Six Wharves

Adding Life to Concrete – How MARKHAM helped extend the service life of several marine structures.

OBJECTIVE

This is a collection of six wharf remediation projects across a variety of ages, five around the New Zealand coastline and one in Australia. The wharves were treated between 1999 and 2010.

The primary aim in each case was to enhance the durability of the structure, in order to reduce maintenance costs and/or avoid replacement of the structure.

The wharves collectively became the subjects of a research paper, by Murray Gilbertson of G-Group Consulting Limited. The results were assessed by an assortment of consultants. G-Group collated the results for the purpose of comparison, and with a view to identifying a common thread in the outcomes.

SOLUTION

In each case, MARKHAM’s approach was to clean the area being treated, back to bare concrete. In some instances cementitious patches were necessary. Spray-applied nanoparticle colloidal silica was then applied, which induces a hydrogel formation within the concrete. This provides protection by blocking the entrance or movement of moisture, and thereby blocking the reactive contaminants carried by that moisture.

Specifically, the G-Group research compared chloride levels before treatment, and some years after. Chlorides are found naturally in the salt of seawater, and are aggressively reactive to reinforcing steel.

RESULTS

In each case, the chloride levels were stable or had declined. In the normal course of events, these chloride levels would have naturally increased; but the opposite was found in the treated concrete.

G-Group’s findings include the following statement:

“The repeatability of the chloride reduction results is positive, considering the different sampling teams, testing laboratories, test methodologies and differing structures.

This range of tests by independent consultants over different structures indicates the penetrating hydrogel treatment resulted in a distinctly similar pattern of reduction of chloride ions available to the corrosion process. These findings are comparable to chloride reduction being achieved by penetrating hydrogels on buildings, bridges and other concrete structures.”

Their summary includes the following:

“The pattern and quantification of the chloride reduction to below or near the corrosion propagation threshold is very distinct. This evidential evidence supports the visual inspections reports on many other coastal and wharf structures treated with penetrating hydrogel but where no records exist of before and after chloride readings.”

Download the full table of findings here.