Lightweight Concrete for High Strength - Expanded Shale & Clay

t′: age of concrete at loading (days)
ψ: constant depending on member shape and size
d: constant depending on member shape and size
ø u : ultimate creep coefficient
ACI-209 recommended a value of 0.6 and 10 for ψ and d, respectively. Ultimate creep
coefficient value depends on the factors are described in Equation B.2. ACI proposed an average
creep coefficient value of 2.35 which is multiplied by six factors depending on particular
conditions, as shown in Equation B.2
φu = 2 . 35⋅γ
la
⋅γ
λ
⋅γ
vs
⋅γ
s
⋅γ
ψ
⋅γ
α
(B.2)
where
ø u : ultimate creep coefficient
−0.118
⎧1.25
⋅ t'
for moist curing
γ
la
= ⎨
; age of loading factor
−0.
094
⎩1.13⋅
t'
for steam curing
t′: age of concrete at loading (days)
⎧1.27
− 0.67 ⋅ h for h ≥ 0.40
γ
λ
= ⎨
; ambient relative humidity factor
⎩ 1.00 otherwise
h: relative humidity in decimals
( 1+
1.13⋅
exp{ − 0. })
2
γ
VS
= 54 ⋅ V
3
S
V: specimen volume (in 3 )
S: specimen surface area (in 2 )
γ = 0.82 + 0. 067 ⋅ s ; slump factor
s
s: slump (in)
; volume-to-surface ratio factor
λ ψ
= 0 .88 + 0. 24 ⋅ψ ; fine aggregate content factor
ψ: fine aggregate-to-total aggregate ratio in decimals
γ α
= 0 .46 + 0. 09 ⋅α ; air content factor
α: air content (%)
After applying the factors above, ultimate creep coefficient value is usually between 1.3 and
4.15, which means that creep strain is between 1.3 and 4.15 times the initial elastic strain.
B-5