Early age and time-dependent behaviour of ternary blends of high-performance concrete
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This dissertation investigates how to proportion high-performance concrete (HPC) mixtures that achieve necessary concrete properties without incurring undue early-age and time-dependent deformations. Motivated by broad adoption of low water-to-binder (w/b) concretes with supplementary cementitious materials (SCMs) such as silica fume and Class C fly ash, the work studies time dependent deformation and durability performance of concrete. Twenty-four mixes systematically vary w/b and binder composition. Autogenous shrinkage is measured immediately after casting using a new method developed for the study. Chloride penetration is studied using the Rapid Chloride Penetration Test. Results show that w/b and SCM selection jointly govern autogenous shrinkage and permeability. Lowering w/b increases autogenous shrinkage; silica fume alone tends to amplify it, while fly ash tends to reduce it. Judicious ternary combinations offset shrinkage amplification while maintaining low permeability. A field study of instrumented prestressed I-girder bridges integrates these earlyage insights at structural scale. An analysis of stresses from prestress transfer, curingstage thermal gradients, autogenous shrinkage, in-service thermal cycles, and service loads shows that their superposition indicates likely cracking near girder ends. A decision method (ELECTRE III) is shown to be effective for selecting appropriate mixtures to satisfy targeted performance goals. It was found that the method will produce recommendations that are supported by the available data so long as the data is complete enough.
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Ph. D.