Lightweight Concrete for High Strength - Expanded Shale & Clay

t: age of concrete (days)
t 0 : age at the beginning of drying (days)
V: specimen volume (in 3 )
S: specimen surface area (in 2 )
k h
⎧2.00
−1.43⋅
h
= ⎨
⎩4.29
− 4.29 ⋅ h
h: relative humidity in decimals
for h < 0.80
; ambient relative humidity factor
for h ≥ 0.80
B.3.3. AASHTO-LRFD as modified by Shams and Kahn (2000) (High Strength
Concrete)
Shams and Kahn (2000), proposed some changes to AASHTO-LRFD creep and shrinkage
expression in order to better predict long-term strains of HPC as given below.
Creep Model. Shams and Kahn method for estimating creep is presented in Equation B.7.
0.6
( t − t'
)
+ ( t − t'
) 0. 6
φ
t
= φ ∞
⋅ kvs
⋅ k
f
⋅ k
H
⋅ kt
'
⋅ k ⋅ k
c
σ m
⋅
(B.7)
d
where
ø t : creep coefficient at “t” loaded at t′
until ⎧ ⎡
⎤⎫
day n
⎪ ⎢ 4000
⎥⎪
t = ∑ ∆ti
⋅ exp⎨−
⎢
−13.
65⎥⎬
; maturity of concrete (days) after “n” days
⎪
T ( ∆t
)
⎢273
+
i
⎥⎪
⎩ ⎣
T 0 ⎦⎭
until ⎧ ⎡
⎤⎫
loading
⎪ ⎢ 4000
⎥⎪
t'
= ∑ ∆ti
⋅ exp⎨−
⎢
−13.
65⎥⎬
; maturity of concrete at loading (days)
⎪
T ( ∆t
)
⎢273
+
i
⎥⎪
⎩ ⎣
T 0 ⎦⎭
∆t i : period of time (days) at temperature T(∆t i ) ( o o
o
C) ( C = 0.556×
F −17.
778)
T 0 : 1 o C
φ
∞
= 2.73: ultimate creep coefficient
B-9