Predicting damage in concrete due to expansive aggregates : modeling to enable sustainable material design.

Final report.PDFTech ReportSWUTC/12/476660-00027-1DTRT07-G-0006Bulk modulusConcreteD crackingPermeabilityPorosityPozzolanWater cement ratioThermal expansionAggregate gradationConcrete aggregatesFreeze thaw durabilityAcoustic emission testsUnited StatesSouthwest Region University Transportation Center (U.S.)Rahman, SyedaGrasley, ZacharyTexas Transportation InstituteUniversity Transportation Centers Program (U.S.)NTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATIONUS Transportation CollectionA poroelastic model is developed that can predict stress and strain distributions and, thus, ostensiblydamage likelihood in concrete under freezing conditions caused by aggregates with undesirablecombinations of geometry and constitutive properties. Sensitivity of the stress distributions to the aggregateand matrix constitutive parameters are assessed to allow improved concrete design. The proposed modeldoes not account for the viscoelastic stress relaxation and may over-predict the stress results. The model isevaluated experimentally through acoustic emission analysis under freeze-thaw cyclic loading, whichreveals that air-entrained concrete may undergo durability cracking (D-cracking) if deleterious materialsare present. It is determined that high-porosity, low-permeability aggregates with fine pore structure are themost vulnerable to D-cracking in non-air-entrained concrete, and the destructive tensile stress is generatedat the aggregate boundary by the Mandel-Cryer effect. On the other hand, low-porosity, high-permeabilityaggregates relax the pore liquid pressure rapidly and prove to be beneficial for the non-air-entrainedconcrete. Reduction in aggregate size is found to be effective in quickly relaxing the tensile tangentialstress, which eventually helps mitigate D-cracking of concrete. The difference between the coefficients ofthermal expansion of the coarse aggregate and the matrix in which they are embedded should not be toohigh since it may cause tensile stress at the aggregate boundary or interfacial transition zone. Low water-tocementmass ratio and addition of pozzolans help increase the bulk modulus, reduce the porosity of theporous body, and improve durability. It is also observed that increase in cooling rate decreases concretedurability under freezing temperatures through the reduction in time available to relax pore pressurebuildup and the related tangential stresses in the aggregate and matrix