Influence of fresh concrete pressure on cover porosity investigated by single-sided proton nuclear magnetic resonance

摘要

In this study, single-sided proton nuclear magnetic resonance (H-1 NMR) was used to quantify the porosity of the concrete cover. Laboratory concrete samples were prepared with different formwork surfaces as well as varying fresh concrete pressures. Furthermore, to separate the influence of aggregates on porosity, hardened cement paste and mortar samples of otherwise similar composition were prepared. All samples were tested with single-sided H-1 NMR, allowing depth-resolved porosity profiles of up to 18 mm. Differences in the porosity between hardened cement paste, mortar and concrete samples were primarily assigned to the formation of the interfacial transition zone. In concrete samples, the inhomogeneous distribution of the porous hardened cement paste as well as porosity and pore size variations with concrete depth appear. With increasing fresh concrete pressure, a reduction of porosity in the concrete cover can be observed, especially on surfaces made with controlled permeability formwork.