United States Department of Transportation
i
Predicting damage in concrete due to expansive aggregates : modeling to enable sustainable material design.
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2012-04-01
[PDF-2.62 MB]
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Edition:Final report.
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Abstract:A poroelastic model is developed that can predict stress and strain distributions and, thus, ostensibly
damage likelihood in concrete under freezing conditions caused by aggregates with undesirable
combinations of geometry and constitutive properties. Sensitivity of the stress distributions to the aggregate
and matrix constitutive parameters are assessed to allow improved concrete design. The proposed model
does not account for the viscoelastic stress relaxation and may over-predict the stress results. The model is
evaluated experimentally through acoustic emission analysis under freeze-thaw cyclic loading, which
reveals that air-entrained concrete may undergo durability cracking (D-cracking) if deleterious materials
are present. It is determined that high-porosity, low-permeability aggregates with fine pore structure are the
most vulnerable to D-cracking in non-air-entrained concrete, and the destructive tensile stress is generated
at the aggregate boundary by the Mandel-Cryer effect. On the other hand, low-porosity, high-permeability
aggregates relax the pore liquid pressure rapidly and prove to be beneficial for the non-air-entrained
concrete. Reduction in aggregate size is found to be effective in quickly relaxing the tensile tangential
stress, which eventually helps mitigate D-cracking of concrete. The difference between the coefficients of
thermal expansion of the coarse aggregate and the matrix in which they are embedded should not be too
high since it may cause tensile stress at the aggregate boundary or interfacial transition zone. Low water-tocement
mass ratio and addition of pozzolans help increase the bulk modulus, reduce the porosity of the
porous body, and improve durability. It is also observed that increase in cooling rate decreases concrete
durability under freezing temperatures through the reduction in time available to relax pore pressure
buildup and the related tangential stresses in the aggregate and matrix.
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