Keywords
Citation
(2001), "Resistance to chloride diffusion", Anti-Corrosion Methods and Materials, Vol. 48 No. 6. https://doi.org/10.1108/acmm.2001.12848fad.007
Publisher
:Emerald Group Publishing Limited
Copyright © 2001, MCB UP Limited
Resistance to chloride diffusion
Resistance to chloride diffusion
Keywords: Max Frank, Concrete, Corrosion prevention
Reduced w/c ratio, increased cement content and early curing result in low porosity and low permeability of the cover zone, the first line of defence against chloride ingress. The surface level of chloride is lower and the diffusion coefficient is reduced substantially.
Chloride ions (Cl–) diffuse into the concrete through the pore water. Once the ions reach a certain concentration (typically 0.4 per cent of cement), rebar corrosion is activated. The result is cracking and spelling of the concrete cover.
The chloride "diffusion coefficient" (Dc) depends on w/c ratio, size and number of capillaries, cement type and severity of exposure. The high porosity of the cover favours a fast initial saturation.
Results suggest that the expected design durability (time before corrosion is activated) can be obtained with 10-15mm less cover if the concrete is cast against Zemdraine.
Actual "Dc" of CEM 1 cast against Zemdraine has reportedly been found similar to that of CEM IIIB (expected to show low "Dc" cast against traditional formwork). The latter mixes will reportedly exhibit their full benefits from the very first mm of cover when cast against Zemdrain.
It is also suggested that dense, impermeable cover can be obtained with low grade concrete or without use of special admixtures.
The following savings are thought to be possible with Zemdrain: reduced cover for equal activation time, reduced concrete grade and full benefit of Cl-resistant mixes (GGBS, PFA) (in the cover zone, the first line of defence). Zemdrain is also considered to be a possible alternative solution to systems involving the use of silica fumes, cathodic protection or protective coatings.
Suggested additional benefits with Zemdrain include actual diffusion coefficient of mixes containing GGBS or PFA being much lower than expected. Improving the resistance to chloride diffusion, this is particularly important in marine works, bridges and road works exposed to de-icing agents, water reservoirs and waste water treatment plants.
Details available from: Max Frank GbmH & Co KG. Tel: +49 9427 18 90; Fax: +49 9427 15 88; E-mail: info@frank-online.de.