This paper provides guidance on the use and manipulation of concrete shrinkage data in accordance with the Australian Concrete Standard AS 3600. Default shrinkage values for use in the absence of test result and prescribed project requirements are included. Concrete shrinkage calculations are typically completed using 30 year shrinkage values while engineers typically specify 56 day values. This paper provides equations to convert between the two. Finally, calculations undertaken by concrete design software RAPT are investigated. Differences between RAPT and AS 3600 calculations are presented.

1. User Defined Shrinkage Strain in RAPT
Christopher J. Wodzinski
Structural Engineer
AECOM, Sydney, New South Wales, Australia
July 6, 2017
1 Abstract
This paper provides guidance on the use and manip-
ulation of concrete shrinkage data in accordance with
the Australian Concrete Standard AS 3600 [1]. Default
shrinkage values for use in the absence of test result and
prescribed project requirements are included. Concrete
shrinkage calculations are typically completed using 30
year shrinkage values while engineers typically specify
56 day values. This paper provides equations to con-
vert between the two. Finally, calculations undertaken
by concrete design software RAPT [4] are investigated.
Differences between RAPT and AS 3600 calculations are
presented.
2 Default Values
When concrete shrinkage values are not defined, AS 3600
3.1.7.2 [1] defines final drying basic shrinkage strain as
the following:
ε∗
csd.b = 800µm/µm for Sydney & Brisbane aggregate
ε∗
csd.b = 900µm/µm for Melbourne aggregate
ε∗
csd.b = 1000µm/µm otherwise
NOTE: These 30 year shrinkage strain values.
3 AS 3600 Conversion
Concrete shrinkage may be defined in design docu-
mentation, typically denoted as a maximum 56 day
shrinkage strain, and therefore calculations may be
undertaken based on suitable/expected test data. In
order to incorporate these design values into RAPT [4],
56 day values must be converted into 30 year values.
Equation (1) & Equation (2) have been derived from
methodology presented AS 3600 C3.1.7.2 [2], these
equations allow conversion between 56 day and 30 year
shrinkage strain values.
The conversion of 56 day to 30 year Shrinkage:
ε30year =
ε56day − 1.5fc + 25
1.466k4(1.0 − 0.008fc)
(1)
Conversly, the conversion of 30 year to 56 day Shrinkage:
ε56day =
ε30year(1.466k4(1.0 − 0.008fc))
1.5fc − 25
(2)
where:
fc = concrete strength, MPa.
k4 = Environment Factor, 0.75 for Arid , 0.65 for
Interior, 0.6 for Temperate & Inland, 0.5 for Tropical &
Coastal Environments.
The impact of varying concrete strengths in an Interior
Environment is presented in Figure 1. Additionally, AS
3600 3.1.7.2 [1] states that consideration shall be given
to the fact that calculated strains have a range of ±30%.
200
400
600
800
1000
1200
1400
1600
400 500 600 700 800 900 1000
ɛ30year
ɛ56day
k4 = 0.65
32MPa
40MPa
50MPa
65MPa
80MPa
Figure 1: AS 3600 Shrinkage Conversion for an Interior
Environment.
1

2. 4 RAPT Conversion
RAPT [4] will automatically convert 56 day to 30 year
shrinkage strain values when the user alters the material
property. RAPT requires the input of relative humidity
in lieu of the AS 3600 [1] Environmental Factor [5].
This can be input via the Crack Control tab in Design
Data.
For the same concrete strength and drying envi-
ronment, a comparison of AS 3600 & RAPT converted
values is presented in Figure 2. Differences between AS
3600 and RAPT shrinkage can be seen in Figure 2, which
clearly shows that RAPT consistently under-predicts
the conversion calculation. Additionally, although it is
shown that the trend is divergent, as the input variables
increase the relative error between the two sets reduces.
0.00%
2.00%
4.00%
6.00%
8.00%
10.00%
12.00%
14.00%
200
400
600
800
1000
1200
1400
1600
400 500 600 700 800 900 1000
ɛ30year
ɛ56day
Interior Enviroment, f'c = 40MPa
AS3600
RAPT
% Error
Figure 2: Comparison of AS 3600 & RAPT Conversions.
5 Conclusion
Where the engineer specifies shrinkage, utilise conver-
sion equations when appropriate to ensure the correct
shrinkage value is used, typically 56 day for documenta-
tion and 30 year for RAPT input.
When no shrinkage data is defined or available,
AS 3600 recommends using the default values presented
in Section 2.
While RAPT tends to under estimate 30 year shrinkage
values, due to the uncertainty the difference between
may be deemed negligible and design continue as per
the engineers judgment.
References
[1] AS 3600 (2009), ’Concrete structures’, Standards
Australia, Sydney, Australia.
[2] AS 3600 Supplement 1 (2014), ’Concrete structures-
Commentary’, Standards Australia, Sydney, Aus-
tralia.
[3] AS 1012.13 (2015), ’Method 13: Determination of the
drying shrinkage of concrete for samples prepared in
the field or in the laboratory’, Standards Australia,
Sydney, Australia.
[4] RAPT v6.5.13.0 (2017), Prestressed Concrete Design
Consultants Pty Ltd, Sydney, Australia.
[5] RAPT Release Notes (2017), Prestressed Concrete
Design Consultants Pty Ltd, Sydney, Australia.
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