Estimation models for creep and shrinkage of concrete made with natural, recycled and secondary aggregates

Abstract

Besides strength and elastic modulus properties of concrete, creep and shrinkage are also important in designing structures as they can affect seriously their integrity in the long term. It is shown that design codes internationally, as well as researchers in general, have omitted to consider the influence of aggregate, in particular its stiffness, in the models developed for estimating creep and shrinkage of concrete. This paper shows that the American ACI, Australian AS 3600, European Eurocode 2, Japanese JSCE and B4 models are mostly found to estimate creep coefficient and shrinkage strain of concrete inaccurately, irrespective of the type of aggregate used – natural, recycled or secondary. It is proposed that the stiffness of aggregate can be represented reasonably by its pore structure and in turn, for ease of measurement, by its water absorption. Two empirical models are proposed for estimating creep coefficient and shrinkage strain of concrete covering a wide range of natural, recycled and secondary aggregates alone or in any combination of these, as well as the cement effect and its proportion effect in the form of aggregate/cement ratio.

Full text

Estimation models for creep and shrinkage
of concrete made with natural, recycled
and secondary aggregates
Chao-Qun Lye
Senior Technical Manager, G&W Ready-Mix Pte Ltd, Singapore
Ravindra K. Dhir
Professor, School of Civil Engineering, University of Birmingham,
Birmingham, UK (corresponding author: r.k.dhir@bham.ac.uk)
Gurmel S. Ghataora
Senior Lecturer, School of Civil Engineering, University of Birmingham,
Birmingham, UK
Besides strength and elastic modulus properties of concrete, creep and shrinkage are also important in designing
structures as they can affect seriously their integrity in the long term. It is shown that design codes internationally,
as well as researchers in general, have omitted to consider the influence of aggregate, in particular its stiffness,
in the models developed for estimating creep and shrinkage of concrete. This paper shows that the American ACI,
Australian AS 3600, European Eurocode 2, Japanese JSCE and B4 models are mostly found to estimate creep
coefficient and shrinkage strain of concrete inaccurately, irrespective of the type of aggregate used –natural,
recycled or secondary. It is proposed that the stiffness of aggregate can be represented reasonably by its pore
structure and in turn, for ease of measurement, by its water absorption. Two empirical models are proposed for
estimating creep coefficient and shrinkage strain of concrete covering a wide range of natural, recycled and
secondary aggregates alone or in any combination of these, as well as the cement effect and its proportion effect in
the form of aggregate/cement ratio.
Notation
A/Ctotal aggregate/cement ratio of concrete
A
c
cross-sectional area of the member (mm
2
)
f
ck
characteristic compressive cylinder strength at
28 days (MPa)
f
cm
28 days mean compressive cylinder
strength (MPa)
f
cm0
a constant value of 10 MPa
h
0
notional size of the cross-section of the
member (mm)
k
h
coefficient depending on the notional size of
the member, h
0
RH ambient relative humidity (%)
RH
0
a constant relative humidity value at 100%
T(Δt
i
) temperature during the time period Δt
i
(°C)
tage of the concrete at the moment
considered (days)
t−t
0
unadjusted duration of loading (days)
t
0
age of the concrete at loading (days)
t
0,T
temperature-adjusted age of the concrete at
loading (days)
t
s
age of the concrete at the beginning of drying
(when curing ceased) (days)
t
T
temperature-adjusted concrete age, which
replaces tin the corresponding equations
uthe perimeter of the member in contact with
the atmosphere (mm)
w
agg1
and w
agg2
water absorption of aggregate type 1 and
aggregate type 2, respectively (%)
w
ca
and w
fa
water absorption of coarse aggregate and fine
aggregate, respectively (%)
αcement-dependent power term
α
1
to α
3
coefficients that affect the concrete strength
α
agg1
and α
agg2
proportion of aggregate type 1 and aggregate
type 2, respectively
α
c
,α
c1
to α
c4
,
α
ds1
,α
ds2
cement-dependent coefficients
α
RH
coefficient relevant to the ambient relative
humidity
β(f
cm
) coefficient relevant to the compressive
strength of concrete
β(t
0
) coefficient for the effect of concrete age at
loading t
0
β
A/C
aggregate/cement ratio coefficient
β
agg
coefficient relevant to the aggregate factor
β
as
(t) time-dependent coefficient to describe the
development of autogenous shrinkage
β
c
(t,t
0
) coefficient to describe the development of
creep with time tafter loading at t
0
β
ca
and β
fa
coefficients relevant to the coarse aggregate
and fine aggregate, respectively
β
ds
(t) time-dependent coefficient to describe the
development of drying shrinkage
β
H
coefficient depending on the relative humidity
(RH in %) and the notional member size (h
0
)
β
RH
ambient humidity coefficient
Δt
i
number of days during which a temperature
Tprevails
392
Cite this article
Lye CQ, Dhir RK and Ghataora GS (2022)
Estimation models for creep and shrinkage of concrete made with natural, recycled and sec-
ondary aggregates.
Magazine of Concrete Research 74(8): 392–418,
https://doi.org/10.1680/jmacr.20.00007
Magazine of Concrete Research
Research Article
Paper 2000007
Received 18/12/2019; Revised 26/08/2020;
Accepted 04/09/2020;
Published online 19/05/2021
ICE Publishing: All rights reserved
Keywords: aggregates/creep/shrinkage