Abstract:
Durability of concrete structures requires an integrated approach consisting of permeability, cracking resistance, and strength of material. Permeability is influenced by the volume fraction of the aggregate, the interfacial zone around each aggregate, many factors related to material heterogeneities including tortuosity of ion path around the aggregates, and cracking. A systematic study is being conducted at NSF Center for ACBM at Northwestern University to study the effect of above parameters on chloride and water permeability of concrete. Initial results indicate that a simple definition of tortuosity and interfacial zone around each aggregate can be used to interpret rapid chloride permeability (ASTM C1202-93) results for a composite consisting of alumina spheres and cement matrix. Preliminary models using conductivity and percolation concepts are used to further explain the conclusions. The influence of cracks on permeability in paste, normal strength concrete (N"SC) and high strength concrete (HSC) is examined using a feedback controlled splitting tensile test. Effect of crack roughness on water permeability measurements has been quantified using laminar flow through a parallel sided slot with modifications for crack geometry. Water and rapid chloride permeability of NSC and HSC slices is also described and compared.
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