In Situ Durability Characteristics of New and Old Concrete Structures

This paper analyzes field experimental data obtained on about 30 concrete structures, both new (age up to 1 year) and old (age up to 60 years). The data include in situ non-destructive tests (NDT) of air-permeability kT, electrical resistivity rho and surface moisture m, as well as tests conducted on drilled cores: O-2-permeability kO, water sorptivity a(24), MIP, carbonation rate K-c. and chloride content Cl at 10 to 20 mm depth. The main conclusions are that in situ kT of new structures is a good indicator of both kO and a(24). Regarding old structures, high values of kT and kO are accompanied by low a(24) values and by tight MIP pore structure. This phenomenon is attributed to microcracks, with strong effect on permeation but not so much on capillary suction. Similarly, high values of kT are not always accompanied by deep carbonation depths. The chloride content did not show correlation with either kT or rho. In situ measurements of rho, under the testing conditions, did not correlate with any other durability test. Finally, the spread of kT values for old structures is significantly wider than for young structures, suggesting that age improves durable concrete but weathering and damage impair non-durable concrete.