What is it about?

Nowadays, Cement-Polymer-Composites are widely used to coat steel rebars to delay the initiation of corrosion in reinforced concrete (RC) structures. However, Cement-Polymer-Composite (CPC) coating is sometimes inadequately applied on rusted steel and can lead to premature under film/crevice corrosion. This paper investigates the effect of such inadequate applications of CPC coating and premature corrosion on the service life of RC structures. For this, maximum surface chloride concentrations, diffusion coefficients, and chloride thresholds were determined by a one-year-long laboratory study on the specimens obtained from a 6-year-old bridge and prepared in the laboratory. Studies found that the chloride threshold of inadequately coated steel rebar (i.e., coating on ‘as received’ surface) is significantly lower than that of the adequately coated steel rebars (i.e., coating on ‘sandblasted’ surface). Also, the corrosion initiation time for systems with inadequately coated steel rebar was about 50% less than that of the systems with adequately coated steel rebars. The corrosion mechanisms were justified with micrographs. It is recommended not to use CPC coated steel rebars if adequate surface preparation (say, cleaning/sandblasting) is not implemented.

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Why is it important?

Recently, many developing countries are witnessing construction boom. Unfortunately, many constructions are happening with poor quality materials and poor applications due to the race for fast-track construction and low quest for quality/durability among some of the stakeholders. One such example is the use of steel rebars with the inadequate application of cement polymer composite (CPC) coating material. This paper provides the field and laboratory data indicating that the use of inadequately coated steel rebars (coating on as-received rebars) can lead to at least 40% lower service life than the adequately coated systems (coating on sand-blasted rebars). If the use of poorly coated rebars continues, then many large scale infrastructure systems will incur the high cost of corrosion. This paper will help engineers to quantitatively estimate the effect of poorly coated rebars on the service life of reinforced concrete structures and develop strategies to ensure the use of quality materials and construction/maintenance practices


When CPC coatings are used, sandblasting of steel rebar can enhance the service life by twice. The coating on rusted steel can result in premature initiation of corrosion and significant disbanding. Be careful, one mistake can lead to significant economic loss...

Deepak Kumar Kamde
Indian Institute of Technology Madras

Read the Original

This page is a summary of: Effect of surface preparation on corrosion of steel rebars coated with cement-polymer-composites (CPC) and embedded in concrete, Construction and Building Materials, March 2020, Elsevier,
DOI: 10.1016/j.conbuildmat.2019.117616.
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