ICOLD Bulletin: The Physical Properties of Hardened Conventional Concrete in Dams
Appendix C (Physical properties of concrete subjected to expansion phenomena such
as AAR in dams)
As submitted for ICOLD review, march 2008 Appendix C-7
C4 THE PHYSICAL PROPERTIES OF ASR AFFECTED CONCRETE IN DAMS
During ASR process the gel products initially fill voids, cracks and pores in concrete.
Further gel formation causes a volume increase and a swelling phenomenon into the
concrete, with internal stresses, micro-cracks.
Small amounts of expansion can actually enhance the strength and properties of
concrete by offsetting hydration shrinkage effects and making a less permeable
material. However, if the expansion is large enough, the deterioration due to the volume
change leads to excessive micro- and macro-cracking and will degrade the material
properties.
The level of damage depends on the amount of expansion developed and may be
evaluated through a variety of conventional parameters such compressive and tensile
strength and modulus of elasticity. Creep behavior and fracture energy are also
influenced.
This Section provides information of the ASR effects on the physical properties of
concrete in dams through the analysis of testing results from technical literature [C.13]
[C.14] [C.15] [C.16] [C.17] [C.18] [C.19] [C.20] [C.21] and especially from ASR-affected
dams, mainly derived from the Bureau of Reclamation experience in USA [C.22]. A
database model of ageing concrete was developed by Bureau of Reclamation, in order
to identify the changes in materials properties over time for their mass concrete dams.
Material properties data on mass concrete were input to the “Reclamation Ageing
Concrete Information System” (ACIS). The data were analysed for trends in the
deterioration of concretes subject to ageing, including Alkali Silica Reaction (ASR). The
ageing concretes were compared to dams of similar age, but not suffering from ASR
phenomena. Trends were established for comparing the compressive strength, splitting
and direct tensile strength, and elastic properties of ageing and non-ageing dams. They
are briefly illustrated in the following paragraphs.
C4.1 Compressive strength
The concrete compressive strength decreases as the ASR mechanical damage
increases. Consistent reduction of compressive strength (up to about 40%) have been
found only at very high free expansion levels (about 5 mm/m, i.e. 0.5% or 5000 µε)
[C.13]. However this very high level of expansions is usually not reached in concrete
dams in restrained conditions: for example a concrete with an expansion rate of as high
as 0.05 mm/m/year (i.e. 0.005%/year or 50 µε/year), after 50 years of constant
expansion can reach an expansion level as high as 2.5 mm/m (i.e. 0.25% or 2500 µε).
More usual dam concrete low expansion rates of about 0.01 mm/m/year (i.e.
0.001%/year or 10 µε/year) lead to 50 year expansions of 0.5 mm/m (i.e. 0.05% or 500
µε).