanism Presented:
Chemical: alkali silica reaction (ASR) and alkali
carbonate reaction (ACR), corrosion of
metals, chloride induced reinforcing steel,
and epoxy coated reinforcing steel (ECR),
and carbonation induced corrosion of the
reinforcing steel
Physical: freezing and thawing of the cement paste
and aggregate (popouts)
Deterioration Mechanisms to be Presented:
Chemical: sulfate attack and acid attack
Physical: D-cracking (freezing and thawing
mechanism), and fire damage
Durability
Sulfate Attack (two step mechanism)
1 st^ step: concrete exposed to sulfate (SO 3
=) in soil or water, sulfate
diffuses through the cement paste pore water, reacts with the
calcium hydroxide to form hydrated gypsum
(Ca(OH) 2 + SO 3 =^ = CaSO 4 H 2 O))
2 nd^ step: Gypsum reacts with the monosulfate to form ettringite
(Ca 4 Al 2 O 3 SO 4 12 H 2 O + 2 CaSO 4 + 2O H 2 O
= Cab Al 2 O 3 3SO 4 32 H 2 O)
Hydrated gypsum to ettringite is an expansive reaction which
creates internal pressure which cracks the hardened cement paste
(^) Prevention:
reduces the permeability and thus reduce the rate of sulfate ingress
into the hardened cement paste, use pozzolans
reduce the amount of calcium hydroxide, use pozzolans, limit the
amount of C 3 A and thus reduce the amount of monosulfate, use
Type II or Type V cement
Durability
D - cracking - a freezing and thawing mechanism
Occurs in slabs on grade (at pavement joints),
degradation of the coarse aggregate, starts at
the bottom of the slab where the aggregate is
saturated, progresses to the top of the slab
Fire Damage is a function of the exposure
temperature
Surface color of the concrete indicates the
reduction in modulus of elasticity and strength,
and the increase in shrinkage
Field Control
- (^) Temperature: measurement of the rate of hydration,
typical specification: not less than 50F and not more
than 90F
- (^) Air content:
- (^) Normal weight concrete: pressure meter is typically used
- (^) Pressuremeter: measures the total volume of air voids in the
concrete mixture (entrapped, entrained and air voids in the
aggregate not filled with water)
- (^) Lightweight concrete: rollometer which measure the amount
of air (entrapped and entrained) in the concrete
Field Control
- (^) Unit Weight: measures the density of the fresh concrete
mixture, used to determine relative yield
- (^) Yield a measure of the volume of the concrete produced,
used to determine the relative yield
- (^) Relative yield: measure of the relative volume of the
concrete produced to the proportioned volume
Greater than 1.00 excessive volume of concrete produced than the
proportioned amount
Less than 1.00 smaller volume of concrete produced than the
proportioned amount
ft
Measured Unit Weight (ft^ )
Total of all the materials batched (lbs ) Yield (ft^ )
3
3
3
Proportionedvolume(ft^ )
Yield(ft ) Re lative yield 3
3
Field Control
Hardened Properties
Tensile splitting,
d
2 P
T
